Battery cell, battery apparatus and electrical apparatus

Abstract

The present application relates to a battery cell, a battery apparatus and an electrical apparatus. The battery cell comprises a positive electrode sheet, a negative electrode sheet and an electrolyte. The positive electrode sheet comprises a positive electrode current collecting portion and a positive electrode film layer, the positive electrode film layer comprising a lithium-containing phosphate. The negative electrode sheet comprises a negative electrode current collecting portion and a negative electrode film layer, the negative electrode film layer comprising a carbon-based material and a silicon-based material, and the mass content of silicon elements of the silicon-based material in the negative electrode film layer being 0.3% to 10%. The electrolyte comprises a linear carboxylic ester solvent and an additive, the mass content of the linear carboxylic ester solvent in the electrolyte being 5% to 35%; the additive comprises one or more of a carbonate additive, a sulfur-containing additive and a lithium salt additive, the mass content of the additive in the electrolyte being 0.5% to 10%. The fast charging capability and cycle performance of the battery cell of the present application can be further improved.

Description

Battery cell, battery device and electric device TECHNICAL FIELD

[0001] The present application relates to a battery cell, a battery device and an electric device. BACKGROUND

[0002] Battery cells have characteristics such as high capacity and long service life, and are therefore widely used in electronic devices such as mobile phones, notebook computers, electric vehicles, electric cars, electric planes, electric ships, electric toy cars, electric toy ships, electric toy planes and electric tools. Due to the great progress made in batteries, higher requirements are placed on the performance of batteries. However, the rapid charging capability and cycle performance of battery cells need to be further improved. SUMMARY

[0003] The present application provides a battery cell, a battery device and an electric device, and the rapid charging capability and cycle performance of the battery cell of the present application can be further improved.

[0004] In a first aspect, the embodiments of the present application provide a battery cell, the battery cell comprising a positive electrode sheet and a negative electrode sheet and an electrolyte, the positive electrode sheet comprising a positive electrode current collecting part and a positive electrode film layer arranged on at least one side of the positive electrode current collecting part, the positive electrode film layer comprising a lithium-containing phosphate; the negative electrode sheet comprising a negative electrode current collecting part and a negative electrode film layer arranged on at least one side of the negative electrode current collecting part, the negative electrode film layer comprising a carbon-based material and a silicon-based material, the mass content of silicon in the silicon-based material in the negative electrode film layer being 0.3% to 10%; the electrolyte comprising a chain carboxylic acid ester solvent and an additive, the mass content of the chain carboxylic acid ester solvent in the electrolyte being 5% to 35%; the additive comprising one or more of a carbonate additive, a sulfur-containing additive and a lithium salt additive, the mass content of the additive in the electrolyte being 0.5% to 10%.

[0005] Thus, the negative electrode sheet of the embodiments of the present application comprises a silicon-based material, which can make the coating thickness of the negative electrode sheet relatively thin at a preset energy density, and can shorten the migration path of active ions in the negative electrode film layer; and when the mass content of the chain carboxylic acid ester solvent of the electrolyte is in the above range, on the one hand, the migration rate of active ions in the electrolyte is relatively fast; on the other hand, the interface side reaction between the negative electrode active material and the electrolyte can be alleviated, the high-temperature gas production can be reduced, and the cycle performance of the battery cell can be improved; further, the electrolyte further comprises an additive, the additive can repair the SEI film on the negative electrode side, and the impedance of the formed SEI film is relatively low, which can effectively improve the rapid charging capability and cycle performance of the battery cell.

[0006] In some embodiments, the mass content of silicon element in the silicon-based material is 3% to 6% in the negative electrode film layer. When the mass content of silicon element is in the above range, the capacity of the negative electrode active material can be improved, which is beneficial to improve the energy density of the battery cell; and in the charging and discharging process, the volume expansion of the silicon element is not too large, which is beneficial to maintain the stability of the negative electrode SEI film and improve the cycle performance of the battery cell.

[0007] In some embodiments, the silicon-based material includes one or more of silicon carbide and silicon oxide.

[0008] In some embodiments, the negative electrode film layer includes a first region and a second region, the first region is arranged 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; the second region is connected to the side of the first region away from the negative electrode current collector, and the thickness of the second region is 1 / 3 of the thickness of the negative electrode film layer, wherein 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 particle size difference between the first region and the second region can improve the rapid charging performance of the battery cell.

[0009] 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 in the above range, on the one hand, the solid-phase transmission path of lithium ions can be shortened, and the rapid charging performance can be improved, and on the other hand, the material is not easy to agglomerate during preparation, and the stability of the material can be improved.

[0010] In some embodiments, the average particle size of the carbon-based material in the second region is 5 μm to 12 μm. When the average particle size of the carbon-based material in the second region is in the above range, it is beneficial to improve the rapid charging capacity of the battery cell and improve the stability of the material.

[0011] 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. The above material setting is beneficial to form the pore difference between the first region and the second region, and improve the rapid charging capacity of the battery cell.

[0012] In some embodiments, at least one of the first region and the second region includes a silicon-based material. The silicon-based material is beneficial to improve the energy density of the battery cell.

[0013] 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 arranged 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 away from the negative electrode current collector. The double-layer film layer is beneficial to improve the rapid charging capacity and the energy density of the battery cell.

[0014] In some embodiments, the negative electrode film layer comprises a negative electrode conductive agent, and the negative electrode conductive agent comprises one or more of conductive carbon and carbon nanotubes. The negative electrode conductive agent can improve the electrical conductivity of the negative electrode film layer and improve the rapid charging capability.

