Battery cell, battery and electric device

Abstract

Disclosed in the embodiments of the present application are a battery cell, a battery and an electric device. The battery cell comprises: an electrode assembly, wherein the electrode assembly comprises a positive electrode sheet, the positive electrode sheet comprises a positive electrode active material capable of realizing reversible de-intercalation and intercalation of metal ions, and the positive electrode active material comprises a compound containing nickel; and a case, which is used for accommodating the electrode assembly, wherein the tensile strength of at least some regions of the case at 500°C is Rn, and Rn satisfies: 100 MPa≤Rn≤1200 MPa. According to the battery cell, the battery and the electric device in the embodiments of the present application, the reliability of the battery cell can be improved.

Description

Battery cells, batteries and electrical equipment Technical Field

[0001] The present application relates to the field of batteries, and more specifically, to a battery cell, a battery, and an electrical device. Background Art

[0002] Energy conservation and emission reduction are key to the sustainable development of the automotive industry. In this context, electric vehicles, due to their energy-saving and environmentally friendly advantages, have become a crucial component of the industry's sustainable development. Battery technology, in turn, is a crucial factor in the development of electric vehicles.

[0003] In the development of battery technology, in addition to improving battery performance, safety is also an issue that cannot be ignored. If battery safety cannot be guaranteed, the battery will be unusable. Therefore, how to improve battery performance while ensuring battery safety has become a particularly important issue in the development of battery technology.

[0004] Summary of the Invention

[0005] The embodiments of the present application provide a battery cell, a battery, and an electrical device, which can improve the reliability of the battery cell.

[0006] In a first aspect, a battery cell is provided, comprising: an electrode assembly, the electrode assembly comprising a positive electrode plate, the positive electrode plate comprising a positive electrode active material capable of reversibly extracting and embedding metal ions, the positive electrode active material comprising a nickel-containing compound; a shell for accommodating the electrode assembly, at least a portion of the shell having a tensile strength Rn at a temperature of 500°C, and Rn satisfying: 100MPa≤Rn≤1200MPa.

[0007] Therefore, in the battery cells of the embodiments of the present application, when the positive electrode active material of the positive electrode plate includes a nickel-containing compound, the energy density and cycle life of the battery cells can be effectively increased. However, this also increases the gas generated during the use of the battery cells. In particular, when the battery cells experience thermal runaway, the internal temperature of the battery cells rapidly increases and a large amount of gas is generated. Therefore, appropriately increasing the tensile strength Rn of at least a portion of the shell at a high temperature of 500°C can improve the deformation capacity of this portion of the shell when the battery cells experience thermal runaway, making the shell less susceptible to rapid damage and explosion, thereby reducing the risk of thermal runaway of adjacent battery cells and improving battery reliability. However, the tensile strength Rn of at least a portion of the shell at a high temperature of 500°C should not be too high to save costs and facilitate processing.

[0008] In some embodiments, the housing includes a weld, and at least a portion of the housing includes an area of ​​the housing within a predetermined distance from the weld, where the predetermined distance is L, and L satisfies the following: L = 10 mm. If the positive active material of the positive electrode plate of the electrode assembly includes a nickel-containing compound, if a battery cell experiences thermal runaway, the internal temperature of the battery cell will rapidly increase and a large amount of gas will be generated. However, under the same conditions, the structural strength of the area of ​​the housing near the weld is lower than that of other areas of the housing. Therefore, the housing is prone to rupture in the area near the weld, which may in turn trigger thermal runaway of the connected battery cells, i.e., cause thermal diffusion. Therefore, setting the area within the predetermined distance L from the weld to meet the tensile strength Rn requirement under high temperature conditions can improve the deformation capacity of this portion of the housing, making it less susceptible to rapid damage, reducing the risk of thermal diffusion or even explosion between multiple battery cells, and thus improving battery reliability.

[0009] In some embodiments, the nickel-containing compound includes a layered lithium-containing transition metal oxide, and the molar amount of the nickel element in the layered lithium-containing transition metal oxide accounts for more than 50% of the total molar amount of the transition metal elements in the layered lithium-containing transition metal oxide, optionally more than 70%, optionally more than 80%, and optionally more than 90%, thereby further improving the energy density of the battery cell.

[0010] In some embodiments, the layered lithium-containing transition metal oxide includes LiaNibCocMdOeAf, wherein 0<a≤1.2, 0.5≤b<1, optionally, 0.9≤b<1; 0<c<1; 0<d<1; 1≤e≤2; 0≤f≤1, M includes but is not limited to one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A includes but is not limited to one or more of N, F, S and Cl, so as to improve the energy density of the battery cell.

[0011] In some embodiments, the material of at least a portion of the housing includes at least one of the following: steel, copper alloy, titanium alloy, and nickel alloy. These materials are relatively strong, can meet the strength requirements of the housing, are easy to process, and have low cost.

[0012] In some embodiments, the material of at least a portion of the housing includes steel with a resistance of 112 MPa ≤ Rn ≤ 720 MPa, which can easily meet design requirements and improve the reliability of the battery cell and the battery.

[0013] In some embodiments, at least a portion of the housing is constructed from at least one of the following materials: stainless steel and carbon steel. Stainless steel provides a greater structural strength and generally meets the aforementioned tensile strength Rn requirement under high-temperature conditions. Furthermore, stainless steel is less susceptible to rust, which can extend the housing's service life compared to other materials. Carbon steel also provides a greater structural strength and easily meets the aforementioned tensile strength Rn requirement under high-temperature conditions.

[0014] In some embodiments, the mass content of chromium in the material of at least a portion of the housing is m, where m satisfies the following: 10% ≤ m ≤ 30%. Properly increasing the amount of chromium in the material of at least a portion of the housing can improve the strength of the material, making it easier to meet the tensile strength Rn requirements under high-temperature conditions in the embodiments of this application. Furthermore, because chromium reacts with oxygen to form a dense chromium oxide film, it can also form a corrosion-resistant protective film on the surface of the housing, improving the corrosion resistance of the housing.

[0015] In some embodiments, the shell is in a cylindrical or polygonal shape to facilitate processing.

[0016] In some embodiments, the melting point of at least a portion of the shell is p, and p satisfies: 1200°C ≤ p ≤ 2000°C. When the positive active material of the positive electrode plate includes a nickel-containing compound, it can effectively increase the energy density and long cycle life of the battery cell, but it will also increase the gas generated during the use of the battery cell. In particular, when the battery cell experiences thermal runaway, the internal temperature of the battery cell increases rapidly and a large amount of gas is generated. Therefore, appropriately increasing the melting point p of at least a portion of the shell will make the shell less likely to melt, reduce the possibility of explosion of the battery cell, and further reduce the risk of thermal runaway of adjacent battery cells, thereby improving the reliability of the battery. However, the melting point p of the shell should not be too large to reduce the difficulty of selecting the material and processing the shell, save costs, and facilitate processing.

[0017] In some embodiments, the electrode assembly further comprises a negative electrode plate comprising a negative electrode active material capable of reversibly extracting and intercalating metal ions, the negative electrode active material comprising a silicon-based material. The tensile strength Rm of at least a portion of the housing at 25°C satisfies the following conditions: 250 MPa ≤ Rm ≤ 2000 MPa. The silicon-based material incorporated into the negative electrode plate can accommodate more metal ions, effectively increasing the energy density of the battery cell. Furthermore, when the negative electrode active material of the negative electrode plate comprises a silicon-based material, deformation of the electrode assembly within the battery cell during use can be increased. In particular, during charging of the battery cell, metal ions intercalating into the silicon-based material of the negative electrode plate can cause volumetric expansion of the electrode assembly, thereby increasing the pressure exerted by the electrode assembly on the housing of the battery cell. Therefore, increasing the tensile strength Rm of at least a portion of the housing at room temperature (25°C) can improve the housing's deformability, making it less susceptible to damage during use, thereby enhancing the structural stability of the battery cell and, consequently, increasing the battery cell's service life. However, the tensile strength Rm of at least part of the shell at room temperature of 25° C. should not be too large, so as to reduce the difficulty of selecting the material and processing the shell, save costs, and facilitate processing.

[0018] In some embodiments, the electrode assembly further comprises a negative electrode plate comprising a negative electrode active material capable of reversibly extracting and inserting metal ions, the negative electrode active material comprising a silicon-based material; and at least a portion of the housing has a yield strength Re at a temperature of 25°C, where Re satisfies the following: 140 MPa ≤ Re ≤ 1000 MPa. Providing a silicon-based material on the negative electrode plate can accommodate more metal ions, effectively increasing the energy density of the battery cell. Furthermore, when the negative electrode active material of the negative electrode plate comprises a silicon-based material, deformation of the electrode assembly within the battery cell during use can be increased. In particular, during charging of the battery cell, metal ions embedded in the silicon-based material of the negative electrode plate can cause the electrode assembly to expand in volume, thereby increasing the pressure exerted by the electrode assembly on the battery cell housing. Therefore, increasing the yield strength Re of at least a portion of the housing at a room temperature of 25°C can improve the housing's deformability, thereby enhancing the structural stability of the battery cell and, consequently, its service life. During the charge and discharge process of a battery cell, the electrode assembly undergoes cyclic volume expansion and contraction. Increasing the room-temperature yield strength (Re) of at least a portion of the housing can increase the maximum compressive force the housing can withstand. Within the housing's yield strength limit, the housing is less susceptible to damage and its deformation is recoverable, thereby extending its service life. However, the room-temperature yield strength (Re) of at least a portion of the housing should not be excessively high to reduce the difficulty in selecting and processing the housing material, saving costs and facilitating fabrication.

[0019] In some embodiments, at least a portion of the housing has a tensile strength Rm at a temperature of 25°C. At least a portion of the housing includes a third housing wall having an average thickness T, and Rm and T satisfy the following conditions: 250 MPa ≤ Rm ≤ 2000 MPa, 0.05 mm ≤ T ≤ 0.5 mm, and 60 mm·MPa ≤ T×Rm ≤ 500 mm·MPa. Increasing the tensile strength Rm of at least a portion of the housing at a room temperature of 25°C can improve the housing's deformability, making it less susceptible to damage during battery cell use, thereby increasing the structural stability and service life of the battery cells. However, the tensile strength Rm of at least a portion of the housing at room temperature should not be too high to reduce the difficulty in selecting and processing the housing's material, saving costs, and facilitating processing. If the average thickness T of the third shell wall of the housing is relatively thin, the structural strength of the third shell wall can be increased by increasing its tensile strength Rm at a room temperature of 25°C. This can both increase the energy density of the battery cell and improve its structural strength and stability. Conversely, if the average thickness T of the third shell wall of the housing is relatively thick, the structural strength of the housing can be improved. By appropriately reducing the tensile strength Rm of the third shell wall at a room temperature, the difficulty in selecting the shell material can be reduced, thereby reducing the difficulty and cost of manufacturing the battery cell. Furthermore, T×Rm represents the stiffness of the third shell wall. Limiting the stiffness of the third shell wall to a value neither too small nor too large ensures that the third shell wall has good deformability while reducing processing difficulty and costs.

[0020] In some embodiments, the capacity of the battery cell is C, and the tensile strength of at least a portion of the housing at a temperature of 25°C is Rm, where Rm and C satisfy the following: 250 MPa ≤ Rm ≤ 2000 MPa, and 25 Ah ≤ C ≤ 550 Ah. Increasing the capacity C of a battery cell can increase the capacity density of a battery comprising multiple such cells. Alternatively, while maintaining the total battery capacity, increasing the capacity C of a single battery cell can reduce the number of battery cells required. This, in turn, reduces the number of electrical connections between the multiple battery cells, lowering the probability of electrical connection failure and improving battery reliability. Furthermore, for battery cells with larger capacity C, increasing the tensile strength Rm of at least a portion of the housing at a room temperature of 25°C can meet the structural strength requirements of the housing for high-capacity battery cells, thereby improving the reliability and service life of the battery cells. On the other hand, a larger capacity battery cell intensifies the internal reactions within it, increasing the structural strength requirements of the housing. Therefore, the capacity C of the battery cell should not be too large to limit the design requirements for the structural strength of the shell, which can reduce the difficulty of material selection and processing of the battery cell, reduce costs and improve processing efficiency.

[0021] In some embodiments, the shell has an opening, and the shell includes a first shell wall and at least two second shell walls arranged opposite to the opening, and the first shell wall and the second shell wall are arranged to intersect; there is a transition area between two adjacent second shell walls among the at least two second shell walls, and the maximum thickness T1 of the transition area and the maximum thickness T0 of the second shell wall with the largest thickness among the two second shell walls satisfy: T1>T0.

[0022] In this embodiment, by setting a transition area between two adjacent second shell walls, the stress concentration between the two adjacent second shell walls can be reduced, and the risk of structural failure caused by stress concentration can be reduced; in addition, the maximum thickness T1 of the transition area is set to be greater than the maximum thickness T0 of the second shell wall with the largest thickness among the two adjacent second shell walls. The thickened transition area can enhance the structural strength of the shell, which is conducive to solving the problem of shell deformation during the production and assembly of battery cells, and the problem of shell deformation caused by gas expansion during use of battery cells.

[0023] In some embodiments, the housing is an integrally formed structure. The housing has an opening. The housing includes a first housing wall disposed opposite to the opening and at least two second housing walls. The first housing wall and the second housing walls intersect. Two of the at least two second housing walls are connected by a first rounded corner. The depth H of the housing and the inner diameter R1 of the first rounded corner satisfy: 2.5 mm ≤ R1 ≤ 20 mm, 50 mm < H ≤ 250 mm. This can reduce the cracking risk caused by stress during the integral forming process of the housing as much as possible without affecting the energy density of the battery cell, thereby reducing the forming difficulty of the housing.

[0024] In some embodiments, the housing is an integrally formed structure. The housing has an opening. The housing includes a first housing wall disposed opposite to the opening and at least two second housing walls. The first housing wall and the second housing walls intersect. Two of the at least two second housing walls are connected by a first rounded corner. The yield strength Re of the housing at a temperature of 25 °C and the inner diameter R1 of the first rounded corner satisfy: 140 MPa ≤ Re ≤ 1000 Mpa, 2.5 mm ≤ R1 ≤ 20 mm.

[0025] In this embodiment, by using a material with a yield strength Re satisfying 140 MPa ≤ Re ≤ 1000 Mpa to make the housing, the wall thickness of the housing can be thinned without reducing the strength of the housing, thereby increasing the capacity space of the battery cell. In addition, by setting the inner diameter R1 of the first rounded corner between adjacent second housing walls to satisfy 2.5 mm ≤ R1 ≤ 20 mm, the cracking risk caused by stress during the integral forming process of the housing can be reduced as much as possible, and the forming difficulty of the housing can be reduced.

[0026] In some embodiments, the housing has an opening. The housing includes a first housing wall and a second housing wall disposed opposite to the opening. The first housing wall and the second housing wall intersect. The first housing wall and the second housing wall are connected by a second rounded corner. The inner diameter r1 of the second rounded corner and the minimum thickness T2 of the second housing wall with the smallest thickness among the at least two second housing walls satisfy: 2.0 ≤ r1 / T2 ≤ 30. By setting the ratio of the inner diameter r1 of the second rounded corner between the first housing wall and the second housing wall to the minimum thickness T2 of the second housing wall with the smallest thickness within [2.0, 30], it helps to balance the processing difficulty of the housing, the space capacity of the battery cell, and the strength.

[0027] In some embodiments, the housing includes: a first housing portion having an opening, the first housing portion including a first wall opposite the opening and a second wall connected to the first wall, the first wall and the second wall being integrally formed; and a second housing portion fixedly connected to the second wall. The housing, in a depth direction of the first housing portion, is formed by the first and second housing portions together, forming at least a portion of the housing. Compared to a direct integrally formed housing, a housing fabricated in this manner can reduce the risk of cracking during the deep drawing process.

[0028] In some embodiments, the battery cell is used in a battery, wherein the electrode assembly includes a first tab and a second tab of opposite polarity. The housing includes a barrel and a cover connected to the barrel. The cover and the barrel are integrally formed. The barrel is disposed around the periphery of the electrode assembly. The cover is provided with an electrode lead-out hole. At least a portion of the cover is used to electrically connect the first connecting member of the battery to the first tab. The battery cell also includes a second electrode terminal for electrically connecting the second connecting member of the battery to the second tab. The second electrode terminal is insulated from the cover and mounted in the electrode lead-out hole. One of the cover and the second electrode terminal serves as the positive output terminal of the battery cell, and the other serves as the negative output terminal of the battery cell. By using the cover and the second electrode terminal as the output terminals, the structure of the battery cell can be simplified while ensuring the current handling capacity of the battery cell. The cover and the second electrode terminal are located at the same end of the battery cell, so that the first connecting member and the second connecting member can be assembled to the same side of the battery cell. This simplifies the assembly process and improves the efficiency of assembling multiple battery cells into groups.

[0029] In some embodiments, the second tab is disposed at one end of the electrode assembly facing the cover, and the first tab is disposed at the other end of the electrode assembly facing away from the cover; the barrel is configured to connect the first tab and the cover so that the first tab is electrically connected to the cover. In this embodiment of the present application, disposing the first and second tabs at both ends of the electrode assembly can reduce the risk of conduction between the first and second tabs and increase the flow area of ​​the first and second tabs.

[0030] In some embodiments, the electrode assembly includes a first tab; the housing includes a barrel and a cover connected to the barrel, the barrel being disposed around the periphery of the electrode assembly; the cover including the first electrode terminal; the first tab being electrically connected to the first electrode terminal via the barrel; and the housing having a multi-layer structure having different resistivities. The electrode assembly includes a first tab, the first tab being electrically connected to the first electrode terminal of the battery cell via the housing; the housing having a multi-layer structure having different resistivities. The first tab being electrically connected to the first electrode terminal via the barrel can simplify the structure of the battery cell; providing the housing with a multi-layer structure having different resistivities can improve the current carrying capacity of the battery cell by using a layer with a lower resistivity, and improve the structural strength of the housing by using a layer with a higher resistivity, thereby improving both the performance and structural strength of the battery cell and thereby increasing the service life of the battery cell.

[0031] In some embodiments, the housing has a multi-layer structure, and the material of the outermost shell of the housing includes at least one of the following: aluminum, aluminum alloy, copper, copper alloy, and chromium. When the material of the outermost shell contains aluminum, the aluminum will oxidize into dense aluminum oxide, which is corrosion-resistant. When the material of the outermost shell contains copper, the copper will oxidize into copper oxide, i.e., verdigris, which is corrosion-resistant. When the material of the outermost shell contains chromium, the chromium will oxidize into chromium oxide, which is also corrosion-resistant. Therefore, when the outermost shell is made of the above-mentioned corrosion-resistant materials, the outermost shell can protect the other shell layers located inside it, thereby improving the structural stability of the shell and extending the service life of the shell.

[0032] In a second aspect, a battery is provided, comprising: a plurality of battery cells, wherein the battery cells are the battery cells described in the first aspect or any one embodiment of the first aspect.

[0033] In a third aspect, an electrical device is provided, comprising: a battery, the battery comprising the battery cell as described in the first aspect or any one embodiment of the first aspect, the battery being used to power the electrical device.

[0034] In some embodiments, the electrical equipment is a vehicle, a ship, or a spacecraft. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] FIG1 is a schematic diagram of a vehicle according to an embodiment of the present application;

[0036] FIG2 is a schematic diagram of the exploded structure of a battery according to an embodiment of the present application;

[0037] FIG3 is a schematic structural diagram of a battery cell according to an embodiment of the present application;

[0038] FIG4 is a schematic diagram of the exploded structure of a battery cell according to an embodiment of the present application;

[0039] FIG5 is a cross-sectional schematic diagram of an electrode assembly according to an embodiment of the present application;

[0040] FIG6 is a schematic cross-sectional view of a negative electrode sheet or a positive electrode sheet of an electrode assembly according to one embodiment of the present application;

[0041] FIG7 is a schematic structural diagram of a fixture for cyclic charging fatigue testing according to one embodiment of the present application;

[0042] FIG8 is a schematic side view of the housing of a battery cell according to an embodiment of the present application;

[0043] FIG9 is a schematic cross-sectional view of a housing of a battery cell according to an embodiment of the present application;

[0044] FIG10 is an exploded schematic diagram of a battery cell according to an embodiment of the present application;

[0045] FIG11 is a cross-sectional view of a housing according to an embodiment of the present application;

[0046] FIG12 is a schematic diagram of a transition area of ​​a housing according to an embodiment of the present application;

[0047] FIG13 is a schematic diagram of another transition area of ​​a housing according to an embodiment of the present application;

[0048] FIG14 is a schematic diagram of material flow during the integral molding process of a housing according to an embodiment of the present application;

[0049] FIG15 is a schematic diagram of the forces acting on a housing during an integral molding process according to an embodiment of the present application;

[0050] FIG16 is another cross-sectional view of a housing according to an embodiment of the present application;

[0051] FIG17 is a partial enlarged schematic diagram of portion B in FIG10 ;

[0052] FIG18 is an exploded schematic diagram of a housing according to an embodiment of the present application;

[0053] FIG19 is a schematic structural diagram of a second housing portion according to an embodiment of the present application;

[0054] FIG20 is another structural schematic diagram of the second housing portion according to an embodiment of the present application;

[0055] FIG21 is another exploded schematic diagram of a housing according to an embodiment of the present application;

[0056] FIG22 is a schematic cross-sectional view of a housing according to an embodiment of the present application;

[0057] FIG23 is an enlarged view of a partial structure of a housing according to an embodiment of the present application;

[0058] FIG24 is a schematic cross-sectional view of a partial structure of a battery according to another embodiment of the present application;

[0059] FIG25 is a schematic diagram of the exploded structure of a battery cell according to another embodiment of the present application;

[0060] FIG26 is a schematic cross-sectional view of a battery cell according to another embodiment of the present application;

[0061] FIG27 is a schematic cross-sectional view of a partial structure of a battery according to another embodiment of the present application;

[0062] FIG28 is a cross-sectional schematic diagram of another partial structure of a battery according to another embodiment of the present application.

[0063] In the drawings, the drawings are not drawn to scale. DETAILED DESCRIPTION

[0064] The technical solutions in the embodiments of the present application will be described below with reference to the accompanying drawings.

[0065] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0066] Unless otherwise defined, all technical and scientific terms used in this application have the same meanings as commonly understood by those skilled in the art to which this application belongs. The terms used in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application. The terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned drawings are intended to cover non-exclusive inclusions. The terms "first" and "second" in the specification and claims of this application or the above-mentioned drawings are used to distinguish different objects, rather than to describe a specific order or a primary-secondary relationship.

[0067] References to "embodiments" in this application mean that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described in this application may be combined with other embodiments.

[0068] In the description of this application, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," "connected," and "attached" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; they may refer to direct connections, indirect connections through an intermediate medium, or internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms in this application based on specific circumstances.

[0069] The term "and / or" in this application simply describes an association between related objects, indicating that three possible relationships exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this application generally indicates that the related objects are in an "or" relationship.

[0070] In the embodiments of this application, the same reference numerals represent the same components, and for the sake of brevity, detailed descriptions of the same components in different embodiments are omitted. It should be understood that the thickness, length, width, and other dimensions of the various components in the embodiments of this application, as well as the overall thickness, length, width, and other dimensions of the integrated device shown in the drawings are merely illustrative and should not constitute any limitation on this application.

[0071] The term "multiple" in this application refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0072] In the embodiment of the present application, the battery cell may be a secondary battery. A secondary battery refers to a battery cell that can be continuously used by activating active materials by charging after the battery cell is discharged.

[0073] The battery cells can be lithium-ion batteries, sodium-ion batteries, sodium-lithium-ion batteries, lithium metal batteries, sodium metal batteries, lithium-sulfur batteries, magnesium-ion batteries, nickel-hydrogen batteries, nickel-cadmium batteries, lead-acid batteries, etc., which are not limited in the embodiments of the present application.

[0074] In some implementations, the battery cell in the embodiment of the present application may be a metal battery. Specifically, the metal battery may include a lithium metal secondary battery, a sodium metal battery, or a magnesium metal battery, etc., which is not limited in the embodiment of the present application.

[0075] A battery cell typically includes an electrode assembly. This assembly includes a positive electrode, a negative electrode, and a separator. During the charge and discharge process of a battery cell, active ions (such as lithium ions) are inserted and removed between the positive and negative electrodes. The separator, placed between the positive and negative electrodes, prevents short circuits between the positive and negative electrodes while allowing the active ions to pass through.

[0076] In some embodiments, the positive electrode may be a positive electrode sheet, which may include a positive electrode current collector and a positive electrode active material disposed on at least one surface of the positive electrode current collector.

[0077] As an example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material is provided on either or both of the two facing surfaces of the positive electrode current collector.

[0078] As an example, the positive electrode current collector can be a metal foil, a foamed metal or a composite current collector. For example, as the metal foil, aluminum or stainless steel with a silver surface treatment, stainless steel, copper, aluminum, nickel, carbon electrode, carbon, nickel or titanium can be used. The foamed metal can be nickel foam, copper foam, aluminum foam, alloy foam, or carbon foam. The composite current collector may include a polymer material base and a metal layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0079] As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0080] In some embodiments, the negative electrode may be a negative electrode sheet, which may include a negative electrode current collector and a negative electrode active material disposed on at least one surface of the negative electrode current collector.

[0081] As an example, the negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode active material is provided on either or both of the two facing surfaces of the negative electrode current collector.

[0082] As an example, the negative electrode current collector may be a metal foil, a metal foam, or a composite current collector. For example, the metal foil may be silver-surface-treated aluminum or stainless steel, stainless steel, copper, aluminum, nickel, a carbon electrode, carbon, nickel, or titanium. The composite current collector may include a polymer material base layer and a metal layer. The metal foam may be nickel foam, copper foam, aluminum foam, alloy foam, or carbon foam. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, or silver alloy, etc.) on a polymer material substrate (such as a substrate made of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0083] As an example, the negative electrode active material may be a negative electrode active material known in the art for use in battery cells. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate.

[0084] In some embodiments, the electrode assembly further includes a separator disposed between the positive electrode and the negative electrode.

[0085] In some embodiments, the separator is a separator. The present application has no particular limitation on the type of separator, and any known separator with a porous structure having good chemical and mechanical stability can be selected.

[0086] As an example, the main material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and ceramics.

[0087] In some embodiments, the separator is a solid electrolyte, which is disposed between the positive electrode and the negative electrode and serves to transport ions and isolate the positive and negative electrodes.

[0088] In some embodiments, the battery cell also includes an electrolyte, which acts as a conductor of ions between the positive and negative electrodes. This application does not specifically limit the type of electrolyte, and the electrolyte can be selected based on needs. The electrolyte can be liquid, gel, or solid.

[0089] In some embodiments, the electrode assembly is provided with tabs that can conduct current from the electrode assembly. The tabs include a positive tab and a negative tab.

[0090] In some embodiments, a battery cell may include a housing. The housing is used to encapsulate components such as the electrode assembly and electrolyte. The housing may be a steel housing, an aluminum housing, a plastic housing (e.g., polypropylene), a composite metal housing (e.g., a copper-aluminum composite housing), or an aluminum-plastic film. The housing includes a shell and a cover.

[0091] The battery mentioned in the embodiments of the present application may include one or more battery cells to provide a single physical module with higher voltage and capacity. When there are multiple battery cells, the multiple battery cells are connected in series, in parallel or in hybrid through a busbar.

[0092] In some embodiments, the battery may be a battery pack, which includes a case and battery cells, wherein the battery cells or battery modules are housed in the case.

[0093] In some embodiments, the box body can be used as a part of the chassis structure of the vehicle. For example, part of the box body can become at least a part of the floor of the vehicle, or part of the box body can become at least a part of the cross beam and longitudinal beam of the vehicle.

[0094] In some embodiments, the battery may be located in an energy storage device, such as an energy storage container or an energy storage cabinet.

[0095] The development of battery technology must simultaneously consider multiple design factors, such as performance parameters such as energy density, cycle life, discharge capacity, and charge and discharge rate. In addition, the safety and stability of the battery also need to be considered. For example, by rationally selecting the positive active material of the positive electrode plate of the electrode assembly, or the negative active material of the negative electrode plate, the energy of the battery cell can be effectively improved, thereby increasing the energy of the battery. Taking the positive electrode plate of the electrode assembly as an example, nickel-containing compounds can be appropriately added to the positive active material of the positive electrode plate to improve the energy and long cycle life of the battery cell, but the reaction inside the battery cell will also be more intense. Especially in the case of thermal runaway of the battery cell, the runaway speed is faster and the gas production is more intense. If the shell strength of the battery cell is insufficient, it is easy to be damaged, which in turn causes the connected battery cells to be affected by the thermal runaway battery cell, causing heat diffusion.

[0096] Therefore, embodiments of the present application provide a battery cell, a battery, and an electrical device that can address the aforementioned issues. The battery cell of the present embodiment includes an electrode assembly and a housing for housing the electrode assembly. The electrode assembly includes a positive electrode plate, the positive electrode plate including a positive electrode active material capable of reversibly extracting and inserting metal ions, the positive electrode active material including a nickel-containing compound. At least a portion of the housing has a tensile strength Rn at 500°C, where Rn satisfies the following conditions: 100 MPa ≤ Rn ≤ 1200 MPa. When the positive electrode active material of the positive electrode plate includes a nickel-containing compound, the energy density and cycle life of the battery cell can be effectively increased. However, this also increases the gas generated during battery cell use, particularly when the battery cell experiences thermal runaway, which rapidly increases the internal temperature of the battery cell and generates a large amount of gas. Therefore, appropriately increasing the tensile strength Rn of at least a portion of the housing at 500°C can improve the deformation capability of this portion of the housing when the battery cell experiences thermal runaway, making it less susceptible to rapid damage and explosion. This, in turn, reduces the risk of thermal runaway in adjacent battery cells, thereby improving battery reliability. However, the tensile strength Rn of at least part of the shell should not be too large under high temperature conditions of 500° C., in order to save costs and facilitate processing.

[0097] The technical solutions described in the embodiments of this application are applicable to various electrical devices that use batteries.

[0098] Electrical equipment can be vehicles, mobile phones, portable devices, laptops, ships, spacecraft, electric toys, and electric tools, etc. Vehicles can be fuel vehicles, gas vehicles, or new energy vehicles. New energy vehicles can be pure electric vehicles, hybrid vehicles, or extended-range vehicles, etc. Spacecraft include airplanes, rockets, space shuttles, and spacecraft, etc. Electric toys include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Electric tools include metal cutting electric tools, grinding electric tools, assembly electric tools, and railway electric tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, etc. The embodiments of the present application do not impose any special restrictions on the above-mentioned electrical equipment.

[0099] For the convenience of description, the following embodiments are described by taking the electric device as a vehicle as an example.

