Battery cell, battery device and electric device

Abstract

A battery cell, a battery device and an electric device. The battery cell comprises a positive electrode sheet, a negative electrode sheet and an electrolyte, 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 comprises a lithium-containing phosphate, and the single-sided coating weight of the positive electrode film layer is 150 mg / 1540.25 mm2 to 370 mg / 1540.25 mm2; the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer arranged on at least one side of the negative electrode current collector, the negative electrode film layer comprises a carbon-based material and a silicon-based material, the mass content of silicon in the silicon-based material of the negative electrode film layer is 0.3% to 10%, and the single-sided coating weight of the negative electrode film layer is 70 mg / 1540.25 mm2 to 175 mg / 1540.25 mm2; and the electrolyte comprises an acyclic carboxylic ester solvent, the mass content of which in the electrolyte is 5% to 35%. The rapid charging capability and cycling performance of the battery cell can be further improved.

Description

Battery cells, battery packs and electrical devices Technical Field

[0001] This application relates to a battery cell, a battery device, and an electrical device. Background Technology

[0002] Battery cells possess characteristics such as high capacity and long lifespan, making them widely used in electronic devices such as mobile phones, laptops, electric vehicles, electric cars, electric airplanes, electric ships, electric toy cars, electric toy ships, electric toy airplanes, and power tools. Due to significant advancements in battery technology, higher performance requirements have been placed on batteries. However, the fast-charging capability and cycle performance of battery cells still need further improvement. Summary of the Invention

[0003] This application provides a battery cell, a battery device, and an electrical device. The fast charging capability and cycle performance of the battery cell in this application can be further improved.

[0004] In a first aspect, this application proposes a battery cell, comprising a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive current collector and a positive electrode film disposed on at least one side of the positive current collector. The positive electrode film contains lithium phosphate, and the single-sided coating weight of the positive electrode film is 150 mg / 1540.25 mm. 2 Up to 370mg / 1540.25mm 2 The negative electrode includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The negative electrode film layer includes a negative electrode active material, which includes carbon-based materials and silicon-based materials. The silicon content of the silicon element in the negative electrode film layer is 0.3% to 10% by mass. The single-sided coating weight of the negative electrode film layer is 70 mg / 1540.25 mm. 2 Up to 175mg / 1540.25mm 2 The electrolyte includes chain-like carboxylic acid ester solvents, which constitute 5% to 35% of the electrolyte by mass.

[0005] Therefore, the negative electrode sheet of the present application includes silicon-based material, and the mass content of silicon element and the coating weight of positive and negative electrode films are matched to make the battery cell have a relatively high energy density and facilitate the rapid migration of active ions in the positive and negative electrode films. The electrolyte contains an appropriate range of chain carboxylic acid ester solvents, which can reduce side reactions on the negative electrode side while improving the lithium ion migration rate, alleviate the interfacial side reactions between silicon-based material and electrolyte, reduce high-temperature gas generation, and thus comprehensively improve the fast charging performance and cycle performance of the battery cell.

[0006] In some embodiments, the single-sided coating weight of the positive electrode film is 200 mg / 1540.25 mm. 2 Up to 300mg / 1540.25mm 2 When the single-sided coating weight of the positive electrode film is within the above range, the heat generation per unit area of ​​the positive electrode sheet will not be too large, which is beneficial to reduce the polarization phenomenon under high-rate charging, and can also improve the energy density and fast charging performance of the battery cell.

[0007] In some embodiments, the single-sided coating weight of the negative electrode film is 95 mg / 1540.25 mm. 2 Up to 142mg / 1540.25mm 2 When the single-sided coating weight of the negative electrode film meets the above range, its combination with an appropriate mass content of silicon is beneficial to improving the energy density of the battery cell. Moreover, the migration rate of active ions in the negative electrode film is faster, which helps to reduce polarization under high-rate charging and improves the fast charging capability of the battery cell.

[0008] In some embodiments, the compaction density of the positive electrode film layer is 2.50 g / cm³ when the battery cell is 100% charged. 3 Up to 2.80 g / cm 3 The compaction density of the positive electrode film is within a reasonable range, and the battery cell has both high energy density and fast charging performance.

[0009] In some embodiments, the compaction density of the negative electrode film layer is 1.5 g / cm³ when the battery cell is 100% charged. 3 Up to 1.7 g / cm 3 With the compaction density of the negative electrode film within a reasonable range, the battery cell possesses both high energy density and fast charging performance.

[0010] In some embodiments, the specific charge capacity of the positive electrode active material is 150 mAh / g to 170 mAh / g; when the specific charge capacity of the positive electrode active material is within the above range, the energy density of the battery cell is relatively high.

[0011] In some embodiments, the specific charge capacity of the negative electrode active material is between 350 mAh / g and 540 mAh / g. When the specific charge capacity of the negative electrode active material is within the above range, the energy density of the battery cell is relatively high.

[0012] In some embodiments, the silicon content in the negative electrode film layer of the silicon-based material is 3% to 6% by mass. When the silicon content is within the above range, the capacity of the negative electrode active material can be increased, which is beneficial to improving the energy density of the battery cell; moreover, during the charge and discharge process, the volume expansion of silicon will not be too large, which is beneficial to maintaining the stability of the solid electrolyte interphase (SEI) film and improving the cycle performance of the battery cell.

[0013] In some embodiments, the silicon-based material includes one or more of silicon carbide and silicon oxide.

[0014] In some embodiments, the negative electrode film includes a first region and a second region. The first region is disposed on the surface of the negative electrode current collector, and its thickness is one-third of the thickness of the negative electrode film. The second region is connected to the side of the first region opposite to the negative electrode current collector, and its thickness is one-third of the thickness of the negative electrode film. The average particle size of the carbon-based material in the first region is greater than or equal to the average particle size of the carbon-based material in the second region. The difference in particle size between the first and second regions can improve the fast-charging performance of the battery cell.

[0015] In some embodiments, the average particle size of the carbon-based material in the first region is 10 μm to 20 μm. When the average particle size of the carbon-based material in the first region is within the above range, on the one hand, it can shorten the solid-phase transport path of lithium ions and improve the fast charging performance; on the other hand, the material is less prone to agglomeration during the preparation process, which can improve the stability of the material.

[0016] In some embodiments, the average particle size of the carbon-based material in the second region is between 5 μm and 12 μm. When the average particle size of the carbon-based material in the second region is within this range, it is beneficial to improve the fast-charging capability of the battery cell and enhance the stability of the material.

[0017] In some embodiments, the carbon-based material in the first region includes at least one of artificial graphite and natural graphite, and the carbon-based material in the second region includes artificial graphite. This material configuration facilitates the creation of a porosity difference between the first and second regions, thereby improving the fast-charging capability of the battery cell.

[0018] In some embodiments, at least one of the first and second regions comprises a silicon-based material. Silicon-based materials are advantageous for increasing the energy density of a single battery cell.

[0019] In some embodiments, the negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer. The first negative electrode film layer is disposed on the surface of the negative electrode current collector; the second negative electrode film layer is connected to the side of the first negative electrode film layer opposite to the negative electrode current collector. This dual-layer film layer is beneficial for improving the fast charging capability and energy density of the battery cell.

[0020] In some embodiments, the negative electrode film layer includes a negative electrode conductive agent, which includes one or more of conductive carbon and carbon nanotubes. The negative electrode conductive agent can improve the conductivity of the negative electrode film layer and enhance fast charging capability.

[0021] In some embodiments, the mass content of conductive carbon in the negative electrode film is 0.4% to 0.7%; when the mass content of conductive carbon is within the above range, the conductivity of the negative electrode film can be improved, thereby enhancing the fast charging capability.

[0022] In some embodiments, the mass content of carbon nanotubes in the negative electrode film is 0.1% to 1%. When the mass content of carbon nanotubes is within the above range, the conductivity of the negative electrode film can be improved, thereby enhancing the fast charging capability.

[0023] In some embodiments, the electrolyte has a conductivity of 10.5 mS / cm to 13.5 mS / cm at room temperature. When the conductivity of the electrolyte is within the above range, the migration rate of lithium ions in the electrolyte is relatively high, which can further reduce the internal resistance of the battery cell and improve the fast charging performance of the battery cell.

[0024] In some embodiments, the viscosity of the electrolyte at room temperature is between 1.5 mPa·s and 5.5 mPa·s. When the viscosity of the electrolyte is within the above range, the migration rate of lithium ions in the electrolyte is relatively high, which can further reduce the internal resistance of the battery cell and improve the fast charging performance of the battery cell.

[0025] In some embodiments, the electrolyte density at room temperature is between 1.05 g / mL and 1.35 g / mL. When the electrolyte density is within this range, the lithium ion migration rate in the electrolyte is higher, which can further reduce the internal resistance of the battery cell and improve the fast charging performance of the battery cell.

[0026] In some embodiments, the mass content of the chain-like carboxylic acid ester solvent in the electrolyte is 8% to 20%. When the mass content of the chain-like carboxylic acid ester solvent is within the above range, it can improve the fast charging capability and cycle performance of the battery cell.

[0027] In some embodiments, the chain carboxylic acid ester solvent includes compounds represented by Formula I.

[0028] In formula I,

[0029] R1 includes a hydrogen atom, a C1 to C5 alkyl group, or a C1 to C5 haloalkyl group.

[0030] R2 includes C1 to C5 alkyl or C1 to C5 haloalkyl.

[0031] The aforementioned chain-like carboxylic acid ester solvents have high conductivity, which is beneficial for improving the fast charging capability of battery cells.

[0032] In some embodiments, the chain carboxylic acid ester solvent includes one or more compounds of formulas I-1 to I-8.

[0033] In some embodiments, the organic solvent includes carbonate solvents, wherein the carbonate solvent content in the electrolyte is 65% to 75% by mass.

[0034] When the mass content of carbonate solvents and chain carboxylic acid ester solvents meets the above conditions, the stability of the electrolyte can be improved and its high-temperature gas production can be reduced.

[0035] In some embodiments, the carbonate solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0036] In some implementations, the lithium-containing phosphate includes lithium iron phosphate, which has excellent cycle stability and can improve the cycle performance of individual battery cells.

[0037] In some embodiments, the positive electrode film has a length dimension of 265 mm to 655 mm. When the size of the positive electrode film is within this range, the electron transport path is not too long, the internal resistance is relatively small, which is beneficial to improving the fast charging capability and energy density of the battery cell.

[0038] Secondly, embodiments of this application also propose a battery device, including a battery cell of any embodiment of the first aspect of this application.

[0039] Thirdly, embodiments of this application also propose an electrical device, which includes a battery device as described in any of the embodiments of the second or third aspects of this application. Attached Figure Description

[0040] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0041] Figure 1 is a schematic diagram of the structure of an electrical device provided in some embodiments of this application.

[0042] Figure 2 is a schematic diagram of the structure of a battery pack provided in some embodiments of this application;

[0043] Figure 3 is a schematic diagram of the structure of a battery module provided in some embodiments of this application;

[0044] Figure 4 is a schematic diagram of the structure of a battery cell provided in some embodiments of this application;

[0045] Figure 5 is a schematic diagram of the structure of the electrode assembly of a battery cell provided in some embodiments of this application;

[0046] Figure 6 is a schematic diagram of the structure of the first electrode of a battery cell provided in some embodiments of this application;

[0047] Figure 7 is a schematic diagram of the structure of the first electrode of a battery cell provided in some other embodiments of this application;

[0048] Figure 8 is a schematic diagram of the structure of the first electrode of a battery cell provided in some embodiments of this application;

[0049] Figure 9 is a schematic diagram of the structure of the first electrode of a battery cell provided in some embodiments of this application;

[0050] Figure 10 is a schematic diagram of the structure of the first electrode of a battery cell provided in some embodiments of this application;

[0051] Figure 11 is a schematic diagram of the structure of the first electrode of a battery cell provided in some embodiments of this application;

[0052] Figure 12 is a schematic diagram of the structure of the first electrode of a battery cell provided in some embodiments of this application;

[0053] Figure 13 is a schematic diagram of the structure of the second electrode of a battery cell provided in some embodiments of this application;

[0054] Figure 14 is a schematic diagram of the structure of the second electrode of a battery cell provided in some other embodiments of this application;

[0055] Figure 15 is a schematic diagram of the structure of a battery cell provided in some other embodiments of this application;

[0056] Figure 16 is a schematic diagram of the structure of a battery cell provided in some other embodiments of this application;

[0057] Figure 17 is a schematic diagram of the structure of the negative electrode sheet of a battery cell provided in some embodiments of this application;

[0058] Figure 18 is a schematic diagram of the structure of the electrode assembly of a battery cell provided in some embodiments of this application.

[0059] The accompanying drawings may not be drawn to scale.

[0060] The reference numerals in the attached drawings are explained as follows: X, thickness direction; Y, width direction; Z, length direction; 1, electrical device; 2, battery pack; 3, controller; 4, motor; 5, housing; 5a, first housing section; 5b, second housing section; 5c, accommodating space; 6, battery module; 7, battery cell; 10, electrode assembly; 11, first electrode; 111, first tab; 1111, first end; 112, first coating section; 12, second electrode; 121, second tab; 1211, second end; 122, second coating section; 13, separator; 14, negative electrode; 141, negative electrode film; 142, negative electrode current collector; 1411, first negative electrode film; 1412, second negative electrode film; 141a, first region; 141b, second region; 141c, third region; 20, outer casing assembly; 21. Housing; 22. End cap; 31. First electrode terminal; 32. Second electrode terminal. Detailed Implementation

[0061] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the battery cell, battery device, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0062] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a specific parameter, it is also expected that ranges of 60 to 110 and 80 to 120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise stated, the numerical range "a to b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0 to 5" means that all real numbers between "0 and 5" have been listed in this article; "0 to 5" is just a shortened representation of these numerical combinations. In addition, when a parameter is stated as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0063] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0064] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0065] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it 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 it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0066] In this application, "multiple" means two or more (including two).

[0067] In this embodiment of the application, the battery cell can be a secondary battery, which refers to a battery cell that can be recharged to activate the active materials and continue to be used after the battery cell has been discharged.

[0068] The battery cell can be a lithium-ion battery, a sodium-lithium-ion battery, etc., but this application does not limit this.

[0069] With the rapid development of the battery industry, the performance requirements for individual battery cells are gradually increasing. For example, with the increasing demand for fast charging performance, this can be achieved by increasing the conductivity of the electrolyte in related technologies. However, increasing the conductivity may lead to electrolyte decomposition at high temperatures, which increases the amount of gas generated by the battery cell at high temperatures and may deteriorate the cycle performance of the battery cell. This makes it impossible to improve both the fast charging performance and cycle performance of the battery cell at the same time, especially at high energy density.

[0070] In view of the above problems, the embodiments of this application improve the fast charging performance and cycle performance of the battery cell by synergistically regulating the positive electrode, negative electrode and electrolyte; specifically, the negative electrode of the battery cell includes a negative electrode active material containing silicon, which, with appropriate coating weight, makes the battery cell have a relatively high energy density.

[0071] The negative electrode sheet includes silicon, which is beneficial for thin coating and facilitates the rapid migration of active ions such as lithium ions on the negative electrode sheet. When combined with a positive electrode film layer of appropriate coating weight, it can enhance the rapid migration of active ions on the positive electrode sheet, thereby increasing the migration rate of active ions in both the positive and negative electrode films. Furthermore, by adding an appropriate amount of chain carboxylic acid ester solvent, it can enhance the migration rate of lithium ions in the electrolyte, thereby increasing the liquid phase transport rate of lithium ions and thus improving the fast charging capability of the battery cell.

