Battery cell, battery, and electric device

Abstract

Disclosed in the present disclosure are a battery cell, a battery, and an electric device. The length of the battery cell is 400-650 mm; the battery cell comprises a positive electrode sheet, a negative electrode sheet and an electrolyte; the positive electrode sheet comprises lithium-containing phosphate; the negative electrode sheet comprises a carbon material; the electrolyte comprises cations, anions and an organic solvent; the cations include lithium ions, and the anions include anions shown in formula 1 and hexafluorophosphate anions; R1 and R2 are each independently selected from a fluorine atom or a C1-C6 fluoroalkyl group; the organic solvent comprises dimethyl carbonate, and the mass ratio of the dimethyl carbonate in the organic solvent is less than or equal to 5%. The battery provided by the present disclosure achieves high reliability while maintaining excellent power performance.

Description

Battery cells, batteries and electrical devices

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] The present disclosure claims priority to Chinese patent application No. 202410389512.5, filed on April 1, 2024, entitled “Battery Cell, Battery and Electrical Device,” the entire contents of which are incorporated herein by reference. Technical Field

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

[0004] As the application range of batteries becomes wider and wider, people's demand for battery use is also increasing, for example, the demand for battery energy density is getting higher and higher. In order to achieve higher energy density, the compaction density of the positive electrode sheet is usually increased. Increasing the compaction density of the positive electrode sheet will affect the power performance of the battery. However, the current methods of improving battery power performance often increase the battery's gas and heat production, thereby affecting the battery's reliability. Therefore, how to ensure that the battery has high reliability while maintaining good power performance is a technical problem that needs to be solved urgently.

[0005] Summary of the Invention

[0006] The present disclosure provides a battery cell, a battery, and an electrical device, which can enable the battery to have high reliability while having good power performance.

[0007] In a first aspect, the present disclosure provides a battery cell, wherein the length of the battery cell is 400 mm-650 mm, the battery cell comprises a positive electrode sheet, a negative electrode sheet and an electrolyte, the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer located on at least one side of the positive electrode current collector, the positive electrode film layer comprises a positive electrode active material, and the positive electrode active material comprises a lithium-containing phosphate; the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector, the negative electrode film layer comprises a negative electrode active material, and the negative electrode active material comprises a carbon material; the electrolyte comprises cations, anions and an organic solvent, the cations comprise lithium ions, the anions comprise anions represented by Formula 1 and hexafluorophosphate anions, R1 and R2 are independently selected from fluorine atoms or C1-C6 fluoroalkyl groups, and the organic solvent comprises dimethyl carbonate, and the mass proportion of dimethyl carbonate in the organic solvent is less than or equal to 5%.

[0008] The electrolyte of the battery cell provided by the embodiment of the present disclosure includes the anion shown in Formula 1 and the hexafluorophosphate anion. The anion shown in Formula 1 is a weakly coordinated anion centered on N, containing a conjugated group and a fluorine atom and / or a fluoroalkyl group with strong electron-absorbing properties. The anion charge is highly delocalized, and the anion is not easy to re-associate with the cation, thereby making the electrolyte have a higher ionic conductivity and ion migration rate, thereby improving the power performance of the battery cell; the electrolyte also includes the hexafluorophosphate anion, which can play a role in reducing the gas production of the battery cell and improving the reliability of the battery cell. In the electrolyte of the battery cell provided by the embodiment of the present disclosure, the mass proportion of dimethyl carbonate in the organic solvent is less than or equal to 5%, thereby making the electrode assembly have good electrolyte wettability, which is beneficial to improving the power performance of the battery cell, and can also make the battery cell have a lower gas production, which is beneficial to the high reliability of the battery cell. Therefore, the battery cell provided by the embodiment of the present disclosure can have high reliability under the premise of having good power performance.

[0009] In some embodiments, the length of the battery cell is 500 mm-650 mm.

[0010] In some embodiments, the aspect ratio of the battery cell is greater than or equal to 4, and can be optionally 4-5.5.

[0011] The electrolyte provided by the embodiments of the present disclosure can have good fluidity, high ionic conductivity and high ion migration rate, which is conducive to the battery cells having larger size and larger aspect ratio, and is conducive to the battery cells having high energy density, good power performance and good cycle performance.

[0012] In some embodiments, the mass fraction of dimethyl carbonate in the organic solvent is 3%-5%. Compared with other carbonates, dimethyl carbonate has a lower viscosity and can be used in electrolytes to improve electrolyte fluidity, improve electrolyte wettability of electrode assemblies, and improve the power performance of battery cells.

[0013] In some embodiments, the molar concentration of the anion represented by Formula 1 is 0.3 mol / L-0.8 mol / L, and may be 0.4 mol / L-0.6 mol / L. The molar concentration of the anion represented by Formula 1 within the above range can not only provide the electrolyte with high ionic conductivity and ion migration rate, thereby improving the power performance of the battery cell, but also reduce the heat generation of the battery cell, resulting in low gas production and high reliability.

[0014] In some embodiments, the molar concentration of the hexafluorophosphate anion is greater than the molar concentration of the anion represented by Formula 1. This can fully utilize the respective advantages of the hexafluorophosphate anion and the anion represented by Formula 1, so that the battery cell can better achieve high reliability, good power performance and good cycle performance.

[0015] In some embodiments, the molar concentration of the hexafluorophosphate anion is 0.5 mol / L-0.9 mol / L, and can be optionally 0.55 mol / L-0.7 mol / L. By adjusting the molar concentration of the hexafluorophosphate anion within the above range, the battery cell can better achieve high reliability, good power performance, and good cycle performance.

[0016] In some embodiments, the total molar concentration of the anions is 0.95 mol / L-1.65 mol / L, optionally 1.0 mol / L-1.3 mol / L.

[0017] In some embodiments, the organic solvent further comprises ethyl methyl carbonate, and the mass proportion of ethyl methyl carbonate in the organic solvent is 56%-80%, and optionally 60%-75%. Ethyl methyl carbonate also has a relatively low viscosity, and the boiling point of ethyl methyl carbonate is higher than that of dimethyl carbonate. Therefore, by including ethyl methyl carbonate in the organic solvent, the battery cell can have a relatively low gas production, good electrolyte wettability, and good power performance.

[0018] In some embodiments, the organic solvent further comprises ethylene carbonate, and the mass proportion of the ethylene carbonate in the organic solvent is 15%-40%, optionally 20%-36%.

[0019] In some embodiments, the electrolyte further includes an additive, wherein the additive includes vinylene carbonate.

[0020] Optionally, the mass proportion of the vinylene carbonate in the electrolyte is less than or equal to 3%.

[0021] Vinylene carbonate helps to improve the film-forming quality of the negative electrode solid electrolyte interface film, thereby helping to further improve the performance of the battery cell.

[0022] In some embodiments, the viscosity of the electrolyte at 25° C. is less than or equal to 5 mPa·s.

[0023] In some embodiments, the electrolyte has a conductivity of 8 mS / cm-16 mS / cm at 25°C.

[0024] In some embodiments, the coating weight of the positive electrode film layer is 19 mg / cm 2 -33mg / cm2 .

[0025] In some embodiments, the compaction density of the positive electrode film layer is 2.2 g / cm 3 -2.7g / cm 3 .

[0026] The electrolyte provided by the embodiments of the present disclosure can have good fluidity, high ionic conductivity and high ion migration rate, which is beneficial for the positive electrode sheet to have a high coating weight and / or compaction density, and is beneficial for the battery cell to have both high energy density and good power performance.