[0100] For example, as shown in FIG1 , it is a structural schematic diagram of a vehicle 1 according to an embodiment of the present application. The vehicle 1 may be a fuel vehicle, a gas vehicle or a new energy vehicle. The new energy vehicle may be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc. A motor 80, a controller 70 and a battery 10 may be provided inside the vehicle 1. The controller 70 is used to control the battery 10 to supply power to the motor 80. For example, a battery 10 may be provided at the bottom, front or rear of the vehicle 1. The battery 10 may be used to power the vehicle 1. For example, the battery 10 may be used as an operating power source for the vehicle 1, for the circuit system of the vehicle 1, for example, for the working power requirements during the start-up, navigation and operation of the vehicle 1. In another embodiment of the present application, the battery 10 may not only be used as an operating power source for the vehicle 1, but also as a driving power source for the vehicle 1, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1.

[0101] To meet different power requirements, a battery can include multiple battery cells, which can be connected in series, parallel, or in a hybrid configuration. A hybrid configuration refers to a combination of series and parallel connections. A battery can also be referred to as a battery pack. For example, multiple battery cells can be connected in series, parallel, or in a hybrid configuration to form a battery module, which can then be connected in series, parallel, or in a hybrid configuration to form a battery. In other words, multiple battery cells can be directly connected to form a battery, or they can be first connected to form battery modules, which can then be combined to form a battery.

[0102] Figure 2 shows a schematic structural diagram of a battery 10 according to an embodiment of the present application. The battery 10 may include a plurality of battery cells 20. The battery 10 may further include a housing 11. The interior of the housing 11 is a hollow structure, and the plurality of battery cells 20 are accommodated in the housing 11. Figure 2 shows a possible implementation of the housing 11 of an embodiment of the present application. As shown in Figure 2, the housing 11 may include two housing parts, which are respectively referred to as a first housing part 111 and a second housing part 112. The first housing part 111 and the second housing part 112 are buckled together. The shapes of the first housing part 111 and the second housing part 112 can be determined according to the shapes of the plurality of battery cells 20 after being combined. At least one of the first housing part 111 and the second housing part 112 has an opening. For example, as shown in FIG2 , the first and second housing portions 111, 112 can each be a hollow cuboid with only one open face. The opening of the first and second housing portions 111, 112 are arranged opposite each other, and the first and second housing portions 111, 112 are interlocked to form a housing 11 having a closed chamber. The chamber can be used to accommodate multiple battery cells 20. The multiple battery cells 20 are connected in parallel, in series, or in a mixed combination and then placed in the housing 11 formed by the interlocking of the first and second housing portions 111, 112.

[0103] For another example, unlike that shown in FIG2 , only one of the first and second housing portions 111, 112 may be a hollow rectangular parallelepiped with an opening, while the other may be plate-shaped to cover the opening. For example, in this example, the second housing portion 112 is a hollow rectangular parallelepiped with only one open face, and the first housing portion 111 is plate-shaped. In this example, the first housing portion 111 covers the opening of the second housing portion 112 to form the housing 11 having a closed chamber. However, the embodiments of the present application are not limited to this.

[0104] Figure 3 shows a schematic structural diagram of a battery cell 20 according to an embodiment of the present application. For example, the battery cell 20 shown in Figure 3 can be any battery cell 20 in the battery 10 shown in Figure 2; Figure 4 shows a schematic structural diagram of a partial decomposition of a battery cell 20 according to an embodiment of the present application. For example, Figure 4 can be a schematic structural diagram of a partial decomposition of the battery cell 20 shown in Figure 3.

[0105] In the embodiment of the present application, as shown in Figures 3 and 4, the battery cell 20 may include an electrode assembly 22 and a housing 211. Specifically, the electrode assembly 22 includes a positive electrode plate 223, which includes a positive electrode active material capable of reversibly extracting and inserting metal ions, and the positive electrode active material includes a nickel-containing compound; the housing 211 is used to accommodate the electrode assembly 22, and at least a portion of the housing 211 has a tensile strength Rn at a temperature of 500°C, where Rn satisfies the following conditions: 100 MPa ≤ Rn ≤ 1200 MPa.

[0106] As shown in Figures 3 and 4 , the battery cell 20 of the embodiment of the present application may include a housing 21. Specifically, the housing 21 may include a shell 211, which is a hollow structure having at least one opening. Furthermore, the battery cell 20 may also include a cover plate 212. For example, the housing 21 may include the cover plate 212, which is used to cover the opening of the shell 211 to allow the electrode assembly 22 to be accommodated within the housing 21.

[0107] It should be understood that the housing 211 of the present embodiment is a component for accommodating the electrode assembly 22. The housing 211 may be a hollow structure with an opening at one end or at multiple ends. For example, if the housing 211 is a hollow structure with an opening at one end, a single cover plate 212 may be provided. If the housing 211 is a hollow structure with openings at opposite ends, two cover plates 212 may be provided, with the two cover plates 212 respectively covering the openings at both ends of the housing 211.

[0108] It should be understood that the battery cells 20 of the present embodiment may be cylindrical, prismatic, soft-pack, or other shaped battery cells. Prismatic battery cells may include square-shell, blade-shaped, or other multi-prismatic battery cells, such as hexagonal or octagonal, but the present embodiment is not limited thereto.

[0109] Corresponding to battery cells 20 of different shapes, the shell 211 of the battery cell 20 can be in a variety of shapes. For example, the shell 211 is cylindrical or polygonal. For example, as shown in Figures 3 and 4, in the embodiment of the present application, the shell 211 is mainly described as a hollow rectangular parallelepiped structure. In addition, the embodiment of the present application mainly takes the shell 211 as an example of a hollow structure with an opening at one end. However, the relevant description of the embodiment of the present application is also applicable to battery cells 20 of other shapes. For the sake of brevity, they will not be repeated here one by one.

[0110] It should be understood that the cover plate 212 of the present embodiment is used to cover the opening of the housing 211 to isolate the internal environment of the battery cell 20 from the external environment. The shape of the cover plate 212 can be adapted to the shape of the housing 211. As shown in Figures 3 and 4, the housing 211 is a rectangular parallelepiped structure, and the cover plate 212 is a rectangular plate structure adapted to the housing 211.

[0111] In the battery cell 20, the electrode assembly 22 is the component where the electrochemical reaction occurs. Depending on actual usage requirements, one or more electrode assemblies 22 can be provided within the housing 211. For example, as shown in Figures 3 and 4, two electrode assemblies 22 are provided within the battery cell 20. The electrode assembly 22 can be cylindrical, rectangular, or similar. If the electrode assembly 22 is cylindrical, the housing 211 can also be cylindrical. If the electrode assembly 22 is rectangular, the housing 211 can also be rectangular.

[0112] It should be understood that, as shown in Figures 3 and 4, the electrode assembly 22 of the present embodiment may include a tab 222 and an electrode body 221. The tab 222 of the electrode assembly 22 may include a positive tab 222a and a negative tab 222b. The positive tab 222a may be formed by laminating the portion of the positive electrode sheet 223 that is not coated with the positive electrode active material, and the negative tab 222b may be formed by laminating the portion of the negative electrode sheet 224 that is not coated with the negative electrode active material. The electrode body 221 may be formed by laminating or winding the positive electrode sheet 223 and the negative electrode sheet 224.

[0113] The positive electrode plate 223 of the present embodiment is provided with a positive electrode active material that can reversibly extract and insert metal ions. This positive electrode active material can be flexibly configured according to the actual application. For example, the positive electrode active material may include a nickel-containing compound, which can effectively increase the energy density and cycle life of the battery cell 20. However, it can also increase the gas generated during the use of the battery cell 20. In particular, if the battery cell 20 experiences thermal runaway during use, the internal temperature of the battery cell 20 will rapidly increase and a large amount of gas will be generated.

[0114] Therefore, appropriately increasing the tensile strength Rn of at least a portion of the shell 211 under high temperature conditions of 500°C can improve the deformation ability of this portion of the shell 211 when the battery cell 20 experiences thermal runaway, making the shell 211 less likely to be quickly destroyed and exploded, thereby reducing the risk of thermal runaway of adjacent battery cells 20 and improving the reliability of the battery 10. However, the tensile strength Rn of at least a portion of the shell 211 under high temperature conditions should not be too large, otherwise it will increase the difficulty of processing, such as easily scratching the mold and reducing the service life of the mold. Therefore, appropriately reducing the tensile strength Rn can save costs and facilitate processing. For example, the tensile strength Rn can usually be set to meet 100MPa≤Rn≤1200MPa.

[0115] It should be understood that the value range of the tensile strength Rn of at least a portion of the shell 211 of the embodiment of the present application under high temperature conditions of 500°C can be adjusted according to actual applications. For example, the value of the high temperature tensile strength Rn can satisfy 100MPa≤Rn≤1200MPa. For another example, the value of the high temperature tensile strength Rn can also satisfy 112MPa≤Rn≤720MPa. On the one hand, appropriately increasing the value of the tensile strength Rn can improve the deformation ability of this portion of the shell 211 when the battery cell 20 has a thermal runaway, which will make the shell 211 less likely to be quickly destroyed and explode, thereby reducing the risk of thermal runaway of adjacent battery cells 20, thereby improving the reliability of the battery 10. At the same time, the tensile strength Rn of at least a portion of the shell 211 under high temperature conditions is controlled not to be too large to reduce the difficulty of processing, thereby saving costs and facilitating processing.

[0116] Furthermore, the high-temperature tensile strength Rn can be set to a value that satisfies 152 MPa ≤ Rn ≤ 480 MPa. This can improve the deformation capability of the portion of the housing 211 when thermal runaway occurs in the battery cell 20, thereby increasing the structural strength of the housing 211 and making it less susceptible to rapid damage and explosion. This in turn reduces the risk of thermal runaway in adjacent battery cells 20, thereby improving the reliability of the battery 10. This can also reduce processing difficulty and save costs.

[0117] In some embodiments, the value of the high temperature tensile strength Rn of the embodiment of the present application can also be set to other values. For example, the value of the high temperature tensile strength Rn can be any of the following values ​​or between any two of the following values: 100MPa, 112MPa, 130MPa, 150MPa, 152MPa, 168MPa, 180MPa, 200MPa, 228MPa, 250MPa, 280MPa, 300MPa, 320MPa, 350MPa, 380MPa, 400MPa, 430MPa, 450MPa, 480MPa, 500MPa, 600MPa, 700MPa, 800MPa, 900MPa, 1000MPa, 1100MPa, 1200MPa, 1300MPa, 1500MPa, 152MPa, 168MPa, 180MPa, 200MPa, 228MPa, 250MPa, 280MPa, 300MPa, 320MPa, 350MPa, 380MPa, 400MPa, 430MPa, 450MPa, 480MPa, 500MPa, 600MPa, 700MPa, 8 ... Pa, 530MPa, 550MPa, 580MPa, 600MPa, 630MPa, 650MPa, 680MPa, 700MPa, 720MPa, 750MPa, 780MPa, 800MPa, 8 30MPa, 850MPa, 880MPa, 900MPa, 930MPa, 950MPa, 980MPa, 1000MPa, 1050MPa, 1100MPa, 1150MPa and 1200MPa.

[0118] It should be understood that the tensile strength of the present embodiment refers to the maximum stress a material can withstand before breaking. The method for testing the tensile strength Rn of at least a portion of the housing 211 at a high temperature of 500°C can be selected based on the actual application. For example, the national standard GB / T 228.1-2010 can be used to test the tensile strength Rn at a high temperature of 500°C.

[0119] FIG5 shows a schematic cross-sectional view of an electrode assembly 22 according to an embodiment of the present application. For example, the schematic cross-sectional view shown in FIG5 may be a schematic cross-sectional view of the electrode assembly 22 shown in FIG4 , where the cross-section is perpendicular to the height direction Z of the battery cell 20. FIG6 shows a schematic partial cross-sectional view of a positive electrode tab 223 or a negative electrode tab 224 according to an embodiment of the present application. For example, FIG6 may be a schematic partial cross-sectional view of the negative electrode tab 224 of the electrode assembly 22 shown in FIG5 along its thickness direction, or may be a schematic partial cross-sectional view of the positive electrode tab 223 of the electrode assembly 22 shown in FIG5 along its thickness direction.

[0120] As shown in Figures 3 to 6, the electrode assembly 22 of the embodiment of the present application includes a positive electrode sheet 223 and a negative electrode sheet 224. The electrode assembly 22 can be formed by stacking or winding the positive electrode sheets 223 and the negative electrode sheets 224. For example, the electrode assembly 22 can include multiple positive electrode sheets 223 and multiple negative electrode sheets 224; along the thickness direction Y of the electrode assembly 22, the multiple positive electrode sheets 223 and the multiple negative electrode sheets 224 are alternately stacked to form a stacked electrode assembly 22. For another example, the electrode assembly 22 can include multiple positive electrode sheets 223, and the negative electrode sheet 224 includes multiple bent sections and multiple stacked sections that are connected and alternately arranged. After the bent sections are bent, the multiple stacked sections of the positive electrode sheets 223 and the negative electrode sheets 224 are alternately stacked to form a stacked electrode assembly 22. For another example, the electrode assembly can also be formed by winding the positive electrode sheet 223 and the negative electrode sheet 224 together to form a wound electrode assembly 22. For ease of explanation, the drawings of the embodiment of the present application use the wound electrode assembly 22 as an example, but the embodiment of the present application is not limited to this. Furthermore, the electrode assembly 22 can also include a separator 225 for separating the positive electrode sheet 223 and the negative electrode sheet 224.

[0121] In the embodiment of the present application, the positive electrode sheet 223 includes a positive electrode active material. For example, the positive electrode active material coated on the positive electrode sheet 223 can be used to form a positive electrode active material layer 2231. The positive electrode active material layer 2231 can be disposed on at least one side of the positive electrode current collector 2232. For example, the positive electrode active material layer 2241 can be disposed on both sides of the positive electrode current collector 2232 perpendicular to the thickness direction thereof, but the embodiment of the present application is not limited thereto.

[0122] In some embodiments, the positive electrode current collector 2232 may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0123] It should be understood that the positive electrode active material of the embodiment of the present application can be flexibly set according to the actual application. For example, the positive electrode active material may include a nickel-containing compound. As an example, the nickel-containing compound includes a layered lithium-containing transition metal oxide, and the molar amount of nickel element in the layered lithium-containing transition metal oxide accounts for more than 50% of the total molar amount of transition metal elements in the layered lithium-containing transition metal oxide. Increasing the proportion of the molar amount of nickel element in the layered lithium-containing transition metal oxide to more than 50% can effectively improve the energy density and long cycle life of the battery cell 20, but the proportion should not be set too large, otherwise it will increase the processing difficulty of the electrode assembly 22, thereby increasing the processing cost of the battery cell 20.

[0124] Furthermore, the molar proportion of nickel in the layered lithium-containing transition metal oxide can be greater than 70%, or greater than 80%, or 90%. This effectively increases the energy density of the battery cell 20 while also reducing the processing difficulty of the electrode assembly 22 and the processing cost of the battery cell 20.

[0125] In some embodiments, the value of the molar ratio of nickel in the layered lithium-containing transition metal oxide of the embodiment of the present application can also be set to other values. For example, the value of the molar ratio of nickel in the layered lithium-containing transition metal oxide can be any of the following values ​​or between any two of the following values: 50%, 53%, 55%, 58%, 60%, 63%, 65%, 68%, 70%, 73%, 75%, 78%, 80%, 83%, 85%, 88%, 90%, 92%, 94%, 96% and 98%.

[0126] It should be understood that the test method for the molar amount of nickel in the layered lithium-containing transition metal oxide and the total molar amount of transition metal elements in the layered lithium-containing transition metal oxide of the embodiment of the present application can be selected according to the actual application and can be measured using instruments and methods known in the art. For example, the positive electrode active material can be laid and adhered to the conductive glue to form a sample to be tested with a length × width of 6 cm × 1.1 cm; the particle morphology is tested using a scanning electron microscope & energy dispersive spectrometer (such as ZEISS Sigma300). The test can refer to JY / T010-1996. In order to ensure the accuracy of the test results, 20 different areas can be randomly selected from the sample to be tested for scanning testing, and at a certain magnification (for example, more than 1000 times), the content of the layered lithium-containing transition metal oxide in each area is counted and calculated. For example, the average value of the test results of the 20 test areas can be taken as the amount of layered lithium-containing transition metal oxide in the positive electrode active material, and then the molar amount of the layered lithium-containing transition metal oxide is determined; similarly, the molar amount of nickel in the layered lithium-containing transition metal oxide can also be determined by this method.

[0127] In some embodiments, the layered lithium-containing transition metal oxide may include one or more of lithium cobalt oxide and ternary materials. As an example, the layered lithium-containing transition metal oxide includes LiaNibCocMdOeAf, wherein 0<a≤1.2, 0.5≤b<1, optionally, 0.9≤b<1; 0<c<1; 0<d<1; 1≤e≤2; 0≤f≤1, M includes but is not limited to one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A includes but is not limited to one or more of N, F, S and Cl. Wherein, the molar ratio b of the nickel element in the layered lithium-containing transition metal oxide is set to be greater than 50%, that is, the ratio b satisfies: 0.5≤b<1, and can further satisfy 0.8≤b<1, or 0.9≤b<1, thereby further improving the energy density of the battery cell 20.

[0128] As an example, the layered lithium-containing transition metal oxide may include but is not limited to one or more of LiNi0.5 Co0.2 Mn0.3 O2 (abbreviated as NCM523), LiNi0.5 Co0.25 Mn0.25 O2 (abbreviated as NCM211), LiNi0.6 Co0.2 Mn0.2 O2 (abbreviated as NCM622), LiNi0.8 Co0.1 Mn0.1 O2 (abbreviated as NCM811), LiNi0.9 Co0.06 Mn0.04 O2, LiNi0.96 Co0.02 Mn0.02 O2, and LiNi0.85 Co0.15 Al0.05 O2.

[0129] In some embodiments, the positive electrode active material may further include other materials. For example, the positive electrode active material may further include a positive electrode conductive agent. The present application does not particularly limit the type of positive electrode conductive agent. As an example, the positive electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0130] In some embodiments, the positive electrode active material may further include a positive electrode binder. The present application has no particular restrictions on the type of positive electrode binder. As an example, the positive electrode binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic resin.

[0131] In some embodiments, the positive electrode sheet 223 can be prepared by the following method: The positive electrode active material layer 2231 is typically formed by coating a positive electrode slurry onto a positive electrode current collector 2232, drying, and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, positive electrode binder, positive electrode conductive agent, etc. in a solvent and stirring them uniformly. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but the embodiments of the present application are not limited thereto.

[0132] The following is a comparative explanation through a number of comparative examples and a number of embodiments. Specifically, the battery cells 20 in the following embodiments and comparative examples are all based on the square-shell battery shown in FIG3 and FIG4 , wherein the shell 211 adopts a hollow structure with one end open.

[0133] In the following embodiments and comparative examples, the preparation methods of the positive electrode sheet 223 , the negative electrode sheet 224 , the electrolyte and the separator 225 of the battery cell 20 are as follows.

[0134] 1. Preparation of positive electrode sheet 223

[0135] The positive electrode active material LiNi 0.95 Co 0.04 Mn 0.01 O2, conductive agent Super P, and binder polyvinylidene fluoride (PVDF) are prepared into positive electrode slurry in N-methylpyrrolidone (NMP), wherein the solid content in the positive electrode slurry is 50wt%, and the solid content of LiNi 0.7 Co 0.1 Mn 0.1 The mass ratio of O2, Super P, and PVDF is 8:1:1. The positive electrode slurry is coated on the upper and lower surfaces of the current collector aluminum foil and dried at 85°C and then cold pressed. Then, it is trimmed, cut, and striped, and then dried under vacuum conditions at 85°C for 4 hours to form a positive electrode sheet 223.

[0136] 2. Preparation of negative electrode sheet 224

[0137] The negative electrode active material is mixed evenly with the conductive agent Super P, the thickener carboxymethyl cellulose (CMC), and the adhesive styrene butadiene rubber (SBR) in deionized water to prepare a negative electrode slurry, wherein the negative electrode active material includes graphite and silicon-based material, and the silicon-based material is a silicon oxide compound. The solid content in the negative electrode slurry is 30wt%, and the mass ratio of the negative electrode active material, silicon oxide, Super P, CMC and adhesive styrene butadiene rubber (SBR) in the solid component is 88:7:3:2. The negative electrode slurry is coated on the upper and lower surfaces of the current collector copper foil and dried at 85°C, and then cold pressed, trimmed, cut into pieces, and slit, and then dried under vacuum conditions at 120°C for 12 hours to prepare a negative electrode sheet 224.

[0138] 3. Preparation of electrolyte

[0139] In an argon atmosphere glove box (H2O <0.1ppm, O2 <0.1ppm), the fully dried electrolyte salt LiPF6 was dissolved in a mixed solvent (the mixed solvent included ethylene carbonate (EC) and diethyl carbonate (DEC), and ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a mass ratio of 50:50), and after mixing evenly, an electrolyte solution with a concentration of 1 mol / L was obtained.

[0140] 4. Preparation of Isolator 225

[0141] A 16 μm polyethylene film was used as the separator 225 .

[0142] 5. Preparation of lithium-ion battery cell 20

[0143] The positive electrode sheet 223, the separator 225 and the negative electrode sheet 224 are stacked in order, so that the separator 225 is located between the positive electrode sheet 223 and the negative electrode sheet 224 to isolate the positive and negative electrodes. The bare battery cell is wound and the tabs are welded. The bare battery cell is placed in a shell made of different materials, and the prepared electrolyte is injected into the dried shell. The battery cell is packaged, allowed to stand, formed, shaped, and capacity tested to complete the preparation of the lithium-ion battery cell 20.

[0144] In the following embodiments and comparative examples, the tensile strength of the housing 211 of the battery cell 20 at a temperature of 500°C is Rn, and different materials are selected to achieve different tensile strengths Rn. The capacity of the battery cell 20 is C, and the thickness of the wall with the largest area of ​​the battery cell 20 is T. The specific parameters are shown in Table 1 below. In addition, in each embodiment and comparative example, the material of the housing 211 is the same throughout. The tensile strength Rn of the housing 211 at 500°C is measured using the method specified in GB / T 228.1-2010. The battery cells 20 in the following embodiments and comparative examples all have the same settings except for the parameters shown in Table 1. For example, in each embodiment, the positive electrode active material of the positive electrode plate 223 of the electrode assembly 22 of the battery cell 20 includes a nickel-containing compound, wherein the nickel-containing compound includes a layered lithium-containing transition metal oxide, and the molar amount of the nickel element in the layered lithium-containing transition metal oxide accounts for 95% of the total molar amount of the transition metal element in the layered lithium-containing transition metal oxide.

[0145] The battery cells 20 in the following comparative examples and embodiments are tested with reference to the short-circuit test method in Section 6.2.4 of GBT31485-2015 Safety Requirements and Test Methods for Power Batteries for Electric Vehicles. After the test, the integrity of the shell 211 is observed, i.e., whether the shell 211 is broken.

[0146] Table 1

[0147] Comparing the two comparative examples in Table 1 above with the six embodiments shows that different materials for the housing 211 can result in different tensile strengths Rn. When the tensile strength Rn satisfies 100 MPa ≤ Rn ≤ 1200 MPa, for example, in Examples 1-6, the housing 211 of the battery cell 20 does not crack, meeting the design requirements of the battery cell 20. Furthermore, when other parameters of the battery cell 20 fluctuate, such as the capacity C of the battery cell 20 or the thickness of the largest wall of the housing 211, the battery cell 20 does not crack, meeting the design requirements of the battery cell 20. However, when the tensile strength Rn does not satisfy 100 MPa ≤ Rn ≤ 1200 MPa, for example, in Comparative Examples 1-2, the housing 211 of the battery cell 20 cracks, failing to meet the design requirements of the battery cell 20.

[0148] It should be understood that the battery cell 20 of the embodiment of the present application can also meet other design requirements. Specifically, the melting point of at least a portion of the housing 211 is p, and p satisfies: 1200°C≤p≤2000°C.

[0149] The positive electrode plate 223 of the present embodiment is provided with a positive electrode active material that can reversibly extract and insert metal ions. The positive electrode active material can be flexibly configured according to the actual application. For example, the positive electrode active material may include a nickel-containing compound, which can effectively increase the energy density and cycle life of the battery cell 20. However, it also increases the temperature and gas generated during the use of the battery cell 20. In particular, if the battery cell 20 experiences thermal runaway during use, the internal temperature of the battery cell 20 will rapidly increase and a large amount of gas will be generated.

[0150] Therefore, appropriately increasing the melting point p of at least a portion of the housing 211 will prevent the housing 211 from melting, reducing the possibility of explosion of the battery cell 20 and, in turn, the risk of thermal runaway of adjacent battery cells 20, thereby improving the reliability of the battery 10. However, the melting point p of at least a portion of the housing 211 should not be too high, to reduce the difficulty in selecting the material and processing the housing 211, saving costs and facilitating processing. For example, the melting point p of at least a portion of the housing 211 can typically be set to satisfy 1200°C ≤ p ≤ 2000°C.

[0151] It should be understood that the value range of the melting point p of at least part of the shell 211 in the embodiment of the present application can be adjusted according to the actual application. For example, the melting point p of at least part of the shell 211 usually satisfies 1200℃≤p≤2000℃. For another example, the melting point p of at least part of the shell 211 may also satisfy 1300℃≤p≤1800℃. On the one hand, appropriately increasing the value of the melting point p can improve the ability of this part of the shell 211 to resist melting when the battery cell 20 has thermal runaway, which will make the shell 211 less likely to be melted, thereby reducing the risk of thermal runaway of adjacent battery cells 20, that is, reducing the risk of heat diffusion, so as to improve the reliability of the battery 10. At the same time, the melting point p cannot be too large, so as to facilitate the selection of suitable materials, reduce the difficulty of processing, and thus save costs and facilitate processing.

[0152] Furthermore, the melting point p of at least a portion of the housing 211 can be set to satisfy 1400°C ≤ p ≤ 1600°C. This can improve the structural strength of the housing 211 when thermal runaway occurs in the battery cell 20, making it less likely to melt, maintaining the structural integrity of that portion of the housing 211, and reducing the risk of thermal runaway in adjacent battery cells 20. This can also reduce processing difficulty and save costs.

[0153] In some embodiments, the melting point p of at least a portion of the housing 211 may also be set to a range of other values. For example, the melting point p may be any one of the following values ​​or between any two of the following values: 1200°C, 1250°C, 1300°C, 1350°C, 1400°C, 1450°C, 1500°C, 1550°C, 1600°C, 1650°C, 1700°C, 1750°C, 1800°C, 1850°C, 1900°C, 1950°C, and 2000°C.

[0154] In the embodiment of the present application, the positive electrode sheet 223 includes a positive electrode active material. For example, the positive electrode active material coated on the positive electrode sheet 223 can be used to form a positive electrode active material layer 2231. The positive electrode active material layer 2231 can be disposed on at least one side of the positive electrode current collector 2232. For example, the positive electrode active material layer 2241 can be disposed on both sides of the positive electrode current collector 2232 perpendicular to the thickness direction thereof, but the embodiment of the present application is not limited thereto.

[0155] In some embodiments, the positive electrode current collector 2232 may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0156] It should be understood that the positive electrode active material of the embodiment of the present application can be flexibly set according to the actual application. For example, the positive electrode active material may include a nickel-containing compound. As an example, the nickel-containing compound includes a layered lithium-containing transition metal oxide, and the molar amount of nickel element in the layered lithium-containing transition metal oxide accounts for more than 50% of the total molar amount of transition metal elements in the layered lithium-containing transition metal oxide. Increasing the proportion of the molar amount of nickel element in the layered lithium-containing transition metal oxide to more than 50% can effectively improve the energy density and long cycle life of the battery cell 20, but the proportion should not be set too large, otherwise it will increase the processing difficulty of the electrode assembly 22, thereby increasing the processing cost of the battery cell 20.

[0157] Furthermore, the molar proportion of nickel in the layered lithium-containing transition metal oxide can be greater than 70%, or greater than 80%, or 90%. This effectively increases the energy density of the battery cell 20 while also reducing the processing difficulty of the electrode assembly 22 and the processing cost of the battery cell 20.

[0158] In some embodiments, the value of the molar ratio of nickel in the layered lithium-containing transition metal oxide of the embodiment of the present application can also be set to other values. For example, the value of the molar ratio of nickel in the layered lithium-containing transition metal oxide can be any of the following values ​​or between any two of the following values: 50%, 53%, 55%, 58%, 60%, 63%, 65%, 68%, 70%, 73%, 75%, 78%, 80%, 83%, 85%, 88%, 90%, 92%, 94%, 96% and 98%.

[0159] It should be understood that the test method for the molar amount of nickel in the layered lithium-containing transition metal oxide and the total molar amount of transition metal elements in the layered lithium-containing transition metal oxide of the embodiment of the present application can be selected according to the actual application and can be measured using instruments and methods known in the art. For example, the positive electrode active material can be laid and adhered to the conductive glue to form a sample to be tested with a length × width of 6 cm × 1.1 cm; the particle morphology is tested using a scanning electron microscope & energy dispersive spectrometer (such as ZEISS Sigma300). The test can refer to JY / T010-1996. In order to ensure the accuracy of the test results, 20 different areas can be randomly selected from the sample to be tested for scanning testing, and at a certain magnification (for example, more than 1000 times), the content of the layered lithium-containing transition metal oxide in each area is counted and calculated. For example, the average value of the test results of the 20 test areas can be taken as the amount of layered lithium-containing transition metal oxide in the positive electrode active material, and then the molar amount of the layered lithium-containing transition metal oxide is determined; similarly, the molar amount of nickel in the layered lithium-containing transition metal oxide can also be determined by this method.

[0160] In some embodiments, the layered lithium-containing transition metal oxide may include one or more of lithium cobalt oxide and ternary materials. As an example, the layered lithium-containing transition metal oxide includes LiaNibCocMdOeAf, wherein 0<a≤1.2, 0.5≤b<1, optionally, 0.9≤b<1; 0<c<1; 0<d<1; 1≤e≤2; 0≤f≤1, M includes but is not limited to one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A includes but is not limited to one or more of N, F, S and Cl. Wherein, the molar ratio b of the nickel element in the layered lithium-containing transition metal oxide is set to be greater than 50%, that is, the ratio b satisfies: 0.5≤b<1, and can further satisfy 0.8≤b<1, or 0.9≤b<1, thereby further improving the energy density of the battery cell 20.

[0161] As an example, the layered lithium-containing transition metal oxide may include but is not limited to one or more of LiNi0.5 Co0.2 Mn0.3 O2 (abbreviated as NCM523), LiNi0.5 Co0.25 Mn0.25 O2 (abbreviated as NCM211), LiNi0.6 Co0.2 Mn0.2 O2 (abbreviated as NCM622), LiNi0.8 Co0.1 Mn0.1 O2 (abbreviated as NCM811), LiNi0.9 Co0.06 Mn0.04 O2, LiNi0.96 Co0.02 Mn0.02 O2, and LiNi0.85 Co0.15 Al0.05 O2.

