Battery cell, battery and electrical apparatus

Abstract

Disclosed in the present disclosure are a battery cell, a battery and an electrical apparatus. The battery cell comprises a casing, an electrode assembly and an end cover assembly. The casing is provided with an accommodating chamber and an opening, the electrode assembly being arranged in the accommodating chamber, and the end cover assembly covering the opening. The electrode assembly comprises a positive electrode sheet, the positive electrode sheet comprising a positive electrode current collector and a positive electrode film layer located on at least one side of the positive electrode current collector. The positive electrode film layer comprises a positive electrode active material, the positive electrode active material comprising a layered lithium-containing transition metal oxide of monocrystal morphology. The bursting strength between the casing and the end cover assembly is greater than or equal to 1.2 MPa. The present disclosure can reduce exploding and bursting conditions occurring in thermal runaway processes of battery cells, and allows the battery cells to have high energy density and high reliability.

Description

Battery cells, batteries and electrical devices

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] The present disclosure claims priority to Chinese patent application No. 202410294562.5, filed on March 14, 2024, 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 battery cell, a battery, and an electric device. Background Art

[0004] As battery applications expand, so too does the demand for battery use, including ever-increasing energy density requirements. When a battery cell experiences thermal runaway, the violent chemical reactions within the electrode assembly release large amounts of heat, gas, and other released substances, making the cell susceptible to explosive discharges. This vulnerability is exacerbated by the increasing energy density of battery cells. When a battery cell explodes, its location cannot be controlled or predicted, making it susceptible to fires, explosions, and other safety incidents.

[0005] Summary of the Invention

[0006] The present disclosure provides a battery cell, a battery, and an electrical device, which can reduce explosions during thermal runaway of the battery cell and enable the battery cell to have both high energy density and high reliability.

[0007] In a first aspect, the present disclosure provides a battery cell, comprising a shell, an electrode assembly and an end cover assembly, the shell having a accommodating cavity and an opening, the electrode assembly being placed in the accommodating cavity, the end cover assembly covering the opening, the electrode assembly comprising a positive electrode plate, the positive electrode plate comprising a positive electrode current collector and a positive electrode film layer located on at least one side of the positive electrode current collector, the positive electrode film layer comprising a positive electrode active material, the positive electrode active material comprising a layered lithium-containing transition metal oxide with a single crystal morphology; the burst strength between the shell and the end cover assembly is greater than or equal to 1.2 MPa.

[0008] High energy density is a common goal for current battery cells. Improving the positive electrode's compaction density can improve the energy density of battery cells. Including a single-crystal layered lithium-containing transition metal oxide as the positive electrode active material can increase the positive electrode's compaction density and, consequently, the energy density of the battery cell. However, the particle size of single-crystal layered lithium-containing transition metal oxides is typically very small, which can increase gas production during battery cell use. This increased gas production increases the risk of thermal runaway and makes the battery cell more susceptible to explosions.

[0009] By ensuring that the burst strength between the battery cell housing and the end cap assembly is greater than or equal to 1.2 MPa, the present disclosure can reduce the occurrence of explosions during thermal runaway of the battery cell and improve the reliability of the battery cell. Therefore, the battery cell provided by the present disclosure can achieve both high energy density and high reliability.

[0010] In some embodiments, the end cap assembly includes a pressure relief mechanism, and the burst strength between the housing and the end cap assembly is greater than or equal to 1.35 times the burst strength of the pressure relief mechanism. This can further reduce the risk of battery cell explosions and enhance battery cell reliability.

[0011] In some embodiments, the battery cells are prismatic battery cells, and the burst strength between the housing and the end cap assembly of the prismatic battery cells is 1.2 MPa to 1.5 MPa. This can reduce the risk of explosions during thermal runaway of the battery cells, improve the reliability of the battery cells, and also enable the battery cells to have a high volumetric energy density.

[0012] In some embodiments, the battery cells are prismatic battery cells, and the burst strength between the housing and the end cap assembly of the prismatic battery cells is 1.35 to 2 times the burst strength of the pressure relief mechanism of the prismatic battery cells. This can further reduce the risk of battery cell explosions, enhance battery cell reliability, and achieve a high volumetric energy density.

[0013] In some embodiments, the battery cells are cylindrical, and the burst strength between the housing and the end cap assembly of the cylindrical battery cells is 1.5 MPa to 2.8 MPa, optionally 1.7 MPa to 2.8 MPa. This can reduce the risk of explosions during thermal runaway of the battery cells, improve the reliability of the battery cells, and also enable the battery cells to have a high volumetric energy density.

[0014] In some embodiments, the battery cells are cylindrical battery cells, and the burst strength between the housing and the end cap assembly of the cylindrical battery cells is 2 to 4 times, optionally 2.2 to 4 times, and more preferably 2.5 to 4 times, the burst strength of the pressure relief mechanism of the cylindrical battery cells. This can further reduce the risk of battery cell explosions, improve battery cell reliability, and enable the battery cells to have a high volumetric energy density.

[0015] In some embodiments, the burst strength of the pressure relief mechanism is 0.6 MPa-0.9 MPa, thereby enabling the pressure relief mechanism to timely and directional pressure relief, reducing the risk of explosion of the battery cell and ensuring high reliability of the battery cell.

[0016] In some embodiments, the housing is connected to the end cover assembly by welding.

[0017] In some embodiments, the molten pool depth of the weld between the shell and the end cover assembly is 300 μm-400 μm.

[0018] In some embodiments, the width of the weld between the shell and the end cover assembly is 910 μm-1100 μm, and optionally 940 μm-1100 μm.

[0019] In some embodiments, the depth-to-width ratio of the weld between the housing and the end cover assembly is 0.33-0.37.

[0020] In some embodiments, the molten pool depth of the weld between the shell and the end cover assembly is less than 1 / 2 of the thickness of the end cover assembly.

[0021] In some embodiments, the wall thickness of the shell is 0.3 mm-0.6 mm.

[0022] In some embodiments, the shell is made of steel or aluminum alloy.

[0023] In some embodiments, the end cap assembly has a thickness of 0.6 mm to 2.0 mm.

[0024] In some embodiments, the single crystal layered lithium-containing transition metal oxide accounts for 20%-100% of the positive electrode active material.

[0025] In some embodiments, the positive electrode active material includes both a single-crystal layered transition metal oxide containing lithium and a polycrystalline layered transition metal oxide containing lithium. The single-crystal layered transition metal oxide containing lithium accounts for greater than or equal to 30% and less than 50% of the positive electrode active material, and the polycrystalline layered transition metal oxide containing lithium accounts for greater than 50% and less than or equal to 70% of the positive electrode active material. By making the positive electrode active material include both a single-crystal layered transition metal oxide containing lithium and a polycrystalline layered transition metal oxide containing lithium, the compaction density of the positive electrode sheet can be increased, the energy density of the battery cell can be increased, and the battery cell can also be helped to have both good cycle stability and good power performance.

[0026] In some embodiments, the volume distribution particle size Dv50 of the positive electrode active material is 6 μm-10 μm, optionally 6.9 μm-10 μm.

[0027] In some embodiments, the electrode assembly includes a negative electrode sheet, wherein the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector, and the negative electrode film layer includes a negative electrode active material.

[0028] In some embodiments, the negative electrode active material includes graphite.

[0029] In some embodiments, the negative electrode active material includes graphite, and the graphite includes at least one of artificial graphite and natural graphite.

[0030] In some embodiments, the negative electrode active material includes a silicon-based material.

[0031] In some embodiments, the battery cell further includes an electrolyte, the electrolyte includes an organic solvent, the organic solvent includes a chain carbonate, the chain carbonate includes one or both of dimethyl carbonate and ethyl methyl carbonate, and the mass proportion of the chain carbonate in the organic solvent is 50%-80%.

[0032] In some embodiments, the organic solvent further comprises a cyclic carbonate, wherein the cyclic carbonate comprises one or both of ethylene carbonate and fluoroethylene carbonate, and the mass proportion of the cyclic carbonate in the organic solvent is 20%-50%.

[0033] In some embodiments, the battery cell further includes an electrolyte, the electrolyte containing cations and anions, the cations including one or both of lithium ions and sodium ions, and the anions including one or more of hexafluorophosphate anions and anions shown in Formula 1.

[0034] R1 and R2 each independently include a fluorine atom or a C1-C6 fluoroalkyl group.