[0027] In some embodiments, the positive electrode active material includes lithium iron phosphate and modified compounds thereof.

[0028] In some embodiments, the mass proportion of the positive electrode active material in the positive electrode film layer is greater than or equal to 93%.

[0029] The electrolyte provided by the embodiments of the present disclosure can have good fluidity, high ionic conductivity and high ion migration rate, which is beneficial for the positive electrode active material in the positive electrode film layer to have a high mass ratio and is beneficial for the battery cell to have both high energy density and good power performance.

[0030] In some embodiments, the negative electrode active material includes graphite. Optionally, the graphite includes one or both of artificial graphite and natural graphite.

[0031] In a second aspect, the present disclosure provides a battery comprising the battery cell according to the first aspect of the present disclosure.

[0032] In a third aspect, the present disclosure provides an electrical device comprising the battery according to the second aspect of the present disclosure, wherein the battery is configured to provide electrical energy.

[0033] The electric device of the present disclosure includes the battery provided by the present disclosure, and thus has at least the same advantages as the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] To more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the embodiments of the present disclosure. Obviously, the drawings described below are only some embodiments of the present disclosure, and those skilled in the art can derive other drawings based on the drawings without inventive effort.

[0035] FIG1 is a schematic structural diagram of a vehicle provided in some embodiments of the present disclosure.

[0036] FIG2 is a schematic diagram of an explosion of a battery provided in some embodiments of the present disclosure.

[0037] In the accompanying drawings, the drawings are not necessarily drawn to scale.

[0038] The description of the accompanying drawings is as follows: 1. Vehicle; 2. Battery; 3. Controller; 4. Motor; 5. Box; 5a. First box part; 5b. Second box part; 5c. Accommodation space; 6. Battery module. DETAILED DESCRIPTION

[0039] Below, the embodiments of the battery cell, battery, and electrical device disclosed herein are described in detail with appropriate reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of substantially identical structures may be omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure and are not intended to limit the subject matter described in the claims.

[0040] " scope " disclosed in the present disclosure is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and selected lower limit and upper limit define the boundary of special scope.The scope that this mode limits can be to include end value or not include end value, and can be combined arbitrarily, and promptly any lower limit can form a scope with any upper limit combination.For example, if the scope of 60-120 and 80-110 is listed for specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected.In addition, if the minimum range value 1 and 2 listed, and if the maximum range value 3,4 and 5 listed, then the following scope can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5.In the present disclosure, unless otherwise specified, numerical range " ab " represents the abbreviation of any real number combination between a and b, and wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0041] Unless otherwise specified, all embodiments and optional embodiments of the present disclosure can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure content of the present disclosure.

[0042] Unless otherwise specified, all technical features and optional technical features of the present disclosure can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure content of the present disclosure.

[0043] Unless otherwise specified, all steps of the present disclosure may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0044] If not otherwise specified, in the present disclosure, the terms "first", "second", etc. are used to distinguish different objects rather than to describe a specific order or a primary-secondary relationship.

[0045] In the present disclosure, the terms "plurality" and "multiplicity" refer to two or more.

[0046] In the description of the embodiments of the present disclosure, unless otherwise specified, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. Furthermore, a first feature being "above," "above," and "above" a second feature may mean that the first feature is directly above or diagonally above the second feature, or simply means that the first feature is at a higher level than the second feature. A first feature being "below," "below," and "below" a second feature may mean that the first feature is directly below or diagonally below the second feature, or simply means that the first feature is at a lower level than the second feature.

[0047] Unless otherwise specified, terms used in the present disclosure have common meanings that are commonly understood by those skilled in the art.

[0048] Unless otherwise stated, the numerical values ​​of the various parameters mentioned in this disclosure can be measured using various test methods commonly used in the art, for example, they can be measured according to the test methods given in the examples of this disclosure. Unless otherwise stated, the test temperature of each parameter is 25°C.

[0049] The battery mentioned in the embodiments of the present disclosure may be a single physical module including one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in the present disclosure may include a battery cell, a battery module or a battery pack, etc. A battery cell is the smallest unit that makes up a battery, which can realize the function of charging and discharging on its own. When there are multiple battery cells, the multiple battery cells are connected in series, in parallel or in mixed connection through a busbar. In some embodiments, the battery may be a battery module; when there are multiple battery cells, the multiple battery cells are arranged and fixed to form a battery module. In some embodiments, the battery may be a battery pack, which includes a case and battery cells, and the battery cells or battery modules are housed in the case. In some embodiments, the case may serve as part of the chassis structure of a vehicle. For example, part of the case may become at least a part of the floor of the vehicle, or part of the case may become at least a part of the crossbeam and longitudinal beam of the vehicle.

[0050] In some embodiments, the battery may be an energy storage device, including an energy storage container, an energy storage cabinet, and the like.

[0051] The technical solutions described in the embodiments of the present disclosure are applicable to batteries and electrical devices using batteries.

[0052] Batteries can be used as power sources or energy storage units for electrical devices. Electrical devices include, but are not limited to, mobile devices (e.g., mobile phones, tablets, laptops, etc.), vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, and energy storage systems.

[0053] The electrical device can select the type of battery according to its usage requirements, such as a battery cell, a battery module or a battery pack.

[0054] For the convenience of description, the following embodiments are described by taking a vehicle as an example of an electrical device.

[0055] FIG1 is a schematic structural diagram of a vehicle provided in some embodiments of the present disclosure.

[0056] As shown in FIG1 , a battery 2 is provided inside the vehicle 1. The battery 2 may be provided at the bottom, head, or tail of the vehicle 1. The battery 2 may be used to power the vehicle 1. For example, the battery 2 may serve as an operating power source for the vehicle 1.

[0057] The vehicle 1 may further include a controller 3 and a motor 4 . The controller 3 is used to control the battery 2 to supply power to the motor 4 , for example, to meet the power requirements of the vehicle 1 during startup, navigation, and driving.

[0058] In some embodiments, the battery 2 can serve not only as an operating power source for the vehicle 1 , but also as a driving power source for the vehicle 1 , replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1 .

[0059] FIG2 is an exploded view of a battery according to some embodiments of the present disclosure. As shown in FIG2 , the battery 2 includes a housing 5 and battery cells (not shown), which are housed in the housing 5 .

[0060] The housing 5 is used to house battery cells and can have various structures. In some embodiments, the housing 5 can include a first housing portion 5a and a second housing portion 5b. The first housing portion 5a and the second housing portion 5b overlap each other, and the first housing portion 5a and the second housing portion 5b together define a storage space 5c for accommodating the battery cells. The second housing portion 5b can be a hollow structure with one end open. The first housing portion 5a is a plate-like structure, and the first housing portion 5a overlaps the open side of the second housing portion 5b to form the housing 5 with the storage space 5c. The first housing portion 5a and the second housing portion 5b can also be hollow structures with one end open. The open side of the first housing portion 5a overlaps the open side of the second housing portion 5b to form the housing 5 with the storage space 5c. Of course, the first housing portion 5a and the second housing portion 5b can have various shapes, such as a cylinder, a rectangular parallelepiped, etc.

[0061] In order to improve the sealing performance after the first box body 5a and the second box body 5b are connected, a sealing member, such as a sealant, a sealing ring, etc., may also be provided between the first box body 5a and the second box body 5b.

