Battery cell, battery and electric device

Abstract

The present invention belongs to the technical field of batteries. Disclosed are a battery cell, a battery and an electric device. The battery cell comprises: an electrode assembly; a housing; an end cover, wherein the housing and the end cover form a space for accommodating the electrode assembly, and the end cover is provided with a pressure relief mechanism; and an electrolyte solution, wherein the electrolyte solution comprises a solvent and an electrolyte salt, the solvent comprising dimethyl carbonate, and the electrolyte salt comprising lithium bisfluorosulfonimide. In the thickness direction of the end cover, the gap D between the electrode assembly and the inner side of the pressure relief mechanism satisfies: 1 mm≤D≤7 mm; and the capacity Q of the battery cell satisfies: 30 Ah≤Q≤40 Ah. The battery cell has a fast charging capacity, a high energy density and high reliability.

Description

Battery cell, battery, and electric device Cross-reference to related applications

[0001] This application claims priority to Chinese Patent Application No. 202411060661.3, filed on August 5, 2024, entitled “Battery cell, battery, and electric device”, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0002] The present application relates to the technical field of batteries, and more particularly, to a battery cell, a battery, and an electric device. BACKGROUND

[0003] New energy industry is attracting more and more attention. In the new energy industry, battery technology is an important factor for its development.

[0004] The development of battery technology needs to consider various design factors, such as energy density, cycle life, capacity, fast charging performance, reliability, etc. Therefore, how to provide a battery cell with fast charging capability, high reliability and high energy density is an urgent technical problem to be solved. SUMMARY

[0005] The present application is made in view of the above-mentioned problem, and aims to provide a battery cell with fast charging capability, high reliability and high energy density.

[0006] To achieve the above-mentioned purpose, the present application provides a battery cell, a battery, and an electric device.

[0007] In a first aspect, a battery cell is provided, comprising: an electrode assembly; a shell; an end cover, the shell and the end cover form a space containing the electrode assembly, the end cover is provided with a pressure relief mechanism; an electrolyte, the electrolyte comprises a solvent and an electrolyte salt, the solvent comprises dimethyl carbonate, and the electrolyte salt comprises a lithium bisfluorosulfonylimide salt; an electrode assembly contained in the shell; along the thickness direction of the end cover, the gap D between the electrode assembly and the inner side of the pressure relief mechanism satisfies: 1mm≤D≤7mm; the capacity Q of the battery cell satisfies: 30Ah≤Q≤40Ah.

[0008] In the embodiment of the present application, the capacity Q of the battery monomer satisfies: 30 Ah≤Q≤40 Ah; in the battery monomer, due to the fact that the electrolyte includes dimethyl carbonate and lithium bisfluorosulfonylimide salt, the battery monomer has fast charging capability, and in the case that the battery monomer has thermal runaway, more gas will be generated in the battery monomer; by setting the gap D≥1 mm between the electrode assembly and the inner side of the pressure relief mechanism of the end cover in the thickness direction of the end cover, there is enough space in the battery monomer to facilitate the opening of the valve of the pressure relief mechanism, which can reduce the risk of the electrode terminal of the battery monomer being separated from the shell and the shell being broken; by setting D≤7 mm, the waste of the space in the battery monomer can be reduced, which is conducive to improving the energy density of the battery monomer. Therefore, the battery monomer of the embodiment of the present application has fast charging capability, high energy density and high reliability.

[0009] In a possible implementation manner, 2 mm≤D≤6 mm. In the case of D≥2 mm, there is enough space in the battery monomer, on the one hand, enough space can be provided to accommodate the gas generated in the battery monomer, and on the other hand, there is enough space in the battery monomer to facilitate the opening of the valve of the pressure relief mechanism, thereby facilitating the discharge of the high-temperature and high-pressure substances in the battery monomer when the battery monomer has thermal runaway, reducing the risk of the electrode terminal of the battery monomer being separated from the shell and the shell being broken; in the case of D≤6 mm, the waste of the space in the battery monomer can be reduced. Therefore, by setting 2 mm≤D≤6 mm, the volume energy density and reliability of the battery monomer can be considered.

[0010] In a possible implementation manner, the mass content A of the dimethyl carbonate satisfies: 20wt%≤A≤80wt%, based on the total mass of the electrolyte; and / or, the mass content B of the lithium bisfluorosulfonylimide salt satisfies: 1wt%≤B≤16wt%, based on the total mass of the electrolyte.

[0011] In the above technical solution, the mass content of the dimethyl carbonate and the mass content of the lithium bisfluorosulfonylimide salt satisfy the above range, which is conducive to improving the fast charging performance of the battery monomer.

[0012] In a possible implementation manner, 50wt%≤A≤75wt%; and / or, 1wt%≤B≤11wt%. In the above technical solution, the mass content of the lithium bisfluorosulfonylimide salt and the dimethyl carbonate satisfies the above range, which can further consider the fast charging performance and reliability of the battery monomer.

[0013] In a possible implementation manner, 20wt%≤A≤65wt%, the mass content of the lithium bisfluorosulfonylimide salt satisfies the above range, which is further conducive to considering the fast charging performance and reliability of the battery monomer.

[0014] In a possible implementation, a mass content ratio A:B of the dimethyl carbonate and the lithium bisfluorosulfonylimide salt satisfies: 3≤A:B≤40.

[0015] In the technical solution, 3≤A:B≤40, so that the battery monomer has good fast charging performance and less gas production, and the fast charging performance and reliability of the battery monomer can be considered.

[0016] In a possible implementation, 5≤A:B≤30. In this way, the battery monomer has good fast charging performance and high reliability.

[0017] In a possible implementation, in the battery monomer, a ratio C of the mass of the electrolyte to the capacity of the battery monomer satisfies: C≤1.6 g / Ah. In this way, the mass of the electrolyte in the battery monomer is small, which is beneficial to reduce the gas production in the battery monomer when the battery monomer is in thermal runaway, reduce the severity when the battery monomer is in thermal runaway, and further improve the reliability of the battery monomer.

[0018] In a possible implementation, 1.2 g / Ah≤C≤1.4 g / Ah. In the case of C≤1.4 g / Ah, the mass of the electrolyte in the battery monomer is small, which is beneficial to further improve the reliability of the battery monomer; in the case of C≥1.2 g / Ah, the mass of the electrolyte can meet the normal work of the battery monomer, and the influence on the cycle performance and other electrical properties of the battery monomer can be reduced. Therefore, the technical solution is beneficial to consider the reliability and electrical properties of the battery monomer.

[0019] In a possible implementation, in the battery monomer, a ratio E of the mass of the remaining electrolyte to the capacity of the battery monomer satisfies: 0.7 g / Ah≤E≤1.1 g / Ah, within 1000 cycles of the battery monomer. In the technical solution, within 1000 cycles of the battery monomer, the ratio of the mass of the remaining electrolyte to the capacity of the battery monomer is in the range of 0.7 g / Ah to 1.1 g / Ah.

[0020] In a possible implementation, along the thickness direction of the end cover, the size H of the battery monomer satisfies: 90 mm≤H≤120 mm. In this way, the battery monomer has a suitable capacity and height, and the battery monomer has a relatively suitable energy density.

[0021] In a possible implementation, in the battery monomer, the mass K of the electrolyte satisfies: 30 g≤K≤60 g. In this way, the battery monomer has good fast charging performance.

[0022] In a possible implementation, in the battery monomer, 35g≤K≤55g. In this way, the battery monomer has better fast-charging performance and higher reliability.

[0023] In a possible implementation, within 1000 cycles of the battery monomer, the mass P of the remaining electrolyte in the battery monomer satisfies: 22g≤P≤36g. In this technical solution, within 1000 cycles of the battery monomer, the mass of the remaining electrolyte in the battery monomer is in the range of 22g to 36g.

[0024] In a possible implementation, the electrode assembly includes a positive electrode sheet and a negative electrode sheet, the positive electrode sheet has a compaction density greater than or equal to 3.4g / cm 3 , and / or the negative electrode sheet has a compaction density greater than or equal to 1.2g / cm 3 .

[0025] In a possible implementation, the compaction density of the positive electrode sheet is 3.4g / cm 3 ~3.7g / cm 3 , and / or the compaction density of the negative electrode sheet is 1.2g / cm 3 ~1.7g / cm 3 .

[0026] In the above technical solution, the positive electrode sheet and / or the negative electrode sheet has a higher compaction density, which is conducive to improving the energy density of the battery monomer. In addition, when the compaction density of the positive electrode sheet and / or the negative electrode sheet is high, the demand for electrolyte of the battery monomer is reduced, which is conducive to reducing the electrolyte injection coefficient of the battery monomer, and further reducing the gas production amount and the degree of severity of the battery monomer in thermal runaway, and improving the reliability of the battery monomer.

[0027] In a possible implementation, within 1000 cycles of the battery monomer, the compaction density of the positive electrode sheet is 3.35g / cm 3 ~3.69g / cm 3 , and / or the compaction density of the negative electrode sheet is 1.2g / cm 3 ~1.65g / cm 3 . After a certain number of charge and discharge cycles of the battery monomer, the positive electrode sheet and the negative electrode sheet swell, and the compaction densities of the positive electrode sheet and the negative electrode sheet change.

[0028] In a possible implementation, the porosity of the positive electrode sheet is 22% to 26%, and / or the porosity of the negative electrode sheet is 23% to 30%. In this way, the positive electrode sheet and / or the negative electrode sheet has a lower porosity, which is beneficial to reducing the amount of electrolyte required in the battery cell, thereby reducing the gas production amount and the severity of thermal runaway of the battery cell, and improving the reliability of the battery cell.

[0029] In a possible implementation, the positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes lithium nickel oxide or metal phosphate. In this way, the battery cell including lithium nickel oxide can have a higher energy density, and the battery cell including metal phosphate has higher reliability.

[0030] In a possible implementation, the chemical formula of the lithium nickel oxide satisfies: Li 1+a [Ni x Co y Mn z M b ]O 2-c , M includes at least one of Zr, Al, Ti, Sb, Nb, Te, Mg, B, Ca, V, Ta or Sr, 0.2 >= a >= -0.2, 1 > x >= 0.7, 0.3 > y > 0, 0.3 > z > 0, 0.3 >= b >= 0, 0.5 >= c >= 0. The above positive electrode active material has a higher content of Ni, which is beneficial to improving the energy density of the battery cell.

[0031] In a possible implementation, in the battery cell, the gram weight per unit area of the positive electrode active material is 15 mg / cm 2 ~ 23 mg / cm 2 . In the above technical solution, the gram weight of the positive electrode active material is larger, and the battery cell has a higher energy density.

[0032] In a possible implementation, the negative electrode sheet includes a negative electrode active material, and the negative electrode active material includes graphite and a silicon-containing material, the silicon-containing material includes at least one of elemental silicon, silicon-oxygen composite, silicon-carbon composite, silicon-nitrogen composite, silicon-containing alloy or silicon-oxygen-carbon composite material, and the graphite includes at least one of natural graphite or artificial graphite. The arrangement of the above negative electrode active material is beneficial to improving the energy density of the battery cell.

[0033] In a possible implementation, the silicon-containing material includes silicon-carbon composite, and the mass fraction of silicon in the silicon-carbon composite is 40wt% to 60wt% based on the total mass of the silicon-containing material. The mass content of silicon in the silicon-carbon composite is within the above range, and the electrode assembly has a relatively appropriate expansion rate, which is beneficial to the normal use of the battery cell.

[0034] In a possible implementation, the mass content of the silicon-containing material is 1wt%-20wt% based on the total mass of the negative active material. In this way, the silicon-containing material has a suitable mass content in the negative active material, so that the electrode assembly has a relatively suitable expansion rate, facilitating normal use of the battery cell.

[0035] In a possible implementation, the battery cell has a gram weight per unit area of the negative active material of 6mg / cm 2 -13mg / cm 2 In the above technical solution, the gram weight per unit area of the negative active material is relatively large, and the battery cell has a higher energy density.

[0036] In a possible implementation, the electrode assembly further includes a separator film, the separator film is arranged between the positive electrode sheet and the negative electrode sheet, and the separator film includes a base film and a ceramic coating, the ceramic coating is arranged on a side of the base film facing the positive electrode sheet. In this way, the separator film has a relatively small absorption amount of electrolyte, which is conducive to reducing the mass of electrolyte in the battery cell, thereby reducing the gas production amount and the degree of severity of thermal runaway of the battery cell, and improving the reliability of the battery cell.

[0037] In a possible implementation, the porosity of the separator film is 30%-45%. In this way, the separator film has a relatively low porosity, and the separator film is not easily punctured, so that the battery cell has relatively high reliability; meanwhile, the arrangement of the electrolyte is conducive to improving the transmission rate of ions; in cooperation of the separator film and the electrolyte, the battery cell has good fast-charging performance and relatively high reliability.

[0038] In a possible implementation, the end cover includes an end cover body, and the pressure relief mechanism is arranged on the inner side or the outer side of the end cover body. By arranging the pressure relief mechanism on the inner side of the end cover body, the risk of rupture of the pressure relief mechanism during normal use of the battery cell can be reduced, which is conducive to improving the long-term reliability of the pressure relief mechanism; by arranging the pressure relief mechanism on the outer side of the end cover body, the preparation difficulty of the pressure relief mechanism can be reduced.

[0039] In a possible implementation, the end cover body is provided with a score groove, and the area defined by the score groove forms the pressure relief mechanism. In this way, the preparation of the pressure relief mechanism is facilitated, and the risk of interference between the pressure relief mechanism and the components in the battery cell can be reduced.

[0040] In a possible implementation, an area S defined by the pressure relief mechanism and an area S0 of the end cover satisfy: 25%≤S / S0≤50%. In the case of S / S0≥25%, when the battery cell is in thermal runaway, the pressure relief mechanism is more prone to rupture, thereby facilitating the end cover to have a larger tearing opening and facilitating the discharge of high-temperature and high-pressure substances inside the battery cell; in the case of S / S0≤50%, the interference of the pressure relief mechanism on the connection between the end cover and the shell can be reduced, thereby facilitating the connection between the end cover and the shell.