[0162] In some embodiments, the positive electrode active material may further include other materials. For example, the positive electrode active material may further include a positive electrode conductive agent. The present application does not particularly limit the type of positive electrode conductive agent. As an example, the positive electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0163] In some embodiments, the positive electrode active material may further include a positive electrode binder. The present application has no particular restrictions on the type of positive electrode binder. As an example, the positive electrode binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic resin.

[0164] In some embodiments, the positive electrode sheet 223 can be prepared by the following method: The positive electrode active material layer 2231 is typically formed by coating a positive electrode slurry onto a positive electrode current collector 2232, drying, and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, positive electrode binder, positive electrode conductive agent, etc. in a solvent and stirring them uniformly. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but the embodiments of the present application are not limited thereto.

[0165] The following is a comparative explanation through a number of comparative examples and a number of embodiments. Specifically, the battery cells 20 in the following embodiments and comparative examples are all based on the square-shell battery shown in FIG3 and FIG4 , wherein the shell 211 adopts a hollow structure with one end open.

[0166] In the following embodiments and comparative examples, the preparation methods of the positive electrode sheet 223 , the negative electrode sheet 224 , the electrolyte and the separator 225 of the battery cell 20 are as follows.

[0167] 1. Preparation of positive electrode sheet 223

[0168] The positive electrode active material LiNi 0.95 Co 0.04 Mn 0.01 O2, conductive agent Super P, and binder polyvinylidene fluoride (PVDF) are prepared into positive electrode slurry in N-methylpyrrolidone (NMP), wherein the solid content in the positive electrode slurry is 50wt%, and the solid content of LiNi 0.7 Co 0.1 Mn 0.1 The mass ratio of O2, Super P, and PVDF is 8:1:1. The positive electrode slurry is coated on the upper and lower surfaces of the current collector aluminum foil and dried at 85°C and then cold pressed. Then, it is trimmed, cut, and striped, and then dried under vacuum conditions at 85°C for 4 hours to form a positive electrode sheet 223.

[0169] 2. Preparation of negative electrode sheet 224

[0170] The negative electrode active material is mixed evenly with the conductive agent Super P, the thickener carboxymethyl cellulose (CMC), and the adhesive styrene butadiene rubber (SBR) in deionized water to prepare a negative electrode slurry, wherein the negative electrode active material includes graphite and silicon-based material, and the silicon-based material is a silicon oxide compound. The solid content in the negative electrode slurry is 30wt%, and the mass ratio of the negative electrode active material, silicon oxide, Super P, CMC and adhesive styrene butadiene rubber (SBR) in the solid component is 88:7:3:2. The negative electrode slurry is coated on the upper and lower surfaces of the current collector copper foil and dried at 85°C, and then cold pressed, trimmed, cut into pieces, and slit, and then dried under vacuum conditions at 120°C for 12 hours to prepare a negative electrode sheet 224.

[0171] 3. Preparation of electrolyte

[0172] In an argon atmosphere glove box (H2O <0.1ppm, O2 <0.1ppm), the fully dried electrolyte salt LiPF6 was dissolved in a mixed solvent (the mixed solvent included ethylene carbonate (EC) and diethyl carbonate (DEC), and ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a mass ratio of 50:50), and after mixing evenly, an electrolyte solution with a concentration of 1 mol / L was obtained.

[0173] 4. Preparation of Isolator 225

[0174] A 16 μm polyethylene film was used as the separator 225 .

[0175] 5. Preparation of lithium-ion battery cell 20

[0176] The positive electrode sheet 223, the separator 225 and the negative electrode sheet 224 are stacked in order, so that the separator 225 is located between the positive electrode sheet 223 and the negative electrode sheet 224 to isolate the positive and negative electrodes. The bare battery cell is wound and the tabs are welded. The bare battery cell is placed in a shell made of different materials, and the prepared electrolyte is injected into the dried shell. The battery cell is packaged, allowed to stand, formed, shaped, and capacity tested to complete the preparation of the lithium-ion battery cell 20.

[0177] In the following embodiments and comparative examples, the melting point of the shell 211 of the battery cell 20 is p, and different materials are selected for the shell 211 to obtain different melting points; the capacity of the battery cell 20 is C; the thickness of the wall with the largest area of ​​the battery cell 20 is T, and the above-mentioned specific parameter settings are shown in Table 2 below. In addition, in each embodiment and comparative example, the material of all areas of the shell 211 is the same. In addition, except for the different parameter settings shown in Table 2, the other setting conditions of the battery cells 20 in the following embodiments and comparative examples are the same. For example, in each embodiment, the positive active material of the positive electrode sheet 223 of the electrode assembly 22 of the battery cell 20 includes a nickel-containing compound, wherein the nickel-containing compound includes a layered lithium-containing transition metal oxide, and the molar amount of nickel in the layered lithium-containing transition metal oxide accounts for 95% of the total molar amount of transition metal elements in the layered lithium-containing transition metal oxide.

[0178] The battery cells 20 in the following comparative examples and embodiments are tested with reference to the short-circuit test method in Section 6.2.4 of GBT31485-2015 Safety Requirements and Test Methods for Power Batteries for Electric Vehicles. After the test, the integrity of the shell 211 is observed, i.e., whether the shell 211 is melted.

[0179] Table 2

[0180] Comparing the two comparative examples in Table 2 above with the six embodiments shows that different melting points p can be determined for different materials used for the housing 211. When the melting point p satisfies 1200°C ≤ p ≤ 2000°C, for example, in Examples 1-6, the housing 211 of the battery cell 20 does not melt, thus meeting the design requirements of the battery cell 20. Furthermore, when other parameters of the battery cell 20 fluctuate, such as the capacity C of the battery cell 20 or the thickness of the largest wall of the housing 211, the battery cell 20 does not melt, thus meeting the design requirements of the battery cell 20. However, when the melting point p does not satisfy 1200°C ≤ p ≤ 2000°C, for example, in Comparative Examples 1-2, the housing 211 of the battery cell 20 melts, thus failing to meet the design requirements of the battery cell 20.

[0181] In some embodiments, the electrode assembly 22 further includes a negative electrode plate 224, which includes a negative electrode active material capable of reversibly extracting and inserting metal ions, wherein the negative electrode active material includes a silicon-based material. The tensile strength Rm of at least a portion of the housing 211 at a temperature of 25°C is satisfied: 250 MPa ≤ Rm ≤ 2000 MPa. Increasing the tensile strength Rm of at least a portion of the housing 211 at a room temperature of 25°C can improve the deformability of this portion of the housing 211, making it less susceptible to damage during use of the battery cell 20, thereby improving the structural stability and service life of the battery cell 20. However, the tensile strength Rm of at least a portion of the housing 211 at room temperature should not be too high, to reduce the difficulty in selecting and processing the material of the housing 211, saving costs, and facilitating processing. For example, the tensile strength Rm of at least a portion of the housing 211 at room temperature may generally be set to satisfy 250 MPa≤Rm≤2000 MPa.

[0182] It should be understood that the range of values ​​of the tensile strength Rm of at least a portion of the shell 211 at room temperature of 25°C in the embodiment of the present application can be adjusted according to actual applications. For example, the value of the tensile strength Rm at room temperature can satisfy 250MPa≤Rm≤2000MPa. For another example, the value of the tensile strength Rm at room temperature can also satisfy 400MPa≤Rm≤1200MPa. On the one hand, increasing the tensile strength Rm of at least a portion of the shell 211 at room temperature can improve the deformation capacity of the portion of the shell 211 to resist the expansion of the electrode assembly 22, making the portion of the shell 211 less likely to be damaged, thereby improving the structural stability and service life of the battery cell 20. On the other hand, controlling the tensile strength Rm of at least a portion of the shell 211 at room temperature to not be too large can reduce the difficulty of selecting and processing the material of the shell 211, save costs, and facilitate processing.

[0183] Furthermore, the tensile strength Rm of at least a portion of the housing 211 at room temperature can be set to satisfy 450 MPa ≤ Rm ≤ 800 MPa. The tensile strength Rm of at least a portion of the housing 211 at room temperature is neither too high nor too low, which improves the deformation capacity of the portion of the housing 211 to resist the expansion of the electrode assembly 22 while facilitating implementation and saving costs.

[0184] In some embodiments, the tensile strength Rm of at least a portion of the housing 211 of the embodiment of the present application at room temperature can also be set to other values. For example, the tensile strength Rm at room temperature can be any one of the following values ​​or between any two of the following values: 250MPa, 280MPa, 300MPa, 330MPa, 350MPa, 380MPa, 400MPa, 450MPa, 500MPa, 550MPa, 600MPa, 650MPa, 700MPa, 750MPa, 800MPa, 850MPa, 900MPa, 950MPa, 10 ... MPa, 1800 MPa, 1850 MPa, 1900 MPa, 1950 MPa, and 2000 MPa.

[0185] It should be understood that the tensile strength of the present embodiment refers to the maximum stress a material can withstand before breaking. The method for testing the tensile strength Rm of at least a portion of the housing 211 at a temperature of 25°C in the present embodiment can be selected based on the actual application. For example, the tensile strength Rm can be tested at a room temperature of 25°C using the national standard GB / T 228.1-2010.

[0186] In the embodiment of the present application, the negative electrode sheet 224 includes a negative electrode active material. For example, the negative electrode active material coated on the negative electrode sheet 224 can be used to form a negative electrode active material layer 2241. The negative electrode active material layer 2241 can be disposed on at least one side of the negative electrode current collector 2242. For example, the negative electrode active material layer 2241 can be disposed on both sides of the negative electrode current collector 2242 perpendicular to the thickness direction thereof.

[0187] In some embodiments, the negative electrode current collector 2242 may be a metal foil or a composite current collector. Examples of metal foils include copper foil, copper alloy foil, aluminum foil, and aluminum alloy foil. The composite current collector may include a polymer base layer and a metal material layer formed on at least one surface of the polymer base layer. As an example, the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0188] It should be understood that the negative electrode active material of the embodiment of the present application can be flexibly set according to the actual application. Specifically, the negative electrode active material of the embodiment of the present application may include a silicon-based material, thereby improving the energy density of the battery. For example, the silicon-based material may include at least one of elemental silicon, a silicon-oxygen compound, a silicon-carbon composite, a silicon-nitrogen composite, a silicon-containing alloy, or a silicon-oxygen-carbon composite material.

[0189] In some embodiments, the silicon-based material may include silicon and one or more of an alkali metal element and an alkaline earth metal element. For example, the alkali metal element may include Li. For example, the alkaline earth metal element may include Mg. For example, the silicon-based material may be a silicon-based material pre-embedded with an alkali metal and / or alkaline earth metal, such as a silicon-based material pre-embedded with Li and / or Mg.

[0190] It should be understood that the mass proportion g of the silicon-based material in the embodiment of the present application can be flexibly set according to actual applications.

[0191] For example, the mass proportion g of the silicon-based material can be set to a value range of 2% ≤ g ≤ 40%. Adding silicon-based material to the negative active material of the negative electrode plate 224 can effectively improve the energy density of the battery cell 20 because silicon-based material can accommodate more metal ions than other elements. For example, the capacity of silicon-based material is about ten times that of graphite. At the same time, the mass proportion g of the silicon-based material should not be set too large, otherwise it will increase the difficulty of processing the electrode assembly 22. It will also increase the deformation of the electrode assembly 22 in the battery cell 20 during use. In particular, during the charging process of the battery cell 20, metal ions are embedded in the silicon-based material of the negative electrode plate 224, which will cause the volume expansion of the electrode assembly 22, thereby increasing the pressure of the electrode assembly 22 on the shell 211 of the battery cell 20, thereby increasing the difficulty of processing the battery cell 20.

[0192] Furthermore, the mass ratio g of the silicon-based material can be set to a value range of 8% ≤ g ≤ 40%. Appropriately reducing the mass ratio g of the silicon-based material can reduce the difficulty of processing the electrode assembly 22 and reduce the deformation of the electrode assembly 22 during the charge and discharge of the battery cell 20, that is, reduce the volume expansion of the electrode assembly 22, thereby reducing the pressure of the electrode assembly 22 on the housing 211 of the battery cell 20, lowering the structural strength requirements of the housing 211, facilitating processing, and reducing costs.

[0193] Furthermore, the mass ratio g of the silicon-based material can be set to a value range of 10% ≤ g ≤ 30%. Reasonable adjustment of the mass ratio g of the silicon-based material can effectively increase the energy density of the battery cell 20, reduce the processing difficulty of the electrode assembly 22, and effectively reduce the deformation of the electrode assembly 22 during the charge and discharge of the battery cell 20, thereby reducing the structural strength requirements of the housing 211.

[0194] In some embodiments, the mass percentage g of the silicon-based material in the embodiments of the present application can also be set to other values. For example, the mass percentage g of the silicon-based material can be any of the following values ​​or between any two of the following values: 5%, 8%, 10%, 13%, 15%, 18%, 20%, 23%, 25%, 28%, 30%, 33%, 35%, 38%, 40%, 43%, 45%, 48%, and 50%.

[0195] It should be understood that the mass proportion g of the silicon-based material in the negative electrode active material of the embodiment of the present application represents the ratio of the mass of the silicon-based material in the negative electrode active material to the total mass of the negative electrode active material, which is g. The test method for the mass proportion g of the silicon-based material can be selected according to the actual application, and can be tested using methods known in the art.

[0196] In the embodiments of the present application, the negative electrode active material may further include other materials. For example, the negative electrode active material may further include a negative electrode binder. For example, the negative electrode binder may include one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS), and the embodiments of the present application are not limited thereto.

[0197] In some embodiments, the negative electrode active material may further include a negative electrode conductive agent. The present application does not particularly limit the type of the negative electrode conductive agent. As examples, the negative electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0198] In some embodiments, the negative electrode active material may further include other additives, such as thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, and the like.

[0199] The negative electrode plate 224 does not exclude other additional functional layers in addition to the negative electrode active material layer 2241. For example, in some embodiments, the negative electrode plate 224 may further include a conductive primer layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector 2242 and the negative electrode active material layer 2241 and disposed on the surface of the negative electrode current collector 2242; in some embodiments, the negative electrode plate 224 may further include a protective layer covering the surface of the negative electrode active material layer 2241.

[0200] In some embodiments, the negative electrode sheet 224 can be prepared as follows: the negative electrode active material, optional negative electrode binder, optional negative electrode conductive agent, and optional other additives are dispersed in a solvent and stirred to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector 2242, and after drying, cold pressing, and other processes, the negative electrode sheet 224 is formed. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but the embodiments of the present application are not limited thereto.

[0201] In the embodiment of the present application, the mass fraction g of the silicon-based material and the tensile strength Rm of at least a portion of the housing 211 at 25°C may be mutually constrained to balance the energy density and structural strength of the battery cell 20. For example, if the mass fraction of the silicon-based material in the negative electrode active material is g, and the material of at least a portion of the housing 211 includes iron, Rm and g may satisfy 2% < g < 40% and 300 MPa < Rm < 2000 MPa. The inclusion of iron in at least a portion of the housing 211 can increase the structural strength of the material in that portion of the housing 211, thereby meeting design requirements.

[0202] In some embodiments, at least a portion of the housing 211 is made of carbon steel or stainless steel, with Rm and g satisfying 2.5% ≤ g ≤ 15% and 315 MPa ≤ Rm < 800 MPa. For example, at least a portion of the housing 211 can be made of Q195 carbon steel, which is easy to process and meets the required tensile strength Rm at 25°C.

[0203] In some embodiments, at least a portion of the housing 211 is made of carbon steel or stainless steel, and Rm and g satisfy 4.5% ≤ g ≤ 40%, and 380 MPa ≤ Rm < 2000 MPa. For example, at least a portion of the housing 211 may be made of SPCC carbon steel, which is easy to process and meets the required tensile strength Rm at 25°C.

[0204] In some embodiments, Rm and g satisfy 8%≤g≤40%, 400MPa≤Rm<2000MPa. For example, at least part of the housing 211 may be made of modified stainless steel, which is easy to process and meets the tensile strength Rm value at 25°C.

[0205] In some embodiments, Rm and g satisfy 10%≤g≤40%, 480MPa≤Rm<2000MPa. For example, at least part of the housing 211 may be made of 316 stainless steel, which is easy to process and meets the tensile strength Rm value at 25°C.

[0206] In some embodiments, Rm and g satisfy 15%≤g≤40%, 520MPa≤Rm<2000MPa. For example, at least part of the housing 211 may be made of 304 stainless steel, which is easy to process and meets the tensile strength Rm value at 25°C.

[0207] In some embodiments, Rm and g satisfy 20%≤g≤40%, 600 MPa≤Rm<2000 MPa.

[0208] The following is a comparative explanation through a number of comparative examples and a number of embodiments. Specifically, the battery cells 20 in the following embodiments and comparative examples are all based on the square-shell battery shown in FIG3 and FIG4 , wherein the shell 211 adopts a hollow structure with one end open.

[0209] In the following embodiments and comparative examples, the preparation methods of the positive electrode sheet 223 , the negative electrode sheet 224 , the electrolyte and the separator 225 of the battery cell 20 are as follows.

[0210] 1. Preparation of positive electrode sheet 223

[0211] The positive electrode active material LiNi 0.95 Co 0.04 Mn 0.01 O2, conductive agent Super P, and binder polyvinylidene fluoride (PVDF) are prepared into positive electrode slurry in N-methylpyrrolidone (NMP), wherein the solid content in the positive electrode slurry is 50wt%, and the solid content of LiNi 0.7 Co 0.1 Mn 0.1 The mass ratio of O2, Super P, and PVDF is 8:1:1. The positive electrode slurry is coated on the upper and lower surfaces of the current collector aluminum foil and dried at 85°C and then cold pressed. Then, it is trimmed, cut, and striped, and then dried under vacuum conditions at 85°C for 4 hours to form a positive electrode sheet 223.

[0212] 2. Preparation of negative electrode sheet 224

[0213] The negative electrode active material is mixed evenly with the conductive agent Super P, the thickener carboxymethyl cellulose (CMC), and the adhesive styrene butadiene rubber (SBR) in deionized water to prepare a negative electrode slurry, wherein the negative electrode active material includes graphite and silicon-based material, and the silicon-based material is a silicon oxide compound. The solid content in the negative electrode slurry is 30wt%, and the mass ratio of the negative electrode active material, silicon oxide, Super P, CMC and adhesive styrene butadiene rubber (SBR) in the solid component is 88:7:3:2. The negative electrode slurry is coated on the upper and lower surfaces of the current collector copper foil and dried at 85°C, and then cold pressed, trimmed, cut into pieces, and slit, and then dried under vacuum conditions at 120°C for 12 hours to prepare a negative electrode sheet 224.

[0214] 3. Preparation of electrolyte

[0215] In an argon atmosphere glove box (H2O <0.1ppm, O2 <0.1ppm), the fully dried electrolyte salt LiPF6 was dissolved in a mixed solvent (the mixed solvent included ethylene carbonate (EC) and diethyl carbonate (DEC), and ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a mass ratio of 50:50), and after mixing evenly, an electrolyte solution with a concentration of 1 mol / L was obtained.

[0216] 4. Preparation of Isolator 225

[0217] A 16 μm polyethylene film was used as the separator 225 .

[0218] 5. Preparation of lithium-ion battery cell 20

[0219] The positive electrode sheet 223, the separator 225 and the negative electrode sheet 224 are stacked in order, so that the separator 225 is located between the positive electrode sheet 223 and the negative electrode sheet 224 to isolate the positive and negative electrodes. The bare battery cell is wound and the tabs are welded. The bare battery cell is placed in a shell made of different materials, and the prepared electrolyte is injected into the dried shell. The battery cell is packaged, allowed to stand, formed, shaped, and capacity tested to complete the preparation of the lithium-ion battery cell 20.

[0220] In the following embodiments and comparative examples, the tensile strength of the housing 211 of the battery cell 20 at a temperature of 25°C is Rm. To achieve different tensile strengths Rm, different materials are selected for the housing 211. The negative electrode active material of the negative electrode tab 224 of the electrode assembly 22 of the battery cell 20 comprises a silicon-based material, with the mass percentage of the silicon-based material being g. The specific parameters are shown in Table 3 below. Furthermore, in each embodiment and comparative example, the material of the housing 211 is the same throughout the entire area. The tensile strength Rm of the housing 211 at 25°C is measured using the method specified in GB / T 228.1-2010. The battery cells 20 in the following embodiments and comparative examples are identical except for the parameters shown in Table 3. For example, the wall thickness of each wall of the housing 211 of the battery cell 20 in each embodiment is 0.25 mm. For another example, the capacity of the battery cell 20 in each embodiment is 350 Ah.

[0221] Cyclic charging fatigue tests were performed on the battery cells 20 in the following embodiments and comparative examples. Specifically, Figure 7 shows a schematic diagram of the structure of a fixture 700 used for cyclic charging fatigue testing according to an embodiment of the present application. As shown in Figure 7, the fixture 700 comprises three 10 mm thick steel plates that completely cover the largest wall of the battery cell 20. For ease of explanation, the three fixture steel plates are defined herein as the first steel plate 710, the second steel plate 720, and the third steel plate 730. The first and third steel plates 710, 730 are located at opposite ends of the fixture 700 and are secured by bolts. The second steel plate 720 in the middle is constrained by guide rails, allowing it to move only in a direction perpendicular to its larger surface. The battery cell 20 is clamped between the first and second steel plates 710, 720, with the largest wall of the battery cell 20 contacting the first and second steel plates 710, 720. A pressure sensor 740 is located between the second and third steel plates 720, 730. The initial pressing force of the second steel plate 720 on the battery cell 20 can be adjusted by adjusting the position of the second steel plate 720 .

[0222] Specifically, the battery cell 20 is clamped and fixed in the dedicated fixture 700, ensuring that the two oppositely disposed walls with the largest areas of the battery cell 20 are clamped, and the initial pressure is set to 2000N, and the electrode terminals 214 of the battery cell 20 are connected to the dedicated battery charging and discharging equipment.

[0223] The fixture 700 holding the battery cell 20 is placed in a constant temperature environment of 25±2° C., and the test is started after the battery cell 20 reaches temperature equilibrium.

[0224] The specific test steps are carried out in accordance with Chapter 6.4 "Standard Cycle Life" of "GBT31484-2015 Requirements and Test Methods for Cycle Life of Power Batteries for Electric Vehicles", and the test cycle end condition is changed to "stop testing until the weld 2113 of the battery cell 20 is damaged."

[0225] For example, the test can be carried out according to the following steps: step a, discharge at 1I(A) to the discharge termination condition specified by the enterprise; step b, leave it for no less than 30 minutes or the shelf condition specified by the enterprise; step c, charge according to the method of 6.1.1.3; step d, leave it for no less than 30 minutes or the shelf condition specified by the enterprise; step e, discharge at 1I1(A) to the discharge termination condition specified by the enterprise; step f, cycle according to steps b to e until the weld 2113 is damaged and the test is stopped.

[0226] During the above test process, the weld 2113 of the battery cell 20 was continuously observed until leakage occurred at the weld 2113. The number of cycles was recorded to obtain the condition of the housing 211 at 1000 cycles as shown in Table 3 below. In the following embodiments and comparative examples, the weld 2113 refers to the weld between the housing 211 and the cover plate 212, i.e., the weld 2113 surrounds the open end of the housing 211, which is an integrally molded structure.

[0227] Table 3

[0228] It should be understood that in Table 3 above, the material of the shell 211 can be Q195 carbon steel, and the tensile strength Rm of Q195 carbon steel at room temperature of 25°C is generally at least 315 MPa to 430 MPa. The above embodiment only takes 328 MPa as an example, but is not limited to this. Similarly, the material of the shell 211 can be SPCC carbon steel, and the tensile strength Rm of SPCC carbon steel at room temperature of 25°C is generally at least 380MPa to 430MPa, and the above embodiment only takes 396MPa as an example; the material of the shell 211 can be modified stainless steel, and the tensile strength Rm of modified stainless steel at room temperature of 25°C is generally at least 400MPa to 600MPa, and the above embodiment only takes 421MPa as an example; the material of the shell 211 can be SUS430 stainless steel, and the tensile strength Rm of SUS430 stainless steel at room temperature of 25°C is generally at least 450MPa, and the above embodiment only takes 459MPa as an example; the material of the shell 211 can be SUS304 stainless steel, and the tensile strength Rm of SUS304 stainless steel at room temperature of 25°C is generally at least 520MPa, and the above embodiment only takes 533MPa and 625MPa as examples.

[0229] Comparing the two comparative examples in Table 3 above with the 12 embodiments shows that when different materials are used for the housing 211, different tensile strengths Rm can be determined accordingly. When the tensile strength Rm satisfies 250MPa≤Rm≤2000MPa, for example, in Examples 1-12, even if the mass proportion g of the silicon-based material in the material of the negative electrode tab 224 of the battery cell 20 is different, the number of failure fatigue cycles of the battery cell 20 can reach more than one thousand, thereby meeting the design requirements of the battery cell 20. However, when the tensile strength Rm does not satisfy 250MPa≤Rm≤2000MPa, for example, in Comparative Example 1-2, even if the mass proportion g of the silicon-based material in the material of the negative electrode tab 224 of the battery cell 20 is low, the number of failure fatigue cycles of the battery cell 20 does not reach one thousand, failing to meet the design requirements of the battery cell 20.

[0230] In some embodiments, the electrode assembly 22 also includes a negative electrode plate 224, which includes a negative electrode active material that can reversibly extract and embed metal ions, and the negative electrode active material includes a silicon-based material; the yield strength of at least a portion of the shell 211 at a temperature of 25°C is Re, and Re satisfies: 140MPa≤Re≤1000MPa.

[0231] Increasing the yield strength Re of at least a portion of the housing 211 at room temperature can improve the deformation capacity of the housing 211, thereby increasing the structural stability and service life of the battery cell 20. During the charge and discharge process of the battery cell 20, the electrode assembly 22 undergoes cyclic volume expansion and contraction. Increasing the yield strength Re of at least a portion of the housing 211 at room temperature can increase the maximum compressive force that the housing 211 can withstand. As long as the yield strength limit of the housing 211 is not exceeded, the housing 211 is not easily damaged, and the deformation of the housing 211 is recoverable, thereby increasing the service life of the housing 211. However, the yield strength Re of at least a portion of the housing 211 at room temperature should not be too high, to reduce the difficulty in selecting the material and processing the housing 211, save costs, and facilitate processing. For example, the yield strength Re of at least a portion of the housing 211 at room temperature can typically be set to meet the following requirements: 140 MPa ≤ Re ≤ 1000 MPa.

[0232] It should be understood that the yield strength Re of at least a portion of the housing 211 in the embodiment of the present application at room temperature (25°C) can be adjusted based on actual application. For example, the yield strength Re can satisfy 140 MPa ≤ Re ≤ 1000 MPa. Another example is 180 MPa ≤ Re ≤ 600 MPa. Increasing the yield strength Re of at least a portion of the housing 211 at room temperature improves the deformation capacity of this portion of the housing 211, thereby resisting the expansion of the electrode assembly 22 and making it less susceptible to damage. Furthermore, if the expansion of the electrode assembly 22 decreases, the deformation of the housing 211 can be restored without exceeding the yield strength limit of the housing 211, thereby improving the structural stability and service life of the battery cell 20. Furthermore, by limiting the yield strength Re of at least a portion of the housing 211 at room temperature to a minimum, the material selection and processing difficulty of the housing 211 can be reduced, saving costs and facilitating processing.

[0233] Furthermore, the yield strength Re of at least a portion of the housing 211 at room temperature can be set to satisfy 220 MPa ≤ Re ≤ 400 MPa. The yield strength Re of at least a portion of the housing 211 at room temperature is neither too high nor too low, which not only improves the deformation capacity of this portion of the housing 211 to resist the expansion of the electrode assembly 22, but also facilitates implementation and saves costs.

[0234] In some embodiments, the yield strength Re of at least a portion of the housing 211 of the embodiment of the present application at room temperature may be set to other values. For example, the yield strength Re at room temperature may be any one of the following values ​​or between any two of the following values: 140MPa, 150MPa, 160MPa, 180MPa, 200MPa, 220MPa, 250MPa, 280MPa, 300MPa, 330MPa, 350MPa, 380MPa, 400MPa, 430MPa, 450MPa, 480MPa. a. 500MPa, 530MPa, 550MPa, 580MPa, 600MPa, 630MPa, 650MPa, 680MPa, 700MPa, 730MPa, 750 MPa, 780MPa, 800MPa, 830MPa, 850MPa, 880MPa, 900MPa, 930MPa, 950MPa, 980MPa and 1000MPa.

[0235] It should be understood that the yield strength of the embodiments of the present application can be understood as the critical stress value at which the material yields. Generally, after being subjected to stress, a material may undergo plastic deformation in addition to elastic deformation as the stress increases. The point at which the material undergoes plastic deformation can be called the yield point, and the strength corresponding to the yield point is called the yield strength. In addition, the yield strength of the embodiments of the present application generally refers to the upper yield strength, that is, the upper yield strength of at least a portion of the housing 211 at a temperature of 25°C is Re.

[0236] The test method for the yield strength Re of at least a portion of the housing 211 of the embodiment of the present application at a temperature of 25° C. can be selected according to actual application. For example, the yield strength Re can be tested at a room temperature of 25° C. using the national standard GB / T 228.1-2010.

[0237] In an embodiment of the present application, the value of the mass proportion g of the silicon-based material and the value of the yield strength Re of at least a portion of the shell 211 at a temperature of 25°C can be mutually restricted, so as to improve the structural strength of the shell 211 while increasing the energy density of the battery cell 20, thereby improving the structural strength and service life of the battery cell 20.

[0238] For example, in the negative electrode active material, the mass proportion of the silicon-based material is g, and g and Re satisfy the following: 2% < g < 40%, 140 MPa < Re < 600 MPa. Adding silicon-based material to the negative electrode active material of the negative electrode plate 224 can effectively improve the energy density of the battery cell 20 because silicon-based materials can accommodate more metal ions than other elements. For example, the capacity of silicon-based materials is about ten times that of graphite. At the same time, the mass proportion g of the silicon-based material should not be set too large, otherwise it will increase the difficulty of processing the electrode assembly 22. It will also increase the deformation of the electrode assembly 22 during use in the battery cell 20. In particular, during the charging process of the battery cell 20, metal ions are embedded in the silicon-based material of the negative electrode plate, causing the electrode assembly 22 to expand in volume, thereby increasing the pressure of the electrode assembly 22 on the housing 211 of the battery cell 20, thereby increasing the difficulty of processing the battery cell 20. Therefore, the yield strength Re of at least a portion of the housing 211 at room temperature can be appropriately increased to improve the deformation capacity of this portion of the housing 211, thereby resisting the expansion of the electrode assembly 22 and making this portion of the housing 211 less susceptible to damage. Furthermore, if the expansion of the electrode assembly 22 decreases, the deformation of the housing 211 can be restored without exceeding the yield strength limit of the housing 211, thereby improving the structural stability and service life of the battery cell 20. Furthermore, by controlling the yield strength Re of at least a portion of the housing 211 at room temperature to be appropriately small, the difficulty in selecting and processing the material for the housing 211 can be reduced, thereby saving costs and facilitating processing.