[0062] Assuming that the first box body portion 5a covers the top of the second box body portion 5b, the first box body portion 5a can also be called an upper box cover, and the second box body portion 5b can also be called a lower box body.

[0063] In battery 2, there can be one or more battery cells. If there are multiple battery cells, they can be connected in series, in parallel, or in a hybrid configuration. A hybrid configuration refers to a combination of series and parallel connections. Multiple battery cells can be directly connected in series, in parallel, or in a hybrid configuration, and then the entire battery cell structure can be housed within housing 5. Alternatively, multiple battery cells can be first connected in series, in parallel, or in a hybrid configuration to form a battery module 6, and then multiple battery modules 6 can be connected in series, in parallel, or in a hybrid configuration to form a single unit and housed within housing 5.

[0064] In some embodiments, there are multiple battery cells, which are first connected in series, in parallel, or in hybrid to form a battery module 6. The multiple battery modules 6 are then connected in series, in parallel, or in hybrid to form a whole, which is then housed in a box.

[0065] The multiple battery cells in the battery module 6 can be electrically connected via a busbar component to achieve parallel connection, series connection, or mixed connection of the multiple battery cells in the battery module 6 .

[0066] The battery cells mentioned in the embodiments of the present disclosure may include lithium-ion battery cells.

[0067] The battery cell provided by the embodiment of the present disclosure includes an electrode assembly, an outer packaging and an electrolyte. The length of the battery cell is 400mm-650mm.

[0068] The electrode assembly can be a wound structure or a laminated structure. The number of electrode assemblies contained in a battery cell can be one or more, which can be adjusted according to demand.

[0069] The outer packaging is used to encapsulate the electrode assembly and electrolyte. The outer packaging can be a hard shell, such as a hard plastic shell, aluminum shell, steel shell, etc.

[0070] In some embodiments, the outer packaging includes a shell and an end cap assembly, the shell having a housing cavity and an opening, the electrode assembly being placed in the housing cavity, and the end cap assembly covering the opening. The shell may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates enclosing a housing cavity. In other embodiments, the shell may be a hollow structure with openings on opposite sides, the number of end cap assemblies is two, and one end cap assembly corresponds to covering one opening of the shell and forming a sealed connection to form a housing cavity for accommodating the electrode assembly. In some embodiments, the end cap assembly may be located at one or both ends of the shell in the longitudinal direction.

[0071] The electrode assembly includes a positive electrode sheet and a negative electrode sheet. The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer located on at least one side of the positive electrode current collector. The positive electrode film layer includes a positive electrode active material, which includes a lithium-containing phosphate. The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector. The negative electrode film layer includes a negative electrode active material, which includes a carbon material.

[0072] The electrolyte includes cations, anions and an organic solvent, wherein the cations include lithium ions, and the anions include the anions shown in Formula 1 and hexafluorophosphate anions (PF6 - ), R1 and R2 are independently selected from a fluorine atom or a C1-C6 fluoroalkyl group.

[0073] The organic solvent includes dimethyl carbonate (DMC), and the mass proportion of dimethyl carbonate in the organic solvent is less than or equal to 5%.

[0074] Compared with ternary positive electrode active materials, lithium-containing phosphates have a higher decomposition temperature and do not have an oxygen-releasing thermal chain reaction similar to ternary positive electrode active materials. In addition, lithium-containing phosphates are also cheaper, so battery cells using lithium-containing phosphates have received widespread attention. However, one problem with lithium-containing phosphates is their low compaction density. In order to make such battery cells have a higher energy density, the positive electrode coating weight is usually increased. As the positive electrode coating weight increases, the power performance of the battery cell will be affected. In addition, the energy density of the battery cell can also be increased by increasing the length of the battery cell, but as the length of the battery cell increases, the electrolyte wettability of the electrode assembly is usually reduced, which will also affect the power performance of the battery cell.

[0075] Generally speaking, energy density and power performance are two conflicting indicators in the design and production of battery cells. Generally, to increase energy density, it is necessary to increase the electrode coating weight and increase the mass ratio of active materials, which leads to a decrease in the power performance of the battery cell. To improve power performance, it is necessary to reduce the electrode coating weight and increase the mass ratio of conductive agents, which leads to a decrease in the energy density of the battery cell.

[0076] The power performance of a battery cell refers to the amount of electrical energy that can be released by the battery cell in a short period of time. Battery cells with good power performance help improve the acceleration and driving experience of electric vehicles.

[0077] In order to ensure that battery cells containing lithium phosphates have good power performance and meet the current demand for high energy density and good power performance, the commonly used strategy is to add an appropriate amount of sulfonimide lithium salts to the electrolyte to improve the conductivity of the electrolyte, and to use organic solvents with lower viscosity to improve the electrolyte wettability of the electrode assembly.

[0078] Furthermore, for battery cells using ternary cathode active materials, their reliability is primarily determined by the cathode. The basic process of thermal runaway is as follows: at high temperatures, the SEI film of the anode decomposes. As the temperature rises, the charged cathode active material begins to decompose at around 200°C, releasing oxygen, and the electrolyte undergoes a violent oxidation reaction. For battery cells using lithium phosphates, however, their reliability is primarily determined by the anode. Because lithium phosphates have a more stable structure, there's no risk of violent decomposition and oxygen release. Initial heat generation in the battery cell primarily comes from the anode-electrolyte reaction.

[0079] The inclusion of sulfonyl imide lithium salts in the electrolyte can significantly improve the power performance of battery cells. For battery cells using ternary positive electrode active materials, the sulfonyl imide lithium salts in the electrolyte can react with the lithium spontaneously leached from the fully charged carbon material of the negative electrode to form lithium sulfide. The lithium sulfide can then diffuse to the positive electrode due to the concentration difference, allowing the lithium ions to be re-intercalated into the fully charged positive electrode active material. In addition, sulfonyl imide lithium salts can enhance the redox resistance of the electrolyte, thereby improving not only the power performance of the battery cells but also the reliability of the battery cells. However, for battery cells using lithium phosphate, after the SEI film of the negative electrode decomposes, the sulfonyl imide lithium salts in the electrolyte tend to react violently with the fully charged carbon material of the negative electrode, releasing heat and releasing NO2 and SO2 gases. Furthermore, the low-viscosity organic solvent in the electrolyte is easily volatilized and decomposed when heated, which can increase the gas production of the battery cells and affect the reliability of the battery cells.

[0080] Dimethyl carbonate is a known organic solvent with a very low viscosity. It can significantly improve electrolyte fluidity and electrolyte wettability of electrode assemblies. It is currently widely used in battery systems with high compaction density and high energy density. However, dimethyl carbonate has a very low boiling point, resulting in easy volatilization and decomposition, as well as high gas production.

[0081] The electrolyte of the battery cell provided by the embodiment of the present disclosure includes the anion shown in Formula 1 and the hexafluorophosphate anion. The anion shown in Formula 1 is a weakly coordinated anion centered on N, containing a conjugated group and a fluorine atom and / or a fluoroalkyl group with strong electron-absorbing properties. The anion charge is highly delocalized, and the anion is not easy to reassociate with the cation, thereby making the electrolyte have higher ionic conductivity and ion migration rate, thereby improving the power performance of the battery cell; the electrolyte also includes the hexafluorophosphate anion, which can play a role in reducing the gas production of the battery cell and improving the reliability of the battery cell. In the electrolyte of the battery cell provided by the embodiment of the present disclosure, the mass proportion of dimethyl carbonate in the organic solvent is less than or equal to 5%, thereby making the electrode assembly have good electrolyte wettability, which is beneficial to improving the power performance of the battery cell, and also making the battery cell have a lower gas production, which is beneficial to the high reliability of the battery cell.

