Secondary battery cell, secondary battery and electric device

Abstract

A secondary battery cell, a secondary battery and an electric device. The secondary battery cell comprises a cylindrical casing, an electrode assembly, a first end cover assembly and a second end cover assembly, wherein the cylindrical casing is provided with an accommodating cavity and a first opening and a second opening which are communicated with the accommodating cavity; the electrode assembly is arranged in the accommodating cavity, the first end cover assembly covers the first opening, and the second end cover assembly covers the second opening; and the first end cover assembly comprises a first pressure relief mechanism, and the second end cover assembly comprises a second pressure relief mechanism. The secondary battery cell further comprises an electrolyte, wherein the electrolyte comprises a solvent, the solvent comprises dimethyl carbonate, and the mass percentage content of the dimethyl carbonate in the solvent is greater than or equal to 50 wt%. The secondary battery cell satisfies that (S1+S2) / C0 is greater than or equal to 2.5 mm2 / Ah. The secondary battery has high energy density, good cycle performance and high reliability.

Description

Secondary battery cell, secondary battery and electric device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] The present disclosure claims priority to Chinese patent application 202311763673.8, filed on December 20, 2023, entitled “Battery Cell, Battery and Electrical Device,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to a secondary battery cell, a secondary battery, and an electric device. Background Art

[0004] As the application of secondary batteries expands, demand for their use is also increasing, with demands for higher energy density being placed on them. Generally, as the energy density of a secondary battery increases, so too does the amount of side reactions within the battery. This increase in side reactions and the resulting gas generation can negatively impact the battery's reliability. Developing a secondary battery that achieves both high energy density and high reliability remains a pressing challenge.

[0005] Summary of the Invention

[0006] The present disclosure provides a secondary battery cell, a secondary battery, and an electric device, which can enable the secondary battery to have high energy density, good cycle performance, and high reliability.

[0007] In a first aspect, the present disclosure provides a secondary battery cell, comprising a cylindrical shell, an electrode assembly, a first end cap assembly, and a second end cap assembly. The cylindrical shell has a housing cavity and a first opening and a second opening communicating with the housing cavity. The electrode assembly is disposed within the housing cavity. The first end cap assembly covers the first opening, and the second end cap assembly covers the second opening. The first end cap assembly includes a first pressure relief mechanism, and the second end cap assembly includes a second pressure relief mechanism. The secondary battery cell also includes an electrolyte, the electrolyte includes a solvent, the solvent includes dimethyl carbonate, and the mass percentage of dimethyl carbonate in the solvent is greater than or equal to 50 wt%. The first pressure relief mechanism includes a first pressure relief portion, and the area of ​​the first pressure relief portion is denoted as S1, in units of mm. 2 The second pressure relief mechanism has a second pressure relief portion, the area of ​​the second pressure relief portion is denoted as S2, in mm 2 The capacity of the secondary battery cell is recorded as C0, the unit is Ah, and the secondary battery cell satisfies (S1 + S2) / C0 is greater than or equal to 2.5mm 2 / Ah.

[0008] By making the mass percentage of dimethyl carbonate in the electrolyte solvent greater than or equal to 50wt%, the electrolyte can be made to have a low viscosity, which facilitates the flow of the electrolyte, thereby improving the electrolyte wettability of the electrode assembly and enhancing the cycle performance of the secondary battery cell. By providing a pressure relief mechanism at both ends of the secondary battery cell, it is helpful to quickly discharge the emissions inside the secondary battery cell, thereby achieving the purpose of pressure relief in a short period of time. At the same time, the emissions ejected from the two pressure relief mechanisms exert impact forces on the cylindrical shell in opposite directions, thereby also reducing the risk of deformation and tearing of the secondary battery cell to a certain extent. By adjusting (S1+S2) / C0 within the above range, it is helpful to achieve a dynamic balance between the gas production and exhaust volume of the secondary battery cell, thereby effectively reducing or even avoiding safety accidents such as fire and explosion of the secondary battery cell.

[0009] Therefore, the secondary battery cell provided by the embodiment of the present disclosure has good electrolyte wettability, thereby making the secondary battery cell have good cycle performance. In addition, the secondary battery cell provided by the embodiment of the present disclosure can also quickly release pressure under abuse conditions, thereby making the secondary battery cell have high reliability.

[0010] In some embodiments, the secondary battery cell satisfies (S1+S2) / C0 of 4.0 mm 2 / Ah-5.0mm 2 / Ah.

[0011] By adjusting (S1+S2) / C0 within the above range, a dynamic balance between the gas production and exhaust volume of the secondary battery cells is achieved, effectively reducing or even preventing safety accidents such as fires and explosions in the secondary battery cells. This also improves the processing performance of the end cap assembly, as a larger pressure relief area of ​​the pressure relief mechanism increases the difficulty of processing the end cap assembly, hindering the cost reduction and large-scale production of secondary battery cells.

[0012] In some embodiments, the axial dimension of the secondary battery cell is denoted as L, in mm; the secondary battery cell satisfies (S1+S2) / L greater than or equal to 0.6 mm, and may be 0.7 mm-0.9 mm.

[0013] By adjusting the ratio (S1+S2) / L of the total area of ​​the pressure relief parts of the two pressure relief mechanisms to the axial dimension of the secondary battery cell within the above range, it is helpful to quickly discharge the emissions inside the secondary battery cell and achieve the purpose of pressure relief in a short time, thereby effectively reducing or even avoiding safety accidents such as fire and explosion of the secondary battery cell.

[0014] In some embodiments, a ratio of an area of ​​the first pressure relief portion to an area of ​​the second pressure relief portion is 0.8-1.2.

[0015] In some embodiments, the ratio of the area of ​​the first pressure relief portion to the area of ​​the first end cover assembly is greater than or equal to 0.02:1, and can optionally be (0.04-0.10):1.

[0016] This helps to quickly discharge the emissions inside the secondary battery cell and achieve the purpose of pressure relief in a short time, thereby effectively reducing or even avoiding safety accidents such as fire and explosion in the secondary battery cell; at the same time, it can also make the first end cover assembly have good processing performance.

[0017] In some embodiments, the ratio of the area of ​​the second pressure relief portion to the area of ​​the second end cover assembly is greater than or equal to 0.02:1, and can be optionally (0.04-0.10):1.

[0018] This helps to quickly discharge the emissions inside the secondary battery cell and achieve the purpose of pressure relief in a short time, thereby effectively reducing or even avoiding safety accidents such as fire and explosion in the secondary battery cell; at the same time, it can also make the first end cover assembly have good processing performance.

[0019] In some embodiments, the center of the electrode assembly has a central hole extending along the axial direction of the secondary battery cell, and the diameter of the central hole is greater than or equal to 5 mm, and can be optionally 6 mm to 8 mm.

[0020] By adjusting the diameter of the center hole within the above range, it is helpful to quickly discharge the emissions inside the secondary battery cell and achieve the purpose of pressure relief in a short time, thereby effectively reducing or even avoiding safety accidents such as fire and explosion of the secondary battery cell.

[0021] In some embodiments, the diameter of the secondary battery cell is greater than or equal to 40 mm, and may be 45 mm to 60 mm, thereby enabling the secondary battery cell to have a high capacity.

[0022] In some embodiments, the axial dimension L of the secondary battery cell is greater than or equal to 130 mm, and can be optionally 150 mm to 320 mm, thereby enabling the secondary battery cell to have a high capacity.

[0023] In some embodiments, the capacity C0 of the secondary battery cell is greater than or equal to 20 Ah, and can be optionally greater than or equal to 30 Ah.

[0024] In some embodiments, the mass percentage of dimethyl carbonate in the solvent is 55 wt % to 70 wt %, thereby improving the electrolyte wettability of the electrode assembly and enabling the secondary battery cell to have good cycle performance.

[0025] In some embodiments, the solvent further comprises one or both of ethylene carbonate and ethyl methyl carbonate. This allows the electrolyte to have good fluidity, high ionic conductivity and a wide electrochemical window, thereby enabling the secondary battery cell to have better cycle performance.

[0026] Optionally, the mass percentage of the ethylene carbonate in the solvent is less than or equal to 25 wt %.

[0027] Optionally, the mass percentage of the ethyl methyl carbonate in the solvent is less than or equal to 25 wt %.

[0028] In some embodiments, the electrolyte further includes an additive, wherein the additive includes one or both of fluoroethylene carbonate and vinylene carbonate.

[0029] The additives can participate in the formation of a solid electrolyte interface film on the surface of the negative electrode, thereby helping to improve the cycle performance of the secondary battery cell.

[0030] In some embodiments, the viscosity of the electrolyte at 25° C. is less than or equal to 5 mPa·s, and can be optionally less than or equal to 3 mPa·s.

[0031] In some embodiments, the conductivity of the electrolyte at 25° C. is 8 mS / cm-16 mS / cm, optionally 9 mS / cm-12 mS / cm.

[0032] In some embodiments, the first and second pressure relief mechanisms are symmetrically arranged, thereby aligning the discharge path of the exhaust gas in a straight line, thereby facilitating the rapid discharge of the exhaust gas from the secondary battery cell, achieving the purpose of pressure relief in a short period of time, and thereby effectively reducing or even preventing safety accidents such as fire and explosion of the secondary battery cell.

[0033] In some embodiments, the shapes of the first pressure relief mechanism and the second pressure relief mechanism are independently circular, elliptical, or racetrack.

[0034] In some embodiments, the first end cover assembly includes a first cover plate, and the first pressure relief mechanism is located on the first cover plate or the first pressure relief mechanism is formed integrally with the first cover plate.