[0239] In some embodiments, at least a portion of the housing 211 is made of carbon steel or stainless steel, with g and Re satisfying 4.5% ≤ g ≤ 40% and 170 MPa ≤ Re < 600 MPa. For example, at least a portion of the housing 211 may be made of SPCC carbon steel, which is easy to process and meets the required yield strength Re at 25°C.

[0240] In some embodiments, g and Re satisfy 8%≤g≤40%, 180MPa≤Re<600MPa. For example, at least part of the housing 211 may be made of modified stainless steel, which is easy to process and meets the yield strength Re value at 25°C.

[0241] In some embodiments, g and Re satisfy 10%≤g≤40%, 190MPa≤Re<600MPa. For example, at least part of the housing 211 may be made of 316 stainless steel, which is easy to process and meets the yield strength Re value at 25°C.

[0242] In some embodiments, g and Re satisfy 15%≤g≤40%, 200MPa≤Re<600MPa. For example, at least part of the housing 211 may be made of 304 stainless steel, which is easy to process and meets the yield strength Re value at 25°C.

[0243] In some embodiments, g and Re satisfy 20%≤g≤40%, 210 MPa≤Re<600 MPa.

[0244] The following is a comparative explanation through a number of comparative examples and a number of embodiments. Specifically, the battery cells 20 in the following embodiments and comparative examples are all based on the square-shell battery shown in FIG3 and FIG4 , wherein the shell 211 adopts a hollow structure with one end open.

[0245] In the following embodiments and comparative examples, the preparation methods of the positive electrode sheet 223 , the negative electrode sheet 224 , the electrolyte and the separator 225 of the battery cell 20 are as follows.

[0246] 1. Preparation of positive electrode sheet 223

[0247] The positive electrode active material LiNi 0.95 Co 0.04 Mn 0.01 O2, conductive agent Super P, and binder polyvinylidene fluoride (PVDF) are prepared into positive electrode slurry in N-methylpyrrolidone (NMP), wherein the solid content in the positive electrode slurry is 50wt%, and the solid content of LiNi 0.7 Co0.1 Mn 0.1 The mass ratio of O2, Super P, and PVDF is 8:1:1. The positive electrode slurry is coated on the upper and lower surfaces of the current collector aluminum foil and dried at 85°C and then cold pressed. Then, it is trimmed, cut, and striped, and then dried under vacuum conditions at 85°C for 4 hours to form a positive electrode sheet 223.

[0248] 2. Preparation of negative electrode sheet 224

[0249] The negative electrode active material is mixed evenly with the conductive agent Super P, the thickener carboxymethyl cellulose (CMC), and the adhesive styrene butadiene rubber (SBR) in deionized water to prepare a negative electrode slurry, wherein the negative electrode active material includes graphite and silicon-based material, and the silicon-based material is a silicon oxide compound. The solid content in the negative electrode slurry is 30wt%, and the mass ratio of the negative electrode active material, silicon oxide, Super P, CMC and adhesive styrene butadiene rubber (SBR) in the solid component is 88:7:3:2. The negative electrode slurry is coated on the upper and lower surfaces of the current collector copper foil and dried at 85°C, and then cold pressed, trimmed, cut into pieces, and slit, and then dried under vacuum conditions at 120°C for 12 hours to prepare a negative electrode sheet 224.

[0250] 3. Preparation of electrolyte

[0251] In an argon atmosphere glove box (H2O <0.1ppm, O2 <0.1ppm), the fully dried electrolyte salt LiPF6 was dissolved in a mixed solvent (the mixed solvent included ethylene carbonate (EC) and diethyl carbonate (DEC), and ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a mass ratio of 50:50), and after mixing evenly, an electrolyte solution with a concentration of 1 mol / L was obtained.

[0252] 4. Preparation of Isolator 225

[0253] A 16 μm polyethylene film was used as the separator 225 .

[0254] 5. Preparation of lithium-ion battery cell 20

[0255] The positive electrode sheet 223, the separator 225 and the negative electrode sheet 224 are stacked in order, so that the separator 225 is located between the positive electrode sheet 223 and the negative electrode sheet 224 to isolate the positive and negative electrodes. The bare battery cell is wound and the tabs are welded. The bare battery cell is placed in a shell made of different materials, and the prepared electrolyte is injected into the dried shell. The battery cell is packaged, allowed to stand, formed, shaped, and capacity tested to complete the preparation of the lithium-ion battery cell 20.

[0256] In the following embodiments and comparative examples, the yield strength of the housing 211 of the battery cell 20 at a temperature of 25°C is Re, and different materials are selected for the housing 211 to achieve different yield strengths Re. The negative electrode active material of the negative electrode tab 224 of the electrode assembly 22 of the battery cell 20 includes a silicon-based material, with the mass percentage of the silicon-based material being g. The specific parameters are shown in Table 4 below. In addition, in each embodiment and comparative example, the material of the housing 211 is the same throughout the entire area, and the yield strength Re of the housing 211 at 25°C is measured using the method specified in GB / T 228.1-2010. The battery cells 20 in the following embodiments and comparative examples are identical except for the parameters shown in Table 4. For example, the wall thickness of each wall of the housing 211 of the battery cell 20 in each embodiment is 0.25 mm. For another example, the capacity of the battery cell 20 in each embodiment is 350 Ah.

[0257] A cyclic charging fatigue test is performed on the battery cells 20 in the following embodiments and comparative examples. Specifically, the test can be performed using a fixture 700 for cyclic charging fatigue testing as shown in FIG7 .

[0258] Specifically, the battery cell 20 is clamped and fixed in the dedicated fixture 700, ensuring that the two oppositely disposed walls with the largest areas of the battery cell 20 are clamped, and the initial pressure is set to 2000N, and the electrode terminals 214 of the battery cell 20 are connected to the dedicated battery charging and discharging equipment.

[0259] The fixture 700 holding the battery cell 20 is placed in a constant temperature environment of 25±2° C., and the test is started after the battery cell 20 reaches temperature equilibrium.

[0260] The specific test steps are carried out in accordance with Chapter 6.4 "Standard Cycle Life" of "GBT31484-2015 Requirements and Test Methods for Cycle Life of Power Batteries for Electric Vehicles", and the test cycle end condition is changed to "stop testing until the weld 2113 of the battery cell 20 is damaged."

[0261] For example, the test can be carried out according to the following steps: step a, discharge at 1I(A) to the discharge termination condition specified by the enterprise; step b, leave it for no less than 30 minutes or the shelf condition specified by the enterprise; step c, charge according to the method of 6.1.1.3; step d, leave it for no less than 30 minutes or the shelf condition specified by the enterprise; step e, discharge at 1I1(A) to the discharge termination condition specified by the enterprise; step f, cycle according to steps b to e until the weld 2113 is damaged and the test is stopped.

[0262] During the above test process, the weld 2113 of the battery cell 20 was continuously observed until leakage occurred at the weld 2113. The number of cycles was recorded to obtain the fatigue failure condition of the housing 211 at 1000 cycles, as shown in Table 4 below. In the following embodiments and comparative examples, the weld 2113 refers to the weld between the housing 211 and the cover plate 212, i.e., the weld 2113 surrounds the open end of the housing 211, which is an integrally molded structure.

[0263] Table 4

[0264] It should be understood that in Table 4 above, the material of housing 211 may be modified stainless steel, and the yield strength Re of modified stainless steel at room temperature (25°C) is typically at least 140 MPa to 180 MPa. In the above embodiment, only 145 MPa and 173 MPa are used as examples, but are not limited thereto. Similarly, the material of housing 211 may be SUS316 stainless steel, and the yield strength Re of SUS316 stainless steel at room temperature (25°C) is typically at least 177 MPa. In the above embodiment, only 182 MPa and 193 MPa are used as examples. The material of housing 211 may be Q195 carbon steel, and the yield strength Re of Q195 carbon steel at room temperature (25°C) is typically at least 195 MPa. In the above embodiment, only 203 MPa is used as an example. The material of housing 211 may be SUS304 stainless steel, and the yield strength Re of SUS304 stainless steel at room temperature (25°C) is typically at least 205 MPa. In the above embodiment, only 212 MPa is used as an example.

[0265] Comparing the two comparative examples in Table 4 above with the 12 examples shows that different yield strengths Re can be determined when different materials are used for the housing 211. When the yield strength Re satisfies 140 MPa ≤ Re ≤ 1000 MPa, for example, in Examples 1-12, even if the mass percentage g of the silicon-based material in the negative electrode tab 224 of the battery cell 20 varies, the battery cell 20 can still achieve over one thousand fatigue failures, thus meeting the design requirements of the battery cell 20. However, when the yield strength Re does not satisfy 140 MPa ≤ Re ≤ 1000 MPa, for example, in Comparative Examples 1-2, even if the mass percentage g of the silicon-based material in the negative electrode tab 224 of the battery cell 20 is low, the battery cell 20 can still fail to reach one thousand fatigue failures, failing to meet the design requirements of the battery cell 20.

[0266] It should be understood that in the embodiments of the present application, the at least partial area of ​​the housing 211 may include a partial area of ​​the housing 211 or the entire area of ​​the housing 211. In some embodiments, the housing 211 includes a weld 2113, and the at least partial area of ​​the housing 211 includes an area of ​​the housing 211 within a predetermined distance from the weld 2113, where the predetermined distance is L, and L satisfies the following: L = 10 mm. When the negative active material of the negative electrode tab 224 of the electrode assembly 22 includes a silicon-based material, since the silicon-based material can accommodate more metal ions, the deformation of the electrode assembly 22 within the battery cell 20 during use increases, causing the electrode assembly 22 to expand in volume, thereby increasing the pressure exerted by the electrode assembly 22 on the housing 211 of the battery cell 20. Under the same conditions, the structural strength of the area of ​​the housing 211 near the weld 2113 is lower than that of other areas of the housing 211. Therefore, the area of ​​the housing 211 near the weld 2113 is more susceptible to damage during use of the battery cell 20. Therefore, setting an area within a preset distance L from the weld 2113 to meet the requirements of tensile strength Rm or yield strength Re under normal temperature conditions can improve the deformation capacity of the area of ​​the shell 211 close to the weld 2113, making this part of the shell 211 less prone to damage, thereby improving the structural stability and service life of the battery cell 20.

[0267] If the positive active material of the positive electrode tab 223 of the electrode assembly 22 includes a nickel-containing compound, if thermal runaway occurs in the battery cell 20, the internal temperature of the battery cell 20 will rapidly increase and a large amount of gas will be generated. However, under the same conditions, the structural strength of the area near the weld 2113 of the shell 211 is lower than that of other areas of the shell 211. Therefore, the shell 211 is prone to rupture in the area near the weld 2113, which may in turn trigger thermal runaway of the connected battery cells 20, i.e., thermal diffusion. Therefore, by setting the area within a predetermined distance L from the weld 2113 to meet the tensile strength Rn or melting point p requirements under high temperature conditions, the deformation capacity of this portion of the shell 211 can be improved, making it less likely to be rapidly damaged or completely melted, reducing the risk of thermal diffusion or even explosion between multiple battery cells 20, and thus improving the reliability of the battery 10.

[0268] It should be understood that the weld 2113 included in the shell 211 of the embodiment of the present application may include a weld 2113 at any position of the shell 211. For example, the weld 2113 included in the shell 211 may include a weld between the shell 211 and the cover plate 212, that is, the area around the open end of the shell 211 is a weld. For another example, the weld 2113 of the shell 211 may also include a weld between different parts of the shell 211. For example, the shell 211 may include at least two parts, and the at least two parts are connected by welding to form the shell 211. In Figure 4, the shell 211 includes two parts along the height direction Z of the battery cell 20 as an example, and there is a weld 2113 between the upper half shell and the lower half shell; or, unlike what is shown in Figure 4, other parts of the shell 211 may also be provided with welds 2113. The embodiment of the present application is not limited to this.

[0269] In some embodiments, at least a portion of the housing 211 includes a surrounding region 2111 of the housing 211. The surrounding region 2111 surrounds the electrode assembly 22 and comprises at least a portion of the sidewall of the housing 211. Therefore, when the negative active material of the negative electrode tab 224 of the electrode assembly 22 comprises a silicon-based material, because the silicon-based material can accommodate more metal ions, the deformation of the electrode assembly 22 within the battery cell 20 during use increases, causing the electrode assembly 22 to expand in volume, thereby increasing the pressure exerted by the electrode assembly 22 on the housing 211 of the battery cell 20. Therefore, providing the surrounding region 2111 to meet the requirements for tensile strength Rm or yield strength Re at room temperature can improve the deformation capacity of the housing 211. Furthermore, the surrounding region 2111 surrounding the electrode assembly 22 can limit the radial compressive force exerted by the internal electrode assembly 22 on the housing 211, making the housing 211 less susceptible to damage and thereby improving the structural stability and service life of the battery cell 20.

[0270] When the positive active material of the positive electrode plate 223 of the electrode assembly 22 includes a nickel-containing compound, if the battery cell 20 undergoes thermal runaway, the internal temperature of the battery cell 20 will increase rapidly and a large amount of gas will be generated; and the surrounding area 2111 meets the requirements of tensile strength Rn or melting point p under high temperature conditions, then the deformation ability of the surrounding area 2111 of the shell 211 can be improved, which will make the surrounding area 2111 not easily destroyed or completely melted, and can limit the excessive expansion of the electrode assembly 22 inside the shell 211 along its thickness direction, thereby reducing the possibility of explosion of the battery cell 20, and thereby reducing the risk of thermal runaway of adjacent battery cells 20, thereby improving the reliability of the battery 10.

[0271] It should be understood that the position and size of the surrounding area 2111 of the embodiment of the present application can be flexibly set according to actual applications. For example, along the height direction Z of the battery cell 20, the height of the surrounding area 2111 can be less than or equal to the height of the shell 211. Specifically, if the height of the surrounding area 2111 along the height direction Z of the battery cell 20 is less than the height of the shell 211, then the surrounding area 2111 can be located at any position of the shell 211 along the height direction Z of the battery cell 20. For example, the surrounding area 2111 can be located in the middle of the shell 211 along the height direction Z of the battery cell 20 to limit the deformation of the corresponding middle position of the electrode assembly 22.

[0272] If the height of the surrounding area 2111 along the height direction Z of the battery cell 20 is equal to the height of the shell 211, then the surrounding area 2111 includes all the side walls of the shell 211 and can wrap the sides of the electrode assembly 22, thereby improving the structural strength of the side walls of the shell 211 and reducing the risk of explosion and heat diffusion of the battery cell 20 after thermal runaway due to damage to the local weak areas of the side walls of the shell 211, thereby improving the reliability of the battery 10.

[0273] In some embodiments, at least a portion of the housing 211 includes the entire wall of the housing 211. That is, in the embodiments of the present application, at least a portion of the housing 211 may refer to the entire area of ​​the housing 211. Thus, when the negative active material of the negative electrode tab 224 of the electrode assembly 22 includes a silicon-based material, since the silicon-based material can accommodate more metal ions, the deformation of the electrode assembly 22 within the battery cell 20 during use will increase, causing the electrode assembly 22 to expand in volume, thereby increasing the pressure exerted by the electrode assembly 22 on the housing 211 of the battery cell 20. Therefore, ensuring that the entire area of ​​the housing 211 meets the requirements for tensile strength Rm or yield strength Re at room temperature can improve the overall deformation capacity of the housing 211 and limit the compressive force of the internal electrode assembly 22 on the housing 211 in all directions, thereby achieving balanced strength among various parts of the housing 211 and preventing damage in local weak areas. This in turn improves the structural stability and service life of the battery cell 20.

[0274] When the positive active material of the positive electrode plate 223 of the electrode assembly 22 includes a nickel-containing compound, if the battery cell 20 undergoes thermal runaway, the internal temperature of the battery cell 20 will increase rapidly and a large amount of gas will be generated; and the entire area of ​​the shell 211 meets the requirements of tensile strength Rn or melting point p under high temperature conditions, then the overall deformation ability of the shell 211 can be improved, making the shell 211 less likely to be damaged or melted, and can limit the high-temperature and high-pressure gas inside the shell 211, reducing the impact on the connected battery cells 20, and thereby reducing the risk of thermal runaway of adjacent battery cells 20, thereby improving the reliability of the battery 10.

[0275] Furthermore, the cover plate 212 of the embodiment of the present application can be made of the same material as at least a portion of the housing 211 of the embodiment of the present application, so that the structural strength of the cover plate 212 also meets the design requirements. For example, the cover plate 212 can also meet at least one of the requirements for tensile strength Rm and yield strength Re at room temperature, and tensile strength Rn and melting point p at high temperature, thereby improving the structural strength of the cover plate 212 and thereby improving the structural stability of the battery cell 20, but the embodiment of the present application is not limited to this.

[0276] In some embodiments, the tensile strength of at least a portion of the shell 211 at a temperature of 25°C is Rm, and at least a portion of the shell 211 includes a third shell wall 2112, the average thickness of the third shell wall is T, and Rm and T satisfy: 250MPa≤Rm≤2000MPa, 0.05mm≤T≤0.5mm, 60mm·MPa≤T×Rm≤500mm·MPa.

[0277] It should be understood that the third shell wall 2112 of the shell 211 of the embodiment of the present application can be any wall of the shell 211. Specifically, the battery cell 20 can be any polyhedral structure, the shell 211 can be a hollow structure with at least one end open, the shell 211 can include one or more walls, the third shell wall 2112 can be any wall of the shell 211, and the shell 211 can include one or more third shell walls 2112. For example, if the shell 211 is a polygonal prism, the third shell wall 2112 can be any wall of the polygonal prism, and the surface of the third shell wall 2112 can be any polygon. For another example, as shown in Figures 3 and 4, if the shell 211 is a rectangular parallelepiped, the third shell wall 2112 can be any wall of the shell 211, and the surface of the third shell wall 2112 is a rectangle. For another example, if the housing 211 is cylindrical, the third housing wall 2112 can be the bottom surface of the cylinder or the side surface of the cylinder, but the present embodiment is not limited to this. In addition, if two adjacent walls of the housing 211 are connected by a rounded corner, then in the embodiment of the present application, when the third housing wall 2112 is any wall of the housing 211, the third housing wall 2112 does not include the rounded corner connection area between the wall and the adjacent wall.

[0278] In the embodiment of the present application, at least a portion of the housing 211 includes a third housing wall 2112. The tensile strength of the third housing wall 2112 at a room temperature of 25°C is Rm. Increasing the tensile strength Rm of at least a portion of the housing 211 at a room temperature of 25°C can improve the deformation capacity of the housing 211, making the housing 211 less susceptible to damage during use of the battery cell 20, thereby improving the structural stability and service life of the battery cell 20. However, the tensile strength Rm of at least a portion of the housing 211 at room temperature should not be too high, to reduce the difficulty in selecting the material and processing the housing 211, saving costs and facilitating processing.

[0279] If the average thickness T of the third shell wall 2112 of the housing 211 is relatively thin, the structural strength of the third shell wall 2112 can be increased by increasing its tensile strength Rm at a room temperature of 25°C. This can both increase the energy density of the battery cell 20 and improve its structural strength and stability. Conversely, if the average thickness T of the third shell wall 2112 of the housing 211 is relatively thick, the structural strength of the housing 211 can be improved. By appropriately lowering the requirement for the tensile strength Rm of the third shell wall 2112 at room temperature, the difficulty in selecting the material for the housing 211 can be reduced, thereby reducing the difficulty and cost of manufacturing the battery cell 20. Furthermore, T×Rm represents the stiffness of the third shell wall. Limiting the stiffness of the third shell wall to a value neither too small nor too large ensures that the third shell wall has good deformability while reducing manufacturing difficulty and cost.

[0280] It should be understood that the range of values ​​for the average thickness T of the third shell wall 2112 in the embodiment of the present application can also be flexibly set according to actual applications. For example, the average thickness T of the third shell wall 2112 satisfies the following: 0.05mm≤T≤0.5mm. Furthermore, the average thickness T of the third shell wall 2112 satisfies the following: 0.1mm≤T≤0.4mm. Appropriately thinning the average thickness T of the third shell wall 2112 can reduce the space occupied by the shell 211 within the battery 10, thereby increasing the energy density of the battery 10. It can also compensate for the structural strength requirement of the shell 211 by increasing the tensile strength Rm of the third shell wall 2112 at room temperature to maintain the stability of the shell 211. Appropriately increasing the average thickness T of the third shell wall 2112 can also reduce the difficulty of processing the third shell wall 2112.

[0281] Furthermore, the average thickness T of the third shell wall 2112 satisfies the following relationship: 0.1 mm ≤ T ≤ 0.3 mm. This average thickness T of the third shell wall 2112 is neither too large nor too small, thereby improving the structural strength and stability of the shell 211 while reducing the space occupied by the shell 211 within the battery 10, thereby increasing the energy density of the battery 10.

[0282] In some embodiments, the average thickness T of the third housing wall 2112 of the present application can also be set to other values. For example, the average thickness T of the third housing wall 2112 can be any of the following values ​​or between any two of the following values: 0.05 mm, 0.075 mm, 0.1 mm, 0.125 mm, 0.15 mm, 0.175 mm, 0.2 mm, 0.225 mm, 0.25 mm, 0.275 mm, 0.3 mm, 0.325 mm, 0.35 mm, 0.375 mm, 0.4 mm, 0.425 mm, 0.45 mm, 0.475 mm, and 0.5 mm.

[0283] In some embodiments, the value range of T×Rm can be adjusted based on actual application. For example, Rm and T satisfy the following relationship: 60 mm·MPa ≤ T×Rm ≤ 500 mm·MPa; further, Rm and T can satisfy the following relationship: 100 mm·MPa ≤ T×Rm ≤ 500 mm·MPa. By selecting appropriate materials, the tensile strength Rm of the third shell wall 2112 at room temperature can be increased, thereby reducing the average thickness T of the third shell wall 2112. This ensures that the stiffness of the third shell wall 2112 meets design requirements, thereby improving the structural strength and stability of the third shell wall 2112 of the shell 211 and increasing the energy density of the battery cell 20 and battery 10.

[0284] Furthermore, the value range of T×Rm can also be set to: Rm and T satisfy: 100mm·MPa≤T×Rm≤300mm·MPa, so that the stiffness value of the third shell wall 2112 is more appropriate, which can not only make the third shell wall 2112 have good deformation ability to improve the service life of the battery cell 20, but also reduce the difficulty of material selection, thereby reducing the processing difficulty and processing cost.

[0285] In some embodiments, the value of T×Rm in the embodiments of the present application can also be set to other values. For example, the value of T×Rm can be any one of the following values ​​or between any two of the following values: 60mm·MPa, 65mm·MPa, 70mm·MPa, 75mm·MPa, 80mm·MPa, 85mm·MPa, 90mm·MPa, 95mm·MPa, 100mm·MPa, 130mm·MPa, 150mm·MPa, 180mm·MPa, 200mm·MPa, 230mm·MPa, 250mm·MPa, 280mm·MPa, 300mm·MPa, 330mm·MPa, 350mm·MPa, 380mm·MPa, 400mm·MPa, 430mm·MPa, 450mm·MPa, 480mm·MPa, and 500mm·MPa.

[0286] In the embodiment of the present application, the mass proportion g of the silicon-based material and the average thickness T of the third shell wall 2112 can be mutually restricted, and can also be mutually restricted with the tensile strength Rm of at least a portion of the shell 211 at a temperature of 25°C, so as to balance the relationship between the energy density and structural strength of the battery cell 20. For example, in the negative electrode active material, the mass proportion of the silicon-based material is g, and g and T satisfy: 2% < g < 20%, 0.15mm ≤ T ≤ 0.4mm. When the mass proportion g of the silicon-based material is small, the average thickness T of the third shell wall 2112 can be appropriately reduced to improve the space utilization of the shell 211, increase the energy density of the battery cell 20, and balance the structural strength of the shell 211.

[0287] In some embodiments, the mass percentage of the silicon-based material in the negative electrode active material is g, where g, T, and Rm satisfy the following conditions: 15% < g < 40%, 0.2 mm ≤ T ≤ 0.4 mm, and 100 mm·MPa ≤ T×Rm ≤ 500 mm·MPa. Increasing the mass g of the silicon-based material can effectively increase the energy density of the battery cell 20. Furthermore, increasing the thickness and stiffness T×Rm of the third housing wall 2112 can improve the structural strength and stability of the battery cell 20.

[0288] It should be understood that the average thickness T of the third housing wall 2112 in the embodiment of the present application may refer to the average thickness of at least a portion of the third housing wall 2112. For example, the average thickness T of the third housing wall 2112 may refer to the average thickness T of the entire region of the third housing wall 2112. In particular, when the third housing wall 2112 is relatively flat, that is, when the thickness of most regions of the third housing wall 2112 is substantially equal or has a small difference, or when the thickness of all regions of the third housing wall 2112 is substantially equal or has a small difference, the average thickness of the entire region of the third housing wall 2112 can be determined as T.

[0289] For another example, the average thickness T of the third housing wall 2112 may also refer to the average thickness T of a local area of ​​the third housing wall 2112, that is, the average thickness T of the remaining area after excluding the partial area of ​​the third housing wall 2112. For example, if the third housing wall 2112 includes a special area, and the thickness of the special area is significantly different from that of other areas, for example, the special area includes a protruding structure or a recessed area, making the thickness of the special area greater or smaller than that of other areas, then the special area can be excluded to calculate the average thickness T of the remaining area of ​​the third housing wall 2112.

[0290] In some embodiments, the third housing wall 2112 includes a functional area. The average thickness T of the third housing wall 2112 is the average thickness of the area of ​​the third housing wall 2112 excluding the functional area. The functional area includes at least one of the following areas: a pressure relief area, an area where the electrode terminals 214 are located, a liquid injection area, and a welding area. The thickness of the functional area is typically significantly different from the thickness of other areas of the third housing wall 2112. Therefore, when calculating the average thickness T of the third housing wall 2112 excluding the functional area, the design of the third housing wall 2112 can be made more consistent with strength requirements, thereby improving the structural strength and stability of the battery cell 20.

[0291] Specifically, the functional area of ​​the embodiment of the present application may include an area on the third shell wall 2112 that is provided with a specific structure or has a specific purpose. For example, the functional area may include a pressure relief area, which is used to set a pressure relief mechanism. The pressure relief mechanism is used to activate an element or component to release the internal pressure or temperature when the internal pressure or temperature of the battery cell 20 reaches a predetermined threshold. The predetermined threshold can be adjusted according to different design requirements. For example, the predetermined threshold may depend on one or more materials of the positive electrode plate, negative electrode plate, electrolyte, and separator in the battery cell 20.

[0292] The "activation" mentioned in this application refers to the action of the pressure relief mechanism or its activation to a certain state, so that the internal pressure and temperature of the battery cell 20 can be released. The action produced by the pressure relief mechanism may include but is not limited to: at least a part of the pressure relief mechanism is broken, shattered, torn or opened, etc. When the pressure relief mechanism is actuated, the high-temperature and high-pressure substances inside the battery cell 20 will be discharged outward from the actuated part as emissions. In this way, the pressure and temperature of the battery cell 20 can be relieved under controllable pressure or temperature, thereby avoiding potential more serious accidents.

[0293] The emissions from the battery cells 20 mentioned in this application include, but are not limited to: electrolyte, dissolved or split positive and negative electrode plates, fragments of the separator, high-temperature and high-pressure gas generated by the reaction, flames, etc.

[0294] The pressure relief mechanism of the embodiment of the present application can be disposed on any wall of the battery cell 20. For example, the pressure relief mechanism can be disposed in the pressure relief area of ​​the third shell wall 2112 of the battery cell 20. The pressure relief mechanism can be a part of the third shell wall 2112; alternatively, it can be a separate structure from the third shell wall 2112 and fixed to the third shell wall 2112 by, for example, welding. For example, when the pressure relief mechanism is a part of the third shell wall 2112, the pressure relief mechanism can be formed by providing a notch on the third shell wall 2112, that is, the third shell wall 2112 is provided with a notch in the pressure relief area, and the thickness of the notch is significantly less than the thickness of other areas of the third shell wall 2112. Therefore, the thickness at the notch can be excluded from the average thickness T of the third shell wall 2112. The notch is the weakest point of the pressure relief mechanism. When the battery cell 20 generates too much gas, causing the internal pressure to rise and reach a threshold, or the internal reaction of the battery cell 20 generates heat, causing the internal temperature of the battery cell 20 to rise and reach a threshold, the pressure relief mechanism can rupture at the notch, causing the inside and outside of the battery elevator 20 to communicate with each other, and the gas pressure and temperature are released outward through the rupture of the pressure relief mechanism, thereby preventing the battery cell 20 from exploding.

[0295] For another example, the pressure relief mechanism may be a separate structure from the third shell wall 2112. The pressure relief mechanism may take the form of an explosion-proof valve, an air valve, a pressure relief valve, or a safety valve, and may specifically employ a pressure-sensitive or temperature-sensitive element or structure. For example, the third shell wall 2112 may be provided with a through hole in the pressure relief area, and the pressure relief mechanism may be mounted and fixed to the third shell wall 2112 via the through hole. After installation, the pressure relief mechanism may protrude or be recessed relative to other areas of the third shell wall 2112. Therefore, the calculation of the average thickness T of the third shell wall 2112 may not include the pressure relief area where the pressure relief mechanism is located. When the internal pressure or temperature of the battery cell 20 reaches a predetermined threshold, the pressure relief mechanism activates or a weak structure provided in the pressure relief mechanism is destroyed, thereby forming an opening or channel for the internal pressure or temperature to be released.

[0296] In some embodiments, the functional area may also include an area where the electrode terminals 214 are located. Specifically, the electrode terminals 214 in the embodiments of the present application are used to electrically connect to the electrode assembly 22 within the battery cell 20 to output electrical energy from the battery cell 20. Furthermore, the battery cell 20 may include at least two electrode terminals 214, each of which includes at least one first electrode terminal 214a and at least one second electrode terminal 214b. The first electrode terminal 214a and the second electrode terminal 214b have opposite polarities. For example, the first electrode terminal 214a may be a positive electrode terminal, and the second electrode terminal 214b may be a negative electrode terminal; alternatively, the first electrode terminal 214a may be a negative electrode terminal, and the second electrode terminal 214b may be a positive electrode terminal. The positive electrode terminal is used to electrically connect to the positive tab 222a of the electrode assembly 22, and the negative electrode terminal is used to electrically connect to the negative tab 222b of the electrode assembly 22. The positive electrode terminal and the positive electrode tab 222a can be directly or indirectly connected, and the negative electrode terminal and the negative electrode tab 222b can be directly or indirectly connected. For example, the positive electrode terminal can be electrically connected to the positive electrode tab 222a through a connecting member 23, and the negative electrode terminal can be electrically connected to the negative electrode tab 222b through a connecting member 23.

