Secondary battery cell, secondary battery, and electric device

Abstract

The embodiment of the invention provides a secondary battery monomer, a secondary battery and a power utilization device, the secondary battery monomer comprises a laminated electrode assembly, the laminated electrode assembly comprises a positive pole piece, a negative pole piece and an isolation film, the positive pole piece comprises a positive pole film layer, the positive pole film layer comprises a positive pole active material, the negative pole piece comprises a negative pole film layer, and the isolation film comprises a negative pole active material; the negative electrode film layer comprises a negative electrode active material; the positive electrode active material comprises lithium-containing transition metal phosphate and lithium-containing transition metal oxide; and the thickness h of the isolating membrane is more than or equal to 8 microns and less than or equal to 21 microns. The secondary battery cell can give consideration to both high energy density and good safety performance.

Description

Technical Field

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

[0002] In recent years, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal, wind and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields, and have thus achieved great development.

[0003] Improving the energy density of secondary battery cells is a research focus in the battery field. At present, the energy density of secondary batteries is mainly limited by the positive electrode active materials, and the purpose of improving energy density is usually achieved by combining different positive electrode active materials. However, while improving the energy density, the mixed positive electrode active materials may affect other properties of the secondary battery cells, such as cycle performance, safety performance, etc. Therefore, how to balance the energy density and safety performance of secondary battery cells has become a technical problem that needs to be solved urgently. Summary of the invention

[0004] The present application is made in view of the above technical problems, and its purpose is to provide a secondary battery cell, a secondary battery and an electrical device, wherein the secondary battery cell can have both high energy density and good safety performance.

[0005] In a first aspect, a secondary battery cell is provided, the secondary battery cell comprising: a laminated electrode assembly, comprising a positive electrode plate, a negative electrode plate and a separator, the positive electrode plate comprising a positive electrode film layer, the positive electrode film layer comprising a positive electrode active material, the negative electrode plate comprising a negative electrode film layer, the negative electrode film layer comprising a negative electrode active material; the positive electrode active material comprises a lithium-containing transition metal phosphate and a lithium-containing transition metal oxide; the thickness h of the separator satisfies: 8μm≤h≤21μm.

[0006] In the embodiments of the present application, the positive electrode active material includes a lithium-containing transition metal phosphate and a lithium-containing transition metal oxide, a laminated electrode assembly is used and the thickness of the isolation membrane is controlled within a specific range of 8μm-12μm, thereby being able to improve the energy density of the secondary battery cell and provide good safety performance.

[0007] In a possible implementation, based on the total mass of the positive electrode active material, the mass content m1 of the lithium-containing transition metal phosphate satisfies: 40 wt % ≤ m1 ≤ 70 wt %.

[0008] By controlling the mass content of the lithium-containing transition metal phosphate in the positive electrode active material within a suitable range, it helps to further improve the energy density and safety performance of the secondary battery cell.

[0009] In a possible implementation, the isolation film includes a base film and a coating layer disposed on at least one side of the base film, and a thickness h1 of the coating layer on one side satisfies: 3 μm≤h1≤6 μm.

[0010] In the embodiments of the present application, by controlling the thickness of the coating within a suitable range, the mechanical strength of the separator can be improved, while meeting the infiltration requirements of the electrolyte, thereby helping to improve the safety performance of the secondary battery cell.

[0011] In a possible implementation, the coating includes heat-resistant particles, and the heat-resistant particles include at least one of inorganic particles and organic particles.

[0012] In a possible implementation, the inorganic particles include at least one of aluminum oxide, silicon oxide, titanium oxide, and barium titanate.

[0013] Inorganic particles have good thermal stability. As a coating of the separator, they can provide good support for the base film during the cycle of the secondary battery cell, reduce the risk of thermal shrinkage of the base film during the cycle, and improve the thermal stability of the separator. Thus, the thermal stability of the secondary battery cell can be further improved.

[0014] In a possible implementation, the coating includes binder particles, and the binder particles include: polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, polyethylene, polypropylene, polyacrylonitrile, polyethylene oxide, copolymers of different fluorine-containing olefinic monomer units, copolymers of fluorine-containing olefinic monomer units and vinyl monomer units, copolymers of fluorine-containing olefinic monomer units and acrylic monomer units, copolymers of fluorine-containing olefinic monomer units and acrylic ester monomer units, and one or more of modified compounds of the above homopolymers or copolymers.

[0015] In a possible implementation, the laminated electrode assembly includes a plurality of positive electrode sheets and a plurality of negative electrode sheets, and the plurality of positive electrode sheets and the plurality of negative electrode sheets are alternately stacked in a thickness direction.

[0016] In a possible implementation, the single-side loading a of the binder particles on the isolation film satisfies: 0.5 mg / 1540.25 mm 2 ≤a≤1.2mg / 1540.25mm 2 .

[0017] In the embodiments of the present application, by controlling the loading amount of polyvinylidene fluoride on the isolation membrane within a suitable range, the bonding force between the isolation membrane and the pole piece can be increased, thereby improving the structural stability of the laminated motor assembly and further improving the safety performance of the secondary battery.

[0018] In a possible implementation, the positive electrode plate includes a conductive agent, the conductive agent includes carbon nanotubes, and the diameter l of the carbon nanotubes satisfies: 7nm≤l≤13nm.

[0019] In the embodiments of the present application, by selecting carbon nanotubes with diameters within a suitable range as the conductive agent, a conductive network between the conductive agent and the positive electrode active material can be constructed, thereby improving the rate performance and cycle performance of the secondary battery cell.

[0020] In a possible implementation, the average particle size D1 of the particles of the lithium-containing transition metal oxide satisfies: 2 μm≤D1≤5 μm.

[0021] In the embodiments of the present application, by controlling the average particle size of the lithium-containing transition metal oxide particles within the range of 2 μm-5 μm, the lithium-containing transition metal oxide can have better structural stability, improve the thermal stability of the lithium-containing transition metal oxide, and further enhance the safety performance of the secondary battery cell.

[0022] In a possible implementation, the lithium-containing transition metal oxide includes: Li 1+c [Ni x Co y Mn z M d ]O 2-e ; wherein M includes at least one of Zr, Al, Ti, Sb, Nb, Te, Mg, B, Ca, V, Ta or Sr, 0.2≥c≥-0.2, 0.95≥x≥0.5, 0.2≥y≥0.05, 0.3>z>0, 0.3>d≥0, 0.5≥e≥0.

[0023] In the embodiments of the present application, by selecting a lithium-containing transition metal oxide doped or coated with heteroatoms, it is helpful to improve the thermal stability of the lithium-containing transition metal oxide and further improve the safety performance of the secondary battery cell.

[0024] In a possible implementation, the positive electrode sheet satisfies at least one of the following (1)-(3): (1) The compaction density ρ1 of the positive electrode sheet satisfies: 2.5 g / cm 3 ≤ρ1≤2.9g / cm 3 (2) The single-sided coating weight CW1 of the positive electrode film layer satisfies: 190g / m 2 ≤CW1≤230g / m 2 ; (3) The thickness h1 of the positive electrode current collector satisfies: 10μm≤h1≤13μm.

[0025] In the embodiments of the present application, by controlling the compaction density of the positive electrode plate and the coating weight of the positive electrode film layer within a suitable range, it helps to improve the lithium ion dynamics, thereby reducing the polarization of the secondary battery cell during the cycle process, and helping to improve the safety performance of the secondary battery cell; by controlling the thickness of the positive electrode collector within a suitable range, it helps to reduce the thickness of the positive electrode plate, and helps to improve the energy density of the secondary battery cell.

[0026] In a possible implementation, the negative electrode sheet satisfies at least one of the following (4)-(6): (4) The compaction density ρ2 of the negative electrode sheet satisfies: 1.3 g / cm 3 ≤ρ2≤1.55g / cm 3 (5) The single-sided coating weight CW2 of the negative electrode film layer satisfies: 90g / m 2 ≤CW2≤110g / m 2 ; (6) The thickness h2 of the negative electrode current collector satisfies: 4μm≤h2≤6μm.

[0027] In the embodiments of the present application, by controlling the compaction density of the negative electrode pole piece and the coating weight of the negative electrode film layer within a suitable range, it helps to improve the lithium ion dynamics, thereby reducing the polarization of the secondary battery cell during the cycle process, and helping to improve the safety performance of the secondary battery cell; by controlling the thickness of the negative electrode current collector within a suitable range, it helps to reduce the thickness of the negative electrode pole piece, and helps to improve the energy density of the secondary battery cell.

[0028] In a possible implementation, the negative electrode active material includes graphite, and an average volume particle size Dv50 of the graphite satisfies: 10 μm≤Dv50≤14 μm.

[0029] In the embodiments of the present application, by controlling the average volume particle size of graphite within a suitable range, it helps to improve lithium ion kinetics, helps to reduce the polarization of secondary battery cells during the cycle process, and improves the safety performance of secondary battery cells.

[0030] In a possible implementation, the secondary battery includes an electrolyte, the electrolyte includes: a solvent, the solvent includes a linear carbonate; based on the total mass of the electrolyte, a mass content m2 of the linear carbonate satisfies 40wt%≤m2≤70wt%.

[0031] In the embodiments of the present application, by selecting a linear carboxylate as a solvent and controlling its mass content in the electrolyte within a suitable range, it helps to reduce the viscosity of the electrolyte, thereby helping to improve the lithium ion kinetics.

[0032] In a possible implementation, the electrolyte includes: a lithium salt, wherein the lithium salt includes LiPF6 and LiFSI; based on the total mass of the electrolyte, a mass content m3 of the lithium salt satisfies 13wt%≤m3≤18wt%.

[0033] In the embodiments of the present application, by selecting LiPF6 and LiFSI as lithium salts, it helps to improve the lithium ion conductivity and thermal stability of the electrolyte, thereby helping to improve the lithium ion dynamics during the cycle of the secondary battery cells, reduce the polarization of the secondary battery cells during the cycle, and improve the safety performance of the secondary battery cells.

[0034] In a possible implementation, the ionic conductivity σ of the electrolyte at 25° C. satisfies: 7 mS / cm≤σ≤10 mS / cm.

[0035] In the embodiments of the present application, selecting an electrolyte with higher ion conductivity helps to improve the lithium ion dynamics during the cycle of the secondary battery cell, helps to reduce the polarization of the secondary battery cell during the cycle, and improves the safety performance of the secondary battery cell.

[0036] In one possible implementation, the secondary battery cell includes a shell and a current collecting member; the shell is used to accommodate the laminated electrode assembly, the shell includes a first wall, and the first wall is provided with an electrode terminal; the laminated electrode assembly includes a main body and a pole ear, and the pole ear is connected to one end of the main body facing the first wall; the current collecting member is arranged between the first wall and the main body, and the current collecting member includes a first connecting portion and a second connecting portion connected to each other, the first connecting portion is connected to the electrode terminal, and the second connecting portion is connected to the pole ear, and along the thickness direction of the first wall, the thickness of the first connecting portion is greater than the thickness of the second connecting portion.

[0037] In the embodiments of the present application, by setting the thickness of the first connecting portion of the current collecting member to be greater than the thickness of the second connecting portion, the thickness of the area where the current collecting member is connected to the electrode terminal is greater than the thickness of the area where the current collecting member is connected to the pole tab. Since the thickness requirement of the area where the current collecting member is connected to the pole tab is less than the thickness requirement of the area where the current collecting member is connected to the electrode terminal, the thickness of the current collecting member can be effectively optimized while the current collecting member can be connected to the electrode terminal and the pole tab, so as to reduce the overall weight of the current collecting member and save the space occupied by the current collecting member, thereby optimizing the weight and internal space utilization of the secondary battery cell, and further improving the energy density of the secondary battery cell.