[0041] In a possible implementation, an area S of the pressure relief mechanism and a capacity Q of the battery cell satisfy: 12mm 2 / Ah≤S / Q≤20mm 2 / Ah. In this way, the battery cell with different capacities can be provided with the pressure relief mechanism with different areas, thereby facilitating the discharge of high-temperature and high-pressure substances when the battery cell is in thermal runaway and facilitating the connection between the shell and the end cover.

[0042] In a possible implementation, an area S of the pressure relief mechanism is greater than or equal to 500mm 2 . In this way, when the battery cell is in thermal runaway, the pressure relief mechanism is more prone to rupture, thereby facilitating the end cover to have a larger tearing opening and facilitating the discharge of high-temperature and high-pressure substances inside the battery cell.

[0043] In a possible implementation, an area S of the pressure relief mechanism satisfies: 600mm 2 ≤S≤800mm 2 . In the case of S≥600mm 2 , when the battery cell is in thermal runaway, the pressure relief mechanism is more prone to rupture, thereby facilitating the end cover to have a larger tearing opening and facilitating the discharge of high-temperature and high-pressure substances inside the battery cell; in the case of S≤800mm 2 , the interference of the pressure relief mechanism on the connection between the end cover and the shell can be reduced, thereby facilitating the connection between the end cover and the shell.

[0044] In a possible implementation, a voltage platform of the battery cell is 3.5V to 3.7V. In the case that the voltage window of the battery cell is in the above range, the battery cell has a higher energy density.

[0045] In a possible implementation, the solvent further includes methyl ethyl carbonate and ethylene carbonate, and the electrolyte salt further includes lithium hexafluorophosphate. In the above technical solution, the electrolyte has a lower viscosity and a higher ionic conductivity, thereby facilitating the improvement of the fast-charging performance of the battery cell.

[0046] In a possible implementation, the electrolyte further includes an additive, and the additive includes at least one of fluoroethylene carbonate or vinylene carbonate. The addition of the additive can reduce decomposition of the electrolyte, and facilitate improvement of fast charging performance of the battery cell.

[0047] In a possible implementation, the shell has a first opening facing downward, and the end cover covers the first opening. By arranging the end cover to cover the opening of the shell facing downward, the influence of the pressure relief mechanism on other parts of the shell during opening of the valve is reduced, thereby facilitating improvement of reliability of the battery cell in a thermal runaway situation.

[0048] In a possible implementation, the battery cell further includes a current collecting member accommodated in the shell, located between the electrode assembly and the end cover in the thickness direction of the end cover, and electrically connected to the tab of the electrode assembly and the shell. In this way, the current collecting member can be used to electrically connect the electrode assembly and the shell.

[0049] In a possible implementation, the tabs of the electrode assembly are located close to the same end of the end cover, which can shorten the distance of electrical connection between the tabs and the shell, reduce waste of internal space of the battery cell, improve the capacity of the battery cell, and thereby improve the energy density of the battery cell.

[0050] In a possible implementation, an inner side surface of the shell is provided with a limiting portion, and the limiting portion is located between the electrode assembly and the end cover in the thickness direction of the end cover, and the current collecting member abuts against a side of the limiting portion facing the electrode assembly. The limiting portion not only limits the movement of the end cover in the direction facing the electrode assembly, but also facilitates realization of a proper gap size between the electrode assembly and the pressure relief mechanism of the end cover, thereby providing a space for actuation of the pressure relief mechanism.

[0051] In a possible implementation, the battery cell further includes a sealing member arranged between the end cover and the shell. The sealing member facilitates improvement of the sealing performance of the battery cell, and thereby facilitates improvement of the reliability of the battery cell.

[0052] In a possible implementation, the end cover is provided with at least one protrusion in a direction perpendicular to the thickness direction of the end cover, and the at least one protrusion is arranged on the end cover body and protrudes away from the electrode assembly; and in the thickness direction of the end cover, the size L of the at least one protrusion satisfies: 1 mm≤L≤5 mm.

[0053] Due to the above electrolyte, the battery cell generates more gas when thermal runaway occurs, and the degree of thermal runaway is more severe. On the one hand, the end cover body is provided with at least one protrusion in the plane perpendicular to the thickness direction of the end cover. In the case of 1mm≤D≤3mm, the space between adjacent protrusions can provide additional buffer space to avoid direct abutment of the battery cell and the pressure relief mechanism. In the case of not occupying too much space inside the battery cell, the pressure relief mechanism can be opened in time when the battery cell is in thermal runaway, reducing the risk of shell rupture and electrode terminal separation from the shell, and having high reliability. On the other hand, the size of the protrusion in the thickness direction of the end cover satisfies 1mm~5mm, and the protrusion can play the role of a local reinforcing rib to ensure directional pressure relief of the pressure relief mechanism during valve opening and reduce the phenomenon of irregular rupture of the shell. Therefore, the above technical scheme can improve the energy density and reliability of the battery cell while taking into account the fast charging performance of the battery cell.

[0054] In a second aspect, a battery is provided, including the battery cell in the first aspect and any possible implementation manner thereof.

[0055] In a third aspect, a use electric device is provided, including the battery in the second aspect. BRIEF DESCRIPTION OF DRAWINGS

[0056] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can be obtained by the drawings without creative labor.

[0057] FIG. 1 is a schematic view of a battery cell according to an embodiment of the present application;

[0058] FIG. 2 is a schematic view of a cross section of the battery cell in FIG. 1 along the A-A direction;

[0059] FIG. 3 is an enlarged schematic view of the C region in FIG. 2;

[0060] FIG. 4 is a schematic view of a cross section of a battery cell according to another embodiment of the present application;

[0061] FIG. 5 is an exploded structural schematic view of a battery cell according to an embodiment of the present application;

[0062] FIG. 6 is an exploded structural schematic view of a battery cell according to another embodiment of the present application;

[0063] FIG. 7 is a schematic view of the force on the pressure relief mechanism arranged inside the end cover body according to an embodiment of the present application;

[0064] FIG. 8 is a schematic view of the force on the pressure relief mechanism arranged outside the end cover body according to an embodiment of the present application;

[0065] Fig. 9 is a structural schematic view of an end cap according to an embodiment of the present application;

[0066] Fig. 10 is a structural schematic view of a current collecting member according to an embodiment of the present application;

[0067] Fig. 11 is a schematic view of a battery according to an embodiment of the present application;

[0068] Fig. 12 is a schematic view of an electric device according to an embodiment of the present application.

[0069] Reference Signs: 1: vehicle; 10: battery; 30: controller; 40: motor; 3: case; 31: first case portion; 32: second case portion; 20: battery cell; 21: housing; 22: electrode assembly; 23: end cap; 24: current collecting member; 25: electrode terminal; 26: pressure relief mechanism; 261: score groove; 262: notch; 240: current collecting body; 241: elastic portion; 242: current collecting tab; 2411: first tab; 2412: second tab; 243: center portion; 2414: abutting region; 231: end cap body; 232: protrusion; 211: stopper; 212: seal; 27: current collecting disk; 28: insulating member; 29: tab; 233: protruding portion; 213: first opening. DETAILED DESCRIPTION

[0070] Embodiments of the battery cell, battery, and electric device according to the present application are described in detail with appropriate reference to the accompanying drawings. However, there are cases where unnecessary detailed description is omitted. For example, there are cases where detailed description of matters that are well known, repeated description of substantially identical structures are omitted. This is to avoid the following description becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the drawings and the following description are provided so that those skilled in the art can fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0071] The ranges disclosed herein are intended to be "open" ranges, i.e., the upper and lower limits of the range are not included. The ranges are also intended to include any and all sub-ranges of the same, wherein each sub-range is inclusive of the end values. For example, if a range is from 1 to 10, then the range includes any and all sub-ranges between (and including) the minimum of 1 and the maximum of 10, that is, any of 1 to 3, 4 to 6, 7 to 9, etc. In other words, unless context dictates otherwise, each numerical range is intended to mean the range including the minimum value and including the maximum value. For example, the numerical range "a-b" or "a to b" indicates "greater than or equal to a, and less than or equal to b." Also, when a parameter is stated to be an integer, it is understood that the parameter is an integer greater than or equal to the minimum value and less than or equal to the maximum value, unless otherwise stated. For example, if a parameter is stated to be an integer ≥ 2, it is understood that the parameter is an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0072] Unless otherwise stated, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0073] Unless otherwise stated, all technical features of the present application and optional technical features can be combined with each other to form new technical solutions.

[0074] Unless otherwise stated, all steps of the present application can be performed in sequence or randomly, and preferably in sequence. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method also comprises step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0075] The battery cell in the embodiments of the present application can refer to the smallest structural unit of the battery. A plurality of battery cells can first form a battery module, and then form a battery from the battery module; or a plurality of battery cells can directly form a battery.

[0076] The battery cell in the embodiments of the present application refers to a battery cell capable of reversible charging and discharging.

[0077] During charging of the battery cell, lithium ions are extracted from the positive active material, move and intercalate into the negative electrode; and during discharging, lithium ions are extracted from the negative electrode, move and intercalate into the positive active material.

[0078] It should be understood that the "intercalation" process described in the present application refers to the process of lithium ions intercalating into the positive active material or the negative electrode due to electrochemical reactions, and the "extraction" or "deintercalation" process described in the present application refers to the process of lithium ions being extracted from the positive active material or the negative electrode due to electrochemical reactions.

[0079] The development of battery technology needs to consider multiple design factors, such as energy density, cycle life, discharge capacity, charge-discharge rate, fast charging capability, reliability, first-cycle charge capacity, etc. With the wide use of batteries, the requirements for the fast charging performance of the batteries are gradually increasing. In the related art, by adding dimethyl carbonate and lithium bisfluorosulfonylimide salt in the electrolyte, the transmission and diffusion of lithium ions are promoted, and the fast charging performance of the battery cell is improved. However, the applicant found in the process of researching the battery cell including the above-mentioned electrolyte that, in the case of thermal runaway of the battery cell, the battery cell including the above-mentioned electrolyte has more gas production and more severe thermal runaway, and the pressure relief mechanism is difficult to open in time, resulting in the phenomenon of electrode terminal separation from the shell and flying out, shell rupture, which is not conducive to the improvement of the reliability of the battery cell.

[0080] In the related art, in some processing methods, in order to improve the reliability of the battery cell, a water-cooled plate is arranged between the surfaces with the largest surface area of adjacent battery cells to cool / insulate the battery cells, so as to reduce the influence of the thermal runaway battery cell on the adjacent battery cells, and to improve the reliability of the battery including the battery cells; in other processing methods, a fire-fighting pipeline is arranged in the battery, and when the battery cell in the battery experiences thermal runaway, the fire-fighting medium in the fire-fighting pipeline flows out to cool the battery cell experiencing thermal runaway, and to reduce the influence of the battery cell experiencing thermal runaway on the adjacent battery cells. In the related art, the design is mainly from the perspective of the battery to improve the reliability of the battery cell, and there is less research on designing from the perspective of the battery cell itself to improve the reliability of the battery cell.

[0081] Therefore, the battery monomer provided in the embodiments of the present application has a capacity Q satisfying 30 Ah≤Q≤40 Ah, and the electrolyte includes dimethyl carbonate and lithium bisfluorosulfonylimide salt, and the gap D between the electrode assembly and the inner side of the pressure relief mechanism in the thickness direction of the end cover satisfies 1 mm≤D≤7 mm. In this way, the battery monomer not only has the fast charging performance, but also can timely open the valve when the battery monomer has thermal runaway, thereby reducing the risk of shell rupture and electrode terminal separation from the shell, and has high reliability. In addition, the gap D is in the above range, and the utilization rate of the internal space of the battery monomer is high, and the battery monomer also has high energy density.

[0082] [The battery monomer]

[0083] FIG. 1 is a schematic diagram of a battery monomer according to an embodiment of the present application, FIG. 2 is a schematic diagram of a cross section of the battery monomer in FIG. 1 along the A-A direction, FIG. 3 is an enlarged schematic diagram of the C region in FIG. 2, FIG. 4 is a schematic diagram of a cross section of a battery monomer according to another embodiment of the present application, FIG. 5 is an exploded structural schematic diagram of a battery monomer according to an embodiment of the present application, and FIG. 6 is an exploded structural schematic diagram of a battery monomer according to another embodiment of the present application.

[0084] In combination with FIGS. 1 to 6, the embodiments of the present application provide a battery monomer 20, which includes a shell 21, an end cover 23, an electrode assembly 22, and an electrolyte.

[0085] The shell 21 can be a hollow structure having an opening at one end, or a hollow structure having openings at both ends.

[0086] As an example, in combination with FIGS. 5 and 6, the shell 21 is a hollow structure having an opening at one end, and the end cover 23 is used to cover the opening of the shell 21.

[0087] The material of the shell 21 can be various, such as copper, iron, aluminum, steel, aluminum alloy, etc. The shell 21 can have various shapes, such as a cylinder, a cuboid, etc. As an example, in the embodiments of the present application, the material of the shell 21 is steel, and the shell 21 is a cylinder.

[0088] The electrode assembly 22 is a component in which electrochemical reactions occur in the battery cell 20. The electrode assembly 22 can include a positive electrode tab, a negative electrode tab, and a separator film between the positive electrode tab and the negative electrode tab. The positive electrode tab includes a positive electrode current collector and a positive electrode film layer coated on a surface of the positive electrode current collector, and the current collector without the positive electrode film layer protrudes from the current collector with the positive electrode film layer, and the current collector without the positive electrode film layer serves as a positive electrode tab. The negative electrode tab includes a negative electrode current collector and a negative electrode film layer coated on a surface of the negative electrode current collector, and the current collector without the negative electrode film layer protrudes from the current collector with the negative electrode film layer, and the current collector without the negative electrode film layer serves as a negative electrode tab. The positive electrode tab, the separator film, and the negative electrode tab can form the electrode assembly 22 by winding or stacking. In combination with FIG. 6, in some embodiments, the housing 21 has a first opening 213 facing downward, and the end cover 23 covers the first opening 213. By providing the end cover 23 to cover the first opening 213 of the housing 21 facing downward, the influence of the pressure relief mechanism 26 on other parts of the housing 21 during the opening process is reduced, thereby facilitating the improvement of the reliability of the battery cell 20 in the case of thermal runaway.