[0297] It should be understood that each electrode terminal 214 of the embodiment of the present application can be disposed on any wall, and multiple electrode terminals 214 can be disposed on the same wall or on different walls of the battery cell 20. For example, as shown in Figures 3 and 4 , taking the example of each battery cell 20 including two electrode terminals 214, and the two electrode terminals 214 being located on the same wall, for example, the two electrode terminals 214 can both be located on the cover plate 212.

[0298] For another example, assuming that each battery cell 20 includes two electrode terminals 214, and that the two electrode terminals 214 are located on the same wall, unlike what is shown in Figures 3 and 4 , the two electrode terminals 214 may also be located in the housing 211. For example, the two electrode terminals 214 may both be located in the third housing wall 2112 of the housing 211. When the electrode terminals 214 are located in the third housing wall 2112, they typically protrude from other areas of the third housing wall 2112. That is, the thickness of the area where the electrode terminals 214 are located is much greater than the thickness of other areas of the third housing wall 2112. Therefore, the area where the electrode terminals 214 are located may not be included when calculating the average thickness T of the third housing wall 2112.

[0299] In some embodiments, the functional area may also include a liquid injection area. For example, the liquid injection area of ​​the third housing wall 2112 may be provided with an injection hole through which electrolyte is injected into the interior of the housing 211. After the electrolyte is injected, the injection hole can be sealed with a sealant. Given that the thickness of the liquid injection area where the sealant is located is typically much greater than the thickness of other areas of the third housing wall 2112, the liquid injection area may not be included in the calculation of the average thickness T of the third housing wall 2112.

[0300] In some embodiments, the functional area may also include a welding area. For example, the third shell wall 2112 may be fixed to other walls by welding, or the third shell wall 2112 itself may need to be formed by welding, in which case the third shell wall 2112 may include a welding area. For example, as shown in Figure 4, the shell 211 may be welded by splicing, and the shell 211 may have a weld 2113. Specifically, the shell 211 may include at least two parts, which are connected by welding to form the shell 211. Figure 4 uses the example of the shell 211 including two parts along the height direction Z of the battery cell 20, with a weld 2113 between the upper and lower shell halves. Alternatively, other parts of the shell 211 may also be provided with a weld 2113, unlike what is shown in Figure 4. The embodiments of the present application are not limited to this. The welding area of ​​the functional area in the embodiments of the present application may also include the weld 2113. Due to processing reasons, the thickness of the welding area is generally greater than the thickness of other areas of the third shell wall 2112 . Therefore, the calculation of the average thickness T of the third shell wall 2112 may not include the welding area.

[0301] In the embodiment of the present application, the third housing wall 2112 of the housing 211 can be any wall of the housing 211. For example, the third housing wall 2112 is the wall with the smallest thickness of the housing 211. That is, by limiting the thickness T of the wall with the smallest thickness of the housing 211, the thicknesses of the other walls of the housing 211 are limited, so that each wall of the housing 211 can meet the structural strength requirements, thereby improving the structural strength and stability of the battery cell 20.

[0302] In some embodiments, the third housing wall 2112 is the wall with the largest area of ​​the housing 211. Considering that when multiple battery cells 20 are arranged in the battery 10, the multiple battery cells 20 are generally abutted against each other through the wall with the largest area of ​​the housing 211. Therefore, the wall with the largest area is generally subjected to the greatest compression force from the electrode assembly 22. Therefore, by limiting the average thickness T and room-temperature tensile strength Rm of the third housing wall 2112, the deformation capacity of the housing 211 can be effectively improved, thereby improving the structural strength and stability of the battery cells 20.

[0303] It should be understood that the position of the wall with the largest area of ​​the housing 211 in the embodiment of the present application can be set according to actual application. For example, the battery 10 may include multiple battery cells 20, and the arrangement direction of the multiple battery cells 20 can be perpendicular or parallel to the wall with the largest area of ​​the housing 211, but the embodiment of the present application is not limited to this.

[0304] In some embodiments, the shell 211 includes an intersecting bottom wall and side walls, wherein the bottom wall is used to support the electrode assembly contained in the shell 211. Specifically, the shell 211 can be a hollow structure with an opening at least at one end, and the bottom wall and side wall of the shell 211 do not necessarily refer to the walls opposite to and adjacent to the opening, respectively. The electrode assembly 22 is contained inside the shell 211. Taking into account that in actual applications, the setting direction of the electrode assembly 22 may be different due to different application scenarios, the shell 211 may include a wall for supporting the electrode assembly 22. Therefore, the bottom wall of the shell 211 in the embodiment of the present application is a wall for supporting the electrode assembly 22, that is, the bottom wall of the shell 211 is used to withstand the gravity of the electrode assembly 22. Conversely, the wall of the shell 211 that directly intersects with the bottom wall is the side wall of the shell 211.

[0305] In some embodiments, the third housing wall 2112 serves as a sidewall of the housing 211. Considering the different uses of the bottom wall and sidewalls of the housing 211, the design requirements for the bottom wall and sidewalls may also differ. For example, the sidewalls of the housing 211 typically require higher deformation capacity. Therefore, if the third housing wall 2112 serves as the sidewall of the housing 211, by limiting the tensile strength Rm of the sidewall of the housing 211 at room temperature and the average thickness T of the sidewall, the deformation capacity of the sidewall of the housing 211 can be effectively improved, thereby improving the structural stability of the battery cell 20.

[0306] In some embodiments, the housing 211 includes a plurality of side walls having equal thickness to facilitate processing.

[0307] In some embodiments, the thickness of the bottom wall of the housing 211 is equal to the thickness of the side walls of the housing 211 to facilitate processing and optimize the space occupied by the housing 211 .

[0308] In some embodiments, the third shell wall 2112 is perpendicular to the stacking direction of the pole pieces of the electrode assembly 22. The stacking direction of the pole pieces of the electrode assembly 22 is generally the thickness direction of the electrode assembly 22. Considering that the electrode assembly 22 is prone to expansion in the thickness direction during the cyclic charge and discharge of the battery cell 20, the deformation requirements of the corresponding shell 211 wall are relatively high. Therefore, the third shell wall 2112 is set to be a wall perpendicular to the stacking direction of the pole pieces of the electrode assembly 22, or in other words, the third shell wall 2112 and the electrode assembly 22 are arranged along the stacking direction of the pole pieces of the electrode assembly 22. By limiting the tensile strength Rm and average thickness T of the third shell wall 2112 at room temperature, it is possible to improve the energy density of the battery cell 20, effectively improve the deformation capacity of the third shell wall 2112, and thus improve the structural stability of the battery cell 20.

[0309] It should be understood that the cover plate 212 of the embodiment of the present application can have the same or different designs as the third housing wall 2112. For example, the cover plate 212 can have the same design as the third housing wall 2112, that is, the average thickness of the cover plate 212 can be T, the room temperature tensile strength of the cover plate 212 can be b, and the design requirements of b and T can be met to improve the deformation capability of the cover plate 212, thereby improving the structural strength and stability of the battery cell 20.

[0310] In some embodiments, the ratio of the volume of the interior space of the housing 211 to the outer volume of the housing 211 is greater than or equal to 93%. That is, the thickness of the housing 211 is relatively thin, so that the housing 211 itself occupies less space, thereby improving the space utilization and energy density of the battery 10.

[0311] It should be understood that the specific calculation method for the volume of the internal space of the housing 211 and the external volume of the housing 211 in the embodiment of the present application is related to the shape of the housing 211. For example, taking the housing 211 as a rectangular parallelepiped as an example. Figure 8 shows a side view of the housing 211 in the embodiment of the present application, and Figure 9 shows a top view of the housing 211 in the embodiment of the present application. For example, the housing 211 shown in Figures 8 and 9 can be the housing 211 of the battery cell 20 shown in Figures 3 and 4.

[0312] As shown in Figures 8 and 9, a rectangular shell 211 is taken as an example, and the shell 211 is a hollow rectangular parallelepiped with one end open. When calculating the volume of the internal space of the shell 211 and the external volume of the shell 211, the fillet connections between adjacent walls of the shell 211 can be ignored. As shown in Figures 8 and 9, since each wall of the shell 211 has a certain thickness, in the length direction Y, the internal length of the shell 211 is Y1, and the external length is Y2, and Y2 is greater than Y1; similarly, in the width direction X, the internal width of the shell 211 is X1, and the external width is X2, and X2 is greater than X1; in the height direction Z, the internal height of the shell 211 is Z1, and the external height is Z2, and Z2 is greater than Z1. Therefore, the volume V1 of the internal space of the shell 211 = X1 × Y1 × Z1; the volume V2 of the external space of the shell 211 = X2 × Y2 × Z2, and V1 / V2 is greater than or equal to 93%, so as to reduce the space occupied by the shell 211 itself, thereby improving the space utilization and energy density of the battery 10.

[0313] The following is a comparative explanation through a number of comparative examples and a number of embodiments. Specifically, the battery cells 20 in the following embodiments and comparative examples are all based on the square-shell battery shown in FIG3 and FIG4 , wherein the shell 211 adopts a hollow structure with one end open.

[0314] In the following embodiments and comparative examples, the preparation methods of the positive electrode sheet 223 , the negative electrode sheet 224 , the electrolyte and the separator 225 of the battery cell 20 are as follows.

[0315] 1. Preparation of positive electrode sheet 223

[0316] The positive electrode active material LiNi 0.95 Co 0.04 Mn 0.01 O2, conductive agent Super P, and binder polyvinylidene fluoride (PVDF) are prepared into positive electrode slurry in N-methylpyrrolidone (NMP), wherein the solid content in the positive electrode slurry is 50wt%, and the solid content of LiNi 0.7 Co 0.1 Mn 0.1The mass ratio of O2, Super P, and PVDF is 8:1:1. The positive electrode slurry is coated on the upper and lower surfaces of the current collector aluminum foil and dried at 85°C and then cold pressed. Then, it is trimmed, cut, and striped, and then dried under vacuum conditions at 85°C for 4 hours to form a positive electrode sheet 223.

[0317] 2. Preparation of negative electrode sheet 224

[0318] The negative electrode active material is mixed evenly with the conductive agent Super P, the thickener carboxymethyl cellulose (CMC), and the adhesive styrene butadiene rubber (SBR) in deionized water to prepare a negative electrode slurry, wherein the negative electrode active material includes graphite and silicon-based material, and the silicon-based material is a silicon oxide compound. The solid content in the negative electrode slurry is 30wt%, and the mass ratio of the negative electrode active material, silicon oxide, Super P, CMC and adhesive styrene butadiene rubber (SBR) in the solid component is 88:7:3:2. The negative electrode slurry is coated on the upper and lower surfaces of the current collector copper foil and dried at 85°C, and then cold pressed, trimmed, cut into pieces, and slit, and then dried under vacuum conditions at 120°C for 12 hours to prepare a negative electrode sheet 224.

[0319] 3. Preparation of electrolyte

[0320] In an argon atmosphere glove box (H2O <0.1ppm, O2 <0.1ppm), the fully dried electrolyte salt LiPF6 was dissolved in a mixed solvent (the mixed solvent included ethylene carbonate (EC) and diethyl carbonate (DEC), and ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a mass ratio of 50:50), and after mixing evenly, an electrolyte solution with a concentration of 1 mol / L was obtained.

[0321] 4. Preparation of Isolator 225

[0322] A 16 μm polyethylene film was used as the separator 225 .

[0323] 5. Preparation of lithium-ion battery cell 20

[0324] The positive electrode sheet 223, the separator 225 and the negative electrode sheet 224 are stacked in order, so that the separator 225 is located between the positive electrode sheet 223 and the negative electrode sheet 224 to isolate the positive and negative electrodes. The bare battery cell is wound and the tabs are welded. The bare battery cell is placed in a shell made of different materials, and the prepared electrolyte is injected into the dried shell. The battery cell is packaged, allowed to stand, formed, shaped, and capacity tested to complete the preparation of the lithium-ion battery cell 20.

[0325] In the following embodiments and comparative examples, the tensile strength of the housing 211 of the battery cell 20 at a temperature of 25°C is Rm. To achieve different tensile strengths Rm, different materials are selected for the housing 211. The average thickness of the third housing wall 2112 of the housing 211 is T. The specific parameters are shown in Table 5 below. Furthermore, in each embodiment and comparative example, the material of the housing 211 is the same throughout the entire area. The tensile strength Rm of the housing 211 at 25°C is measured using the method specified in GB / T 228.1-2010. The battery cells 20 in the following embodiments and comparative examples are identical except for the parameters shown in Table 5. For example, the capacity of the battery cell 20 in each embodiment is 350 Ah.

[0326] A cyclic charging fatigue test is performed on the battery cells 20 in the following embodiments and comparative examples. Specifically, the test can be performed using a fixture 700 for cyclic charging fatigue testing as shown in FIG7 .

[0327] Specifically, the battery cell 20 is clamped and fixed in the dedicated fixture 700, ensuring that the two oppositely disposed walls with the largest areas of the battery cell 20 are clamped, and the initial pressure is set to 2000N, and the electrode terminals 214 of the battery cell 20 are connected to the dedicated battery charging and discharging equipment.

[0328] The fixture 700 holding the battery cell 20 is placed in a constant temperature environment of 25±2° C., and the test is started after the battery cell 20 reaches temperature equilibrium.

[0329] The specific test steps are carried out in accordance with Chapter 6.4 "Standard Cycle Life" of "GBT31484-2015 Requirements and Test Methods for Cycle Life of Power Batteries for Electric Vehicles", and the test cycle end condition is changed to "stop testing until the weld 2113 of the battery cell 20 is damaged."

[0330] For example, the test can be carried out according to the following steps: step a, discharge at 1I(A) to the discharge termination condition specified by the enterprise; step b, leave it for no less than 30 minutes or the shelf condition specified by the enterprise; step c, charge according to the method of 6.1.1.3; step d, leave it for no less than 30 minutes or the shelf condition specified by the enterprise; step e, discharge at 1I1(A) to the discharge termination condition specified by the enterprise; step f, cycle according to steps b to e until the weld 2113 is damaged and the test is stopped.

[0331] During the above test process, the weld 2113 of the battery cell 20 was continuously observed until leakage occurred at the weld 2113. The number of cycles was recorded to obtain the condition of the housing 211 at 1000 cycles as shown in Table 5 below. In the following embodiments and comparative examples, the weld 2113 refers to the weld between the housing 211 and the cover plate 212, i.e., the weld 2113 surrounds the open end of the housing 211, which is an integrally molded structure.

[0332] Table 5

[0333] It should be understood that in Table 5 above, the material of the shell 211 can be Q195 carbon steel, and the tensile strength Rm of Q195 carbon steel at room temperature of 25°C is generally at least 315 MPa to 430 MPa. The above embodiment only takes 328 MPa as an example, but is not limited to this. Similarly, the material of the shell 211 can be SPCC carbon steel, and the tensile strength Rm of SPCC carbon steel at room temperature of 25°C is generally at least 380MPa to 430MPa, and the above embodiment only takes 396MPa as an example; the material of the shell 211 can be SUS430 stainless steel, and the tensile strength Rm of SUS430 stainless steel at room temperature of 25°C is generally at least 450MPa, and the above embodiment only takes 459MPa as an example; the material of the shell 211 can be SUS304 stainless steel, and the tensile strength Rm of SUS304 stainless steel at room temperature of 25°C is generally at least 520MPa, and the above embodiment only takes 533MPa, 625MPa and 763MPa as examples.

[0334] As shown in Table 5 above, in the above-mentioned Examples 1-12, the Rm and T of the third shell wall 2112 of the shell 211 satisfy the following conditions: 250 MPa ≤ Rm ≤ 2000 MPa, 0.05 mm ≤ T ≤ 0.5 mm, and 60 mm·MPa ≤ T×Rm ≤ 500 mm·MPa. Consequently, the number of fatigue failures of the battery cell 20 can reach over one thousand, thus meeting the design requirements of the battery cell 20. Furthermore, even with a smaller average thickness T of the third shell wall 2112, the number of fatigue failures of the battery cell 20 can still reach over one thousand. Furthermore, a smaller average thickness T of the third shell wall 2112 can also increase the energy density of the battery 10. However, in the two comparative examples, the structural strength of the third shell wall 2112 is insufficient, and neither Rm nor T×Rm satisfies the aforementioned values. Even with a larger average thickness T of the third shell wall 2112, the number of fatigue failures of the battery cell 20 does not reach one thousand, failing to meet the design requirements of the battery cell 20.

[0335] In some embodiments, the capacity of the battery cell is C, and the tensile strength of at least a portion of the housing 211 at a temperature of 25°C is Rm. Rm and C satisfy the following conditions: 250 MPa ≤ Rm ≤ 2000 MPa, and 25 Ah ≤ C ≤ 550 Ah. Increasing the capacity C of a battery cell 20 can improve the capacity density of a battery 10 comprising multiple battery cells 20. Alternatively, while the total capacity of the battery 10 remains unchanged, increasing the capacity C of a single battery cell 20 can reduce the number of battery cells 20 required. This, in turn, reduces the number of electrical connections between the multiple battery cells 20, lowering the probability of electrical connection failure and improving battery reliability. Furthermore, when the capacity C of a battery cell 20 is relatively large, increasing the tensile strength Rm of at least a portion of the housing 211 at a room temperature of 25°C can meet the structural strength requirements of the housing 211 for the high-capacity battery cells 20, thereby improving the reliability and service life of the battery cells 20. On the other hand, if the battery cell 20 has a larger capacity, the internal reaction will be more intense, thereby increasing the structural strength requirements of the housing 211. Therefore, the capacity C of the battery cell 20 should not be too large to limit the design requirements for the structural strength of the housing 211. This can also reduce the difficulty in selecting materials and processing the battery cell 20, reduce costs, and improve processing efficiency.

[0336] It should be understood that the range of values ​​for the capacity C of the battery cell 20 in the embodiments of the present application can be adjusted based on actual applications. For example, the capacity C of the battery cell 20 can be reasonably selected based on the actual needs of the battery 10. In some embodiments, the capacity C of the battery cell 20 can be set to further satisfy the following: 100Ah ≤ C ≤ 300Ah. Appropriately increasing the capacity C of the battery cell 20 can increase the energy density of the battery 10; at the same time, the capacity C of the battery cell 20 should not be too large to balance the relationship between the capacity C of the battery cell 20 and the structural strength of the housing 211, thereby improving the reliability and service life of the battery cell 20.

[0337] Furthermore, the capacity C of the battery cell 20 can also satisfy: 150Ah≤C≤250Ah. Further limiting the capacity C of the battery cell 20 can not only increase the energy density of the battery 10, but also improve the structural strength of the housing 211, thereby improving the reliability and service life of the battery cell 20 and the battery 10.

[0338] In some embodiments, the capacity C of the battery cell 20 of the embodiment of the present application can also be set to other values. For example, the capacity C of the battery cell 20 can be any one of the following values ​​or between any two of the following values: 25Ah, 30Ah, 35Ah, 40Ah, 45Ah, 50Ah, 55Ah, 60Ah, 65Ah, 70Ah, 75Ah, 80Ah, 85Ah, 90Ah, 95Ah, 100Ah, 130Ah, 150Ah, 180Ah, 200Ah, 230Ah, 250Ah, 280Ah, 300Ah, 330Ah, 350Ah, 380Ah, 400Ah, 430Ah, 450Ah, 480Ah, 500Ah, 530Ah, and 550Ah.

[0339] It should be understood that the capacity C of a battery cell 20 in the embodiments of the present application represents the amount of electricity output by the battery cell 20 when fully charged and discharged to the termination voltage under specified discharge conditions. The testing method for the capacity C of the battery cell 20 can be selected based on the actual application. For example, a discharge test according to GB / T 31467.1 can be used to determine the capacity C of the battery cell 20, but the embodiments of the present application are not limited thereto.

[0340] The following is a comparative explanation through a number of comparative examples and a number of embodiments. Specifically, the battery cells 20 in the following embodiments and comparative examples are all based on the square-shell battery shown in FIG3 and FIG4 , wherein the shell 211 adopts a hollow structure with one end open.

[0341] In the following embodiments and comparative examples, the preparation methods of the positive electrode sheet 223 , the negative electrode sheet 224 , the electrolyte and the separator 225 of the battery cell 20 are as follows.

[0342] 1. Preparation of positive electrode sheet 223

[0343] The positive electrode active material LiNi 0.95 Co 0.04 Mn 0.01 O2, conductive agent Super P, and binder polyvinylidene fluoride (PVDF) are prepared into positive electrode slurry in N-methylpyrrolidone (NMP), wherein the solid content in the positive electrode slurry is 50wt%, and the solid content of LiNi 0.7 Co 0.1 Mn 0.1 The mass ratio of O2, Super P, and PVDF is 8:1:1. The positive electrode slurry is coated on the upper and lower surfaces of the current collector aluminum foil and dried at 85°C and then cold pressed. Then, it is trimmed, cut, and striped, and then dried under vacuum conditions at 85°C for 4 hours to form a positive electrode sheet 223.

[0344] 2. Preparation of negative electrode sheet 224

[0345] The negative electrode active material is mixed evenly with the conductive agent Super P, the thickener carboxymethyl cellulose (CMC), and the adhesive styrene butadiene rubber (SBR) in deionized water to prepare a negative electrode slurry, wherein the negative electrode active material includes graphite and silicon-based material, and the silicon-based material is a silicon oxide compound. The solid content in the negative electrode slurry is 30wt%, and the mass ratio of the negative electrode active material, silicon oxide, Super P, CMC and adhesive styrene butadiene rubber (SBR) in the solid component is 88:7:3:2. The negative electrode slurry is coated on the upper and lower surfaces of the current collector copper foil and dried at 85°C, and then cold pressed, trimmed, cut into pieces, and slit, and then dried under vacuum conditions at 120°C for 12 hours to prepare a negative electrode sheet 224.

[0346] 3. Preparation of electrolyte

[0347] In an argon atmosphere glove box (H2O <0.1ppm, O2 <0.1ppm), the fully dried electrolyte salt LiPF6 was dissolved in a mixed solvent (the mixed solvent included ethylene carbonate (EC) and diethyl carbonate (DEC), and ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a mass ratio of 50:50), and after mixing evenly, an electrolyte solution with a concentration of 1 mol / L was obtained.

[0348] 4. Preparation of Isolator 225

[0349] A 16 μm polyethylene film was used as the separator 225 .

[0350] 5. Preparation of lithium-ion battery cell 20

[0351] The positive electrode sheet 223, the separator 225 and the negative electrode sheet 224 are stacked in order, so that the separator 225 is located between the positive electrode sheet 223 and the negative electrode sheet 224 to isolate the positive and negative electrodes. The bare battery cell is wound and the tabs are welded. The bare battery cell is placed in a shell made of different materials, and the prepared electrolyte is injected into the dried shell. The battery cell is packaged, allowed to stand, formed, shaped, and capacity tested to complete the preparation of the lithium-ion battery cell 20.

[0352] In the following embodiments and comparative examples, the tensile strength of the housing 211 of the battery cell 20 at a temperature of 25°C is Rm, and different materials are selected to achieve different tensile strengths Rm. The capacity of the battery cell 20 is C. The specific parameter settings are shown in Table 6 below. In addition, in each embodiment and comparative example, the material of the housing 211 is the same throughout the entire area, and the tensile strength Rm of the housing 211 at 25°C is measured using the method specified in GB / T 228.1-2010. Furthermore, except for the different parameter settings shown in Table 6, the battery cells 20 in the following embodiments and comparative examples all have the same settings. For example, the thickness of the largest wall of the battery cell 20 in each embodiment is 0.15 mm. For another example, the chemical system of the battery cell 20 in each embodiment is a nickel-cobalt-manganese ternary system.

[0353] Table 6

[0354] Comparing the two comparative examples in Table 6 above with the six embodiments shows that different materials for the housing 211 can result in different tensile strengths Rm. When the tensile strength Rm satisfies 250 MPa ≤ Rm ≤ 2000 MPa and the capacity C of the battery cell 20 satisfies 25 Ah ≤ C ≤ 550 Ah, for example, in Examples 1-6, the housing 211 of the battery cell 20 does not crack. The structural strength of the housing 211 is sufficient for larger-capacity battery cells 20 and meets the design requirements of the battery cell 20. However, when the tensile strength Rm does not satisfy 250 MPa ≤ Rm ≤ 2000 MPa, for example, in Comparative Example 1-2, the housing 211 of the battery cell 20 cracks, failing to meet the design requirements of the battery cell 20.

[0355] It should be understood that in order to meet the above-mentioned design requirements, the material of at least a portion of the housing 211 in the embodiment of the present application can be flexibly selected according to actual applications.

[0356] In some embodiments, the material of at least a portion of the housing 211 includes at least one of steel, copper alloy, titanium alloy, and nickel alloy. These materials are relatively strong, can meet the strength requirements of the housing 211, are easy to process, and have low cost.

[0357] In some embodiments, at least a portion of the housing 211 is made of at least one of the following materials: stainless steel, carbon steel, and high-strength alloy steel. For example, if the housing 211 is made of stainless steel, it has greater structural strength and generally meets the aforementioned requirements for tensile strength Rm at room temperature, yield strength Re at room temperature, tensile strength Rn at high temperature, and melting point p. For example, the melting point of stainless steel is generally between 1400°C and 1500°C. Furthermore, the housing 211 is less susceptible to rust, which can extend the service life of the housing 211 compared to other materials.

[0358] If the housing 211 is made of carbon steel, its structural strength is high and it can easily meet the aforementioned requirements for tensile strength Rm at room temperature, yield strength Re at room temperature, tensile strength Rn at high temperature, and melting point p. For example, the melting point of carbon steel is typically between 1425°C and 1525°C. Furthermore, considering that carbon steel may be susceptible to corrosion during use, the outer surface of the carbon steel housing 211 may be nickel-plated. For example, the nickel plating layer may typically have a thickness of 1 μm to 10 μm to protect the surface of the housing 211 from oxidation and corrosion, thereby increasing the service life of the housing 211.

[0359] The shell 211 can also be made of other high-strength alloy steel materials to effectively improve the structural strength of the shell 211. For example, when the structural strength requirements of the shell 211 are high, a high-strength alloy steel material can be selected, which can easily meet the above-mentioned tensile strength Rm under normal temperature conditions, yield strength Re under normal temperature conditions, tensile strength Rn under high temperature conditions and melting point p requirements.

[0360] In some embodiments, when at least a portion of the housing 211 is made of steel, the steel may include at least one of the following types: SPCC, Q195, Q215, Q235, SUS 304, SUS 316, and other modified stainless steels. These steels are readily available, have strengths that meet design requirements, and are relatively low in cost. For example, the approximate values ​​of the tensile strength Rm at room temperature (25°C), the yield strength Re at room temperature (25°C), the tensile strength Rn at high temperature (500°C), and the melting point p of different steels can be found in Table 7 below.

[0361] Table 7

[0362] It should be understood that the material of at least a portion of the housing 211 in the embodiment of the present application may also be other materials. For example, different materials may be reasonably selected based on the mass content of different elements in the material and the role played by the elements.

[0363] In some embodiments, the mass content of chromium in the material of at least a portion of the housing 211 is m, where m satisfies the following: 10% ≤ m ≤ 30%. Properly adding chromium to the material of at least a portion of the housing 211 can increase the material's melting point and strength, making it easier to meet the requirements for tensile strength Rm at room temperature, yield strength Re at room temperature, tensile strength Rn at high temperature, and melting point p in the embodiments of this application. Furthermore, because chromium reacts with oxygen to form a dense chromium oxide film, it can also form a corrosion-resistant protective film on the surface of the housing 211, improving the corrosion resistance of the housing 211.

[0364] In some embodiments, the mass content of nickel in the material of at least a portion of the housing 211 is n, where n satisfies 8% ≤ n ≤ 25%. Properly adding nickel to the material of at least a portion of the housing 211 can improve the structural strength and plasticity of the housing 211. For example, it can increase the tensile strength Rm at room temperature, the yield strength Re at room temperature, and the tensile strength Rn at high temperature, and can also improve the corrosion resistance of the material.

[0365] In some embodiments, using steel as an example, different types of steel contain different mass contents of different elements. For example, in stainless steel, the mass content of iron, one of the basic elements of stainless steel, is typically between 60% and 70%. For another example, Table 8 shows the mass contents of different elements in several steels. The values ​​in Table 8 represent the maximum mass percentages of each element in the material. In other words, the mass percentages of each element in the corresponding steel are typically no greater than the values ​​shown in Table 8.

[0366] Table 8

[0367] It should be understood that when at least a portion of the housing 211 is made of steel, increasing the carbon content of the steel can improve the strength and hardness of the steel. For example, generally, a higher carbon content increases the hardness and strength of the steel, but may reduce its corrosion resistance.

[0368] If the mass content of chromium in steel is increased, the corrosion resistance of the steel can be improved because chromium can react with oxygen to form a dense chromium oxide film, which forms a corrosion-resistant protective film on the surface of the steel.

[0369] Increasing the nickel content in steel can improve the corrosion resistance, strength and plasticity of the steel.

[0370] Increasing the molybdenum content in steel can improve the corrosion resistance and strength of the steel, especially in corrosive media such as acid and salt.

[0371] Increasing the manganese content in steel can increase the toughness and fatigue resistance of the steel.

[0372] Increasing the mass content of silicon in steel can increase the corrosion resistance and strength of stainless steel.

[0373] If the mass content of phosphorus and sulfur in steel is reduced, the negative impact of these two elements on the corrosion resistance, plasticity and toughness of the steel can be reduced.

[0374] In addition, steel may also contain other elements. For example, steel may also contain copper. For example, the copper content of Q195, Q215, and Q235 is generally no more than 0.3% by weight, while modified stainless steel generally contains no more than 2% to 3.5% by weight. For another example, steel may also contain nitrogen. For example, the nitrogen content of Q195, Q215, and Q235 is generally no more than 0.12% by weight.

[0375] It should be understood that the test method for the mass content of each element in the steel in the embodiments of the present application can be set according to actual application. For example, inductively coupled plasma atomic emission spectrometry (ICP) can be used, but the embodiments of the present application are not limited thereto.

[0376] Figure 10 shows another exploded schematic diagram of the battery cell 20 according to an embodiment of the present application, and Figure 11 shows a schematic cross-sectional view of the housing 30 according to an embodiment of the present application. It should be noted that the housing 30 shown in Figures 10 and 11 can be applied to the battery cell 20. For example, the housing 30 can be applied to the battery cell 20 shown in Figures 3 and 4 , and the housing 30 shown in Figures 10 and 11 can be the housing 211 shown in Figures 3 and 4 . The above descriptions are applicable and, for the sake of brevity, will not be detailed here.

[0377] As shown in FIG. 10 and FIG. 11 , the housing 30 has an opening 301 . The housing 30 includes a first housing wall 31 and at least two second housing walls 32 arranged opposite to the opening 301 . The first housing wall 31 and the second housing wall 32 are arranged to intersect with each other.