[0038] In a possible implementation, along the thickness direction of the current collecting member, a thickness D1 of the first connection portion satisfies: 0.5 mm ≤ D1 ≤ 1.2 mm; and a thickness D2 of the second connection portion satisfies: 0.3 mm ≤ D2 ≤ 1 mm.

[0039] In the embodiment of the present application, by controlling the thickness of the first connection part and the thickness of the second connection part within a suitable range, the connection strength between the first connection part and the electrode terminal and between the second connection part and the tab can be met while improving the energy density of the secondary battery cell.

[0040] In a possible implementation, 0.1 mm≤D1-D2≤0.9 mm.

[0041] In an embodiment of the present application, by setting the thickness of the first connecting portion to be within the range of 0.1mm-0.9mm greater than the thickness of the second connecting portion, the thickness of the area of ​​the current collecting member used to connect to the pole ear can be further reduced, thereby being able to further optimize the thickness of the current collecting member to reduce the overall weight of the current collecting member and save the space occupied by the current collecting member, which is beneficial to further reduce the weight of the secondary battery cell and improve the internal space utilization of the secondary battery cell, so as to improve the energy density of the secondary battery cell.

[0042] In one possible implementation, the first wall includes a first through hole; the electrode terminal includes a main body and a step portion, at least a portion of the main body is passed through the first through hole, the step portion protrudes from the outer peripheral surface of the main body, and the step portion is located on the side of the first wall facing the outside of the secondary battery cell; the secondary battery cell includes a fixing member, and the fixing member includes a second through hole for the main body to pass through; in the thickness direction of the first wall, at least a portion of the fixing member is located between the first wall and the step portion and abuts against the step portion, the main body has a first end face facing the outside of the secondary battery cell, and the fixing member has a second end face facing the outside of the secondary battery cell, and the first end face exceeds the second end face.

[0043] In the embodiments of the present application, the structure of the electrode terminal is designed so that the surface of the secondary battery cell that exceeds the maximum height of the outer surface of the first wall is the first end face. When electrode terminals of the same specification are used, the height of the secondary battery cell that exceeds the first wall can be reduced accordingly, thereby increasing the proportion of the space inside the secondary battery cell shell to the total space of the battery, thereby improving the energy density of the battery.

[0044] In a possible implementation, in the thickness direction of the first wall, a height difference H between the first end surface and the second end surface satisfies: 0.5 mm≤H≤1.5 mm.

[0045] In the embodiment of the present application, by controlling the height difference between the first end face and the second end face within a suitable range in the thickness direction of the first wall, it is possible to improve the energy density of the battery while ensuring that the connection stability between the first end face and the second end face is as good as possible.

[0046] In a possible implementation, in the radial direction of the main body, a dimension W1 of the step portion protruding from the outer circumferential surface of the main body satisfies: 0.1 mm≤W1≤5 mm.

[0047] In the embodiment of the present application, by controlling the size of the step portion protruding from the outer peripheral surface of the main body within a suitable range, it is helpful to increase the contact area between the step portion and the fixing member, thereby helping to improve the connection strength between the step portion and the fixing member.

[0048] In a second aspect, a secondary battery is provided, wherein the secondary battery comprises the secondary battery cell according to any implementation of the first aspect.

[0049] In a third aspect, an electrical device is provided, wherein the electrical device comprises a secondary battery cell in any implementation manner of the first aspect, and / or a secondary battery in the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without paying creative work.

[0051] Figure 1 It is a cross-sectional schematic diagram of a laminated electrode assembly.

[0052] Figure 2 A cross-sectional schematic diagram of another laminated electrode assembly.

[0053] Figure 3 A cross-sectional schematic diagram of a wound electrode assembly.

[0054] Figure 4 A schematic structural diagram of a secondary battery cell.

[0055] Figure 5 for Figure 4 An exploded view of a secondary battery cell is shown.

[0056] Figure 6 It is a partial schematic diagram of a secondary battery cell.

[0057] Figure 7 A partial exploded view of a secondary battery cell.

[0058] Figure 8 A partial cross-sectional view of a secondary battery cell.

[0059] Fig. 9 for Figure 8 Schematic diagram of a local area.

[0060] Fig.10 A schematic diagram of a secondary battery. DETAILED DESCRIPTION

[0061] Hereinafter, the embodiments of the secondary battery cell, secondary battery and electric device of the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0062] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0063] In the description of this application, it should be noted that, unless otherwise specified, "multiple" means more than two; the terms "upper", "lower", "left", "right", "inner", "outer", etc., indicating directions or positional relationships, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting this application. In addition, the terms "first", "second", "third", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0064] If not otherwise specified, in this application, the phrase "A and / or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A and / or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0065] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0066] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0067] Unless otherwise specified, the following terms have the following meanings. Any undefined terms have their generally accepted meanings in the art.

[0068] Where mentioned, "lithium-containing phosphate" refers to a class of salts including the element lithium and phosphate ions.

[0069] When the “lithium-containing phosphate” further includes a transition metal, it may be referred to as a “lithium-containing transition metal phosphate”.

[0070] “Lithium-containing transition metal phosphate” may include, for example, lithium iron phosphate materials, lithium iron manganese phosphate materials, and the like.

[0071] As mentioned, "lithium-containing transition metal oxides" refers to a class of oxides including lithium elements and transition metal elements. Structurally, it includes ternary materials with layered structures, LiCoO2, LiNiO2, etc., and also includes LiMn2O4 with spinel structure, etc. Ternary materials refer to lithium transition metal oxides including three different transition metal elements. It should be understood that trace amounts of other transition metal elements can also be doped in ternary materials, and it is generally believed that ternary materials doped with other transition metal elements are still ternary materials.

[0072] If mentioned, "linear carbonate" refers to a class of substances with a chain structure and containing carbonate groups (-OCO-O-), such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), etc.

[0073] Next, embodiments of the present application are introduced.

[0074] In recent years, secondary batteries have been widely used in power tools, electronic products, electric vehicles, aerospace and other fields, and are an important field for the development of new energy. Usually, the secondary battery cell of a secondary battery includes a positive electrode plate, a negative electrode plate, an electrolyte and a separator. During the charge and discharge process of the secondary battery cell, the active ions are embedded and released back and forth between the positive electrode plate and the negative electrode plate. Among them, the electrolyte plays a role in conducting active ions between the positive electrode plate and the negative electrode plate. The separator is arranged between the positive electrode plate and the negative electrode plate, which allows the active ions to pass through while preventing the positive and negative electrodes from short-circuiting, so that the electrochemical reaction in the secondary battery cell proceeds normally.

[0075] Improving the energy density of secondary battery cells has always been a research focus in the battery field. The positive electrode active material is one of the direct factors that directly affect the energy density of battery cells. Current research on energy density is focused on improving the gram capacity of the positive electrode active material. However, the improvement in energy density is often accompanied by deficiencies in other battery performance, such as safety performance. However, from the perspective of practical applications, safety performance is an important performance indicator of secondary battery cells that cannot be ignored. Existing methods for improving safety performance usually only consider the compounding of materials, which is often accompanied by the sacrifice of energy density, and it is impossible to achieve a balance between energy density and safety performance.

[0076] In view of this, the embodiments of the present application provide a secondary battery cell, a secondary battery and an electrical device, wherein the secondary battery cell can have both high energy density and good safety performance.

[0077] Next, the secondary battery cell provided by the present application is introduced.

[0078] [Secondary battery cell]

[0079] First, a secondary battery cell is provided, the secondary battery cell includes a laminated electrode assembly, the laminated electrode assembly includes a positive electrode sheet, a negative electrode sheet and a separator. The positive electrode sheet includes a positive electrode film layer, the positive electrode film layer includes a positive electrode active material, the negative electrode sheet includes a negative electrode film layer, and the negative electrode film layer includes a negative electrode active material. The positive electrode active material includes a lithium-containing transition metal phosphate and a lithium-containing transition metal oxide; the thickness h of the separator satisfies: 8μm≤h≤21μm.

[0080] Specifically, h can be 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, or its value is within the range obtained by combining any two of the above values.

[0081] Figure 1 and Figure 2 It is a cross-sectional schematic diagram of a laminated electrode assembly. Figure 3 FIG. 1 is a cross-sectional schematic diagram of a wound electrode assembly. For ease of explanation, the pole ears included in each pole piece are not shown here. Figure 1-3 As shown, the laminated electrode assembly 10 includes a positive electrode sheet 11 and a negative electrode sheet 12 and a separator 13 disposed between the positive electrode sheet 11 and the negative electrode sheet 12 .

[0082] In one embodiment, Figure 1 As shown, the laminated electrode assembly 10 includes a plurality of positive electrode sheets 11 and a plurality of negative electrode sheets 12; the plurality of positive electrode sheets 11 and the plurality of negative electrode sheets 12 are alternately stacked in the direction indicated by the arrows in the figure. Figure 2 As shown, the laminated electrode assembly 10 includes a plurality of positive pole sheets 11 and negative pole sheets 12, the negative pole sheet 12 may include at least one bending section and a plurality of stacking sections, each bending section is used to connect two stacking sections, and a plurality of positive pole sheets 11 and a plurality of stacking sections of the negative pole sheets 12 are alternately stacked in the direction indicated by the arrow in the figure to form another laminated electrode assembly 10. Alternatively, the laminated electrode assembly 10 includes a plurality of negative pole sheets 12 and a positive pole sheet 11, the positive pole sheet 11 may include at least one bending section and a plurality of stacking sections, each bending section is used to connect two stacking sections, and a plurality of negative pole sheets 12 and a plurality of stacking sections of the positive pole sheet 11 are alternately stacked in the direction indicated by the arrow in the figure.

[0083] Figure 3 A wound electrode assembly is shown. The positive electrode sheet 11, the separator 13 and the negative electrode sheet 12 of the wound electrode assembly are wound to form an electrode assembly. Figure 1-2 and Figure 3It can be seen from the comparison that when the outer shell volume of the secondary battery cell is the same, the space utilization rate of the wound electrode assembly in the outer shell will be lower than that of the laminated electrode assembly 10 due to the corners.

[0084] In addition, considering the difference between the laminated electrode assembly 10 and the wound electrode assembly in the processing process, the four edges of the sheet-shaped pole piece used for the laminated electrode assembly 10 need to be cut, while the long sheet-shaped pole piece of the wound electrode assembly only needs to be cut on two edges. Due to process limitations, the cutting process of the pole piece will inevitably produce burrs, and the burr problem on the edge of the pole piece in the laminated electrode assembly 10 is more serious. The burrs may pierce the isolation membrane 13 during the cycle of the secondary battery cell 20, causing a short circuit between the positive and negative electrodes, and thus causing more serious safety problems.

[0085] As positive electrode active materials, lithium-containing transition metal oxides have high specific capacity, but poor thermal stability. They are prone to produce a large amount of gas by side reaction with the electrolyte at high temperature, which causes the capacity of the secondary battery monomer to decay rapidly, which is not conducive to the safety performance of the secondary battery monomer. Lithium-containing transition metal phosphates have good thermal stability, but their specific capacity is not as good as lithium-containing transition metal oxides.