[0035] In some embodiments, the second end cover assembly includes a second cover plate, and the second pressure relief mechanism is located on the second cover plate or the second pressure relief mechanism is formed integrally with the second cover plate.

[0036] In some embodiments, the first end cap assembly includes a first electrode terminal, the second end cap assembly includes a second electrode terminal, the polarity of the first electrode terminal and the second electrode terminal are opposite, the distance between the geometric center point of the first pressure relief mechanism and the geometric center point of the first electrode terminal is 6mm-14mm; and / or, the distance between the geometric center point of the second pressure relief mechanism and the geometric center point of the second electrode terminal is 6mm-14mm.

[0037] In some embodiments, the electrode assembly includes a positive electrode plate, the positive electrode plate includes a positive electrode current collector and a positive electrode film layer located on at least one surface of the positive electrode current collector, the positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes one or more of lithium-containing phosphates and lithium transition metal oxides; optionally, the positive electrode active material includes a lithium-containing phosphate, and the mass proportion of the lithium-containing phosphate in the positive electrode active material is greater than or equal to 60wt%.

[0038] In some embodiments, the coating weight of the positive electrode film is greater than or equal to 16 mg / cm 2 , optional 18mg / cm 2 -25mg / cm 2 .

[0039] In some embodiments, the compaction density of the positive electrode film is greater than or equal to 2.2 g / cm 3 , optional 2.25g / cm 3 -2.6g / cm 3 .

[0040] In a second aspect, the present disclosure provides a secondary battery comprising the secondary battery cell according to the first aspect of the present disclosure.

[0041] In a third aspect, the present disclosure provides an electrical device comprising the secondary battery according to the second aspect of the present disclosure. The secondary battery is used to provide electrical energy.

[0042] The electric device of the present disclosure includes the secondary battery provided by the present disclosure, and thus has at least the same advantages as the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] To more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the embodiments of the present disclosure. Obviously, the drawings described below are only some embodiments of the present disclosure, and those skilled in the art can derive other drawings based on the drawings without inventive effort.

[0044] FIG1 is a schematic structural diagram of a vehicle provided in some embodiments of the present disclosure.

[0045] FIG2 is a schematic diagram of an explosion of a secondary battery provided in some embodiments of the present disclosure.

[0046] FIG3 is a schematic diagram of an explosion of the battery module shown in FIG2 .

[0047] FIG4 is a schematic diagram of an explosion of a secondary battery cell provided by some embodiments of the present disclosure.

[0048] FIG5 is a schematic structural diagram of a first end cover assembly provided in some embodiments of the present disclosure.

[0049] FIG6 is a schematic structural diagram of a second end cover assembly provided in some embodiments of the present disclosure.

[0050] FIG7 is a schematic diagram showing the connection between the first pressure relief mechanism and the first cover plate provided in some embodiments of the present disclosure.

[0051] FIG8 is a schematic diagram showing the connection between the second pressure relief mechanism and the second cover plate provided in some embodiments of the present disclosure.

[0052] In the accompanying drawings, the drawings are not necessarily drawn to scale.

[0053] The accompanying drawings are described as follows: 1. Vehicle; 2. Secondary battery; 3. Controller; 4. Motor; 5. Box; 5a. First box part; 5b. Second box part; 5c. Accommodation space; 6. Battery module; 7. Secondary battery cell; 8. First end cover assembly; 81. First pressure relief mechanism; 811. First pressure relief part; 812. First connecting part; 82. First electrode terminal; 83. First cover plate; 84. Liquid injection hole; 9. Second end cover assembly; 91. Second pressure relief mechanism; 911. Second pressure relief part; 912. Second connecting part; 92. Second electrode terminal; 93. Second cover plate; 10. Cylindrical shell. DETAILED DESCRIPTION

[0054] Below, the embodiments of the secondary battery cell, secondary battery, and electrical device disclosed in the present invention are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be 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 description are provided for those skilled in the art to fully understand the present disclosure and are not intended to limit the subject matter described in the claims.

[0055] " scope " disclosed in the present disclosure is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and selected lower limit and upper limit define the boundary of special scope.The scope that this mode limits can be to include end value or not include end value, and can be combined arbitrarily, and promptly any lower limit can form a scope with any upper limit combination.For example, if the scope of 60-120 and 80-110 is listed for specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected.In addition, if the minimum range value 1 and 2 listed, and if the maximum range value 3,4 and 5 listed, then the following scope can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5.In the present disclosure, unless otherwise specified, numerical range " ab " represents the abbreviation of any real number combination between a and b, and wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this 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.

[0056] Unless otherwise specified, all embodiments and optional embodiments of the present disclosure can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure content of the present disclosure.

[0057] Unless otherwise specified, all technical features and optional technical features of the present disclosure can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure content of the present disclosure.

[0058] Unless otherwise specified, all steps of the present disclosure may 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.

[0059] If not otherwise specified, in the present disclosure, the terms "first", "second", etc. are used to distinguish different objects rather than to describe a specific order or a primary-secondary relationship.

[0060] In the present disclosure, the terms "plurality" and "multiplicity" refer to two or more.

[0061] In the description of the embodiments of the present disclosure, unless otherwise specified, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. Furthermore, a first feature being "above," "above," and "above" a second feature may mean that the first feature is directly above or diagonally above the second feature, or simply means that the first feature is at a higher level than the second feature. A first feature being "below," "below," and "below" a second feature may mean that the first feature is directly below or diagonally below the second feature, or simply means that the first feature is at a lower level than the second feature.

[0062] Unless otherwise defined, terms used in the present disclosure have the common meanings that are commonly understood by those skilled in the art.

[0063] Unless otherwise stated, the numerical values ​​of the various parameters mentioned in this disclosure can be measured using various test methods commonly used in the art, for example, they can be measured according to the test methods given in the examples of this disclosure. Unless otherwise stated, the test temperature of each parameter is 25°C.

[0064] The secondary battery mentioned in the embodiments of the present disclosure may be a single physical module including one or more secondary battery cells to provide higher voltage and capacity. For example, the secondary battery mentioned in the present disclosure may include a secondary battery cell, a battery module or a battery pack, etc. A secondary battery cell is the smallest unit that makes up a secondary battery, which can independently realize the function of charging and discharging. When there are multiple secondary battery cells, the multiple secondary battery cells are connected in series, in parallel or in mixed connection through a busbar. In some embodiments, the secondary battery may be a battery module; when there are multiple secondary battery cells, the multiple secondary battery cells are arranged and fixed to form a battery module. In some embodiments, the secondary battery may be a battery pack, which includes a case and secondary battery cells, and the secondary battery cells or battery modules are housed in the case. In some embodiments, the case may serve as part of the chassis structure of a vehicle. For example, part of the case may become at least part of the floor of the vehicle, or part of the case may become at least part of the crossbeam and longitudinal beam of the vehicle.

[0065] In some embodiments, the secondary battery may be an energy storage device, including an energy storage container, an energy storage cabinet, and the like.

[0066] The technical solutions described in the embodiments of the present disclosure are applicable to secondary batteries and electrical devices using the secondary batteries.

[0067] Secondary batteries can be used as power sources or energy storage units for electrical devices. These devices include, but are not limited to, mobile devices (e.g., mobile phones, tablets, laptops), vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks), electric trains, ships, satellites, and energy storage systems.

[0068] The electric device can select the type of secondary battery according to its usage requirements, such as a secondary battery cell, a battery module or a battery pack.

[0069] For the convenience of description, the following embodiments are described by taking a vehicle as an example of an electrical device.

[0070] FIG1 is a schematic structural diagram of a vehicle provided in some embodiments of the present disclosure.

[0071] As shown in FIG1 , a secondary battery 2 is provided inside a vehicle 1. The secondary battery 2 can be provided at the bottom, head, or tail of the vehicle 1. The secondary battery 2 can be used to power the vehicle 1. For example, the secondary battery 2 can serve as an operating power source for the vehicle 1.

[0072] The vehicle 1 may further include a controller 3 and a motor 4 . The controller 3 is used to control the secondary battery 2 to supply power to the motor 4 , for example, to meet the power requirements of the vehicle 1 during startup, navigation, and driving.

[0073] In some embodiments, the secondary battery 2 can serve not only as an operating power source for the vehicle 1 , but also as a driving power source for the vehicle 1 , replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1 .

[0074] FIG2 is an exploded view of a secondary battery according to some embodiments of the present disclosure. As shown in FIG2 , the secondary battery 2 includes a housing 5 and a secondary battery cell (not shown), which is accommodated in the housing 5 .

[0075] The housing 5 is used to house secondary battery cells and can have various structures. In some embodiments, the housing 5 can include a first housing portion 5a and a second housing portion 5b. The first housing portion 5a and the second housing portion 5b overlap each other, and the first housing portion 5a and the second housing portion 5b together define a storage space 5c for accommodating the secondary battery cells. The second housing portion 5b can be a hollow structure with one end open. The first housing portion 5a is a plate-like structure, and the first housing portion 5a overlaps the open side of the second housing portion 5b to form the housing 5 with the storage space 5c. The first housing portion 5a and the second housing portion 5b can also each be a hollow structure with one end open. The open side of the first housing portion 5a overlaps the open side of the second housing portion 5b to form the housing 5 with the storage space 5c. Of course, the first housing portion 5a and the second housing portion 5b can have various shapes, such as a cylinder, a rectangular parallelepiped, etc.

[0076] In order to improve the sealing performance after the first box body 5a and the second box body 5b are connected, a sealing member, such as a sealant, a sealing ring, etc., may also be provided between the first box body 5a and the second box body 5b.

[0077] Assuming that the first box body portion 5a covers the top of the second box body portion 5b, the first box body portion 5a can also be called an upper box cover, and the second box body portion 5b can also be called a lower box body.