[0089] It should be noted that "down" in the embodiments of the present application refers to the direction of gravity.

[0090] As an example, the positive electrode tab, the separator film, and the negative electrode tab are wound into the electrode assembly 22, and the region provided with the positive electrode film layer and / or the negative electrode film layer in the electrode assembly 22 after winding can be referred to as the main body of the electrode assembly 22, and the region without the positive electrode film layer and the negative electrode film layer is referred to as the tab of the electrode assembly 22. As an example, along the thickness direction of the end cover 23, the positive electrode tab and the negative electrode tab are provided at both ends of the electrode assembly 22.

[0091] The end cover 23 forms a space with the housing 21 to accommodate the electrode assembly 22. As an example, the housing 21 has an opening, and the end cover 23 covers the opening to isolate the internal environment of the battery cell 20 from the external environment. The end cover 23 covers the opening of the housing 21, and the end cover 23 and the housing 21 together define a space for accommodating the electrode assembly 22 and the electrolyte.

[0092] The shape of the end cover 23 can be adapted to the shape of the housing 21, for example, the housing 21 is a rectangular plate structure adapted to the shape of the housing 21, and the housing 21 is a cylindrical structure, and the end cover 23 is a circular plate structure adapted to the shape of the housing 21. The material of the end cover 23 can also be various, for example, the end cover 23 can be a metal material, such as copper, iron, aluminum, steel, aluminum alloy, etc. The material of the end cover 23 can be the same as or different from the material of the housing 21. As an example, the material of the end cover 23 is copper.

[0093] In the battery cell 20, the end cover 23 can be one or two. If the shell 21 is a hollow structure with an opening at one end, one end cover 23 is correspondingly arranged; if the shell 21 is a hollow structure with openings at both ends, two end covers 23 are correspondingly arranged, covering the two openings of the shell 21, one of the positive and negative electrode tabs of the electrode assembly 22 is electrically connected with one end cover 23, and the other is electrically connected with the shell 21. In the embodiment in which the shell 21 is a hollow structure with an opening at one end, the end of the shell 21 away from the end cover 23 can be provided with an electrode terminal 25, which is insulatedly connected with the shell 21, one of the positive and negative electrode tabs of the electrode assembly 22 is electrically connected with the shell 21, and the other is electrically connected with the electrode terminal 25.

[0094] The end cover 23 is provided with a pressure relief mechanism 26. The pressure relief mechanism 26 is an element or component for actuating when the internal pressure or temperature of the battery cell 20 reaches a predetermined threshold value to release the internal pressure or temperature of the battery cell 20. The predetermined threshold value can be adjusted according to different design requirements. For example, the predetermined threshold value can depend on the material of one or more of the positive and negative electrode tabs, the electrolyte and the separator in the battery cell.

[0095] "Actuating" means that the pressure relief mechanism 26 generates an action or is activated to a certain state, so that the internal pressure and temperature of the battery cell 20 can be released. The action generated by the pressure relief mechanism 26 can include but is not limited to: at least part of the pressure relief mechanism 26 is broken, broken, torn or opened, etc. When the pressure relief mechanism 26 is actuated, the high-temperature and high-pressure substances inside the battery cell 20 will be discharged outward from the actuated part as the discharge. In this way, the battery cell 20 can be relieved of pressure and temperature under controllable pressure or temperature, thereby reducing the risk of more serious accidents.

[0096] The discharge from the battery cell 20 mentioned in the embodiments of the present application includes but is not limited to: electrolyte, dissolved or split positive and negative electrode tabs, fragments of the separator, high-temperature and high-pressure gas generated by reaction, flame, etc.

[0097] The pressure relief mechanism 26 can be a separate structure from the end cover 23, for example, the pressure relief mechanism 26 is an independent component mounted on the end cover 23. The pressure relief mechanism 26 can be a component such as a rupture disc, a burst disc, a gas valve, a pressure relief valve or a safety valve mounted on the end cover 23, and can specifically adopt a pressure-sensitive or temperature-sensitive element or structure.

[0098] The pressure relief mechanism 26 can be integrated with the end cover 23, for example, the pressure relief mechanism 26 is part of the end cover 23. For example, the pressure relief mechanism can be formed by providing a notch on the end cover 23, the thickness of the notch is significantly smaller than the thickness of other areas of the end cover 23. The notch is the weakest position of the pressure relief mechanism. When the gas generated by the battery cell 20 is too much to cause the internal pressure to rise and reach a threshold value, or the heat generated by the internal reaction of the battery cell 20 causes the internal temperature of the battery cell 20 to rise and reach a threshold value, the pressure relief mechanism 26 can break at the notch to cause the inside and outside of the battery cell 20 to communicate, and the gas pressure and temperature are released outward through the cracking of the pressure relief mechanism 26, thereby avoiding the explosion of the battery cell 20. As an example, a notch groove is provided on the end cover 23, and the area defined by the notch groove forms the pressure relief mechanism 26. The electrolyte includes a solvent and an electrolyte salt, the solvent includes dimethyl carbonate, and the electrolyte salt includes lithium bisfluorosulfonylimide salt.

[0099] The viscosity of dimethyl carbonate DMC is low, which is beneficial to the transmission and diffusion of active ions (such as lithium ions); lithium bisfluorosulfonylimide LiFSI has high ionic conductivity, which is beneficial to the transmission and diffusion of active ions (such as lithium ions). The inclusion of DMC and LiFSI in the electrolyte is beneficial to the transmission of ions, and the battery cell has good fast charging performance.

[0100] In the charging and discharging cycle of the battery cell, the battery cell generates heat, and in the case of heat generation of the battery cell, DMC undergoes decarboxylation reaction to generate CO2; in addition, in the case of thermal runaway of the battery cell, the temperature inside the battery cell further increases (for example, the temperature inside the battery cell can reach 200°C and higher), and at high temperature, LiFSI will have a strong exothermic reaction with the lithium-embedded negative electrode (including the graphite negative electrode embedded with lithium to become LiC6), and a large amount of SO2 and NO2 gas will be generated. Therefore, in the case of thermal runaway of the battery cell, a large amount of gas is generated inside the battery cell, and the degree of thermal runaway is more severe, the risk of shell rupture and electrode terminal separation from the shell flying out is higher; in addition, in the case of shell rupture and electrode terminal separation from the shell flying out, it will have an adverse effect on the adjacent battery cell.

[0101] The gap D between the electrode assembly 22 and the inner side of the pressure relief mechanism 26 along the thickness direction of the end cover 23 satisfies: 1mm≤D≤7mm.

[0102] The inner side of the pressure relief mechanism 26 can refer to, along the thickness direction of the end cover 23, the end of the pressure relief mechanism 26 close to the electrode assembly 22.

[0103] The gap D between the electrode assembly 22 and the inner side of the pressure relief mechanism 26 can be the distance between the electrode assembly 22 and the pressure relief mechanism 26 along the thickness direction of the end cover 23, for example, the z direction in FIG. 3.

[0104] As an example, the gap D can be confirmed by the following way: in the area defined by the pressure relief mechanism 26, 5 points are taken along the direction z on the side surface of the area defined by the pressure relief mechanism 26 close to the electrode assembly 22; 5 points are taken along the direction z on the end of the electrode assembly 22 close to the end cover 23; the average value of the distance between the 5 points taken on the pressure relief mechanism 26 and the 5 points taken on the electrode assembly 22 is calculated, and the average value is taken as the value of the gap D.

[0105] D can be 1 mm, 1.1 mm, 1.3 mm, 1.5 mm, 1.7 mm, 1.9 mm, 2 mm, 2.1 mm, 2.3 mm, 2.5 mm, 2.7 mm, 2.9 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, 5.5 mm, 6 mm, 6.5 mm, 7 mm, or any value within the above range.

[0106] In the case of D≥1 mm, there is more accommodation space between the electrode assembly 22 and the end cover 23. Due to the above-mentioned setting of the electrolyte, the battery monomer 20 has more gas generation and more severe thermal runaway when the battery monomer 20 has thermal runaway, and the space between the electrode assembly 22 and the end cover 23 can accommodate the gas generated inside the battery monomer 20, and the space can also provide space for the actuation of the pressure relief mechanism 26, so as to facilitate the opening of the pressure relief mechanism 26 and the discharge of the high-temperature and high-pressure discharge in the battery monomer 20 when the battery monomer has thermal runaway, thereby reducing the risk of shell rupture and electrode terminal flying out of the shell.

[0107] In the case of D≤7 mm, the waste of the space inside the battery monomer can be reduced, the utilization rate of the internal space of the battery monomer can be improved, and the energy density of the battery monomer can be improved.

[0108] The capacity Q of the battery monomer satisfies: 30 Ah≤Q≤40 Ah.

[0109] Q can be 30 Ah, 33 Ah, 35 Ah, 37 Ah, 40 Ah, or any value within the above range.

[0110] In the embodiment of the present application, the capacity Q of the battery monomer satisfies: 30 Ah≤Q≤40 Ah; in the battery monomer, due to the fact that the electrolyte includes dimethyl carbonate and lithium bisfluorosulfonylimide salt, the battery monomer has fast charging capability; by setting the gap D≥1 mm between the electrode assembly 22 and the inner side of the pressure relief mechanism of the end cover 23 along the thickness direction of the end cover 23, there is enough space in the battery monomer to facilitate the opening of the valve of the pressure relief mechanism, which can reduce the risk of the electrode terminal of the battery monomer being separated from the shell 21 and the shell 21 being broken when the battery monomer is in thermal runaway; by setting D≤7 mm, the waste of the space in the battery monomer can be reduced, the space utilization in the battery monomer is improved, and thus the energy density of the battery monomer is improved. Therefore, the battery monomer of the embodiment of the present application has fast charging capability, high energy density, and high reliability.

[0111] In some embodiments, the size D of the gap satisfies: 2 mm≤D≤6 mm.

[0112] When D≥2 mm, there is a large gap between the electrode assembly 22 and the inner side of the pressure relief mechanism 26, and there is a large space between the electrode assembly 22 and the end cover 23, on the one hand, there is enough space to accommodate the gas generated inside the battery monomer 20, and on the other hand, it is convenient for the pressure relief mechanism 26 to open the valve, so as to facilitate the discharge of the high-temperature and high-pressure substances inside the battery monomer 20 when the battery monomer 20 is in thermal runaway, which can reduce the risk of the electrode terminal of the battery monomer 20 being separated from the shell 21 and the shell 21 being broken, and is conducive to improving the reliability of the battery monomer 20; when D≤6 mm, the waste of the space inside the battery monomer 20 can be reduced, which is conducive to improving the volumetric energy density of the battery monomer. Therefore, when 2 mm≤D≤6 mm, the volumetric energy density and the reliability of the battery monomer can be considered.

[0113] In some embodiments, the mass content A of dimethyl carbonate satisfies: 20 wt%≤A≤80 wt%, based on the total mass of the electrolyte; and / or, the mass content B of lithium bisfluorosulfonylimide salt satisfies: 1 wt%≤B≤16 wt%, based on the total mass of the electrolyte.

[0114] The mass content A of dimethyl carbonate can be 20wt%, 22wt%, 24wt%, 26wt%, 28wt%, 30wt%, 32wt%, 34wt%, 36wt%, 38wt%, 40wt%, 42wt%, 44wt%, 46wt%, 48wt%, 50wt%, 52wt%, 54wt%, 56wt%, 58wt%, 60wt%, 62wt%, 64wt%, 66wt%, 68wt%, 70wt%, 72wt%, 74wt%, 76wt%, 78wt%, 80wt%, or any value within the above range, and the mass content B of lithium bisfluorosulfonylimide can be 1wt%, 2wt%, 4wt%, 6wt%, 8wt%, 10wt%, 12wt%, 14wt%, 16wt%, or any value within the above range.

[0115] The higher the mass content of dimethyl carbonate and the mass content of lithium bisfluorosulfonylimide, the better the fast-charging performance of the battery cell, but in the case of thermal runaway, the battery cell generates more gas, and the severity of the thermal runaway of the battery cell is greater, and the reliability of the battery cell is lower. By setting the mass content of dimethyl carbonate and the mass content of lithium bisfluorosulfonylimide to meet the above range, the fast-charging performance and reliability of the battery cell can be considered.

[0116] In some embodiments, 50wt%≤A≤75wt%; and / or, 1wt%≤B≤11wt%.

[0117] When 50wt%≤A≤75wt%, the battery cell generates less gas and has better fast-charging performance, and the risk of dimethyl carbonate precipitation at low temperature is lower; when 1wt%≤B≤11wt%, the battery cell has a certain mass content of lithium bisfluorosulfonylimide, and has good fast-charging performance, and the mass content of lithium bisfluorosulfonylimide is not too large, so that the battery cell generates less gas when thermal runaway, and the severity of thermal runaway is smaller, and the battery cell has higher reliability.

[0118] In some embodiments, 20wt%≤A≤65wt%, and the mass content of lithium bisfluorosulfonylimide meets the above range, which is further beneficial to consider the fast-charging performance and reliability of the battery cell.

[0119] In some embodiments, the mass content of dimethyl carbonate is 50g-65g, and the mass content of lithium bisfluorosulfonylimide is 1g-65g, within 1000 cycles of the battery cell.

[0120] During the cycling of the battery cell, both the dimethyl carbonate and the lithium bisfluorosulfonylimide salt are consumed. Within 1000 cycles of the battery cell, the mass content of the dimethyl carbonate is 50g-65g, and the mass content of the lithium bisfluorosulfonylimide salt is 1g-8g.

[0121] In the related art, in order to improve the fast charging performance of the battery cell, more lithium bisfluorosulfonylimide salt is usually added. However, when the mass content of the lithium bisfluorosulfonylimide salt in the electrolyte is relatively high, the battery cell generates more gas and the thermal runaway is more severe when thermal runaway occurs. In addition, the lithium bisfluorosulfonylimide salt also reacts with aluminum in the positive electrode plate, causing corrosion of the current collector and cracking of the positive electrode plate, which is not conducive to improving the reliability of the battery cell.