[0082] Therefore, the battery cell provided by the embodiment of the present disclosure can have high reliability while having good power performance.

[0083] The length of the battery cell is 400 mm to 650 mm, for example, 400 mm, 410 mm, 420 mm, 430 mm, 440 mm, 450 mm, 460 mm, 470 mm, 480 mm, 490 mm, 500 mm, 510 mm, 520 mm, 530 mm, 540 mm, 550 mm, 560 mm, 570 mm, 580 mm, 590 mm, 600 mm, 610 mm, 620 mm, 630 mm, 640 mm, 650 mm, or any range thereof. In some embodiments, the length of the battery cell can optionally be 500 mm to 650 mm.

[0084] The electrolyte provided by the embodiments of the present disclosure can have good fluidity, high ionic conductivity and high ion migration rate, which is conducive to the battery cells having larger sizes and the battery cells having high energy density, good power performance and good cycle performance.

[0085] In some embodiments, the aspect ratio of the battery cell can be greater than or equal to 4, for example, 4, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5, 5.1, 5.2, 5.3, 5.4, 5.5, or any range thereof. Alternatively, the aspect ratio of the battery cell can be 4-5.5 or 4-5.

[0086] Increasing the aspect ratio of a battery cell generally increases its energy density, but the electrolyte wettability of the electrode assembly typically decreases, which can affect the power and cycle performance of the battery cell. The electrolyte provided by the embodiments of the present disclosure can have good fluidity, high ionic conductivity, and high ion mobility, thereby facilitating battery cells with larger aspect ratios and achieving both high energy density, good power performance, and good cycle performance.

[0087] The length of the battery cell is greater than the width of the battery cell, and the width of the battery cell is greater than the thickness of the battery cell.

[0088] The length of a battery cell can be measured using a laser thickness gauge. During the test, 3-5 random points can be selected and the average value calculated. The width of a battery cell can be measured using a laser thickness gauge. During the test, 3-5 random points can be selected and the average value calculated. The thickness of a battery cell can be measured using a laser thickness gauge. During the test, 9 random points can be selected and the average value calculated. It should be understood that the dimensions of a battery cell do not include the dimensions of the electrode terminals provided on the end cap assembly.

[0089] The mass proportion of dimethyl carbonate in the organic solvent is less than or equal to 5%. Optionally, the mass proportion of dimethyl carbonate in the organic solvent is 1%-5%, 1.5%-5%, 2%-5%, 2.5%-5%, 3%-5%, 1%-4%, 1.5%-4%, 2%-4%, 2.5%-4%, or 3%-4%. Compared with other carbonates, dimethyl carbonate has a lower viscosity. When used in electrolytes, it can better improve the fluidity of the electrolyte, improve the electrolyte wettability of the electrode assembly, and improve the power performance of the battery cell.

[0090] In some embodiments, the organic solvent further comprises ethyl methyl carbonate (EMC).

[0091] Optionally, the mass proportion of ethyl methyl carbonate in the organic solvent may be greater than the mass proportion of dimethyl carbonate in the organic solvent.

[0092] Optionally, the mass proportion of ethyl methyl carbonate in the organic solvent can be 56%-80%, for example, it can be 56%, 58%, 60%, 62%, 65%, 68%, 70%, 72%, 75%, 78%, 80%, or a range consisting of any of the above values.

[0093] Optionally, the mass proportion of ethyl methyl carbonate in the organic solvent can be 56%-78%, 56%-75%, 56%-72%, 56%-70%, 58%-75%, 58%-72%, 60%-75%, 60%-72%.

[0094] Dimethyl carbonate has a low boiling point and is prone to volatilization and decomposition when heated, which can easily increase the gas production of the battery cells. Ethyl methyl carbonate also has a low viscosity and a higher boiling point than dimethyl carbonate. Therefore, by including ethyl methyl carbonate in the organic solvent, the battery cells can have lower gas production while also having good electrolyte wettability and good power performance.

[0095] In some embodiments, the organic solvent further comprises ethylene carbonate (EC).

[0096] Optionally, the mass proportion of ethylene carbonate in the organic solvent can be 15%-40%, for example, it can be 15%, 18%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 40%, or a range consisting of any of the above values.

[0097] Optionally, the mass proportion of ethylene carbonate in the organic solvent can be 15%-38%, 15%-36%, 15%-34%, 20%-38%, 20%-36%, 20%-34%, 25%-38%, 25%-36%, 25%-34%.

[0098] Dimethyl carbonate and ethyl methyl carbonate can make the electrolyte have low viscosity, which facilitates the flow of the electrolyte, but their dielectric constant is small and their ability to dissociate electrolyte salts is slightly weak. By mixing dimethyl carbonate, ethyl methyl carbonate and ethylene carbonate, the electrolyte can have good fluidity while also having high ionic conductivity and high ion migration rate.

[0099] R1 and R2 each independently include a fluorine atom or a C1-C6 fluoroalkyl group. A C1-C6 fluoroalkyl group means that at least one hydrogen atom in the C1-C6 alkyl group is replaced by a fluorine atom, or all hydrogen atoms are replaced by fluorine atoms, and can be, for example, a trifluoromethyl group, a pentafluoroethyl group, a heptafluoropropyl group, or the like.

[0100] Optionally, R1 and R2 each independently include a fluorine atom or a trifluoromethyl group.

[0101] In some embodiments, the anion represented by Formula 1 may include a bis(fluorosulfonyl)imide anion (FSI - ), bis(trifluoromethanesulfonyl)imide anion (TFSI - ) or two thereof. Optionally, the anion shown in Formula 1 may include a bis(fluorosulfonyl)imide anion (FSI - ).

[0102] This can further improve the power performance of the battery cells.

[0103] In some embodiments, the molar concentration of the anion shown in Formula 1 can be 0.3 mol / L-0.8 mol / L, for example, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, 0.45 mol / L, 0.5 mol / L, 0.55 mol / L, 0.6 mol / L, 0.65 mol / L, 0.7 mol / L, 0.75 mol / L, 0.8 mol / L, or a range consisting of any of the above values. Alternatively, the molar concentration of the anion shown in Formula 1 can be 0.4 mol / L-0.6 mol / L.

[0104] When the molar concentration of the anion shown in Formula 1 is within the above range, the electrolyte can have high ionic conductivity and ion migration rate, thereby improving the power performance of the battery cell; it can also reduce the heat generation of the battery cell, so that the battery cell has lower gas production and high reliability.

[0105] In some embodiments, the molar concentration of the hexafluorophosphate anion can be greater than the molar concentration of the anion shown in Formula 1. One drawback of the anion shown in Formula 1 is that it easily corrodes the positive electrode current collector, especially aluminum foil, which can cause poor contact between the positive electrode active material and the positive electrode current collector. The hexafluorophosphate anion can passivate the positive electrode current collector and reduce the corrosion of the anion shown in Formula 1 on the positive electrode current collector. In addition, the negative electrode film-forming property of the hexafluorophosphate anion is better than that of the anion shown in Formula 1. Therefore, by making the anion include the anion shown in Formula 1 and the hexafluorophosphate anion at the same time, and making the molar concentration of the hexafluorophosphate anion greater than the molar concentration of the anion shown in Formula 1, the respective advantages of the hexafluorophosphate anion and the anion shown in Formula 1 can be fully utilized, so that the battery cell can better have high reliability, good power performance and good cycle performance, and the battery cell can also have a lower production cost.