[0078] In the secondary battery 2, there can be one or more secondary battery cells. If there are multiple secondary battery cells, they can be connected in series, in parallel, or in a hybrid connection. A hybrid connection refers to a combination of series and parallel connections. Multiple secondary battery cells can be directly connected in series, in parallel, or in a hybrid connection, and then the entire battery system can be housed within the housing 5. Alternatively, multiple secondary battery cells can be first connected in series, in parallel, or in a hybrid connection to form a battery module 6, and then the multiple battery modules 6 can be connected in series, in parallel, or in a hybrid connection to form a single unit, which can then be housed within the housing 5.

[0079] FIG3 is a schematic diagram of an explosion of the battery module shown in FIG2 .

[0080] As shown in FIG3 , in some embodiments, there are multiple secondary battery cells 7, which are first connected in series, parallel, or in series to form a battery module 6. The multiple battery modules 6 are then connected in series, parallel, or in series to form a whole and housed in a box.

[0081] The multiple secondary battery cells 7 in the battery module 6 can be electrically connected via a busbar component to achieve parallel connection, series connection, or mixed connection of the multiple secondary battery cells 7 in the battery module 6 .

[0082] The secondary battery cells mentioned in the embodiments of the present disclosure may include lithium-ion secondary battery cells.

[0083] Figure 4 is an exploded view of a secondary battery cell according to some embodiments of the present disclosure. Figure 5 is a structural diagram of a first end cap assembly according to some embodiments of the present disclosure. Figure 6 is a structural diagram of a second end cap assembly according to some embodiments of the present disclosure.

[0084] As shown in Figures 4 to 6, the secondary battery cell 7 includes a cylindrical housing 10, an electrode assembly (not shown), a first end cap assembly 8, and a second end cap assembly 9. The cylindrical housing 10 has a receiving cavity and a first opening and a second opening communicating with the receiving cavity. The electrode assembly is placed within the receiving cavity. The first end cap assembly 8 covers the first opening, and the second end cap assembly 9 covers the second opening. The first end cap assembly 8 includes a first pressure relief mechanism 81, and the second end cap assembly 9 includes a second pressure relief mechanism 91.

[0085] The secondary battery cell 7 further includes an electrolyte, the electrolyte includes a solvent, the solvent includes dimethyl carbonate (DMC), and the mass percentage of dimethyl carbonate in the solvent is greater than or equal to 50 wt %.

[0086] The first pressure relief mechanism 81 has a first pressure relief portion. The area of ​​the first pressure relief portion is denoted as S1 in mm. 2 The second pressure relief mechanism 91 has a second pressure relief portion, the area of ​​the second pressure relief portion is denoted as S2, in mm 2 The capacity of the secondary battery cell 7 is recorded as C0, in Ah, and the secondary battery cell 7 satisfies (S1 + S2) / C0 is greater than or equal to 2.5mm 2 / Ah.

[0087] With the widespread use of cylindrical secondary battery cells, the demand for their capacity is getting higher and higher, so the size of the secondary battery cells is also being designed to be larger and larger, which easily leads to the problem of electrolyte infiltration, thereby affecting the service life of the secondary battery cells.

[0088] The disclosed embodiment can make the electrolyte have a low viscosity by making the mass percentage of dimethyl carbonate in the electrolyte solvent greater than or equal to 50wt%, thereby facilitating the flow of the electrolyte, thereby improving the electrolyte wettability of the electrode assembly and enhancing the cycle performance of the secondary battery cell. However, when the mass percentage of dimethyl carbonate in the electrolyte solvent is greater than or equal to 50wt%, the electrochemical window of the electrolyte is generally low, and the electrolyte is more likely to decompose and produce gas during the use of the secondary battery cell and when the secondary battery cell is abused, resulting in a large amount of gas inside the secondary battery cell. If the gas generated inside the secondary battery cell cannot be removed in time, it will squeeze the electrode assembly and affect the electrolyte wettability of the electrode assembly. In severe cases, fire, explosion and other safety accidents may occur.

[0089] Currently, secondary battery cell designs often incorporate a pressure relief mechanism. When a secondary battery cell is misused, side reactions within the cell increase, and as a result, the gas generated by these reactions increases. This pressure relief mechanism is designed to release the gas within the cell. However, in practical applications, the pressure relief mechanism often fails to release pressure promptly or at a slow rate, making it susceptible to fires, explosions, and other safety incidents.

[0090] A pressure relief mechanism is an element or component that activates to release the internal pressure of a secondary battery cell when the internal pressure reaches a predetermined threshold. This threshold varies depending on the design requirements of the secondary battery cell. The pressure relief mechanism can take the form of an explosion-proof valve, air valve, pressure relief valve, or safety valve, and can specifically employ a pressure-sensitive element or structure. Specifically, when the internal pressure of a secondary battery cell reaches a predetermined threshold, the pressure relief mechanism activates or a weak structure within the pressure relief mechanism ruptures, thereby creating an opening or channel for the internal pressure to be released.

[0091] The term "activation" as used in this disclosure refers to the action of the pressure relief mechanism or its activation to a certain state, thereby releasing the internal pressure of the secondary battery cell. The action of the pressure relief mechanism may include, but is not limited to, at least a portion of the pressure relief mechanism rupturing, breaking, tearing, or opening. When the pressure relief mechanism is activated, the gas inside the secondary battery cell is discharged from the activated portion as exhaust. In this way, the pressure of the secondary battery cell can be relieved under controllable pressure, thereby reducing the potential for more serious safety accidents such as fire and explosion.

[0092] The emissions from the interior of the secondary battery cells mentioned in the present disclosure include, but are not limited to: electrolyte, dissolved or split pole pieces, fragments of the separator, gases generated by the reaction, etc.

[0093] The disclosed embodiments provide pressure relief mechanisms at both ends of the secondary battery cell, facilitating the rapid expulsion of waste from the cell, achieving short-term pressure relief. Furthermore, the waste ejected from the two pressure relief mechanisms exerts opposite impact forces on the cylindrical housing, thereby reducing the risk of deformation and tearing of the secondary battery cell.

[0094] As the capacity of a secondary battery cell increases, the gas production of the secondary battery cell generally increases accordingly, especially under abuse conditions, where gas production of the secondary battery cell increases further. By adjusting the pressure relief area per unit capacity, i.e., (S1+S2) / C0 within the above range, it helps to achieve a dynamic balance between the gas production and exhaust volume of the secondary battery cell, thereby effectively reducing or even preventing safety accidents such as fires and explosions of the secondary battery cell.

[0095] Therefore, the secondary battery cell provided by the embodiment of the present disclosure has good electrolyte wettability, thereby making the secondary battery cell have good cycle performance. In addition, the secondary battery cell provided by the embodiment of the present disclosure can also quickly release pressure under abuse conditions, thereby making the secondary battery cell have high reliability.

[0096] The capacity C0 of a secondary battery cell can be obtained by testing as follows: at 25°C, allow the secondary battery cell to stand for 5 minutes, and discharge it at a constant current of 0.33C to the lower cut-off voltage; after standing for 5 minutes, charge it at a constant current of 0.33C to the upper cut-off voltage, and then charge it at a constant voltage at the upper cut-off voltage to a current of 0.05C; after standing for 5 minutes, discharge it at a constant current of 0.33C to the lower cut-off voltage, and record the discharge capacity at this time, which is the capacity C0 of the secondary battery cell.

[0097] The upper cut-off voltage and the lower cut-off voltage may adopt the charge and discharge voltages recommended in the product specification of the secondary battery cell.

[0098] For example, when the positive electrode active material includes lithium iron phosphate and the negative electrode active material includes graphite, the upper cutoff voltage of the secondary battery cell may be 3.65V and the lower cutoff voltage may be 2.5V.

[0099] For example, the positive electrode active material includes a lithium transition metal oxide with a molar ratio of Ni of less than 0.8, such as LiNi 0.5 Co 0.2 Mn 0.3 When the negative electrode active material includes graphite, the upper cutoff voltage of the secondary battery cell can be 4.35V, and the lower cutoff voltage can be 2.8V.

[0100] For example, the positive electrode active material includes a lithium transition metal oxide with a molar ratio of Ni greater than or equal to 0.8, such as LiNi 0.8 Co 0.1 Mn 0.1 O2、LiNi 0.8 Co 0.15 Al 0.05 O2、LiNi 0.9 Co 0.06 Mn 0.04 When the negative electrode active material includes graphite, the upper cutoff voltage of the secondary battery cell can be 4.25V, and the lower cutoff voltage can be 2.8V.

[0101] The molar ratio of Ni element refers to the ratio of the molar amount of Ni element in the lithium transition metal oxide to the total molar amount of transition metal elements.

[0102] When the internal pressure of a secondary battery cell reaches a predetermined threshold, the pressure relief mechanism activates or a weak structure within the pressure relief mechanism ruptures, thereby forming an opening or channel through which the internal pressure can be released. The area S1 of the first pressure relief portion of the first pressure relief mechanism refers to the maximum area of ​​the opening or channel formed by the first pressure relief mechanism for internal pressure release. The area S2 of the second pressure relief portion of the second pressure relief mechanism refers to the maximum area of ​​the opening or channel formed by the second pressure relief mechanism for internal pressure release.

[0103] Secondary battery cell 7 satisfies (S1+S2) / C0 greater than or equal to 2.5mm 2 / Ah, for example, it can be 2.8mm 2 / Ah, 3.0mm 2 / Ah, 3.2mm 2 / Ah, 3.4mm 2 / Ah, 3.6mm 2 / Ah, 3.8mm 2 / Ah, 4.0mm 2 / Ah, 4.2mm 2 / Ah, 4.4mm 2 / Ah, 4.5mm 2 / Ah, 4.8mm 2 / Ah, 5.0mm 2 / Ah, 5.2mm 2 / Ah, 5.5mm 2 / Ah, or any range consisting of the above values.