[0122] In some embodiments, the mass content ratio A:B of the dimethyl carbonate and the lithium bisfluorosulfonylimide salt satisfies: 3≤A:B≤40.

[0123] The mass content ratio A:B of the dimethyl carbonate and the lithium bisfluorosulfonylimide salt can be 3, 5, 7, 9, 11, 13, 15, 16, 17, 19, 21, 23, 25, 27, 29, 30, 31, 33, 35, 37, 39, 40, or any value within the above range.

[0124] When A:B≥3, the severity of the thermal runaway of the battery cell is smaller, and the risk of cracking of the positive electrode plate is lower, and the battery cell has higher reliability; when A:B≤40, it is conducive to the transmission of lithium ions, and the battery cell has better fast charging performance. By setting 3≤A:B≤40, the battery cell has better fast charging performance and higher reliability.

[0125] In some embodiments, 5≤A:B≤30. In this way, the fast charging performance and the reliability of the battery cell are further considered.

[0126] In some embodiments, in the battery cell, the ratio C of the mass of the electrolyte to the capacity of the battery cell satisfies: C≤1.6g / Ah.

[0127] C can be the ratio of the mass of the electrolyte to the capacity of the battery cell in a battery cell that has not been used (for example, a battery cell in a factory state).

[0128] C can be 1.6g / Ah, 1.5g / Ah, 1.4g / Ah, 1.3g / Ah, 1.2g / Ah, or any value within the above range.

[0129] The value of C in the factory state is small, so that the mass of the electrolyte in the battery cell is small, the mass of DMC and LiFSI in the electrolyte is small, in the case of thermal runaway of the battery cell, the gas generation in the battery cell is small, and the severity of the battery cell thermal runaway is low, which is beneficial to improve the reliability of the battery cell.

[0130] In some embodiments, 1.2 g / Ah≤C≤1.4 g / Ah. In the case of C≤1.4 g / Ah, the mass of the electrolyte in the battery cell is small, which is beneficial to further improve the reliability of the battery cell; in the case of C≥1.2 g / Ah, the mass of the electrolyte can meet the normal work of the battery cell, which can reduce the influence on the cycle performance and other electrical properties of the battery cell. Therefore, the above technical solution is beneficial to balance the reliability and electrical performance of the battery cell.

[0131] In some embodiments, the ratio of the mass of the electrolyte remaining in the battery cell to the capacity of the battery cell E satisfies: 0.7 g / Ah≤E≤1.1 g / Ah within 1000 cycles of the battery cell.

[0132] Within 1000 cycles, E can be 0.7 g / Ah, 0.8 g / Ah, 0.9 g / Ah, 1.0 g / Ah, 1.1 g / Ah or any value within the above range.

[0133] During the cycle process of the battery cell, the electrolyte will be consumed, and as the number of charge and discharge cycles increases, the mass of the electrolyte remaining in the battery cell gradually decreases, and the ratio of the mass of the electrolyte to the capacity of the battery cell also changes. After the battery cell is cycled for a period of time, for example, within 1000 cycles, the ratio E of the mass of the electrolyte remaining in the battery cell to the capacity of the battery cell is approximately in the range of 0.7 g / Ah to 1.1 g / Ah.

[0134] In some embodiments, along the thickness direction of the end cover 23, the size H of the battery cell 20 satisfies: 90 mm≤H≤120 mm. In this way, the battery cell 20 has a suitable capacity and height, and the battery cell 20 has a relatively suitable energy density.

[0135] The size H of the battery cell 20 can be the distance between the electrode terminal 25 and the end cover 23 along the thickness direction (for example, the z direction in FIG. 2) of the end cover 23. H can be 90 mm, 95 mm, 100 mm, 105 mm, 110 mm, 120 mm or any value within the above range.

[0136] In some embodiments, the mass K of the electrolyte in the battery cell satisfies: 35 g≤K≤60 g.

[0137] K can be the mass of the electrolyte in the battery cell that has not been used (e.g., the battery cell in a factory state).

[0138] K can be 35 g, 38 g, 40 g, 42 g, 50 g, 55 g, 59 g, 60 g, or any value within the above range.

[0139] When 35 g≤K≤60 g, the battery cell has better fast-charging performance.

[0140] In some embodiments, 35 g≤K≤50 g. When 35 g≤K≤50 g, the battery cell has lower intensity of thermal runaway, lower risk of shell rupture and electrode terminal flying out of the shell, and higher reliability.

[0141] In some embodiments, within 1000 cycles of the battery cell, the mass P of the electrolyte remaining in the battery cell satisfies: 22 g≤P≤36 g.

[0142] Within 1000 cycles, the mass P of the electrolyte remaining can be 22 g, 25 g, 28 g, 30 g, 32 g, 34 g, 36 g, or any value within the above range.

[0143] During the charging and discharging cycles of the battery cell, the mass of the electrolyte in the battery cell gradually decreases with the increase of the number of charging and discharging cycles. After the battery cell is cycled for a period of time, for example, within 1000 cycles, the mass of the electrolyte remaining is approximately in the range of 22 g to 36 g.

[0144] The energy density of the battery cell is related to the compaction density of the positive electrode tab and the negative electrode tab. The greater the compaction density of the positive electrode tab and the negative electrode tab, the more conducive to improving the energy density of the battery cell. In the related art, in order to improve the fast charging performance of the battery cell, a positive electrode tab and / or a negative electrode tab with a smaller compaction density is usually selected. The reason is that, in the case of a larger compaction density of the positive electrode tab and the negative electrode tab, the transmission path of lithium ions is more tortuous, and under a large current, the capacity that the battery cell can develop is reduced, and the fast charging performance of the battery cell is reduced. In addition, in the related art, in order to improve the reliability of the battery cell, the compaction density of the positive electrode tab and the negative electrode tab is appropriately reduced to reduce the energy density of the battery cell. This is because the higher the energy density of the battery cell, the more severe the thermal runaway of the battery cell, which is also not conducive to improving the reliability of the battery cell. In some embodiments of the present application, by reasonably regulating the mass content of DMC and LiFSI in the electrolyte and the spatial size of the gap D, the compaction density of the positive electrode tab and the negative electrode tab is set to a larger value, which has less effect on the fast charging performance of the battery cell, and there is sufficient space for the actuation of the pressure relief mechanism in the battery cell, which can reduce the risk that the pressure relief mechanism cannot be opened in time in the event of thermal runaway.

[0145] In some embodiments, the electrode assembly 22 includes a positive electrode tab and a negative electrode tab, the compaction density of the positive electrode tab is greater than or equal to 3.4 g / cm 3 , and / or the compaction density of the negative electrode tab is greater than or equal to 1.2 g / cm 3 .

[0146] The compaction density of the positive electrode tab can be 3.4 g / cm 3 , 3.5 g / cm 3 , 3.65 g / cm 3 , 3.7 g / cm 3 , or any value within the above range.

[0147] The compaction density of the negative electrode tab can be 1.2 g / cm 3 , 1.4 g / cm 3 , 1.6 g / cm 3 , 1.65 g / cm 3 , or any value within the above range.

[0148] The compaction density of the positive electrode tab and the negative electrode tab can be the compaction density after cold pressing. After the positive electrode tab and the negative electrode tab are prepared into a battery cell, the compaction density of the fresh battery cell in the full discharge state decreases by about 0.1 g / cm 3 after 1000 times or less of charge and discharge cycles, the compaction density decreases by about 0.05 g / cm 3 ~0.1 g / cm.3 .

[0149] As an example, after cold-pressing, the compaction density of the positive electrode sheet is greater than or equal to 3.4 g / cm 3 , and the compaction density of the negative electrode sheet is less than 1.2 g / cm 3 .

[0150] As an example, after cold-pressing, the compaction density of the positive electrode sheet is less than 3.4 g / cm 3 , and the compaction density of the negative electrode sheet is greater than or equal to 1.2 g / cm 3 .

[0151] As an example, after cold-pressing, the compaction density of the positive electrode sheet is greater than or equal to 3.4 g / cm 3 , and / or, the compaction density of the negative electrode sheet is greater than or equal to 1.2 g / cm 3 .

[0152] In the case where the compaction density of the positive electrode sheet is greater than or equal to 3.4 g / cm 3 , and / or, in the case where the compaction density of the negative electrode sheet is greater than or equal to 1.2 g / cm 3 , the battery cell has a higher energy density, while the battery cell also has better fast-charging performance and higher reliability.

[0153] In some embodiments, the compaction density of the positive electrode sheet is 3.4 g / cm 3 ~ 3.7 g / cm 3 , and / or, the compaction density of the negative electrode sheet is 1.2 g / cm 3 ~ 1.7 g / cm 3 .

[0154] In the above embodiments, the positive electrode sheet and / or the negative electrode sheet have a higher compaction density, and the battery cell can have a higher energy density with higher reliability and better fast-charging performance.

[0155] In some embodiments, the battery cell is cycled for 1000 times or less, the compaction density of the positive electrode sheet is 3.35 g / cm 3 ~ 3.69 g / cm 3 , and / or, the compaction density of the negative electrode sheet is 1.2 g / cm 3 ~ 1.65 g / cm 3 .

[0156] During the charge-discharge cycle of the battery cell, the positive electrode sheet and the negative electrode sheet expand, the thickness of the positive electrode sheet and the negative electrode sheet can change, and the compaction density of the positive electrode sheet and the negative electrode sheet will also change. Within 1000 cycles of the battery cell, the compaction density of the positive electrode sheet is about 3.35 g / cm 3 ~ 3.69 g / cm 3 , and the compaction density of the negative electrode sheet is about 1.2 g / cm 3 ~ 1.65 g / cm 3 .

[0157] The porosity of the electrode sheet is related to the compaction density of the electrode sheet. The greater the compaction density of the electrode sheet, the smaller the porosity of the electrode sheet. In some embodiments, the porosity of the positive electrode sheet is 22%~26%, and / or the porosity of the negative electrode sheet is 23%~30%. In this way, it is beneficial to improve the energy density of the battery cell while the battery cell has good reliability and fast charging performance.

[0158] In some embodiments, the positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes lithium nickel oxide or metal phosphate.

[0159] The metal phosphate can include lithium iron phosphate, lithium manganese iron phosphate, etc.

[0160] Different positive electrode active materials included in the battery cell can have different performances. For example, the battery cell includes lithium nickel oxide, and the lithium nickel oxide has a high gram capacity, which is beneficial to obtain a battery cell with high energy density; for another example, the battery cell includes metal phosphate, and the metal phosphate has high stability, which is beneficial to obtain a battery cell with high reliability.

[0161] In some embodiments, the chemical formula of the lithium nickel oxide satisfies: Li 1+a [Ni x Co y Mn z M b ]O 2-c , M includes at least one of Zr, Al, Ti, Sb, Nb, Te, Mg, B, Ca, V, Ta or Sr, 0.2≥a≥-0.2, 1>x≥0.7, 0.3>y>0, 0.3>z>0, 0.3>b≥0, 0.5≥c≥0. Among them, as an example, x+y+z+b=1 the Ni content in the above positive electrode active material is high, which is beneficial to improve the energy density of the battery cell.

[0162] a can be -0.2, -0.1, -0.04, 0, 0.04, 0.1, 0.2, or any value within the above range, x can be 0.7, 0.75, 0.8, 0.9, 0.95, 0.96, or any value within the above range, y can be 0.1, 0.2, or any value within the above range, z can be 0.1, 0.2, or any value within the above range, b can be 0, 0.1, 0.2, or any value within the above range, c can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, or any value within the above range. As an example, b is 0, and the positive electrode active material includes LiNi 0.8 Co 0.1 Mn 0.1 O2. As another example, b > 0, and the positive electrode active material includes LiNi 0.7 Co 0.1 Mn 0.1 Al 0.1 O2.

[0163] The positive electrode active material satisfying the above formula can be referred to as a high-nickel ternary material. Compared with a ternary material with a lower nickel content or a material such as lithium iron phosphate, the high-nickel ternary material has a higher gram capacity, and thus the use of the high-nickel ternary material is beneficial to improve the capacity and energy density of the battery cell under the same mass.

[0164] It should be noted that the battery cell is accompanied by Li deintercalation and consumption during charging and discharging, and the molar content of Li is different when the battery cell is discharged to different states. In the enumeration of the positive electrode active material in the embodiments of the present application, the molar content of Li is in the initial state of the material, and the positive electrode active material is applied to the battery system. After charging and discharging cycles, the molar content of Li changes. In the enumeration of the positive electrode active material in the embodiments of the present application, the molar content of O is only the theoretical state value, and the release of oxygen from the lattice causes the molar content of oxygen to change, and the actual molar content of O will fluctuate.

[0165] In some embodiments, the positive electrode active material includes: LiNi 0.90 Co 0.06 Mn 0.04 O2, LiNi 0.7 Co 0.1 Mn 0.2 O2, LiNi 0.7 Co 0.2 Mn 0.1 O2, or LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0166] In some embodiments, in the battery cell, the gram weight per unit area of the positive electrode active material is 15 mg / cm2 23 mg / cm2 2 For example, the gram weight per unit area of the positive electrode active material is 15 mg / cm2 2 16 mg / cm2 2 17 mg / cm2 2 18 mg / cm2 2 20 mg / cm2 2 23 mg / cm2 2 or any value within the above range. The gram weight per unit area of the positive electrode active material is 15 mg / cm2 2 23 mg / cm2 2 In this case, the battery monomer has a higher energy density.

[0167] In some embodiments, the negative electrode tab includes a negative electrode active material, the negative electrode active material includes graphite and a silicon-containing material, the silicon-containing material includes at least one of elemental silicon, a silicon-oxygen composite, a silicon-carbon composite, a silicon-nitrogen composite, a silicon-containing alloy, or a silicon-oxygen-carbon composite material, and the graphite includes at least one of natural graphite or artificial graphite. The above negative electrode active material is beneficial to improve the energy density of the battery monomer.