[0072] However, silicon-based materials containing silicon are more prone to side reactions with the electrolyte, leading to increased gas production, especially at high temperatures. In contrast, the chain carboxylic acid ester solvent in this embodiment has a mass content of less than or equal to 35%, which enables active ions, such as lithium ions, to migrate rapidly, thereby mitigating the side reactions between the silicon-based materials and the electrolyte, reducing gas production, and thus comprehensively improving the cycle performance and fast charging capability of the battery cell at high energy density, and also improving the cycle performance under fast charging conditions.

[0073] The battery cell described in this application is applicable to various battery devices and electrical appliances that use battery cells.

[0074] For example, the electrical device can be a mobile phone, portable device, laptop computer, electric vehicle, electric toy, power tool, vehicle, ship, and spacecraft, etc. Alternatively, for example, the electrical device can be a spacecraft, including airplanes, rockets, space shuttles, and spacecraft, etc.

[0075] Figure 1 is a schematic diagram of an example electrical device 1. This electrical device 1 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of this electrical device 1, a battery pack or battery module can be used.

[0076] The electrical device 1 has a battery pack installed inside. The battery pack can be located at the bottom, head, or tail of the electrical device 1. The battery pack can be used to supply power to the electrical device 1. For example, the battery pack can be used as the operating power source for the electrical device 1, and it can also be used as the driving power source for the electrical device 1, replacing or partially replacing fuel oil or natural gas to provide driving power for the electrical device 1. The battery pack shown in Figure 1 is a battery pack 2.

[0077] Electrical device 1 may also include controller 3 and motor 4. Controller 3 is used to control the battery device to supply power to motor 4, for example, to meet the power needs of electrical device 1 during startup, navigation and driving.

[0078] A battery apparatus may include one or more battery cell assemblies for providing voltage and capacity. A battery cell assembly may include multiple battery cells connected in series, parallel, or mixed connections via busbars.

[0079] In some implementations, a battery cell assembly is typically formed by arranging multiple battery cells.

[0080] As an example, a battery cell assembly can be a battery module, which is formed by arranging and fixing multiple battery cells together to form a single module. As another example, a battery module can be formed by bundling multiple battery cells together with cable ties.

[0081] As shown in Figure 2, in some embodiments, the battery device can be a battery pack 2, which includes a housing 5 and one or more battery cell assemblies housed in the housing 5.

[0082] As an example, the battery cell assembly can also be housed in the housing 5 by directly fixing multiple battery cells to the housing 5.

[0083] As an example, the housing 5 includes a first housing portion 5a and a second housing portion 5b. The housing 5 has an accommodating space 5c. The first housing portion 5a and the second housing portion 5b are fastened together to form a closed space inside the housing 5 to accommodate the battery cell assembly. Here, "closed" refers to covering or closing, which can be either sealed or unsealed. The first housing portion 5a can be a top cover or a bottom plate.

[0084] As an example, the housing 5 may include a top cover, a frame, and a bottom plate. The top cover and the bottom plate are respectively connected to the frame, so that the interior of the housing 5 forms an enclosed space to accommodate the battery cell assembly.

[0085] In some embodiments, the housing 5 can be part of the vehicle's chassis structure. For example, a portion of the housing 5 can be at least a part of the vehicle's floor, or a portion of the housing 5 can be at least a part of the vehicle's crossbeams and longitudinal beams.

[0086] As an example, the battery cell assembly can be a battery module 6, which can be housed in the housing 5 by fixing the battery module 6 in the housing 5.

[0087] As shown in Figure 3, the battery module 6 includes multiple battery cells 7.

[0088] In some embodiments, during the charging process of the battery device or any of the battery cells 7 constituting the battery device from 20% SOC to 80% SOC, the ambient temperature of the external environment in which the battery device is located is room temperature, for example, 25°C.

[0089] For example, the charging step of the battery device or any of the battery cells 7 constituting the battery device from 20% SOC to 80% SOC can be performed as follows:

[0090] Charge from 20% SOC to 25% SOC at a constant current of 8.00C;

[0091] Charge from 25% SOC to 30% SOC at a constant current of 8.00C;

[0092] Charge from 30% SOC to 35% SOC at a constant current of 7.50C;

[0093] Charge from 35% SOC to 40% SOC at a constant current of 6.87C;

[0094] Charge from 40% SOC to 45% SOC at a constant current of 6.38C;

[0095] Charge from 45% SOC to 50% SOC at a constant current of 5.95C;

[0096] Charge from 50% SOC to 55% SOC at a constant current of 5.53C;

[0097] Charge from 55% SOC to 60% SOC at a constant current of 5.14C;

[0098] Charge from 60% SOC to 65% SOC at a constant current of 4.76C;

[0099] Charge from 65% SOC to 70% SOC at a constant current of 4.36C;

[0100] Charge from 70% SOC to 75% SOC at a constant current of 3.94C;

[0101] Charge from 75% SOC to 80% SOC at a constant current of 3.57C.

[0102] In some embodiments, the charging time for the battery device or any of the battery cells 7 constituting the battery device from 20% state of charge to 80% state of charge is 5 min to 30 min, optionally 5 min to 20 min, and the ambient temperature of the battery device at 20% state of charge is room temperature, for example 25°C. For example, the charging time of the battery device from 20% state of charge to 80% state of charge is 30 min, 29 min, 28 min, 27 min, 26 min, 25 min, 24 min, 23 min, 22 min, 21 min, 20 min, 19 min, 18 min, 17 min, 16 min, 15 min, 14.5 min, 14 min, 13.5 min, 13 min, 12.5 min, 12 min, 11.5 min, 11 min, 10.5 min, 10 min, 9.5 min, 9 min, 8.5 min, 8 min, 7.5 min, 7 min, 6.5 min, 6 min, 5 min, or any range of two of the above values.

[0103] As shown in Figures 4 and 5, in some embodiments, the battery cell 7 includes an electrode assembly 10 and a housing assembly 20.

[0104] The housing assembly 20 has a receiving cavity for accommodating the electrode assembly 10 and the electrolyte.

[0105] In some embodiments, housing assembly 20 includes a housing and a terminal assembly disposed on the housing.

[0106] For example, the terminal assembly includes a first electrode terminal 31 and a second electrode terminal 32, one of which is a positive terminal and the other is a negative terminal.

[0107] The outer casing can be made of steel, aluminum, plastic (such as polypropylene), composite metal (such as copper-aluminum composite), or aluminum-plastic film, etc. In some embodiments, the outer casing can be a sealed structure or a non-sealed structure. As an example, when the outer casing is a non-sealed structure, it serves to protect the electrode assembly 10, and a sealing bag is included between the outer casing and the electrode assembly 10 to encapsulate the electrode assembly 10 and the electrolyte. Specifically, the sealing bag can be a bag-shaped insulating component or an aluminum-plastic film. When the outer casing is a sealed structure, it is used to encapsulate the electrode assembly 10 and electrolyte components.

[0108] As an example, the battery cell 7 can be a cylindrical battery cell, a prismatic battery cell, a pouch battery cell, or a battery cell of other shapes. Prismatic battery cells include prismatic battery cells, blade-shaped battery cells, and multi-prismatic batteries, such as hexagonal prismatic batteries. This application does not have any particular limitations.

[0109] In some embodiments, the housing includes an end cap 22 and a housing 21, the housing 21 having an opening, and the end cap 22 covering the opening. The housing 21 may have one or more openings. The end cap 22 may also have one or more.

[0110] The shape of the housing 21 can be determined according to the specific shape of the electrode assembly 10. For example, if the electrode assembly 10 is a cylindrical structure, then a cylindrical housing 21 can be selected; if the electrode assembly 10 is a cuboid structure, then a cuboid housing 21 can be selected. Optionally, both the electrode assembly 10 and the housing 21 are cuboid structures.

[0111] The electrode assembly 10 includes a first electrode 11, a second electrode 12, and an insulating member 13. One of the first electrode 11 and the second electrode 12 is a positive electrode, and the other is a negative electrode.

[0112] The electrode assembly 10 can be a wound structure, a stacked structure, or a hybrid structure of wound and stacked. The electrode assembly 10 can be selected as a stacked structure, which is beneficial for improving the energy density of the battery cell 7.

[0113] In some embodiments, the electrode assembly 10 has a wound structure. The first electrode 11 and the second electrode 12 are wound into a wound structure.

[0114] In other embodiments, the electrode assembly 10 has a stacked structure. As an example, multiple first electrode plates 11 and multiple second electrode plates 12 can be provided, and multiple first electrode plates 11 and multiple second electrode plates 12 are stacked.

[0115] As an example, multiple first electrode plates 11 can be provided, and second electrode plates 12 can be folded to form multiple stacked folded segments, with a first electrode plate 11 sandwiched between adjacent folded segments.

[0116] As an example, both the first electrode 11 and the second electrode 12 are folded to form multiple stacked folded segments.

[0117] As an example, multiple separators 13 can be provided, respectively disposed between any adjacent first electrode 11 or second electrode 12.

[0118] As an example, the spacer 13 can be continuously arranged between any adjacent first electrode 11 or second electrode 12 by folding or rolling.

[0119] In some embodiments, each electrode is provided with a tab that allows current to be drawn from the electrode assembly 10. The tab includes a positive tab and a negative tab.

[0120] In some embodiments, the first electrode 11 and the second electrode 12 both include a coating portion and a tab portion. The coating portion is coated with an active material layer, and the tab portion is disposed on at least one side of the coating portion along a first direction and is not coated with an active material layer. The first direction is parallel to the length direction Z of the battery cell 7 or parallel to the width direction Y of the battery cell 7.

[0121] In the embodiments of this application, the first direction, the second direction, and the thickness direction X of the battery cell 7 are perpendicular to each other.

[0122] When the first direction is parallel to the length direction Z of the battery cell 7, the dimension of the component in that direction can be considered as the length of the component. For example, the dimension of the coating part along the first direction is the length of the coating part. In this case, the second direction is parallel to the width direction Y of the battery cell 7.

[0123] When the first direction is parallel to the width direction Y of the battery cell 7, the dimension of the component in that direction can be considered as the width of the component. For example, the dimension of the coating part along the first direction is the width of the coating part. In this case, the second direction is parallel to the length of the battery cell 7.

[0124] To more clearly illustrate this application, the tab portion of the first electrode 11 is defined as the first tab 111, and the coating portion of the first electrode 11 is defined as the first coating portion 112. The tab portion of the second electrode 12 is defined as the second tab 121, and the coating portion of the second electrode 12 is defined as the second coating portion 122. The electrode terminal with the same electrical charge and electrically connected to the first tab 111 is the aforementioned first electrode terminal 31, and the electrode terminal with the same electrical charge and electrically connected to the second tab 121 is the aforementioned second electrode terminal 32.

[0125] The first electrode 11 and the second electrode 12 have opposite polarities. When the first electrode 11 is the positive electrode, the second electrode 12 is the negative electrode. The first coating part 112 is the positive coating part, the first tab 111 is the positive tab, the first electrode terminal 31 is the positive terminal, the second coating part 122 is the negative coating part, the second tab 121 is the negative tab, and the second electrode terminal 32 is the negative terminal.

[0126] Alternatively, when the first electrode 11 is the negative electrode, the second electrode 12 is the positive electrode, the first coating part 112 is the negative coating part, the first tab 111 is the negative tab, the first electrode terminal 31 is the negative terminal, the second coating part 122 is the positive coating part, the second tab 121 is the positive tab, and the second electrode terminal 32 is the positive terminal.

[0127] The coating portion includes a current collector and a membrane layer disposed on the current collector and containing an active material. For example, the positive electrode coating portion includes a positive electrode current collector and a positive electrode membrane layer disposed on the positive electrode current collector and containing a positive electrode active material. Another example is the negative electrode coating portion, which includes a negative electrode current collector and a negative electrode membrane layer disposed on the negative electrode current collector and containing a negative electrode active material.

[0128] As shown in Figures 6 to 8, in some embodiments, in the first electrode 11, the electrode tab is disposed on at least one side of the coating portion along the first direction, and the first electrode 11 satisfies: n*W1 / W2 is 0.2 to 1.0;

[0129] n represents the number of all tabs located on the same side of the coating section;

[0130] W1 represents the average size of the tab portion along the second direction;

[0131] W2 represents the dimension of the coated portion along the second direction, which is perpendicular to the first direction and to the thickness direction X.

[0132] For example, n*W1 / W2 is 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 2 / 3, 0.7, 0.75, 0.8, 0.85, 0.9, 1.0, or a range of any two of the above values. Optionally, n*W1 / W2 is from 0.5 to 1.0.

[0133] When n*W1 / W2 meets the above range, the overcurrent area of ​​the tab is relatively large, which is beneficial to improving the fast charging performance of the battery cell 7.

[0134] W1 represents the average dimension of the first tab 111 along the second direction.

[0135] When the first electrode tab 111 has an irregular shape, for example, its size gradually increases along the second direction along the first direction. In this case, the size of the first electrode tab 111 along the second direction can be measured at multiple points, and the average size of the first electrode tab 111 along the second direction can be calculated. Of course, the size of the first electrode tab 111 along the second direction at all points can be the same value. In this case, the value can be used as the average size of the first electrode tab 111.

[0136] There can be one or more first electrodes 111, for example, n is 1 to 4. When there are multiple first electrodes 111, the average size of each first electrode 111 can be measured separately, and the average size of each first electrode 111 can be calculated by summing the average size of each first electrode 111 and dividing by the number of first electrodes 111.

[0137] The first tab 111 is connected to the first coating part 112. The first tab 111 includes a first end 1111 connected to the first coating part 112. When n*W1 / W2 meets the above range, it means that the cross section of the first end 1111 along the thickness direction of the first tab 111 itself is relatively large, the contact surface between the first tab 111 and the first coating part 112 is relatively large, the current carrying capacity of the first tab 111 is strong, and it can improve the fast charging performance and cycle performance of the battery cell 7.

[0138] Optionally, the current collection portion of the first tab 111 and the first coating portion 112 is an integral structure, which makes the internal resistance of the first electrode 11 lower and can further improve the fast charging performance and cycle performance of the battery cell 7.

[0139] In some embodiments, the first electrode 11 includes at least one first tab 111, for example, one to four first tabs 111. Optionally, the first electrode 11 includes at least two first tabs 111, optionally four first tabs 111.

[0140] In some embodiments, one or more first tabs 111 are disposed on at least one side of the coating portion along the width direction Y.

[0141] As shown in Figures 6 to 8, for example, one or more first tabs 111 are disposed on one side of the first coating portion 112 along the width direction Y. In this case, it can be understood that all the first tabs 111 are disposed on the same side of the first coating portion 112 along the width direction Y. This arrangement is beneficial to increasing the space occupied by the electrode assembly 10, thereby improving the energy density of the battery cell 7. In Figure 6, W1 represents the dimension of a single first tab 111 along the length direction Z, and n is 1; W2 represents the dimension of the first coating portion 112 along the length direction Z. In Figure 7, n is 4, and the dimensions of each first tab 111 are the same. W1 can represent the dimension of a single first tab 111, although the dimensions of each first tab 111 can also be slightly different. In Figure 8, n is 1, and n*W1 / W2 is 1.