[0104] Optionally, (S1+S2) / C0 is 4.0 mm 2 / Ah-5.5mm 2 / Ah,4.0mm 2 / Ah-5.0mm 2 / Ah.

[0105] By adjusting the pressure relief area per unit capacity, i.e., (S1+S2) / C0, within the above range, it helps achieve a dynamic balance between the gas production and exhaust volume of the secondary battery cells, thereby effectively reducing or even preventing safety accidents such as fires and explosions in the secondary battery cells. At the same time, it also improves the processing performance of the end cap assembly. A larger pressure relief area increases the difficulty of processing the end cap assembly, which is not conducive to reducing the cost of the secondary battery cells or promoting large-scale production of secondary battery cells.

[0106] Optionally, the mass percentage of dimethyl carbonate in the solvent may be 55 wt % to 70 wt %, thereby improving the electrolyte wettability of the electrode assembly and enabling the secondary battery cell to have good cycle performance.

[0107] In some embodiments, the solvent further comprises one or both of ethylene carbonate (EC) and ethyl methyl carbonate (EMC). Alternatively, the solvent further comprises both ethylene carbonate (EC) and ethyl methyl carbonate (EMC).

[0108] Dimethyl carbonate can make the electrolyte have low viscosity, which facilitates the flow of the electrolyte, but its ability to dissolve electrolyte salts is weak. By mixing it with ethylene carbonate and / or ethyl methyl carbonate, the electrolyte can have good fluidity while also having high ionic conductivity and a wide electrochemical window, thereby making the secondary battery monomer have better cycle performance.

[0109] Optionally, the mass percentage of ethylene carbonate in the solvent may be greater than 0 and less than or equal to 25 wt %.

[0110] Optionally, the mass percentage of ethyl methyl carbonate in the solvent may be greater than 0 and less than or equal to 25 wt %.

[0111] In some embodiments, the solvent includes dimethyl carbonate (DMC), ethylene carbonate (EC), and ethyl methyl carbonate (EMC), wherein the mass percentage of dimethyl carbonate in the solvent may be 55 wt%-70 wt%, the mass percentage of ethylene carbonate in the solvent may be 5 wt%-25 wt%, and the mass percentage of ethyl methyl carbonate in the solvent may be 5 wt%-25 wt%. This allows the electrolyte to have good fluidity, high ionic conductivity, and a wide electrochemical window, thereby enabling the secondary battery cell to have better cycle performance.

[0112] In some embodiments, the electrolyte further includes an electrolyte salt. Optionally, the electrolyte salt may include, but is not limited to, one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalatophosphate) (LiDFOP), and lithium tetrafluorooxalatophosphate (LiTFOP).

[0113] In some embodiments, the electrolyte may further include additives, which may include but are not limited to one or both of fluoroethylene carbonate (FEC) and vinylene carbonate (VC). Optionally, the additives may include both fluoroethylene carbonate (FEC) and vinylene carbonate (VC).

[0114] Optionally, based on the total mass of the electrolyte, the mass percentage of fluoroethylene carbonate (FEC) is less than or equal to 5 wt %, and can be optionally 0.05 wt %-5 wt %, or 0.1 wt %-3 wt %.

[0115] Optionally, based on the total mass of the electrolyte, the mass percentage of vinylene carbonate (VC) is less than or equal to 5 wt %, and can be optionally 0.05 wt %-5 wt %, or 0.1 wt %-3 wt %.

[0116] The additives can participate in the formation of a solid electrolyte interface film on the surface of the negative electrode, thereby helping to improve the cycle performance of the secondary battery cell.

[0117] In some embodiments, the viscosity of the electrolyte at 25° C. may be greater than 0 and less than or equal to 5 mPa·s, and may be greater than 0 and less than or equal to 3 mPa·s. This helps improve the electrolyte wettability of the electrode assembly and ensures good cycle performance of the secondary battery cell.

[0118] The viscosity of the electrolyte can be measured using a viscometer. The shear force applied to the rotor as it rotates continuously at a constant speed in the sample causes the spring to generate torque, which is proportional to the viscosity, thus providing the viscosity value of the sample.

[0119] For example, the viscosity of an electrolyte can be tested as follows: Under ambient humidity conditions of <80%, take a 30mL sample and place it in a water bath at 25°C for at least 30 minutes. Place a spindle (e.g., No. 18) in the sample cup and add the sample to a point approximately 0.3cm from the cup opening. Start the connected viscometer and rotate at 70 RPM for 5 minutes before reading the viscosity value. Ten data points can be collected and averaged during the test. The test instrument can be a Brookfield DV-2TLV viscometer.

[0120] In some embodiments, the conductivity of the electrolyte at 25° C. may be 8 mS / cm-16 mS / cm, optionally 9 mS / cm-12 mS / cm.

[0121] The conductivity of the electrolyte can be measured using a conductivity meter. For example, an appropriate amount of electrolyte can be taken and divided into three equal parts. The conductivity of each sample is then measured at 25°C using a conductivity meter. The average of the test results is then taken as the conductivity of the electrolyte. The measuring instrument can be a DDS-307 conductivity meter.

[0122] In some embodiments, the electrolyte retention coefficient may be 2.5 g / Ah-4.2 g / Ah, and may be optionally 2.8 g / Ah-3.5 g / Ah.

[0123] The electrolyte retention coefficient refers to the ratio of the electrolyte retention volume to the capacity C0 of the secondary battery cell.

[0124] The electrolyte retention capacity can be tested as follows: Weigh the secondary battery cell, recording its mass as m0. Then, disassemble the secondary battery cell and centrifuge to separate the electrolyte. Immerse all disassembled solid components in acetonitrile for 2 hours, remove them, air dry at room temperature, and bake them in a 60°C oven for at least 4 hours. Weigh them again, recording their mass as m1. The difference between m0 and m1 is the electrolyte retention capacity.

[0125] The components and their contents in the electrolyte can be measured using conventional methods in the art. For example, the mass percentage of the electrolyte salt in the electrolyte can be measured using ion chromatography (IC), and the mass percentage of dimethyl carbonate (DMC) in the solvent can be measured using gas chromatography-mass spectrometry (GC-MS).

[0126] The electrolyte can be sampled and analyzed during the preparation process, or it can be obtained by discharging, disassembling and centrifuging the prepared secondary battery cells.

[0127] As shown in Figure 5, in some embodiments, the first end cover assembly 8 includes a first cover plate 83, which covers the first opening. The first cover plate 83 can be of various structures, such as a plate-shaped structure.

[0128] The first pressure relief mechanism 81 can be located on the first cover plate 83. For example, the first pressure relief mechanism 81 and the first cover plate 83 can be two components provided separately, and the two are connected by welding, riveting, bonding or other means. The first cover plate 83 has a first through hole, and the first pressure relief mechanism 81 can be located in the first through hole. Figure 7 is a schematic diagram of the connection between the first pressure relief mechanism and the first cover plate provided in some embodiments of the present disclosure. As shown in Figure 7, the first pressure relief mechanism 81 can be located on the first cover plate 83. The first pressure relief mechanism 81 includes a first pressure relief portion 811 and a first connecting portion 812 arranged on the periphery of the first pressure relief portion 811. The first connecting portion 812 can be arranged on the side wall of the first through hole by welding, riveting, bonding or other means.

[0129] Alternatively, the first pressure relief mechanism 81 is formed integrally with the first cover plate 83 . For example, the first pressure relief mechanism 81 may be a part of the first cover plate 83 .

[0130] As shown in Figure 6, in some embodiments, the second end cover assembly 9 includes a second cover plate 93, which covers the second opening. The second cover plate 93 can be of various structures, such as a plate-shaped structure.

[0131] The second pressure relief mechanism 91 is located on the second cover plate 93. For example, the second pressure relief mechanism 91 and the second cover plate 93 can be two components provided separately, and the two are connected by welding, riveting, bonding or other means. The second cover plate 93 has a second through hole, and the second pressure relief mechanism 91 can be located in the second through hole. Figure 8 is a schematic diagram of the connection between the second pressure relief mechanism and the second cover plate provided in some embodiments of the present disclosure. As shown in Figure 8, the second pressure relief mechanism 91 can be located on the second cover plate 93. The second pressure relief mechanism includes a second pressure relief portion 911 and a second connecting portion 912 arranged on the periphery of the second pressure relief portion 911. The second connecting portion 912 can be arranged on the side wall of the second through hole by welding, riveting, bonding or other means. Alternatively, the second pressure relief mechanism 91 can be formed integrally with the second cover plate 93. For example, the second pressure relief mechanism 91 can be a part of the second cover plate 93.

[0132] In some embodiments, the area of ​​the first pressure relief portion can be smaller than the area of ​​the first pressure relief mechanism, and the area of ​​the second pressure relief portion can be smaller than the area of ​​the second pressure relief mechanism. As shown in Figures 7 and 8, the area of ​​the first pressure relief portion 811 is smaller than the area of ​​the first pressure relief mechanism 81, and the area of ​​the second pressure relief portion 911 is smaller than the area of ​​the second pressure relief mechanism 91.

[0133] In some embodiments, the area of ​​the first pressure relief portion may be equal to the area of ​​the first pressure relief mechanism, and the area of ​​the second pressure relief portion may be equal to the area of ​​the second pressure relief mechanism.