[0168] In some embodiments, the silicon-containing material includes a silicon-carbon composite, and the mass fraction of silicon in the silicon-carbon composite is 40wt% to 60wt% based on the total mass of the silicon-containing material. When the mass content of silicon in the silicon-carbon composite is within the above range, the electrode assembly has a relatively appropriate expansion rate, which is beneficial to the normal use of the battery monomer.

[0169] In some embodiments, the mass content B1 of the silicon-containing material satisfies: 1wt%≤B1≤20wt% based on the total mass of the negative electrode active material.

[0170] B1 can be 1wt%, 5wt%, 8wt%, 15wt%, 20wt%, or any value within the above range.

[0171] By setting the mass content of the silicon-containing material to satisfy the above range, it is not only beneficial to obtain a negative electrode tab with a higher compaction density, but also beneficial to reduce the risk of excessive expansion of the battery monomer due to excessive mass content of the silicon-containing material. Therefore, the energy density of the battery monomer can be improved while facilitating the normal use of the battery monomer.

[0172] As an example, the negative electrode active material includes artificial graphite and a silicon-carbon composite, the mass content of the silicon-carbon composite is 6wt% based on the total mass of the negative electrode active material, and the mass content of silicon in the silicon-carbon composite is 50wt%.

[0173] In some embodiments, in the negative electrode tab, the gram weight per unit area of the negative electrode active material is 8 mg / cm2 2~ 13 mg / cm 2 The mass of the negative active material can be 8 mg / cm 2 , 10 mg / cm 2 , 12 mg / cm 2 , 13 mg / cm 2 or any value within the above range. The negative active material has a higher gram weight per unit area, and the battery cell has a higher energy density.

[0174] In the related art, the surface of the separator film is coated with a polyvinylidene fluoride (PVDF) coating to better bond the separator film to the positive electrode sheet and the negative electrode sheet. In some embodiments of the present application, the electrode assembly 22 further comprises a separator film disposed between the positive electrode sheet and the negative electrode sheet, and the separator film comprises a base film and a ceramic coating disposed on the side of the base film facing the positive electrode sheet.

[0175] The ceramic coating is disposed on the side of the base film facing the positive electrode sheet in the thickness direction of the base film. Compared to the related art in which a ceramic coating and a PVDF coating are sequentially disposed on both sides of the base film, disposing only a ceramic coating on the side of the base film facing the positive electrode sheet can reduce the absorption of electrolyte by the separator film, and the amount of electrolyte absorbed by the separator film is less, which can reduce the amount of electrolyte injected into the battery cell, thereby reducing the amount of gas generated and the severity of thermal runaway of the battery cell, and improving the reliability of the battery cell.

[0176] In the related art, in order to improve the fast charging performance of the battery cell, a separator film with a large porosity is usually selected. However, a separator film with a large porosity is easily pierced by burrs (such as burrs of the positive electrode sheet or burrs of the negative electrode sheet), which is not conducive to improving the reliability of the battery cell. In some embodiments of the present application, a separator film with a small porosity is selected to improve the reliability of the battery cell; and the mass content of DMC and LiFSI in the electrolyte is reasonably controlled, the ion transmission rate is fast, and the battery cell still has good fast charging performance under the condition that the porosity of the separator film is small.

[0177] In some embodiments, the porosity of the separator film is 30% to 45%. In this way, the separator film has a low porosity, which is conducive to reducing the amount of electrolyte required in the battery cell, thereby reducing the amount of gas generated and the severity of thermal runaway of the battery cell, and improving the reliability of the battery cell.

[0178] In some embodiments, the end cover 23 comprises an end cover body 231, and the pressure relief mechanism 26 is disposed on the inner side or the outer side of the end cover body 231.

[0179] As an example, the pressure relief mechanism 26 is arranged at the inner side of the end cover body 231, which can mean that, along the thickness direction of the end cover 23, the pressure relief mechanism 26 is arranged at the side of the end cover body 231 facing the electrode assembly.

[0180] As another example, the pressure relief mechanism 26 is arranged at the outer side of the end cover body 231, which can mean that, along the thickness direction of the end cover 23, the pressure relief mechanism 26 is arranged at the side of the end cover body 231 away from the electrode assembly.

[0181] Fig. 7 is a schematic diagram of the force on the pressure relief mechanism arranged at the inner side of the end cover body according to an embodiment of the present application, and Fig. 8 is a schematic diagram of the force on the pressure relief mechanism arranged at the outer side of the end cover body according to an embodiment of the present application. In combination of Figs. 7 and 8, the pressure relief mechanism 26 is arranged at the side of the end cover body 231 away from the electrode assembly (the outer side of the end cover body 231). In the case of swelling of the battery cell, the end cover 23 protrudes away from the electrode assembly 22, and the pressure relief mechanism 26 is subjected to a force that pulls the pressure relief mechanism 26 outwardly, so that the pressure relief mechanism 26 is more likely to be torn.

[0182] By arranging the pressure relief mechanism 26 at the inner side of the end cover body 231, in the case of swelling of the battery cell and protrusion of the end cover 23 away from the electrode assembly 22, the pressure relief mechanism 26 is subjected to a force that pulls the pressure relief mechanism 26 inwardly, so that the pressure relief mechanism 26 is less likely to be torn, thereby facilitating improvement of the long-term reliability of the pressure relief mechanism.

[0183] By arranging the pressure relief mechanism 26 at the outer side of the end cover body 231, it is convenient to reduce the complexity of preparation of the pressure relief mechanism 26.

[0184] Fig. 9 is a schematic diagram of the structure of an end cover according to an embodiment of the present application. In some embodiments, as shown in Fig. 9, the end cover body 231 is provided with a score groove 261, and the area defined by the score groove 261 forms the pressure relief mechanism 26.

[0185] As an example, the end cover 23 is a circular end cover, the shape of the end cover body 231 is circular, and the shape of the score groove 261 is circular or arc-shaped with a notch 262. The area of the pressure relief mechanism 26 is the area of the region defined by the score groove 261. For example, the score groove 261 is circular, and the area of the region defined by the score groove 261 can be obtained according to the diameter R of the circle.

[0186] By arranging the score groove 261 on the end cover body 231, it is convenient to prepare the pressure relief mechanism 26, and it is also convenient to reduce the risk of interference between the pressure relief mechanism 26 and the components in the battery cell.

[0187] In some embodiments, the area S of the region defined by the pressure relief mechanism 26 and the area S0 of the end cover satisfy: 25%≤S / S0≤50%.

[0188] S / S0 can be 25%, 30%, 35%, 40%, 50% or any value within the above range.

[0189] In the case of S / S0≥25%, the pressure relief mechanism 26 is more likely to break when the battery cell is in thermal runaway, thereby facilitating the end cover to have a larger tearing opening and facilitating the discharge of high-temperature and high-pressure substances inside the battery cell; in the case of S / S0≤50%, the interference of the pressure relief mechanism 26 on the connection between the end cover and the shell can be reduced, facilitating the connection between the end cover and the shell.

[0190] In some embodiments, the area S of the pressure relief mechanism 26 and the capacity Q of the battery cell satisfy: 12mm 2 / Ah≤S / Q≤20mm 2 / Ah.

[0191] S / Q can be 12mm 2 / Ah, 14mm 2 / Ah, 16mm 2 / Ah, 18mm 2 / Ah, 20mm 2 / Ah or any value within the above range.

[0192] The larger the capacity of the battery cell, the more severe the thermal runaway of the battery cell, and the larger the area of the pressure relief mechanism 26 facilitates the actuation and breakage during thermal runaway, so as to smoothly discharge the discharge inside the battery cell.

[0193] In the case of S / Q≥12mm 2 / Ah, it is beneficial to make the end cover 23 have a larger tearing opening and tearing degree, and facilitate the discharge of high-temperature and high-pressure substances inside the battery cell 20 in the case of thermal runaway of the battery cell 20; in the case of S / Q≤20mm 2 / Ah, the interference of the pressure relief mechanism 26 on the connection (such as welding) between the end cover 23 and the shell 21 can be reduced, facilitating the connection (such as welding) between the end cover 23 and the shell 21.

[0194] In the above embodiments, battery cells of different capacities can be provided with pressure relief mechanisms 26 of different area sizes, which facilitate the discharge of high-temperature and high-pressure substances during thermal runaway of the battery cell, and facilitate the connection between the shell and the end cover.

[0195] In some embodiments, the area S of the pressure relief mechanism 26 is greater than or equal to 500mm 2 .

[0196] S can be 500mm 2 , 550mm 2 , 600mm 2 , 700mm2 800mm 2 900mm 2 1000mm 2 or any value within the above range.

[0197] The larger the area S of the pressure relief mechanism 26, the easier the pressure relief mechanism 26 is to tear when the battery cell is in thermal runaway, and the larger the opening and degree of tearing of the end cover 23, which is conducive to the discharge of the high-temperature and high-pressure substances inside the battery cell 20.

[0198] By setting S greater than or equal to 500mm 2 , it is conducive to making the end cover 23 have a larger tearing opening and tearing degree in the case of thermal runaway of the battery cell 20, which is conducive to the discharge of the high-temperature and high-pressure substances inside the battery cell 20.

[0199] In some embodiments, the area S of the pressure relief mechanism 26 satisfies: 600mm 2 ≤ S ≤ 800mm 2 .

[0200] The area S of the pressure relief mechanism 26 can be 500mm 2 , 550mm 2 , 600mm 2 , 700mm 2 , 800mm 2 or any value within the above range.

[0201] In the case of S greater than or equal to 600mm 2 , it is conducive to making the end cover 23 have a larger tearing opening and tearing degree in the case of thermal runaway of the battery cell 20, which is conducive to the discharge of the high-temperature and high-pressure substances inside the battery cell 20; in the case of S less than or equal to 800mm 2 , the interference of the pressure relief mechanism 26 on the connection (such as welding) between the end cover 23 and the shell 21 can be reduced, and the connection (such as welding) between the end cover 23 and the shell 21 is facilitated.

[0202] In the above technical solution, by setting the area of the pressure relief mechanism 26 to satisfy the above range, both the risk of cracking of the pressure relief mechanism 26 in the normal use process of the battery cell can be reduced, and the pressure relief mechanism 26 can be broken in time when the battery cell is in thermal runaway, so as to balance the long-term use reliability and the reliability in thermal runaway of the battery cell.

[0203] In some embodiments, the voltage platform of the battery cell is 3.5V-3.7V. In the case of the above range of the voltage window of the battery cell, the battery cell has a higher energy density.

[0204] In some embodiments, the solvent further includes methylethyl carbonate and ethylene carbonate, and the electrolyte salt further includes lithium hexafluorophosphate.

[0205] In the above embodiments, the solvent of the electrolyte includes dimethyl carbonate, methylethyl carbonate and ethylene carbonate, and the electrolyte salt of the electrolyte includes lithium hexafluorophosphate and lithium bisfluorosulfonylimide salt. The electrolyte has a lower viscosity and a higher ionic conductivity, which is conducive to improving the fast-charging performance of the battery cell.

[0206] In some embodiments, the electrolyte further includes an additive, and the additive includes at least one of fluoroethylene carbonate or vinylene carbonate. The addition of the additive can reduce the decomposition of the electrolyte, which is conducive to improving the fast-charging performance of the battery cell. In some embodiments, the battery cell 20 further includes: a current collecting member 24 accommodated in the shell 21, and arranged between the electrode assembly 22 and the end cover 23 along the thickness direction of the end cover 23 (for example, the z direction in FIG. 3), and the current collecting member 24 is electrically connected to the tab of the electrode assembly 22 and the shell 21. Through the arrangement of the current collecting member 24, the electrical connection between the electrode assembly 22 and the shell 21 is facilitated.

[0207] The current collecting member 24 is arranged between the electrode assembly 22 and the end cover 23, which means that the current collecting member 24 is arranged on the side of the electrode assembly 22 facing the end cover 23. As an example, part of the current collecting member 24 is welded to the tab of the electrode assembly 22, and the other part is abutted or welded to the end cover 23.

[0208] In some embodiments, the shell 21 includes an electrode terminal 25, and the end cover 23 is arranged on the side of the shell 21 away from the electrode terminal 25, and the electrode terminal 25 is insulatedly connected to the shell 21. By arranging the end cover 23 on the side of the shell 21 away from the electrode terminal 25, the electrode terminal 25 and the end cover 23 can be arranged separately, reducing the influence of the end cover 23 on the stability of the electrode terminal 25 when bearing internal pressure or pressure relief action, thereby facilitating the improvement of the reliability of the battery cell 20 in the case of thermal runaway.

[0209] In some embodiments, the tabs of the electrode assembly 22 are close to the same end of the end cover 23, which can shorten the electrical connection distance between the tabs and the shell 2121, reduce the waste of internal space of the battery cell 20, and improve the capacity of the battery cell 20, thereby improving the energy density of the battery cell 20.

[0210] In some embodiments, the inner side of the shell 21 is provided with a limiting portion 211, and in the thickness direction of the end cover 23, the limiting portion 211 is located between the electrode assembly 22 and the end cover 23, and the current collecting member 24 is abutted to the side of the limiting portion 211 facing the electrode assembly 22.

[0211] The inner side of the shell 21 refers to the inner side surface of the side wall of the shell 21 extending along the thickness direction of the end cover 23. Understandably, the inner side extends substantially along the thickness direction of the end cover 23. In the embodiment where the shell 21 is a cylinder, the inner side of the shell 21 is a cylindrical surface. In the embodiment where the shell 21 is a cuboid, the inner side of the shell 21 is composed of four side surfaces located at different positions and connected in sequence.

[0212] The inner side of the shell 21 is provided with a limiting portion 211. Understandably, the limiting portion 211 protrudes from the inner side. The limiting portion 211 is a structure for limiting the movement of the end cover 23 towards the electrode assembly 22.

[0213] The limiting portion 211 and the shell 21 can be an integrally formed structure, or can be a structure connected together after being formed separately, for example, the limiting portion 211 and the shell 21 are welded. The limiting portion 211 can be various structures, for example, the limiting portion 211 is a boss protruding from the inner side of the shell 21, or for example, the limiting portion 211 is an annular structure extending along the circumference of the shell 21.