[0035] In some embodiments, the anion includes both a hexafluorophosphate anion and an anion represented by Formula 1, and the molar concentration of the anion represented by Formula 1 is greater than the molar concentration of the hexafluorophosphate anion.

[0036] In some embodiments, the anion includes both a hexafluorophosphate anion and an anion represented by Formula 1, and the molar concentration of the anion represented by Formula 1 is 0.6 mol / L-0.9 mol / L.

[0037] In some embodiments, the anion includes both a hexafluorophosphate anion and an anion represented by Formula 1, and the molar concentration of the hexafluorophosphate anion is 0.3 mol / L-0.5 mol / L.

[0038] In a second aspect, the present disclosure provides a battery comprising the battery cell according to the first aspect of the present disclosure.

[0039] In a third aspect, the present disclosure provides an electrical device comprising the battery according to the second aspect of the present disclosure, wherein the battery is configured to provide electrical energy.

[0040] The electric device of the present disclosure includes the battery provided by the present disclosure, and thus has at least the same advantages as the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] 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.

[0042] FIG1 is a schematic structural diagram of a vehicle provided in some embodiments of the present disclosure.

[0043] FIG2 is a schematic diagram of an explosion of a battery provided in some embodiments of the present disclosure.

[0044] FIG3 is a schematic diagram of an explosion of the battery module shown in FIG2 .

[0045] In the accompanying drawings, the drawings are not necessarily drawn to scale.

[0046] The description of the accompanying drawings is as follows: 1. vehicle; 2. battery; 3. controller; 4. motor; 5. housing; 5a. first housing portion; 5b. second housing portion; 5c. storage space; 6. battery module; 7. battery cell. DETAILED DESCRIPTION

[0047] Below, the embodiments of the battery cell, battery, and electrical device disclosed herein are described in detail with appropriate reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of substantially identical structures may be omitted. This is to avoid unnecessary lengthiness in the following description and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure and are not intended to limit the subject matter described in the claims.

[0048] " 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] In the present disclosure, the terms "plurality" and "multiplicity" refer to two or more.

[0054] 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.

[0055] Unless otherwise defined, terms used in the present disclosure have the common meanings that are commonly understood by those skilled in the art.

[0056] 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.

[0057] The battery mentioned in the embodiments of the present disclosure may be a single physical module including one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in the present disclosure may include a battery cell, a battery module or a battery pack, etc. A battery cell is the smallest unit that makes up a battery, which can realize the function of charging and discharging on its own. When there are multiple battery cells, the multiple battery cells are connected in series, in parallel or in mixed connection through a busbar. In some embodiments, the battery may be a battery module; when there are multiple battery cells, the multiple battery cells are arranged and fixed to form a battery module. In some embodiments, the battery may be a battery pack, which includes a case and battery cells, and the 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 a part of the floor of the vehicle, or part of the case may become at least a part of the crossbeam and longitudinal beam of the vehicle.

[0058] In some embodiments, the battery may be an energy storage device, including an energy storage container, an energy storage cabinet, and the like.

[0059] The technical solutions described in the embodiments of the present disclosure are applicable to batteries and electrical devices using batteries.

[0060] Batteries can be used as power sources or energy storage units for electrical devices. Electrical devices include, but are not limited to, mobile devices (e.g., mobile phones, tablets, laptops, etc.), vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, and energy storage systems.

[0061] The electrical device can select the type of battery according to its usage requirements, such as a battery cell, a battery module or a battery pack.

[0062] For the convenience of description, the following embodiments are described by taking a vehicle as an example of an electrical device.

[0063] FIG1 is a schematic structural diagram of a vehicle provided in some embodiments of the present disclosure.

[0064] As shown in FIG1 , a battery 2 is provided inside the vehicle 1. The battery 2 may be provided at the bottom, head, or tail of the vehicle 1. The battery 2 may be used to power the vehicle 1. For example, the battery 2 may serve as an operating power source for the vehicle 1.

[0065] The vehicle 1 may further include a controller 3 and a motor 4 . The controller 3 is used to control the 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.

[0066] In some embodiments, the 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 .

[0067] FIG2 is an exploded view of a battery according to some embodiments of the present disclosure. As shown in FIG2 , the battery 2 includes a housing 5 and battery cells (not shown), which are housed in the housing 5 .

[0068] The housing 5 is used to house 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 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 be hollow structures 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.

[0069] 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.

[0070] 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.

[0071] In battery 2, there can be one or more battery cells. If there are multiple battery cells, they can be connected in series, in parallel, or in a hybrid configuration. A hybrid configuration refers to a combination of series and parallel connections. Multiple battery cells can be directly connected in series, in parallel, or in a hybrid configuration, and then the entire battery cell structure can be housed within housing 5. Alternatively, multiple battery cells can be first connected in series, in parallel, or in a hybrid configuration to form a battery module 6, which can then be connected in series, in parallel, or in a hybrid configuration to form a single unit and housed within housing 5.

[0072] FIG3 is a schematic diagram of an explosion of the battery module shown in FIG2 .

[0073] As shown in FIG3 , in some embodiments, there are multiple battery cells 7, which are first connected in series, in parallel, or in hybrid to form a battery module 6. The multiple battery modules 6 are then connected in series, in parallel, or in hybrid to form a whole and housed in a box.

[0074] The multiple 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 battery cells 7 in the battery module 6 .

[0075] The battery cells mentioned in the embodiments of the present disclosure may include lithium-ion battery cells.

[0076] The battery cell mentioned in the embodiment of the present disclosure includes a shell, an electrode assembly and an end cover assembly.

[0077] The housing has a cavity and an opening, with the electrode assembly positioned within the cavity and the end cap assembly covering the opening. The battery cell can be a prismatic or cylindrical battery cell. A prismatic battery cell can contain one or more electrode assemblies, adjustable based on demand.

[0078] The electrode assembly includes a positive electrode plate, which includes a positive electrode current collector and a positive electrode film layer located on at least one side of the positive electrode current collector. The positive electrode film layer includes a positive electrode active material, which includes a layered lithium-containing transition metal oxide with a single crystal morphology.

[0079] The burst strength between the shell and the end cover assembly is greater than or equal to 1.2Mpa.

[0080] High energy density is a common goal for current battery cells. Improving the compaction density of the positive electrode can improve the energy density of the battery cell. Including a single-crystal layered lithium-containing transition metal oxide in the positive electrode active material can increase the compaction density of the positive electrode and thus the energy density of the battery cell. However, the particle size of single-crystal layered lithium-containing transition metal oxides is typically very small, which increases the gas production during battery cell use. This increased gas production increases the risk of thermal runaway in the battery cell and makes the battery cell more susceptible to explosion.

[0081] By ensuring that the burst strength between the battery cell housing and the end cap assembly is greater than or equal to 1.2 MPa, the present disclosure can reduce the occurrence of explosions during thermal runaway of the battery cell and improve the reliability of the battery cell. Therefore, the battery cell provided by the present disclosure can achieve both high energy density and high reliability.

[0082] The end cap assembly typically includes a pressure relief mechanism. A pressure relief mechanism is an element or component that activates to release pressure from a battery cell when the internal pressure reaches a predetermined threshold. This threshold varies depending on the design requirements of the 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 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.

[0083] As used herein, "activation" refers to the pressure relief mechanism being activated or brought to a certain state, thereby releasing pressure from the battery cell. The action of the pressure relief mechanism may include, but is not limited to, rupturing, breaking, tearing, or opening at least a portion of the pressure relief mechanism.

[0084] When the pressure relief mechanism is actuated, the gas inside the battery cell will be discharged outward from the actuated part as exhaust. In this way, the battery cell can be directionally depressurized under controllable pressure, thereby reducing the risk of battery cell explosion, and further reducing the potential for more serious safety accidents such as fire and explosion.

[0085] Optionally, the burst strength between the housing and the end cover assembly may be greater than or equal to 1.35 times the burst strength of the pressure relief mechanism.

[0086] By ensuring that the burst strength between the shell and the end cover assembly is greater than or equal to 1.35 times the burst strength of the pressure relief mechanism, the structure of the battery cell will not be broken when the battery cell thermally runs away and the pressure relief mechanism is actuated. This allows the pressure relief mechanism to better play a role in directional pressure relief, thereby further reducing the risk of battery cell explosions and making the battery cell more reliable.