[0142] As shown in Figure 9, for example, when the first electrode 11 includes a plurality of first tabs 111, the plurality of first tabs 111 are disposed on both sides of the first coating portion 112 along the width direction Y.

[0143] Optionally, when multiple first tabs 111 are disposed on at least one side of the first coating portion 112 along the width direction Y, the number of first tabs 111 located on the same side of the first coating portion 112 along the width direction Y is at least two, such as two, three, four, five, six, etc.; optionally, four. This arrangement is beneficial for the uniform distribution of electrons on the first electrode 11, and is beneficial for improving fast charging performance.

[0144] Optionally, the distance between two adjacent first tabs 111 along the length direction Z is 0 to 300 mm, such as 0 mm, 50 mm, 100 mm, 150 mm, 200 mm, 250 mm, 300 mm, or any range of two of the above values. In Figure 9, Z1 represents the distance between two adjacent first tabs 111 along the length direction Z.

[0145] When the spacing between two adjacent first tabs 111 along the length direction Z meets the above range, it is beneficial for the current to be evenly distributed in the current collector, which is beneficial for improving fast charging performance.

[0146] In other embodiments, the first electrode 11 includes one or more first tabs 111; the one or more first tabs 111 are disposed on at least one side of the first coating portion 112 along the length direction Z.

[0147] As shown in Figure 10, for example, one or more first tabs 111 are disposed on one side of the first coating portion 112 along the length direction Z. In this case, it can be understood that all the first tabs 111 are disposed on the same side of the first coating portion 112 along the length direction Z.

[0148] As shown in Figures 11 and 12, for example, when the first electrode 11 includes a plurality of first electrode tabs 111, the plurality of first electrode tabs 111 are respectively disposed on both sides of the first coating portion 112 along the length direction Z.

[0149] Optionally, multiple first tabs 111 are respectively disposed on both sides of the first coating portion 112 along the length direction Z. This arrangement can shorten the transmission path of electrons in the first electrode 11, which is beneficial to improving fast charging performance. For example, two first tabs 111 are located on one side of the first coating portion 112 along the length direction Z, and the other two first tabs 111 are located on the other side of the first coating portion 112 along the length direction Z.

[0150] Optionally, when multiple first tabs 111 are respectively disposed on at least one side of the first coating portion 112 along the length direction Z, the number of first tabs 111 located on the same side of the first coating portion 112 along the length direction Z is at least two, such as two, three, four, five, six, etc. This arrangement is beneficial for the uniform distribution of electrons on the first electrode 11 and for improving fast charging performance.

[0151] Optionally, the distance between two adjacent first tabs 111 along the width direction Y is 0 to 300 mm, such as 0 mm, 50 mm, 100 mm, 150 mm, 200 mm, 250 mm, 300 mm or any two of the above values.

[0152] As shown in Figure 13, in some embodiments, in the second electrode 12, the electrode tab is disposed on at least one side of the coating portion along the first direction, and the second electrode 12 satisfies: m*W3 / W4 is 0.2 to 1.0;

[0153] m represents the number of all tabs located on the same side of the coating section;

[0154] W3 represents the average size of the tab portion along the second direction;

[0155] W4 indicates the dimension of the coated portion along the second direction.

[0156] For example, m*W3 / W4 is 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 2 / 3, 0.7, 0.75, 0.8, 0.85, 0.9, 1.0, or a range of any two of the above values. Optionally, m*W3 / W4 is from 0.5 to 1.0.

[0157] When m*W3 / W4 meets the above range, the overcurrent area of ​​the second tab 121 is relatively large, which is beneficial to improving the fast charging performance of the battery cell 7.

[0158] W3 represents the average size of the second tab 121 along the second direction. There can be one or more second tabs 121, for example, m is 1 to 4. When there are multiple second tabs 121, the average size can be calculated by measuring the size of each second tab 121 with a micrometer.

[0159] The second tab 121 is connected to the second coating part 122. The second tab 121 includes a second end 1211 connected to the second coating part 122. When n*W3 / W4 meets the above range, it means that the cross section of the second end 1211 along the thickness direction of the second tab 121 itself is relatively large, the contact surface between the second tab 121 and the second coating part 122 is relatively large, the current carrying capacity of the second tab 121 is strong, and it can improve the fast charging performance and cycle performance of the battery cell 7.

[0160] Optionally, the current collection portion of the second tab 121 and the second coating portion 122 is an integral structure, which makes the internal resistance of the second electrode 12 lower and can further improve the fast charging performance and cycle performance of the battery cell 7.

[0161] In some embodiments, the second electrode 12 includes at least one second electrode tab 121, optionally at least two second electrode tabs 121, optionally four second electrode tabs 121.

[0162] In some embodiments, one or more second tabs 121 are disposed on at least one side of the coating portion along the width direction Y. For example, one or more second tabs 121 are disposed on one side of the second coating portion 122 along the width direction Y. In this case, it can be understood that all second tabs 121 are disposed on the same side of the second coating portion 122 along the width direction Y. Or, for example, when the second electrode 12 includes a plurality of second tabs 121, the plurality of second tabs 121 are disposed on both sides of the second coating portion 122 along the width direction Y.

[0163] Optionally, one or more second tabs 121 are respectively disposed on one side of the second coating portion 122 along the width direction Y. This arrangement is beneficial to increase the space occupied by the electrode assembly 10, thereby improving the energy density of the battery cell 7.

[0164] Optionally, when multiple second tabs 121 are disposed on at least one side of the coating portion along the width direction Y, the number of second tabs 121 located on the same side of the second coating portion 122 along the width direction Y is at least two, such as two, three, four, five, six, etc.; optionally, four. This arrangement is beneficial for the uniform distribution of electrons on the second electrode 12, and is beneficial for improving fast charging performance.

[0165] Optionally, the distance between two adjacent second pole pieces 121 along the length direction Z is 0 to 300 mm, such as 0 mm, 50 mm, 100 mm, 150 mm, 200 mm, 250 mm, 300 mm or any range of two of the above values.

[0166] As shown in Figure 14, in some embodiments, the second electrode 12 includes one or more second tabs 121; the one or more second tabs 121 are disposed on at least one side of the second coating portion 122 along the length direction Z. For example, if one or more second tabs 121 are disposed on one side of the second coating portion 122 along the length direction Z, it can be understood that all second tabs 121 are disposed on the same side of the second coating portion 122 along the length direction Z. Or, for example, if the second electrode 12 includes multiple second tabs 121, the multiple second tabs 121 are respectively disposed on both sides of the second coating portion 122 along the length direction Z.

[0167] Optionally, multiple second tabs 121 are respectively disposed on both sides of the second coating portion 122 along the length direction Z. This arrangement can shorten the transmission path of electrons in the second electrode 12, which is beneficial to improving fast charging performance.

[0168] Optionally, when multiple second tabs 121 are disposed on at least one side of the second coating portion 122 along the length direction Z, the number of second tabs 121 located on the same side of the second coating portion 122 along the length direction Z is at least two, such as two, three, four, five, six, etc. This arrangement facilitates the uniform distribution of electrons on the second electrode 12 and improves fast charging performance.

[0169] Optionally, the distance between two adjacent second pole pieces 121 along the width direction Y is 0 to 300 mm, such as 0 mm, 50 mm, 100 mm, 150 mm, 200 mm, 250 mm, 300 mm or any range of two of the above values.

[0170] As shown in Figure 15, in some embodiments, the terminal assembly may be disposed on the housing 21, or the terminal assembly may be disposed on the end cover 22.

[0171] The terminal assembly includes a first electrode terminal 31 and a second electrode terminal 32. The first electrode terminal 31 is connected to a first tab 111, and the second electrode terminal 32 is connected to a second tab 121.

[0172] For example, the first electrode terminal 31 and the second electrode terminal 32 may be disposed on the housing 21, or the first electrode terminal 31 and the second electrode terminal 32 may be disposed on the end cover 22. Optionally, the first electrode terminal 31 and the second electrode terminal 32 may be disposed on the end cover 22.

[0173] On the same end cap 22, a first electrode terminal 31 and a second electrode terminal 32 can be provided simultaneously. For example, there is one end cap 22, on which the first electrode terminal 31 and the second electrode terminal 32 are provided at intervals. Or, for example, there are two end caps 22, which are arranged opposite each other, and each end cap 22 is provided with a first electrode terminal 31 and a second electrode terminal 32.

[0174] A first electrode terminal 31 and a second electrode terminal 32 are respectively provided on different end caps 22. For example, there are two end caps 22, which are arranged opposite each other. A first electrode terminal 31 is provided on one end cap 22, and a second electrode terminal 32 is provided on the other end cap 22.

[0175] In some embodiments, the first electrode terminal 31 is at least one, and may be selected as at least two, such as two, three or four, etc.

[0176] In some embodiments, at least one first electrode terminal 31 is disposed on at least one side of the electrode assembly 10 along the length direction Z.

[0177] As shown in Figure 15, for example, all the first electrode terminals 31 are disposed on one side of the electrode assembly 10 along the length direction Z.

[0178] As shown in Figure 16, for example, multiple first electrode terminals 31 are respectively disposed on both sides of the electrode assembly 10 along the length direction Z. This arrangement can shorten the electron migration path and is beneficial to improving fast charging performance.

[0179] For example, there are two first electrode terminals 31, one of which is disposed on one side of the electrode assembly 10 and the other is disposed on the other side of the electrode assembly 10. Alternatively, for example, there are four first electrode terminals 31, two of which are disposed on one side of the electrode assembly 10 and the other two are disposed on the other side of the electrode assembly 10.

[0180] In this embodiment of the application, the first tab 111 and the first electrode terminal 31 can be directly connected or indirectly connected; when the first tab 111 and the first electrode terminal 31 are indirectly connected, the battery cell 7 may include a first adapter 51, which is located between the first electrode terminal 31 and the first tab 111 and connects the first electrode terminal 31 and the first tab 111.

[0181] In the above embodiments, the first adapter 51 may include a conductive polymer or a conductive metal material, and the conductive metal material may include copper, aluminum, or an alloy containing the above-mentioned metal elements.

[0182] In other embodiments, at least one first electrode terminal 31 is disposed on at least one side of the electrode assembly 10 along the width direction Y. For example, all first electrode terminals 31 are disposed on one side of the electrode assembly 10 along the width direction Y. Yet another example is that a plurality of first electrode terminals 31 are disposed on both sides of the electrode assembly 10 along the width direction Y.

[0183] In some embodiments, the second electrode terminal 32 is at least one, and may be selected as at least two, such as two, three or four, etc.

[0184] In some embodiments, at least one second electrode terminal 32 is disposed on at least one side of the electrode assembly 10 along the length direction Z.

[0185] As shown in Figure 16, for example, at least two second electrode terminals 32 are respectively disposed on both sides of the electrode assembly 10 along the length direction Z. This arrangement can shorten the electron migration path and is beneficial to improving fast charging performance.

[0186] Figure 16 shows that the battery cell 7 includes four electrode terminals. Specifically, there are two second electrode terminals 32, one of which is located on one side of the electrode assembly 10 along the length direction Z, and the other is located on the other side of the electrode assembly 10 along the length direction Z. There are two first electrode terminals 31, one of which is located on one side of the electrode assembly 10, and the other is located on the other side of the electrode assembly 10.

[0187] For example, all the second electrode terminals 32 are disposed on one side of the electrode assembly 10 along the length direction Z. In this case, the first electrode terminal 31 and the second electrode terminal 32 can be disposed on both sides of the electrode assembly 10 along the length direction Z, respectively, and will not interfere with each other when they are electrically connected to the tabs.

[0188] For example, there is one first electrode terminal 31 and one second electrode terminal 32. The first electrode terminal 31 is disposed on one side of the electrode assembly 10 along the length direction Z, and the second electrode terminal 32 is disposed on the other side of the electrode assembly 10 along the length direction Z. Optionally, the first electrode terminal 31 and the second electrode terminal 32 can be staggered along the width direction Y. Of course, the first electrode terminal 31 and the second electrode terminal 32 can also be disposed opposite each other along the length direction Z. Figure 15 shows a schematic diagram of the first electrode terminal 31 and the second electrode terminal 32 respectively disposed on both sides of the electrode assembly 10.

[0189] For example, there are two first electrode terminals 31 and two second electrode terminals 32. The two first electrode terminals 31 are disposed on one side of the electrode assembly 10 along the length direction Z, and the two second electrode terminals 32 are disposed on the other side of the electrode assembly 10 along the length direction Z.

[0190] In this embodiment of the application, the second tab 121 and the second electrode terminal 32 can be directly connected or indirectly connected; when the second tab 121 and the second electrode terminal 32 are indirectly connected, the battery cell 7 may include a second adapter, which is located between the second electrode terminal 32 and the second tab 121 and connects the second electrode terminal 32 and the second tab 121.

[0191] For example, when the second electrode terminal 32 is disposed on one side of the electrode assembly 10 along the length direction Z and the second electrode tab 121 is disposed on one side of the second coating portion 122 along the width direction Y, the connection between the second electrode tab 121 and the second electrode terminal 32 is more facilitated by the second adapter.

[0192] In the above embodiments, the second adapter may include a conductive polymer or a conductive metal material, and the conductive metal material may include copper, aluminum, or an alloy containing the above-mentioned metal elements.

[0193] In other embodiments, at least one second electrode terminal 32 is disposed on at least one side of the electrode assembly 10 along the width direction Y. For example, all the second electrode terminals 32 are disposed on one side of the electrode assembly 10 along the width direction Y, or a plurality of second electrode terminals 32 are respectively disposed on both sides of the electrode assembly 10 along the width direction Y.

[0194] In some embodiments, the battery cell 7 includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector. The positive electrode film layer includes a positive electrode active material, which includes a lithium phosphate-containing material. The single-sided coating weight of the positive electrode film layer is 150 mg / 1540.25 mm. 2 Up to 370mg / 1540.25mm 2 The negative electrode includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The negative electrode film layer includes a negative electrode active material, which includes carbon-based materials and silicon-based materials. The silicon content of the silicon element in the negative electrode film layer is 0.3% to 10% by mass. The single-sided coating weight of the negative electrode film layer is 70 mg / 1540.25 mm. 2 Up to 175mg / 1540.25mm 2 The electrolyte includes organic solvents, including chain carboxylic acid ester solvents, with the chain carboxylic acid ester solvents accounting for 5% to 35% of the electrolyte by mass.

[0195] The negative electrode sheet comprises silicon-based materials, with silicon content in the negative electrode active material being greater than or equal to 0.3% by mass, and the coating weight of the negative electrode film being greater than or equal to 80 mg / 1540.25 mm. 2 The coating weight of the positive electrode film is greater than or equal to 150mg / 1540.25mm. 2 This results in a higher energy density for battery cell 7;

[0196] During the charging process of battery cell 7, active ions, such as lithium ions, migrate from the positive electrode to the negative electrode via the electrolyte. The mass content of chain carboxylic acid ester solvent in the electrolyte is greater than or equal to 5%, which results in a faster migration rate of active ions in the electrolyte; and the coating weight of the negative electrode film is less than or equal to 150 mg / 1540.25 mm. 2 This facilitates the rapid migration of active ions in the negative electrode film, and the coating weight of the positive electrode film is less than or equal to 370 mg / 1540.25 mm. 2 It facilitates the rapid migration of active ions in the positive electrode film. Through the coating weight of the positive and negative electrode films and the combination of components in the electrolyte, it is beneficial to improve the liquid phase migration rate of lithium ions and enhance the fast charging capability of the battery cell 7.