[0214] In the above embodiment, the inner side of the shell 21 is provided with the limiting portion 211. The limiting portion 211 not only plays a limiting role on the end cover 23 to limit the movement of the end cover 23 towards the electrode assembly 22, but also facilitates the realization of the gap between the electrode assembly 22 and the end cover 23, thereby providing space for the expansion of the electrode assembly 22 and providing a rupture space for the rupture of the end cover.

[0215] In some embodiments, the battery monomer further comprises a sealing member 212 arranged between the end cover 23 and the shell 21. The arrangement of the sealing member 212 is conducive to improving the sealing performance of the battery monomer, and thus is conducive to improving the reliability of the battery monomer.

[0216] As an example, the sealing member 212 is an insulating member, which can electrically isolate the end cover 23 and the shell 21. The shape of the sealing member 212 can be adapted to the shape of the limiting portion 211, for example, S-shaped, and the embodiments of the present application include but are not limited to this.

[0217] FIG. 10 is a structural schematic diagram of the current collecting member according to an embodiment of the present application. In some embodiments, in combination with FIGS. 3 to 6 and FIG. 10, the current collecting member 24 comprises a current collecting body 240, an elastic portion 241, a current collecting sheet 242 and a center portion 243. The current collecting sheet 242 and the elastic portion 241 are both connected with the circular ring-shaped current collecting body 240, the elastic portion 241 is located between the current collecting body 240 and the center portion 243, and the elastic portion 241 and the current collecting sheet 242 are arranged in a spaced manner.

[0218] In the thickness direction of the end cover 23, the elastic portion 241 protrudes away from the electrode assembly 22 relative to the current collecting body 240 and abuts against the end cover 23, so that the connection between the current collecting member 24 and the end cover 23 is achieved through the elastic portion 241. As an example, the end cover body 231 is provided with a protrusion 232, and the elastic portion 241 abuts against the protrusion 232.

[0219] As an example, the elastic portion 241 includes a first sheet 2411 and a second sheet 2412, the first sheet 2411 is connected to the inner side of the current collecting body 240 and extends obliquely towards the end cover 23, the second sheet 2412 is connected to the outer side of the central portion 243 and extends obliquely towards the end cover 23, and the first sheet 2411 and the second sheet 2412 are connected at an included angle greater than 0° and less than 180° and form an abutment region 2414, which abuts against the end cover 23.

[0220] As an example, the current collecting member 24 includes three current collecting sheets 242, which are arranged at intervals in the circumferential direction of the current collecting body 240, and the current collecting sheets 242 are welded to the tabs 29 of the electrode assembly 22 to achieve the electrical connection between the current collecting member 24 and the electrode assembly 22.

[0221] In combination with FIG. 4, in some embodiments, in the direction perpendicular to the thickness direction of the end cover 23, the end cover 23 is provided with at least one protrusion 233, which is arranged on the end cover body 231 and protrudes away from the electrode assembly 22; in the thickness direction of the end cover 23, the size L of the at least one protrusion 233 satisfies: 1 mm≤L≤5 mm.

[0222] The size L of the protrusion 233 can be 1.0 mm, 1.2 mm, 1.4 mm, 1.6 mm, 1.8 mm, 2.0 mm, 2.2 mm, 2.4 mm, 2.6 mm, 2.8 mm, 3.0 mm, 3.2 mm, 3.4 mm, 3.6 mm, 3.8 mm, 4.0 mm, 4.2 mm, 4.4 mm, 4.6 mm, 4.8 mm, 5.0 mm, or any value within the above range.

[0223] Due to the above electrolyte, the battery cell generates more gas when it overheats, and the degree of thermal runaway is more severe. On the one hand, along the thickness direction perpendicular to the end cover 23, the end cover 23 is provided with at least one protrusion 233, and in the case of 1mm≤D≤3mm, the space between adjacent protrusions 233 can provide additional buffer space to avoid direct abutment between the battery cell 20 and the pressure relief mechanism 26. In the case of not occupying too much space inside the battery cell 20, the pressure relief mechanism 26 can be opened in time when the battery cell 20 overheats, reducing the risk of shell 21 rupture and electrode terminal 25 separation from shell 21, and has higher reliability. On the other hand, the size of the protrusion 233 in the thickness direction of the end cover 23 satisfies 1mm~5mm, and the protrusion 233 can play the role of a local reinforcing rib to ensure the directional pressure relief of the pressure relief mechanism 26 during valve opening, reducing the phenomenon of irregular rupture of the shell 21. Therefore, the above technical scheme can improve the energy density and reliability of the battery cell 20 while taking into account the fast charging performance of the battery cell 20.

[0224] In the embodiments of the present application, the "at least one protrusion 233" refers to two or more protrusions 233. The protrusion 233 and the protrusion 232 are different structures and can be provided on the same end cover 23. The distance between the two adjacent protrusions 233 and the distance between the protrusion 232 and the protrusion 233 can be set according to actual needs, which is not limited in the embodiments of the present application. For example, the at least one protrusion 233 can be arranged at equal intervals. In another example, the protrusion 233 is arranged between the shell 21 and the protrusion 232.

[0225] It should be understood that in the embodiments of the present application, the protrusion 233 and the end cover 23 can be integrally formed or separately formed. In the case that the protrusion 233 and the end cover 23 are separately formed, the protrusion 233 can be welded to the end cover 23; in the case that the protrusion 233 and the end cover 23 are integrally formed, the protrusion 233 can be formed by stamping the end cover 23.

[0226] In some embodiments, the material of the shell 21 includes carbon steel or stainless steel.

[0227] In some embodiments, the battery cell 20 is a cylindrical battery cell 20.

[0228] In some embodiments, the shell 21 includes a cylinder and a cover connected to the cylinder, the cover and the cylinder are integrally or separately formed structures, the cylinder is arranged around the outer periphery of the electrode assembly 22, and the cover is provided with an electrode lead-out hole; the battery cell 20 further includes an electrode terminal 25, and the electrode terminal 25 is insulated and arranged in the electrode lead-out hole.

[0229] As an example, the cover and the cylinder are integrally formed structures.

[0230] As another example, the cover and the cylinder are formed as separate structures. The cover can be disc-shaped, and the cylinder can be cylindrical.

[0231] In this embodiment, one of the housing 21 and the electrode terminal 25 is the positive output pole of the battery cell 20, and the other is the negative output pole of the battery cell 20. At least part of the housing 21 itself can serve as one output pole of the battery cell 20, so that one electrode terminal can be omitted, which is conducive to simplifying the structure of the battery cell 20.

[0232] In some embodiments, the battery cell 20 further includes a current collecting disc 27. The current collecting disc 27 can have a different structure from the current collecting member 24, and the current collecting disc 27 can be disc-shaped. The current collecting disc 27 and the current collecting member 24 are respectively located at two ends of the housing 21 and connected to electrodes of opposite polarity. As an example, the current collecting disc 27 is connected to the positive electrode tab, and the current collecting member 24 is connected to the negative electrode tab.

[0233] In some embodiments, the battery cell 20 further includes an insulating member 28 for isolating the electrode terminal 25 and the housing 21.

[0234] In some embodiments, the battery cell can be assembled into a battery module, and the number of battery cells contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0235] [Battery]

[0236] Embodiments of the present application provide a battery including the battery cell in the above embodiments. The battery can be a single physical module including one or more battery cells to provide higher voltage and capacity. When there are multiple battery cells, the multiple battery cells are connected in series, in parallel, or in a mixed connection through a current collecting component.

[0237] In some embodiments, the battery can be a battery pack, and the battery includes a box body and a battery cell, and the battery cell or the battery module is contained in the box body.

[0238] In some embodiments, the box body can be part of the chassis structure of the vehicle. For example, part of the box body can be at least part of the floor of the vehicle, or part of the box body can be at least part of the cross beam and the longitudinal beam of the vehicle.

[0239] In some embodiments, the battery can be located in an energy storage device. The energy storage device includes an energy storage container, an energy storage cabinet, etc.

[0240] FIG. 11 is a schematic diagram of a battery according to an embodiment of the present application. As shown in FIG. 11, the battery 10 can include multiple battery cells 20 to meet different power requirements.

[0241] The battery 10 can further include a box 3, which has a hollow structure inside, and the plurality of battery cells 20 are accommodated in the box 3. For example, the plurality of battery cells 20 are placed in the box 3 in parallel, series or hybrid combination with each other. The box 3 can include a first box part 31 and a second box part 32, which are overlapped with each other to form the box 3. The shapes of the first box part 31 and the second box part 32 can be determined according to the shapes of the components accommodated inside, for example, according to the shape of the combination of the plurality of battery cells 20, and at least one of the first box part 31 and the second box part 32 has an opening. For example, as shown in FIG. 11, the first box part 31 and the second box part 32 can each be a hollow cuboid and each have an opening face, the opening of the first box part 31 and the opening of the second box part 32 are oppositely arranged, and the first box part 31 and the second box part 32 are buckled with each other to form the box 3 having a closed cavity, which can be used to accommodate the plurality of battery cells 20. The plurality of battery cells 20 are placed in the box 3 formed by buckling the first box part 31 and the second box part 32 in parallel, series or hybrid combination with each other.

[0242] For another example, unlike that shown in FIG. 11, only one of the first box part 31 and the second box part 32 can be a hollow cuboid having an opening, and the other can be a plate to cover the opening. Taking the second box part 32 as a hollow cuboid having an opening and the first box part 31 as a plate as an example, the first box part 31 covers the opening of the second box part 32 to form the box 3 having a closed cavity, which can be used to accommodate the plurality of battery cells 20.

[0243] In some embodiments, the battery 10 can further include other components. For example, the battery 10 can further include a busbar component, which can be used to realize the electrical connection between the plurality of battery cells 20, for example, in parallel, series or hybrid combination. Specifically, the busbar component can realize the electrical connection between the battery cells 20 by connecting the electrode terminals of the battery cells 20; or the busbar component can also realize the electrical connection between the battery cells 20 by connecting other components of the battery cells 20. The busbar component can be fixed to the corresponding components of the battery cells 20 by welding, for example, can be fixed to the electrode terminals, the sealing structure or the shell, etc., and the embodiments of the present application are not limited thereto.

[0244] The battery cells 20 can directly constitute the battery 10, or can first constitute a battery module, and then constitute the battery 10 by a plurality of battery modules.

[0245] [Electric device]

[0246] The embodiments of the present application provide an electric device, which includes the battery described in the above embodiments.

[0247] The electric device can be a vehicle, a mobile phone, a portable device, a notebook computer, a ship, a spacecraft, an electric toy, and an electric tool, etc. The vehicle can be a fuel automobile, a gas automobile, or a new energy automobile, and the new energy automobile can be a pure electric automobile, a hybrid electric automobile, or a range extended automobile, etc. The spacecraft includes an airplane, a rocket, a space shuttle, and a spacecraft, etc. The electric toy includes a fixed or mobile electric toy, such as a game machine, an electric automobile toy, an electric ship toy, and an electric airplane toy, etc. The electric tool includes a metal cutting electric tool, a grinding electric tool, an assembling electric tool, and a railway electric tool, such as an electric drill, an electric grinder, an electric wrench, an electric screwdriver, an electric hammer, an impact electric drill, a concrete vibrator, and an electric planer, etc. The electric device is not specially limited in the embodiments of the present application.

[0248] FIG. 12 is a schematic diagram of an electric device according to an embodiment of the present application. As shown in FIG. 12, the present application provides an electric device, and the electric device is a vehicle.

[0249] The vehicle 1 can be a fuel automobile, a gas automobile, or a new energy automobile, and the new energy automobile can be a pure electric automobile, a hybrid electric automobile, or a range extended automobile, etc. The vehicle 1 can be provided with a motor 40, a controller 30, and a battery 10 inside, and the controller 30 is used to control the battery 10 to supply power to the motor 40. For example, the battery 10 can be arranged at the bottom, the front, or the rear of the vehicle 1. The battery 10 can be used for power supply of the vehicle 1, for example, the battery 10 can be used as an operating power source of the vehicle 1, and used for the circuit system of the vehicle 1, for example, used for the working power demand of the vehicle 1 during starting, navigation, and running. In another embodiment of the present application, the battery 10 can not only be used as an operating power source of the vehicle 1, but also be used as a driving power source of the vehicle 1, to replace or partially replace fuel or natural gas to provide driving power for the vehicle 1.

[0250] [Positive electrode sheet]

[0251] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on the positive electrode current collector.

[0252] The positive electrode current collector can be a metal foil or a composite positive electrode current collector. For example, the positive electrode current collector can be an aluminum foil.

[0253] The composite positive electrode current collector can include a high polymer material base layer and a metal layer formed on at least one surface of the high polymer material base layer. The composite positive electrode current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a high polymer material base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0254] The positive electrode film layer can also optionally include a binder. As an example, the binder can include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0255] The positive electrode film layer can also optionally include a conductive agent. The conductive agent can be selected from one or more of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0256] [Anode electrode sheet]

[0257] The anode electrode sheet includes an anode current collector and an anode film layer disposed on the anode current collector.

[0258] The anode current collector can be a metal foil or a composite anode current collector. The anode current collector can be a copper foil. The composite anode current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0259] The anode film layer includes an anode active material. The anode active material can be any anode active material known in the art for use in a battery. As an example, the anode active material can include one or more of artificial graphite, natural graphite, soft carbon, hard carbon, a silicon-based material, a tin-based material, and lithium titanate, etc. The silicon-based material can be selected from one or more of elemental silicon, silicon-oxygen composite, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. The tin-based material can be selected from one or more of elemental tin, tin-oxygen composite, and tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as anode active materials for batteries can also be used. The anode active material can be used alone or in combination with two or more types.

[0260] The anode film layer can also optionally include a binder. As an example, the binder can include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0261] The anode film layer can also optionally include a conductive agent. The conductive agent can be selected from one or more of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0262] [Electrolyte]

[0263] The electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet. The electrolyte includes an electrolyte salt and a solvent.