[0134] In some embodiments, the axial dimension of the secondary battery cell 7 is denoted as L, in mm; the secondary battery cell 7 satisfies (S1+S2) / L greater than or equal to 0.6 mm, for example, it can be 0.6 mm, 0.63 mm, 0.66 mm, 0.69 mm, 0.7 mm, 0.74 mm, 0.77 mm, 0.8 mm, 0.82 mm, 0.84 mm, 0.86 mm, 0.88 mm, 0.9 mm, or a range consisting of any of the above values.

[0135] Optionally, (S1+S2) / L may be 0.7 mm to 0.9 mm.

[0136] Secondary battery cell 7 is a cylindrical secondary battery cell. The axial direction of secondary battery cell 7 refers to the direction of the central axis of rotation of the cylinder, i.e., the direction shared by the central axis. The radial direction of secondary battery cell 7 is perpendicular to the axial direction and is the direction of the diameter of the end face of the cylinder. The axial dimension of secondary battery cell 7 is generally referred to as the length of secondary battery cell 7.

[0137] The axial dimension L of the secondary battery cell 7 refers to the distance between the outer surface of the first end cap assembly 8 and the outer surface of the second end cap assembly 9, that is, the distance between the outer surface of the first cover plate 83 and the outer surface of the second cover plate 93. It will be understood that the axial dimension L of the secondary battery cell 7 does not include the dimensions of the electrode terminals.

[0138] As the axial dimension of the secondary battery cell increases, the exhaust path of the secondary battery cell becomes longer. By adjusting the area of ​​the pressure relief portion corresponding to the unit length, that is, (S1+S2) / L within the above range, it helps to quickly discharge the emissions inside the secondary battery cell and achieve the purpose of pressure relief in a short time, thereby effectively reducing or even avoiding safety accidents such as fire and explosion in the secondary battery cell.

[0139] In some embodiments, the ratio of the area of ​​the first pressure relief portion to the area of ​​the second pressure relief portion may be 0.8-1.2.

[0140] In some embodiments, the area of ​​the first pressure relief portion may be equal to the area of ​​the second pressure relief portion.

[0141] In some embodiments, the ratio of the area of ​​the first pressure relief portion to the area of ​​the first end cover assembly 8 may be greater than or equal to 0.02:1, and may be (0.04-0.10):1 or (0.06-0.08):1.

[0142] This helps to quickly discharge the emissions inside the secondary battery cell and achieve the purpose of pressure relief in a short time, thereby effectively reducing or even avoiding safety accidents such as fire and explosion in the secondary battery cell; at the same time, it can also make the first end cover assembly have good processing performance.

[0143] In some embodiments, the ratio of the area of ​​the second pressure relief portion to the area of ​​the second end cover assembly 9 may be greater than or equal to 0.02:1, and may be (0.04-0.10):1 or (0.06-0.08):1.

[0144] This helps to quickly discharge the emissions inside the secondary battery cell and achieve the purpose of pressure relief in a short time, thereby effectively reducing or even avoiding safety accidents such as fire and explosion in the secondary battery cell; at the same time, it can also make the second end cover assembly have good processing performance.

[0145] The electrode assembly includes a main body and a lug portion extending axially from the main body. The lug portion is used to lead the current generated by the main body. The main body is the core part of the secondary battery cell to realize the charging and discharging functions. The main body usually includes a positive electrode sheet, a negative electrode sheet, and a separator. When preparing the electrode assembly, the positive electrode sheet, the separator, and the negative electrode sheet are usually connected to the winding needle first, and then the winding needle is rotated to wind the positive electrode sheet, the separator, and the negative electrode sheet on the winding needle. After the winding is completed, the winding needle is pulled out to form a cylindrical electrode assembly. After the winding needle is pulled out, a center hole is usually formed at the winding center of the electrode assembly.

[0146] In some embodiments, the center of the electrode assembly has a central hole extending along the axial direction of the secondary battery cell, and the diameter of the central hole is greater than or equal to 5 mm, and can be optionally 6 mm-8 mm.

[0147] By adjusting the diameter of the center hole within the above range, it is helpful to quickly discharge the emissions inside the secondary battery cell and achieve the purpose of pressure relief in a short time, thereby effectively reducing or even avoiding safety accidents such as fire and explosion of the secondary battery cell.

[0148] In some embodiments, the first pressure relief mechanism 81 and the second pressure relief mechanism 91 are symmetrically arranged. This allows the discharge path of the exhaust to be in a straight line, thereby facilitating the rapid discharge of the exhaust from the secondary battery cell, achieving the purpose of pressure relief in a short period of time, and thus effectively reducing or even preventing safety accidents such as fire and explosion of the secondary battery cell.

[0149] In some embodiments, the shapes of the first pressure relief mechanism 81 and the second pressure relief mechanism 91 independently include a circle, an ellipse, or a racetrack.

[0150] In some embodiments, the first end cap assembly 8 includes a first electrode terminal 82, and the second end cap assembly 9 includes a second electrode terminal 92. The first electrode terminal 82 and the second electrode terminal 92 have opposite polarities. The first electrode terminal 82 can be mounted on the first cover plate 83, and the second electrode terminal 92 can be mounted on the second cover plate 93.

[0151] The first electrode terminal 82 and the second electrode terminal 92 are used to be electrically connected to the electrode assembly to output the electrical energy generated by the electrode assembly.

[0152] In some embodiments, there may be two electrode tabs. The two electrode tabs are defined as a positive electrode tab and a negative electrode tab, respectively. The two electrode tabs are electrically connected to the first electrode terminal 82 and the second electrode terminal 92, respectively. The electrode tabs may be directly connected to the first electrode terminal 82 and the second electrode terminal 92 by welding or other means, or indirectly connected to the first electrode terminal 82 and the second electrode terminal 92 via other components.

[0153] Alternatively, the first electrode terminal 82 may be a positive terminal, and the second electrode terminal may be a negative terminal.

[0154] Optionally, the positive electrode tab is electrically connected to the first electrode terminal 82 , and the negative electrode tab is electrically connected to the second electrode terminal 92 .

[0155] In some embodiments, the distance between the geometric center point of the first pressure relief mechanism 81 and the geometric center point of the first electrode terminal 82 may be greater than or equal to 5 mm, and may be 6 mm to 14 mm.

[0156] In some embodiments, the distance between the geometric center point of the second pressure relief mechanism 91 and the geometric center point of the second electrode terminal 92 may be greater than or equal to 5 mm, and may be 6 mm to 14 mm.

[0157] In some embodiments, a liquid injection hole 84 is provided on one of the first cover plate 83 and the second cover plate 93. As shown in Figures 4 and 5, the liquid injection hole 84 is provided on the first cover plate 83.

[0158] The injection hole is used to inject electrolyte into the secondary battery cell.

[0159] In some embodiments, the diameter of the secondary battery cell 7 may be greater than or equal to 40 mm, and may be 45 mm to 60 mm, thereby enabling the secondary battery cell to have a high capacity.

[0160] In some embodiments, the axial dimension of the secondary battery cell 7 may be greater than or equal to 130 mm, and may be 150 mm-320 mm, 200 mm-320 mm, 240 mm-320 mm, or 280 mm-320 mm, thereby enabling the secondary battery cell to have a high capacity.

[0161] In some embodiments, the capacity C0 of the secondary battery cell 7 may be greater than or equal to 20 Ah, and may optionally be greater than or equal to 30 Ah.

[0162] In some embodiments, the material of the cylindrical housing 10 may include but is not limited to hard plastic, aluminum, or steel.

[0163] [Positive electrode]

[0164] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer located on at least one side of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0165] The positive electrode active material is capable of extracting and inserting lithium ions.

[0166] In some embodiments, the positive electrode active material may include one or more of lithium-containing phosphates and lithium transition metal oxides.

[0167] The lithium-containing phosphate may include one or more of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, and their respective modified compounds. Examples of lithium transition metal oxides may include one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds. The modified compounds of the above-mentioned positive electrode active materials may be doping-modified and / or surface-coated to modify the positive electrode active materials.

[0168] Alternatively, the positive electrode active material may include a lithium-containing phosphate. More preferably, the positive electrode active material may include one or more of lithium iron phosphate and its modified compounds. Alternatively, the modified lithium iron phosphate compound may be obtained by one or more modification methods selected from element doping, conductive carbon coating, conductive metal coating, and conductive polymer coating.

[0169] In some embodiments, the positive electrode active material may include a lithium-containing phosphate, and the mass proportion of the lithium-containing phosphate in the positive electrode active material may be greater than or equal to 60wt%, for example, it may be 60wt%, 70wt%, 80wt%, 90wt%, 100wt%, or a range consisting of any of the above values.

[0170] In some embodiments, the positive electrode active material may include both lithium-containing phosphate and lithium transition metal oxide. The mass proportion of lithium-containing phosphate in the positive electrode active material may be 60wt%-99wt%, and the mass proportion of lithium transition metal oxide in the positive electrode active material may be 1wt%-40wt%.

[0171] In some embodiments, the volume distribution particle size Dv50 of the positive electrode active material may be 0.8 μm to 10 μm.

[0172] By adjusting the volume distribution particle size Dv50 of the positive electrode active material within the above range, the side reactions of the secondary battery monomer can be reduced, the capacity attenuation rate of the secondary battery monomer can be reduced, and the secondary battery monomer can have a long cycle life.

[0173] In some embodiments, the positive electrode film layer may further include a positive electrode conductive agent. As an example, the positive electrode conductive agent may include, but is not limited to, one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0174] In some embodiments, the positive electrode film layer may further include a positive electrode binder. As an example, the positive electrode binder may include, but is not limited to, one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic resin.