[0197] Increasing the mass content of silicon is beneficial to improving energy density, and increasing the amount of chain-like carboxylic acid ester solvent is beneficial to improving the migration rate of lithium ions. However, with the increase of the mass content of silicon and carboxylic acid ester solvent, the interfacial reaction between silicon-based materials and electrolyte intensifies, and the gas production increases. Therefore, in this embodiment, the mass content of silicon is further controlled to be less than or equal to 10%, and the mass content of chain-like carboxylic acid ester solvent in electrolyte is less than or equal to 35%. This can alleviate the interfacial side reaction between negative electrode active material and electrolyte, reduce gas production, and improve the cycle performance of battery cell 7. The positive electrode of this application also includes lithium phosphate, and the negative electrode also includes carbon-based material, which has excellent cycle stability and can further improve the cycle performance of battery cell 7.

[0198] Therefore, the embodiments of this application can improve the fast charging performance and cycle performance of the battery cell 7 under high energy density, and are beneficial to improving the cycle performance of the battery cell 7 under fast charging conditions.

[0199] Negative electrode sheet

[0200] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector and comprising a negative electrode active material. For example, the negative current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative current collector.

[0201] The upper limit voltage for charging and the lower limit voltage for discharging a single battery cell vary depending on the positive electrode active material. For example, when the phosphate material includes lithium iron phosphate, the upper limit voltage for charging can be 3.65V and the lower limit voltage for discharging can be 2.0V, or the upper limit voltage for charging can be 3.8V and the lower limit voltage for discharging can be 2.0V. Another example is when the phosphate material includes lithium manganese iron phosphate, the upper limit voltage for charging can be 4.3V and the lower limit voltage for discharging can be 2.0V. Taking a charging upper limit voltage of 3.8V and a discharging lower limit voltage of 2.0V as an example, the state of a single battery cell will be described as follows: In this embodiment, the 100% state of charge (SOC) and the 0% state of charge (SOC) of a single battery cell are defined as follows...

[0202] Charge the battery cell at a constant current charging rate of 0.05C to the upper limit of the charging voltage, which corresponds to the battery cell being 100% SOC. Discharge the battery cell at a constant current discharging rate of 0.05C to the cutoff voltage, which corresponds to the battery cell being 0% SOC.

[0203] In some embodiments, the compaction density of the negative electrode film layer is 1.5 g / cm³ when the battery cell is at 100% state of charge (SOC). 3 Up to 1.7 g / cm 3For example, the compaction density of the negative electrode film layer of a single battery cell at 100% charge is 1.50 g / cm³. 3 1.55g / cm 3 1.60g / cm 3 1.65g / cm 3 1.66 g / cm 3 1.68g / cm 3 1.70g / cm 3 Or a range consisting of any two of the above values.

[0204] When the compaction density of the negative electrode film is within the aforementioned range, it is beneficial to improve the energy density of the battery cell. Furthermore, because the negative electrode active material in the negative electrode film is densely packed, the contact resistance between particles is low, which can further reduce the resistance of the electrode sheet, thereby reducing heat generation and improving cycle performance. Therefore, by adjusting the compaction density of the negative electrode film to a reasonable range, the battery cell can improve its fast charging capability and cycle performance at high energy densities.

[0205] In this embodiment, the single-sided coating weight of the negative electrode film is 70 mg / 1540.25 mm. 2 Up to 175mg / 1540.25mm 2 For example, the single-sided coating weight of the negative electrode film is 70 mg / 1540.25 mm. 2 80mg / 1540.25mm 2 85mg / 1540.25mm 2 90mg / 1540.25mm 2 95mg / 1540.25mm 2 100mg / 1540.25mm 2 105mg / 1540.25mm 2 110mg / 1540.25mm 2 115mg / 1540.25mm 2 120mg / 1540.25mm 2 120mg / 1540.25mm 2 122mg / 1540.25mm 2 125mg / 1540.25mm 2 128mg / 1540.25mm 2 130mg / 1540.25mm 2 140mg / 1540.25mm 2 150mg / 1540.25mm 2 160mg / 1540.25mm2 170mg / 1540.25mm 2 175mg / 1540.25mm 2 Or a range consisting of any two of the above values. Optionally, the single-sided coating weight of the negative electrode film is 95 mg / 1540.25 mm. 2 Up to 142mg / 1540.25mm 2 .

[0206] When the single-sided coating weight of the negative electrode film meets the above range, its combination with an appropriate mass content of silicon element is beneficial to improving the energy density of the battery cell. Moreover, the migration rate of active ions in the negative electrode film is faster, which is beneficial to reducing polarization under high-rate charging and improving the fast charging capability of the battery cell at high energy density.

[0207] In this embodiment, the compaction density of the negative electrode film layer of a battery cell at 100% State of Charge (SOC) is a well-known concept in the art. This means that the negative electrode sheet is disassembled from the battery cell at 100% SOC, and the compaction density of the negative electrode film layer is measured. For example, a single-sided coated negative electrode sheet (if double-sided coated, the negative electrode film layer on one side can be wiped off first) is cut into small circular pieces with an area of ​​S1, weighed, and recorded as M1, and its thickness H1 is measured. Then, the negative electrode film layer of the weighed negative electrode sheet is wiped off, the weight of the negative electrode current collector is weighed and recorded as M0, and its thickness H0 is measured. The single-sided coating weight of the negative electrode film = (weight of the negative electrode sheet M1 - weight of the negative electrode current collector M0) / S1, the thickness of the negative electrode film = the thickness of the negative electrode sheet H1 - the thickness of the negative electrode current collector H0, and the compaction density of the negative electrode film = the single-sided coating weight of the negative electrode film / the thickness of the negative electrode film.

[0208] In some embodiments, the specific charge capacity of the negative electrode active material is from 350 mAh / g to 540 mAh / g. Exemplarily, the specific charge capacity of the negative electrode active material is 350 mAh / g, 355 mAh / g, 360 mAh / g, 365 mAh / g, 370 mAh / g, 375 mAh / g, 380 mAh / g, 385 mAh / g, 390 mAh / g, 395 mAh / g, 400 mAh / g, 410 mAh / g, 420 mAh / g, 430 mAh / g, 440 mAh / g, 450 mAh / g, 460 mAh / g, 470 mAh / g, 480 mAh / g, 500 mAh / g, 530 mAh / g, 540 mAh / g, or a range of any two of the above values.

[0209] When the charge capacity of the negative electrode active material is within the above range, the energy density of the battery cell is relatively high.

[0210] In the embodiments of this application, the specific capacity of the active material has a meaning known in the art and can be tested using equipment and methods known in the art. The test methods for the first coulombic efficiency and the first discharge specific capacity in Appendix G of the national standard GB / T 24533-2019 can be used to test the charging specific capacity of the negative electrode active material in a half-coin cell at a rate of 0.1C. A half-coin cell is assembled with lithium metal as the negative electrode and a sample electrode containing the above-mentioned material as the positive electrode. The half-coin cell is charged and discharged at a rate of 0.1C under the condition of 23℃±2℃ on a battery tester or other test equipment with equivalent performance to obtain the coin capacity. The capacity is then divided by the mass of the electrode active material to obtain the charging specific capacity parameter.

[0211] In some embodiments, the negative electrode active material includes a silicon-based material. Optionally, the silicon-based material may include elemental silicon, silicon-carbon composites, or silicon oxide (SiO2). x At least one of (0 < x ≤ 2). For example, the silicon-carbon composite can be silicon carbide.

[0212] In some embodiments, the mass content of silicon in the negative electrode film layer of the silicon-based material is from 0.3% to 10%, for example, 0.3%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, or any range of two of the above values. Optionally, the mass content of silicon in the negative electrode film layer of the silicon-based material is from 3% to 6%.

[0213] When the mass content of silicon is within the above range, the capacity of the negative electrode active material can be improved, which is beneficial to increasing the energy density of the battery cell. Moreover, during the charging and discharging process, the volume expansion of silicon will not be too large, which is beneficial to maintaining the stability of the negative electrode SEI film and improving the cycle performance of the battery cell at high energy density.

[0214] In some embodiments, the negative electrode active material includes a carbon-based material, which has high cycle stability and can improve the cycle performance of the battery cell.

[0215] Optionally, the carbon-based material includes at least one of artificial graphite and natural graphite.

[0216] In some embodiments, the negative electrode active material may include, in addition to the aforementioned carbon-based materials and optionally silicon-based materials, at least one of tin-based materials and lithium titanate. Tin-based materials may include at least one of elemental tin, tin oxides, and tin alloys.

[0217] The qualitative and quantitative analysis of each substance or element in this application can be performed using suitable equipment and methods known to those skilled in the art. Relevant testing methods can be referenced from domestic and international testing standards and enterprise standards. Furthermore, those skilled in the art can adaptively modify certain testing steps / instrument parameters from the perspective of testing accuracy to obtain more accurate results. One testing method can be used for qualitative or quantitative analysis, or several testing methods can be used in combination for qualitative or quantitative determination.

[0218] For example, this application can combine the general rules of X-ray diffraction analysis in JIS / K0131-1996 to perform X-ray powder diffraction tests and qualitative analysis on negative electrode sheets or negative electrode active materials.

[0219] Artificial graphite and natural graphite can be distinguished by SEM cross-sectional images taken by scanning electron microscope (SEM). Natural graphite has gaps between the sheet-like structures in its SEM cross-section, while artificial graphite has a dense structure with no obvious gaps. Alternatively, they can be distinguished by XRD patterns obtained by X-ray diffraction. Natural graphite has obvious 2H and 3R phases in its XRD pattern, while artificial graphite only has the 2H phase in its XRD pattern.

[0220] As shown in Figure 17, in this embodiment of the application, the negative electrode film layer 141 of the negative electrode sheet 14 includes at least one film layer, which can be a single film layer or at least two film layers. Optionally, the negative electrode film layer 141 includes at least two film layers.

[0221] When the negative electrode film layer 141 is a single layer, the negative electrode active material in the negative electrode film layer 141 includes carbon-based materials and optional silicon-based materials.

[0222] When the negative electrode film 141 employs at least two film layers, the negative electrode active material in the negative electrode film 141 includes carbon-based materials and optionally silicon-based materials. The negative electrode film 141 may include two, three, four, or even more film layers.

[0223] In some embodiments, the negative electrode film 141 includes a first negative electrode film 1411 and a second negative electrode film 1412. The first negative electrode film 1411 is disposed on the surface of the negative electrode current collector 142, and the negative electrode active material of the first negative electrode film 1411 includes a carbon-based material. The second negative electrode film 1412 is connected to the side of the first negative electrode film 1411 facing away from the negative electrode current collector 142, and the negative electrode active material of the second negative electrode film 1412 also includes a carbon-based material. The interface between the first negative electrode film 1411 and the second negative electrode film 1412 may be regular or irregular, optionally irregular; or there may be no obvious interface between the first negative electrode film 1411 and the second negative electrode film 1412.

[0224] The negative electrode film 141 comprises at least two layers, and the layered coating is beneficial to improving the fast charging performance of the battery cell. In particular, when there is a difference in porosity between the first negative electrode film 1411 and the second negative electrode film 1412, it is beneficial to improve the fast charging performance of the battery cell.

[0225] In some embodiments, at least one of the first negative electrode film 1411 and the second negative electrode film 1412 comprises a silicon-based material.

[0226] Optionally, the first negative electrode film layer 1411 may also include a silicon-based material.

[0227] Optionally, the second negative electrode film 1412 may also include a silicon-based material.

[0228] For example, the first negative electrode film layer 1411 includes carbon-based materials and silicon-based materials, and the second negative electrode film layer 1412 includes carbon-based materials and silicon-based materials. When both the first negative electrode film layer 1411 and the second negative electrode film layer 1412 include silicon-based materials, it is more beneficial to improve the energy density of the battery cell; and the carbon-based materials can mitigate the volume expansion of the silicon-based materials, making the negative electrode SEI film more stable and improving cycle performance at high energy densities; and since each layer includes silicon-based materials, the coating thickness is relatively thin, which helps to shorten the lithium-ion transport path and improve fast charging performance at high energy densities.

[0229] Alternatively, the first negative electrode film 1411 may comprise carbon-based and silicon-based materials, and the second negative electrode film 1412 may comprise carbon-based materials. When the first negative electrode film 1411 comprises silicon-based materials and the second negative electrode film 1412 does not, the second negative electrode film 1412 can mitigate the volume expansion of the first negative electrode film 1411, reduce side reactions between the negative electrode film 141 and the electrolyte, and improve cycle performance at high energy densities.

[0230] Alternatively, the first negative electrode film 1411 may comprise a carbon-based material, and the second negative electrode film 1412 may comprise both a carbon-based material and a silicon-based material. When the second negative electrode film 1412 comprises a silicon-based material, it is advantageous to form more film pores through volume changes in the silicon-based material, thereby improving the liquid-phase transport capability of lithium ions, enhancing the kinetic performance of the battery cell, and improving cycle performance at high energy densities.

[0231] When the negative electrode film 141 uses at least two film layers, the cross-sectional shape of the negative electrode film 141 can be the same or similar, or it can be different, along the thickness direction X of the negative electrode film 141. When the electrode assembly is a stacked structure, the thickness direction of the battery cell can be parallel to the thickness direction of the electrode assembly and the thickness direction X of the negative electrode film 141.

[0232] Along the thickness direction X of the negative electrode film layer 141, the negative electrode film layer 141 is divided into three regions, namely the first region 141a, the third region 141c, and the second region 141b. The first region 141a is the region of the negative electrode film layer 141 close to the negative electrode current collector 142 along the thickness direction X, and the thickness of the first region 141a is 1 / 3 of the thickness of the negative electrode film layer 141. The second region 141b is the region of the negative electrode film layer 141 away from the negative electrode current collector 142 along the thickness direction X, and the thickness of the second region 141b is 1 / 3 of the thickness of the negative electrode film layer 141.

[0233] The cross-sectional shapes of the first region 141a and the second region 141b can be the same or similar, or they can be different. The cross-sectional shapes of the first region 141a and the third region 141c can be the same or similar, or they can be different. The cross-sectional shapes of the second region 141b and the third region 141c can be the same or similar, or they can be different.

[0234] There may or may not be a clear layer interface between the first region 141a, the second region 141b, and the third region 141c. For example, the first negative electrode film layer 1411 includes the first region 141a, the second negative electrode film layer 1412 includes the second region 141b, and the third region 141c may be a part of the first negative electrode film layer 1411, or the third region 141c may be a part of the second negative electrode film layer 1412, or the third region 141c may be a part of both the first negative electrode film layer 1411 and the second negative electrode film layer 1412.

[0235] Optionally, the average particle size of the carbon-based material in the first region 141a can be greater than or equal to the average particle size of the carbon-based material in the second region 141b. More preferably, the average particle size of the carbon-based material in the first region 141a can be greater than the average particle size of the carbon-based material in the second region 141b, which facilitates the rapid migration of lithium ions from the second region 141b to the first region 141a, thereby improving the fast-charging capability of the battery cell. Of course, the average particle size of the carbon-based material in the first region 141a can be smaller than the average particle size of the carbon-based material in the second region 141b.

[0236] Optionally, the average particle size of the carbon-based material of the first negative electrode film layer 1411 may be greater than or equal to the average particle size of the carbon-based material of the second negative electrode film layer 1412. More preferably, the average particle size of the carbon-based material of the first negative electrode film layer 1411 may be greater than the average particle size of the carbon-based material of the second negative electrode film layer 1412.