[0086] Based on this, in this embodiment, lithium-containing transition metal phosphate and lithium-containing transition metal oxide are selected as positive electrode active materials, and a laminated electrode assembly 10 is used. Under the condition that the volume of the secondary battery cell is constant, more active materials can be accommodated inside the secondary battery cell, thereby improving the space utilization inside the secondary battery cell and thus improving the energy density of the secondary battery cell; and, under the premise that the positive electrode active material includes lithium-containing transition metal phosphate and lithium-containing transition metal oxide, by matching the separator 13 with a thickness of 8μm-21μm, the risk of the burr of the pole piece in the laminated electrode assembly 10 piercing the separator 13 during the cycle of the secondary battery cell can be improved. Therefore, this solution can make the secondary battery cell have both high energy density and good safety performance.

[0087] In one embodiment, based on the total mass of the positive electrode active material, the mass content m1 of the lithium-containing transition metal phosphate satisfies: 40 wt %≤m1≤70 wt %.

[0088] Specifically, m1 can be 40wt%, 42wt%, 44wt%, 45wt%, 46wt%, 48wt%, 50wt%, 52wt%, 54wt%, 56wt%, 58wt%, 60wt%, 62wt%, 64wt%, 66wt%, 68wt%, 70wt%, or its value is within the range obtained by combining any two of the above values.

[0089] Lithium-containing phosphates have good thermal stability. When the positive electrode active material includes both lithium-containing phosphates and lithium-containing transition metal oxides, controlling the content of the lithium-containing phosphates within the above range can further improve the energy density of the secondary battery while maintaining high safety. Because the thermal stability of lithium-containing transition metal oxides is generally not as good as that of lithium-containing phosphates, they are prone to side reactions with the electrolyte at high temperatures, which may affect the safety performance of the secondary battery monomer.

[0090] In one embodiment, the isolation film 13 includes a base film and a coating layer disposed on at least one side of the base film, and the thickness h1 of the coating layer on one side satisfies: 3 μm≤h1≤6 μm.

[0091] Specifically, h1 may be 3 μm, 4 μm, 5 μm, 6 μm, or a value within a range obtained by combining any two of the above values.

[0092] The material of the base film of the isolation film can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The base film can be a single-layer film or a multi-layer composite film, without particular limitation. When the base film is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation. The coating of the isolation film can play a role of heat resistance and / or bonding.

[0093] In one embodiment, the thickness of the base film is generally in the range of 5 μm-9 μm. For example, the thickness of the base film is 5 μm, 6 μm, 7 μm, 8 μm, 9 μm.

[0094] The thickness of the coating affects the mechanical properties of the isolation membrane 13 and the rate at which it is wetted by the electrolyte. The thicker the coating, the thicker the isolation membrane 13, the greater its mechanical strength, and the less likely it is to be pierced by burrs or lithium dendrites on the pole piece. At the same time, the electrolyte infiltration rate slows down, affecting the transmission efficiency of lithium ions. During the cycle of the secondary battery cell, the polarization inside the battery cell may be aggravated, resulting in lithium precipitation, and is not conducive to the energy density of the secondary battery cell. Therefore, in this embodiment, under the system of the aforementioned positive electrode active material, by further controlling the thickness of the coating within the range of 3μm-6μm, the isolation membrane 13 can have good mechanical strength and wettability, so that the secondary battery cell has high energy density and good safety performance.

[0095] In one embodiment, the coating layer includes heat-resistant particles, and the heat-resistant particles include at least one of inorganic particles and organic particles.

[0096] Specifically, the inorganic particles may include boehmite, aluminum oxide, barium sulfate, magnesium oxide, magnesium hydroxide, silicon oxide, tin dioxide, titanium oxide, calcium oxide, zinc oxide, zirconium oxide, yttrium oxide, nickel oxide, hafnium dioxide, cerium oxide, zirconium titanate, barium titanate, magnesium fluoride, aluminum hydroxide, barium oxide, silicon carbide, boron carbide, aluminum nitride, silicon nitride, boron nitride, calcium fluoride, barium fluoride, magnesium aluminum silicate, lithium magnesium silicate, sodium magnesium silicate, bentonite, hectorite, Pb(Zr,Ti)O3 (abbreviated as PZT), Pb1-mLamZr1-nTinO3 (abbreviated as PLZT, 0<m<1, 0<n<1), Pb(Mg3Nb 2 / 3 )O3-PbTiO3 (abbreviated as PMN-PT), and one or more of their respective modified inorganic particles. Optionally, the modification of each inorganic particle can be chemical modification and / or physical modification. The organic particles can include at least one of a thermoplastic resin polymer, a thermosetting resin polymer or a cross-linked polymer.

[0097] Preferably, the coating includes inorganic particles, and the inorganic particles include at least one of aluminum oxide, silicon oxide, titanium oxide, and barium titanate. By selecting these inorganic components as the coating, it helps to improve the coating's support capacity for the base film and reduce the risk of the base film shrinking due to heat during the cycle of the secondary battery cell, thereby further improving the situation where the pole piece burrs pierce the isolation membrane 13 and improving the safety performance of the secondary battery cell.

[0098] Illustratively, a composite isolation membrane having a bulk layer may be obtained by subjecting a base membrane to a ceramic coating treatment (also known as a CCS treatment).

[0099] Furthermore, when both sides of the base film are coated, the wettability, thermal stability and safety performance of the isolation film 13 are better than those of the isolation film 13 with a coating on one side, which can further improve the safety performance of the secondary battery cell.

[0100] In one embodiment, the coating includes binder particles, and the binder particles include: polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, polyethylene, polypropylene, polyacrylonitrile, polyethylene oxide, copolymers of different fluorine-containing olefinic monomer units, copolymers of fluorine-containing olefinic monomer units and vinyl monomer units, copolymers of fluorine-containing olefinic monomer units and acrylic monomer units, copolymers of fluorine-containing olefinic monomer units and acrylate monomer units, and one or more of the modified compounds of the above homopolymers or copolymers.

[0101] In one embodiment, the laminated electrode assembly 10 includes a plurality of positive electrode sheets 11 and a plurality of negative electrode sheets 12, and the plurality of positive electrode sheets 11 and the plurality of negative electrode sheets 12 are alternately stacked in the thickness direction. In this type of laminated electrode assembly 10, the single-side loading amount a of the binder particles on the separator 13 satisfies: 0.5 mg / 1540.25 mm 2 ≤a≤1.2mg / 1540.25mm 2 . Optionally, 0.6mg / 1540.25mm 2 ≤a≤0.8mg / 1540.25mm 2 , for example, a = 0.7 mg / 1540.25 mm 2 .

[0102] Under the premise that the positive electrode active material includes lithium-containing transition metal phosphate and lithium-containing transition metal oxide, this type of laminated electrode assembly 10 has a relatively higher space utilization rate in the shell of the secondary battery cell, which helps to further improve the energy density of the secondary battery cell. However, due to the expansion and contraction of the pole pieces during the cycle of the secondary battery cell, the risk of slippage between the pole pieces of this laminated electrode assembly 10 is high, which can easily lead to local lithium deposition in the secondary battery cell. Therefore, by controlling the loading amount of the binder particles on the isolation film 13 to 0.5mg / 1540.25mm 2 -1.2mg / 1540.25mm 2 Within a specific range, the adhesion between the isolation film 13 and the electrode sheet can be improved, thereby improving the structural stability of the laminated electrode assembly 10 and further improving the safety performance of the secondary battery cell.

[0103] Figure 4-Figure 5 Schematic diagram of the structure of a secondary battery cell 20 of the present application.

[0104] like Figure 4-5 As shown, in one embodiment, the secondary battery cell 20 includes a housing 21 , the laminated electrode assembly 10 is accommodated in the housing 21 , the housing 21 includes a first wall 211 , and the electrode terminal 22 is disposed on the first wall 211 .

[0105] More specifically, the housing 21 may include a shell 212 and an end cap 213. The shell 212 is formed with a receiving cavity inside, and the receiving cavity has an opening 2121, that is, the shell 212 is a hollow structure with one end open, and the end cap 213 covers the opening 2121 of the shell 212 and forms a sealed connection to form a sealed space for accommodating the laminated electrode assembly 10 and the electrolyte. Optionally, the first wall 211 for mounting the electrode terminal 22 may be the end cap 213, or may be one of the multiple walls of the shell 212. Exemplarily, in Figure 4 and Figure 5In the figure, the first wall 211 is the end cover 213 of the shell 21. Of course, in other embodiments, the first wall 211 can also be the bottom wall of the shell 212 arranged opposite to the end cover 213 in the thickness direction X of the end cover 213 or the side wall adjacent to the end cover 213 and abutting against each other.

[0106] The shell 212 can be in various shapes, such as a cube, a rectangular parallelepiped, etc. The shape of the shell 212 can be determined according to the specific shape of the laminated electrode assembly 10. For example, if the laminated electrode assembly 10 is a rectangular parallelepiped structure, the shell 212 can be a rectangular parallelepiped structure. Of course, the end cap 213 can also be in various structures, such as a plate-like structure or a hollow structure with one end open. For example, in Figure 4 and Figure 5 In the embodiment, the shell 212 is a rectangular parallelepiped structure. It should be understood that the shell 21 is not limited to the aforementioned structure, and the shell 21 may also be other structures, for example, the shell 21 includes a shell 212 and two end caps 213, the shell 212 is a hollow structure with openings 2121 on opposite sides, and one end cap 213 is correspondingly covered at one opening 2121 of the shell 212 to form a sealed connection, so as to form a sealed space for accommodating the electrode assembly 10 and the electrolyte in a laminated manner.

[0107] Figure 6 It is a partial schematic diagram of a secondary battery cell 20 in the electrode terminal 22 area of ​​the present application.

[0108] refer to Figure 4-6 In one embodiment, the laminated electrode assembly 10 includes a main body 101 and a tab 102, wherein the tab 102 is connected to one end of the main body 101 facing the first wall 211. The secondary battery cell 20 includes a current collecting member 24, which is disposed between the first wall 211 and the main body 101. The current collecting member 24 includes a first connecting portion 241 and a second connecting portion 242 connected to each other, wherein the first connecting portion 241 is connected to the electrode terminal 22, and the second connecting portion 242 is connected to the tab 102. Along the thickness direction X of the first wall 211, the thickness of the first connecting portion 241 is greater than the thickness of the second connecting portion 242.

[0109] Specifically, the main body 101 of the laminated electrode assembly 10 is the main area where the electrochemical reaction of the laminated electrode assembly 10 occurs in the secondary battery cell 20. The main body 101 is a layout formed by winding or stacking the area of ​​the positive electrode plate 11 coated with the positive electrode active material, the separator, and the area of ​​the negative electrode plate 12 coated with the negative electrode active material. The tab 102 is used to output or input the positive or negative electrode of the laminated electrode assembly 10. The tab 102 is used to connect to the electrode terminal 22 to achieve electrical connection between the electrode assembly 10 and the electrode terminal 22. It should be noted that the tab 102 of the laminated electrode assembly 10 is a component formed by stacking and connecting the areas on the positive electrode plate 11 that are not coated with the positive electrode active material or a component formed by stacking and connecting the areas on the negative electrode plate 12 that are not coated with the negative electrode active material. If the tab 102 is used to output the positive electrode of the laminated electrode assembly 10, the tab 102 is a component formed by the regions on the positive electrode sheet 11 that are not coated with the positive electrode active material being stacked and connected to each other; if the tab 102 is used to output the negative electrode of the laminated electrode assembly 10, the tab 102 is a component formed by the regions on the negative electrode sheet 12 that are not coated with the negative electrode active material being stacked and connected to each other. Exemplarily, the tab 102 is connected to one end of the body 101 facing the end cover 213 in the thickness direction X of the end cover 213.