[0087] The bursting strength (also known as bursting pressure) between the shell and end cover assembly can be tested as follows: the pressure relief mechanism of the battery cell is glued firmly, and then an air pipe is inserted into the interior of the battery cell through the liquid injection hole of the battery cell. The area around the liquid injection hole is glued firmly, and then nitrogen is continuously introduced into the battery cell until the battery cell explodes. The peak data is recorded as the bursting strength (or bursting pressure) between the shell and end cover assembly, and the unit is MPa.

[0088] The burst strength of the pressure relief mechanism can be tested as follows: remove the end cap assembly from the battery cell and place it in a burst detector. The peak value of the pressure relief mechanism's burst is recorded as the burst strength (or burst pressure) of the pressure relief mechanism in MPa. The burst detector is loaded with nitrogen.

[0089] In some embodiments, the burst strength of the pressure relief mechanism can be 0.6 MPa-0.9 MPa, for example, 0.6 MPa, 0.62 MPa, 0.64 MPa, 0.66 MPa, 0.68 MPa, 0.7 MPa, 0.72 MPa, 0.74 MPa, 0.76 MPa, 0.78 MPa, 0.8 MPa, 0.82 MPa, 0.84 MPa, 0.86 MPa, 0.88 MPa, 0.9 MPa, or any range thereof. This allows the pressure relief mechanism to provide timely and targeted pressure relief, reducing the risk of explosion or blowout of the battery cell and ensuring high reliability of the battery cell.

[0090] During battery cell manufacturing, after the electrode assembly is placed in the housing, the housing and end cap assembly need to be connected. In some embodiments, the housing and end cap assembly are welded together. Alternatively, the housing and end cap assembly are connected by laser welding. After welding, a weld seam is formed between the housing and end cap assembly.

[0091] By adjusting the laser welding process parameters, such as laser power, spot diameter, laser power density, welding speed, laser wavelength and other parameters, the blasting strength between the shell and the end cover assembly and the weld parameters formed can be adjusted. For example, the laser power can be 1500W-2500W, the spot diameter can be 0.18mm-0.22mm, and the laser power density can be 4.5×10 6 W / cm 2 -6.0×10 6 W / cm 2 The welding speed can be 150mm / s-250mm / s, and the laser wavelength can be 1050nm-1070nm. During the laser welding process, argon or nitrogen is used as a shielding gas to protect the weld area to prevent oxidation of the molten metal at high temperatures. The shielding gas flow rate can be 10L / min-30L / min.

[0092] The burst strength between the shell and the end cover assembly is related to the welding process and parameters such as the molten pool depth, weld width, and depth-to-width ratio of the weld between the shell and the end cover assembly.

[0093] The molten pool depth of the weld between the shell and the end cap assembly increases, and the blasting strength between the shell and the end cap assembly increases. However, in order to avoid welding through the end cap assembly, the design thickness of the end cap assembly also increases, which leads to a decrease in the space utilization in the height direction of the battery cell, thereby reducing the volume energy density of the battery cell. Optionally, the molten pool depth of the weld between the shell and the end cap assembly can be 300μm-400μm, for example, 300μm, 310μm, 320μm, 325μm, 330μm, 340μm, 350μm, 360μm, 370μm, 380μm, 390μm, 400μm, or a range consisting of any of the above values. More optionally, the molten pool depth of the weld between the shell and the end cap assembly can be 310μm-360μm, 320μm-360μm, 325μm-360μm, or 330μm-360μm.

[0094] The molten pool depth is the distance between the deepest point of the molten area of ​​the workpiece and the workpiece surface. The molten pool depth can be measured by cutting the workpiece and observing it through metallographic measurement.

[0095] As the width of the weld between the shell and the end cap assembly increases, the burst strength between the shell and the end cap assembly increases. Optionally, the width of the weld between the shell and the end cap assembly is 910 μm-1100 μm, for example, 910 μm, 920 μm, 930 μm, 940 μm, 950 μm, 960 μm, 970 μm, 980 μm, 990 μm, 1000 μm, 1010 μm, 1020 μm, 1030 μm, 1040 μm, 1050 μm, 1060 μm, 1070 μm, 1080 μm, 1090 μm, 1100 μm, or a range consisting of any of the above values. More optionally, the width of the weld between the shell and the end cover assembly is 920 μm-1100 μm, 930 μm-1100 μm, 940 μm-1100 μm, 950 μm-1100 μm, 940 μm-1000 μm, or 950 μm-1000 μm.

[0096] The depth-to-width ratio of the weld between the shell and the end cap assembly increases, thereby increasing the burst strength between the shell and the end cap assembly. Optionally, the depth-to-width ratio of the weld between the shell and the end cap assembly is 0.33-0.37, for example, 0.33, 0.332, 0.334, 0.336, 0.338, 0.34, 0.342, 0.344, 0.346, 0.348, 0.35, 0.352, 0.354, 0.356, 0.358, 0.36, 0.362, 0.364, 0.366, 0.368, 0.37, or any range thereof. More preferably, the depth-to-width ratio of the weld between the shell and the end cap assembly is 0.344-0.37, or 0.344-0.358.

[0097] The depth-to-width ratio of a weld refers to the ratio of the molten pool depth to the weld width.

[0098] Optionally, the molten pool depth of the weld between the shell and the end cover assembly may be less than 1 / 2 of the thickness of the end cover assembly.

[0099] In some embodiments, the thickness of the end cap assembly may be 0.6 mm to 2.0 mm.

[0100] The thickness of the end cap assembly refers to the distance between the upper and lower surfaces of the end cap assembly. It is understood that the thickness of the end cap assembly does not include the size of the electrode terminal.

[0101] In some embodiments, the burst strength between the housing and the end cap assembly of a prismatic battery cell can be 1.2 MPa-1.5 MPa, for example, 1.2 MPa, 1.22 MPa, 1.24 MPa, 1.26 MPa, 1.28 MPa, 1.3 MPa, 1.32 MPa, 1.34 MPa, 1.36 MPa, 1.38 MPa, 1.4 MPa, 1.42 MPa, 1.44 MPa, 1.46 MPa, 1.48 MPa, 1.5 MPa, or any range thereof. This can reduce the risk of explosion during thermal runaway of the battery cell, improve the reliability of the battery cell, and enable the battery cell to have a high volumetric energy density.

[0102] In some embodiments, the burst strength between the shell and the end cover assembly of the square shell battery cell can be 1.35 times to 2 times the burst strength of the pressure relief mechanism of the square shell battery cell, for example, it can be 1.35 times, 1.4 times, 1.45 times, 1.5 times, 1.55 times, 1.6 times, 1.65 times, 1.7 times, 1.75 times, 1.8 times, 1.85 times, 1.9 times, 1.95 times, 2 times, or a range consisting of any of the above values.

[0103] By adjusting the multiple of the burst strength between the shell and the end cover assembly of the square-shell battery cell and the burst strength of the pressure relief mechanism, the structure of the battery cell will not be broken when the battery cell thermal runaway and the pressure relief mechanism is actuated. This allows the pressure relief mechanism to better play the role of directional pressure relief, thereby further reducing the occurrence of battery cell explosions, making the battery cell more reliable, and also making the battery cell have a high volume energy density.

[0104] Optionally, the battery cell is a cylindrical battery cell.

[0105] In some embodiments, the burst strength between the cylindrical battery cell housing and the end cap assembly can be 1.5 MPa-2.8 MPa, for example, 1.5 MPa, 1.6 MPa, 1.7 MPa, 1.8 MPa, 1.9 MPa, 2 MPa, 2.1 MPa, 2.2 MPa, 2.3 MPa, 2.4 MPa, 2.5 MPa, 2.6 MPa, 2.7 MPa, 2.8 MPa, or any range thereof. Alternatively, the burst strength between the cylindrical battery cell housing and the end cap assembly can be 1.6 MPa-2.8 MPa, 1.7 MPa-2.8 MPa, 1.8 MPa-2.8 MPa, 1.9 MPa-2.8 MPa, or 2.0 MPa-2.8 MPa.

[0106] This can reduce the explosion and spraying of battery cells during thermal runaway, improve the reliability of battery cells, and also enable the battery cells to have a high volume energy density.