[0264] The electrolyte salt can include one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorobisoxalate borate, lithium bisoxalate borate, lithium difluorobisoxalate phosphate, and lithium tetrafluorobisoxalate phosphate.

[0265] The solvent can include one or more of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclobutane sulfone, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0266] The electrolyte can also optionally include a negative electrode film-forming additive, a positive electrode film-forming additive, and can also include a performance additive capable of improving certain performance of the battery, such as a performance additive for improving overcharge performance of the battery, a performance additive for improving high-temperature or low-temperature performance of the battery, etc.

[0267] [Separator]

[0268] The separator is used to separate the positive electrode sheet and the negative electrode sheet. The type of the separator is not particularly limited in the embodiments of the present application, and any known porous structure separator having good chemical stability and mechanical stability can be used.

[0269] The separator can include a base film. The material of the base film can be selected from one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The base film can be a single layer film or a multi-layer composite film, and is not particularly limited. When the base film is a multi-layer composite film, the materials of the layers can be the same or different, and are not particularly limited.

[0270] The separator can also include a coating layer provided on the surface of the base film. The coating layer can be a ceramic coating layer, and the ceramic coating layer can include alumina, boehmite, etc.

[0271] The positive electrode sheet, the negative electrode sheet, and the separator can be made into an electrode assembly through a winding process or a stacking process.

[0272] Hereinafter, Examples of the present application will be described. The Examples described below are illustrative and are for the purpose of explanation only and are not to be taken as limiting of the present application. In the Examples, unless otherwise noted, techniques or conditions are in accordance with those described in the literature or in accordance with the product manual. In the Examples, unless otherwise noted, the reagents or instruments are commercially available products.

[0273] [Examples]

[0274] Example 1

[0275] In Example 1, referring to FIGS. 1 to 6, the battery cell includes an end cap 23, a current collecting member 24, and a case 21, an electrode assembly 22 and an electrolyte are accommodated in the case 21, a limit portion 211 is protruded on an inner side of the case 21, the current collecting member 24 is located between the electrode assembly 22 and the end cap 23 and abuts against the limit portion 211, a tab of the electrode assembly 22 is electrically connected to the case 21 through the current collecting member 24, the electrode assembly 22 includes a positive electrode sheet, a negative electrode sheet, and a separator between the positive electrode sheet and the negative electrode sheet, and the battery cell is a cylindrical battery cell. For the specific parameters of the battery cell in Examples 1-4 and Examples 8-13 and the serial numbers of the test methods of the parameters, see Table 1. For the specific parameters of the battery cell in Examples 5-7 and the serial numbers of the test methods of the parameters, see Table 2.

[0276] Table 1 Parameters of the battery cell in Examples 1-4 and Examples 8-13 and serial numbers of test methods

[0277] Table 2 Parameters of the battery cell in Examples 5-7 and serial numbers of test methods

[0278] Examples 2-3

[0279] Examples 2-3 differ from Example 1 in that the gap D between the inner side of the electrode assembly and the pressure relief mechanism is different.

[0280] Examples 4-7

[0281] Examples 4-7 differ from Example 1 in that the ratio A:B of the mass content A of dimethyl carbonate DMC to the mass content B of lithium bisfluorosulfonylimide salt LiFSI based on the total mass of the electrolyte is different. Here, the value of A:B can be adjusted by adjusting the values of A and / or B.

[0282] Examples 8-10

[0283] Examples 8-10 differ from Example 1 in that the mass K of the electrolyte is different.

[0284] Example 11

[0285] Example 11 differs from Example 1 in that the capacity of the battery cell is different, wherein the mass of the electrolyte, the mass of the positive active material in the battery cell of different capacity are also changed; in addition, different gaps D are designed for battery cells of different capacities.

[0286] Examples 12-13

[0287] Examples 12-13 differ from Example 1 in that the gap D between the electrode assembly and the inside of the pressure relief mechanism is different, and the mass of the positive active material is different.

[0288] wherein the size of the battery cell of different capacity can be adaptively adjusted according to the mass of the positive active material, the gap D.

[0289] Example 14

[0290] Example 14 differs from Example 1 in that the porosity of the separator film is different, and the porosity of the separator film is 48%; in addition, due to the change of the porosity of the separator film, the mass of the electrolyte added in the battery cell and the liquid injection coefficient are also changed. In Example 14, the liquid injection coefficient is 1.4 g / Ah.

[0291] Examples 15-17

[0292] Examples 15-17 differ from Example 1 in that the ratio A:B of the mass content A of dimethyl carbonate DMC to the mass content B of lithium bisfluorosulfonylimide salt LiFSI based on the total mass of the electrolyte is different. Wherein the value of A:B can be adjusted by adjusting the value of A and / or B, and the same end of the tab is close to the end cover.

[0293] Comparative Example 1

[0294] Comparative Example 1 differs from Example 1 in that the gap D is 3 mm.

[0295] The specific parameters of Examples 1-13 and Comparative Example 1 are shown in Table 3, and the test results are shown in Table 4. Among them, each example and comparative example is tested by using 10 battery monomers, and Table 4 shows the number of battery monomers passing the needle puncture test. In Table 3, K is the mass of the electrolyte in the battery monomer, A is the mass content of DMC in the electrolyte based on the total mass of the electrolyte, B is the mass content of LiFSI in the electrolyte based on the total mass of the electrolyte, A:B is the mass content ratio of DMC and LiFSI, G is the mass of the positive electrode active material, G0 is the mass of the positive electrode film layer, D is the gap between the electrode assembly and the inner side of the pressure relief mechanism along the thickness direction of the end cover, Q is the capacity of the battery monomer, and C is the ratio of the mass of the electrolyte to the capacity of the battery monomer.

[0296] Table 3 Specific parameters of Examples 1-14 and Comparative Example 1

[0297] Table 4 Specific parameters of Examples 1-17 and Comparative Example 1

[0298] Table 5 Test results of Examples 1-14 and Comparative Example 1

[0299] Table 6 Test results of Examples 1-17 and Comparative Example 1

[0300] [Preparation of battery monomer]

[0301] Preparation of positive electrode sheet: the positive electrode active material LiNi 0.9 Co 0.06 Mn 0.04 O2, the binder polyvinylidene fluoride (PVDF), the conductive agent (carbon black), and the conductive agent carbon nanotube (CNT) are mixed uniformly in a mass content ratio of 97.5:1.0:1.0:0.5, dissolved in the solvent N-methyl pyrrolidone (NMP), and then fully stirred and mixed uniformly to prepare a positive electrode slurry; the positive electrode slurry is uniformly coated on the opposite two surfaces of the positive electrode current collector aluminum foil, and then subjected to drying, cold pressing, and slitting to obtain a positive electrode sheet.

[0302] Preparation of negative electrode sheet: the negative electrode active material graphite and silicon-carbon composite material are mixed in a mass content ratio of 95:5, and then the mixed negative electrode active material, the conductive agent acetylene black, the binder styrene-butadiene rubber (SBR), and the thickening agent sodium carboxymethyl cellulose (CMC-Na) are dissolved in deionized water in a mass content ratio of 96.5:0.9:1.5:1.1, fully stirred and mixed uniformly to prepare a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector copper foil, and then subjected to drying, cold pressing, and slitting to obtain a negative electrode sheet.

[0303] The separator film is a polyethylene film with a thickness of 9 pm, and a ceramic coating with a thickness of 3 pm is arranged on the side of the base film facing the positive electrode sheet.

[0304] Preparation of the electrolyte: ethylene carbonate (EC), methyl ethyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed according to the requirements in Table 3, then LiPF6 and LiFSI were mixed in a mass content ratio of 1:1 and uniformly dissolved in the above solution to obtain the electrolyte; in addition, 2% of FEC additive based on the total mass of the electrolyte was added to the electrolyte.

[0305] Preparation of the battery cell: the above positive electrode sheet, separator film, and negative electrode sheet were stacked and wound in order to obtain an electrode assembly; the electrode assembly was placed in a shell, and the above prepared electrolyte was added, and after processes such as packaging, standing, formation, and aging, a battery cell was obtained.

[0306] [Parameter testing method of the battery cell]

[0307] The tested battery cell can be a battery cell that has just been assembled and has not been formed, or a battery cell that has been removed from a power device (such as a vehicle).

[0308] (1) Test of the capacity of the battery cell

[0309] The capacity of the battery cell can be tested by a charge-discharge machine. Specifically, with a nominal capacity of 32.5 Ah, a current density of 0.33 C is used to charge and discharge the battery cell in a voltage range of 2.5 V-4.25 V, and after 3 cycles, the discharge capacity of the third cycle is recorded as the actual capacity of the battery cell.

[0310] The capacity of the battery cell obtained by testing has a certain deviation, which is about 5% within a certain range.

[0311] (2) Test of the fast charging performance of the battery cell

[0312] The battery cell is made into a three-electrode battery cell for fast charging performance testing. Specifically, the electrode assembly is prepared by winding in the order of positive electrode sheet, separator film, third electrode (copper wire is selected as the third electrode), separator film, and negative electrode sheet, and then the electrode assembly is placed in an outer package, and the above prepared electrolyte is added, and after processes such as packaging, standing, formation, and aging, a battery cell is obtained. The remaining preparation steps can be referred to in the description above and will not be repeated here.

[0313] The battery is tested at different states of charge (SOC), and the maximum charging current corresponding to each different SOC at 10% SOC, 20% SOC, 30% SOC, 40% SOC, 50% SOC, 60% SOC, 70% SOC, 80% SOC is measured and recorded, and the time from 10% SOC to 80% SOC at the maximum charging current is recorded, which measures the fast charging performance of the battery monomer.

[0314] The maximum charging current corresponding to different SOC can be obtained by selecting different current densities to charge the battery monomer, and recording the SOC when charging to the anode potential to 0mV at the current. The current corresponds to the maximum charging current of the SOC.

[0315] (3) Test of the volume energy density of the battery monomer

[0316] The height of the battery monomer and the diameter of the end cap are tested, the area of the end cap is calculated according to the diameter of the end cap, and the volume of the battery monomer is the area of the end cap x the height of the battery monomer.

[0317] The volume energy density of the battery monomer = the energy of the battery monomer / the volume of the battery monomer.

[0318] The energy of the battery monomer is measured by charging and discharging test of the battery monomer in the voltage range of 2.5V-4.25V with a current density of 0.33C. After 3 cycles, the discharge energy of the third cycle is recorded as the energy of the battery monomer. The unit of the energy of the battery monomer is Wh, and the unit of the capacity of the battery monomer is Ah.

[0319] (4) Test of the needle test of the battery monomer

[0320] The reliability of the battery monomer can be tested by needle test, the specific method is as follows:

[0321] A steel needle with a diameter of 3mm is used to pierce the largest surface of the battery monomer at a speed of 0.1mm / s until thermal runaway occurs. It is observed whether the pressure relief mechanism is broken and whether the electrode terminal is ejected, the shell is broken or not. A group of battery monomers can be used for testing, a group of battery monomers includes 10 battery monomers, and the probability of occurrence of the above conditions in the battery monomers is observed.

[0322] (5) Test of the diameter of the end cap, the area defined by the pressure relief mechanism, the height of the battery monomer, and the gap D in the battery monomer

[0323] The battery monomer is subjected to CT scanning, and the scanned image is tested.

[0324] According to the scanned image, the diameter of the end cover, the height of the battery monomer, and the diameter R of the circular area defined by the pressure relief mechanism can be measured, wherein the area defined by the pressure relief mechanism can be calculated by the formula S = π × (R / 2) 2 The calculation is as follows.

[0325] According to the scanned image, the gap D is tested along the thickness direction of the end cover. Specifically, in the area defined by the pressure relief mechanism, 5 points are selected on the side of the pressure relief mechanism close to the electrode assembly along the thickness direction of the end cover; 5 points are selected on the end of the negative electrode tab close to the end cover in the electrode assembly along the thickness direction of the end cover, which correspond to the 5 points selected on the pressure relief mechanism along the thickness direction of the end cover; the average value of the distances between the 5 points selected on the pressure relief mechanism and the 5 points selected on the electrode assembly is calculated, which is taken as the value of the gap D.

[0326] (6) Test of the liquid injection coefficient, the mass of the electrolyte, the mass content of DMC, and the mass content of LiFSI

[0327] i) The mass of the electrolyte before formation is the mass of the electrolyte injected into the battery monomer during the preparation process of the battery monomer.

[0328] The liquid injection coefficient of the electrolyte before formation is the ratio of the mass of the electrolyte before formation to the nominal capacity of the battery monomer.

[0329] The mass content of DMC and the mass content of LiFSI can be calculated according to the mass of DMC and the mass of LiFSI added during the preparation of the electrolyte.

[0330] ii) After the battery monomer undergoes a certain number of charge and discharge cycles, the liquid injection coefficient, the mass of the electrolyte, the mass content of DMC, and the mass content of LiFSI can be obtained as follows.

[0331] The battery monomer is disassembled, the electrode assembly is taken out and dried, and the mass of the electrolyte in the battery monomer after the cycle is calculated according to the total mass of the battery monomer before disassembly minus the total mass of the electrode assembly after disassembly.

[0332] After the cycle, the liquid injection coefficient is the mass of the electrolyte after the cycle divided by the nominal capacity of the battery monomer.

[0333] The battery monomer is disassembled, the electrolyte in the battery monomer is taken out, and the organic components in the electrolyte are quantitatively analyzed by gas chromatography according to the standard GB / T 9722-2006, and the inorganic components / lithium salt concentration in the electrolyte is quantitatively analyzed by ion chromatography according to the standard JY / T 020-1996.

[0334] (7) Test of the voltage platform

[0335] Voltage plateau = Discharge energy of the battery cell / Discharge capacity of the battery cell. Wherein, the test of the discharge energy and the discharge capacity is shown in the test methods (3) and (1).

[0336] (8) Test of positive active material, negative active material, and separator material

[0337] The positive active material, the negative active material, and the material of the separator can be determined according to the materials selected in the process of preparing the battery cell.