[0110] The stacked electrode assembly 10 contained in the housing 21 may be one or more. Figure 5 In the embodiment, the outer shell 21 of the secondary battery cell 20 is provided with two laminated electrode assemblies 10, and the two electrode assemblies 10 are stacked along the thickness direction thereof, that is, the two laminated electrode assemblies 10 are stacked along the thickness direction of the secondary battery cell 20. Of course, in other embodiments, the laminated electrode assemblies 10 accommodated in the outer shell 21 may be one, three, four, five, six, seven or eight, etc.

[0111] The electrode terminal 22 is a component for outputting or inputting electric energy to the secondary battery cell 20. For example, the material of the electrode terminal 22 can also be multiple, for example, the material of the electrode terminal 22 can be copper, iron, aluminum, steel, aluminum alloy, etc. The end of the electrode terminal 22 facing the laminated electrode assembly 10 is connected to the current collecting component 24, and the end of the electrode terminal 22 away from the laminated electrode assembly 10 is used to connect to the current collecting component to realize the input or output of electric energy of the secondary battery cell 20. The end cover 213 is provided with a first through hole 2111, and the first through hole 2111 penetrates both sides of the end cover 213 along the thickness direction X of the end cover 213. The electrode terminal 22 is penetrated in the first through hole 2111 to install the electrode terminal 22 on the end cover 213, and the first through holes 2111 are extended from both ends of the electrode terminal 22. The electrode terminal 22 is insulated and installed on the end cover 213, that is, no electrical connection is formed between the electrode terminal 22 and the end cover 213. The secondary battery cell 20 may further include an insulating member 26 to insulate and separate the end cap 213 and the electrode terminal 22. The secondary battery cell 20 may further include a sealing member 27 to seal a gap between the electrode terminal 22 and a hole wall surface of the first through hole 2111.

[0112] exist Figure 4 and Figure 5 In the embodiment, the secondary battery cell 20 includes two electrode terminals 22, and correspondingly, each laminated electrode assembly 10 has two tabs 102, and the polarities of the two tabs 102 are opposite. The two electrode terminals 22 are electrically connected to the two tabs 102 of the laminated electrode assembly 10, respectively, to realize the input or output of the positive electrode and the negative electrode of the secondary battery cell 20.

[0113] The current collecting component 24 serves to connect the electrode terminal 22 and the tab 102 to achieve electrical connection between the laminated electrode assembly 10 and the electrode terminal 22. Exemplarily, the material of the current collecting component 24 can be various, such as copper, iron, aluminum, steel, aluminum alloy, etc. The connection structure between the current collecting component 24 and the electrode terminal 22 can be various, such as welding, abutment or bonding, etc. Similarly, the connection structure between the current collecting component 24 and the tab 102 can also be various, such as welding or abutment, etc. There are two electrode terminals 22 and two current collecting components 24, and the two current collecting components 24 are arranged at intervals along the first direction Z. Each electrode terminal 22 is connected to the laminated electrode assembly 10 through a current collecting component 24 to output the positive and negative electrodes of the secondary battery cell 20. As shown Figure 6 As shown, the current collecting member 24 may further include a bending portion 243 , and the first connection portion 241 and the second connection portion 242 are connected via the bending portion 243 .

[0114] In this embodiment, the thickness of the region of the current collecting member 24 used for connecting the electrode terminal 22 is greater than the thickness of the region of the current collecting member 24 used for connecting the electrode tab 102. Since the thickness requirement of the region where the current collecting member 24 is connected to the electrode tab 102 is less than the thickness requirement of the region where the current collecting member 24 is connected to the electrode terminal 22, the thickness of the current collecting member 24 can be effectively optimized while the current collecting member 24 can be connected to the electrode terminal 22 and the electrode tab 102, so as to reduce the overall weight of the current collecting member 24 and save the space occupied by the current collecting member 24, thereby optimizing the weight and internal space utilization of the secondary battery cell 20, which is conducive to improving the energy density of the secondary battery cell 20.

[0115] In one embodiment, along the thickness direction X of the current collecting member 24 , the thickness D1 of the first connection portion 241 satisfies: 0.5 mm≤D1≤1.2 mm; and the thickness D2 of the second connection portion 242 satisfies: 0.3 mm≤D2≤1 mm.

[0116] For example, D1 can be 0.5 mm, 0.55 mm, 0.6 mm, 0.65 mm, 0.7 mm, 0.75 mm, 0.8 mm, 0.9 mm, 1 mm, 1.1 mm, 1.15 mm, 1.2 mm, or a value thereof within the range obtained by combining any two of the above values. D2 can be 0.3 mm, 0.35 mm, 0.4 mm, 0.45 mm, 0.5 mm, 0.55 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 0.95 mm, 1 mm, or a value thereof within the range obtained by combining any two of the above values.

[0117] In this embodiment, by setting the thickness of the first connection part 241 and the thickness of the second connection part 242 within a suitable range, on the one hand, the structural strength of the first connection part 241 and the second connection part 242 can be improved, so that the first connection part 241 and the second connection part 242 have sufficient thickness to be connected to the electrode terminal 22 and the pole tab 102, which is conducive to improving the connection stability and reliability between the first connection part 241 and the second connection part 242 and the electrode terminal 22 and the pole tab 102, and reducing the phenomenon of insufficient overcurrent between the current collecting component 24 and the electrode terminal 22, and between the current collecting component 24 and the pole tab 102. On the other hand, the connection difficulty between the first connection part 241 and the electrode terminal 22, and between the second connection part 242 and the pole tab 102 can be reduced, and the space occupied by the current collecting component 24 in the housing 21 can be reduced, which is conducive to improving the energy density of the secondary battery cell 20.

[0118] In one embodiment, 0.1 mm ≤ D1 - D2 ≤ 0.9 mm.

[0119] Specifically, it can be 0.1mm, 0.2mm, 0.3mm, 0.4mm, 0.5mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm, or a value within the range obtained by combining any two of the above values.

[0120] In this embodiment, by setting the thickness D1 of the first connecting portion 241 to be greater than or equal to 0.1 mm and less than or equal to 0.9 mm than the thickness D2 of the second connecting portion 242, the thickness of the area of ​​the current collecting member 24 used to connect with the pole ear 102 can be further reduced, so that the thickness of the current collecting member 24 can be further optimized to reduce the overall weight of the current collecting member 24 and save the space occupied by the current collecting member 24, which is beneficial to further reduce the weight of the secondary battery cell 20 and improve the internal space utilization of the secondary battery cell 20, so as to improve the energy density of the secondary battery cell 20.

[0121] In other implementations, the current collecting member 24 may be omitted, and the tab 102 may be directly connected to the electrode terminal 22. However, this method is extremely difficult to process, and this application will not elaborate on it.

[0122] Figure 7 It is an exploded view of a partial structure of a secondary battery cell 20 of the present application. Figure 8 This is a cross-sectional view of a partial structure of a secondary battery cell 20 of the present application. Fig. 9 for Figure 8 Schematic diagram of a local area.

[0123] like Figure 7-9 As shown, in one embodiment, the first wall 211 includes a first through hole 2111, and the electrode terminal 22 includes a main body 221 and a step portion 222, the step portion 222 protrudes from the outer peripheral surface of the main body 221, and the step portion 222 is located on the side of the first wall 211 facing the outside of the secondary battery cell 20. The secondary battery cell 20 includes a fixing member 28, and the fixing member 28 includes a second through hole 281 for the main body 221 to pass through. In the thickness direction of the first wall 211, at least a portion of the fixing member 28 is located between the first wall 211 and the step portion 222 and abuts against the step portion 222. The main body 221 has a first end face 2211 facing the outside of the secondary battery cell 20, and the fixing member 28 has a second end face 282 facing the outside of the secondary battery cell 20, and the first end face 2211 exceeds the second end face 282.

[0124] Specifically, the exterior of the secondary battery cell 20 refers to the portion outside the housing 21 of the secondary battery cell 20. The first end face 2211 exceeds the second end face 282, which means that, outside the secondary battery cell 20, in the thickness direction of the first wall 211, the second end face 282 is located between the first end face 2211 and the outer surface of the first wall 211. In other words, the surface farthest from the outer surface of the first wall 211 is the first end face 2211 of the electrode terminal 22.

[0125] The outer peripheral surface of the main body 221 may refer to the outer peripheral surface of a cylinder, or may refer to the peripheral surface of a prism connecting the top surface and the bottom surface of the prism. Taking the main body 221 as a quadrangular prism as an example, the main body 221 includes a top surface, a bottom surface and four side surfaces, the four side surfaces are sequentially connected and surrounded by the top surface, and the four side surfaces are respectively connected to the top surface and the bottom surface at both ends in the direction from the top surface to the bottom surface. The above four side surfaces refer to the outer peripheral surface of the main body 221. In some embodiments, the first end surface 2211 is provided with a first groove 2212, and the side surface of the first groove 2212 may also be referred to as the outer peripheral surface of the main body 221. In this embodiment, the main body 221 is shaped like a "convex" character. In some embodiments, the step portion 222 has a third end surface 2221 facing away from the first wall 211.

[0126] The outer contour of the fixing member 28 may include, but is not limited to, circular, elliptical, polygonal, semicircular, etc. The fixing member 28 is made of metal material, for example, aluminum, copper, iron, steel, alloy or composite metal. The step portion 222 may be continuously distributed along the circumference of the main body 221, that is, in a ring shape. It may also be arranged in segments along the circumference of the main body 221, that is, divided into multiple parts, at least one part of which abuts against the fixing member 28. The first through hole 2111 and the second through hole 281 may be light holes or segmented step holes. In the embodiment where the first through hole 2111 and the second through hole 281 are step holes, the cross section of the step hole may include at least one straight line segment and / or at least one oblique line segment and / or at least one arc segment.

[0127] As mentioned above, lithium-containing transition metals have high specific capacity as positive electrode active materials, but poor thermal stability. They are prone to side reactions with the electrolyte at high temperatures, which is not conducive to the safety performance of the secondary battery cell 20. Lithium-containing transition metal phosphates have good thermal stability. In addition, considering that in some cases, the electrode terminal 22 of the secondary battery cell 20 is riveted to the wall of the outer shell 21 through a rivet block that wraps the end of the electrode terminal 22. In the direction of the wall of the outer shell 21, the surface of the rivet block away from the wall of the outer shell 21 will exceed the outer end surface of the electrode terminal 22. This design is to give additional protection and support to the electrode terminal to reduce the risk of loosening of the electrode terminal. At the same time, the electrical energy of the secondary battery cell 20 can be transferred to the inside of the secondary battery cell 20 through the rivet block.

[0128] In the present embodiment, in the thickness direction of the first wall 211, the surface of the secondary battery cell 20 that exceeds the outer surface of the first wall 211 by the maximum height is the first end surface 2211. When the electrode terminals 22 of the same specification are used, the height of the secondary battery cell 20 that exceeds the first wall 211 can be reduced accordingly, thereby increasing the proportion of the space inside the shell 21 of the secondary battery cell 20 to the total space of the secondary battery cell 20, thereby increasing the energy density of the secondary battery cell 20.

[0129] In one embodiment, the electrode terminal 22 further includes a limiting portion 223 , which protrudes from the outer peripheral surface of the main body 221 and is located on the inner side of the first wall 211 . The limiting portion 223 is used to limit the movement of the electrode terminal 22 to the outside of the shell 21 .

[0130] Exemplarily, the insulating member 26 includes a body portion 261 and a first extension portion 262, the body portion 261 is located between the fixing member 28 and the first wall 211, the body portion 261 is provided with a third through hole 2611 through which the supply terminal 22 passes, and the first extension portion 262 is located at the periphery of the fixing member 28 and is arranged around the edge of the body portion 261. The sealing member 27 is at least partially located between the first wall 211 and the limiting portion 223.