[0378] As shown in the partial enlarged view of part A in Figure 11, a transition area 33 is provided between two adjacent second shell walls 32 of the at least two second shell walls 32 of the shell 30, and the maximum thickness of the transition area 33 is T1. The maximum thickness of the second shell wall 32 with the largest thickness among the two adjacent second shell walls 32 is T0, wherein T1 is greater than T0.

[0379] In some embodiments, the second housing wall 32 may be perpendicular to the first housing wall 31 .

[0380] In some embodiments, at least two second shell walls 32 may be connected end to end to form a hollow structure with openings at both ends, wherein the first shell wall 31 covers the opening at one end of the hollow structure.

[0381] In some embodiments, the shell 30 can be placed as shown in Figure 10, then the first shell wall 31 can be the bottom wall of the shell 30, used to support the electrode assembly 22, and the second shell wall 32 is the side wall of the shell 30, arranged around the electrode assembly 22.

[0382] Typically, the second housing wall 32 is not independently fabricated; that is, the at least two second housing walls 32 can be integrally formed. In other embodiments, the at least two second housing walls 32 and the first housing wall 31 are integrally formed, meaning that the housing 30 is a one-piece structure. For example, a plate-like structure can be stamped into a hollow structure with an opening using a mold. The stamped housing 30 can have an opening of various shapes. For example, the opening 301 can be circular, polygonal, or racetrack-shaped. Polygonal shapes include, for example, squares, pentagons, hexagons, or other irregular shapes.

[0383] In some embodiments, the thickness of the transition region 33 may be uniform or non-uniform. The following takes the uniform thickness of the transition region 33 as an example to define the maximum thickness T1 of the transition region 33 .

[0384] As can be seen from Figure 10, the transition region 33 has two surfaces, namely an inner surface and an outer surface. In some embodiments, the inner surface and the outer surface can be arc surfaces, and the inner surface and the outer surface are coaxially arranged. The maximum thickness T1 of the transition region 33 can be defined as the length of the extension line between the center of the circle where the inner arc is located and the center of the circle where the outer arc is located in any cross-section along the direction perpendicular to the axis of the inner surface and the outer surface in the transition region 33. In other embodiments, the inner surface and the outer surface can be planes, and the inner surface and the outer surface are parallel, and the maximum thickness T1 of the transition region 33 can be defined as the vertical distance between the inner surface and the outer surface. Similarly, the second shell wall 32 also has two surfaces, namely an inner surface and an outer surface, wherein the maximum value of the vertical distance between the inner surface and the outer surface is the maximum thickness of the second shell wall 32.

[0385] If the at least two second shell walls 32 of the shell 30 have unequal wall thicknesses, for example, the two second shell walls 32 in a transition region 33 have unequal wall thicknesses, then in this embodiment of the application, T0 is the second shell wall 32 with the largest wall thickness among the two second shell walls 32 adjacent to the transition region 33 in the shell 30. If the at least two second shell walls 32 of the shell 30 have equal wall thicknesses, for example, the two second shell walls 32 in a transition region 33 have equal wall thicknesses, then in this embodiment of the application, T0 is the thickness of any second shell wall 32 of the shell 30.

[0386] It should be noted that if a second shell wall 32 includes a functional area, the maximum thickness of the second shell wall 32 actually refers to the maximum thickness of the area of ​​the second shell wall 32 other than the functional area, and the functional area includes at least one of the following areas: a pressure relief area, an area where the electrode terminal is located, a liquid injection area, and a welding area.

[0387] In this embodiment, by setting a transition area 33 between two adjacent second shell walls 32, the stress concentration between the two adjacent second shell walls 32 can be reduced, and the risk of structural failure caused by stress concentration can be reduced; in addition, the maximum thickness T1 of the transition area 33 is set to be greater than the maximum thickness T0 of the second shell wall with the largest thickness among the two adjacent second shell walls. The thickened transition area 33 can enhance the structural strength of the shell 30, which is conducive to solving the problem of deformation of the shell 30 during the production and assembly process of the battery cell 20, and the problem of deformation of the shell 30 caused by gas production and expansion of the battery cell 20 during use.

[0388] In some embodiments, the maximum thickness T1 of the transition region 33 and the maximum thickness T0 of the second shell wall 32 with the largest thickness among the two adjacent second shell walls 32 satisfy the following: 1.5≤T1 / T0≤7.

[0389] In this embodiment, by setting the ratio of the maximum thickness T1 of the transition region 33 to the maximum thickness T0 of the second shell wall 32 with the largest thickness among the two adjacent second shell walls 32 to be between [1.5, 7], on the one hand, the strength of the shell can be enhanced by the thicker transition region 33, and on the other hand, the difficulty in manufacturing the shell 30 due to excessive thickening of the transition region 33 can be limited, thereby achieving a balance between the strength of the shell 30 and the difficulty of manufacturing the shell 30.

[0390] In practical applications, the ratio of T1 to T0 can be adjusted. For example, the maximum thickness T1 of the transition region 33 and the maximum thickness T0 of the thickest second shell wall 32 of the two adjacent second shell walls 32 can satisfy: 2≤T1 / T0≤4.

[0391] For example, T1 / T0 can be equal to 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, etc.

[0392] In this embodiment, by setting the ratio of the maximum thickness T1 of the transition area 33 to the maximum thickness T0 of the second shell wall 32 with the largest thickness among the two adjacent second shell walls 32 between [2, 4], a maximum balance can be achieved between the strength of the shell 30 and the difficulty of manufacturing the shell 30.

[0393] Optionally, as shown in Figures 11 and 12, two adjacent second shell walls 32 are connected by a first rounded corner 331, and the transition area 33 includes the first rounded corner 331. In other words, the transition area 33 is realized by the rounded corner.

[0394] In this embodiment, the transition area 33 between the two adjacent second shell walls 32 is realized by rounding the corners, which can make the shell 30 easier to form and have a better surface finish. At the same time, when affected by gas production inside the battery cell 20, the risk of cracking of the shell 30 due to sharp point stress concentration can be reduced.

[0395] As shown in FIG. 12 , the inner diameter of the first rounded corner 331 is R1 , and the outer diameter of the first rounded corner 331 is R2 .

[0396] In some embodiments, the first fillet 331 has an inner surface and an outer surface, and both the inner surface and the outer surface are arc surfaces. The inner diameter R1 of the first fillet 331 can be understood as the radius of the circle where the inner arc of the first fillet 331 is located, and the outer diameter R2 of the first fillet 331 can be understood as the radius of the circle where the outer arc of the first fillet 331 is located.

[0397] In some embodiments, the inner diameter R1 of the first fillet 331 satisfies the following: 2 mm ≤ R1 ≤ 4 mm. For example, R1 = 2 mm, 2.1 mm, 2.2 mm, 2.3 mm, 2.4 mm, 2.5 mm, 2.6 mm, 2.7 mm, 2.8 mm, 2.9 mm, 3.0 mm, 3.1 mm, 3.2 mm, 3.3 mm, 3.4 mm, 3.5 mm, 3.6 mm, 3.7 mm, 3.8 mm, 3.9 mm, 4.0 mm, etc.

[0398] In this embodiment, the inner diameter of the first fillet 331 between two adjacent second shell walls 32 is set between [2mm, 4mm]. On the one hand, the internal space of the shell 30 will not be occupied due to the excessive inner diameter, which will increase the gas production pressure inside the shell 30; on the other hand, the wall thickness increment of the first fillet 331 will not be insufficient due to the inner diameter being too small, which will further lead to insufficient strength of the shell 30, so that a balance can be achieved between the internal space utilization of the shell 30 and the strength of the shell 30.

[0399] In some embodiments, the outer diameter R2 of the first rounded corner 331 satisfies: 1.5 mm ≤ R2 ≤ 3.5 mm. For example, R2 = 1.5 mm, 2 mm, 2.5 mm, 3.0 mm, 3.5 mm, etc.

[0400] In this embodiment, when the cover plate 40 and the shell 30 are fixedly connected by side welding, the larger the outer diameter R2 of the first fillet 331 between two adjacent second shell walls 32, the more difficult it is to control the welding quality and the more likely it is to have a cold weld; and the smaller the outer diameter R2 of the first fillet 331, the more difficult it is to form the shell 30. Therefore, controlling the outer diameter R2 of the first fillet 331 within the range of [1.5mm, 3.5mm] can balance the welding quality and the difficulty of forming the shell.

[0401] In other embodiments, as shown in FIG. 13 , two adjacent second shell walls 32 are connected via a C-angle. For example, the angles between the C-angle and the two adjacent second shell walls 32 are both 45°.

[0402] In one embodiment, the housing 30 may be an integrally formed structure. As shown in FIG10 , the depth of the housing 30 is H, wherein the depth H of the housing 30 and the inner diameter R1 of the first fillet 331 satisfy the following conditions: 2.5 mm ≤ R1 ≤ 20 mm, 50 mm <H≤250mm。

[0403] In the embodiment of the present application, the depth can be understood as the distance from the opening to the bottom. For example, the depth H of the housing 30 can be understood as the distance from the opening 301 to the first housing wall 31.

[0404] Figure 14 shows a schematic diagram of the material flow during the integral molding process of the housing 30. Figure 15 shows a schematic diagram of the force on the housing 30 during the integral molding process. As can be seen from Figures 14 and 15, when the housing 30 is molded, the material of the housing 30 is prone to material accumulation at the position of the first rounded corner 331, resulting in a large frictional force between the housing 30 and the mold, and the housing 30 is prone to cracking. Therefore, in this embodiment, by setting the depth H of the housing 30 and the inner diameter R1 of the first rounded corner 331 to satisfy 2.5 mm ≤ R1 ≤ 20 mm and 50 mm < H ≤ 250 mm, it is possible to reduce the cracking risk caused by stress during the integral molding process of the housing 30 as much as possible without affecting the energy density of the battery cell 20, thereby reducing the molding difficulty of the housing 30.

[0405] For example, R1 = 2.5 mm, 5 mm, 7.5 mm, 10 mm, 12.5 mm, 15 mm, 17.5 mm, 20 mm; and / or, H = 50 mm, 100 mm, 150 mm, 200 mm, 250 mm.

[0406] In some embodiments, H and R1 satisfy: 75 mm ≤ H ≤ 180 mm, 4 mm ≤ R1 ≤ 15 mm.

[0407] For example, H = 75 mm, 100 mm, 125 mm, 150 mm, 175 mm, 180 mm. For example: R1 = 4 mm, 6 mm, 8 mm, 10 mm, 12 mm, 14 mm, 15 mm.

[0408] In this embodiment, by setting H and R1 to satisfy: 4 mm ≤ R1 ≤ 15 mm, 75 mm ≤ H ≤ 180 mm, on the one hand, the energy density of the battery cell 20 will not be reduced due to too small H or too large R, and on the other hand, the housing 30 will not be prone to material accumulation during the molding process due to too large H or too small R, thereby avoiding the situation where the housing 30 is overstressed and cracked.

[0409] In other embodiments, H and R1 satisfy: 5 mm ≤ R1 ≤ 10 mm, 90 mm ≤ H ≤ 140 mm. For example, R1 = 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm. Again, for example, H = 90 mm, 100 mm, 110 mm, 120 mm, 130 mm, 140 mm.

[0410] In other embodiments, the housing 30 is an integral molding structure, and the yield strength of the housing 30 at a temperature of 25 °C is Re. Among them, the yield strength Re and the inner diameter R1 of the first rounded corner 331 satisfy: 140 MPa ≤ Re ≤ 1000 Mpa, 2.5 mm ≤ R1 ≤ 20 mm.

[0411] For example, Re=140MPa, 180MPa, 200MPa, 230MPa, 250MPa, 280MPa, 300MPa, 320MPa, 350MPa, 380MPa, 400MPa, 430MPa, 450MPa, 480MPa, 500MPa, 550MPa, 600MPa, 650MPa, 700MPa, 750MPa, 800MPa, 850MPa, 900MPa, 950MPa, 1000MPa.

[0412] For example, R1 = 2.5mm, 5mm, 7.5mm, 10mm, 12.5mm, 15mm, 17.5mm, 20mm.

[0413] Yield strength can be understood as the critical stress value at which a material yields. Generally, after a material is subjected to stress, as the stress increases, in addition to elastic deformation, it may also undergo plastic deformation. The point at which plastic deformation occurs is called the yield point, and the strength corresponding to the yield point is called the yield strength. The test method for the yield strength Re of the housing 30 at a temperature of 25°C in the embodiment of the present application can be selected based on the actual application. For example, the yield strength Re can be tested at room temperature of 25°C using GB / T 228.1-2010.

[0414] In order to solve the problem that when the shell 30 is integrally formed, the material is easily piled up at the first fillet 331, resulting in high friction between the shell 30 and the mold, and the shell 30 is prone to cracking, the embodiment of the present application also provides another solution, that is, for the shell 30 with a yield strength Re satisfying 140MPa≤Re≤1000Mpa, the inner diameter R1 of the first fillet 331 is set to 2.5mm≤R1≤20mm, so that R1 cannot be too small, thereby reducing the difficulty of forming the shell 30, and R1 cannot be too large, thereby reducing the stress deformation of the shell 30.

[0415] In this embodiment, by using a material having a yield strength Re satisfying 140 MPa≤Re≤1000 MPa to manufacture the shell 30, the wall thickness of the shell can be thinned without reducing the strength of the shell 30, thereby increasing the capacity space of the battery cell 20; in addition, by setting the inner diameter R1 of the first fillet 331 between adjacent second shell walls 32 to satisfy 2.5 mm≤R1≤20 mm, the risk of cracking of the shell 30 due to stress during the one-piece molding process is minimized, and the molding difficulty of the shell 30 is reduced.

[0416] In some embodiments, the yield strength Re and R1 of the housing 30 may satisfy: 150 MPa≤Re≤400 MPa, 4 mm≤R1≤15 mm.

[0417] For example, Re = 150 MPa, 170 MPa, 190 MPa, 210 MPa, 230 MPa, 260 MPa, 290 MPa, 310 MPa, 330 MPa, 370 MPa, 390 MPa, 400 MPa.

[0418] For example, R1=4mm, 6mm, 8mm, 10mm, 12mm, 14mm, 15mm.

[0419] In this embodiment, by defining 150 MPa≤Re≤400 MPa and 4 mm≤R1≤15 mm, it is helpful to achieve a balance between the molding difficulty and the deformation degree of the shell 30.

[0420] In some embodiments, the yield strength Re and R1 of the housing 30 may satisfy: 160 MPa≤Re≤300 MPa, 5 mm≤R1≤10 mm.

[0421] For example, Re = 160 MPa, 170 MPa, 180 MPa, 190 MPa, 200 MPa, 210 MPa, 220 MPa, 230 MPa, 240 MPa, 250 MPa, 260 MPa, 270 MPa, 280 MPa, 290 MPa, 300 MPa.

[0422] For example, R1 = 5mm, 6mm, 7mm, 8mm, 9mm, 10mm.

[0423] In this embodiment, by limiting 160 MPa≤Re≤300 MPa and 5 mm≤R1≤10 mm, the stress deformation of the shell 30 during use can be reduced as much as possible without affecting the difficulty of forming the shell 30 .

[0424] In some embodiments, the tensile strength of the housing 30 at a temperature of 25° C. is Rm, and Rm and R1 satisfy the following conditions: 250 MPa≤Rm≤2000 MPa, 2.5 mm≤R1≤20 mm.

[0425] Tensile strength can be understood as the maximum stress a material can withstand before breaking. The tensile strength Rm of the housing 30 of the present embodiment at 25°C can be tested using a method selected based on the actual application. For example, ISO 6892-2:2018 can be used to test the tensile strength Rm at room temperature of 25°C.

[0426] For example, Rm=250 MPa, 300 MPa, 350 MPa, 400 MPa, 450 MPa, 500 MPa, 550 MPa, 600 MPa, 650 MPa, 700 MPa, 750 MPa, 800 MPa, 850 MPa, 900 MPa, 950 MPa, 1000 MPa, 1100 MPa, 1200 MPa, 1300 MPa, 1400 MPa, 1500 MPa, 1600 MPa, 1700 MPa, 1800 MPa, 1900 MPa, 2000 MPa.

[0427] In this embodiment, by setting 250MPa≤Rm≤1000MPa and 2.5mm≤R1≤20mm, the force on the mold can be reduced as much as possible during the manufacturing process of the shell 30 without affecting the strength of the shell 30, thereby ensuring that the size or surface of the shell 30 is not affected.

[0428] In some embodiments, Rm and R1 satisfy: 280 MPa≤Rm≤800 MPa, 4 mm≤R1≤15 mm.

[0429] For example, Rm=280MPa, 310MPa, 340MPa, 370MPa, 390MPa, 430MPa, 470MPa, 510MPa, 540MPa, 580MPa, 610MPa, 630MPa, 660MPa, 690MPa, 720MPa, 740MPa, 780MPa, 800MPa.

[0430] In other embodiments, Rm and R1 satisfy: 380 MPa≤Rm≤600 MPa, 5 mm≤R1≤10 mm.

[0431] For example, Rm=380MPa, 390MPa, 410MPa, 440MPa, 480MPa, 520MPa, 535MPa, 570MPa, 596MPa, 600MPa.

[0432] In some embodiments, the maximum wall thicknesses of at least two second housing walls 32 of the housing 30 are equal.

[0433] Further optionally, the wall thickness of each of the at least two second shell walls 32 of the shell 30 is uniform, and the wall thicknesses of the at least two second shell walls 32 are equal.

[0434] In this embodiment, by setting the wall thickness of at least two second shell walls 32 to be equal, on the one hand, the processing difficulty of the shell 30 can be reduced, and on the other hand, at least two second shell walls 32 can also be set to the minimum processing wall thickness, which helps to fully improve the space utilization of the shell 30.

[0435] In other embodiments, a transition region 33 is defined between any two adjacent second shell walls 32 of the at least two second shell walls 32 , and the maximum thicknesses of the at least two transition regions 33 corresponding to the at least two second shell walls 32 are equal.

[0436] In this embodiment, by setting the maximum thickness of at least two transition areas 33 between at least two second shell walls 32 of the shell 30 to be equal, it helps to prepare the shell 30 into a symmetrical structure, which is easy to process, and there is no need to worry about reverse installation when assembling the shell 30 and the cover plate 40, which has an anti-foolproof function.

[0437] Figure 16 shows another schematic cross-sectional view of the housing 30 according to an embodiment of the present application. As shown in the partially enlarged view of portion B in Figure 16 , the first housing wall 31 and the second housing wall 32 are connected via a second fillet 34. As shown in the enlarged schematic view of portion B in Figure 16 , the inner diameter of the second fillet 34 is r1, and the minimum thickness of the at least two second housing walls 32, the smallest second housing wall 32, is T2. The relationship between the inner diameter r1 of the second fillet 34 and the minimum thickness T2 of the at least two second housing walls 32 satisfies the following: 2.0 ≤ r1 / T2 ≤ 30.

[0438] It should be understood that each first housing wall 31 is connected to at least two second housing walls 32. Optionally, each second housing wall 32 is connected to the first housing wall 31 via a second fillet 34, as shown in FIG16 . Furthermore, the second fillet 34 here is similar in implementation to the first fillet 331 in FIG12 , namely, the second fillet 34 has an inner surface and an outer surface, both of which are arc-shaped surfaces. The inner radius r1 of the second fillet 34 can be understood as the radius of the circle within which the inner arc is formed.

[0439] It should be noted that if each second housing wall 32 has a uniform thickness, the minimum thickness T2 of the second housing wall 32 may refer to the thickness of the thinnest second housing wall 32 among the at least two second housing walls 32. If the thickness of each second housing wall 32 is non-uniform, the minimum thickness T2 of the second housing wall 32 may refer to the thickness of the thinnest region among all the second housing walls 32.

[0440] It should also be noted that if a second shell wall 32 includes a functional area, the minimum thickness of the second shell wall 32 actually refers to the minimum thickness of the area of ​​the second shell wall 32 other than the functional area, and the functional area includes at least one of the following areas: a pressure relief area, an area where the electrode terminal is located, a liquid injection area, and a welding area.

[0441] In this embodiment, by setting the ratio of the inner diameter r1 of the second fillet 34 between the first shell wall 31 and the second shell wall 32 to the minimum thickness T2 of the second shell wall 32 with the smallest thickness between [2.0, 30], it helps to balance the processing difficulty of the shell 30 with the spatial capacity and strength of the battery cell 20.

[0442] In some embodiments, the inner radius r1 of the second fillet 34 and the minimum thickness T2 of the second shell wall 32 with the smallest thickness among the at least two second shell walls 32 satisfy the following relationship: 2.5≤r1 / T2≤10. For example, r1 / T2=2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, 10, etc.

[0443] Optionally, the inner diameter r1 of the second fillet 34 may satisfy: 0.8 mm ≤ r1 ≤ 1.5 mm. For example, r1 = 0.8 mm, 0.9 mm, 1.0 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, 1.5 mm.

[0444] In this embodiment, by setting the inner diameter r1 of the second fillet 34 within [0.8 mm, 1.5 mm], on the one hand, the difficulty of manufacturing the shell 30 will not be increased due to r1 being too small, and on the other hand, the interference between the electrode assembly 22 and the second fillet 34 will not be reduced due to r1 being too large, that is, there is no need to lower the height of the electrode assembly 22 and sacrifice the capacity of the electrode assembly 22 to meet the assembly of the shell 30 and the electrode assembly 22. In addition, if r1 is too large, the shell 30 is also prone to deformation.

[0445] Figure 17 shows another enlarged partial view of section B in Figure 16. As shown in Figure 17, the outer diameter of the second fillet 34 is r2, where r2 satisfies the following: 1mm≤r2≤2.5mm. For example, r2 = 1.0mm, 1.1mm, 1.2mm, 1.3mm, 1.4mm, 1.5mm, 1.6mm, 1.7mm, 1.8mm, 1.9mm, 2.0mm, 2.1mm, 2.2mm, 2.3mm, 2.4mm, 2.5mm.

[0446] Similar to the definition of the inner diameter r1 of the second rounded corner 34 , the outer diameter r2 of the second rounded corner 34 can be understood as the radius of the circle where the outer arc of the second rounded corner 34 lies.

[0447] In this embodiment, by setting the outer diameter r2 of the second fillet 34 within [1.0 mm, 2.5 mm], on the one hand, the insulating film on the outside of the battery cell 20 will not be punctured by the sharp points due to r2 being too small, thereby causing insulation failure; on the other hand, the thickness of the second fillet 34 will not be too thin due to r2 being too large, thereby affecting the strength of the shell 30.

[0448] In some embodiments, H and T2 satisfy the following relationship: 300≤H / T2≤800. For example, H / T2=300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, etc.

[0449] In this embodiment, by setting the ratio between the depth H of the housing 30 and the minimum thickness T2 of the second housing wall 32 with the smallest thickness to be between [300, 800], both the volume utilization and the strength of the battery cell 20 can be taken into consideration.

[0450] As shown in FIG17 , the maximum thickness of the second fillet 34 is T3, where the ratio of T3 to T2 satisfies: 0.8≤T3 / T2≤2. For example, T3 / T2=0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0.

[0451] The thickness of the second fillet 34 can be uniform or non-uniform. Below, the maximum thickness T3 of the second fillet 34 will be defined using the uniform thickness of the second fillet 34 as an example. In some embodiments, the maximum thickness T3 of the second fillet 34 can be defined as the length of the second fillet 34 of the extended line connecting the center points of the inner and outer arcs at any cross section perpendicular to the axis of the inner and outer surfaces.

[0452] In this embodiment, by setting the ratio between the maximum thickness T3 of the second fillet 34 and the minimum thickness T2 of the second housing wall 32, which has the smallest thickness, at [0.8, 2], a balance can be achieved between the strength and manufacturability of the housing 30. That is, the housing 30 will not be insufficiently strong due to excessive thinning of the second fillet 34, nor will the housing 30 be difficult to manufacture due to excessive thinning of the second fillet 34.

[0453] In some embodiments, the wall thickness of the housing 30 is uniform, that is, all walls of the housing 30 have the same wall thickness.

[0454] In this embodiment, by setting the wall thickness of the shell 30 to be uniform, on the one hand, the processing difficulty of the shell 30 can be reduced, and on the other hand, each wall of the shell 30 can be set to the minimum processing wall thickness, which helps to fully improve the space utilization of the shell 30.

[0455] In some embodiments, the battery cell 20 further includes a cover plate 40 for covering the opening 301 of the housing 30 to enclose the electrode assembly 22 in the cavity of the housing 30 .

[0456] In this embodiment, by setting the inner diameter R1 of the first fillet between the depth H of the shell and the second shell wall to satisfy 2.5mm≤R1≤20mm, 50mm≤H≤250mm, the risk of cracking of the shell caused by stress during the one-piece molding process can be reduced as much as possible without affecting the energy density of the battery cell, thereby reducing the difficulty of molding the shell.

[0457] In some embodiments, the battery cell 20 is substantially rectangular, for example, the battery cell 20 is a rectangular parallelepiped battery cell. In another example, the battery cell 20 is a runway-shaped battery cell, and the thickness of the battery cell 20 is D1, where H, R1, and D1 satisfy: 0.15 mm ≤ R1*D1 / H ≤ 36 mm.

[0458] For example, R1*D1 / H=0.15, 0.5, 1, 5, 10, 15, 17.5, 20, 22.5, 25, 27.5, 30, 32.5, 35, 36.

[0459] In some embodiments, D2 may be a dimension of the battery cell 20 in an expansion direction of the electrode assembly 22 .

[0460] In this embodiment, by setting 0.15mm≤R1*D1 / H≤36mm, the risk of easy accumulation of materials during the molding process of the shell 30 due to the excessively small value of R1*D1 / H, which may cause the shell 30 to be subjected to excessive force and crack, can be reduced. In addition, the impact of the excessively large value of R1*D1 / H on the energy density of the battery cell 20 can be reduced.

[0461] In this embodiment, D1 satisfies the following: 15 mm ≤ D1 ≤ 90 mm. For example, D1 = 15 mm, 20 mm, 25 mm, 30 mm, 35 mm, 40 mm, 45 mm, 50 mm, 55 mm, 60 mm, 65 mm, 70 mm, 75 mm, 80 mm, 85 mm, 90 mm.

[0462] In this embodiment, H and R1 satisfy: 50 mm ≤ H ≤ 250 mm, 2.5 mm ≤ R1 ≤ 20 mm.

[0463] In some embodiments, H, R1, and D1 satisfy: 0.34 mm ≤ R1 * D1 / H ≤ 18 mm.

[0464] In this embodiment, by setting 0.34 mm ≤ R1 * D1 / H ≤ 18 mm, a balance can be achieved between the difficulty of forming the housing 30 and the energy density.

[0465] For example, R1*D1 / H=0.34, 0.5, 1, 3, 5, 8, 11, 13, 16, 18.

[0466] Similarly, in this embodiment, D1 satisfies: 15 mm ≤ D1 ≤ 90 mm.

[0467] In this embodiment, H and R1 satisfy: 75 mm ≤ H ≤ 180 mm, 4 mm ≤ R1 ≤ 15 mm.

[0468] In some embodiments, H, R1, and D1 satisfy: 0.9 mm ≤ R*D / H ≤ 6.6 mm.

[0469] For example, R1*D1 / H=0.9, 1, 1.3, 1.5, 1.8, 2.0, 2.3, 2.6, 2.8, 3.0, 3.3, 3.5, 3.8, 4.0, 4.3, 4.5, 4.7, 4.9, 5.1, 5.4, 5.7, 6.0, 6.2, 6.5, 6.6.

[0470] In this embodiment, D1 satisfies the following: 25 mm ≤ D1 ≤ 60 mm. For example, D1 = 25 mm, 28 mm, 31 mm, 34 mm, 37 mm, 39 mm, 41 mm, 43 mm, 46 mm, 49 mm, 51 mm, 54 mm, 58 mm, 50 mm.

[0471] And in this embodiment, H and R1 satisfy: 90mm≤H≤140mm, 3mm≤R≤10mm.

[0472] It should be noted that the value ranges of R1, H, D1, and R1*D1 / H may be interrelated. For example, when 15 mm ≤ D1 ≤ 90 mm, 50 mm ≤ H ≤ 250 mm, and 2.5 mm ≤ R1 ≤ 20 mm, 0.15 mm ≤ R1*D1 / H ≤ 36 mm. For another example, when 15 mm ≤ D1 ≤ 90 mm, 75 mm ≤ H ≤ 180 mm, and 4 mm ≤ R1 ≤ 15 mm, 0.34 mm ≤ R*D / H ≤ 18 mm. For another example, when 25 mm ≤ D1 ≤ 60 mm, 90 mm ≤ H ≤ 140 mm, and 3 mm ≤ R1 ≤ 10 mm, 0.9 mm ≤ R1*D1 / H ≤ 6.6 mm.

[0473] In some embodiments, the thickness of the electrode assembly 22 is D2, and R1 and D2 satisfy: 0.125≤R1 / D2≤0.45.

[0474] For example, R1 / D2=0.125, 0.15, 0.175, 0.2, 0.225, 0.25, 0.275, 0.3, 0.325, 0.35, 0.375, 0.4, 0.425, 0.45.

[0475] Alternatively, D2 may be the dimension of the electrode assembly 22 in the expansion direction.

[0476] In this embodiment, by setting 0.125≤R1 / D2≤0.45, on the one hand, R1 will not interfere with the electrode assembly 22 or the residual space inside the battery cell 20 will not be insufficient due to R1 being too large, thereby affecting the performance of the battery cell 20; on the other hand, R1 will not be too small, which will lead to difficulty in molding the shell 30.

[0477] Figure 18 shows a schematic diagram of an exploded view of the shell 40 of an embodiment of the present application. Figure 19 shows a schematic diagram of the structure of the second shell part 42 of an embodiment of the present application. Figure 20 shows another schematic diagram of the structure of the second shell part 42 of an embodiment of the present application. Figure 21 shows another schematic diagram of the exploded view of the shell 40 of an embodiment of the present application. It should be noted that the shell 40 can be applied to the battery cell 20. For example, the shell 40 shown in Figures 18 to 21 can be applied to the battery cell 20 shown in Figures 3 and 4, and the shell 40 can include only the shell 211 shown in Figure 4, or it can include both the shell 211 shown in Figure 4 and the cover plate 212 shown in Figure 4. In addition, the placement of the shell 40 can also be as shown in Figure 3 or Figure 4.

[0478] As shown in Figure 18, the housing 40 includes a first housing portion 41 having an opening 401 formed therein. The first housing portion 41 includes a first wall 411 opposite the opening 401 and a second wall 412 connected to the first wall 411. The first wall 411 and the second wall 412 are integrally formed. The second housing portion 42 is fixedly connected to the second wall 412. In the depth direction X of the first housing portion 41, at least a portion of the housing 40 is formed jointly by the first housing portion 41 and the second housing portion 42.