[0237] The difference in particle size between the first negative electrode film layer 1411 and the second negative electrode film layer 1412 can improve the fast charging performance of the battery cell. Specifically, during fast charging, the overpotential of the second negative electrode film layer 1412 is usually high, and the bottleneck of fast charging is mainly the second negative electrode film layer 1412. However, in the embodiment of this application, the particle size of the second negative electrode film layer 1412 is relatively small, which can shorten the solid-phase transport path of lithium ions, improve fast charging performance, improve the lithium deposition problem on the surface of the negative electrode sheet 14, and improve the cycle performance under high energy density.

[0238] Optionally, the average particle size of the carbon-based material in the first region 141a is from 10 μm to 20 μm, for example, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, or any combination of two of the above values. When the average particle size of the carbon-based material in the first region 141a is within the above range, on the one hand, it can shorten the solid-phase transport path of lithium ions and improve fast charging performance; on the other hand, the material is less prone to agglomeration during preparation, which can improve the stability of the material and improve the cycling performance at high energy densities.

[0239] Optionally, the average particle size of the carbon-based material in the first negative electrode film 1411 is between 10 μm and 20 μm. When the average particle size of the carbon-based material in the first negative electrode film 1411 is within the above range, on the one hand, it can shorten the solid-phase transport path of lithium ions and improve fast charging performance; on the other hand, the material is less prone to agglomeration during the preparation process, which can improve the stability of the material.

[0240] Optionally, the average particle size of the carbon-based material in the second region 141b is from 5 μm to 12 μm, for example, 5 μm, 8 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, or any combination of two of the above values. When the average particle size of the carbon-based material in the second negative electrode film layer 1412 is within the above range, the stability of the material is improved, which is beneficial to improving the fast charging capability and cycle performance of the battery cell at high energy density.

[0241] Optionally, the average particle size of the carbon-based material in the second negative electrode film 1412 is between 5 μm and 12 μm. When the average particle size of the carbon-based material in the second negative electrode film 1412 is within the above range, on the one hand, it can shorten the solid-phase transport path of lithium ions and improve fast charging performance; on the other hand, the material is less prone to agglomeration during preparation, which can improve the stability of the material. Furthermore, the combination of the negative electrode active material in the second negative electrode film 1412 and the negative electrode active material in the first negative electrode film 1411 within the above average particle size range is beneficial to constructing a gradient porosity difference between the second negative electrode film 1412 and the first negative electrode film 1411, reducing the tortuosity of lithium ion transport, and improving the fast charging capability of the battery cell at high energy density.

[0242] For example, the carbon-based material of the first region 141a includes at least one of artificial graphite and natural graphite, and the carbon-based material of the second region 141b includes artificial graphite. For instance, the negative electrode active material of the first region 141a includes silicon-based material, artificial graphite, and natural graphite, and the negative electrode active material of the second region 141b includes silicon-based material and artificial graphite.

[0243] For example, the carbon-based material of the first negative electrode film layer 1411 includes at least one of artificial graphite and natural graphite, and the carbon-based material of the second negative electrode film layer 1412 includes artificial graphite. For instance, the negative electrode active material of the first negative electrode film layer 1411 includes silicon-based materials, artificial graphite, and natural graphite, and the negative electrode active material of the second negative electrode film layer 1412 includes silicon-based materials and artificial graphite.

[0244] In this embodiment, the average particle size of the carbon-based material in the first region 141a and the second region 141b has a meaning known in the art and can be detected using equipment and methods known in the art. For example, the negative electrode sheet 14 can be used as a sample, and the cross-section can be polished along the thickness direction X of the negative electrode film layer 141, for example, using an argon ion beam. The cross-section can be photographed using a scanning electron microscope (SEM) to obtain an SEM cross-sectional image. The particle size of the carbon-based material in the SEM cross-section can be counted, and the average particle size of the carbon-based material can be calculated based on the counted number. When the proportion of carbon-based material in the negative electrode film layer is relatively high, the average particle size of the carbon-based material can be used to roughly estimate the average particle size of the negative electrode active material.

[0245] In some embodiments, the negative electrode film layer may optionally include a negative electrode conductive agent. This application does not impose particular limitations on the type of negative electrode conductive agent; as an example, the negative electrode conductive agent may include at least one of conductive carbon and carbon nanotubes. In some embodiments, the mass content of the negative electrode conductive agent is ≤5% based on the total weight of the negative electrode film layer.

[0246] Negative electrode conductive agents can compensate for the insufficient conductivity of silicon-based materials, improve the conductivity of the negative electrode film, and help improve the dynamic performance of battery cells and the fast charging capability of battery cells at high energy densities.

[0247] Optionally, the mass content of conductive carbon in the negative electrode film is 0.4% to 0.7%, for example, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, or any combination of two of the above values. A mass content of conductive carbon within the above range can improve the fast charging capability of the battery cell at high energy density.

[0248] Optionally, the mass content of carbon nanotubes in the negative electrode film layer is 0.1% to 1%, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or any combination of two of the above values. Optionally, the mass content of carbon nanotubes in the negative electrode film layer is 0.1% to 0.5%. A mass content of carbon nanotubes at the above-mentioned levels can improve the fast charging capability of the battery cell at high energy density.

[0249] In some embodiments, the negative electrode film layer may optionally include a negative electrode binder. In some embodiments, the mass content of the negative electrode binder is ≤5% based on the total weight of the negative electrode film layer.

[0250] In some embodiments, the negative electrode film layer may optionally include other additives. As examples, other additives may include thickeners, dispersants, etc., such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, etc. In some embodiments, the mass content of other additives is ≤2% based on the total weight of the negative electrode film layer.

[0251] In some embodiments, the negative current collector may be a metal foil or a composite current collector. Examples of metal foils include at least one foil made of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. A composite current collector may include a polymer base material and a metal material layer formed on at least one surface of the polymer base material. As an example, the metal material layer may include at least one of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer base material may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0252] In some embodiments, the thickness of the negative current collector is from 4 μm to 8.5 μm, for example 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm or any combination of the above values.

[0253] In some embodiments, the negative electrode sheet further includes a negative electrode tab connected to the negative current collector. The thickness of the negative electrode tab is 4 μm to 8.5 μm, for example, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, or any combination of two of the above values. A negative electrode tab thickness within the above range is beneficial for improving overcurrent capacity and enhancing the fast charging capability of the battery cell.

[0254] The negative electrode film is typically formed by coating a negative electrode slurry onto the negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is usually formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0255] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of the present application further includes a negative electrode conductive layer sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector. In other embodiments, the negative electrode sheet of the present application further includes a protective layer covering the surface of the negative electrode film layer.

[0256] Positive electrode sheet

[0257] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector and comprising a positive electrode active material. For example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0258] When a battery cell includes a stacked electrode assembly, the length direction of the battery cell is parallel to the length direction of the positive electrode sheet. The dimension of the battery cell along the length direction can be understood as the length of the battery cell, and the dimension of the positive electrode film along the length direction can be understood as the length of the positive electrode film. The width direction of the battery cell is parallel to the width direction of the positive electrode sheet. The dimension of the battery cell along the width direction can be understood as the width of the battery cell, and the dimension of the positive electrode film along the width direction can be understood as the width of the positive electrode film.

[0259] In some embodiments, the dimension of the positive electrode film layer along the length of the positive electrode sheet is 265 mm to 1200 mm, such as 265 mm, 350 mm, 450 mm, 550 mm, 650 mm, 750 mm, 850 mm, 950 mm, 1050 mm, 1150 mm, 1200 mm or any combination of two of the above values.

[0260] In some embodiments, the ratio of the dimension of the positive electrode film layer along the length direction of the positive electrode sheet to the dimension of the positive electrode film layer along the width direction of the positive electrode sheet is greater than 1 and less than or equal to 18.5, and can be selected from 1.25 to 18.5, for example 1.25, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13, 13.5, 14, 14.5, 15, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 or any range of two of the above values.

[0261] For example, the dimension of the positive electrode film along the length of the positive electrode sheet is 265 mm to 655 mm, and the ratio of the dimension of the positive electrode film along the length of the positive electrode sheet to the dimension of the positive electrode film along the width of the positive electrode sheet is greater than 1 and less than or equal to 12.5, and can be selected as 2 to 12.5. When the positive electrode active material of the positive electrode film includes lithium phosphate, the conductivity of lithium phosphate is relatively poor, and the size of the positive electrode film should not be too long. When the size of the positive electrode film is within the above range, the electron transport path is not too long, the internal resistance is relatively small, which is beneficial to improving the fast charging capability of the battery cell at high energy density.

[0262] Optionally, the dimension of the positive electrode film layer along the length direction of the positive electrode sheet is 400 mm to 600 mm, and the ratio of the dimension of the positive electrode film layer along the length direction of the positive electrode sheet to the dimension of the positive electrode film layer along the width direction of the positive electrode sheet is 4 to 8.

[0263] For example, the dimension of the positive electrode film along the length of the positive electrode sheet is greater than 655 mm and less than or equal to 1155 mm, and the ratio of the dimension of the positive electrode film along the length of the positive electrode sheet to the dimension of the positive electrode film along the width of the positive electrode sheet is 2 to 12.5.

[0264] In some embodiments, the dimension of the negative electrode film layer along the first direction is larger than that of the positive electrode film layer along the first direction, so that almost all lithium ions extracted from the positive electrode film layer can be embedded in the negative electrode film layer, mitigating the risk of lithium deposition from the negative electrode and improving the reliability of the battery cell. Of course, the dimension of the negative electrode film layer along the first direction can also be smaller than or equal to the dimension of the positive electrode film layer along the first direction.

[0265] Optionally, the difference between the dimension of the negative electrode film layer along the first direction and the dimension of the positive electrode film layer along the first direction is 5 mm to 11 mm, such as 5 mm, 5.5 mm, 6 mm, 6.5 mm, 7 mm, 7.5 mm, 8 mm, 8.5 mm, 9 mm, 9.5 mm, 10 mm, 10.5 mm, 11 mm or any range of two of the above values.

[0266] In some embodiments, the dimension of the negative electrode film layer along the second direction is larger than that of the positive electrode film layer along the second direction, so that almost all lithium ions extracted from the positive electrode film layer can be embedded in the negative electrode film layer, mitigating the risk of lithium deposition from the negative electrode and improving the cycle life of the battery cell. Of course, the dimension of the negative electrode film layer along the second direction can also be smaller than or equal to the dimension of the positive electrode film layer along the second direction.

[0267] Optionally, the difference between the dimension of the negative electrode film layer along the second direction and the dimension of the positive electrode film layer along the second direction is 5 mm to 11 mm, such as 5 mm, 5.5 mm, 6 mm, 6.5 mm, 7 mm, 7.5 mm, 8 mm, 8.5 mm, 9 mm, 9.5 mm, 10 mm, 10.5 mm, 11 mm or any range of two of the above values.

[0268] The first direction is perpendicular to the second direction. The first direction can be parallel to the length direction of the battery cell, or it can be parallel to the width direction of the battery cell. If the first direction is parallel to the length direction of the battery cell, the second direction is parallel to the width direction of the battery cell. If the first direction is parallel to the width direction of the battery cell, the second direction is parallel to the length direction of the battery cell.

[0269] In some embodiments, the dimension of the separator along the first direction is larger than the dimension of the negative electrode film layer along the first direction, so that the separator can effectively isolate the positive electrode and the negative electrode, reduce the risk of short circuit, and improve the reliability of the battery cell. Of course, the dimension of the separator along the first direction can also be less than or equal to the dimension of the negative electrode film layer along the first direction.

[0270] Optionally, the difference between the dimension of the separator along the first direction and the dimension of the negative electrode film layer along the first direction is 6 mm to 10 mm, such as 6 mm, 6.5 mm, 7 mm, 7.5 mm, 8 mm, 8.5 mm, 9 mm, 9.5 mm, 10 mm or any range of two of the above values.

[0271] In some embodiments, the dimension of the separator along the second direction is larger than the dimension of the negative electrode film layer along the second direction, so that the separator can effectively isolate the positive electrode and the negative electrode, reduce the risk of short circuit, and improve the reliability of the battery cell. Of course, the dimension of the separator along the second direction can also be less than or equal to the dimension of the negative electrode film layer along the second direction.

[0272] Optionally, the difference between the dimension of the separator along the second direction and the dimension of the negative electrode film layer along the second direction is 6 mm to 10 mm, such as 6 mm, 6.5 mm, 7 mm, 7.5 mm, 8 mm, 8.5 mm, 9 mm, 9.5 mm, 10 mm or any range of two of the above values.

[0273] As shown in Figure 18, taking an example where the first direction is parallel to the length direction Z, the second direction is parallel to the width direction Y, and the first electrode 11 is the positive electrode and the second electrode 12 is the negative electrode, this will be explained accordingly.

[0274] The dimension of the positive electrode film layer of the first electrode 11 along the length direction Z is the length of the positive electrode film layer of the first electrode 11, the dimension of the negative electrode film layer of the second electrode 12 along the length direction Z is the length of the negative electrode film layer of the second electrode 12, and the dimension of the separator 13 along the length direction Z is the length of the separator 13.

[0275] The difference between the length of the negative electrode film layer of the second electrode 12 and the length of the positive electrode film layer of the first electrode 11 is OH. 11 Figure 18 shows that the negative electrode film extends beyond the positive electrode film on both sides along the Z-direction of length, and each side extends beyond the OH group. 11 / 2. Of course, the negative electrode film layer can also extend beyond the positive electrode film layer on one side along the length direction Z.

[0276] The difference between the length of the separator 13 and the length of the negative electrode film layer of the second electrode 12 is OH. 21 As shown in Figure 18, the separator 13 extends beyond the negative electrode film layer on both sides along the length direction Z, and each side extends beyond the OH group. 21 / 2. Of course, the separator 13 can extend beyond the negative electrode film layer on one side along the length direction Z.

[0277] The positive electrode film layer of the first electrode 11 has a width Y along the width direction, the negative electrode film layer of the second electrode 12 has a width Y along the width direction, and the separator 13 has a width Y along the width direction.

[0278] The difference between the width of the negative electrode film layer of the second electrode 12 and the width of the positive electrode film layer of the first electrode 11 is OH. 12 Figure 8 shows that the negative electrode film extends beyond the positive electrode film on both sides along the width direction Y, and each side extends beyond the OH group. 12 / 2. Of course, the negative electrode film layer can also extend beyond the positive electrode film layer on one side along the width direction Y.

[0279] The difference between the width of the separator 13 and the width of the negative electrode film layer of the second electrode 12 is OH. 22 As shown in Figure 18, the separator 13 extends beyond the negative electrode film layer on both sides along the width direction Y, and extends beyond the OH group on each side. 22 / 2. Of course, the separator 13 may extend beyond the negative electrode film layer on one side along the width direction Y.

[0280] In some embodiments, the compaction density of the positive electrode film layer is 2.50 g / cm³ when the battery cell is at 100% state of charge (SOC). 3 Up to 2.80 g / cm 3 For example, when the battery cell is at 100% state of charge (SOC), the compaction density of the positive electrode film is 2.50 g / cm³. 3 2.52g / cm 32.55g / cm 3 2.56 g / cm 3 2.57g / cm 3 2.58g / cm 3 2.60g / cm 3 2.62 g / cm 3 2.65g / cm 3 2.68g / cm 3 2.70 g / cm 3 2.75g / cm 3 2.80g / cm 3 Or a range consisting of any two of the above values.