[0107] In some embodiments, the burst strength between the housing of the cylindrical battery cell and the end cap assembly can be 2 to 4 times the burst strength of the pressure relief mechanism of the cylindrical battery cell, for example, 2 times, 2.1 times, 2.2 times, 2.3 times, 2.4 times, 2.5 times, 2.6 times, 2.7 times, 2.8 times, 2.9 times, 3 times, 3.1 times, 3.2 times, 3.3 times, 3.4 times, 3.5 times, 3.6 times, 3.7 times, 3.8 times, 3.9 times, 4 times, or any range thereof. Alternatively, the burst strength between the housing of the cylindrical battery cell and the end cap assembly can be 2.2 to 4 times, 2.4 to 4 times, or 2.6 to 4 times the burst strength of the pressure relief mechanism of the cylindrical battery cell.

[0108] By adjusting the multiple of the burst strength between the shell and the end cover assembly of the cylindrical battery cell and the burst strength of the pressure relief mechanism, the structure of the battery cell will not be broken when the battery cell thermal runaway and the pressure relief mechanism is actuated. This can enable the pressure relief mechanism to better play the role of directional pressure relief, thereby further reducing the occurrence of battery cell explosions, making the battery cell more reliable, and also making the battery cell have a high volume energy density.

[0109] In some embodiments, the diameter of the cylindrical battery cell may be greater than or equal to 35 mm, and may be 40 mm to 60 mm, thereby enabling the battery cell to have a high capacity.

[0110] In some embodiments, the axial dimension of the cylindrical battery cell may be greater than or equal to 70 mm, and may be 80 mm to 135 mm, thereby enabling the battery cell to have a high capacity.

[0111] The axial direction of a cylindrical battery cell refers to the direction of the cylinder's central axis of rotation, i.e., the direction shared by the central axis. The radial direction of a cylindrical battery cell is perpendicular to the axial direction and is the direction of the diameter of the cylinder's end face. The axial dimension of a cylindrical battery cell is usually referred to as the length of the cylindrical battery cell.

[0112] The axial dimension of a cylindrical battery cell refers to the distance between the top and bottom outer surfaces of the battery cell. It is understood that the axial dimension of a cylindrical battery cell does not include the dimensions of the electrode terminals.

[0113] In some embodiments, the wall thickness of the housing may be less than or equal to 0.6 mm, and may be optionally 0.3 mm-0.6 mm, or 0.3 mm-0.5 mm.

[0114] In some embodiments, the shell is made of metal, which can be any one of steel and aluminum alloy.

[0115] In some embodiments, the end cover assembly includes an end cover, which covers the opening of the shell. The material of the end cover may include metal, which can be any one of steel and aluminum alloy.

[0116] In some embodiments, the end cap assembly may further include an electrode terminal mounted on the end cap. There may be two electrode terminals, each defined as a positive electrode terminal and a negative electrode terminal. Both the positive electrode terminal and the negative electrode terminal are used to electrically connect to the electrode assembly to output the electrical energy generated by the electrode assembly.

[0117] In other embodiments, the housing is a hollow structure with two opposing openings. Two end cap assemblies are provided, with one end cap assembly correspondingly covering one opening of the housing and forming a sealed connection to form a cavity for accommodating the electrode assembly. In this structure, one end cap assembly may be provided with two electrode terminals while the other end cap assembly is not provided with an electrode terminal, or both end cap assemblies may each be provided with one electrode terminal.

[0118] The electrode assembly consists of a main body and tabs extending from the main body. The tabs are used to conduct the current generated by the main body. The main body is the core part of the battery cell that realizes the charging and discharging functions.

[0119] The number of tabs can be two. These two tabs are defined as a positive tab and a negative tab, respectively. The two tabs are electrically connected to the positive electrode terminal and the negative electrode terminal, respectively. The positive tab can be formed by stacking multiple positive tabs together, and the negative tab can be formed by stacking multiple negative tabs together.

[0120] [Positive electrode]

[0121] The positive electrode active material includes a layered lithium-containing transition metal oxide having a single crystal morphology. Examples of the layered lithium-containing transition metal oxide 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 modified compounds thereof.

[0122] In some embodiments, the layered lithium-containing transition metal oxide may include a Ni element. The molar amount of the Ni element may account for more than 70% of the total molar amount of the transition metal elements in the layered lithium-containing transition metal oxide; alternatively, the molar amount of the Ni element may account for more than 80% of the total molar amount of the transition metal elements in the layered lithium-containing transition metal oxide; more alternatively, the molar amount of the Ni element may account for more than 90% of the total molar amount of the transition metal elements in the layered lithium-containing transition metal oxide.

[0123] In some embodiments, the layered lithium-containing transition metal oxide may include Li a Ni b Co c M d O e A f , 0 < a ≤ 1.2; 0.5 ≤ b < 1; 0 < c < 1; 0 < d < 1; 1 ≤ e ≤ 2; 0 ≤ f ≤ 1; M includes, but is not limited to, one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B; A includes, but is not limited to, one or more of N, F, S, and Cl. Optionally, 0.7 ≤ b < 1, 0.8 ≤ b < 1, and 0.9 ≤ b < 1. This can further increase the energy density of the battery cell.

[0124] In some embodiments, as an example, the layered lithium-containing transition metal oxide may include but is not limited to LiNi 0.8 Co 0.1 Mn 0.1 O2、LiNi 0.80 Co 0.15 Al 0.05 O2、LiNi 0.9 Co 0.06 Mn 0.04 O2、LiNi 0.92 Co0.06 Mn 0.02 O2、LiNi 0.96 Co 0.02 Mn 0.02 One or more of O2.

[0125] The charge and discharge process of a battery cell is accompanied by the intercalation and deintercalation of Li, and the molar content of Li in the battery cell varies at different discharge states. The molar content of Li in the examples of the present disclosure regarding the positive electrode active materials refers to the material's initial state, i.e., the state before the materials are added. The molar content of Li in the positive electrode active materials used in the battery cell may change after charge and discharge cycles.

[0126] In the examples of the present disclosure regarding the positive electrode active materials, the molar content of O is only a theoretical value. Lattice oxygen release will cause the molar content of O to change, and the actual molar content of O will fluctuate.

[0127] The higher the content of Ni element in the layered lithium-containing transition metal oxide, the higher the energy density of the battery cell.

[0128] The modified compounds of the above-mentioned positive electrode active materials may be used to perform doping modification and / or surface coating modification on the positive electrode active materials.

[0129] In some embodiments, the single crystal layered lithium-containing transition metal oxide may account for 20% to 100% of the positive electrode active material.

[0130] In some embodiments, the positive electrode active material may include both a single-crystal layered lithium-containing transition metal oxide and a polycrystalline layered lithium-containing transition metal oxide.

[0131] To achieve higher energy density, higher requirements are usually placed on the compaction density of the positive electrode sheet. Generally, the volume distribution particle size Dv50 of a single-crystal layered lithium-containing transition metal oxide is smaller than the volume distribution particle size Dv50 of a polycrystalline layered lithium-containing transition metal oxide. By including both single-crystal layered lithium-containing transition metal oxide and polycrystalline layered lithium-containing transition metal oxide in the positive electrode active material, the compaction density of the positive electrode sheet can be increased, thereby improving the energy density of the battery cell.

[0132] For the same type of layered lithium-containing transition metal oxide and the same upper charge cutoff voltage for the battery cells, the cycling stability of single-crystalline layered lithium-containing transition metal oxides is higher than that of polycrystalline layered lithium-containing transition metal oxides. Polycrystalline layered lithium-containing transition metal oxides have a higher lithium ion diffusion coefficient and better electrolyte wettability, which can better improve the power performance of battery cells.

[0133] Therefore, the positive electrode active material includes both a layered lithium-containing transition metal oxide with a single crystal morphology and a layered lithium-containing transition metal oxide with a polycrystalline morphology, which also helps the battery cell to have both good cycle stability and good power performance.

[0134] Optionally, the amount of layered lithium-containing transition metal oxides with a single crystal morphology in the positive electrode active material accounts for greater than or equal to 30% and less than 50%, and the amount of layered lithium-containing transition metal oxides with a polycrystalline morphology in the positive electrode active material accounts for greater than 50% and less than or equal to 70%.