[0479] It should be explained that the first wall 411 and the second wall 412 in the first shell portion 41 are an integrally formed structure, which may mean that the first shell portion 41 is made through an integral deep drawing process. For example, the first shell part 41 can be prepared by the following steps: Step 1, select steel suitable for deep drawing; Step 2, prepare a suitable stamping die according to the shell design and process requirements. The die is usually made of die steel, carbon steel, or cemented carbide, and includes components such as a punch, a die, and a blank holder; Step 3, fix the steel between the fixture and the die to ensure that the steel remains stable during the deep drawing process; Step 4, move the punch downward into the die to apply tensile stress to the steel to deform it and fill the shape of the die; Step 5, control the speed and pressure of the punch to ensure that the steel is uniformly deformed during the deep drawing process, so that it is drawn to a certain depth and obtains the desired shape; Step 6, as needed, perform auxiliary operations such as perforation, trimming, and marking during the deep drawing process; Step 7, after completing the deep drawing, remove the product from the die and perform necessary processing, such as cleaning, deburring, etc., to obtain the first shell part 41.

[0480] Since the first housing portion 41 is formed by deep drawing as a single piece, it generally has an opening 401. The opening 401 can be circular, polygonal, or racetrack-shaped. The polygonal shape can be, for example, a square, pentagon, hexagon, or other irregular shapes.

[0481] The first shell portion 41 is a hollow structure formed by a first wall 411 and a second wall 412 opposite to the opening 401, wherein the second wall 412 is arranged to intersect with the first wall 411. For example, the first wall 411 and the second wall 412 are arranged perpendicularly. In some embodiments, the first shell portion 41 includes a second wall 412, which is connected end to end and together with the first wall 411 forms a cylindrical hollow structure. In other embodiments, the first shell portion 41 includes four second walls 412, which are arranged opposite to each other in pairs, and two adjacent second walls 412 intersect perpendicularly, so that the four second walls 412 and the first wall 411 together form a square columnar hollow structure.

[0482] Since the first wall 411 is arranged opposite to the opening 401 of the first shell part 41, the depth direction X of the first shell part 41 can be understood as a direction perpendicular to the first wall 411, and the distance from the opening 401 to the first wall 411 of the first shell part 41 is the depth of the first shell part 41.

[0483] In the embodiment of the present application, the second housing portion 42 is fixedly connected to the second wall 412, and does not include the second housing portion 42 being a flat plate structure and the second housing portion 42 being embedded in the opening 401 of the first housing portion 41. In other words, in the embodiment of the present application, the second housing portion 42 includes at least one third wall 421, wherein the at least one third wall 421 together encloses a hollow structure having at least one opening. For example, the second housing portion 42 includes at least the opening 402 shown in Figure 19, and the opening 402 of the second housing portion 42 is arranged opposite to the opening 401 of the first housing portion 41, and the second wall 412 and the third wall 421 are fixedly connected, so that in the depth direction X of the first housing portion 41, the second wall 412 and the third wall 421 together form at least a partial area of ​​the housing 40, that is, the depth H of the housing 40 is at least greater than the depth of the first housing portion 41. The depth H of the housing 40 can be understood as the size of the housing 40 along the depth direction of the first housing portion 41. Generally, the wall of the housing 40 has a certain thickness, but here, the thickness of the wall of the housing 40 can be ignored.

[0484] In this embodiment, the housing 40 includes a first housing portion 41 and a second housing portion 42. The first housing portion 41 has an opening 401 and includes a first wall 411 opposite the opening 401 and a second wall 412 connected to the first wall 411. The first wall 411 and the second wall 412 are integrally formed. In the depth direction X of the first housing portion 41, at least a portion of the housing 40 is formed jointly by the first housing portion 41 and the second housing portion 42. Compared to a technical solution in which the housing 40 is directly integrally formed, the housing 40 prepared in this manner can reduce the risk of cracking during the integral deep drawing process.

[0485] In some embodiments, the second wall 412 has the same dimensions throughout the depth direction X of the first housing portion 41. Similarly, the third wall 421 has the same dimensions throughout the depth direction X of the first housing portion 41. Thus, in the depth direction X of the first housing portion 41, the entire area of ​​the housing 40 is formed by the first housing portion 41 and the second housing portion 42.

[0486] In other embodiments, the dimensions of the second wall 412 are not completely equal in the depth direction X of the first housing portion 41. For example, the second wall 412 can be semicircular or triangular after deployment. Similarly, the dimensions of the third wall 421 are not completely equal in the depth direction X of the first housing portion 41. For example, the third wall 421 can be semicircular or triangular after deployment. In this case, a portion of the housing 40 in the depth direction X of the first housing portion 41 can be formed jointly by the first housing portion 41 and the second housing portion 42.

[0487] In one embodiment, the first shell portion 41 and the second shell portion 42 are fixedly connected by welding. In this way, the shell 40 prepared by the method of the embodiment of the present application is less likely to crack or break, as compared to a shell formed by welding a flat plate structure and a tubular structure with an opening.

[0488] Optionally, the second housing portion 42 has two communicating openings in the depth direction X of the first housing portion 41. For example, the second housing portion 42 includes an opening 402 and an opening 403 as shown in FIG19 , and the opening 402 and the opening 403 are arranged opposite to each other in the depth direction X of the first housing portion 41.

[0489] In this embodiment, by setting the second shell portion 42 to have two connected openings in the depth direction X of the first shell portion 41, the cover plate and the shell 40 can be set independently, and then the electrode terminals and other components can be better set on the cover plate, making the preparation of the shell 40 simpler.

[0490] In other embodiments, the second housing portion 42 may have only one opening. For example, the second housing portion 42 is similar to the first housing portion 41 and is also manufactured through an integral deep drawing process. In addition to the third wall 421, the second housing portion 42 further includes a wall intersecting the third wall 421 and opposite the opening of the second housing portion 42, such as a cover plate.

[0491] In one embodiment, the second housing portion 42 is an integrally formed structure.

[0492] In this embodiment, by providing the second shell portion 42 as an integrally formed structure, the welds of the shell 40 can be reduced, thereby increasing the reliability of the shell 40 and reducing the risk of deformation, cracking, and damage to the shell 40.

[0493] In another embodiment, when the second shell portion 42 has only one opening, the second shell portion 42 may be formed by welding at least two parts.

[0494] It should be noted that when the second housing portion 42 is formed by welding at least two parts, the weld seam of the second housing portion 42 should not be on an edge, also known as a right-angled edge. For example, as shown in Figure 20, the second housing portion 42 includes four third walls 421, including a fourth wall 4211, a fifth wall 4212, a sixth wall 4213, and a seventh wall 4214. The fourth wall 4211 and the fifth wall 4212 are disposed opposite each other, and the sixth wall 4213 and the seventh wall 4214 are disposed opposite each other. The sixth wall 4213 includes a first sub-wall 4213a and a second sub-wall 4213b, which are symmetrical with respect to the first centerline 4251. The seventh wall 4214 includes a third sub-wall 4214a and a fourth sub-wall 4214b, which are symmetrical with respect to the second centerline 4261. The second housing portion 42 is formed by welding a first portion 423 and a second portion 424. The first portion 423 includes a first sub-wall 4213a, a fourth wall 4211, and a third sub-wall 4214a. The second portion 424 includes a second sub-wall 4213b, a fifth wall 4212, and a fourth sub-wall 4214b. The first centerline 4251 and the second centerline 4261 are the welds of the second housing portion 42.

[0495] In this embodiment, the second shell portion 42 is configured to be formed by welding at least two parts, which is easy to process and has easier size control, thereby improving the assembly accuracy of the shell 40 .

[0496] In some embodiments, a surface 4121 of the second wall 412 facing away from the first wall 411 is welded to the second housing portion 42, where the wall thickness of the housing 40 should be considered. It can be understood that the second wall 412 is welded to the third wall 421, and the inner surface of the second wall 412 and the inner surface of the third wall 421 are spliced ​​to form a plane.

[0497] In other words, the depth of the housing 40 is equal to the sum of the depth of the first housing portion 41 and the depth of the second housing portion 42 .

[0498] In this embodiment, the surface 4121 of the second wall 412 facing away from the first wall 411 is welded to the second housing portion 42 , which can improve the space utilization of the housing 40 .

[0499] In other embodiments, a surface of the second wall 412 perpendicular to the thickness direction Y of the second wall 412 is welded to the second housing portion 42. For example, as shown in FIG21 , an inner surface 4122 of the second wall 412 is welded to the second housing portion 42 at the opening 401 of the first housing portion 41 and to the outer surface 4215 of the third wall 421 of the second housing portion 42.

[0500] In this embodiment, by welding the surface of the second wall 412 perpendicular to the thickness direction Y of the second wall 412 to the second shell part 42, it is beneficial to enhance the welding area of ​​the first shell part 41 and the second shell part 42, thereby improving the welding strength between the two.

[0501] Figure 22 shows a schematic cross-sectional view of the housing 40 according to an embodiment of the present application. As shown in Figure 22 , in the depth direction X of the first housing portion 41 , the maximum dimension of the first housing portion 41 is h1, and the maximum dimension of the housing 40 is H, where H and h1 satisfy the following relationship: 3≤H / h1≤80.

[0502] It should be explained that, without considering the wall thickness, the dimensions of the first housing portion 41 may be uneven in the depth direction X of the first housing portion 41, and the maximum dimension h1 of the first housing portion 41 may refer to the maximum distance between the end of the second wall 412 away from the first wall 411 and the first wall 411. Similarly, without considering the wall thickness, the dimensions of the housing 40 may also be uneven in the depth direction X of the first housing portion 41, and the maximum dimension H of the housing 40 may refer to the maximum distance between the end of the second housing portion 42 away from the first wall 411 and the first wall 411.

[0503] In some embodiments, in the depth direction X of the first housing portion 41 , the size of the first housing portion 41 is uniform and the size of the housing 40 is also uniform.

[0504] For example, H / h1=3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80.

[0505] In this embodiment, the ratio of H to h1 is set in the range of [3, 80]. This prevents the welding positions of the first shell portion 41 and the second shell portion 42 from being too close to the first shell portion 41 due to the ratio being too large, causing the weld to be subjected to excessive stress and prone to cracking during use of the battery cell; nor does it prevent the shell 40 from being subjected to excessive stress and cracking during the drawing process due to the ratio being too small, thereby making the manufacturing of the first shell portion 41 difficult.

[0506] Further optionally, H and h1 satisfy: 5≤H / h1≤20. For example, H / h1=5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20.

[0507] In some embodiments, h1 satisfies: 3 mm ≤ h1 ≤ 50 mm.

[0508] For example, h1=3mm, 5mm, 10mm, 15mm, 20mm, 25mm, 30mm, 35mm, 40mm, 45mm, 50mm.

[0509] In this embodiment, by setting h1 within the range of [3 mm, 50 mm], the weld will not be too close to the first shell portion 41 due to h1 being too small, which would cause the battery cell to crack during the charging and discharging process; nor will h1 be too large, which would cause the first shell portion 41 to crack during the integral drawing process, making the manufacturing of the first shell portion 41 difficult.

[0510] Further optionally, h1 satisfies: 5mm≤h1≤30mm.

[0511] It should be noted that, when h1 meets the above conditions, H may also meet the following conditions: H is greater than or equal to 100 mm. For example, H is equal to 400 mm.

[0512] In some embodiments, the yield strength of the shell 40 at a temperature of 25° C. is Re, and Re satisfies: 125 MPa≤Re≤1000 MPa.

[0513] Yield strength can be understood as the critical stress value at which a material yields. Generally, after a material is subjected to stress, as the stress increases, in addition to elastic deformation, it may also undergo plastic deformation. The point at which plastic deformation occurs is called the yield point, and the strength corresponding to the yield point is called the yield strength. The test method for the yield strength Re of the housing 40 at a temperature of 25°C in the embodiment of the present application can be selected based on the actual application. For example, the yield strength Re can be tested at a room temperature of 25°C using GB / T 228.1-2010.

[0514] For example, Re=125MPa, 130MPa, 150MPa, 180MPa, 200MPa, 230MPa, 250MPa, 280MPa, 300MPa, 320MPa, 350MPa, 380MPa, 400MPa, 430MPa, 450MPa, 480MPa, 500MPa, 530MPa, 5 50MPa, 570MPa, 600Mpa, 610Mpa, 640Mpa, 680Mpa, 700Mpa, 720Mpa, 750Mpa, 780Mpa, 800Mpa, 830Mpa, 850Mpa, 880Mpa, 900Mpa, 920Mpa, 950Mpa, 980Mpa, 1000Mpa.

[0515] In this embodiment, by using a material with a yield strength Re satisfying 125 MPa≤Re≤1000 MPa to manufacture the first housing portion, the wall thickness of the first housing portion can be reduced without reducing the strength of the first housing portion, thereby increasing the capacity space of the battery cell.

[0516] Figure 23 shows a schematic diagram of a partial structure of the housing 211 according to an embodiment of the present application. For example, Figure 23 may be a partial enlarged view of area A' shown in Figure 9. As shown in Figure 23, the housing 211 according to the embodiment of the present application has a multi-layer structure, and the material of the outermost shell 2117 of the housing 211 includes at least one of the following: aluminum, aluminum alloy, copper, copper alloy, and chromium.

[0517] It should be understood that the housing 211 of the embodiment of the present application is a multi-layer structure, that is, for any wall of the housing 211, a multi-layer structure is stacked along the thickness direction of the wall, so that the housing 211 is a multi-layer structure. In addition, the installation method between the multi-layer structures of the housing 211 can be flexibly set according to the actual application. For example, it is possible to first process to obtain multiple single-layer housing structures of different sizes but basically the same shape, for example, each single-layer housing structure is a hollow structure with an opening; then, the relatively larger housing structures among the multiple single-layer housing structures are sequentially placed on the outside of the relatively smaller housing structures, so that the multiple single-layer housing structures can be combined into a multi-layer housing 211. For another example, it is also possible to first process to obtain an approximately plate-like structure with a multi-layer structure; then, multiple of these plate-like structures are spliced ​​and combined to form a multi-layer housing 211, but the embodiment of the present application is not limited to this.

[0518] It should be understood that the outermost shell 2117 of the shell 211 in the embodiment of the present application includes the outermost structure of each wall of the shell 211 , that is, the outermost shell 2117 is a shell structure including the outer surface of the shell 211 .

[0519] In the embodiment of the present application, the material of the outermost shell 2117 of the shell 211 may include at least one of the following: aluminum, aluminum alloy, copper, copper alloy, and chromium. When the material of the outermost shell 2117 contains aluminum, the aluminum will be oxidized into dense aluminum oxide, which is corrosion-resistant. When the material of the outermost shell 2117 contains copper, the copper will be oxidized into copper oxide, i.e., verdigris, which is corrosion-resistant. When the material of the outermost shell 2117 contains chromium, the chromium will be oxidized into chromium oxide, which is also corrosion-resistant. Therefore, when the material of the outermost shell 2117 is made of the above-mentioned corrosion-resistant materials, the outermost shell 2117 can protect the other shell layers located inside it, thereby improving the structural stability of the shell 211 and increasing the service life of the shell 211.

[0520] It should be understood that the specific thickness of the outermost shell 2117 of the embodiment of the present application can also be flexibly set according to actual application. For example, the thickness of the outermost shell 2117 can be set according to a certain ratio based on the thickness of the shell 211.

[0521] In some embodiments, the average thickness of the outermost shell 2117 is T11, and the average thickness of the shell 211 is T10, where T11 and T10 satisfy the following: 0.15 ≤ T11 / T10 ≤ 0.5. If the ratio T11 / T10 is set too small, the average thickness T11 of the outermost shell 2117 will be too small due to the limited average thickness T10 of the shell 211. This will increase the difficulty of processing and reduce the corrosion protection of the outermost shell 2117, thereby affecting the structural reliability of the shell 211. Conversely, if the ratio T11 / T10 is set too large, the average thickness T11 of the outermost shell 2117 will be too large, while the thicknesses of the other shell layers of the shell 211, excluding the outermost shell 2117, will be too small. However, the structural strength of the outermost shell 2117 may be insufficient, especially after oxidation, resulting in poor deformation capacity. If the average thickness T11 is too large, it will affect the overall structural strength of the shell 211, thereby reducing the stability of the shell 211.

[0522] Furthermore, T11 and T10 satisfy the following: 0.15≤T11 / T10≤0.4. By appropriately reducing the maximum value of the ratio T11 / T10 and increasing the minimum value of the ratio T11 / T10, the average thickness T11 of the outermost shell 2117 can be limited to be neither too large nor too small, thereby improving both the anti-corrosion effect and the structural strength and stability of the shell 211.

[0523] Furthermore, T11 and T10 satisfy: 0.2≤T11 / T10≤0.3, so as to better improve the anti-corrosion effect and enhance the stability and reliability of the housing 211 .

[0524] In some embodiments, the ratio T11 / T10 of the average thickness T11 of the outermost shell 2117 to the average thickness T10 of the shell 211 can also be set to other values. For example, the ratio T11 / T10 can be any of the following values ​​or between any two of the following values: 0.15, 0.18, 0.2, 0.23, 0.25, 0.28, 0.3, 0.33, 0.35, 0.38, 0.4, 0.43, 0.45, 0.48, and 0.5.

[0525] It should be understood that the range of values ​​for the average thickness T10 of the shell 211 of the embodiment of the present application can also be flexibly set according to actual applications. For example, the average thickness T10 of the shell 211 satisfies the following conditions: 0.05mm≤T10≤0.5mm. The average thickness T10 of the shell 211 should not be too small to reduce the difficulty of processing the multi-layer shell 211 and improve the structural strength of the shell 211. For example, the shell 211 is not easy to break, thereby increasing the service life of the shell 211. Conversely, the average thickness T10 of the shell 211 should not be too large to reduce the space occupied by the shell 211, thereby increasing the space utilization of the battery cell 20 and increasing the energy density of the battery 10 provided with multiple battery cells 20.

[0526] Furthermore, the average thickness T10 of the shell 211 satisfies the following condition: 0.075 mm ≤ T10 ≤ 0.4 mm. Properly reducing the average thickness T10 of the shell 211 can reduce the space occupied by the shell 211 within the battery 10, thereby increasing the energy density of the battery 10. Properly increasing the average thickness T10 of the shell 211 can also reduce the difficulty of processing the shell 211.

[0527] Furthermore, the average thickness T10 of the housing 211 satisfies the following relationship: 0.1 mm ≤ T10 ≤ 0.3 mm. The average thickness T10 of the housing 211 is neither too large nor too small, which not only improves the structural strength and stability of the housing 211 but also reduces the space occupied by the housing 211 within the battery 10, thereby increasing the energy density of the battery 10.

[0528] In some embodiments, the average thickness T10 of the housing 211 of the present invention can also be set to other values. For example, the average thickness T10 of the housing 211 can be any of the following values ​​or between any two of the following values: 0.05 mm, 0.075 mm, 0.1 mm, 0.125 mm, 0.15 mm, 0.175 mm, 0.2 mm, 0.225 mm, 0.25 mm, 0.275 mm, 0.3 mm, 0.325 mm, 0.35 mm, 0.375 mm, 0.4 mm, 0.425 mm, 0.45 mm, 0.475 mm, and 0.5 mm.

[0529] It should be understood that the average thickness T11 of the outermost shell 2117 of the embodiment of the present application can also be flexibly set according to actual applications. For example, T11 satisfies the following conditions: 0.015 mm ≤ T11 ≤ 0.25 mm. The average thickness T11 of the outermost shell 2117 should not be too small to reduce the difficulty of processing, improve the corrosion resistance of the outermost shell 2117, and thus improve the structural reliability of the shell 211. Conversely, the average thickness T11 of the outermost shell 2117 should not be too large. Considering that the outermost shell 2117 has poor deformation ability after being oxidized, if the average thickness T11 is too large, it will affect the deformation ability of the overall structure of the shell 211, thereby reducing the reliability and stability of the shell 211.

[0530] Furthermore, the average thickness T11 of the outermost shell 2117 can also satisfy the following condition: 0.05 mm ≤ T11 ≤ 0.2 mm. Properly increasing the minimum value of the average thickness T11 of the outermost shell 2117 can enhance the corrosion resistance of the outermost shell 2117; and properly reducing the maximum value of the average thickness T11 of the outermost shell 2117 can enhance the deformation capacity of the overall structure of the shell 211, thereby improving the reliability and stability of the shell 211.

[0531] Furthermore, the average thickness T11 of the outermost shell 2117 can also satisfy: 0.075mm≤T11≤0.15mm, which can not only improve the corrosion resistance of the outermost shell 2117 but also enhance the deformation capability of the overall structure of the shell 211, thereby improving the reliability and stability of the shell 211.

[0532] In some embodiments, the average thickness T11 of the outermost shell 2117 of the embodiment of the present application can also be set to other values. For example, the average thickness T11 of the outermost shell 2117 can be any one of the following values ​​or between any two of the following values: 0.015mm, 0.02mm, 0.025mm, 0.03mm, 0.035mm, 0.04mm, 0.045mm, 0.05mm, 0.055mm, 0.06mm, 0.065mm, 0.07mm, 0.075mm, 0.08mm, 0.085mm, 0.09mm, 0.095mm, 0.1mm, 0.11mm, 0.12mm, 0.13mm, 0.14mm, 0.15mm, 0.16mm, 0.17mm, 0.18mm, 0.19mm, 0.2mm, 0.21mm, 0.22mm, 0.23mm, 0.24mm and 0.25mm.

[0533] It should be understood that the thickness of the inner shell 2118 of the housing 211 of the embodiment of the present application can also be flexibly adjusted according to actual applications. The inner shell 2118 is any shell layer of the housing 211 other than the outermost shell 2117. Furthermore, the housing 211 can include one or more inner shells 2118. When the housing 211 includes multiple inner shells 2118, the thicknesses of the multiple inner shells 2118 can be uniform for ease of processing, or can be different to flexibly adjust the thickness of the inner shells 2118 at different locations according to actual applications. For example, as shown in FIG23 , the housing 211 includes a three-layer structure. The three-layer structure includes an outermost shell 2117 located on the outermost side and two inner shells 2118 located on the inner side. The two inner shells 2118 include an innermost shell 2118b and an intermediate shell 2118a. The average thickness of the innermost shell 2118b and the average thickness of the middle shell 2118a can be the same or different. For example, the average thickness of the innermost shell 2118b and the average thickness of the middle shell 2118a can both be set to T12, and the value of T12 can be set according to the application. For example, T12 can be greater than, equal to, or less than T11. The embodiments of the present application are not limited to this.

[0534] It should be understood that the average thickness T10 of the housing 211 in the embodiment of the present application may refer to the average thickness of at least a portion of the housing 211. The average thickness T11 of the outermost shell 2117 of the housing 211 may also refer to the average thickness of at least a portion of the outermost shell 2117. The average thickness T12 of the inner shell 2118 of the housing 211 may also refer to the average thickness of at least a portion of the inner shell 2118. Furthermore, the calculation area for the average thickness T10 of the housing 211 is generally consistent with the calculation area for the average thickness T11 of the outermost shell 2117 and the calculation area for the average thickness T12 of the inner shell 2118. For example, if a portion of the housing 211 is excluded from the calculation of the average thickness T10, the same portion of the housing 211 should also be excluded from the calculation of the average thickness T11 of the outermost shell 2117 and the average thickness T12 of the inner shell 2118. For ease of explanation, the following description takes the calculation of the average thickness T10 of the shell 211 as an example, but the relevant description is also applicable to determining the average thickness T11 of the outermost shell 2117 and the average thickness T12 of the inner shell 2118, which will not be repeated here.

[0535] For example, the average thickness T10 of the shell 211 may refer to the average thickness T10 of the entire area of ​​the shell 211, especially when the overall surface of the shell 211 is relatively flat, that is, the thickness of most areas of the shell 211 is basically equal or has a small difference, or when the thickness of all areas of the shell 211 is basically equal or has a small difference, then the average thickness of all areas of the shell 211 can be determined to be T10.

[0536] For another example, the average thickness T10 of the housing 211 may also refer to the average thickness T10 of a local area of ​​the housing 211, that is, the average thickness T10 of the remaining area after excluding the portion of the housing 211. For example, if the housing 211 includes a special area, and the thickness of the special area is significantly different from that of other areas, for example, the special area has a protruding structure or a recessed area along the thickness direction, making the thickness of the special area larger or smaller than that of other areas, then the special area can be excluded to calculate the average thickness T10 of the remaining area of ​​the housing 211.

[0537] In some embodiments, the housing 211 may include a functional area, and the average thickness T10 of the housing 211 is the average thickness of the areas of the housing 211 excluding the functional area. For example, the functional area includes at least one of the following areas: a pressure relief area, an area where the electrode terminals 214 are located, a liquid injection area, and a welding area. The thickness of the functional area is generally significantly different from the thickness of other areas of the housing 211. Therefore, when calculating the average thickness T10 of the housing 211 excluding the functional area, the design of the housing 211 can be made more consistent with strength requirements, thereby improving the structural strength and stability of the battery cell 20.

[0538] It should be understood that the functional areas of the present embodiment may include areas on the housing 211 that have specific structures or specific uses, and are applicable to the "functional areas" described above. For the sake of brevity, they will not be described in detail here. For example, the functional areas may include pressure relief areas, which are used to house a pressure relief mechanism. The pressure relief mechanism of the present embodiment may be located on any wall of the battery cell 20, for example, in the pressure relief area of ​​the housing 211 of the battery cell 20. The pressure relief mechanism may be a component of the housing 211, or it may be a separate structure from the housing 211 and secured to the housing 211 by, for example, welding. For example, when the pressure relief mechanism is a component of the housing 211, the pressure relief mechanism may be formed by providing a notch in the housing 211. That is, the housing 211 may be provided with a notch in the pressure relief area. The thickness of the notch is significantly less than that of other areas of the housing 211. Therefore, the thickness at the notch may not be included in the average thickness T10 of the housing 211. The notch is the weakest point of the pressure relief mechanism. When the battery cell 20 generates too much gas, causing the internal pressure to rise and reach a threshold, or the internal reaction of the battery cell 20 generates heat, causing the internal temperature of the battery cell 20 to rise and reach a threshold, the pressure relief mechanism can rupture at the notch, causing the inside and outside of the battery elevator 20 to communicate with each other, and the gas pressure and temperature are released outward through the rupture of the pressure relief mechanism, thereby preventing the battery cell 20 from exploding.

[0539] For another example, the pressure relief mechanism may be a separate structure from the housing 211. The pressure relief mechanism may take the form of an explosion-proof valve, an air valve, a pressure relief valve, or a safety valve, and may specifically employ a pressure-sensitive or temperature-sensitive element or structure. For example, the housing 211 may be provided with a through-hole at the pressure relief area, and the pressure relief mechanism may be mounted and fixed to the housing 211 via the through-hole. After installation, the pressure relief mechanism may protrude or be recessed relative to other areas of the housing 211. Therefore, the calculation of the average thickness T10 of the housing 211 may not include the pressure relief area where the pressure relief mechanism is located. When the internal pressure or temperature of the battery cell 20 reaches a predetermined threshold, the pressure relief mechanism activates or a weak structure provided in the pressure relief mechanism is destroyed, thereby forming an opening or channel for the internal pressure or temperature to be released.

[0540] In some embodiments, the functional area may also include an area where the electrode terminals 214 are located. Each electrode terminal 214 in the embodiments of the present application may be located on any wall, and multiple electrode terminals 214 may be located on the same wall or on different walls of the battery cell 20. For example, as shown in Figures 3 and 4 , each battery cell 20 includes two electrode terminals 214, and the two electrode terminals 214 are located on the same wall. For example, the two electrode terminals 214 may be located on the cover plate 212.

[0541] For another example, assuming that each battery cell 20 includes two electrode terminals 214, and that the two electrode terminals 214 are located on the same wall, unlike what is shown in Figures 3 and 4 , the two electrode terminals 214 can also be located on any wall of the housing 211. For example, both electrode terminals 214 can be located on the wall with the smallest area of ​​the housing 211. When one or more electrode terminals 214 are located in the housing 211, each electrode terminal 214 typically protrudes from other areas of the housing 211. That is, the thickness of the area where the electrode terminal 214 is located is much greater than the thickness of other areas of the housing 211. Therefore, the calculation of the average thickness T10 of the housing 211 does not need to include the areas where all electrode terminals 214 are located.

[0542] In some embodiments, the functional area may also include a liquid injection area. For example, the liquid injection area of ​​the housing 211 may be provided with a liquid injection hole through which electrolyte is injected into the interior of the housing 211. After the electrolyte is injected, the liquid injection hole can be sealed with a sealant. Considering that the thickness of the liquid injection area where the sealant is located is generally much greater than the thickness of other areas of the housing 211, the liquid injection area may not be included in the calculation of the average thickness T10 of the housing 211.

[0543] In some embodiments, the functional area may also include a welding area. For example, the housing 211 and the cover plate 212 may be secured by welding, or the housing 211 itself may be formed by welding. For example, any two walls of the housing 211 may be welded, or the housing 211 may be formed by splicing at least two parts together. In this case, the housing 211 may include a welding area. For example, the housing 211 may be welded by splicing, and the housing 211 may have a weld seam 2113. Specifically, the housing 211 may include at least two parts, which are connected by welding to form the housing 211. In this embodiment of the present application, the housing 211 includes two parts along the height direction Z of the battery cell 20, with a weld seam 2113 between the upper and lower parts. Alternatively, unlike in FIG. 4 , other parts of the housing 211 may also be provided with a weld seam 2113, but the present embodiment is not limited thereto. The welding area of ​​the functional area in the embodiment of the present application may also include the weld seam 2113. Due to the processing technology, the thickness of the welding area is generally greater than the thickness of other areas of the shell 211 . Therefore, the welding area may not be included in the calculation of the average thickness T10 of the shell 211 .

[0544] It should be understood that to further improve the structural strength and reliability of the housing 211, the inner shell 2118 of the housing 211 can be configured according to actual applications. In some embodiments, the tensile strength of the inner shell 2118 of the housing 211 at 25°C is Rm1, and Rm1 satisfies the following: 250MPa≤Rm1≤2000MPa. By increasing the tensile strength Rm1 of the inner shell 2118 of the housing 211 at room temperature of 25°C, the overall structural strength and stability of the housing 211 are increased; however, the tensile strength Rm1 of the inner shell 2118 at room temperature should not be too large to reduce the difficulty in selecting the material of the inner shell 2118, thereby reducing the difficulty and cost of processing the battery cell 20.

[0545] It should be understood that the value range of the tensile strength Rm1 of the inner shell 2118 at room temperature of 25°C in the embodiment of the present application can be adjusted according to actual applications. For example, the value of the tensile strength Rm1 at room temperature can also satisfy 400MPa≤Rm1≤1200MPa. On the one hand, increasing the tensile strength Rm1 of the inner shell 2118 at room temperature can improve the deformation capacity of the inner shell 2118 to resist the expansion of the electrode assembly 22, making the inner shell 2118 less likely to be damaged, thereby improving the structural stability and service life of the shell 211 and the battery cell 20. On the other hand, controlling the tensile strength Rm1 of the inner shell 2118 at room temperature to not be too large can reduce the difficulty of selecting the material and processing the inner shell 2118, save costs, and facilitate processing.