[0281] When the compaction density of the positive electrode film is within the aforementioned range, it is beneficial to improve the energy density of the battery cell. Furthermore, because the positive electrode active material in the positive electrode film is densely packed, the contact resistance between particles is low, which can further reduce the resistance of the electrode sheet, thereby reducing heat generation and improving cycle performance. Therefore, by adjusting the compaction density of the positive electrode film to a reasonable range, the battery cell can improve its fast charging capability and cycle performance at high energy densities.

[0282] In some embodiments, the single-sided coating weight of the positive electrode film is 150 mg / 1540.25 mm. 2 Up to 370mg / 1540.25mm 2 For example, the single-sided coating weight of the positive electrode film is 150 mg / 1540.25 mm. 2 200mg / 1540.25mm 2 250mg / 1540.25mm 2 300mg / 1540.25mm 2 350mg / 1540.25mm 2 370mg / 1540.25mm 2 Or a range consisting of any two of the above values. Optionally, the single-sided coating weight of the positive electrode film is 200 mg / 1540.25 mm. 2 Up to 300mg / 1540.25mm 2 .

[0283] When the single-sided coating weight of the positive electrode film is within the above range, the heat generation per unit area of ​​the positive electrode sheet will not be too large, which reduces the risk of side reactions being aggravated due to heat accumulation and is conducive to improving the fast charging capability and cycle performance of the battery cell at high energy density.

[0284] In this embodiment, the compaction density of the positive electrode film layer of a single battery cell at 100% State of Charge (SOC) is a well-known concept in the art. This means that the positive electrode sheet is disassembled from the single battery cell at 100% SOC, and the compaction density of the positive electrode film layer is measured. For example, a single-sided coated positive electrode sheet (if double-sided coated, the positive electrode film layer on one side can be wiped off first) is cut into small circular pieces with an area of ​​S1, weighed, and recorded as M1, and its thickness H1 is measured. Then, the positive electrode film layer of the weighed positive electrode sheet is wiped off, the weight of the positive current collector is weighed and recorded as M0, and its thickness H0 is measured. The single-sided coating weight of the positive electrode film = (weight of the positive electrode sheet M1 - weight of the positive current collector M0) / S1, the thickness of the positive electrode film = the thickness of the positive electrode sheet H1 - the thickness of the positive current collector H0, and the compaction density of the positive electrode film = the single-sided coating weight of the positive electrode film / the thickness of the positive electrode film.

[0285] In some embodiments, the specific charge capacity of the positive electrode active material is from 150 mAh / g to 170 mAh / g. Exemplarily, the specific charge capacity of the positive electrode active material is 150 mAh / g, 155 mAh / g, 160 mAh / g, 165 mAh / g, 170 mAh / g, or a range consisting of any two of the above values.

[0286] When the charge capacity of the positive electrode active material is within the above range, the energy density of the battery cell is relatively high.

[0287] In the embodiments of this application, the specific capacity of the positive electrode active material has a meaning known in the art and can be detected using the specific capacity testing method for negative electrode active materials.

[0288] In some embodiments, the positive electrode active material includes a lithium phosphate. The lithium phosphate can have an olivine structure, which is structurally stable during charge and discharge and can improve the cycle life of the battery cell.

[0289] Optionally, the positive electrode active material may also include lithium-containing transition metal oxides. Examples of lithium-containing transition metal oxides may include, but are not limited to, at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds.

[0290] The lithium phosphate with olivine structure can be an unmodified lithium phosphate or a material obtained by coating modification. For example, a carbon-containing material can be disposed on the surface of the lithium phosphate. The carbon-containing material can be used as a coating layer to coat the surface of the lithium phosphate, thereby improving the conductivity of the lithium phosphate, reducing the powder resistivity of the material, and facilitating the migration rate of lithium ions, improving the fast charging capability of the battery cell, and reducing the heat generation of the battery cell.

[0291] In some embodiments, lithium phosphates include those with the general formula Li x1 A y1 Me a M b P 1-c X c Y z The compound contains the following components: 0.5 ≤ x1 ≤ 1.3, 0 ≤ y1 ≤ 1.3, and 0.9 ≤ x1 + y1 ≤ 1.3, 0.9 ≤ a ≤ 1.5, 0 ≤ b ≤ 0.5, and 0.9 ≤ a + b ≤ 1.5, 0 ≤ c ≤ 0.5, 3 ≤ z ≤ 5; A includes one or more of Na, K, and Mg; Me includes one or more of Mn, Fe, Co, and Ni; M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X includes one or more of Cl, C, and N; and Y includes one or more of O and F. Lithium phosphates exhibit superior cycle stability, which is beneficial for improving the cycle performance of individual battery cells.

[0292] For example, lithium phosphates include one or more of LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4. During the charging and discharging process, active ions such as Li are de-intercalated and consumed in a single battery cell, resulting in different molar contents of Li in different discharged states. In the examples of positive electrode active materials such as LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4, the molar contents of Li represent the initial state of the material, i.e., the state before feeding. When the positive electrode active material is applied to the battery system, the molar contents of Li may change after charge-discharge cycles. In the embodiments of this application, the molar contents of oxygen (O) in the examples of positive electrode active materials such as LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4 are only theoretical values. Lattice oxygen release can cause changes in the molar contents of oxygen (O). In reality, the molar contents of oxygen (O) may fluctuate, and all of the above situations are within the scope of protection of this application.

[0293] In this application embodiment, the element content in the positive electrode active material has a meaning known in the art and can be detected using equipment and methods known in the art. For example, referring to EPA6010D-2014, it is tested by inductively coupled plasma atomic emission spectrometry (ICP-OES, instrument model: Thermo ICAP7400). After discharging the battery cell to 0% state of charge (SOC), the positive electrode sheet is disassembled, cleaned with dimethyl carbonate (DMC), dried, and then calcined at high temperature to remove impurities. 0.4g of the positive electrode active material is weighed, and 10ml (50% concentration) of aqua regia is added. Then it is placed on a plate at 180°C for 30min. After digestion on the plate, the volume is adjusted to 100mL, and quantitative testing is performed using the standard curve method.

[0294] In some embodiments, the lithium phosphate is in particulate form, and the volume average particle size Dv50 of the lithium phosphate is 1 μm to 2 μm, for example 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm or any combination of two of the above values.

[0295] When lithium-containing phosphates meet the above conditions, their particle size is relatively small, the lithium ion insertion / extraction path in lithium-containing phosphates is short, and the heat generation is low; moreover, the particle size of the above-mentioned lithium-containing phosphates is not too small, and they basically do not agglomerate during the processing and preparation process, which makes the performance of lithium-containing phosphates stable.

[0296] In some embodiments, the positive electrode film layer further includes a positive electrode additive, which includes one or more of the following: lithium-containing ternary materials, lithium phosphate, lithium hydrogen phosphate, lithium sulfate, lithium sulfite, lithium molybdate, lithium oxalate, lithium titanate, lithium tetraborate, lithium metasilicate, lithium metamanganese oxide, lithium tartrate, lithium trilithium citrate, lithium nickel oxide, and lithium ferrite. These materials can act as lithium replenishing agents, supplementing the positive electrode film layer with lithium ions, compensating for irreversible lithium ion loss within the system, increasing capacity, and improving the energy density of the battery cell.

[0297] In some embodiments, the mass content of the positive electrode additive, based on the total mass of the positive electrode film, is 0.1% to 5%, for example, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any combination thereof. When using a positive electrode additive within this mass range, lithium ions can be replenished to the positive electrode film, compensating for irreversible lithium ion losses within the system. Furthermore, the mass content of the positive electrode additive is not excessively high, ensuring that the specific capacity of the positive electrode discharge remains high and the energy density is not significantly reduced.

[0298] In some embodiments, the volume average particle size (Dv50) of the cathode additive is greater than that of the lithium phosphate-containing additive. The combination of particles of different sizes facilitates uniform dispersion and improves the distribution uniformity of the lithium supplement.

[0299] In some embodiments, the volume average particle size Dv50 of the cathode additive is 8 μm to 10 μm, for example 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm or any combination thereof.

[0300] In the embodiments of this application, the volume average particle size Dv50 is a well-known concept in the art. The volume average particle size Dv50 refers to the particle size corresponding to 50% of the volume distribution. It can be detected using equipment and methods known in the art. After a fresh battery cell is fully charged to 0% SOC, the positive electrode is disassembled, the positive current collector is removed, and the positive electrode film is retained. The positive electrode film is immersed in N-methylpyrrolidone (NMP) to wash out the binder in the positive electrode film. The positive electrode active material or lithium supplement is retained as a sample. After drying the sample, the volume average particle size Dv50 of the particles is tested according to the test standard GB / T 19077-2016 using a Mastersizer 2000E laser particle size analyzer.

[0301] In some embodiments, the positive electrode film layer may optionally include a positive electrode conductive agent. As an example, the positive electrode conductive agent includes at least one selected from superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass content of the positive electrode conductive agent is ≤5% based on the mass of the positive electrode film layer.

[0302] In some embodiments, the positive electrode film layer may optionally include a positive electrode binder. This application does not impose particular limitations on the type of positive electrode binder. As an example, the positive electrode binder may include at least one selected from polyvinylidene fluoride, polytetrafluoroethylene, a terpolymer of vinylidene fluoride-tetrafluoroethylene-propylene, a terpolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, a tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and fluorinated acrylate resins. In some embodiments, the mass content of the positive electrode binder is ≤5% based on the mass of the positive electrode film layer.

[0303] In some embodiments, the positive current collector may be a metal foil or a composite current collector. Examples of metal foils include at least one foil selected from aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. A composite current collector may include a polymer base material and a metal material layer formed on at least one surface of the polymer base material. As an example, the metal material layer may include at least one selected from aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer base material may include at least one selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0304] In some embodiments, the thickness of the positive current collector is 10 μm to 16 μm, for example, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, 15.5 μm, 16 μm or any combination of two of the above values.

[0305] In some embodiments, the positive electrode sheet further includes a positive tab connected to the positive current collector. The thickness of the positive tab is 10 μm to 16 μm, for example, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, 15.5 μm, 16 μm, or any combination of two of the above values. A positive tab thickness within the above range is beneficial for improving current carrying capacity and enhancing the fast charging capability of the battery cell.

[0306] The positive electrode film is typically formed by coating a positive electrode slurry onto the positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is usually formed by dispersing the positive electrode active material, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP), but is not limited to it.

[0307] The positive electrode sheet does not exclude other additional functional layers besides the positive electrode film layer. For example, in some embodiments, the positive electrode sheet of the present application further includes a positive electrode conductive layer sandwiched between the positive electrode current collector and the positive electrode film layer and disposed on the surface of the positive electrode current collector. In other embodiments, the positive electrode sheet of the present application further includes a protective layer covering the surface of the positive electrode film layer.

[0308] Electrolyte

[0309] During the charging and discharging process of a single battery cell, active ions, such as lithium ions, repeatedly insert and extract between the positive and negative electrode plates. The electrolyte acts as a conductor for these active ions between the positive and negative electrode plates. The electrolyte consists of organic solvents and electrolyte salts.

[0310] In some embodiments, the electrolyte has a conductivity of 10.5 mS / cm to 13.5 mS / cm at room temperature. Exemplarily, the electrolyte conductivity at room temperature is 10.5 mS / cm, 11 mS / cm, 11.5 mS / cm, 12 mS / cm, 12.5 mS / cm, 13 mS / cm, 13.5 mS / cm, or a range consisting of any two of the above values.

[0311] When the conductivity of the electrolyte at room temperature, such as 25°C, is within the above range, the migration rate of lithium ions in the electrolyte is relatively high, which can further reduce the internal resistance of the battery cell and improve the fast charging performance of the battery cell.

[0312] In the embodiments of this application, the conductivity of the electrolyte at room temperature, such as 25°C, is the ionic conductivity, which can be detected using equipment and methods known in the art, such as by referring to industry standard HG-T 4067-2015.

[0313] In some embodiments, the viscosity of the electrolyte at room temperature is from 1.5 mPa·s to 5.5 mPa·s. Exemplarily, the viscosity of the electrolyte is 1.5 mPa·s, 2 mPa·s, 2.5 mPa·s, 3 mPa·s, 3.5 mPa·s, 4 mPa·s, 4.5 mPa·s, 5 mPa·s, 5.5 mPa·s, or a range consisting of any two of the above values.

[0314] When the viscosity of the electrolyte at room temperature, such as 25°C, is within the above range, the migration rate of lithium ions in the electrolyte is relatively high, which can further reduce the internal resistance of the battery cell and improve the fast charging performance of the battery cell.

[0315] In the embodiments of this application, the viscosity of the electrolyte has a meaning known in the art and can be detected using equipment and methods known in the art, such as in accordance with GB / T10247-2008.

[0316] In some embodiments, the electrolyte has a density of 1.05 g / mL to 1.35 g / mL at room temperature, such as 25°C. Exemplarily, the electrolyte density is 1.05 g / mL, 1.10 g / mL, 1.15 g / mL, 1.2 g / mL, 1.25 g / mL, 1.3 g / mL, 1.35 g / mL, or a range of any two of the above values.

[0317] When the electrolyte density is within the above range, the migration rate of lithium ions in the electrolyte is relatively high, which can further reduce the internal resistance of the battery cell and improve the fast charging performance of the battery cell.

[0318] In the embodiments of this application, the density of the electrolyte has a meaning known in the art and can be detected using equipment and methods known in the art, such as referring to GB / T 2013-2010 for testing.

[0319] In some embodiments, the organic solvent includes chain carboxylic acid ester solvents.

[0320] Optionally, the chain-like carboxylic acid ester solvent has a mass content of 5% to 35% in the electrolyte. Exemplarily, the mass content of the chain-like carboxylic acid ester solvent is 5%, 8%, 10%, 13%, 15%, 18%, 20%, 23%, 25%, 28%, 30%, 33%, 35%, or a range of any two of the above values. Optionally, the mass content of the chain-like carboxylic acid ester solvent in the electrolyte is 8% to 20%.

[0321] When the mass content of chain carboxylic acid ester solvent is within the above range, the viscosity of the electrolyte is lower, which can improve the conductivity of the electrolyte, reduce the internal resistance of the battery cell, and facilitate the rapid migration of lithium ions. Furthermore, the electrolyte is compatible with the silicon-containing anode, which can effectively reduce the gas production of the battery cell, reduce the impact on the interface film on the anode side, and improve the fast charging capability and cycle performance of the battery cell.

[0322] In some embodiments, the chain carboxylic acid ester solvent includes compounds represented by Formula I.

[0323] In formula I,

[0324] R1 includes a hydrogen atom, a C1 to C5 alkyl group, or a C1 to C5 haloalkyl group.

[0325] R2 includes C1 to C5 alkyl or C1 to C5 haloalkyl.

[0326] The aforementioned chain-like carboxylic acid ester solvents have high conductivity, which is beneficial for improving the fast charging capability of battery cells.

[0327] Optionally, R1 includes a hydrogen atom, a C1 to C3 alkyl group, or a C1 to C3 haloalkyl group. Further optionally, R1 includes a hydrogen atom, a halogen atom, a C1 to C2 alkyl group, or a C1 to C2 haloalkyl group.

[0328] Optionally, R2 comprises a C1 to C3 alkyl group or a C1 to C3 haloalkyl group. More optionally, R2 comprises a C1 to C2 alkyl group or a C1 to C2 haloalkyl group.