[0175] In some embodiments, the coating weight of the positive electrode film layer can be greater than or equal to 16 mg / cm 2 , optional 18mg / cm 2 -25mg / cm 2 This allows the secondary battery cell to have a high energy density.

[0176] In some embodiments, the compaction density of the positive electrode film layer can be greater than or equal to 2.2 g / cm 3 For example, the compaction density of the positive electrode active layer is 2.25 g / cm 3 -2.6g / cm 3 This allows the secondary battery cell to have a high energy density.

[0177] The compacted density of the positive electrode film refers to the ratio of the surface density of the positive electrode film to its thickness. The surface density of the positive electrode film refers to the ratio of the weight of the positive electrode film after coating, drying, and rolling to the coating area.

[0178] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include, but is not limited to, one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include, but is not limited to, one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0179] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, drying it, and rolling it. The positive electrode slurry is typically formed by dispersing the positive electrode active material, positive electrode binder, and positive electrode conductive agent in a solvent and stirring them uniformly. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0180] [Negative electrode]

[0181] In some embodiments, the negative electrode sheet may include a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0182] In some embodiments, the negative electrode active material may include one or more of a carbon-based material and a silicon-based material.

[0183] Alternatively, the carbon-based material may include, but is not limited to, one or more of artificial graphite and natural graphite.

[0184] Optionally, the silicon-based material may include, but is not limited to, one or more of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy material.

[0185] Optionally, the silicon-based material may further include one or more of an alkali metal element and an alkaline earth metal element. Optionally, the alkali metal element includes Li. Optionally, the alkaline earth metal element includes Mg. As an example, the silicon-based material may be a silicon-based material pre-embedded with Li.

[0186] In some embodiments, the mass proportion of the silicon-based material in the negative electrode active material may be greater than or equal to 5 wt %, and more preferably 8 wt %-20 wt %, thereby improving the energy density of the secondary battery cell.

[0187] In some embodiments, the negative electrode active material may include a carbon-based material and a silicon-based material. The silicon-based material may account for 8% to 20% by weight of the negative electrode active material, and the carbon-based material may account for greater than or equal to 80% by weight of the negative electrode active material. This allows the secondary battery cell to have both high energy density and long cycle life.

[0188] In some embodiments, the volume distribution particle size Dv50 of the negative electrode active material may be 6 μm-15 μm, optionally 8 μm-13 μm.

[0189] By adjusting the volume distribution particle size Dv50 of the negative electrode active material within the above range, the side reactions of the secondary battery monomer can be reduced, so that the secondary battery monomer has a long cycle life.

[0190] In some embodiments, the negative electrode film layer may further include a negative electrode conductive agent. As an example, the negative electrode conductive agent may include, but is not limited to, one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0191] In some embodiments, the negative electrode film layer may further include a negative electrode binder. As examples, the negative electrode binder may include, but is not limited to, one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0192] In some embodiments, the negative electrode film layer may further include other additives, such as thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, and the like.

[0193] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As examples of metal foils, copper foil, copper alloy foil, aluminum foil, and aluminum alloy foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include, but is not limited to, one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include, but is not limited to, one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0194] The negative electrode plate does not exclude other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode plate may further include a conductive primer layer sandwiched between the negative electrode current collector and the negative electrode film layer and located on the surface of the negative electrode current collector. The primer layer may be composed of, for example, a conductive agent and a binder. In some embodiments, the negative electrode plate may further include a protective layer covering the surface of the negative electrode film layer.

[0195] The negative electrode sheet can be prepared by dispersing the negative electrode active material, negative electrode binder, negative electrode conductive agent, and optional other additives in a solvent and stirring them uniformly to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector and, after drying and roll pressing, forms the negative electrode sheet. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0196] The Dv50 of materials (e.g., positive electrode active materials, negative electrode active materials, etc.) is well known in the art and can be measured using instruments and methods known in the art. For example, it can be conveniently measured using a laser particle size analyzer (e.g., the Malvern Mastersizer 3000) in accordance with GB / T 19077-2016. The physical definition of Dv50 is the particle size at which the cumulative volume distribution percentage of a material reaches 50%.

[0197] [Isolation film]

[0198] The separator is located between the positive electrode and the negative electrode, and is mainly used to prevent internal short circuits. The present disclosure does not specifically limit the type of separator, and any known porous structure membrane with good chemical and mechanical stability can be selected.

[0199] In some embodiments, the material of the isolation membrane can include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and polyimide. The isolation membrane can be a single-layer film or a multi-layer composite film. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different.

[0200] Methods for preparing secondary battery cells are well known.

[0201] In some embodiments, the preparation method includes the steps of: providing a cylindrical shell, the cylindrical shell having a accommodating cavity and a first opening and a second opening connected to the accommodating cavity; providing an electrode assembly, and placing the electrode assembly in the cylindrical shell; providing a first end cover assembly and a second end cover assembly, the first end cover assembly including a first pressure relief mechanism, the second end cover assembly including a second pressure relief mechanism, and covering the first opening with the first end cover assembly and covering the second opening with the second end cover assembly; injecting the electrolyte into the secondary battery cell, and then subjecting the secondary battery cell to vacuum packaging, standing, formation and other processes to obtain the secondary battery cell.

[0202] In some embodiments, the positive electrode sheet, the separator and the negative electrode sheet can be connected to a winding needle, and then the winding needle is rotated so that the positive electrode sheet, the separator and the negative electrode sheet are wound on the winding needle. After the winding is completed, the winding needle is pulled out to form a cylindrical electrode assembly.

[0203] Example

[0204] The following examples describe the present disclosure in more detail. These examples are intended to be illustrative only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing, and all instruments used in the examples are commercially available.

[0205] Example 1

[0206] The positive electrode active material lithium iron phosphate (LiFePO4), the binder polyvinylidene fluoride, and the conductive agent Super P are mixed in a mass ratio of 97:2:1, and an appropriate amount of solvent N-methylpyrrolidone (NMP) is added and stirred evenly to obtain a positive electrode slurry. The positive electrode slurry is coated on both surfaces of the positive electrode current collector aluminum foil, dried, and cold pressed to obtain a positive electrode sheet. The coating weight of the positive electrode film is 19.5 mg / cm 2 , compacted density is 2.4g / cm 3 .

[0207] The negative electrode active material artificial graphite, conductive agent Super P, binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose were thoroughly stirred and mixed in an appropriate amount of deionized water as a solvent in a mass ratio of 96.2:0.6:1.3:1.9 to obtain a negative electrode slurry. The negative electrode slurry was coated on both surfaces of the negative electrode current collector copper foil, dried, and cold pressed to obtain a negative electrode sheet. The coating weight of the negative electrode film was 9.4 mg / cm 2 , compacted density is 1.4g / cm 3 .

[0208] The isolation membrane is made of porous PP film.

[0209] Dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) are mixed in a mass ratio of 60:20:20 to obtain an organic solvent, and then LiPF6 is dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1.0 mol / L. Then, fluoroethylene carbonate (FEC) and vinylene carbonate (VC) are added, and the content of FEC is 1wt% of the total mass of the electrolyte, and the content of VC is 1wt% of the total mass of the electrolyte.

[0210] The positive electrode sheet, separator and negative electrode sheet are stacked in sequence and connected to the winding needle, and then the winding needle is rotated to wind the positive electrode sheet, separator and negative electrode sheet on the winding needle. After the winding is completed, the winding needle is pulled out to form a cylindrical electrode assembly.

[0211] The electrode assembly is placed in a cylindrical shell with openings at both ends, and a first end cover assembly and a second end cover assembly are welded to both ends of the cylindrical shell respectively. The first end cover assembly includes a first pressure relief mechanism, and the second end cover assembly includes a second pressure relief mechanism. Then, the electrolyte is injected, and the battery is vacuum packaged, allowed to stand, and formed to obtain a secondary battery cell.

[0212] The capacity C0 of the secondary battery cell is 50.0Ah, the diameter is 46mm, the axial dimension L is 280mm, the diameter of the center hole of the electrode assembly is 8mm, and the area S1 of the first pressure relief part of the first pressure relief mechanism is 112.5mm 2 The area S2 of the second pressure relief portion of the second pressure relief mechanism is 112.5 mm 2 .

[0213] Example 2

[0214] The preparation of the secondary battery cell was the same as that of Example 1 except for the following differences.

[0215] Dimethyl carbonate (DMC) and ethylene carbonate (EC) were mixed in a mass ratio of 80:20 to obtain an organic solvent, and then LiPF6 was dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1.0 mol / L. Then, fluoroethylene carbonate (FEC) and vinylene carbonate (VC) were added, and the content of FEC was 1 wt% of the total mass of the electrolyte, and the content of VC was 1 wt% of the total mass of the electrolyte.

[0216] Comparative Example 1

[0217] The positive electrode active material lithium iron phosphate (LiFePO4), the binder polyvinylidene fluoride, and the conductive agent Super P are mixed in a mass ratio of 97:2:1, and an appropriate amount of solvent N-methylpyrrolidone (NMP) is added and stirred evenly to obtain a positive electrode slurry. The positive electrode slurry is coated on both surfaces of the positive electrode current collector aluminum foil, dried, and cold pressed to obtain a positive electrode sheet. The coating weight of the positive electrode film is 19.5 mg / cm 2 , compacted density is 2.4g / cm 3 .

[0218] The negative electrode active material artificial graphite, conductive agent Super P, binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose were thoroughly stirred and mixed in an appropriate amount of deionized water as a solvent in a mass ratio of 96.2:0.6:1.3:1.9 to obtain a negative electrode slurry. The negative electrode slurry was coated on both surfaces of the negative electrode current collector copper foil, dried, and cold pressed to obtain a negative electrode sheet. The coating weight of the negative electrode film was 9.4 mg / cm 2 , compacted density is 1.4g / cm 3 .