[0106] In some embodiments, the molar concentration of the hexafluorophosphate anion can be 0.5 mol / L-0.9 mol / L, for example, 0.5 mol / L, 0.55 mol / L, 0.6 mol / L, 0.65 mol / L, 0.7 mol / L, 0.75 mol / L, 0.8 mol / L, 0.85 mol / L, 0.9 mol / L, or a range consisting of any of the above values. Alternatively, the molar concentration of the fluorophosphate anion can be 0.55 mol / L-0.7 mol / L.

[0107] By adjusting the molar concentration of the hexafluorophosphate anion within the above range, the battery cell can better achieve high reliability, good power performance and good cycle performance.

[0108] In some embodiments, the anion may also include other anions, for example, but not limited to tetrafluoroborate anion (BF4 - ), perchlorate anion (ClO4 - ), hexafluoroarsenate anion (AsF6 - ), trifluoromethanesulfonate anion (TFS - ), difluorooxalatoborate anion (DFOB - ), dioxalatoborate anion (BOB - ), difluorophosphate anion (PO2F2 - ), difluorobis(oxaloyl)phosphate anion (DFOP - ) and tetrafluorooxalophosphate anion (TFOP - )

[0109] In certain embodiments, the total molar concentration of anion can be 0.95mol / L-1.65mol / L, for example, can be 0.95mol / L, 1mol / L, 1.05mol / L, 1.1mol / L, 1.15mol / L, 1.2mol / L, 1.25mol / L, 1.3mol / L, 1.35mol / L, 1.4mol / L, 1.45mol / L, 1.5mol / L, 1.55mol / L, 1.6mol / L, 1.65mol / L or the scope of above-mentioned arbitrary numerical value composition. Alternatively, the total molar concentration of anion can be 1.0mol / L-1.3mol / L. The total molar concentration of anion is the molar concentration of the anion shown in Formula 1, the molar concentration of hexafluorophosphate anion and the molar concentration of optional other anions sum.

[0110] In some embodiments, the electrolyte may further include an additive, and the additive may include vinylene carbonate (VC).

[0111] Vinylene carbonate can play a role in assisting film formation, helping to improve the film formation quality of the negative electrode solid electrolyte interface film (hereinafter referred to as SEI film), thereby helping to further improve the performance of the battery cell.

[0112] Optionally, the mass proportion of vinylene carbonate in the electrolyte may be greater than 0 and less than or equal to 3%, and more optionally 0.5%-3%.

[0113] In some embodiments, the viscosity of the electrolyte at 25° C. may be less than or equal to 5 mPa·s, and may be less than or equal to 3 mPa·s. This helps improve the electrolyte wettability of the electrode assembly and enables the battery cell to have good cycle performance.

[0114] The viscosity of the electrolyte can be measured using a viscometer. The shear force applied to the rotor as it rotates continuously at a constant speed in the sample causes the spring to generate torque, which is proportional to the viscosity, thus providing the viscosity value of the sample.

[0115] For example, the viscosity of an electrolyte can be tested as follows: Under ambient humidity conditions of <80%, take a 30mL sample and place it in a water bath at 25°C for at least 30 minutes. Place a spindle (e.g., No. 18) in the sample cup and add the sample to a point approximately 0.3cm from the cup opening. Start the connected viscometer and rotate at 70 RPM for 5 minutes before reading the viscosity value. Ten data points can be collected and averaged during the test. The test instrument can be a Brookfield DV-2TLV viscometer.

[0116] In some embodiments, the conductivity of the electrolyte at 25° C. may be 8 mS / cm-16 mS / cm, optionally 9 mS / cm-12 mS / cm.

[0117] The conductivity of the electrolyte can be measured using a conductivity meter. For example, an appropriate amount of electrolyte can be taken and divided into three equal parts. The conductivity of each sample is then measured at 25°C using a conductivity meter. The average of the test results is then taken as the conductivity of the electrolyte. The measuring instrument can be a DDS-307 conductivity meter.

[0118] Methods for preparing the electrolyte are well known. In some embodiments, the electrolyte solution can be obtained by uniformly mixing an electrolyte salt, an organic solvent, and optional additives. The order in which the materials are added is not particularly limited and can be selected according to actual conditions. Alternatively, the molar concentration of the electrolyte salt can be 1 mol / L to 1.3 mol / L, and can be 1.05 mol / L to 1.15 mol / L.

[0119] Electrolyte salts can dissociate into cations and anions in organic solvents.

[0120] The electrolyte salt includes an electrolyte salt shown in Formula 2 and lithium hexafluorophosphate (LiPF6), R1 and R2 are independently selected from a fluorine atom or a C1-C6 fluoroalkyl group, and M1 is Li. Alternatively, the electrolyte salt shown in Formula 2 may include one or both of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). More optionally, the electrolyte salt shown in Formula 2 may include lithium bis(fluorosulfonyl)imide (LiFSI).

[0121] Optionally, the electrolyte salt may also include one or more of lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium bisoxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobisoxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0122] The components and their contents in the electrolyte can be measured using conventional methods in the art. For example, the content of the electrolyte salt in the electrolyte can be measured using ion chromatography (IC), and the content of the components in the organic solvent can be measured using gas chromatography-mass spectrometry (GC-MS).

[0123] The electrolyte can be sampled and analyzed during the preparation process, or it can be obtained by disassembling and centrifuging the prepared battery after discharge.

[0124] [Positive electrode]

[0125] The positive electrode active material includes a lithium-containing phosphate. The lithium-containing phosphate may include lithium iron phosphate and its modified compound. The modified compound of each positive electrode active material may be a doping modification and / or surface coating modification of the positive electrode active material.

[0126] Optionally, the modified compound of lithium iron phosphate can be obtained by one or more modification methods selected from the group consisting of element doping, conductive carbon coating, conductive metal coating, and conductive polymer coating.

[0127] In some embodiments, the volume distribution particle size Dv50 of the positive electrode active material may be 0.5 μm-2.5 μm, optionally 0.8 μm-1.6 μm.

[0128] By adjusting the volume distribution particle size Dv50 of the positive electrode active material within the above range, side reactions can be reduced, the capacity attenuation rate can be lowered, and the battery cell can have a long cycle life.

[0129] The volume distribution particle size Dv50 of a material is well known in the art and represents the particle size corresponding to the cumulative volume distribution percentage of the material reaching 50%. It can be measured using instruments and methods known in the art. For example, it can be conveniently measured using a laser particle size analyzer, as per GB / T 19077-2016. The testing instrument can be the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd. in the UK.

[0130] In some embodiments, the mass proportion of the positive electrode active material in the positive electrode film layer may be greater than or equal to 93%, and may optionally be greater than or equal to 95%, greater than or equal to 96%, or greater than or equal to 97%.

[0131] In order to achieve a higher energy density in a battery cell, the mass ratio of the positive electrode active material in the positive electrode film layer is usually increased. However, as the mass ratio of the positive electrode active material in the positive electrode film layer increases, the power performance of the battery cell will be affected. The electrolyte provided by the embodiments of the present disclosure can have good fluidity, high ionic conductivity, and high ion migration rate, thereby facilitating a high mass ratio of the positive electrode active material in the positive electrode film layer, and facilitating the battery cell to have both high energy density and good power performance.