[0329] In the above embodiments, the halogenated alkyl group includes one or more of fluoroalkyl, chloroalkyl, bromoalkyl and iodoalkyl groups, and optionally, the halogenated alkyl group includes fluoroalkyl.

[0330] For example, the chain carboxylic acid ester solvent includes one or more compounds of formula I-1 to formula I-8.

[0331] In some embodiments, the organic solvent includes carbonate solvents.

[0332] The combined use of carbonate solvents and chain carboxylic acid ester solvents improves the conductivity of the electrolyte, which is beneficial for lithium ion migration and improves the fast charging capability of individual battery cells.

[0333] Optionally, the carbonate solvent in the electrolyte contains 65% to 75% by mass. For example, the carbonate solvent contains 65%, 70%, 75% by mass, or any combination of two of the above values.

[0334] When the mass content of carbonate solvents and chain carboxylic acid ester solvents meets the above conditions, the stability of the electrolyte can be improved, its gas production can be reduced, and its cycle performance can be improved.

[0335] For example, carbonate solvents include one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0336] In some embodiments, the electrolyte salt includes a lithium salt, which includes one or more of lithium fluorosulfonylimide and lithium hexafluorophosphate. Optionally, the lithium salt includes lithium fluorosulfonylimide and lithium hexafluorophosphate.

[0337] Lithium hexafluorophosphate may decompose to produce hydrofluoric acid (HF). The hydrofluoric acid reacts with the negative electrode, especially the silicon-containing negative electrode, which may lead to increased gas production during high-temperature storage. The combined use of lithium hexafluorophosphate and lithium fluorosulfonylimide can reduce the hydrofluoric acid content, slow down the side reactions at the negative electrode interface, reduce the amount of gas produced during high-temperature storage, and improve the cycle performance of the battery cells. Furthermore, the increased lithium-ion transference number and lithium-ion conductivity can enhance the fast charging capability of the battery cells.

[0338] For example, lithium fluorosulfonylimide includes one or more of lithium trifluorosulfonylimide and lithium difluorosulfonylimide, optionally lithium difluorosulfonylimide.

[0339] In some embodiments, based on the mass of the electrolyte, the mass content of the lithium salt is greater than 0 and less than or equal to 18%, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, or a range of any two of the above values. Optionally, the mass content of the lithium salt is from 4% to 16%.

[0340] For example, the sum of the mass content of lithium difluorosulfonylimide and the mass content of lithium hexafluorophosphate is greater than 0 and less than or equal to 18%, optionally from 4% to 16%.

[0341] In some embodiments, the ratio of the mass content of lithium fluorosulfonylimide to the mass content of lithium hexafluorophosphate is 0.2 to 1.5, based on the mass of the electrolyte, for example, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, or any range of two of the above values. Optionally, the ratio of the mass content of lithium fluorosulfonylimide to the mass content of lithium hexafluorophosphate is 0.4 to 0.8.

[0342] When the mass ratio of lithium hexafluorophosphate to lithium difluorosulfonylimide meets the above range, on the one hand, the content of hydrofluoric acid can be reduced, the side reaction at the negative electrode interface can be slowed down, and the gas production at high temperature storage can be reduced; on the other hand, the organic component content of the interfacial film formed at the negative electrode interface is appropriate, which can also reduce the gas production at high temperature storage and improve cycle performance.

[0343] In some embodiments, the electrolyte further includes additives, including one or more of carbonate additives, sulfur-containing additives, and lithium salt additives. These additives can improve the interfacial film performance on the negative electrode side, resulting in a more stable interfacial film with relatively low impedance, which is beneficial for improving the fast-charging performance of the battery cell and enhancing cycle performance.

[0344] In some embodiments, the additive content in the electrolyte is from 0.5% to 10% by mass. Exemplarily, the additive content in the electrolyte is 0.5%, 1%, 2%, 3%, 3.5%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a range of any two of the above values. Optionally, the additive content in the electrolyte is from 2% to 6% by mass, and more preferably from 2% to 5%.

[0345] The additives mentioned above can effectively improve the interfacial film performance on the positive and / or negative electrode sides, which is beneficial to improving the fast charging performance of battery cells and improving cycle performance.

[0346] In some embodiments, the carbonate additive includes one or more of fluoroethylene carbonate and vinylene carbonate; alternatively, the additive comprises fluoroethylene carbonate and vinylene carbonate.

[0347] Fluorinated ethylene carbonate can form an interface film rich in lithium fluoride (LiF) on the negative electrode surface, which can alleviate the volume expansion of silicon, improve the lifespan of silicon-containing systems, and reduce high-temperature gas production.

[0348] The combined use of fluoroethylene carbonate and vinylene carbonate results in a denser interfacial film on the negative electrode surface, which can more effectively protect the silicon-containing negative electrode, reduce the degree of side reactions at the negative electrode interface, and reduce the amount of gas produced at high temperatures.

[0349] For example, sulfur-containing additives include one or more of vinyl sulfate, vinyl disulfate, butene sulfite, 1,3-propanesulfonate lactone, vinyl sulfite, and methylene disulfonate.

[0350] Optionally, the lithium salt additives include one or more of lithium difluorophosphate, lithium difluorooxalate borate, lithium tetrafluoroborate, and lithium dioxalate borate.

[0351] In the embodiments of this application, the types and contents of inorganic components / lithium salts in the electrolyte are known in the art and can be detected using equipment and methods known in the art. For example, the inorganic components / lithium salts in the electrolyte can be qualitatively or quantitatively analyzed by ion chromatography analysis method according to standard JY / T020-1996 "General Rules for Ion Chromatography Analysis". In the embodiments of this application, freshly prepared electrolyte can be used as a sample, the free electrolyte of a fresh battery can be used as a sample, or a battery that has been completely discharged (discharged to the lower limit cutoff voltage so that the battery's state of charge is about 0% SOC) can be disassembled in reverse, and the free electrolyte obtained from the battery can be used as a sample for detection by ion chromatography analysis method.

[0352] In the embodiments of this application, the types and contents of organic components in the electrolyte are known in the art and can be detected using equipment and methods known in the art. For example, the organic components in the electrolyte can be qualitatively and quantitatively analyzed by gas chromatography using GB / T9722-2006 "General Rules for Gas Chromatography of Chemical Reagents".

[0353] In the embodiments of this application, after quantitative and qualitative detection of each component in the electrolyte, each component is classified. Chain carboxylic acid ester solvents and carbonate solvents (ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate) are taken as components of organic solvents. The mass content of each component is calculated based on the mass of the electrolyte as 100%.

[0354] Carbonate additives (such as fluorocyclic carbonates and vinylene carbonates) are used as additives in the electrolyte. The mass content of each component is calculated based on the mass of the electrolyte as 100%.

[0355] Isolation component

[0356] In some embodiments, the electrode assembly further includes a spacer disposed between the positive electrode and the negative electrode.

[0357] In some embodiments, the separator is a separator membrane. This application does not impose any particular limitation on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0358] As an example, the main material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and ceramic. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation. The separator can be a single component located between the positive and negative electrodes, or it can be attached to the surfaces of the positive and negative electrodes. An inorganic particle coating, an organic particle coating, or an organic / inorganic composite coating can also be applied to the surface of the separator.

[0359] In some embodiments, the volumetric energy density of the battery cell is between 350 Wh / L and 430 Wh / L. Exemplarily, the volumetric energy density of the battery cell is 350 Wh / L, 370 Wh / L, 380 Wh / L, 390 Wh / L, 400 Wh / L, 410 Wh / L, 420 Wh / L, 430 Wh / L, or a range of any two of the above values. The volumetric energy density of the battery cell is relatively high.

[0360] In the embodiments of this application, the volumetric energy density of a single battery cell has a meaning known in the art and can be detected using equipment and methods known in the art. For example, the following description uses a battery charging upper limit voltage of 3.8V and a battery discharging cutoff voltage of 2.0V as an example.

[0361] Place the battery cell at 25°C and charge it to 3.8V with a constant current of 0.05C, then discharge it to 2.0V with a constant current of 0.33C. Record the discharge capacity A0 at this point, in Ah. Use calipers to measure the length, width, and height of the battery cell (generally calculated based on the battery casing dimensions, excluding the height of the electrode terminals and the insulating film outside the casing). Calculate the volume of the battery cell V0, in L. The volumetric energy density of the battery cell VED = (A0 × discharge plateau voltage) / V0, in Wh / L.

[0362] Example

[0363] The following embodiments describe the contents disclosed in this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of the embodiments of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0364] Example 1

[0365] 1. Preparation of positive electrode sheet

[0366] The positive electrode includes a positive current collector and a positive electrode film layer disposed on both sides of the positive current collector. The positive current collector is an aluminum foil.

[0367] The positive electrode film layer comprises lithium iron phosphate containing lithium phosphate, lithium iron phosphate, positive electrode additive lithium ferrite, binder polyvinylidene fluoride (PVDF) and conductive agent acetylene black in a mass ratio of 95:1.85:2:1.15. The positive electrode film layer is formed by uniformly coating the positive electrode slurry (solvent is N-methylpyrrolidone NMP) on both sides of the positive electrode current collector, and then drying and cold pressing it.

[0368] The volume average particle size (Dv50) of the lithium phosphate is 1.5 μm. The specific charge capacity of the positive electrode active material is 161 mAh / g. The volume average particle size (Dv50) of the positive electrode additive is 9.5 μm.

[0369] The single-sided coating weight of the positive electrode film is 284 mg / 1540.25 mm. 2 The length of the positive electrode film is 592 mm.

[0370] 2. Preparation of negative electrode sheet

[0371] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on both sides of the negative current collector. The negative current collector is a copper foil.

[0372] The negative electrode film is formed by uniformly coating the negative electrode slurry (with deionized water as the solvent) onto the surface of the negative electrode current collector, followed by drying and cold pressing.

[0373] The single-sided coating weight of the negative electrode film is 135 mg / 1540.25 mm. 2 .

[0374] The negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer. The first negative electrode film layer is located on the surface of the negative electrode current collector, and the second negative electrode film layer is located on the surface of the first negative electrode film layer.

[0375] The first negative electrode film layer includes negative electrode active material, conductive agent, negative electrode binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose in a mass ratio of 96.3:0.5:2.5:0.7. The negative electrode active material of the first negative electrode film layer includes artificial graphite and silicon carbide.

[0376] The second negative electrode film layer includes a negative electrode active material, a conductive agent, a negative electrode binder styrene-butadiene rubber, and a thickener sodium carboxymethyl cellulose in a mass ratio of 97.8:0.7:0.8:0.7. The negative electrode active material of the second negative electrode film layer includes artificial graphite and silicon carbide, and the average particle size of artificial graphite is 10 μm.

[0377] A cross-section along the thickness direction of the negative electrode film shows that the average particle size of the artificial graphite in the first negative electrode film is 13 μm, and the average particle size of the artificial graphite in the second negative electrode film is 10 μm. During the preparation of the negative electrode film, the desired average particle size can be obtained by repeatedly adjusting the volume average particle size of the artificial graphite.

[0378] The thickness ratio of the first negative electrode film to the second negative electrode film is 1; the conductive agents in both the first and second negative electrode films include conductive carbon and carbon nanotubes, and the mass ratio of conductive carbon to carbon nanotubes in both the first and second negative electrode films is 5:1.

[0379] The silicon content in the negative electrode film is 3.0% by mass. The specific charging capacity of the negative electrode active material is 420 mAh / g.

[0380] 3. Isolation components

[0381] The separator includes a base film, which is a 7μm polyethylene film layer with a porosity of 42%.

[0382] 4. Preparation of electrolyte

[0383] The electrolyte consists of an organic solvent, a lithium salt, and additives. The components of the organic solvent are mixed, and then the lithium salt and additives are added to prepare the electrolyte.

[0384] The organic solvents include 15% chain carboxylic acid ester solvents (ethyl acetate) and 68.5% carbonate solvents (ethylene carbonate). The mass content of each component in the organic solvents is calculated based on the mass of the electrolyte.

[0385] Based on the mass of the electrolyte, the additive contains 2.5% vinylene carbonate (VC) by mass.

[0386] The lithium salt comprises 10% lithium hexafluorophosphate (LiPF6) and 4% lithium difluorosulfonylimide.

[0387] 5. Preparation of battery cells

[0388] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation, resulting in a stacked electrode assembly. This assembly is then placed in an outer packaging shell, dried, and injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a battery cell is obtained. The compaction density of the positive electrode film at 100% SOC is 2.62 g / cm³. 3 The compaction density of the negative electrode film at 0% SOC is 1.30 g / cm³. 3 .

[0389] Comparative Example 1-1 and Comparative Example 1-2

[0390] Battery cells were prepared using a method similar to that in Example 1, except that the coating weight of the positive and negative electrode films on one side was adjusted.

[0391] Examples 2-1 to 2-4

[0392] Battery cells were prepared using a method similar to that in Example 1, except that the coating weight of the positive and negative electrode films on one side was adjusted.

[0393] Examples 2-5 and Examples 2-6

[0394] Battery cells were prepared using a method similar to that of Example 1, except that the compaction density of the positive and negative electrode films was adjusted.

[0395] Performance testing

[0396] 1. DC resistance (DCR) test of individual battery cells

[0397] You can refer to the methods in GB / T 31467 "Performance Test Specification for High-Power Lithium-ion Power Batteries for HEVs".

[0398] For example, at 25°C, charge a single battery cell to 3.65V with a constant current of 0.33C, let it stand for 1 minute, then charge it to 3.65V with a constant current of 0.1C, let it stand for 30 minutes, and then discharge it to 2.0V with a constant current of 0.33C. Record the discharge capacity A0 at this point in Ah. Then charge it to 0.5A0Ah with a constant current of 0.33C and adjust the SOC to 50%.

[0399] After placing the battery cell at 25°C for 2 hours, it was discharged at a current of 4C for 10 seconds, and ΔU was recorded. 放电 ΔI 放电 The discharge DCR data of a single battery cell is calculated using the following formula, R. 放电 =ΔU 放电 / ΔI 放电 ,

[0400] Wherein, ΔU 放电 ΔI represents the voltage change within 10 seconds of the start of discharge. 放电 This indicates the current value within 10 seconds of the start of discharge.

[0401] 2. High-temperature cycle performance test of individual battery cells

[0402] At 60±5℃, the battery cell is charged at a constant current of 1C to 3.65V, then charged at a constant voltage to the cutoff current of 0.05C, and then discharged at a constant current of 1C to 2.0V. This constitutes one charge-discharge cycle.

[0403] The discharge capacity recorded is denoted as C1, the discharge capacity of the lithium-ion battery cell in the first cycle. This cyclic step is repeated for the same battery cell. After n cycles, the discharge capacity Cn of the nth cycle is recorded. The cycle capacity retention rate of the battery cell is calculated as Cn / C1*100%, and the number of cycles when the cycle capacity retention rate reaches 80% is recorded. For accuracy, the average value of 5 parallel samples is taken as the test result.

[0404] 3. Room temperature cycle performance test of individual battery cells

[0405] At 25±5℃, the battery cells are charged with a constant current using Stercharge:

[0406] Charge from 0% SOC to 20% SOC at a constant current of 0.33C;

[0407] Charge from 20% SOC to 25% SOC at a constant current of 8C.

[0408] Charge from 25% SOC to 30% SOC at a constant current of 8C.