[0546] Furthermore, the tensile strength Rm1 of the inner shell 2118 at room temperature can be set to satisfy 450 MPa ≤ Rm1 ≤ 800 MPa. The tensile strength Rm1 of the inner shell 2118 at room temperature is neither too high nor too low, which improves the deformation capacity of the inner shell 2118 to resist the expansion of the electrode assembly 22, while also facilitating implementation and reducing costs.

[0547] In some embodiments, the tensile strength Rm1 of the inner shell 2118 of the embodiment of the present application at room temperature can also be set to other values. For example, the tensile strength Rm1 at room temperature can be any one of the following values ​​or between any two of the following values: 250MPa, 280MPa, 300MPa, 330MPa, 350MPa, 380MPa, 400MPa, 450MPa, 500MPa, 550MPa, 600MPa, 650MPa, 700MPa, 750MPa, 800MPa, 850MPa, 900MPa, 950MPa, 10 ... MPa, 1800 MPa, 1850 MPa, 1900 MPa, 1950 MPa, and 2000 MPa.

[0548] It should be understood that the tensile strength of the present embodiment refers to the maximum stress a material can withstand before breaking. The method for testing the tensile strength Rm1 of the inner shell 2118 at 25°C in the present embodiment can be selected based on the actual application. For example, the tensile strength Rm1 can be tested at room temperature of 25°C using the national standard GB / T 228.1-2010.

[0549] The above description primarily uses a rectangular battery cell 20 as an example. The following description, combined with the accompanying drawings, uses a cylindrical battery cell 20 as an example. Aside from the shape, the cylindrical battery cell 20 of this embodiment and the rectangular battery cell 20 described above are mutually applicable and will not be further elaborated upon here.

[0550] Figure 24 shows a schematic structural diagram of a battery cell 20 according to an embodiment of the present application. For example, the battery cell 20 shown in Figure 3 may be any battery cell 20 in the battery 10. Figure 25 shows a schematic partial exploded structural diagram of a battery cell 20 according to an embodiment of the present application. For example, Figure 25 may be a schematic partial exploded structural diagram of the battery cell 20 shown in Figure 24. Figure 26 shows a schematic cross-sectional diagram of a housing 211 of a battery cell 20 according to an embodiment of the present application. For example, Figure 26 may be a cross-sectional diagram of the housing 211 of the battery cell 20 shown in Figures 24 and 25, and the cross-sectional diagram is a cross-sectional view of the housing 211.

[0551] In an embodiment of the present application, as shown in Figures 24 to 26, the battery cell 20 includes: an electrode assembly 22, the electrode assembly 22 includes a first electrode tab 2221; a first electrode terminal 214a; a shell 211, the shell 211 includes a barrel 211b and a cover 211a connected to the barrel 211b, the barrel 211b is arranged around the periphery of the electrode assembly 22, the cover 211a includes the first electrode terminal 214a, the first electrode tab 2221 is electrically connected to the first electrode terminal 214a through the barrel 211b, and the shell 211 is a multi-layer structure with different resistivities.

[0552] The housing 211 can be in a variety of shapes, such as a cylinder, a cuboid, or other polyhedron. For example, as shown in Figures 24 to 26, the housing 211 is described as a hollow cylindrical structure. Furthermore, the embodiments of the present application mainly take the housing 211 as a hollow structure with an opening at one end as an example, and the corresponding cover 212 is a circular plate-like structure that matches the housing 211. For a cylindrical housing 211, the barrel 211b is a cylinder, and the cover 211a is a circular plate-like structure.

[0553] The electrode assembly 22 of the embodiment of the present application may include a first electrode tab 2221, which may be electrically connected to the first electrode terminal 214a through the barrel 211b of the shell 211, thereby simplifying the structure of the battery cell 20; the shell 211 is set to a multi-layer structure, and the resistivity of the multi-layer structure is different. The current carrying capacity of the battery cell 20 can be improved by a layer structure with a lower resistivity, and the structural strength of the shell 211 can be improved by a layer structure with a higher resistivity, which can improve the performance of the battery cell 20 and the structural strength of the battery cell 20, thereby increasing the service life of the battery cell 20.

[0554] In the embodiment of the present application, the electrode assembly 22 further includes a second electrode tab 2222, which has an opposite polarity to the first electrode tab 2221. Specifically, from the appearance of the electrode assembly 22, the electrode assembly 22 includes a main body 221 and electrode tabs 222. The electrode tabs 222 include a first electrode tab 2221 and a second electrode tab 2222. The first electrode tab 2221 and the second electrode tab 2222 protrude from the main body 221. The first electrode tab 2221 is the portion of the first electrode sheet not coated with the active material layer, and the second electrode tab 2222 is the portion of the second electrode sheet not coated with the active material layer. The first electrode tab 2221 and the second electrode tab 2222 are used to draw current from the main body 221.

[0555] The first and second electrode tabs 2221, 2222 can extend from the same side of the main body 221, i.e., the first and second electrode tabs 2221, 2222 are located on the same end surface of the electrode assembly 22. Alternatively, the first and second electrode tabs 2221, 2222 can extend from different sides of the main body 221, i.e., the first and second electrode tabs 2221, 2222 are located on different end surfaces of the electrode assembly 22. For example, the first and second electrode tabs 2221, 2222 can extend from opposite sides, i.e., the first and second electrode tabs 2221, 2222 are located on opposite end surfaces of the electrode assembly 22, to facilitate processing. As shown in Figures 24 to 26, the first and second electrode tabs 2221, 2222 can be located on opposite sides of the main body 221 along a first direction Z. In other words, the first and second electrode tabs 2221, 2222 are located at opposite ends of the electrode assembly 22 along the first direction Z. The first direction Z can be the height direction Z of the electrode assembly 22.

[0556] It should be understood that the electrode assembly 22 includes a first electrode sheet, a second electrode sheet, and a separator, which is used to separate the first electrode sheet from the second electrode sheet. The first electrode sheet and the second electrode sheet have opposite polarities. In other words, one of the first electrode sheet and the second electrode sheet is a positive electrode sheet 223, and the other of the first electrode sheet and the second electrode sheet is a negative electrode sheet 224.

[0557] The first pole piece, the second pole piece and the separator are all strip-shaped structures, and the first pole piece, the second pole piece and the separator are wound together to form a wound structure. The wound structure can be a cylindrical structure, a flat structure or a structure of other shapes.

[0558] Optionally, the first pole tab 2221 is wound multiple times around the central axis of the electrode assembly 22, and the first pole tab 2221 includes multiple turns of pole tab layers. After winding, the first pole tab 2221 is generally cylindrical, with a gap between two adjacent turns of pole tab layers. In embodiments of the present application, the first pole tab 2221 may be processed to reduce the gap between the pole tab layers, thereby facilitating connection of the first pole tab 2221 with other conductive structures. For example, in embodiments of the present application, the first pole tab 2221 may be flattened to bring the end regions of the first pole tab 2221 away from the main body 221 together; the flattening process forms a dense end face at the end of the first pole tab 2221 away from the main body 221, thereby reducing the gap between the pole tab layers and facilitating connection of the first pole tab 2221 with other conductive structures. Alternatively, in embodiments of the present application, conductive material may be filled between two adjacent turns of pole tab layers to reduce the gap between the pole tab layers.

[0559] Optionally, the second tab 2222 is wound multiple times around the central axis of the electrode assembly 22, and the second tab 2222 includes multiple tab layers. Exemplarily, the second tab 2222 is also flattened to reduce gaps between the tab layers of the second tab 2222.

[0560] In an embodiment of the present application, the battery cell 20 also includes: a second electrode terminal 214b, which is electrically connected to the second electrode tab 2222, and the first electrode terminal 214a and the second electrode terminal 214b are located on the same wall of the battery cell 20 to improve the integration of the battery cell 20, improve the space utilization of the battery cell 20 in the battery 10, and facilitate processing and assembly.

[0561] It should be understood that the cover 211 a of the embodiment of the present application includes the first electrode terminal 214 a . For example, the first electrode terminal 214 a may be provided on the cover 211 a , or the cover 211 a may directly serve as the first electrode terminal 214 a .

[0562] In some embodiments, the cover 211a serves as the first electrode terminal 214a. The cover 211a is provided with an electrode lead-out hole 211c. The second electrode terminal 214b is insulated and mounted on the cover 211a and in the electrode lead-out hole 211c. One of the cover 211a and the second electrode terminal 214b serves as the positive output electrode of the battery cell, and the other serves as the negative output electrode of the battery cell. At least a portion of the housing 211 itself can serve as an output electrode of the battery cell 20, thereby eliminating a traditional electrode terminal and simplifying the structure of the battery cell 20. When multiple battery cells 20 are assembled into a group, the housing 211 can be electrically connected to the busbar, which not only increases the flow area but also makes the structural design of the busbar more flexible.

[0563] For the convenience of description, the following mainly takes the cover 211 a as the first electrode terminal 214 a as an example, but the embodiments of the present application are not limited thereto.

[0564] Figure 27 is a partial cross-sectional schematic diagram of a battery 10 provided in some embodiments of the present application, and the battery 10 may include multiple battery cells 20; Figure 28 is another partial cross-sectional schematic diagram of a battery 10 provided in some embodiments of the present application, for example, Figure 28 may be an enlarged schematic diagram of the battery 10 shown in Figure 27 at area B'.

[0565] As shown in Figures 24 to 28, the cover body 211a is provided with an electrode lead-out hole 211c, and at least a portion of the cover body 211a is used to electrically connect the first connecting member 81 and the first pole ear 2221 of the battery 10; the second electrode terminal 214b is used to electrically connect the second connecting member 82 and the second pole ear 2222 of the battery 10, and the second electrode terminal 214b is insulated and arranged on the cover body 211a and installed in the electrode lead-out hole 211c. One of the cover body 211a and the second electrode terminal 214b is the positive output pole of the battery cell 20, and the other is the negative output pole of the battery cell 20.

[0566] The cover 211 a is electrically connected to the barrel 211 b , and the cover 211 a and the barrel 211 b may have the same polarity.

[0567] It should be understood that the cover 211a and the cylinder 211b of the embodiment of the present application can be formed as an integral structure, that is, the housing 211 is a one-piece component. This can eliminate the need for the process of connecting the cover 211a and the cylinder 211b. For example, the housing 211 can be formed by a stretching process. Of course, the cover 211a and the cylinder 211b can also be provided as two separate components and then connected together by welding, riveting, bonding, etc. The embodiment of the present application mainly uses the cover 211a and the cylinder 211b as an example of an integral structure.

[0568] The housing 211 of the present embodiment can be a hollow structure with one end open. Specifically, the end of the barrel 211b facing away from the cover 211a has an opening 211d. The battery cell 20 also includes a cover plate 212, which covers the opening 211d of the barrel 211b to seal it. The cover plate 212 can have various structures, for example, a plate-like structure.

[0569] In some embodiments, the cover 211a is provided with an electrode lead-out hole 211c. The area of ​​the cover 211a other than the electrode lead-out hole 211c includes an area for welding to the first connecting member 81. That is, the cover 211a can be welded to the first connecting member 81 to form a first weld W1. Exemplarily, during welding, a laser is applied to the surface of the first connecting member 81 facing away from the cover 211a. The laser melts and connects a portion of the first connecting member 81 and a portion of the cover 211a to form the first weld W1.

[0570] The electrode lead-out hole 211c passes through the cover 211a, so as to facilitate the electrical energy in the electrode assembly 22 to be led out of the housing 211. For example, the electrode lead-out hole 211c passes through the cover 211a along the first direction Z.

[0571] The electrode lead-out hole 211c in the embodiment of the present application is formed after the housing 211 is stretched and formed. For example, in this embodiment, the electrode lead-out hole 211c for mounting the second electrode terminal 214b is formed on the cover 211a using a hole-forming process, thereby positioning the positive and negative output electrodes at the end of the battery cell 20 facing away from the opening of the housing 211. The cover 211a is formed during the molding process of the housing 211, and even after the electrode lead-out hole 211c is formed, its flatness can be maintained, thereby ensuring the connection strength between the cover 211a and the first connecting member 81. Furthermore, the flatness of the cover 211a is not constrained by its own size, so the cover 211a can be larger, thereby improving the current carrying capacity of the battery cell 20.

[0572] In some embodiments, the barrel 211b is cylindrical, the electrode lead-out hole 211c is a circular hole, and the central axis of the barrel 211b and the central axis of the electrode lead-out hole 211c are arranged to coincide with each other. "Coincidence" does not require that the central axis of the barrel 211b and the central axis of the electrode lead-out hole 211c absolutely and completely coincide with each other; there may be deviations allowed by the process.

[0573] The electrode lead-out hole 211c can be used to define the position of the second electrode terminal 214b. In this embodiment, the central axis of the electrode lead-out hole 211c is aligned with the central axis of the barrel 211b, so that at least a portion of the second electrode terminal 214b is located at the center of the cover 211a. This reduces the positioning accuracy requirements for the second electrode terminal 214b when multiple battery cells 20 are assembled, simplifying the assembly process and improving assembly efficiency.

[0574] The central axis of the electrode assembly 22 is a virtual straight line, which is parallel to the first direction Z. The central axis of the electrode assembly 22 may pass through the electrode lead-out hole 211 c or may be staggered with the electrode lead-out hole 211 c, which is not limited in this embodiment.

[0575] The first tab 2221 is electrically connected to the cover 211a. The first tab 2221 can be directly electrically connected to the cover 211a or indirectly electrically connected to the cover 211a through other conductive structures. For example, the first tab 2221 can be electrically connected to the cover 211a through the barrel 211b.

[0576] The second electrode tab 2222 is electrically connected to the second electrode terminal 214b. The second electrode tab 2222 can be directly electrically connected to the second electrode terminal 214b or indirectly electrically connected to the second electrode terminal 214b through other conductive structures. For example, the second electrode tab 2222 can be electrically connected to the second electrode terminal 214b through the current collecting member 23.

[0577] The second electrode terminal 214 b is insulated from the cover 211 a . Therefore, the second electrode terminal 214 b and the cover 211 a may have different polarities, and the second electrode terminal 214 b and the cover 211 a may serve as different output poles.

[0578] The second electrode terminal 214b is fixed to the cover 211a. The second electrode terminal 214b can be fixed as a whole to the outside of the cover 211a, or can extend into the interior of the housing 211 through the electrode lead-out hole 211c.

[0579] When the first electrode tab 2221 is a negative electrode tab and the second electrode tab 2222 is a positive electrode tab, the cover 211a is the negative output terminal of the battery cell 20, and the second electrode terminal 214b is the positive output terminal of the battery cell 20. When the first electrode tab 2221 is a positive electrode tab and the second electrode tab 2222 is a negative electrode tab, the cover 211a is the positive output terminal of the battery cell 20, and the second electrode terminal 214b is the negative output terminal of the battery cell 20.

[0580] In the battery 10, a plurality of battery cells 20 are electrically connected by a busbar. The busbar includes a first connecting member 81 connected to the cover 211a of the battery cell 20 and a second connecting member 82 connected to the second electrode terminal 214b of the battery cell 20.

[0581] The first connecting member 81 can be connected to the cover 211a by welding, bonding, or other means to achieve electrical connection between the first connecting member 81 and the cover 211a. The second connecting member 82 can be connected to the second electrode terminal 214b by welding, bonding, riveting, or other means to achieve electrical connection between the second connecting member 82 and the second electrode terminal 214b.

[0582] Illustratively, the first connecting member 81 connects the cover 211a of one battery cell 20 and the second electrode terminal 214b of another battery cell 20, while the second connecting member 82 connects the second electrode terminal 214b of the one battery cell 20 and the cover 211a of yet another battery cell 20. In this way, the first connecting member 81 and the second connecting member 82 connect the three battery cells 20 in series.

[0583] In this embodiment, by using the cover 211a and the second electrode terminal 214b as the output terminal, the structure of the battery cell 20 can be simplified while ensuring the current carrying capacity of the battery cell 20. The cover 211a and the second electrode terminal 214b are located at the same end of the battery cell 20. In this way, the first connecting member 81 and the second connecting member 82 can be assembled to the same side of the battery cell 20, which simplifies the assembly process and improves the efficiency of assembling multiple battery cells 20 into a group.

[0584] It should be understood that, as shown in Figures 24 to 28 , the second electrode terminal 214b of the present embodiment includes a terminal body 2141. Furthermore, the terminal body 2141 can be fixed to the cover 211a by riveting. For example, at least a portion of the terminal body 2141 is positioned within the electrode lead-out hole 211c, and both ends of the terminal body 2141 are riveted to the electrode lead-out hole 211c.

[0585] In some embodiments, the terminal body 2141 may be provided with a recessed portion that is recessed from the outer surface of the terminal body 2141 in a direction facing the electrode assembly 22. The bottom of the recessed portion is used for welding to the current collecting member 23.

[0586] When the electrode assembly 22 and the current collecting member 23 are installed in the shell 211 through the opening 211d of the cylinder 211b, and the current collecting member 23 is pressed against the cover 211a, the external welding equipment can weld the bottom of the recess and the current collecting member 23 from the side of the bottom of the recess away from the current collecting member 23.

[0587] In this embodiment, the thickness of the terminal body 2141 is reduced by providing a recess, which can reduce the welding power required for welding the bottom of the recess to the current collecting member 23, reduce heat generation, and reduce the risk of burning other components (such as the first insulating member 61 and the second insulating member 60).

[0588] In some embodiments, the second electrode terminal 214b further includes a sealing plate 2142, which is used to seal the opening of the recess. The sealing plate 2142 can be located entirely outside the recess or partially within the recess, as long as the sealing plate 2142 can seal the opening of the recess. The sealing plate 2142 protects the recess from the outside, reduces the ingress of external impurities, reduces the risk of damage to the bottom of the recess by external impurities, and improves the sealing performance of the battery cell 20.

[0589] In some embodiments, the sealing plate 2142 is welded to the second connecting member 82 to form a second welding portion W2. The second welding portion W2 can reduce the contact resistance between the sealing plate 2142 and the second connecting member 82, thereby improving the current carrying capacity.

[0590] In some embodiments, at least a portion of the sealing plate 2142 protrudes from the outer surface of the terminal body 2141. When welding the second connecting member 82 and the sealing plate 2142, the second connecting member 82 is first attached to the upper surface of the sealing plate 2142 (i.e., the surface of the sealing plate 2142 facing away from the recessed portion), and then the second connecting member 82 and the sealing plate 2142 are welded. At least a portion of the sealing plate 2142 protrudes from the outer surface of the terminal body 2141 to prevent the outer surface of the terminal body 2141 from interfering with the attachment of the sealing plate 2142 and the second connecting member 82, thereby ensuring a tight fit between the second connecting member 82 and the sealing plate 2142.

[0591] In the embodiment of the present application, the battery cell 20 further includes a first insulating member 61 for insulating at least a portion of the second electrode terminal 214b from the cover 211a. For example, at least a portion of the first insulating member 61 is sandwiched between the cover 211a and the second electrode terminal 214b to insulate the cover 211a and the second electrode terminal 214b, thereby reducing the risk of a short circuit.

[0592] In the embodiment of the present application, the battery cell 20 further includes a second insulating member 60, which is located between the cover 211a and the electrode assembly 22. Specifically, the second insulating member 60 can separate the electrode assembly 22 from the cover 211a, thereby reducing the risk of contact and conduction between the electrode assembly 22 and the cover 211a when the battery cell 20 vibrates, thereby improving safety.

[0593] In some embodiments, at least one of the first insulating member 61 and the second insulating member 60 can be used to seal the electrode lead-out hole 211c. In other embodiments, the battery cell 20 further includes a sealing ring 62, which is sleeved onto the second electrode terminal 214b and used to seal the electrode lead-out hole 211c. Optionally, a portion of the sealing ring 62 extends into the electrode lead-out hole 211c to separate the hole wall of the electrode lead-out hole 211c from the second electrode terminal 214b.

[0594] In some embodiments, the second tab 2222 is disposed at one end of the electrode assembly 22 facing the cover 211a, and the first tab 2221 is disposed at the other end of the electrode assembly 22 facing away from the cover 211a. The barrel 211b is used to connect the first tab 2221 and the cover 211a so that the first tab 2221 is electrically connected to the cover 211a.

[0595] The barrel 211b can be directly electrically connected to the first electrode tab 2221 or can be electrically connected to the first electrode tab 2221 through other components. For example, the first electrode tab 2221 is electrically connected to the barrel 211b through the cover plate 212.

[0596] In the embodiment of the present application, the first electrode tab 2221 and the second electrode tab 2222 are arranged at both ends of the electrode assembly 22, which can reduce the risk of conduction between the first electrode tab 2221 and the second electrode tab 2222 and increase the flow area of ​​the first electrode tab 2221 and the flow area of ​​the second electrode tab 2222.

[0597] In some embodiments, first tab 2221 is the negative electrode tab, and the base material of housing 211 is steel. Housing 211 is electrically connected to the negative electrode tab, meaning that housing 211 is in a low-potential state. In this low-potential state, steel housing 211 is less susceptible to corrosion by the electrolyte, thereby reducing safety risks.

[0598] In some embodiments, the battery cell 20 further includes a current collecting member 23 for connecting the second electrode tab 2222 and the second electrode terminal 214b. The current collecting member 23 can be connected to the second electrode tab 2222 by welding, abutting, or bonding, and connected to the second electrode terminal 214b by welding, abutting, bonding, riveting, or other methods, thereby achieving electrical connection between the second electrode tab 2222 and the second electrode terminal 214b.

[0599] In the first direction Z, the second electrode terminal 214b is disposed opposite the middle region of the second electrode tab 2222. If the second electrode terminal 214b and the second electrode tab 2222 were directly connected, the conductive path between the edge region of the second electrode tab 2222 and the second electrode terminal 214b would be longer, resulting in uneven current density in the second electrode sheet of the electrode assembly 22, increased internal resistance, and reduced current carrying capacity and charging efficiency of the battery cell 20.

[0600] The current collecting component 23 of the embodiment of the present application and the second pole tab 2222 may have a larger connection area, and the current of the second pole tab 2222 may be collected into the second electrode terminal 214b via the current collecting component 23. In this way, the current collecting component 23 can reduce the difference in the conductive path between different areas of the second pole tab 2222 and the second electrode terminal 214b, improve the uniformity of the current density of the second pole sheet, reduce the internal resistance, and improve the flow capacity and charging efficiency of the battery cell 20.

[0601] It should be understood that the housing 211 of the embodiment of the present application is a multi-layer structure, that is, the barrel 211b and the cover 211a of the housing 211 are both multi-layer structures. For ease of description, the housing 211 hereinafter includes the barrel 211b and the cover 211a.

[0602] In the embodiment of the present application, the housing 211 includes a first housing layer 2115, and the resistivity of the first housing layer 2115 is K1, where K1 satisfies the following conditions: 1×10^-8Ω·m≤K1≤6×10^-8Ω·m. The first housing la...

Claims

1. A battery cell, It is characterized in that include: An electrode assembly, the electrode assembly comprising a positive electrode plate, the positive electrode plate comprising a positive electrode active material capable of reversibly extracting and inserting metal ions, the positive electrode active material comprising a nickel-containing compound; The shell is used to accommodate the electrode assembly, and the tensile strength of at least a part of the shell at a temperature of 500° C. is Rn, and Rn satisfies: 100MPa≤Rn≤1200MPa.

2. The battery cell according to claim 1, It is characterized in that The shell includes a weld, and at least a partial area of ​​the shell includes an area of ​​the shell within a preset distance from the weld, where the preset distance is L, and L satisfies: L=10 mm.

3. The battery cell according to claim 1 or 2, It is characterized in that The nickel-containing compound includes a layered lithium-containing transition metal oxide, and the molar amount of nickel element in the layered lithium-containing transition metal oxide accounts for more than 50% of the total molar amount of transition metal elements in the layered lithium-containing transition metal oxide, optionally more than 70%, optionally more than 80%, and optionally more than 90%.

4. The battery cell according to claim 3, It is characterized in that The layered lithium-containing transition metal oxide includes LiaNibCocMdOeAf, wherein 0<a≤1.2, 0.5≤b<1, optionally, 0.9≤b<1; 0<c<1; 0<d<1; 1≤e≤2; 0≤f≤1, M includes but is not limited to one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A includes but is not limited to one or more of N, F, S and Cl.

5. The battery cell according to any one of claims 1 to 4, It is characterized in that The material of at least a partial area of ​​the shell includes at least one of the following: steel, copper alloy, titanium alloy and nickel alloy.

6. The battery cell according to claim 5, It is characterized in that The material of at least a partial area of ​​the shell includes steel, 112 MPa≤Rn≤720 MPa.

7. The battery cell according to claim 5 or 6, It is characterized in that The material of at least a part of the shell includes at least one of the following: stainless steel and carbon steel.

8. The battery cell according to any one of claims 5 to 7, It is characterized in that The mass content of chromium in the material of at least a partial area of ​​the shell is m, and m satisfies: 10%≤m≤30%.

9. The battery cell according to any one of claims 1 to 8, It is characterized in that The shell is in a cylindrical or polygonal shape.

10. The battery cell according to any one of claims 1 to 9, It is characterized in that The melting point of at least a part of the shell is p, and p satisfies: 1200°C≤p≤2000°C.

11. The battery cell according to any one of claims 1 to 10, It is characterized in that The electrode assembly further comprises a negative electrode plate, wherein the negative electrode plate comprises a negative electrode active material capable of reversibly extracting and inserting metal ions, and the negative electrode active material comprises a silicon-based material; The tensile strength of at least a portion of the shell at a temperature of 25° C. is Rm, and Rm satisfies: 250 MPa≤Rm≤2000 MPa.

12. The battery cell according to any one of claims 1 to 11, It is characterized in that The electrode assembly further comprises a negative electrode plate, wherein the negative electrode plate comprises a negative electrode active material capable of reversibly extracting and inserting metal ions, and the negative electrode active material comprises a silicon-based material; The yield strength of at least a part of the shell at a temperature of 25° C. is Re, and Re satisfies: 140 MPa≤Re≤1000 MPa.

13. The battery cell according to any one of claims 1 to 12, It is characterized in that The tensile strength of at least a portion of the shell at a temperature of 25°C is Rm, and at least a portion of the shell includes a third shell wall, and the average thickness of the third shell wall is T, and Rm and T satisfy: 250MPa≤Rm≤2000MPa, 0.05mm≤T≤0.5mm, 60mm·MPa≤T×Rm≤500mm·MPa.

14. The battery cell according to any one of claims 1 to 13, It is characterized in that The capacity of the battery cell is C, the tensile strength of at least a portion of the shell at a temperature of 25° C. is Rm, and Rm and C satisfy: 250 MPa≤Rm≤2000 MPa, 25 Ah≤C≤550 Ah.

15. The battery cell according to any one of claims 1 to 14, It is characterized in that The shell has an opening, and the shell includes a first shell wall and at least two second shell walls arranged opposite to the opening, and the first shell wall and the second shell wall are arranged to intersect; A transition region is provided between two adjacent second shell walls of the at least two second shell walls, and a maximum thickness T1 of the transition region and a maximum thickness T0 of the thickest second shell wall of the two second shell walls satisfy the following relationship: T1>T0.

16. The battery cell according to any one of claims 1 to 15, It is characterized in that The shell is an integrally formed structure, the shell has an opening, the shell includes a first shell wall and at least two second shell walls arranged opposite to the opening, the first shell wall and the second shell wall are arranged to intersect, two of the at least two second shell walls are connected by a first fillet, and the depth H of the shell and the inner diameter R1 of the first fillet satisfy: 2.5mm≤R1≤20mm, 50mm <H≤250mm。 17. The battery cell according to any one of claims 1 to 16, It is characterized in that The shell is an integrally formed structure, the shell has an opening, the shell includes a first shell wall and at least two second shell walls arranged opposite to the opening, the first shell wall and the second shell wall are arranged to intersect, two of the at least two second shell walls are connected by a first fillet, and the yield strength Re of the shell at a temperature of 25°C and the inner diameter R1 of the first fillet satisfy the following conditions: 140MPa≤Re≤1000Mpa, 2.5mm≤R1≤20mm.

18. The battery cell according to any one of claims 1 to 17, It is characterized in that The shell has an opening, and the shell includes a first shell wall and at least one second shell wall arranged opposite to the opening, the first shell wall and the second shell wall are arranged to intersect, the first shell wall and the second shell wall are connected by a second fillet, and the inner diameter r1 of the second fillet and the minimum thickness T2 of the second shell wall with the smallest thickness among the at least one second shell wall satisfy the following relationship: 2.0≤r1 / T2≤30.

19. The battery cell according to any one of claims 1 to 18, It is characterized in that The housing comprises: A first housing portion is formed with an opening, the first housing portion comprises a first wall opposite to the opening and a second wall connected to the first wall, the first wall and the second wall are integrally formed; A second housing portion, fixedly connected to the second wall; Wherein, in the depth direction of the first shell portion, at least a portion of the shell portion is formed by the first The housing portion and the second housing portion are formed together.

20. The battery cell according to any one of claims 1 to 19, It is characterized in that The battery cell is used in a battery, and the electrode assembly includes a first pole lug and a second pole lug with opposite polarities; The shell comprises a barrel and a cover connected to the barrel, the cover and the barrel are integrally formed, the barrel is arranged around the periphery of the electrode assembly, the cover is provided with an electrode lead-out hole, and at least a portion of the cover is used to electrically connect the first connecting member of the battery and the first electrode tab; The battery cell further comprises: The second electrode terminal is used to electrically connect the second connecting member and the second electrode ear of the battery. The second electrode terminal is insulated and arranged on the cover body and installed in the electrode lead-out hole. One of the cover body and the second electrode terminal is the positive output electrode of the battery cell, and the other is the negative output electrode of the battery cell.

21. The battery cell according to claim 20, It is characterized in that The second electrode tab is arranged at one end of the electrode assembly facing the cover body, and the first electrode tab is arranged at the other end of the electrode assembly away from the cover body; The barrel is used to connect the first electrode tab and the cover body so that the first electrode tab is electrically connected to the cover body.

22. The battery cell according to any one of claims 1 to 21, It is characterized in that The electrode assembly includes a first electrode tab; the shell includes a cylinder and a cover connected to the cylinder, the cylinder is arranged around the periphery of the electrode assembly, the cover includes a first electrode terminal, the first electrode tab is electrically connected to the first electrode terminal through the cylinder, and the shell is a multi-layer structure with different resistivities.

23. The battery cell according to any one of claims 1 to 22, It is characterized in that The shell is a multi-layer structure, and the material of the outermost shell of the shell includes at least one of the following: aluminum, aluminum alloy, copper, copper alloy and chromium.

24. A battery, It is characterized in that include: A plurality of battery cells, wherein the battery cells are the battery cells according to any one of claims 1 to 23.

25. An electrical device, It is characterized in that include: A battery, comprising a battery cell as claimed in any one of claims 1 to 23, wherein the battery is used to supply power to the electrical device.

Images