[0338] After the battery cell is cycled for a certain number of times, the battery cell can be disassembled, the electrode assembly is taken out, and the positive electrode sheet, the negative electrode sheet, and the separator are obtained. The sample (for example, the positive electrode sheet, the negative electrode sheet, or the separator) is placed on a sample stage, and the scanning electron microscope (SEM) and the energy dispersive X-ray spectroscopy (EDS) can be used to determine the types of elements and the proportions of the elements in the sample, and the material composition in the sample can be determined according to the types of elements and the proportions of the elements.

[0339] (9) Mass per unit area of positive active material / negative active material

[0340] The mass per unit area of the positive active material is the ratio of the mass of the positive active material added in the process of preparing the battery cell to the area of the coated region of the positive electrode sheet; and the mass per unit area of the negative active material is the ratio of the mass of the negative active material added in the process of preparing the battery cell to the area of the coated region of the negative electrode sheet.

[0341] (10) Test of compacted density

[0342] The thickness of the electrode sheet with an area of s1 is h1, and the weight is m1; the thickness of the aluminum foil with the same area is h2, and the weight is m2; the compacted density of the electrode sheet = (m1-m2) / [s1x(h1-h2)], and the unit is g / cm 3 .

[0343] The measurement deviation of the compacted density is within ±0.05 g / cm 3 .

[0344] (11) Test of porosity

[0345] The sample is cut into a size of 3 mm x 3 mm, and the apparent volume V0 of the sample is measured (the apparent volume of the sample is the thickness of the sample x the area of the sample); then the true volume of the sample is tested by using the true density instrument, specifically, the sample is placed into the sample test cavity, nitrogen is introduced into the sample test cavity, the sample test cavity is connected with the reference cavity, and the pressure after stabilization is recorded, and the volume of the pores is calculated according to the pressure before the reference cavity is connected with the sample cavity, the pressure after the reference cavity is connected with the sample cavity is stabilized, and the Boyle law PV = nRT. The porosity of the sample = pore volume / apparent volume.

[0346] The fast charging performance of the battery cell in the present application can be embodied by the charging time required from 10% SOC to 80% SOC, and the shorter the charging time, the better the fast charging performance of the battery cell; the reliability of the battery cell can be embodied by the number of battery cells passing the needle puncture test, and the more the number of battery cells passing the needle puncture test, the higher the reliability of the battery cell.

[0347] As shown in Examples 1-13 and Comparative Example 1, when a gap D between the electrode assembly and the inner side of the pressure relief mechanism in the thickness direction of the end cover is greater than or equal to 1 mm, the battery cell requires a shorter time from 10% SOC to 80% SOC, the battery cell has better fast charging performance, and when the battery cell is subjected to a needle puncture test, the pressure relief mechanism can be actuated and ruptured in time, the risk of the electrode terminal being separated from the shell and the shell being broken is lower, and the battery cell has higher reliability; in addition, when the gap D is less than or equal to 7 mm, the battery cell can also improve the fast charging performance and reliability of the battery cell while reducing the waste of space inside the battery cell, and the battery cell has a higher volumetric energy density.

[0348] As shown in Examples 1-7, when the gap D is 2 mm to 6 mm, the battery cell has a higher energy density and fast charging performance, and when the battery cell is in thermal runaway, the risk of the electrode terminal being separated from the shell and the shell being broken is lower, and the battery cell has higher reliability. As shown in Examples 12-13, when the gap D is 4 mm to 5 mm, by reducing the mass of the positive active material or the mass of the electrolyte in the battery cell, the risk of the electrode terminal being separated from the shell and the shell being broken is lower, and the battery cell has higher reliability.

[0349] As shown in Examples 1 and 4-7, when the ratio A:B of the mass content A of DMC and the mass content B of LiFSI based on the total mass of the electrolyte is 3 to 40, the battery cell has better fast charging performance and higher reliability; as shown in Examples 1, 4, 5 and 6-7, when A:B is 3 to 40, the battery cell has higher reliability on the premise that the battery cell has better fast charging performance.

[0350] As shown in combination of Embodiment 1 and Embodiments 8-10, when the mass of the electrolyte is 30g-60g, the battery cell has good fast-charging performance and reliability; as shown in combination of Embodiments 1, 8-9, when the mass of the electrolyte is 35g-55g, the battery cell has good fast-charging performance and higher reliability.

[0351] As shown in combination of Embodiments 8-10, when the ratio of the mass of the electrolyte to the capacity of the battery cell is C≤1.6g / Ah, the battery cell has high fast-charging performance and high reliability; when C is greater than 1.6g / Ah, the reliability of the battery cell can be improved by increasing the gap D; when 1.2g / Ah≤C≤1.4g / Ah, the battery cell has high reliability and good fast-charging performance.

[0352] As shown in combination of Embodiment 1 and Embodiment 13, when the porosity of the separator film is less than or equal to 45%, the battery cell has good fast-charging performance and high reliability.

[0353] As shown in combination of Embodiment 1, Embodiments 4-7, Embodiments 15-17 and Comparative Example 1, when the ratio of the mass content A of DMC to the mass content B of LiFSI based on the total mass of the electrolyte is A:B=3-40, the battery cell has good fast-charging performance and high reliability; as shown in combination of Embodiments 15-17 and Comparative Example 1, when A:B=3-40, the battery cell has high reliability under the premise of good fast-charging performance. In Embodiment 16, the value of A:B is greater than that in Embodiment 17, the fast-charging performance is improved compared with Comparative Example 1, but is slightly lower than that in Embodiment 17, because the mass content of dimethyl carbonate in Embodiment 17 is higher, and the fast-charging performance of the battery cell is better.

[0354] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are only examples, and embodiments having the same technical idea and playing the same role and effect within the scope of the technical solutions of the present application are all included in the technical scope of the present application. In addition, within the scope of the main idea of the present application, various modifications that can be thought of by those skilled in the art, and other modes constructed by combining part of the components of the embodiments are also included in the scope of the present application.

Claims

1. A battery cell, characterized by, The battery cell comprises: an electrode assembly; a housing; an end cover, the housing and the end cover forming a space accommodating the electrode assembly, the end cover being provided with a pressure relief mechanism; an electrolyte, the electrolyte comprising a solvent and an electrolyte salt, the solvent comprising dimethyl carbonate, and the electrolyte salt comprising a lithium bisfluorosulfonylimide salt; a gap D between the electrode assembly and an inner side of the pressure relief mechanism in a thickness direction of the end cover satisfying 1 mm≤D≤7 mm; a capacity Q of the battery cell satisfying 30 Ah≤Q≤40 Ah.

2. The battery cell of claim 1, wherein, 2 mm≤D≤6 mm.

3. The battery cell of claim 1, wherein, A mass content A of the dimethyl carbonate satisfies 20 wt%≤A≤80 wt% based on a total mass of the electrolyte; and / or, a mass content B of the lithium bisfluorosulfonylimide salt satisfies 1 wt%≤B≤16 wt% based on the total mass of the electrolyte.

4. The battery cell of claim 3, wherein, 50 wt%≤A≤75 wt%; and / or, 1 wt%≤B≤11 wt%.

5. The battery cell of claim 3, wherein, 20 wt%≤A≤65 wt%.

6. The battery cell of claim 3, wherein, A mass content ratio A:B of the dimethyl carbonate and the lithium bisfluorosulfonylimide satisfies 3≤A:B≤40.

7. The battery cell of claim 6, wherein, 5≤A:B≤30.

8. The battery cell of claim 1, wherein, In the battery cell, a ratio C of a mass of the electrolyte to a capacity of the battery cell satisfies C≤1.6 g / Ah. 1.2 g / Ah≤C≤1.4 g / Ah. A ratio E of a mass of the electrolyte remaining in the battery cell to the capacity of the battery cell after the battery cell is cycled for 1000 times satisfies 0.7 g / Ah≤E≤1.1 g / Ah.

10. The battery cell of claim 1, wherein, A size H of the battery cell in the thickness direction of the end cover satisfies 90 mm≤H≤120 mm.

11. The battery cell of claim 1, wherein, In the battery cell, a mass K of the electrolyte satisfies 30 g≤K≤60 g.

12. The battery cell of claim 1, wherein, 35 g≤K≤55 g.

13. The battery cell of claim 12, wherein, A mass P of the electrolyte remaining in the battery cell after the battery cell is cycled for 1000 times satisfies 22 g≤P≤36 g.

14. The battery cell of claim 1, wherein, A porosity of the positive electrode sheet is 22% to 26%, and / or, a porosity of the negative electrode sheet is 23% to 30%.

15. The battery cell of claim 1, wherein, The electrode assembly includes a positive electrode tab and a negative electrode tab, the positive electrode tab having a compacted density greater than or equal to 3.4 g / cm 3 , and / or the negative electrode tab having a compacted density greater than or equal to 1.2 g / cm 3 .

16. The battery cell of claim 15, wherein, The positive electrode sheet has a compacted density of 3.4 g / cm 3 ~ 3.7 g / cm 3 , and / or the negative electrode sheet has a compacted density of 1.2 g / cm 3 ~ 1.7 g / cm 3 .

17. The battery cell of claim 16, wherein, The positive electrode sheet has a compaction density of 3.35 g / cm 3 ~ 3.69 g / cm 3 and / or the negative electrode sheet has a compaction density of 1.2 g / cm 3 ~ 1.65 g / cm 3 .

18. The battery cell of claim 16, wherein, The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer arranged 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 lithium nickel oxide or a metal phosphate.

19. The battery cell of claim 15, wherein, The negative electrode sheet comprises a negative electrode active material, the negative electrode active material comprising graphite and a silicon-containing material, the silicon-containing material comprising at least one of elemental silicon, a silicon-oxygen composite, a silicon-carbon composite, a silicon-nitrogen composite, a silicon-containing alloy, or a silicon-oxygen-carbon composite material, the graphite comprising at least one of natural graphite or artificial graphite.

20. The battery cell of claim 19, wherein, The chemical formula of the lithium nickel oxide satisfies: Li 1+a [Ni x Co y Mn z M b ]O 2-c , M includes at least one of Zr, Al, Ti, Sb, Nb, Te, Mg, B, Ca, V, Ta or Sr, 0.2≥a≥-0.2, 1>x≥0.7, 0.3>y>0, 0.3>z>0, 0.3>b≥0, 0.5≥c≥0.

21. The battery cell of claim 19, wherein, In the battery cell, the gram weight per unit area of the positive electrode active material is 15 mg / cm 2 ~ 23 mg / cm 2 .

22. The battery cell of claim 15, wherein, A mass content of the silicon-containing material is 1 wt% to 20 wt% based on a total mass of the negative electrode active material.

23. The battery cell of claim 22, wherein, The silicon-containing material comprises a silicon-carbon composite, a mass proportion of silicon elements in the silicon-carbon composite being 40 wt% to 60 wt% based on a total mass of the silicon-containing material.

24. The battery cell of claim 22, wherein, ​ 25. The battery cell of claim 22, wherein, In the battery cell, the gram weight per unit area of the negative electrode active material is 8 mg / cm 2 ~ 13 mg / cm 2 .

26. The battery cell of claim 15, wherein, The electrode assembly further comprises a separator film disposed between the positive electrode tab and the negative electrode tab, the separator film comprising a base film and a ceramic coating disposed on a side of the base film facing the positive electrode tab.

27. The battery cell of claim 26, wherein, The porosity of the separator film is 30% to 45%.

28. The battery cell of claim 1, wherein, The end cover comprises an end cover body, and the pressure relief mechanism is disposed on the inner side or the outer side of the end cover body.

29. The battery cell of claim 28, wherein, The end cover body is provided with a score groove, and the area defined by the score groove forms the pressure relief mechanism.

30. The battery cell of claim 1, wherein, The area S defined by the pressure relief mechanism and the area S0 of the end cover satisfy: 25%≤S / S0≤50%.

31. The battery cell of claim 1, wherein, The area S of the region defined by the pressure relief mechanism and the capacity Q of the battery cell satisfy: 12 mm 2 / Ah≤ S / Q≤ 20 mm 2 / Ah.

32. The battery cell of claim 1, wherein, The pressure relief mechanism defines an area S greater than or equal to 500 mm 2 .

33. The battery cell of claim 32, wherein, 600 mm 2 ≤ S ≤ 800 mm 2 .

34. The battery cell of claim 1, wherein, The voltage platform of the battery cell is 3.5V to 3.7V.

35. The battery cell of claim 1, wherein, The solvent further comprises methyl ethyl carbonate and ethylene carbonate, and the electrolyte salt further comprises lithium hexafluorophosphate.

36. The battery cell of claim 1, wherein, The electrolyte further comprises an additive, and the additive comprises at least one of fluoroethylene carbonate or vinylene carbonate.

37. The battery cell of any one of claims 1-36, wherein, The housing has a downward first opening, and the end cover covers the first opening.

38. The battery cell of claim 1, wherein, The battery cell further comprises a current collecting member accommodated in the housing, located between the electrode assembly and the end cover along the thickness direction of the end cover, and electrically connected to the tab of the electrode assembly and the housing.

39. The battery cell of claim 38, wherein, The tabs of the electrode assembly are close to the same end of the end cover.

40. The battery cell of claim 39, wherein, The inner side of the housing is provided with a limiting portion, and the limiting portion is located between the electrode assembly and the end cover along the thickness direction of the end cover, and the current collecting member abuts against a side of the limiting portion facing the electrode assembly.

41. The battery cell of claim 40, wherein, The battery cell further comprises a sealing member disposed between the end cover and the housing.

42. The battery cell of claim 38, wherein, Along the thickness direction perpendicular to the end cover, the end cover is provided with at least one protrusion disposed on the end cover body and protruding away from the electrode assembly; along the thickness direction of the end cover, the size L of the at least one protrusion satisfies: 1mm≤L≤5mm.

43. The battery cell of any one of claims 1-42, wherein, The battery cell is a cylindrical battery cell.

44. A battery, comprising: Comprise: The battery cell according to any one of claims 1-43.

45. An electrical device, comprising: Comprise: The battery according to claim 44.

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