[0131] In one embodiment, in the thickness direction of the first wall 211 , a height difference H between the first end surface 2211 and the second end surface 282 satisfies: 0.5 mm≤H≤1.5 mm.

[0132] Specifically, H can be 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, 1.5 mm, or any value thereof within the range obtained by combining any two of the above values. By controlling H within a suitable range, the energy density of the secondary battery cell 20 can be increased while ensuring good connection stability between the first end face 2211 and the second end face 282 as much as possible.

[0133] In one embodiment, in the radial direction of the main body 221 , a dimension W1 of the step portion 222 protruding from the outer circumferential surface of the main body 221 satisfies: 0.1 mm≤W1≤5 mm.

[0134] Specifically, W1 can be 0.1mm, 0.2mm, 0.4mm, 0.6mm, 0.8mm, 1mm, 1.2mm, 1.4mm, 1.6mm, 1.8mm, 2mm, 2.2mm, 2.4mm, 2.6mm, 2.8mm, 3mm, 3.2mm, 3.4mm, 3.6mm, 3.8mm, 4mm, 4.2mm, 4.4mm, 4.6mm, 4.8mm, 5mm, or its value is within the range obtained by combining any two of the above values. By controlling the size of the step portion 222 protruding from the outer peripheral surface of the main body 221 within a suitable range, it is beneficial to increase the contact area between the step portion 222 and the fixing member 28, and then it is beneficial to improve the connection strength between the step portion 222 and the fixing member 28.

[0135] In one embodiment, the positive electrode plate 11 includes a conductive agent, the conductive agent includes carbon nanotubes, and the diameter l of the carbon nanotubes satisfies: 7nm≤l≤13nm.

[0136] Specifically, l can be 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, or its value is within the range obtained by combining any two of the above values. The conductive agent has a direct impact on the internal resistance, rate performance, thermal stability, energy density, cycle performance, etc. of the secondary battery cell 20. Compared with conductive agents such as conductive carbon black and Ketjen black, the carbon nanotubes and the positive electrode active materials are in linear contact, which can form a conductive network between the positive electrode active materials, have a high conductivity efficiency, can reduce the polarization of the secondary battery cell during the cycle, and improve the rate performance and cycle performance of the secondary battery cell 20. In addition, the diameter of the carbon nanotube has a direct impact on its stability. The larger the diameter of the carbon nanotube, the stronger its stability, but the smaller the conductivity. Therefore, in this embodiment, by selecting carbon nanotubes with a diameter within a suitable range as a conductive agent, it is helpful to improve the lithium ion dynamics at the positive electrode plate 11, thereby improving the rate performance and cycle performance of the secondary battery cell.

[0137] In one embodiment, the average particle size D1 of the particles containing the lithium transition metal oxide satisfies: 2 μm≤D1≤5 μm.

[0138] Specifically, D1 can be 2μm, 3μm, 4μm, 5μm, or its value is within the range obtained by combining any two of the above values. The lithium-containing transition metal oxide with an average particle size range of 2μm-5μm has better structural stability and helps to improve the powder compaction density of the positive electrode sheet. As a result, the energy density and safety performance of the secondary battery cell 20 can be further improved.

[0139] According to the present application, the smaller the average particle size of the lithium-containing transition metal oxide, the better its structural stability, which is more conducive to the safety performance and energy density of the secondary battery cell 20. At the same time, if the average particle size of the lithium-containing transition metal oxide is too small, the side reactions between it and the electrolyte may increase, which is not conducive to the circulation of the secondary battery cell 20. Therefore, this embodiment can make the secondary battery cell 20 have high energy density, safety performance and good cycle performance by controlling the average particle size of the primary particles of the lithium-containing transition metal oxide within a suitable range.

[0140] In one embodiment, the lithium-containing transition metal oxide comprises: Li 1+c [Ni x Co y Mn z M d ]O 2-e ; wherein M includes at least one of Zr, Al, Ti, Sb, Nb, Te, Mg, B, Ca, V, Ta or Sr, 0.2≥c≥-0.2, 0.95≥x≥0.6, 0.2≥y≥0.05, 0.3>z>0, 0.3>d≥0, 0.5≥e≥0.

[0141] Specifically, some M elements may be doped into the lithium-containing transition metal oxide. The doping of the M elements helps to improve the structural stability of the lithium-containing transition metal oxide, thereby helping to improve the safety performance of the secondary battery cell 20 .

[0142] In one embodiment, the positive electrode sheet 11 satisfies at least one of the following conditions: (1) the compaction density ρ1 of the positive electrode sheet 11 satisfies: 2.5 g / cm 3 ≤ρ1≤2.9g / cm 3 ; (2) The single-sided coating weight CW1 of the positive electrode film meets the following requirements: 190 g / m 2 ≤CW1≤230g / m 2 ; (3) The thickness h1 of the positive electrode current collector satisfies: 10μm≤h1≤13μm.

[0143] Specifically, ρ1 can be 2.5 g / m 2 , 2.6g / cm 3 , 2.7g / cm 3 , 2.8g / cm 3 , 2.9g / cm 3 , or its value is within the range obtained by combining any two of the above values. CW1 can be 190g / m 2 , 195g / m 2 , 200g / m 2 , 205g / m 2 , 210g / m 2, 215g / m 2 , 220g / m 2 , 225g / m 2 , 230g / m 2 , or its value is within the range obtained by combining any two of the above values. h1 can be 10μm, 10.2μm, 10.4μm, 10.6μm, 10.8μm, 11μm, 11.2μm, 11.4μm, 11.6μm, 11.8μm, 12μm, 12.2μm, 12.4μm, 12.6μm, 12.8μm, 13μm, or its value is within the range obtained by combining any two of the above values.

[0144] According to the present application, the coating weight of the film layer on the pole piece and the compaction density of the pole piece have a certain influence on the lithium ion dynamics during the cycle of the secondary battery cell 20. The greater the coating weight of the film layer and the greater the compaction density of the pole piece, the worse the lithium ion dynamics. Insufficient lithium ion dynamics may cause polarization of the secondary battery cell 20, and then lithium precipitation occurs, affecting the safety performance of the secondary battery cell 20. However, if the coating weight of the film layer is too small and the compaction density of the pole piece is too small, it is not conducive to the energy density of the secondary battery cell 20. The aforementioned pole piece can be a positive pole piece or a negative pole piece. The aforementioned film layer can be a positive electrode film layer or a negative electrode film layer.

[0145] According to the present application, the thinner the thickness of the current collector is, the more conducive it is to reducing the thickness of the pole piece, thereby improving the energy density of the secondary battery cell 20. Too thin a current collector is not conducive to the mechanical strength of the pole piece, and may break during the processing or use of the secondary battery cell 20. The aforementioned current collector can be a positive electrode current collector or a negative electrode current collector.

[0146] Therefore, this embodiment can make the secondary battery cell 20 have both high energy density and good safety performance by controlling the coating weight of the positive electrode film layer, the compacted surface density of the positive electrode sheet 11, and the thickness of the positive electrode collector within a suitable range.

[0147] In one embodiment, the negative electrode sheet 12 satisfies at least one of the following conditions: (4) The compaction density ρ2 of the negative electrode sheet 12 satisfies: 1.3 g / cm 3 ≤ρ2≤1.55g / cm 3 ; (5) The single-sided coating weight CW2 of the negative electrode film layer meets the following requirements: 90 g / m 2 ≤CW2≤110g / m 2 ; (6) The thickness h2 of the negative electrode collector satisfies: 4μm≤h2≤6μm.

[0148] Specifically, ρ2 can be 1.3 g / cm 3 , 1.32g / cm 3, 1.34g / cm 3 , 1.35g / cm 3 , 1.36g / cm 3 , 1.38g / cm 3 , 1.4g / cm 3 , 1.42g / cm 3 , 1.44g / cm 3 , 1.46g / cm 3 , 1.48g / cm 3 , 1.5g / cm 3 , or its value is within the range obtained by combining any two of the above values. CW2 can be 90g / m 2 , 92g / m 2 , 94g / m 2 , 96g / m 2 , 98g / m 2 , 100g / m 2 , 102g / m 2 , 104g / m 2 , 106g / m 2 , 108g / m 2 , 110g / m 2 , or its value is within the range obtained by combining any two of the above values. h2 can be 4μm, 4.2μm, 4.4μm, 4.6μm, 4.8μm, 5μm, 5.2μm, 5.4μm, 5.6μm, 5.8μm, 6μm, or its value is within the range obtained by combining any two of the above values.

[0149] Similar to the positive electrode sheet 11 , in this embodiment, by controlling the coating weight of the negative electrode film layer, the compacted surface density of the negative electrode sheet 12 , and the thickness of the negative electrode collector within a suitable range, the secondary battery cell 20 can have both high energy density and good safety performance.

[0150] In one embodiment, the negative electrode active material includes graphite.

[0151] In one embodiment, the average volume particle size Dv50 of the graphite satisfies: 10 μm≤Dv50≤14 μm.

[0152] Specifically, Dv50 can be 10μm, 10.2μm, 10.4μm, 10.6μm, 10.8μm, 11μm, 11.2μm, 11.4μm, 11.6μm, 11.8μm, 12μm, 12.2μm, 12.4μm, 12.6μm, 12.8μm, 13μm, 13.2μm, 13.4μm, 13.6μm, 13.8μm, 14μm, or its value is within the range obtained by combining any two of the above values. The average volume particle size of graphite affects the capacity and lithium ion dynamics of the secondary battery cell. The smaller the average volume particle size of graphite, the larger the specific surface area, which can provide more active sites in the electrochemical reaction, thereby facilitating the extraction and embedding of lithium ions and improving the capacity and lithium ion dynamics of the secondary battery cell 20. If the average volume particle size of graphite is too small, the contact area between particles may be insufficient, the internal resistance of the secondary battery cell 20 may be increased, and the cycle performance of the secondary battery cell 20 may be affected. Therefore, this embodiment can help improve the capacity and cycle performance of the secondary battery cell 20 by controlling the average volume particle size of graphite within a suitable range.

[0153] In one embodiment, the secondary battery cell 20 includes an electrolyte, the electrolyte includes: a solvent, the solvent includes a linear carbonate; based on the total mass of the electrolyte, the mass content m2 of the linear carbonate satisfies 40wt%≤m2≤70wt%.

[0154] Specifically, m2 can be 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, or a value thereof within the range obtained by combining any two of the above values. In this embodiment, by selecting a linear carboxylate as a solvent and controlling its mass content in the electrolyte within a suitable range, it helps to reduce the viscosity of the electrolyte, thereby helping to improve lithium ion dynamics.

[0155] In one embodiment, the electrolyte includes: a lithium salt, the lithium salt includes LiPF6 and LiFSI; based on the total mass of the electrolyte, the mass content m3 of the lithium salt satisfies 13wt%≤m3≤18wt%.

[0156] Specifically, m3 can be 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, or its value is within the range obtained by combining any two of the above values. In this embodiment, by selecting LiPF6 and LiFSI as lithium salts, it helps to improve the lithium ion conductivity and high temperature resistance of the electrolyte, thereby helping to improve the lithium ion dynamics during the cycle of the secondary battery cell 20 and improve the safety performance of the secondary battery cell 20.

[0157] In one embodiment, based on the total amount of the lithium salt, the molar content n of LiPF6 satisfies: 50%≤n≤70%.

[0158] Specifically, it can be 50%, 55%, 60%, 65%, 70%, or any value within the range obtained by combining any two of the above values. LiPF6 has good film-forming stability. By controlling the molar content of LiPF6 within a higher range, it helps to form a stable SEI film on the surface of the negative electrode 12, thereby improving the safety performance of the secondary battery cell 20.