[0135] The terms "layered lithium-containing transition metal oxide with a single crystal morphology" and "layered lithium-containing transition metal oxide with a polycrystalline morphology" have well-known meanings in the art. "Layered lithium-containing transition metal oxide with a single crystal morphology" also includes layered lithium-containing transition metal oxide with a quasi-single crystal (also known as quasi-single crystal) morphology. Quasi-single crystal (quasi-single crystal) is a well-known meaning in the art, generally referring to particles formed by the agglomeration of a small number (e.g., 2-5) primary particles. Layered lithium-containing transition metal oxide with a polycrystalline morphology refers to a layered lithium-containing transition metal oxide with a secondary particle morphology formed by the agglomeration of multiple (e.g., greater than 5) primary particles. "Layered lithium-containing transition metal oxide with a single crystal morphology" and "Layered lithium-containing transition metal oxide with a polycrystalline morphology" can be distinguished by scanning electron microscopy.

[0136] The percentage of layered lithium-containing transition metal oxides with a single crystal (or polycrystalline) morphology in the positive electrode active material is well known in the art and can be measured using instruments and methods known in the art. For example, the positive electrode active material can be laid and adhered to a conductive adhesive to form a test sample with a length × width of 6 cm × 1.1 cm; the particle morphology can be tested using a scanning electron microscope and an energy dispersive spectrometer (such as a ZEISS Sigma300). The test can refer to JY / T010-1996. To ensure the accuracy of the test results, 20 different areas can be randomly selected from the test sample for scanning testing, and at a certain magnification (for example, 1000 times or more), the ratio of the number of layered lithium-containing transition metal oxides with a single crystal (or polycrystalline) morphology to the total number of particles in each area is calculated, which is the percentage of layered lithium-containing transition metal oxides with a single crystal (or polycrystalline) morphology in the area; the average of the test results of the 20 test areas is taken as the percentage of layered lithium-containing transition metal oxides with a single crystal (or polycrystalline) morphology in the positive electrode active material.

[0137] In some embodiments, the particle size distribution curve of the positive electrode active material has two volume distribution peaks, the volume distribution peak with the maximum peak intensity is recorded as the first peak, and the volume distribution particle size corresponding to the maximum peak intensity of the first peak is recorded as Dv1, and the volume distribution peak with the second maximum peak intensity is recorded as the second peak, and the volume distribution particle size corresponding to the maximum peak intensity of the second peak is recorded as Dv2, Dv1 is between 7μm and 12μm, and Dv2 is between 2μm and 5μm.

[0138] This can increase the actual packing density of the positive electrode active material, increase the compaction density of the positive electrode sheet, and further enable the battery cell to have a higher energy density.

[0139] Optionally, Dv1 is between 8 μm and 11 μm, and Dv2 is between 2 μm and 4 μm.

[0140] In some embodiments, the volume distribution particle size Dv50 of the single-crystal layered lithium-containing transition metal oxide may be less than or equal to 5 μm, and may be optionally 2 μm-4 μm.

[0141] In some embodiments, the volume distribution particle size Dv50 of the polycrystalline layered lithium-containing transition metal oxide may be 7 μm-12 μm, and optionally 8 μm-11 μm.

[0142] In some embodiments, the volume distribution particle size Dv50 of the positive electrode active material may be 6 μm-10 μm, optionally 7 μm-9.5 μm.

[0143] The volume distribution particle size Dv50 of a material is well known in the art and represents the particle size corresponding to the cumulative volume distribution percentage of the material reaching 50%. It can be measured using instruments and methods known in the art. For example, it can be conveniently measured using a laser particle size analyzer, as per GB / T 19077-2016. The testing instrument can be the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd. in the UK.

[0144] In some embodiments, the positive electrode film layer may further optionally 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.

[0145] In some embodiments, the positive electrode film layer may further optionally 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.

[0146] 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 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).

[0147] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, drying it, and cold pressing it. The positive electrode slurry is typically formed by dispersing the positive electrode active material, positive electrode conductive agent, positive electrode binder, and any other components in a solvent and stirring them uniformly. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP).

[0148] [Negative electrode]

[0149] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0150] In some embodiments, the negative electrode active material may include graphite. Optionally, the graphite may include at least one of artificial graphite and natural graphite.

[0151] Optionally, the mass proportion of graphite in the negative electrode active material may be greater than or equal to 75%, for example, greater than or equal to 75%, greater than or equal to 80%, greater than or equal to 85%, greater than or equal to 90%, or greater than or equal to 95%.

[0152] In some embodiments, the negative electrode active material may further include a silicon-based material, thereby increasing the energy density of the battery cell.

[0153] Optionally, the silicon-based material may include one or more of silicon oxide and silicon-carbon materials.

[0154] Optionally, the mass proportion of the silicon-based material in the negative electrode active material may be 5%-25%.

[0155] 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.

[0156] 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).

[0157] 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.

[0158] 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 side 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).

[0159] 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.

[0160] 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.

[0161] [Electrolytes]

[0162] The battery cells include an electrolyte.

[0163] In some embodiments, the electrolyte is an electrolyte solution (ie, a liquid electrolyte), the electrolyte solution includes an organic solvent, and the organic solvent includes a chain carbonate.

[0164] Alternatively, the linear carbonate may include one or both of dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC).

[0165] Optionally, the mass proportion of the linear carbonate in the organic solvent may be 50%-80%, and optionally 55%-80%.

[0166] As the energy density of battery cells increases, their dimensions also become larger, making them more susceptible to electrolyte wetting issues. By increasing the mass fraction of chain carbonates in the organic solvent of the electrolyte, the electrolyte viscosity can be reduced, facilitating electrolyte flow. This improves the electrolyte wetting of the electrode assembly, leading to better cycle performance of the battery cells.

[0167] In some embodiments, the organic solvent further comprises a cyclic carbonate, and the cyclic carbonate may comprise one or both of ethylene carbonate and fluoroethylene carbonate.

[0168] Chain carbonates can make the electrolyte have low viscosity, which facilitates the flow of the electrolyte, but their dielectric constant is small and their ability to dissolve electrolyte salts is weak. By mixing chain carbonates with cyclic carbonates, the electrolyte can have good fluidity while also having high ionic conductivity and a wide electrochemical window, which can in turn make the battery cell have better cycle performance.

[0169] Optionally, the cyclic carbonate includes both ethylene carbonate and fluoroethylene carbonate.

[0170] Fluoroethylene carbonate can participate in the formation of SEI film on the surface of negative electrode active materials, improve the composition and properties of SEI film, and thus effectively protect the negative electrode active materials. Especially when the negative electrode active materials contain silicon-based materials, due to the volume expansion characteristics of silicon-based materials, it is even more necessary to optimize the composition of SEI film.

[0171] The reduction products of fluoroethylene carbonate at the negative electrode are mainly -CHF-OCO2 compounds and LiF. During the charge and discharge process, the -CHF-OCO2 compound forms an initial SEI film that coats the surface of the silicon-based material. This SEI film is flexible and resistant to rupture, effectively blocking contact between the silicon-based material and the electrolyte, thereby reducing electrolyte decomposition and SEI film reconstruction. At the same time, LiF, another reduction product of fluoroethylene carbonate, helps promote the conduction of lithium ions within the SEI film. Therefore, by including both ethylene carbonate and fluoroethylene carbonate in the cyclic carbonate, the battery cell can have a long cycle life.

[0172] Optionally, the mass proportion of the cyclic carbonate in the organic solvent may be 20%-50%, optionally 20%-45%.

[0173] In some embodiments, the electrolyte contains cations and anions.

[0174] The cations include one or both of lithium ions and sodium ions.

[0175] The anion includes one or more of a hexafluorophosphate anion and an anion shown in Formula 1, and R1 and R2 each independently include a fluorine atom or a C1-C6 fluoroalkyl group.

[0176] R1 and R2 each independently include a fluorine atom or a C1-C6 fluoroalkyl group. A C1-C6 fluoroalkyl group means that at least one hydrogen atom in the C1-C6 alkyl group is replaced by a fluorine atom, or all hydrogen atoms are replaced by fluorine atoms, and can be, for example, a trifluoromethyl group, a pentafluoroethyl group, a heptafluoropropyl group, or the like.

[0177] Optionally, R1 and R2 each independently include a fluorine atom or a trifluoromethyl group.

[0178] Alternatively, the anion shown in Formula 1 may include a bis(fluorosulfonyl)imide anion (FSI - ), bis(trifluoromethanesulfonyl)imide anion (TFSI - ) or two thereof. More preferably, the anion shown in Formula 1 may include a bis(fluorosulfonyl)imide anion (FSI - ).