[0132] In some embodiments, the positive electrode film layer may further include a positive electrode conductive agent. As an example, the positive electrode conductive agent may include, but is not limited to, one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0133] In some embodiments, the positive electrode film layer may further include a positive electrode binder. As an example, the positive electrode binder may include, but is not limited to, one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic resin.

[0134] In some embodiments, the coating weight of the positive electrode film layer can be 19 mg / cm 2 -33mg / cm 2 , optional 22mg / cm 2 -30mg / cm 2 .

[0135] In some embodiments, the compaction density of the positive electrode film layer can be 2.2 g / cm 3 -2.7g / cm 3 , optional 2.45g / cm 3 -2.65g / cm 3 .

[0136] The compacted density of the positive electrode film refers to the ratio of the surface density of the positive electrode film to its thickness. The surface density of the positive electrode film refers to the ratio of the weight of the positive electrode film after coating, drying, and rolling to the coating area.

[0137] In order to achieve a higher energy density in a battery cell, the coating weight and / or compaction density of the positive electrode sheet is usually increased. However, as the coating weight and / or compaction density of the positive electrode sheet increases, the power performance of the battery cell is affected. The electrolyte provided by the embodiments of the present disclosure can have good fluidity, high ionic conductivity, and high ion migration rate, thereby facilitating the positive electrode sheet to have a high coating weight and / or compaction density, and facilitating the battery cell to have both high energy density and good power performance.

[0138] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include, but is not limited to, one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include, but is not limited to, one or more of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, and polyethylene.

[0139] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, drying it, and rolling it. The positive electrode slurry is typically formed by dispersing the positive electrode active material, positive electrode binder, and positive electrode conductive agent in a solvent and stirring them uniformly. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0140] [Negative electrode]

[0141] The negative electrode active material includes a carbon material. The carbon material may include graphite. Alternatively, the graphite may include one or both of artificial graphite and natural graphite.

[0142] In some embodiments, the negative electrode active material may further include a silicon-based material, thereby further improving the energy density of the battery cell.

[0143] Optionally, the silicon-based material may include one or more of silicon oxide and silicon-carbon materials.

[0144] Optionally, the mass proportion of the silicon-based material in the negative electrode active material may be less than or equal to 25%, for example, less than or equal to 15%, or less than or equal to 12%.

[0145] In some embodiments, the negative electrode film layer may further include a negative electrode conductive agent. As an example, the negative electrode conductive agent may include, but is not limited to, one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0146] In some embodiments, the negative electrode film layer may further include a negative electrode binder. As examples, the negative electrode binder may include, but is not limited to, one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0147] In some embodiments, the negative electrode film layer may further include other additives, such as thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, and the like.

[0148] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As examples of metal foils, copper foil, copper alloy foil, aluminum foil, and aluminum alloy foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one side of the polymer material base layer. As an example, the metal material may include, but is not limited to, one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include, but is not limited to, one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0149] The negative electrode plate does not exclude other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode plate may further include a conductive primer layer sandwiched between the negative electrode current collector and the negative electrode film layer and located on the surface of the negative electrode current collector. The primer layer may be composed of, for example, a conductive agent and a binder. In some embodiments, the negative electrode plate may further include a protective layer covering the surface of the negative electrode film layer.

[0150] The negative electrode sheet can be prepared by dispersing the negative electrode active material, negative electrode binder, negative electrode conductive agent, and optional other additives in a solvent and stirring them uniformly to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector and, after drying and roll pressing, forms the negative electrode sheet. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0151] [Isolation film]

[0152] The electrode assembly also includes a separator, which is placed between the positive electrode and the negative electrode to prevent internal short circuits.

[0153] The present disclosure has no particular limitation on the type of isolation membrane, and any known isolation membrane with a porous structure having good chemical stability and mechanical stability can be selected.

[0154] In some embodiments, the isolation film may include a base film and a coating layer disposed on at least one side of the base film.

[0155] In some embodiments, the material of the base film may include, but is not limited to, one or more of glass fiber, non-woven fabric, and polyolefin. Alternatively, the material of the base film may include polyolefin, such as polyethylene, polypropylene, polyvinylidene fluoride, etc., and more preferably polyethylene.

[0156] In some embodiments, the thickness of the base film may be less than or equal to 12 μm. Alternatively, the thickness of the base film may be less than or equal to 7 μm, more preferably 3 μm-7 μm, or 3 μm-5 μm.

[0157] In some embodiments, the puncture strength of the base film may be greater than or equal to 390 gf, and may be optionally 400 gf-480 gf.

[0158] The higher the base film's puncture strength, the better its puncture resistance, effectively reducing the risk of positive and negative electrode particles, as well as metallic foreign matter, piercing the separator and causing a short circuit between the positive and negative electrodes. Therefore, a base film puncture strength within the above range can improve the pass rate of battery cell short-circuit testing and enhance battery cell reliability.

[0159] In some embodiments, the base film may have a machine direction (MD) heat shrinkage rate of less than 3% at 105° C. for 1 hour, and may optionally be 1%-2.5%.

[0160] In some embodiments, the transverse direction (TD) thermal shrinkage of the base film at 105° C. for 1 hour may be less than 2%, and may be optionally 1%-1.8%.

[0161] The reduced thermal shrinkage of the base film indicates that the base film has good heat resistance, which can also increase the short-circuit test pass rate of the battery cell and improve the reliability of the battery cell.

[0162] The thermal shrinkage of the base film has a well-known meaning in the art and can be measured using methods known in the art. For example, the test can be performed with reference to GB / T 36363-2018.

[0163] In some embodiments, the longitudinal tensile strength of the base film may be greater than or equal to 2700 kgf / cm 2 , optional 2800kgf / cm 2 -3500kgf / cm 2 .

[0164] In some embodiments, the transverse tensile strength of the base film can be greater than or equal to 2500 kgf / cm 2 , optional 2600kgf / cm 2 -3200kgf / cm 2 .

[0165] The increased tensile strength of the base film is conducive to the effective coating of the positive and negative electrode particles, which can effectively reduce the short circuit between the positive and negative electrodes and improve the reliability of the battery cells.

[0166] The tensile strength of the base film has a well-known meaning in the art and can be measured using methods known in the art. For example, it can be tested with reference to GB / T 36363-2018.

[0167] In some embodiments, the average pore size of the base film may be 10 nm-60 nm, optionally 20 nm-40 nm.

[0168] The average pore size of the basement membrane has a well-known meaning in the art and can be measured using methods known in the art, for example, using a capillary flow pore size analyzer, such as a PMIPorometer.

[0169] In some embodiments, the porosity of the base film may be 20%-60%, optionally 30%-50%.

[0170] The porosity of the base film has a well-known meaning in the art and can be measured using methods known in the art. For example, the porosity can be measured with reference to GB / T 36363-2018.

[0171] In some embodiments, the coating includes a particulate inorganic filler. The particulate inorganic filler may include, but is not limited to, boehmite, alumina, silicon oxide SiO x (0<x≤2), one or more of zinc oxide, magnesium oxide, tin dioxide, titanium oxide, calcium oxide, zirconium oxide, yttrium oxide, nickel oxide, hafnium dioxide, cerium oxide, magnesium hydroxide, aluminum hydroxide, silicon carbide, boron carbide, aluminum nitride, silicon nitride, boron nitride, magnesium fluoride, calcium fluoride, barium fluoride, barium sulfate, magnesium aluminum silicate, lithium magnesium silicate, sodium magnesium silicate, bentonite, hectorite, zirconium titanate, and barium titanate.