[0159] In one embodiment, the secondary battery cell 20 includes an electrolyte, and the ion conductivity σ of the electrolyte at 25° C. satisfies: 7 mS / cm≤σ≤10 mS / cm.

[0160] Specifically, σ can be 7mS / cm, 7.5mS / cm, 8mS / cm, 8.5mS / cm, 9mS / cm, 9.5mS / cm, 10mS / cm, or a value thereof within the range obtained by combining any two of the above values. In this embodiment, selecting an electrolyte with higher ion conductivity helps to improve the lithium ion dynamics during the cycle of the secondary battery cell 20, helps to reduce the probability of polarization of the secondary battery cell 20, and improves the safety performance of the secondary battery cell 20.

[0161] Next, taking a lithium-ion battery as a specific example, the positive electrode sheet 11, the negative electrode sheet 12, the separator 13 and the electrolyte in the secondary battery cell 20 are described in detail. It should be understood that the lithium-ion battery is only used as an example, and the solution provided in this application can also be applied to other types of secondary batteries, such as sodium-ion batteries, magnesium-ion batteries, lithium-sulfur batteries, etc.

[0162] [Negative electrode]

[0163] As mentioned above, the negative electrode sheet 12 generally includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector. The negative electrode film layer includes a negative electrode active material.

[0164] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0165] In one embodiment, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, a copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0166] In one embodiment, the negative electrode active material may adopt the negative electrode active material for batteries known in the art. 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, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0167] In one embodiment, the negative electrode film layer further includes a binder. The binder can be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

[0168] In one embodiment, the negative electrode film layer further includes a conductive agent, which can be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0169] In one embodiment, the negative electrode film layer further includes other additives, such as a thickener (eg sodium carboxymethyl cellulose (CMC-Na)).

[0170] In one embodiment, the negative electrode sheet 12 can be prepared in the following manner: the components for preparing the negative electrode sheet are formed into a negative electrode slurry. For example, the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a negative electrode slurry. Then, the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet 12 can be obtained.

[0171] [Positive electrode]

[0172] As mentioned above, the positive electrode plate 11 includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

[0173] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0174] In one embodiment, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may 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 (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0175] In another embodiment, examples of lithium-containing transition metal oxides may include, but are not limited to, lithium cobalt oxide (e.g., LiCoO2), lithium nickel oxide (e.g., LiNiO2), lithium manganese oxide (e.g., LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05O2) and at least one of its modified compounds. Examples of lithium-containing transition metal phosphates with an olivine structure may include, but are not limited to, 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 at least one of a composite material of lithium iron manganese phosphate and carbon. The battery is accompanied by the deintercalation and consumption of Li during the charging and discharging process, and the molar content of Li in the positive electrode active material is different when the battery is discharged to different states. In the enumeration of positive electrode active materials in this application, the molar content of Li is the initial state of the material, that is, the state before feeding. The positive electrode active material is used in the battery system, and the molar content of Li will change after charge and discharge cycles. In the enumeration of positive electrode active materials in this application, the molar content of O is only an ideal state value. The release of lattice oxygen will cause the molar content of O to change, and the actual molar content of O will fluctuate.

[0176] The positive electrode active material includes Li 1+c [Ni x Co y Mn z M d ]O 2-e In the example, d is 0, and the positive electrode active material includes LiNi 0.7 Co 0.1 Mn 0.2 As another example, d>0, the positive electrode active material includes LiNi 0.7 Co 0.1 Mn 0.1 Al 0.1 O2.

[0177] In one embodiment, the positive electrode active material includes: LiNi 0.90 Co 0.06 Mn 0.04 O2、LiNi 0.7 Co 0.1 Mn 0.2 O2、LiNi 0.7 Co 0.2 Mn 0.1 O2 or LiNi 0.8 Co 0.1 Mn 0.1 At least one of O2.

[0178] In one embodiment, the positive electrode film layer further includes a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0179] In one embodiment, the positive electrode film layer further includes a conductive agent. As an example, the conductive agent may also include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, graphene and carbon nanofibers.

[0180] In one embodiment, the positive electrode sheet 11 can be prepared in the following manner: the components for preparing the positive electrode sheet are respectively formed into positive electrode slurries. For example, the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry. Then, the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet 11 can be obtained.

[0181] [Electrolyte]

[0182] The electrolyte plays a role in conducting ions between the positive electrode plate 11 and the negative electrode plate 12. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

[0183] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent. Some solutions of the electrolyte solution have been mentioned above.

[0184] In addition to the aforementioned scheme, in some embodiments, the electrolyte salt can also be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate and lithium tetrafluorooxalatophosphate.

[0185] In some embodiments, the solvent may also be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0186] In some embodiments, the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0187] [Isolation film]

[0188] As mentioned above, the isolation film 13 includes a coating layer, and the coating layer includes at least one of inorganic particles and organic particles.

[0189] In one embodiment, the inorganic particles may further include one or more of inorganic particles having ion conductivity but not storing ions or inorganic particles capable of undergoing electrochemical reactions.

[0190] In one embodiment, inorganic particles having ion conductivity but not storing ions may include Li3PO4, lithium titanium phosphate, Li x1 Ti y1 (PO4)3, Lithium Aluminum Titanate Phosphate Li x2 Al y2 Ti z1 (PO4)3, (LiAlTiP) x3 O y3 Type glass, lanthanum titanate lithium Li x4 La y4 TiO3, Lithium Germanium Phosphate Thiophosphate x5 Ge y5 P z2 S w 、Lithium Nitride Li x6 N y6 、SiS2 glass Li x7 Si y7 S z3 and P2S5 glass Li x8 P y8 S z4 One or more of 0<x1<2, 0<y1<3, 0<x2<2, 0<y2<1, 0<z1<3, 0<x3<4, 0<y3<13, 0<x4<2, 0<y4<3, 0<x5<4, 0<y5<1, 0<z2<1, 0<w<5, 0<x6<4, 0<y6<2, 0<x7<3, 0<y7<2, 0<z3<4, 0<x8<3, 0<y8<3, 0<z4<7. This can improve the ion conductivity of the isolation membrane.

[0191] In one embodiment, the inorganic particles capable of electrochemical reaction may include one or more of lithium-containing transition metal oxides, lithium-containing phosphates, carbon-based materials, silicon-based materials, tin-based materials, and lithium-titanium compounds.

[0192] As mentioned above, the organic particles may include at least one of a thermoplastic resin polymer, a thermosetting resin polymer, or a cross-linked polymer.

[0193] Among them, in one embodiment, the thermoplastic resin polymer may include one or more of polycarbonate organic particles, polymethyl methacrylate organic particles, polyformaldehyde organic particles, polyamide organic particles, styrene-acrylonitrile copolymer, polyphenylene sulfide organic particles, polyetheretherketone organic particles, polyimide organic particles, polysulfone organic particles, polyethersulfone organic particles, polyphenylene sulfone organic particles, polybenzimidazole organic particles, polyamideimide organic particles, and polyethyleneimine organic particles.

[0194] In one embodiment, the thermosetting resin polymer may include one or more of phenolic resin organic particles, polymer particles containing triazine ring structural units, epoxy resin organic particles, unsaturated polyester resin organic particles, urea-formaldehyde resin organic particles, and furan resin organic particles.

[0195] In one embodiment, the cross-linked polymer may include one or more of cross-linked styrene-based organic particles and silicon-containing organic cross-linked resin particles.

[0196] In one embodiment, the binder particles may include a copolymer of an acrylic acid ester monomer unit-a styrene monomer unit, a copolymer of an acrylic acid monomer unit-a styrene monomer unit, a copolymer of an acrylic acid monomer unit-an acrylic acid ester monomer unit-a styrene monomer unit, a copolymer of a styrene monomer unit-an unsaturated nitrile monomer unit, a copolymer of a styrene monomer unit-an olefin monomer unit-an unsaturated nitrile monomer unit, and one or more of the modified compounds of the above homopolymers or copolymers.

[0197] In one embodiment, the binder particles may include butyl acrylate-styrene copolymer, butyl methacrylate-isooctyl methacrylate copolymer, isooctyl methacrylate-styrene copolymer, methacrylate-methacrylic acid-styrene copolymer, methyl acrylate-isooctyl methacrylate-styrene copolymer, butyl acrylate-isooctyl methacrylate-styrene copolymer, butyl acrylate-isooctyl methacrylate-styrene copolymer, butyl methacrylate-isooctyl methacrylate-styrene copolymer, butyl methacrylate-isooctyl methacrylate-styrene copolymer, butyl methacrylate-isooctyl methacrylate-styrene copolymer, styrene-acrylonitrile copolymer, styrene-butadiene-acrylonitrile copolymer, methyl acrylate-styrene-acrylonitrile copolymer, isooctyl methacrylate-styrene-acrylonitrile copolymer, styrene-vinyl acetate copolymer, styrene-vinyl acetate-pyrrolidone copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-trifluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene-acrylic acid copolymer, vinylidene fluoride-hexafluoropropylene-acrylate copolymer, and one or more of the modified compounds of the above copolymers.

[0198] In one embodiment, the coating may further include a dispersant, for example, may include but not limited to one or more of dispersants such as alkylphenol polyoxyethylene ether, polyacrylic acid dispersants, and cellulose dispersants. As an example, the dispersant may include but not limited to one or more of sodium carboxymethyl cellulose, sodium polyacrylate, and ammonium polyacrylate.

[0199] [Secondary battery]

[0200] The embodiment of the present application provides a secondary battery, including the secondary battery cell 20 in the above embodiment. The secondary battery can be a single physical module including one or more secondary battery cells 20 to provide higher voltage and capacity. When there are multiple secondary battery cells 20, the multiple secondary battery cells 20 are connected in series, in parallel or in mixed connection through a busbar component.

[0201] In some embodiments, the secondary battery may be a battery pack. The secondary battery includes a case and secondary battery cells 20 . The secondary battery cells 20 or battery modules are accommodated in the case.

[0202] 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.

[0203] In some embodiments, the secondary battery may be located in an energy storage device, which includes an energy storage container, an energy storage cabinet, and the like.

[0204] Fig.10 Schematic diagram of a secondary battery according to an embodiment of the present application. Fig.10 As shown, the secondary battery 30 may include a plurality of secondary battery cells 20 to meet different power usage requirements.

[0205] The secondary battery 30 may further include a casing, the interior of which is a hollow structure, and a plurality of secondary battery cells 20 are accommodated in the casing. For example, a plurality of secondary battery cells 20 are connected in parallel, in series, or in a mixed combination and placed in the casing. The casing may include a first casing portion 301 and a second casing portion 302, which cover each other to form the casing. The shapes of the first casing portion 301 and the second casing portion 302 may be determined according to the shapes of the components accommodated therein, for example, they may be determined according to the shape of the combination of the plurality of secondary battery cells 20 accommodated therein, and at least one of the first casing portion 301 and the second casing portion 302 may have an opening. For example, as Fig.10As shown, only one of the first box body 301 and the second box body 302 may be a hollow rectangular parallelepiped with an opening, and the other may be a plate-shaped to cover the opening. Taking the second box body 302 as a hollow rectangular parallelepiped with an opening, and the first box body 301 as a plate-shaped example, the first box body 301 covers the opening of the second box body 302 to form a box with a closed chamber, which can be used to accommodate multiple secondary battery cells 20.