[0179] In some embodiments, the anion includes both a hexafluorophosphate anion and an anion of Formula 1.

[0180] The anion shown in Formula 1 is a weakly coordinated anion centered on N, containing a conjugated group and a fluorine atom and / or a fluoroalkyl group with strong charge absorption. The anion charge is highly delocalized, and the interaction between the anion and the cation is weak, which also helps to improve the ionic conductivity of the electrolyte. However, the anion shown in Formula 1 has the problem of corroding the positive electrode current collector (for example, aluminum foil), which will result in poor contact between the positive electrode active material and the positive electrode current collector. The thermal stability of the hexafluorophosphate anion is not as good as that of the anion shown in Formula 1, but it can passivate the positive electrode current collector and reduce the corrosion of the anion shown in Formula 1 on the positive electrode current collector; at the same time, the negative electrode film forming property of the hexafluorophosphate anion is worse than that of the anion shown in Formula 1.

[0181] Therefore, by making the anions include both hexafluorophosphate anions and the anions shown in Formula 1, a synergistic effect between the two can be exerted, thereby reducing the consumption of electrolyte during the cyclic charge and discharge process of the battery cell, thereby making the battery cell have a long cycle life; in addition, the battery cell can also have a lower production cost.

[0182] Optionally, the molar concentration of the anion represented by Formula 1 may be greater than the molar concentration of the hexafluorophosphate anion.

[0183] By increasing the molar concentration of the anion represented by Formula 1 to a greater molar concentration than the hexafluorophosphate anion, the battery cell can achieve a long cycle life, good power performance, and high reliability. This is because the basic process of thermal runaway in a battery cell is as follows: at high temperatures, the SEI film of the negative electrode decomposes. As the temperature rises, the charged positive electrode active material, the layered lithium-containing transition metal oxide, violently decomposes and releases oxygen, causing a violent oxidation reaction in the electrolyte. By increasing the molar concentration of the anion represented by Formula 1 to a greater molar concentration than the hexafluorophosphate anion, the redox resistance of the electrolyte can be improved.

[0184] Optionally, the molar concentration of the anion represented by Formula 1 may be 0.6 mol / L-0.9 mol / L.

[0185] Alternatively, the molar concentration of the hexafluorophosphate anion may be 0.3 mol / L-0.5 mol / L.

[0186] In some embodiments, the anion may also include other anions, for example, but not limited to tetrafluoroborate anion (BF4 - ), perchlorate anion (ClO4 - ), hexafluoroarsenate anion (AsF6 - ), trifluoromethanesulfonate anion (TFS - ), difluorooxalatoborate anion (DFOB - ), dioxalatoborate anion (BOB - ), difluorophosphate anion (PO2F2 - ), difluorobis(oxaloyl)phosphate anion (DFOP - ) and tetrafluorooxalophosphate anion (TFOP - )

[0187] In some embodiments, the molar concentration of the anion may be 1 mol / L-1.3 mol / L, optionally 1.05 mol / L-1.15 mol / L.

[0188] In some embodiments, the viscosity of the electrolyte at 25° C. may be less than or equal to 5 mPa·s, and may be less than or equal to 3 mPa·s. This helps improve the electrolyte wettability of the electrode assembly and enables the battery cell to have good cycle performance.

[0189] 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.

[0190] 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.

[0191] 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.

[0192] 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.

[0193] Methods for preparing the electrolyte are well known. In some embodiments, the electrolyte solution can be obtained by uniformly mixing an electrolyte salt, an organic solvent, and an additive. The order in which the materials are added is not particularly limited and can be selected according to actual conditions. Alternatively, the molar concentration of the electrolyte salt can be 1 mol / L to 1.3 mol / L, and can be 1.05 mol / L to 1.15 mol / L.

[0194] Electrolyte salts can dissociate into cations and anions in organic solvents.

[0195] The electrolyte salt may include lithium hexafluorophosphate (LiPF6), one or more of the electrolyte salts shown in Formula 2, R1 and R2 each independently include a fluorine atom or a C1-C6 fluoroalkyl group, and M1 is Li. Alternatively, the electrolyte salt shown in Formula 2 may include one or both of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). More optionally, the electrolyte salt shown in Formula 2 may include lithium bis(fluorosulfonyl)imide (LiFSI).

[0196] Furthermore, the electrolyte salt may further include one or more of lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium bisoxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobisoxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0197] The components and their contents in the electrolyte can be determined using conventional methods in the art. For example, ion chromatography (IC) can be used to qualitatively or quantitatively analyze the type and content of electrolyte salts in the electrolyte, and the testing standards can refer to JY / T020-1996. Gas chromatography-mass spectrometry (GC-MS) can be used to qualitatively and quantitatively analyze organic solvents in the electrolyte, and the testing standards can refer to GB / T9722-2006.

[0198] The electrolyte can be sampled and analyzed during the preparation process, or it can be obtained by disassembling and centrifuging the prepared battery after discharge.

[0199] [Isolation film]

[0200] The battery cell also includes a separator, which is placed between the positive and negative electrodes to prevent internal short circuits.

[0201] The present disclosure has no particular limitation on the type of isolation membrane, and any known isolation membrane with a porous structure having good chemical stability and mechanical stability can be selected.

[0202] In some embodiments, the isolation film may include a base film and a coating layer disposed on at least one side of the base film.

[0203] In some embodiments, the material of the base film may include, but is not limited to, one or more of glass fiber, non-woven fabric, and polyolefin. Alternatively, the material of the base film may include polyolefin, such as polyethylene, polypropylene, polyvinylidene fluoride, etc., and more preferably polyethylene.

[0204] In some embodiments, the thickness of the base film may be less than or equal to 12 μm, and may be 3 μm-9 μm, 3 μm-7 μm, or 3 μm-5 μm.

[0205] In some embodiments, the puncture strength of the base film may be greater than or equal to 390 gf, and may be optionally 400 gf-480 gf.

[0206] The higher the base film's puncture strength, the better its puncture resistance, effectively preventing positive and negative electrode particles, as well as metallic foreign particles, from piercing the separator and causing a short circuit between the positive and negative electrodes. Therefore, a base film puncture strength within the above range can improve the pass rate of battery cell short-circuit testing and enhance battery cell reliability.

[0207] In some embodiments, the base film may have a machine direction (MD) heat shrinkage rate of less than 3% at 105° C. for 1 hour, and may optionally be 1%-2.5%.

[0208] In some embodiments, the transverse direction (TD) thermal shrinkage of the base film at 105° C. for 1 hour may be less than 2%, and may be optionally 1%-1.8%.

[0209] The reduced thermal shrinkage of the base film indicates that the base film has good heat resistance, which can also increase the short-circuit test pass rate of the battery cell and improve the reliability of the battery cell.

[0210] The thermal shrinkage of the base film has a well-known meaning in the art and can be measured using methods known in the art. For example, the test can be performed with reference to GB / T 36363-2018.

[0211] In some embodiments, the longitudinal tensile strength of the base film may be greater than or equal to 2700 kgf / cm 2 , optional 2800kgf / cm 2 -3500kgf / cm 2 .

[0212] In some embodiments, the transverse tensile strength of the base film can be greater than or equal to 2500 kgf / cm 2 , optional 2600kgf / cm 2 -3200kgf / cm 2 .

[0213] The increased tensile strength of the base film is conducive to the effective coating of the positive and negative electrode particles, which can effectively reduce the short circuit between the positive and negative electrodes and improve the reliability of the battery cells.

[0214] The tensile strength of the base film has a well-known meaning in the art and can be measured using methods known in the art. For example, it can be tested with reference to GB / T 36363-2018.

[0215] In some embodiments, the average pore size of the base film may be 10 nm-60 nm, optionally 20 nm-40 nm.

[0216] The average pore size of the basement membrane has a well-known meaning in the art and can be measured using methods known in the art, for example, using a capillary flow pore size analyzer, such as a PMIPorometer.

[0217] In some embodiments, the porosity of the base film may be 20%-60%, optionally 30%-50%.

[0218] The porosity of the base film has a well-known meaning in the art and can be measured using methods known in the art. For example, the porosity can be measured with reference to GB / T 36363-2018.