[0219] The isolation membrane is made of porous PP film.

[0220] Dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) were mixed in a mass ratio of 30:50:20 to obtain an organic solvent, and then LiPF6 was dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1.0 mol / L. Then, fluoroethylene carbonate (FEC) and vinylene carbonate (VC) were added, and the content of FEC was 1wt% of the total mass of the electrolyte, and the content of VC was 1wt% of the total mass of the electrolyte.

[0221] The positive electrode sheet, separator and negative electrode sheet are connected to the winding needle, and then the winding needle is rotated to wind the positive electrode sheet, separator and negative electrode sheet on the winding needle. After the winding is completed, the winding needle is pulled out to form a cylindrical electrode assembly.

[0222] The electrode assembly is placed in a cylindrical shell with an open end, and an end cap assembly is welded to the open end of the cylindrical shell. The end cap assembly includes a pressure relief mechanism. Then, the electrolyte is injected, and the battery is vacuum packaged, allowed to stand, and formed to obtain a secondary battery cell.

[0223] The capacity C0 of the secondary battery cell is 50.0Ah, the diameter is 46mm, the axial dimension L is 280mm, the diameter of the center hole of the electrode assembly is 8mm, and the area of ​​the pressure relief part of the pressure relief mechanism is 225.0mm 2 .

[0224] Comparative Example 2

[0225] The preparation of the secondary battery cell was the same as that of Comparative Example 1 except for the following differences.

[0226] Dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) are mixed in a mass ratio of 60:20:20 to obtain an organic solvent, and then LiPF6 is dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1.0 mol / L. Then, fluoroethylene carbonate (FEC) and vinylene carbonate (VC) are added, and the content of FEC is 1wt% of the total mass of the electrolyte, and the content of VC is 1wt% of the total mass of the electrolyte.

[0227] Comparative Example 3

[0228] The preparation of the secondary battery cell was the same as that of Comparative Example 1 except for the following differences.

[0229] The area of ​​the pressure relief part of the pressure relief mechanism is 125.0mm 2 .

[0230] Comparative Example 4

[0231] The preparation of the secondary battery cell was the same as that of Comparative Example 2 except for the following differences.

[0232] The area of ​​the pressure relief part of the pressure relief mechanism is 125.0mm 2 .

[0233] Secondary battery cell performance test

[0234] (1) Capacity test of secondary battery cells

[0235] At 25°C, let the secondary battery cell stand for 5 minutes, discharge it at a constant current of 0.33C to 2.5V; after standing for 5 minutes, charge it at a constant current of 0.33C to 3.65V, and then charge it at a constant voltage to a current of 0.05C; after standing for 5 minutes, discharge it at a constant current of 0.33C to 2.5V, and record the discharge capacity at this time, which is the capacity C0 of the secondary battery cell.

[0236] (2) Energy density test of secondary battery cells

[0237] At 25° C., the secondary battery cell was charged to 3.65 V at a constant current of 0.33 C, and then charged to a current of 0.05 C at a constant voltage. After standing for 5 minutes, the secondary battery cell was discharged to 2.5 V at a constant current of 0.33 C to obtain the discharge energy Q.

[0238] Energy density of a secondary battery cell (Wh / L) = discharge energy Q / volume V of the secondary battery cell.

[0239] The volume V of a secondary battery cell can be calculated according to the volume formula of a cylinder: V = (π × d × d) × L × 0.25. L is the axial dimension of the secondary battery cell, and d is the diameter of the secondary battery cell, both in mm.

[0240] (3) Cycling performance test of secondary battery cells

[0241] At 25°C, charge the battery at a constant current of 1C to an upper cutoff voltage of 3.65V, then charge at a constant voltage to a current of 0.05C. After 5 minutes of rest, discharge the battery at a constant current of 1C to 2.5V. Record the discharge capacity at this point, which is the first cycle discharge capacity. Perform the cyclic charge and discharge test on the battery as described above until the capacity decays to 80% of the first cycle discharge capacity. Record the number of cycles.

[0242] (4) Overcharge performance test of secondary battery cells

[0243] At 25°C, charge the secondary battery cells at a constant current and constant voltage of 0.33C to an upper cutoff voltage of 3.65V, then charge at a constant voltage to a current of 0.05C. Then, charge the secondary battery cells at a constant current of 1C for 1 hour or until the voltage of the secondary battery cells reaches 1.5 times the upper cutoff voltage (i.e., 3.65V). Charging stops when either condition is met, and the cells are left to rest for 1 hour to observe whether the secondary battery cells fail. The criteria for determining whether a secondary battery cell fails are: no fire or explosion. Twenty secondary battery cell samples were collected, and the percentage of secondary battery cells that passed the overcharge test was calculated.

[0244] Table 1

[0245] It can be seen from the test results of Examples 1 to 2 and Comparative Example 1 that by making the mass percentage of dimethyl carbonate in the electrolyte solvent greater than or equal to 50wt%, it is beneficial to the flow of the electrolyte and to improve the electrolyte wettability of the electrode assembly, thereby improving the cycle performance of the secondary battery cell.

[0246] Comparative Examples 1 and 2 only provide a pressure relief mechanism at one end of the secondary battery cell, and the area of ​​the pressure relief portion of the pressure relief mechanism is the same as the total area of ​​the pressure relief portions of the two pressure relief mechanisms of Example 1.

[0247] It can be seen from the test results of Example 1 and Comparative Example 2 that when the capacity of the secondary battery cell and the electrolyte of the secondary battery cell are the same, by providing a pressure relief mechanism at both ends of the secondary battery cell, it is helpful to quickly discharge the emissions inside the secondary battery cell, thereby achieving the purpose of pressure relief in a short time, so that the secondary battery cell can have a high overcharge test pass rate while having good cycle performance.

[0248] It can also be seen from the test results of Comparative Examples 1 to 2 that by reducing the mass percentage of dimethyl carbonate in the electrolyte solvent, the improvement of the overcharge performance of the secondary battery cell is not obvious. This is because when the secondary battery cell is only provided with a pressure relief mechanism at one end, the discharge path of the internal emissions of the secondary battery cell is longer, which leads to the problem of untimely pressure relief and slow pressure relief speed. At the same time, the mass percentage of dimethyl carbonate is reduced, the fluidity of the electrolyte deteriorates, the electrolyte wettability of the electrode assembly deteriorates, and the cycle performance of the secondary battery cell is significantly reduced.

[0249] The test results of Comparative Examples 1 and 3, and Comparative Examples 2 and 4, also show that when a pressure relief mechanism is installed on only one end of a secondary battery cell, increasing the area of ​​the pressure relief portion of the secondary battery cell does not effectively increase the overcharge test ratio of the secondary battery cell. This is because when a pressure relief mechanism is installed on only one end of a secondary battery cell, the discharge path of the secondary battery cell's internal emissions is longer, resulting in delayed and slow pressure relief. Furthermore, due to the limited area of ​​the end cap assembly, the larger the area of ​​the pressure relief portion of the pressure relief mechanism, the more difficult it is to manufacture the end cap assembly, which in turn increases the cost of the secondary battery cell and is not conducive to large-scale production.

[0250] Example 3

[0251] The preparation of the secondary battery cell was the same as that of Example 1 except for the following differences.

[0252] The area S1 of the first pressure relief portion of the first pressure relief mechanism is 125.0 mm 2 The area S2 of the second pressure relief portion of the second pressure relief mechanism is 125.0 mm 2 .

[0253] Example 4

[0254] The preparation of the secondary battery cell was the same as that of Example 1 except for the following differences.

[0255] The area S1 of the first pressure relief portion of the first pressure relief mechanism is 100.0 mm 2The area S2 of the second pressure relief portion of the second pressure relief mechanism is 100.0 mm 2 .

[0256] Example 5

[0257] The preparation of the secondary battery cell was the same as that of Example 1 except for the following differences.

[0258] The area S1 of the first pressure relief portion of the first pressure relief mechanism is 62.5 mm 2 The area S2 of the second pressure relief portion of the second pressure relief mechanism is 62.5 mm 2 .

[0259] Comparative Example 5

[0260] The preparation of the secondary battery cell was the same as that of Example 1 except for the following differences.

[0261] The area S1 of the first pressure relief portion of the first pressure relief mechanism is 50.0 mm 2 The area S2 of the second pressure relief portion of the second pressure relief mechanism is 50.0 mm 2 .

[0262] Table 2

[0263] From the test results in Table 2, it can be seen that by adjusting the ratio of the total area of ​​the pressure relief parts of the two pressure relief mechanisms to the capacity of the secondary battery cell (S1+S2) / C0 to be greater than or equal to 2.5mm 2 / Ah, which can improve the reliability of secondary battery cells.

[0264] The test results in Table 2 also show that the reliability of the secondary battery cell can be further improved by further adjusting the range of the ratio (S1+S2) / L of the total area of ​​the pressure relief parts of the two pressure relief mechanisms to the axial dimension of the secondary battery cell.

[0265] Example 6

[0266] The preparation of the secondary battery cell was the same as that of Example 1 except for the following differences.

[0267] The capacity C0 of the secondary battery cell is 52.5 Ah, the axial dimension L is 320 mm, and the area S1 of the first pressure relief portion of the first pressure relief mechanism is 118.1 mm. 2 The area S2 of the second pressure relief portion of the second pressure relief mechanism is 118.1 mm 2 .

[0268] Example 7

[0269] The preparation of the secondary battery cell was the same as that of Example 1 except for the following differences.