[0172] In some embodiments, the coating further comprises a non-granular binder. The present disclosure does not particularly limit the type of the non-granular binder, and any known material with good adhesive properties may be selected, such as a linear binder, an emulsion binder, and a mixed linear and emulsion binder.

[0173] Optionally, the non-granular binder may have at least one polar group selected from the group consisting of a hydroxyl group (-OH), a carboxyl group (-COOH), an ester group (-COO-), a cyano group (-CN), an imide group (-CO-NH-CO-), a maleic anhydride group (-COOOC-), a sulfonate group (-SO3H) and a pyrrolidone group (-NCO-).

[0174] Alternatively, the non-particulate binder may include a homopolymer or copolymer selected from the group consisting of allyl polyether sulfate, acrylic acid, methacrylic acid, acrylamide, methyl acrylate, butyl acrylate, ethyl acrylate, glycidyl methacrylate, vinyl alcohol, acrylonitrile, hydroxyethyl acrylate, styrene, acetoxyethyl methacrylate, vinyltrimethoxysilane, lithium acrylate, sodium acrylate, lithium methacrylate, isobutylene, and maleic anhydride.

[0175] Optionally, the non-granular binder may include at least one of: polyacrylic acid, polymethyl methacrylate, polyacrylonitrile, polyvinyl pyrrolidone, polyvinyl acetate, polyethylene-co-vinyl acetate, polystyrene-co-methyl methacrylate, polystyrene-co-butyl acrylate, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose, acrylonitrile-styrene-butadiene copolymer, polyimide.

[0176] Optionally, the mass proportion of the non-granular binder in the coating layer may be less than or equal to 10%, based on the total mass of the coating layer.

[0177] The preparation method of battery cells is well known. In some embodiments, a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte can be assembled to form a battery cell. As an example, the positive electrode sheet, separator, and negative electrode sheet can be made into an electrode assembly, which is then placed in an outer packaging, dried, and then injected with electrolyte. After standing and forming, a battery cell is obtained.

[0178] Example

[0179] The following examples describe the present disclosure in more detail. These examples are intended to be illustrative only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing, and all instruments used in the examples are commercially available.

[0180] Example 1-1

[0181] Preparation of positive electrode

[0182] The positive electrode active material lithium iron phosphate LiFePO4, the binder polyvinylidene fluoride, and the conductive agent Super P are mixed in a mass ratio of 97:2:1, and an appropriate amount of solvent N-methylpyrrolidone (NMP) is added and stirred evenly to obtain a positive electrode slurry. The positive electrode slurry is coated on both surfaces of the positive electrode current collector aluminum foil, dried, and cold pressed to obtain a positive electrode sheet. The coating weight of the positive electrode film is 22.7 mg / cm 2 , compacted density is 2.5g / cm 3 .

[0183] Preparation of negative electrode sheet

[0184] The negative electrode active material artificial graphite, conductive agent Super P, binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose were thoroughly stirred and mixed in an appropriate amount of deionized water as a solvent in a mass ratio of 96.2:0.6:1.3:1.9 to obtain a negative electrode slurry. The negative electrode slurry was coated on both surfaces of the negative electrode current collector copper foil, dried, and cold pressed to obtain a negative electrode sheet. The coating weight of the negative electrode film was 10.2 mg / cm 2 , compacted density is 1.45g / cm 3 .

[0185] Preparation of isolation membrane

[0186] The base membrane is a PE porous membrane with a thickness of 7μm. Aluminum oxide and the binder polyacrylic acid are mixed in a mass ratio of 94:6 in an appropriate amount of deionized water to obtain a coating slurry. The prepared coating slurry is applied to both surfaces of the PE porous membrane using a coating machine, and then dried and cut to obtain a separator. The coating thickness on one side of the PE porous membrane is 1.5μm, the total coating thickness is 3μm, and the total thickness of the separator is 10μm.

[0187] Preparation of electrolyte

[0188] Dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and ethylene carbonate (EC) are mixed in a mass ratio of 5:60:35 to obtain an organic solvent. LiFSI and LiPF6 are then dissolved in the organic solvent. Vinylene carbonate (VC) is then added and stirred to obtain an electrolyte. The concentration of LiFSI is 0.5 mol / L, the concentration of LiPF6 is 0.6 mol / L, and the mass proportion of VC in the electrolyte is 1.5%, based on the total mass of the electrolyte.

[0189] Preparation of battery cells

[0190] The positive electrode sheet, separator, and negative electrode sheet are stacked and wound in sequence to form an electrode assembly. The electrode assembly is then placed in a casing, dried, and then filled with electrolyte. After packaging, resting, and forming, a hard-shell rectangular battery cell is obtained. The battery cell is 574mm long, 120mm wide, and 21.5mm thick.

[0191] Example 1-2 to Example 1-7

[0192] Except for the different electrolyte composition, the preparation of the battery cell is the same as that of Example 1-1. The specific parameters are shown in Table 1.

[0193] Example 1-8 to Example 1-9

[0194] Except for the different concentrations of LiFSI and LiPF6 in the electrolyte, the preparation of the battery cell is the same as that of Example 1-1. The specific parameters are detailed in Table 1.

[0195] Comparative Example 1-1

[0196] Except for the different electrolyte composition, the preparation of the battery cell is the same as that of Example 1-1. The specific parameters are shown in Table 1.

[0197] Comparative Example 1-2

[0198] Except for the different electrolyte composition, the preparation of the battery cell is the same as that of Example 1-1. The specific parameters are shown in Table 1.

[0199] Comparative Examples 1-3

[0200] Except for the different electrolyte composition, the preparation of the battery cell is the same as that of Example 1-1. The specific parameters are shown in Table 1.

[0201] Performance Testing

[0202] (1) Power performance test of battery cells

[0203] At 25°C, charge the battery cell at a constant current and constant voltage of 1C to an upper cutoff voltage of 3.65V, then charge at a constant voltage to a current of 0.05C. After a 5-minute rest, discharge the battery cell at 1C for 30 minutes, adjusting the SOC to 50%, and record the voltage U1. Then discharge the battery cell at a constant current of 3C for 30 seconds, and record the voltage U2. Battery cell power (W) = lower cutoff voltage × (U1 - lower cutoff voltage) / (U1 - U2) / 3C. The lower cutoff voltage is 2.5V.

[0204] (2) Battery cell nail penetration test

[0205] At 25°C, the battery cell was charged at a constant current and constant voltage of 0.33C to an upper cut-off voltage of 3.65V, and then charged at a constant voltage to a current of 0.05C, at which point the battery cell was fully charged. The fully charged battery cell was fixed on a fixture, the positive and negative poles of the battery cell were connected to voltage detection wires, a temperature sensing wire was arranged inside the battery cell, and a high-temperature resistant steel needle with a diameter of 5mm was used to vertically penetrate the large surface of the battery cell at a speed of 25mm / s. The battery cell was left to stand for 1 hour and the voltage change of the battery cell over time was recorded.

[0206] The battery cell fails the nail penetration test if it emits smoke or catches fire after nail penetration, or if the battery cell voltage drops by more than 0.5V after standing for one hour. Ten battery cell samples were collected, and the pass rate of the nail penetration test was calculated.