[0206] For example, unlike Fig.10 As shown, the first box body 301 and the second box body 302 can both be hollow cuboids and each have an open face, the opening of the first box body 301 and the opening of the second box body 302 are arranged opposite to each other, and the first box body 301 and the second box body 302 are buckled together to form a box with a closed chamber, which can be used to accommodate multiple secondary battery cells 20. Multiple secondary battery cells 20 are connected in parallel, in series, or in mixed combination and placed in the box formed by the first box body 301 and the second box body 302 buckled together.

[0207] In some embodiments, the secondary battery 30 may further include other components. For example, the secondary battery 30 may further include a busbar component, which may be used to achieve electrical connection between multiple secondary battery cells 20, such as parallel connection, series connection, or mixed connection. Specifically, the busbar component may achieve electrical connection between the secondary battery cells 20 by connecting the electrode terminals of the secondary battery cells 20; or, the busbar component may also achieve electrical connection between the secondary battery cells 20 by connecting other components of the secondary battery cells 20. The busbar component may be fixed to the corresponding components of the secondary battery cell 20 by welding, for example, it may be fixed to the electrode terminal, the sealing structure, or the housing by welding, etc., but the embodiments of the present application are not limited thereto.

[0208] The secondary battery cells 20 may directly form the secondary battery 30 , or may first form a battery module, and then a plurality of battery modules may form the battery 30 .

[0209] [Electrical devices]

[0210] An embodiment of the present application provides an electrical device, comprising the secondary battery described in the above embodiment.

[0211] The electrical device may be a vehicle, a mobile phone, a portable device, a laptop computer, a ship, a spacecraft, an electric toy, an electric tool, and the like. The vehicle may be a fuel vehicle, a gas vehicle, or a new energy vehicle, and the new energy vehicle may be a pure electric vehicle, a hybrid vehicle, or an extended-range vehicle, and the like; the spacecraft may include an airplane, a rocket, a space shuttle, and a spacecraft, and the like; the electric toy may include a fixed or mobile electric toy, such as a game console, an electric car toy, an electric ship toy, and an electric airplane toy, and the like; the electric tool may include a metal cutting electric tool, a grinding electric tool, an assembly electric tool, and an electric tool for railways, such as an electric drill, an electric grinder, an electric wrench, an electric screwdriver, an electric hammer, an impact drill, a concrete vibrator, and an electric planer, and the like. The embodiments of the present application do not impose any special restrictions on the above-mentioned electrical devices.

[0212] The present application provides an electrical device, which is a vehicle.

[0213] The vehicle can be a fuel vehicle, a gas vehicle or a new energy vehicle. The new energy vehicle can be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc. A motor, a controller and a secondary battery 30 can be arranged inside the vehicle, and the controller is used to control the secondary battery 30 to power the motor. For example, a secondary battery 30 can be arranged at the bottom, front or rear of the vehicle. The battery 30 can be used to power the vehicle. For example, the secondary battery 30 can be used as an operating power source for the vehicle and for the circuit system of the vehicle, for example, for the working power requirements during the start-up, navigation and operation of the vehicle. In another embodiment of the present application, the secondary battery 30 can not only be used as an operating power source for the vehicle, but also as a driving power source for the vehicle, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle.

[0214] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0215] [Examples and Comparative Examples]

[0216] Example 1

[0217] (1) Preparation of negative electrode sheet

[0218] The negative electrode active material graphite, sodium carboxymethyl cellulose, styrene butadiene rubber and acetylene black are mixed in a mass ratio of 96:1:1:2, deionized water is added, and the mixture is stirred evenly in a blender. The slurry is then coated on an 8-micron thick copper foil, dried in an oven at 120°C, cold pressed, and cut to obtain negative electrode sheets.

[0219] (2) Preparation of positive electrode sheet

[0220] The positive electrode active material contains lithium transition metal phosphate LiMn 0.6 Fe 0.4 O4 and Li-containing layered metal oxides LiNi 0.65 Co 0.15 Mn 0.2 O2, binder polyvinylidene fluoride (PVDF), conductive agent acetylene black, and carbon nanotubes are mixed in a mass ratio of 96.5:2:1:0.5 (the mass ratio of lithium-containing transition metal phosphate and lithium-containing layered metal oxide is 1:1), NMP is added, and the mixture is stirred evenly in a blender. The slurry is then coated on a 12-micron thick aluminum foil, dried in an oven, cold pressed, and cut to obtain positive electrode sheets.

[0221] (3) Preparation of secondary battery monomers

[0222] Multiple positive electrode sheets, separators, and multiple negative electrode sheets are stacked in order to obtain a laminated electrode assembly, which is placed in a shell, injected with electrolyte, and then packaged to obtain a secondary battery cell. The electrolyte is an electrolyte with ethylene carbonate (EC) and diethyl carbonate (DEC) as solvents (volume ratio 1:2) and a lithium salt (LiPF6 and LiFSI, molar content ratio 2:1) concentration of 1M. The size of the shell is 50mm×194mm×110mm.

[0223] In the secondary battery cell of Example 1, the mass content of lithium transition metal phosphate m1=50%, the average particle size of the particles containing lithium transition metal oxide D1=4 μm, and the single-side coating weight of the positive electrode sheet CW1=215 g / m 2 , the coating weight of the negative electrode film CW2 = 99g / m 2 The thickness of the isolation membrane is h=13 μm, the isolation membrane is a membrane with coatings on both sides, the base membrane thickness is 5 μm, the coating thickness h1=4 μm, the inorganic particles in the coating include aluminum oxide, the binder includes PVDF, and the single-side loading amount of PVDF on the isolation membrane is a=0.75 mg / 1540.25 mm 2 .

[0224] Example 2-3

[0225] Compared with Example 1, the difference is that the mass content m1 of the lithium-containing transition metal phosphate is different from that of Example 1.

[0226] Embodiment 4-5

[0227] Compared with Example 1, the difference lies in that the coating thickness h1 and the isolation film thickness h are different from those in Example 1.

[0228] Example 6

[0229] Compared with Example 1, the difference lies in that an isolation film having a coating on one side is used.

[0230] Embodiment 7-9

[0231] Compared with Example 1, the difference is that the single-side loading amount a of PVDF on the isolation membrane is different from that in Example 1.

[0232] Embodiment 10-11

[0233] Compared with Example 1, the difference is that the average volume particle size Dv501 of the primary particles in the lithium-containing transition metal oxide is different from that in Example 1.

[0234] Examples 12-13

[0235] Compared with Example 1, the difference is that the single-side coating weight CW1 of the positive electrode sheet is different from that of Example 1.

[0236] Comparative Example 1

[0237] A shell having the same size as that of Example 1 is used. Compared with Example 1, the difference is that a wound electrode assembly is used in Comparative Example 1, and the thickness of the separator is 7 μm, and the thickness of the single-side coating is 1 μm.

[0238] Comparative Example 2

[0239] A shell having the same size as that of Example 1 is used. Compared with Example 1, the difference is that Comparative Example 3 uses a wound electrode assembly and the thickness of the separator is 22 μm.

[0240] Comparative Example 3

[0241] A laminated electrode assembly is used. Compared with Example 1, the difference is that the thickness of the isolation film in Comparative Example 2 is 22 μm.

[0242] The product parameters and performance parameters of Examples 1-13 and Comparative Examples 1-3.

[0243] Table 1: Product parameters and performance parameters of Examples 1-13 and Comparative Examples 1-3

[0244] In Table 1, "m1" represents the mass content of lithium-containing transition metal phosphate in the positive electrode active material; "h" represents the thickness of the isolation membrane 13, "h1" represents the thickness of the single-sided coating; "a" represents the single-sided loading amount of the binder particles on the isolation membrane; "D1" represents the average particle size of the particles containing lithium transition metal oxide; "CW1" represents the coating weight of the positive electrode film layer; "thermal runaway temperature" represents the temperature at which thermal runaway occurs in the secondary battery cell 20 in the hot box test; "VED" represents the volume energy density of the secondary battery cell 20.

[0245] According to the comparative analysis of the embodiment and the comparative example, compared with comparative examples 1-3, the embodiments all show a thermal runaway temperature that is better than that of comparative examples 1-3, indicating that the safety performance of the embodiments is better than that of comparative examples 1-3. At the same time, the embodiment also has a volume energy density higher than that of comparative example 1. This proves that through the material system of the embodiment of the present application and the structural design of the electrode assembly 10 and the secondary battery cell 20, the secondary battery cell 20 can have both high energy density and good safety performance.

[0246] According to the comparative analysis of Examples 1-3, it can be seen that increasing the proportion of lithium-containing transition metal phosphate in the positive electrode active material increases the thermal runaway temperature of the secondary battery cell 20, improves the safety performance, and decreases the volume energy density. Therefore, by regulating the mass content of lithium-containing transition metal phosphate within a suitable range, it is helpful to obtain a secondary battery cell 20 that has both high energy density and high safety performance.

[0247] According to the comparative analysis of Examples 1, 4-6, the thicker the coating and the thicker the isolation film 13, the higher the thermal runaway temperature of the secondary battery cell 20, which will also affect the energy density of the secondary battery cell 20, and the double-sided coating is more conducive to the safety performance of the secondary battery cell 20. Therefore, by controlling the thickness of the isolation film 13 within a suitable range, a secondary battery cell 20 with both high energy density and high safety performance can be obtained.

[0248] According to the comparative analysis of Examples 1, 7-9, at 0.5mg / 1540.25mm 2 -1.2mg / 1540.25mm 2 In the range of, the greater the loading amount of the binder particles in the separator 13, the greater the bonding force between the separator 13 and the pole piece, the better the structural stability of the laminated electrode assembly formed by stacking multiple positive pole pieces and multiple negative pole pieces, and the higher the thermal runaway temperature. In Example 9, the loading amount of the binder particles is too large, and the thermal runaway temperature is reduced. The possible reason is that the binder will block the ion channel in the separator 13, aggravate the polarization of the secondary battery monomer during the cycle, and cause the thermal runaway temperature to decrease.

[0249] According to the comparative analysis of Examples 1, 10-11, it can be seen that the smaller the average particle size of the particles containing lithium transition metal oxides, the more conducive it is to improving the compaction density of the positive electrode sheet, and the higher the energy density of the secondary battery cell 20. At the same time, the smaller the average particle size of the particles containing lithium transition metal oxides, the higher the thermal runaway temperature of the secondary battery cell 20, and the better the safety performance. The possible reason is that the smaller the average particle size, the better the structural stability of the lithium transition metal oxide, the more stable the chemical reaction can be during the charging and discharging process of the secondary battery cell 20, and the lower the probability of thermal runaway due to the violent chemical reaction and large amount of heat release. Therefore, regulating the average particle size of the particles containing lithium transition metal oxides helps to further improve the safety performance of the high energy density secondary battery cell 20.

[0250] According to the comparative analysis of Examples 1, 12-13, the greater the coating weight of the positive electrode sheet 11, the greater the energy density of the secondary battery cell 20 and the lower the thermal runaway temperature. Therefore, regulating the coating weight of the positive electrode sheet can also help improve the safety performance of the high energy density secondary battery cell 20.

[0251] The following is a brief introduction to the test methods of the physical and chemical parameters and performance parameters involved in the embodiments of the present application. It should be understood that the following test methods are only examples, and other test methods known in the art may also be used for testing.

[0252] 1. Test method for mass content

[0253] The specific type of lithium-containing transition metal oxide is confirmed by the mass ratio of Ni, Co and Mn in CP-EDS, and the specific type of lithium-containing transition metal phosphate is confirmed by the mass ratio of Mn and Fe. Then, the mass content of lithium-containing transition metal oxide is calculated by the mass content of Ni in the mixed ICP, and the mass content of lithium-containing transition metal phosphate is calculated by the mass content of Fe.