[0270] The capacity C0 of the secondary battery cell is 54.4 Ah, the axial dimension L is 400 mm, and the area S1 of the first pressure relief portion of the first pressure relief mechanism is 122.4 mm 2 The area S2 of the second pressure relief portion of the second pressure relief mechanism is 122.4 mm 2 .

[0271] Table 3

[0272] Compared with Example 1, the diameter of the secondary battery cell of Example 6 and Example 7 remains unchanged, and the size in the axial direction increases. At this time, the capacity of the secondary battery cell will increase. By increasing the area of ​​the pressure relief parts of the two pressure relief mechanisms of Example 6 and Example 7 and making the ratio (S1+S2) / C0 of the total area of ​​the pressure relief parts of the two pressure relief mechanisms to the capacity of the secondary battery cell the same as that of Example 1, the secondary battery cell can have a higher overcharge test pass rate.

[0273] It can also be seen from the test results of Example 1, Example 6 and Example 7 that when the ratio of the total area of ​​the pressure relief parts of the two pressure relief mechanisms to the capacity of the secondary battery cell (S1+S2) / C0 is the same, the ratio of the total area of ​​the pressure relief parts of the two pressure relief mechanisms to the axial dimension of the secondary battery cell (S1+S2) / L increases, which can make the secondary battery cell have a higher overcharge test pass rate.

[0274] Example 8

[0275] The preparation of the secondary battery cell was the same as that of Example 1 except for the following differences.

[0276] The capacity C0 of the secondary battery cell is 51.3Ah, the diameter of the center hole of the electrode assembly is 5mm, and the area S1 of the first pressure relief part of the first pressure relief mechanism is 115.4mm 2 The area S2 of the second pressure relief portion of the second pressure relief mechanism is 115.4 mm 2 .

[0277] Example 9

[0278] The preparation of the secondary battery cell was the same as that of Example 1 except for the following differences.

[0279] The capacity C0 of the secondary battery cell is 52.6Ah, the diameter of the center hole of the electrode assembly is 3mm, and the area S1 of the first pressure relief part of the first pressure relief mechanism is 118.4mm 2 The area S2 of the second pressure relief portion of the second pressure relief mechanism is 118.4 mm 2 .

[0280] Table 4

[0281] The test results in Table 4 also show that when the ratio of the total area of ​​the pressure relief parts of the two pressure relief mechanisms to the capacity of the secondary battery cell (S1+S2) / C0 is the same, by further adjusting the diameter of the center hole, the secondary battery cell can have a higher overcharge test pass rate while having a high energy density.

[0282] It should be noted that the present disclosure is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present disclosure, embodiments having substantially the same structure as the technical concept and exerting the same effects are all included in the technical scope of the present disclosure. In addition, within the scope of the present disclosure, various modifications that can be imagined by those skilled in the art to the embodiments, and other methods constructed by combining some of the constituent elements of the embodiments are also included in the scope of the present disclosure.

Claims

1. A secondary battery cell, wherein: include: A cylindrical shell having a receiving cavity and a first opening and a second opening communicating with the receiving cavity; An electrode assembly is placed in the accommodating cavity; A first end cover assembly, covering the first opening; as well as A second end cover assembly covers the second opening, The first end cap assembly includes a first pressure relief mechanism, and the second end cap assembly includes a second pressure relief mechanism; The secondary battery monomer further comprises an electrolyte, the electrolyte comprises a solvent, the solvent comprises dimethyl carbonate, and the mass percentage of the dimethyl carbonate in the solvent is greater than or equal to 50wt%; The first pressure relief mechanism has a first pressure relief portion, the area of ​​which is denoted as S1 in mm. 2 ; The second pressure relief mechanism has a second pressure relief portion, the area of ​​which is denoted as S2 in units of mm. 2 ; The capacity of the secondary battery cell is recorded as C0, in Ah, and the secondary battery cell satisfies (S1+S2) / C0 greater than or equal to 2.5 mm 2 / Ah.

2. The secondary battery cell according to claim 1, wherein: The secondary battery cell satisfies (S1+S2) / C0 of 4.0 mm 2 / Ah-5.0mm 2 / Ah.

3. The secondary battery cell according to any one of claims 1 to 2, wherein: The axial dimension of the secondary battery cell is denoted as L, in mm; The secondary battery cell satisfies that (S1+S2) / L is greater than or equal to 0.6 mm.

4. The secondary battery cell according to any one of claims 1 to 3, wherein: The secondary battery cell satisfies that (S1+S2) / L is 0.7 mm to 0.9 mm.

5. The secondary battery cell according to any one of claims 1 to 4, wherein: The ratio of the area of ​​the first pressure relief portion to the area of ​​the second pressure relief portion is 0.8-1.2; and / or, The ratio of the area of ​​the first pressure relief portion to the area of ​​the first end cover assembly is greater than or equal to 0.02:1; and / or, The ratio of the area of ​​the second pressure relief portion to the area of ​​the second end cover assembly is greater than or equal to 0.02:

1.

6. The secondary battery cell according to any one of claims 1 to 5, wherein: The ratio of the area of ​​the first pressure relief portion to the area of ​​the first end cover assembly is (0.04-0.10):1; and / or, The ratio of the area of ​​the second pressure relief portion to the area of ​​the second end cover assembly is (0.04-0.10):

1.

7. The secondary battery cell according to any one of claims 1 to 6, wherein: The center of the electrode assembly has a central hole extending in the axial direction of the secondary battery cell, and the diameter of the central hole is greater than or equal to 5 mm.

8. The secondary battery cell according to claim 7, wherein: The diameter of the central hole is 6mm-8mm.

9. The secondary battery cell according to any one of claims 1 to 8, wherein: The diameter of the secondary battery cell is greater than or equal to 40 mm; and / or, The dimension L of the secondary battery cell in the axial direction is greater than or equal to 130 mm; and / or, The capacity C0 of the secondary battery cell is greater than or equal to 20 Ah.

10. The secondary battery cell according to any one of claims 1 to 9, wherein: The diameter of the secondary battery cell is 45 mm to 60 mm; and / or, The dimension L of the secondary battery cell in the axial direction is 150 mm to 320 mm; and / or, The capacity C0 of the secondary battery cell is greater than or equal to 30 Ah.

11. The secondary battery cell according to any one of claims 1 to 10, wherein: The mass percentage of the dimethyl carbonate in the solvent is 55wt%-70wt%.

12. The secondary battery cell according to any one of claims 1 to 11, wherein: The solvent also includes one or both of ethylene carbonate and ethyl methyl carbonate.

13. The secondary battery cell according to claim 12, wherein: The mass percentage of the ethylene carbonate in the solvent is less than or equal to 25wt%; and / or, The mass percentage of the ethyl methyl carbonate in the solvent is less than or equal to 25wt%.

14. The secondary battery cell according to any one of claims 1 to 13, wherein: The electrolyte further includes an additive, and the additive includes one or both of fluoroethylene carbonate and vinylene carbonate.

15. The secondary battery cell according to any one of claims 1 to 14, wherein: The viscosity of the electrolyte at 25° C. is less than or equal to 5 mPa·s; and / or, The conductivity of the electrolyte at 25° C. is 8 mS / cm-16 mS / cm.

16. The secondary battery cell according to any one of claims 1 to 15, wherein: The viscosity of the electrolyte at 25° C. is less than or equal to 3 mPa·s; and / or, The conductivity of the electrolyte at 25° C. is 9 mS / cm-12 mS / cm.

17. The secondary battery cell according to any one of claims 1 to 16, wherein: The first pressure relief mechanism and the second pressure relief mechanism are symmetrically arranged.

18. The secondary battery cell according to any one of claims 1 to 17, wherein: The shapes of the first pressure relief mechanism and the second pressure relief mechanism are respectively and independently circular, elliptical or racetrack-shaped; and / or, The first end cover assembly includes a first cover plate, the first pressure relief mechanism is located on the first cover plate or the first pressure relief mechanism is formed integrally with the first cover plate; and / or, The second end cover assembly includes a second cover plate, and the second pressure relief mechanism is located on the second cover plate or the second pressure relief mechanism is formed integrally with the second cover plate.

19. The secondary battery cell according to any one of claims 1 to 18, wherein: The first end cap assembly includes a first electrode terminal, the second end cap assembly includes a second electrode terminal, the first electrode terminal and the second electrode terminal have opposite polarities, The distance between the geometric center point of the first pressure relief mechanism and the geometric center point of the first electrode terminal is 6 mm-14 mm; and / or, The distance between the geometric center point of the second pressure relief mechanism and the geometric center point of the second electrode terminal is 6 mm-14 mm.

20. The secondary battery cell according to any one of claims 1 to 19, wherein: The electrode assembly includes a positive electrode plate, which includes a positive electrode collector and a positive electrode film layer located on at least one surface of the positive electrode collector, the positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes one or more of lithium-containing phosphates and lithium transition metal oxides.

21. The secondary battery cell according to claim 20, wherein: The positive electrode active material includes a lithium-containing phosphate, and the mass proportion of the lithium-containing phosphate in the positive electrode active material is greater than or equal to 60 wt %.

22. The secondary battery cell according to any one of claims 20 to 21, wherein: The coating weight of the positive electrode film layer is greater than or equal to 16 mg / cm 2 and / or, The compaction density of the positive electrode film layer is greater than or equal to 2.2 g / cm 3 .

23. The secondary battery cell according to claim 22, wherein: The coating weight of the positive electrode film layer is 18 mg / cm 2 -25mg / cm 2 and / or, The compaction density of the positive electrode film layer is 2.25 g / cm 3 -2.6g / cm 3 .

24. A secondary battery comprising the secondary battery cell according to any one of claims 1 to 23.

25. An electrical device comprising the secondary battery according to claim 24.

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