[0207] (3) Cycling performance test of battery cells

[0208] At 25°C, charge the battery at a constant current rate of 0.5C to a charge cut-off voltage of 3.65V. Then, charge at a constant voltage rate to a current of ≤0.05C, let it rest for 5 minutes, and then discharge at a constant current rate of 0.5C to a discharge cut-off voltage of 2.5V, let it rest for 5 minutes. This constitutes one charge-discharge cycle. Repeat this method for cyclic charge and discharge testing until the battery capacity decays to 80%. The number of cycles at this point is the battery's cycle life at 25°C.

[0209] (4) Energy density test of battery cells

[0210] At 25°C, the battery cell was charged at a constant current of 0.33C to 3.65V, and then charged at a constant voltage to a current of 0.05C. After standing for 5 minutes, the battery cell was discharged at a constant current of 0.33C to 2.5V, and the discharge energy Q was obtained.

[0211] The energy density of a battery cell (Wh / L) = discharge energy Q / volume V of the battery cell.

[0212] Table 1

[0213] It can be seen from the above test results that the battery cells provided by the embodiments of the present disclosure can have high reliability while having good power performance.

[0214] The electrolytes of Comparative Examples 1-1 to 1-3 have a high mass proportion of dimethyl carbonate, a serious gas production problem, and poor reliability of the battery cells.

[0215] The electrolyte salt of the electrolyte of Comparative Example 1-2 uses only LiFSI. LiFSI has the problem of violently reacting with the fully charged negative electrode to release heat and NO2 and SO2 gases, thereby causing serious gas production problems in the battery cells and poor reliability.

[0216] Table 2

[0217] From the above test results, it can be seen that by further adjusting the molar concentration of LiPF6 to be greater than the molar concentration of LiFSI, the battery monomer can better combine high reliability, good power performance and good cycle performance; by further adjusting the composition of the organic solvent, the battery monomer can better combine high reliability, good power performance and good cycle performance.

[0218] Example 2-1

[0219] The preparation of the battery cell was the same as that of Example 1-1 except that the size of the battery cell was different.

[0220] The battery cell is 500mm long, 120mm wide and 21.5mm thick.

[0221] Example 2-2

[0222] The preparation of the battery cell was the same as that of Example 1-1 except that the size of the battery cell was different.

[0223] The battery cell is 400mm long, 120mm wide and 21.5mm thick.

[0224] Example 2-3

[0225] The preparation of the battery cell was the same as that of Example 1-1 except that the size of the battery cell was different.

[0226] The battery cell is 600mm long, 120mm wide and 21.5mm thick.

[0227] Comparative Example 2-1

[0228] The preparation of the battery cell was the same as that of Example 1-1 except that the size of the battery cell was different.

[0229] The battery cell is 700mm long, 120mm wide and 21.5mm thick.

[0230] Comparative Example 2-2

[0231] The preparation of the battery cell was the same as that of Example 1-1 except that the size of the battery cell was different.

[0232] The battery cell is 300mm long, 120mm wide and 21.5mm thick.

[0233] Table 3

[0234] It can be seen from the above test results that the electrolyte provided by the embodiments of the present disclosure is more conducive to battery cells with sizes within a specific range having good power performance while having a higher energy density.

[0235] It should be noted that the present disclosure is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present disclosure, embodiments having substantially the same structure as the technical concept and exerting the same effects are all included in the technical scope of the present disclosure. In addition, within the scope of the present disclosure, various modifications that can be imagined by those skilled in the art to the embodiments, and other methods constructed by combining some of the constituent elements of the embodiments are also included in the scope of the present disclosure.

Claims

1. A battery cell, wherein the length of the battery cell is 400 mm to 650 mm, and the battery cell comprises a positive electrode sheet, a negative electrode sheet, and an electrolyte. The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer located on at least one side of the positive electrode current collector, the positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes a lithium-containing phosphate; The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector, the negative electrode film layer includes a negative electrode active material, and the negative electrode active material includes a carbon material; The electrolyte includes cations, anions, and an organic solvent, wherein the cations include lithium ions, the anions include anions represented by Formula 1 and hexafluorophosphate anions, R1 and R2 are independently selected from fluorine atoms or C1-C6 fluoroalkyl groups, The organic solvent includes dimethyl carbonate, and the mass proportion of the dimethyl carbonate in the organic solvent is less than or equal to 5%.

2. The battery cell according to claim 1, wherein: The length of the battery cell is 500mm-650mm.

3. The battery cell according to any one of claims 1 to 2, wherein: The aspect ratio of the battery cell is greater than or equal to 4.

4. The battery cell according to claim 3, wherein: The aspect ratio of the battery cell is 4-5.

5.

5. The battery cell according to any one of claims 1 to 4, wherein: The mass proportion of the dimethyl carbonate in the organic solvent is 3%-5%.

6. The battery cell according to any one of claims 1 to 5, wherein: The molar concentration of the anion represented by Formula 1 is 0.3 mol / L-0.8 mol / L.

7. The battery cell according to claim 6, wherein: The molar concentration of the anion represented by Formula 1 is 0.4 mol / L-0.6 mol / L.

8. The battery cell according to any one of claims 1 to 7, wherein: The molar concentration of the hexafluorophosphate anion is greater than the molar concentration of the anion represented by Formula 1.

9. The battery cell according to any one of claims 1 to 8, wherein: The molar concentration of the hexafluorophosphate anion is 0.5 mol / L-0.9 mol / L.

10. The battery cell according to claim 9, wherein: The molar concentration of the hexafluorophosphate anion is 0.55 mol / L-0.7 mol / L.

11. The battery cell according to any one of claims 1 to 10, wherein: The total molar concentration of the anions is 0.95 mol / L-1.65 mol / L.

12. The battery cell according to claim 11, wherein: The total molar concentration of the anions is 1.0 mol / L-1.3 mol / L.

13. The battery cell according to any one of claims 1 to 12, wherein: The organic solvent further comprises ethyl methyl carbonate, and the mass proportion of the ethyl methyl carbonate in the organic solvent is 56%-80%.

14. The battery cell according to claim 13, wherein: The mass proportion of the ethyl methyl carbonate in the organic solvent is 60%-75%.

15. The battery cell according to any one of claims 1 to 14, wherein: The organic solvent further comprises ethylene carbonate, and the mass proportion of the ethylene carbonate in the organic solvent is 15%-40%.

16. The battery cell according to claim 15, wherein: The mass proportion of the ethylene carbonate in the organic solvent is 20%-36%.

17. The battery cell according to any one of claims 1 to 16, wherein: The electrolyte further includes an additive, and the additive includes vinylene carbonate.

18. The battery cell according to claim 17, wherein: The mass proportion of the vinylene carbonate in the electrolyte is less than or equal to 3%.

19. The battery cell according to any one of claims 1 to 18, wherein: The battery cell satisfies at least one of the following conditions (1) to (7): (1) The viscosity of the electrolyte at 25°C is less than or equal to 5 mPa·s; (2) The conductivity of the electrolyte at 25° C. is 8 mS / cm to 16 mS / cm; (3) The coating weight of the positive electrode film is 19 mg / cm 2 -33mg / cm 2 ; (4) The compaction density of the positive electrode film layer is 2.2 g / cm 3 -2.7g / cm 3 ; (5) The positive electrode active material includes lithium iron phosphate and its modified compound; (6) The mass proportion of the positive electrode active material in the positive electrode film layer is greater than or equal to 93%; (7) The negative electrode active material includes graphite. Optionally, the graphite includes one or both of artificial graphite and natural graphite.

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

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

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