[0409] Charge from 30% SOC to 35% SOC at a constant current of 7.5C;

[0410] Charge from 35% SOC to 40% SOC at a constant current of 6.87C;

[0411] Charge from 40% SOC to 45% SOC at a constant current of 6.38C;

[0412] Charge from 45% SOC to 50% SOC at a constant current of 5.95C;

[0413] Charge from 50% SOC to 55% SOC at a constant current of 5.53C;

[0414] Charge from 55% SOC to 60% SOC at a constant current of 5.14C;

[0415] Charge from 60% SOC to 65% SOC at a constant current of 4.76C;

[0416] Charge from 65% SOC to 70% SOC at a constant current of 4.36C;

[0417] Charge from 70% SOC to 75% SOC at a constant current of 3.94C;

[0418] Charge from 75% SOC to 80% SOC at a constant current of 3.57C;

[0419] Charge from 80% SOC to 85% SOC using 2C constant current;

[0420] Charge from 90% SOC to 95% SOC at a constant current of 1C.

[0421] Charge from 95% SOC to 98% SOC at a constant current of 0.5C;

[0422] Charge from 98% SOC to 100% SOC at a constant current of 0.25C.

[0423] The charging cutoff voltage is set at a constant current of 0.1C.

[0424] Then, constant current discharge is performed at 1C until the discharge cutoff voltage is reached, which constitutes one charge-discharge cycle.

[0425] The discharge capacity in this cycle is recorded as C1, the discharge capacity of the battery cell in the first cycle. This cyclic step is repeated for the same battery cell. After n cycles, the discharge capacity Cn of the nth cycle is recorded. The cycle capacity retention rate of the battery cell is calculated as Cn / C1*100%, and the number of cycles when the cycle capacity retention rate is 80% is recorded. For accuracy, the average value of 5 parallel samples is taken as the test result.

[0426] 4. Fast charging time test of individual battery cells from 20% to 80% SOC

[0427] At 25±5℃, the battery cells are charged with a constant current using Stercharge:

[0428] Charge from 0% SOC to 20% SOC at a constant current of 0.33C;

[0429] Charge from 20% SOC to 25% SOC at a constant current of 8C.

[0430] Charge from 25% SOC to 30% SOC at a constant current of 8C.

[0431] Charge from 30% SOC to 35% SOC at a constant current of 7.5C;

[0432] Charge from 35% SOC to 40% SOC at a constant current of 6.87C;

[0433] Charge from 40% SOC to 45% SOC at a constant current of 6.38C;

[0434] Charge from 45% SOC to 50% SOC at a constant current of 5.95C;

[0435] Charge from 50% SOC to 55% SOC at a constant current of 5.53C;

[0436] Charge from 55% SOC to 60% SOC at a constant current of 5.14C;

[0437] Charge from 60% SOC to 65% SOC at a constant current of 4.76C;

[0438] Charge from 65% SOC to 70% SOC at a constant current of 4.36C;

[0439] Charge from 70% SOC to 75% SOC at a constant current of 3.94C;

[0440] Charge from 75% SOC to 80% SOC at a constant current of 3.57C.

[0441] The test results are shown in Table 1.

[0442] Table 1

[0443] The coating weight of the positive and negative electrode films in Comparative Example 1-1 is relatively small, resulting in a lower volumetric energy density of the battery cell. The coating weight of the positive and negative electrode films in Comparative Example 1-2 is relatively high. Although the volumetric energy density of the battery cell is higher, the migration resistance of lithium ions in the positive and negative electrode films is greater, which is not conducive to the rapid charging of the battery cell at high energy density. Furthermore, the negative electrode side reaction is aggravated, and the cycle is deteriorated, especially the cycle under fast charging.

[0444] As the weight of the positive electrode film coating on one side increases, the energy density of the battery cell increases, but the DCR of the battery cell also increases, which is not conducive to the fast charging of the battery cell.

[0445] In the embodiments 2-1 to 2-4 of this application, the single-sided coating weight of the positive electrode film is 150 mg / 1540.25 mm. 2 Up to 370mg / 1540.25mm 2 The single-sided coating weight of the negative electrode film is 70 mg / 1540.25 mm. 2 Up to 175mg / 1540.25mm 2 This results in relatively high energy density in individual battery cells, and the migration resistance of lithium ions is not too high, which can effectively improve the cycle performance under fast charging conditions and high temperature cycle performance.

[0446] Furthermore, the charging time for the battery cells in the embodiments from 20% SOC to 80% SOC is relatively short, for example, 7 minutes in Embodiment 1 and 14 minutes in Embodiments 2-4. The charging time is relatively short, which can achieve the effect of fast charging.

[0447] Examples 2-5 and 2-6, by setting the compaction density of the positive and negative electrode films within an appropriate range, can effectively improve the volumetric energy density of the battery cells, and can effectively improve the cycle performance of the battery cells under high energy density and fast charging conditions, and is also beneficial to improving the cycle performance under fast charging conditions.

[0448] Comparative Example 2-1

[0449] Battery cells were prepared using a method similar to that of Example 1. The difference from Example 1 is that the negative electrode film did not contain silicon, and the single-sided coating weight of the negative electrode film was adjusted.

[0450] Comparative Example 2-2

[0451] Battery cells were prepared using a method similar to that of Example 1, except that the mass content of silicon was adjusted.

[0452] Examples 3-1 to 3-3

[0453] Battery cells were prepared using a method similar to that of Example 1, except that the mass content of silicon was adjusted.

[0454] Examples 3-4

[0455] Battery cells were prepared using a method similar to that of Example 1, except that the mass content of silicon and the single-sided coating weight of the negative electrode film were adjusted.

[0456] Example 4

[0457] Battery cells were prepared using a method similar to that of Example 1, except that the material of the silicon-based material was adjusted.

[0458] The test results are shown in Table 2.

[0459] Table 2

[0460] Comparative Example 2-1 did not add silicon-based materials. At a higher energy density, the coating weight of the negative electrode film was relatively high, and the migration resistance of active ions on the negative electrode side was relatively large, which was not conducive to fast charging.

[0461] In Comparative Example 2-2, the addition of silicon-based materials was relatively high, which made the side reactions on the negative electrode side more serious, and the gas production was aggravated, especially at high temperature, which worsened the cycle.

[0462] In this application, embodiments 3-1 to 3-4 regulate the mass content of silicon element so that the mass content of silicon element is within an appropriate range and the coating weight is appropriate, which can effectively improve the cycle performance and fast charging performance of battery cells under high energy density.

[0463] For example, in Examples 3-4, when the silicon content is 10%, the single-sided coating weight of the negative electrode film is 80 mg / 1540.25 mm. 2 This ensures that the volumetric energy density of the battery cell is not too low. Furthermore, the thin coating thickness of the negative electrode film results in a shorter lithium-ion migration path, which is beneficial to improving the fast charging capability of the battery cell. Moreover, the low overall coating amount of the negative electrode film reduces the total amount of negative electrode active material participating in side reactions, thus improving cycle life.

[0464] As the mass content of silicon increases, the specific charging capacity of the negative electrode active material increases. For example, in Examples 3-3, the specific charging capacity of the negative electrode active material can reach 534 mAh / g.

[0465] This application is applicable to silicon-based materials of different materials, such as silicon-carbon materials and silicon-oxygen materials, which can effectively improve the cycle performance of battery cells and are beneficial to improving the fast charging performance of battery cells. Compared with the silicon-oxygen material in Example 4, the silicon-carbon material has relatively small volume expansion during the charging and discharging process and has better cycle performance.

[0466] Examples 5-1 to 5-2

[0467] Battery cells were prepared using a method similar to that of Example 1, except that the average particle size of the carbon-based material in the negative electrode film was adjusted.

[0468] Examples 6-1 and 6-2

[0469] Battery cells were prepared using a method similar to that of Example 1, except that the composition and mass content of the negative electrode conductive agent in the negative electrode film were adjusted.

[0470] The test results are shown in Table 3.

[0471] Table 3

[0472] A portion of the first negative electrode film is designated as the first region, and a portion of the second negative electrode film is designated as the second region. The average particle size of the carbon-based material is observed on a cross-section along the thickness direction of the negative electrode film, and the average particle size of the first region and the second region are recorded and statistically analyzed.

[0473] The negative electrode film can be coated with a single layer or a double layer. In Examples 5-1 and 5-2, by differentiating the average particle size of the carbon-based materials in the first and second regions, the porosity of the negative electrode film can be effectively controlled, improving the fast charging capability of the battery cell at high energy density, reducing the risk of lithium plating, and improving cycle life.

[0474] Examples 6-1 and 6-2, by controlling the mass content of the negative electrode conductive agent in the negative electrode film, show that as the mass content of the negative electrode conductive agent increases, the conductivity of the negative electrode sheet increases, which can reduce the DCR of the battery cell and effectively improve the fast charging capability of the battery cell at high energy density. However, excessive mass content of the negative electrode conductive agent will reduce the proportion of negative electrode active material, which is not conducive to improving energy density.

[0475] Comparative Example 3-1 and Comparative Example 3-2

[0476] Battery cells were prepared using a method similar to that of Example 1, except that the composition of the electrolyte was adjusted.

[0477] Examples 7-1 and 7-2

[0478] Battery cells were prepared using a method similar to that of Example 1, except that the composition of the electrolyte was adjusted.

[0479] The test results are shown in Table 4.

[0480] Table 4

[0481] In Table 4,

[0482] In Comparative Example 3-1, the mass content of chain carboxylic acid ester solvents is relatively low, resulting in low electrolyte conductivity, high DCR of battery cells, and relatively high lithium-ion transport resistance, which is not conducive to fast charging.

[0483] In Comparative Example 3-2, the mass content of chain carboxylic acid ester solvents was relatively high, and the conductivity of the electrolyte was high, which was beneficial to reducing the DCR of the battery cells. However, the side reactions between the above solvents and the negative electrode active materials were more serious, and gas production was aggravated, especially at high temperatures, which worsened the cycle.

[0484] The chain carboxylic acid ester solvent in this application embodiment has a mass content within an appropriate range, which can effectively improve the conductivity of the electrolyte, improve the lithium-ion transport capability, and improve the fast charging performance of the battery cell; moreover, the electrolyte composition is relatively stable, which can improve cycle performance; it should be noted that the change of electrolyte composition has little effect on energy density, and energy density is not shown in the table.

[0485] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the implementation of the present application, and that changes, substitutions and modifications can be made to the embodiments without departing from the spirit, principles and scope of the implementation of the present application.

Claims

A single battery cell, comprising: A positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector. The positive electrode film layer includes lithium phosphate, and the single-sided coating weight of the positive electrode film layer is 150 mg / 1540.25 mm. 2 Up to 370mg / 1540.25mm 2 ; A negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The negative electrode film layer includes a carbon-based material and a silicon-based material. The silicon content of the silicon-based material in the negative electrode film layer is 0.3% to 10% by mass. The single-sided coating weight of the negative electrode film layer is 70 mg / 1540.25 mm. 2 Up to 175mg / 1540.25mm 2 ;as well as The electrolyte includes a chain-like carboxylic acid ester solvent, wherein the chain-like carboxylic acid ester solvent comprises 5% to 35% by mass in the electrolyte. According to claim 1, the battery cell, wherein, The single-sided coating weight of the positive electrode film is 200 mg / 1540.25 mm. 2 Up to 300mg / 1540.25mm 2 ; and / or The single-sided coating weight of the negative electrode film is 95 mg / 1540.25 mm. 2 Up to 142mg / 1540.25mm 2 . The battery cell according to claim 1 or 2, wherein, When the battery cell is 100% charged, the compaction density of the positive electrode film is 2.50 g / cm³. 3 Up to 2.80 g / cm 3 ; and / or When the battery cell is 100% charged, the compaction density of the negative electrode film is 1.5 g / cm³. 3 Up to 1.7 g / cm 3 . The battery cell according to any one of claims 1 to 3, wherein, The specific charge capacity of the positive electrode active material is 150 mAh / g to 170 mAh / g; and / or The charge capacity of the negative electrode active material is from 350 mAh / g to 540 mAh / g. The battery cell according to any one of claims 1 to 4, wherein, The silicon content of the silicon-based material in the negative electrode film layer is 3% to 6% by mass. The battery cell according to any one of claims 1 to 5, wherein, The silicon-based material includes one or more of silicon carbide and silicon oxide. The battery cell according to any one of claims 1 to 6, wherein, The negative electrode film layer includes: A first region is disposed on the surface of the negative electrode current collector, and the thickness of the first region is 1 / 3 of the thickness of the negative electrode film layer; and The second region is connected to the side of the first region opposite to the negative electrode current collector, and the thickness of the second region is 1 / 3 of the thickness of the negative electrode film. in, The average particle size of the carbon-based material in the first region is greater than or equal to the average particle size of the carbon-based material in the second region. According to claim 7, the battery cell, wherein, The average particle size of the carbon-based material in the first region is 10 μm to 20 μm; and / or The average particle size of the carbon-based material in the second region is 5 μm to 12 μm. The battery cell according to claim 7 or 8, wherein, The carbon-based material in the first region includes at least one of artificial graphite and natural graphite, and the carbon-based material in the second region includes artificial graphite. The battery cell according to any one of claims 7 to 9, wherein, At least one of the first region and the second region comprises a silicon-based material. The battery cell according to any one of claims 1 to 10, wherein, The negative electrode film layer includes: A first negative electrode film layer is disposed on the surface of the negative electrode current collector; and The second negative electrode film layer is connected to the side of the first negative electrode film layer that is away from the negative electrode current collector. The battery cell according to any one of claims 1 to 11, wherein, The negative electrode film layer includes a negative electrode conductive agent, which includes one or more of conductive carbon and carbon nanotubes. According to claim 12, the battery cell, wherein, The conductive carbon in the negative electrode film layer has a mass content of 0.4% to 0.7%; and / or The carbon nanotubes in the negative electrode film layer have a mass content of 0.1% to 1%. The battery cell according to any one of claims 1 to 13, wherein, The electrolyte has a conductivity of 10.5 mS / cm to 13.5 mS / cm at room temperature; and / or The electrolyte has a viscosity of 1.5 mPa·s to 5.5 mPa·s at room temperature; and / or The electrolyte has a density of 1.05 g / mL to 1.35 g / mL at room temperature. The battery cell according to any one of claims 1 to 14, wherein, The chain-like carboxylic acid ester solvent has a mass content of 8% to 20% in the electrolyte. The battery cell according to any one of claims 1 to 15, wherein, The chain-like carboxylic acid ester solvents include compounds represented by Formula I. In formula I, R1 includes a hydrogen atom, a C1 to C5 alkyl group, or a C1 to C5 haloalkyl group. R2 includes C1 to C5 alkyl or C1 to C5 haloalkyl. According to claim 16, the battery cell, wherein, The chain-like carboxylic acid ester solvents include one or more compounds from Formula I-1 to Formula I-8. The battery cell according to any one of claims 1 to 17, wherein, The electrolyte includes a carbonate solvent, and the carbonate solvent accounts for 65% to 75% of the electrolyte by mass. According to claim 18, the battery cell, wherein, The carbonate solvents include one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. The battery cell according to any one of claims 1 to 19, wherein, The lithium-containing phosphate includes lithium iron phosphate. The battery cell according to any one of claims 1 to 20, wherein, The positive electrode film has a dimension of 265 mm to 655 mm along its length. A battery device comprising a battery cell as described in any one of claims 1 to 21. An electrical device comprising the battery device as described in claim 22.

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