[0254] 2. Test method for element molar ratio

[0255] Test equipment: Inductively coupled plasma emission spectrometer (ICP).

[0256] Test method: Digestion: 1+1 aqua regia, digestion method: plate / acid digestion / microwave digestion (high temperature and high pressure ~ 200°C). Test the element mass fractions of nickel, cobalt, manganese and doping elements, calculate the molar amount based on the molar mass of each element, and finally normalize and calculate the molar ratio of nickel, cobalt and manganese.

[0257] 3. Test method for average particle size of particles

[0258] The particle morphology and size of the sample to be tested are obtained through SEM, and elemental analysis is performed based on the SEM mapping results. The lithium-containing transition metal phosphate particles and the lithium-containing transition metal oxide particles are distinguished by the differences in element types and contents (such as P element). The average particle size of the particles of the corresponding material can be calculated based on the number of each type of particles in the SEM image and the long diameter of each particle.

[0259] 4.Dv50 test method

[0260] Testing equipment: particle size testing instrument.

[0261] Pretreatment: Take a clean beaker, add an appropriate amount of the sample to be tested, add a surfactant dropwise and then add a dispersant, and perform ultrasound at 120W / 5min to ensure that the sample is completely dispersed in the dispersant.

[0262] Test: After the sample is poured into the injection tower, it circulates with the solution to the test optical system. When the particles are irradiated by the laser beam, the particle size distribution characteristics (shading degree: 8-12%) can be obtained by receiving and measuring the energy distribution of the scattered light.

[0263] Calculation: Calculate the particle size at the 50% position on the volume particle size distribution curve from small to large, which is Dv50.

[0264] 5. Test method for pole piece compaction density

[0265] Take a unit area of ​​the electrode to be tested, weigh the mass m1 of the material on the unit area of ​​the electrode except the current collector, measure the electrode thickness T1 and the current collector thickness T0, and the compaction density = m1 / (T1-T0).

[0266] 6. Test method for film coating weight

[0267] Take a unit area of ​​the electrode to be tested and weigh the mass of the material other than the current collector on the unit area of ​​the electrode, that is, the coating weight.

[0268] 7. Test method for volume energy density of secondary battery cells

[0269] On the charging and discharging equipment, charge and discharge for 3 cycles at a current density of 0.33C in the range of 2.5-4.25V, and take the discharge energy Q of the 3rd cycle; measure the volume V of the secondary battery cell 20: take a CT scan image of the secondary battery cell 20, and based on the CT scan image, the length T, height h, width L, diameter d, height H and other data of the secondary battery cell 20 can be measured. The volume of the secondary battery cell 20 can be calculated by the formula V = T × h × L + 2 × π × (d / 2) 2×H, the energy density of the secondary battery cell 20 is Q / V (unit: Wh / L). If the shape of the electrode terminal is irregular, the volume of the electrode terminal can be calculated by fitting the irregular shape into a regular shape on a computer and then using the volume calculation formula of a regular shape.

[0270] 8. Safety performance test methods

[0271] The safety performance of the secondary battery cell 20 is characterized by a hot box test. The specific test process is: a fully charged secondary battery cell 20 is placed in an oven, and the temperature is raised from 30°C to 200°C at a temperature rise rate of 2°C / min, and the temperature is kept at 5°C for 30 minutes, and the temperature at which the secondary battery cell 20 catches fire, i.e., its failure temperature, is observed.

[0272] Although the present application has been described with reference to preferred embodiments, various modifications may be made thereto and parts thereof may be replaced with equivalents without departing from the scope of the present application. In particular, the various technical features mentioned in the various embodiments may be combined in any manner as long as there are no structural conflicts. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A secondary battery cell, characterized in that: The secondary battery cell comprises: A laminated electrode assembly, comprising a positive electrode sheet, a negative electrode sheet and a separator, wherein the positive electrode sheet comprises a positive electrode film layer, wherein the positive electrode film layer comprises a positive electrode active material, and the negative electrode sheet comprises a negative electrode film layer, wherein the negative electrode film layer comprises a negative electrode active material; The positive electrode active material includes a lithium-containing transition metal phosphate and a lithium-containing transition metal oxide. The thickness h of the isolation film satisfies: 8 μm≤h≤21 μm.

2. The secondary battery cell according to claim 1, characterized in that: Based on the total mass of the positive electrode active material, the mass content m1 of the lithium-containing transition metal phosphate satisfies: 40wt%≤m1≤70wt%.

3. The secondary battery cell according to claim 1 or 2, characterized in that: The isolation film includes a base film and a coating layer disposed on at least one side of the base film, and a thickness h1 of the coating layer on one side satisfies: 3 μm≤h1≤6 μm.

4. The secondary battery cell according to claim 2 or 3, characterized in that: The coating layer includes heat-resistant particles, and the heat-resistant particles include at least one of inorganic particles and organic particles.

5. The secondary battery cell according to claim 4, characterized in that: The inorganic particles include at least one of aluminum oxide, silicon oxide, titanium oxide and barium titanate.

6. The secondary battery cell according to any one of claims 2 to 5, characterized in that: The coating comprises binder particles, and the binder particles comprise: polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, polyethylene, polypropylene, polyacrylonitrile, polyethylene oxide, copolymers of different fluorine-containing olefin monomer units, copolymers of fluorine-containing olefin monomer units and vinyl monomer units, copolymers of fluorine-containing olefin monomer units and acrylic monomer units, copolymers of fluorine-containing olefin monomer units and acrylic ester monomer units, and one or more of modified compounds of the above homopolymers or copolymers.

7. The secondary battery cell according to any one of claims 1 to 6, characterized in that: The laminated electrode assembly comprises a plurality of positive electrode sheets and a plurality of negative electrode sheets, and the plurality of positive electrode sheets and the plurality of negative electrode sheets are alternately stacked in a thickness direction.

8. The secondary battery cell according to claim 7, characterized in that: The single-side loading amount a of the binder particles on the isolation film satisfies: 0.5 mg / 1540.25 mm 2 ≤a≤1.2mg / 1540.25mm 2 .

9. The secondary battery cell according to any one of claims 1 to 8, characterized in that: The positive electrode plate includes a conductive agent, the conductive agent includes carbon nanotubes, and the diameter l of the carbon nanotubes satisfies: 7nm≤l≤13nm.

10. The secondary battery cell according to any one of claims 1 to 9, characterized in that: The average particle size D1 of the lithium-containing transition metal oxide particles satisfies: 2 μm≤D1≤5 μm.

11. The secondary battery cell according to any one of claims 1 to 10, characterized in that: The lithium-containing transition metal oxide comprises: Li 1+c [Ni x Co y Mn z M d ]O 2-e ; Wherein, M includes at least one of Zr, Al, Ti, Sb, Nb, Te, Mg, B, Ca, V, Ta or Sr, 0.2≥c≥-0.2, 0.95≥x≥0.5, 0.2≥y≥0.05, 0.3>z>0, 0.3>d≥0, 0.5≥e≥0.

12. The secondary battery cell according to any one of claims 1 to 11, characterized in that: The positive electrode sheet satisfies at least one of the following (1)-(3): (1) The compaction density ρ1 of the positive electrode sheet satisfies: 2.5 g / cm 3 ≤ρ1≤2.9g / cm 3 ; (2) The single-sided coating weight CW1 of the positive electrode film layer satisfies: 190 g / m 2 ≤CW1≤230g / m 2 ; (3) The thickness h1 of the positive electrode current collector satisfies: 10 μm ≤ h1 ≤ 13 μm.

13. The secondary battery cell according to any one of claims 1 to 12, characterized in that: The negative electrode plate satisfies at least one of the following (4)-(6): (4) The compaction density ρ2 of the negative electrode sheet satisfies: 1.3 g / cm 3 ≤ρ2≤1.55g / cm 3 ; (5) The single-sided coating weight CW2 of the negative electrode film layer satisfies: 90 g / m 2 ≤CW2≤110g / m 2 ; (6) The thickness h2 of the negative electrode current collector satisfies: 4 μm ≤ h2 ≤ 6 μm.

14. The secondary battery cell according to any one of claims 1 to 13, characterized in that: The negative electrode active material includes graphite, and the average volume particle size Dv502 of the graphite satisfies: 10 μm≤Dv502≤14 μm.

15. The secondary battery cell according to any one of claims 1 to 14, characterized in that: The secondary battery includes an electrolyte, and the electrolyte includes: a solvent, the solvent comprising a linear carbonate; Based on the total mass of the electrolyte, the mass content m2 of the linear carbonate satisfies 40wt%≤m2≤70wt%.

16. The secondary battery cell according to claim 15, characterized in that: The electrolyte comprises: Lithium salt, the lithium salt comprising LiPF6 and LiFSI; Based on the total mass of the electrolyte, the mass content m3 of the lithium salt satisfies 13wt%≤m3≤18wt%.

17. The secondary battery cell according to claim 15 or 16, characterized in that: The ionic conductivity σ of the electrolyte at 25° C. satisfies: 7 mS / cm≤σ≤10 mS / cm.

18. The secondary battery cell according to any one of claims 1 to 17, characterized in that: The secondary battery cell comprises a housing and a current collecting member; The housing is used to accommodate the laminated electrode assembly, and the housing includes a first wall, and the first wall is provided with an electrode terminal; The laminated electrode assembly comprises a main body and a tab, wherein the tab is connected to one end of the main body facing the first wall; The current collecting member is disposed between the first wall and the main body, and includes a first connecting portion and a second connecting portion connected to each other, the first connecting portion is connected to the electrode terminal, and the second connecting portion is connected to the electrode tab; In a thickness direction of the current collecting member, a thickness of the first connection portion is greater than a thickness of the second connection portion.

19. The secondary battery cell according to claim 18, characterized in that: Along the thickness direction of the current collecting member, a thickness D1 of the first connection portion satisfies: 0.5 mm ≤ D1 ≤ 1.2 mm; a thickness D2 of the second connection portion satisfies: 0.3 mm ≤ D2 ≤ 1 mm.

20. The secondary battery cell according to claim 19, characterized in that: 0.1mm≤D1-D2≤0.9mm.

21. The secondary battery cell according to any one of claims 18 to 20, characterized in that: The first wall includes a first through hole; The electrode terminal comprises a main body and a step portion, wherein at least a portion of the main body is passed through the first through hole, the step portion protrudes from the outer peripheral surface of the main body, and the step portion is located on a side of the first wall facing the outside of the secondary battery cell; The secondary battery cell includes a fixing member, and the fixing member includes a second through hole for the main body to pass through; In the thickness direction of the first wall, at least a portion of the fixing member is located between the first wall and the step portion and abuts against the step portion, the main body portion has a first end face facing the outside of the secondary battery cell, and the fixing member has a second end face facing the outside of the secondary battery cell, and the first end face exceeds the second end face.

22. The secondary battery cell according to claim 21, characterized in that: In the thickness direction of the first wall, a height difference H between the first end surface and the second end surface satisfies: 0.5 mm≤H≤1.5 mm.

23. The secondary battery cell according to claim 21 or 22, characterized in that: In the radial direction of the main body, a dimension W1 of the step portion protruding from the outer peripheral surface of the main body satisfies: 0.1 mm ≤ W1 ≤ 5 mm.

24. A secondary battery, characterized in that: The secondary battery comprises the secondary battery cell according to any one of claims 1 to 23.

25. An electrical device, characterized in that: The electrical device comprises the secondary battery cell according to any one of claims 1 to 23 and / or the secondary battery according to claim 24.

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