[0219] In some embodiments, the coating may include a particulate inorganic filler. The particulate inorganic filler may include, but is not limited to, boehmite, alumina, silicon oxide SiO x(0<x≤2), one or more of zinc oxide, magnesium oxide, tin dioxide, titanium oxide, calcium oxide, zirconium oxide, yttrium oxide, nickel oxide, hafnium dioxide, cerium oxide, magnesium hydroxide, aluminum hydroxide, silicon carbide, boron carbide, aluminum nitride, silicon nitride, boron nitride, magnesium fluoride, calcium fluoride, barium fluoride, barium sulfate, magnesium aluminum silicate, lithium magnesium silicate, sodium magnesium silicate, bentonite, hectorite, zirconium titanate, and barium titanate.

[0220] In some embodiments, the coating further comprises a non-granular binder. The present disclosure does not particularly limit the type of the non-granular binder, and any known material with good adhesive properties may be selected, such as a linear binder, an emulsion binder, and a mixed linear and emulsion binder.

[0221] Optionally, the non-granular binder may have at least one polar group selected from the group consisting of a hydroxyl group (-OH), a carboxyl group (-COOH), an ester group (-COO-), a cyano group (-CN), an imide group (-CO-NH-CO-), a maleic anhydride group (-COOOC-), a sulfonate group (-SO3H) and a pyrrolidone group (-NCO-).

[0222] Alternatively, the non-particulate binder may include a homopolymer or copolymer selected from the group consisting of allyl polyether sulfate, acrylic acid, methacrylic acid, acrylamide, methyl acrylate, butyl acrylate, ethyl acrylate, glycidyl methacrylate, vinyl alcohol, acrylonitrile, hydroxyethyl acrylate, styrene, acetoxyethyl methacrylate, vinyltrimethoxysilane, lithium acrylate, sodium acrylate, lithium methacrylate, isobutylene, and maleic anhydride.

[0223] Optionally, the non-granular binder may include at least one of: polyacrylic acid, polymethyl methacrylate, polyacrylonitrile, polyvinyl pyrrolidone, polyvinyl acetate, polyethylene-co-vinyl acetate, polystyrene-co-methyl methacrylate, polystyrene-co-butyl acrylate, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose, acrylonitrile-styrene-butadiene copolymer, polyimide.

[0224] Optionally, the mass content of the non-particulate binder in the coating layer may be less than or equal to 10 wt %, based on the total mass of the coating layer.

[0225] The preparation method of battery cells is well known. In some embodiments, a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte can be assembled to form a battery cell. As an example, the positive electrode sheet, separator, and negative electrode sheet can be made into an electrode assembly, which is then placed in a housing, dried, and then injected with electrolyte. After standing and forming, a battery cell is obtained.

[0226] Example

[0227] 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.

[0228] Example 1-1

[0229] Preparation of positive electrode

[0230] The positive electrode active material LiNi 0.9 Co 0.06 Mn 0.04 O2, binder polyvinylidene fluoride, and conductive agent Super P are mixed in a mass ratio of 97:2:1. 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. After drying and cold pressing, the positive electrode sheet is obtained.

[0231] The positive electrode active material also includes single crystal morphology of LiNi 0.9 Co 0.06 Mn 0.04 O2 and polycrystalline LiNi 0.9 Co 0.06 Mn 0.04 O2. Single crystal morphology of LiNi 0.9 Co 0.06 Mn 0.04 The amount of O2 accounts for 30%, and the polycrystalline LiNi 0.9 Co 0.06 Mn 0.04 The amount of O2 accounts for 70%. Single crystal morphology of LiNi 0.9 Co 0.06 Mn 0.04 The volume distribution particle size Dv50 of O2 is 4.0μm, and the polycrystalline morphology of LiNi 0.9 Co 0.06 Mn 0.04The volume distribution particle size Dv50 of O2 was 11.0 μm. The volume distribution particle size Dv50 of the mixed positive electrode active material was 8.9 μm.

[0232] Preparation of negative electrode sheet

[0233] The negative electrode active material is a mixture of artificial graphite and silicon oxide in a mass ratio of 93:7. The volume distribution particle size Dv50 of the silicon oxide is 8μm, and the volume distribution particle size Dv50 of the artificial graphite is 10μm. The volume distribution particle size Dv50 of the mixed negative electrode active material is 8.9μm. The negative electrode active material, conductive agent Super P, binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose are thoroughly stirred and mixed in an appropriate amount of deionized water solvent in a mass ratio of 96.2:0.6:1.3:1.9 to obtain a negative electrode slurry. The negative electrode slurry is coated on both surfaces of the negative electrode current collector copper foil, dried, and cold pressed to obtain a negative electrode sheet.

[0234] Preparation of isolation membrane

[0235] The base membrane is a PE porous membrane with a thickness of 7μm. Aluminum oxide and the binder polyacrylic acid are mixed in a mass ratio of 94:6 in an appropriate amount of deionized water to obtain a coating slurry. The prepared coating slurry is applied to both surfaces of the PE porous membrane using a coating machine, and then dried and cut to obtain a separator. The coating thickness on one side of the PE porous membrane is 1.5μm, the total coating thickness is 3μm, and the total thickness of the separator is 10μm.

[0236] Preparation of electrolyte

[0237] Dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and fluoroethylene carbonate (FEC) were mixed in a mass ratio of 15:45:35:5 to obtain an organic solvent, and LiPF6 was dissolved in the organic solvent to obtain an electrolyte solution. The concentration of LiPF6 was 1.1 mol / L.

[0238] Preparation of battery cells

[0239] 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.

[0240] The electrode assembly is placed in a cylindrical shell with one end open, and the contact portion between the shell and the end cap assembly is laser welded. After welding, a weld is formed between the shell and the end cap assembly. The weld pool depth is 350μm, the width is 1000μm, and the aspect ratio is 0.35. The shell and end cap are both made of steel. The end cap assembly is equipped with a pressure relief mechanism, which is an explosion-proof valve. The burst strength A of the pressure relief mechanism is 0.75MPa. The burst strength B between the shell and end cap assembly is 2.8MPa.

[0241] The blasting strength between the shell and the end cover assembly and the weld parameters between the shell and the end cover assembly can be adjusted by adjusting the laser welding parameters. The laser wavelength is 1064nm and the laser power density is 6.0×10 6 W / cm 2 , the spot diameter is 200μm.

[0242] After welding, electrolyte is injected into the electrode assembly, and after a series of resting and forming steps, a cylindrical battery cell is obtained. The cylindrical battery cell has a diameter of 46mm, a length of 95mm, and a shell wall thickness of 0.45mm.

[0243] Example 1-2 to Example 1-5

[0244] The preparation of the battery cell is the same as that of Example 1-1, except that the laser welding process parameters of the contact portion between the shell and the end cover assembly and the weld parameters between the shell and the end cover assembly are different. Specific parameters are shown in Table 1.

[0245] Comparative Example 1-1

[0246] The preparation of the battery cell is the same as that of Example 1-1, except that the laser welding process parameters of the contact portion between the shell and the end cover assembly and the weld parameters between the shell and the end cover assembly are different. Specific parameters are shown in Table 1.

[0247] Battery cell nail penetration test

[0248] At 25°C, the battery cells were charged at a constant current and voltage of 0.33C to an upper cutoff voltage of 4.25V. The cells were then charged at a constant voltage of 0.05C, at which point the cells were fully charged. The fully charged cells were secured in a fixture and a 5mm diameter, high-temperature resistant steel needle was used to penetrate the large surface of the cells vertically at a speed of 25mm / s. The changes in the casing were observed. Ten battery cell samples were collected, and the number of intact casings after the nail penetration test was counted, representing the casing integrity rate. The integrity of the casing was determined by the explosion-proof valve opening properly and the absence of cracks or explosions between the casing and the end cap.

[0249] The nail penetration test can simulate the thermal runaway caused by internal short circuit of the battery cell. After the test, if the shell is intact and the explosion-proof valve opens normally, the directional pressure relief function of the pressure relief mechanism will not be affected, and the battery cell will not explode.

[0250] Table 1

[0251] It can be seen from the test results in Table 1 that by ensuring that the burst strength between the shell and the end cover assembly is greater than or equal to 1.2 MPa, the battery cell can have high reliability. When the battery cell thermal runaway occurs and the pressure relief mechanism is actuated, the structure of the battery cell will not be broken. As a result, the pressure relief mechanism can better play the role of directional pressure relief, thereby further reducing the occurrence of battery cell explosions.

[0252] By further adjusting the burst strength between the shell and the end cap assembly and / or the multiple of the burst strength between the shell and the end cap assembly and the burst strength of the pressure relief mechanism, the cylindrical battery cell can be made more reliable.

[0253] Example 2-1

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

[0255] The positive electrode active material also includes single crystal morphology of LiNi 0.9 Co 0.06 Mn 0.04 O2 and polycrystalline LiNi 0.9 Co 0.06 Mn 0.04 O2. Single crystal morphology of LiNi 0.9 Co 0.06 Mn 0.04 The amount of O2 accounts for 60%, and the polycrystalline LiNi 0.9 Co 0.06 Mn 0.04 The amount of O2 accounts for 40%. Single crystal morphology of LiNi 0.9 Co 0.06 Mn 0.04 The volume distribution particle size Dv50 of O2 is 4.0μm, and the polycrystalline morphology of LiNi 0.9 Co 0.06 Mn 0.04 The volume distribution particle size Dv50 of O2 was 11.0 μm. The volume distribution particle size Dv50 of the mixed positive electrode active material was 6.9 μm.

[0256] Energy density test of battery cells

[0257] At 25°C, charge the battery cell at a constant current of 0.33C to 4.25V, then charge it at a constant voltage to a current of 0.05C. After standing for 5 minutes, discharge the battery cell at a constant current of 0.33C to 2.8V, and calculate the discharge energy Q. The volumetric energy density (Wh / L) of a battery cell is calculated as: discharge energy Q / cell volume V. The volume V of a battery cell can be calculated using the formula for the volume of a cylinder: V = (π × d × d) × L × 0.25. L is the axial dimension of the battery cell, and d is the diameter of the battery cell.

[0258] Battery cell cycle performance test

[0259] At 25°C, charge the battery cell at a constant current of 1C to 4.25V, then charge it at a constant voltage to a current of 0.05C. After 5 minutes of rest, discharge the battery cell at a constant current of 1C to 2.8V. Record the discharge capacity at this point, which is the first cycle discharge capacity. Repeat the battery cell charge and discharge test as described above until the battery cell capacity decays to 80% of the first cycle discharge capacity. Record the number of cycles.

[0260] Table 2

[0261] It can be seen from the test results in Table 2 that by adjusting the ratio of the single-crystal layered lithium-containing transition metal oxide and the polycrystalline layered lithium-containing transition metal oxide in the positive electrode active material, the battery cell can have both high energy density and good cycle performance.

[0262] 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 battery cell, wherein: The battery cell includes a shell, an electrode assembly, and an end cap assembly. The shell has a receiving cavity and an opening. The electrode assembly is placed in the receiving cavity. The end cap assembly covers the opening. The electrode assembly includes a positive electrode sheet. 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. The positive electrode film layer includes a positive electrode active material. The positive electrode active material includes a layered lithium-containing transition metal oxide with a single crystal morphology. The burst strength between the shell and the end cover assembly is greater than or equal to 1.2 MPa.

2. The battery cell according to claim 1, wherein: The end cover assembly includes a pressure relief mechanism, and the burst strength between the shell and the end cover assembly is greater than or equal to 1.35 times the burst strength of the pressure relief mechanism.

3. The battery cell according to claim 2, wherein: The battery cell is a square-shell battery cell, and the bursting strength between the shell and the end cover assembly of the square-shell battery cell is 1.2Mpa-1.5Mpa; and / or the bursting strength between the shell and the end cover assembly of the square-shell battery cell is 1.35 times to 2 times the bursting strength of the pressure relief mechanism of the square-shell battery cell.

4. The battery cell according to claim 2, wherein: The battery cell is a cylindrical battery cell, and the burst strength between the shell and the end cover assembly of the cylindrical battery cell is 1.5 MPa-2.8 MPa; and / or the burst strength between the shell and the end cover assembly of the cylindrical battery cell is 2 to 4 times the burst strength of the pressure relief mechanism of the cylindrical battery cell.

5. The battery cell according to claim 4, wherein: The bursting strength between the shell and the end cover assembly of the cylindrical battery cell is 1.7 MPa-2.8 MPa; and / or, the bursting strength between the shell and the end cover assembly of the cylindrical battery cell is 2.2 to 4 times the bursting strength of the pressure relief mechanism of the cylindrical battery cell, optionally 2.5 to 4 times.

6. The battery cell according to any one of claims 2 to 5, wherein: The bursting strength of the pressure relief mechanism is 0.6MPa-0.9MPa.

7. The battery cell according to any one of claims 1 to 6, wherein: The shell is connected to the end cover assembly by welding.

8. The battery cell according to claim 7, wherein: The battery cell satisfies at least one of the following conditions (1) to (4): (1) The molten pool depth of the weld between the shell and the end cover assembly is 300 μm-400 μm; (2) The width of the weld between the shell and the end cover assembly is 910 μm-1100 μm, and can be optionally 940 μm-1100 μm; (3) The depth-to-width ratio of the weld between the housing and the end cover assembly is 0.33-0.37; (4) The molten pool depth of the weld between the shell and the end cover assembly is less than 1 / 2 of the thickness of the end cover assembly.

9. The battery cell according to any one of claims 1 to 8, wherein: The wall thickness of the housing is 0.3 mm to 0.6 mm; and / or, The material of the housing includes any one of steel and aluminum alloy; and / or, The thickness of the end cover assembly is 0.6 mm to 2.0 mm.

10. The battery cell according to any one of claims 1 to 9, wherein: The single crystal layered lithium-containing transition metal oxide accounts for 20% to 100% of the positive electrode active material.

11. The battery cell according to any one of claims 1 to 10, wherein: The positive electrode active material includes both a layered lithium-containing transition metal oxide with a single crystal morphology and a layered lithium-containing transition metal oxide with a polycrystalline morphology. The amount of the layered lithium-containing transition metal oxide with a single crystal morphology in the positive electrode active material is greater than or equal to 30% and less than 50%, and the amount of the layered lithium-containing transition metal oxide with a polycrystalline morphology in the positive electrode active material is greater than 50% and less than or equal to 70%.

12. The battery cell according to any one of claims 1 to 11, wherein: The volume distribution particle size Dv50 of the positive electrode active material is 6 μm-10 μm, and can be optionally 6.9 μm-10 μm.

13. The battery cell according to any one of claims 1 to 12, wherein: The electrode assembly includes a negative electrode plate, which includes a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

14. The battery cell according to claim 13, wherein: The negative electrode active material satisfies at least one of the following conditions (1) to (3): (1) The negative electrode active material includes graphite; (2) The negative electrode active material includes graphite, and the graphite includes at least one of artificial graphite and natural graphite; (3) The negative electrode active material includes a silicon-based material.

15. The battery cell according to any one of claims 1 to 14, wherein: The battery cell further includes an electrolyte, the electrolyte includes an organic solvent, the organic solvent includes a chain carbonate, the chain carbonate includes one or both of dimethyl carbonate and ethyl methyl carbonate, and the mass proportion of the chain carbonate in the organic solvent is 50%-80%.

16. The battery cell according to claim 15, wherein: The organic solvent further comprises cyclic carbonate, which comprises one or both of ethylene carbonate and fluoroethylene carbonate. The mass proportion of the cyclic carbonate in the organic solvent is 20%-50%.

17. The battery cell according to any one of claims 1 to 16, wherein: The battery cell further includes an electrolyte, the electrolyte containing cations and anions, the cations including one or both of lithium ions and sodium ions, and the anions including one or more of hexafluorophosphate anions and anions shown in Formula 1. R1 and R2 each independently include a fluorine atom or a C1-C6 fluoroalkyl group.

18. The battery cell according to claim 17, wherein: The anions include both hexafluorophosphate anions and anions shown in Formula 1, Optionally, the molar concentration of the anion represented by Formula 1 is greater than the molar concentration of the hexafluorophosphate anion; Optionally, the molar concentration of the anion represented by Formula 1 is 0.6 mol / L-0.9 mol / L; Optionally, the molar concentration of the hexafluorophosphate anion is 0.3 mol / L-0.5 mol / L.

19. A battery comprising the battery cell according to any one of claims 1 to 18.

20. An electrical device comprising the battery according to claim 19, wherein the battery is used to provide electrical energy.

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