[0015] In some embodiments, the mass content of the conductive carbon in the negative electrode film layer is 0.4% to 0.7%. When the mass content of the conductive carbon is in the above range, the electrical conductivity of the negative electrode film layer can be improved, and the rapid charging capability can be improved.

[0016] In some embodiments, the mass content of the carbon nanotubes in the negative electrode film layer is 0.1% to 1%. When the mass content of the carbon nanotubes is in the above range, the electrical conductivity of the negative electrode film layer can be improved, and the rapid charging capability can be improved.

[0017] In some embodiments, the electrical conductivity of the electrolyte at room temperature is 10.5 mS / cm to 13.5 mS / cm. When the electrical conductivity of the electrolyte is in the above range, the migration rate of lithium ions in the electrolyte is higher, which can further reduce the internal resistance of the battery cell and improve the rapid charging performance of the battery cell.

[0018] In some embodiments, the viscosity of the electrolyte at room temperature is 1.5 mPa·s to 5.5 mPa·s. When the viscosity of the electrolyte is in the above range, the migration rate of lithium ions in the electrolyte is higher, which can further reduce the internal resistance of the battery cell and improve the rapid charging performance of the battery cell.

[0019] In some embodiments, the density of the electrolyte at room temperature is 1.05 g / mL to 1.35 g / mL. When the density of the electrolyte is in the above range, the migration rate of lithium ions in the electrolyte is higher, which can further reduce the internal resistance of the battery cell and improve the rapid charging performance of the battery cell.

[0020] In some embodiments, the mass content of the chain carboxylic acid ester solvent in the electrolyte is 8% to 20%. When the mass content of the chain carboxylic acid ester solvent is in the above range, the rapid charging capability and the cycle performance of the battery cell can be improved.

[0021] In some embodiments, the chain carboxylic acid ester solvent comprises a compound represented by Formula I,

[0022] In Formula I,

[0023] R1 comprises a hydrogen atom, a C1 to C5 alkyl group, or a C1 to C5 halogenated alkyl group,

[0024] R2 comprises a C1 to C5 alkyl group or a C1 to C5 halogenated alkyl group.

[0025] The above chain carboxylate solvents have high conductivity, which is beneficial to improve the rapid charging capability of the battery cell.

[0026] In some embodiments, the chain carboxylate solvent includes one or more of compounds shown in formula I-1 to formula I-8.

[0027] In some embodiments, the electrolyte further includes a carbonate solvent, and the mass content of the carbonate solvent in the electrolyte is 65% to 75%.

[0028] When the mass content of the carbonate solvent and the chain carboxylate solvent meets the above conditions, the stability of the electrolyte can be improved, the high-temperature gas production is reduced, and the high-temperature cycle performance is improved.

[0029] In some embodiments, the carbonate solvent includes one or more of vinyl carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

[0030] In some embodiments, the mass content of the additive in the electrolyte is 2% to 6%. The additive with the above mass content can effectively improve the SEI film performance on the negative electrode side, which is beneficial to improve the rapid charging performance and the cycle performance of the battery cell.

[0031] In some embodiments, the carbonate additive includes one or more of fluorinated vinyl carbonate and vinylene carbonate.

[0032] In some embodiments, the sulfur-containing additive includes one or more of vinyl sulfate, bis-vinyl sulfate, butylene sulfite, 1,3-propane sultone, vinyl sulfite, and methyl methylene disulfonate.

[0033] In some embodiments, the lithium salt additive includes one or more of lithium difluorophosphate, lithium difluoro oxalate borate, lithium tetrafluoroborate, and lithium bis-oxalate borate.

[0034] In some embodiments, the electrolyte further includes one or more of lithium-containing fluorosulfimide and lithium hexafluorophosphate. The above lithium salt is easy to dissociate, which is beneficial to the rapid migration of lithium ions, and the electrolyte system is relatively stable and is not easy to decompose, which can improve the cycle performance of the battery cell.

[0035] In some embodiments, the lithium-containing fluorosulfimide includes one or more of lithium trifluorosulfimide and lithium bis-fluorosulfimide.

[0036] In some embodiments, the mass content of the lithium-containing fluorosulfimide and lithium hexafluorophosphate in the electrolyte is greater than 0 and less than or equal to 18%, which can be optionally 4% to 16%. The above lithium salt is beneficial to improve the cycle performance of the battery cell.

[0037] In some embodiments, the single-side coating weight of the positive electrode film layer is 150 mg / 1540.25 mm 2 to 370 mg / 1540.25 mm 2 When the single-side coating weight of the positive electrode film layer is within the above range, the heat generation per unit area of the positive electrode tab will not be too large, and it is beneficial to reduce the polarization phenomenon under large-rate charging, and it can balance the improvement of the energy density and the fast charging performance of the battery monomer.

[0038] In some embodiments, the single-side coating weight of the negative electrode film layer is 80 mg / 1540.25 mm 2 to 135 mg / 1540.25 mm 2 When the single-side coating weight of the negative electrode film layer is within the above range, it is beneficial to improve the energy density of the battery monomer in cooperation with the appropriate mass content of silicon element, and the migration rate of active ions in the negative electrode film layer is faster, and it is beneficial to reduce the polarization phenomenon under large-rate charging, and it is beneficial to improve the fast charging capability of the battery monomer.

[0039] In a second aspect, the embodiments of the present application further provide a battery device, which comprises the battery monomer of any of the embodiments of the first aspect of the present application.

[0040] In a third aspect, the embodiments of the present application further provide a power utilization device, which comprises the battery device of any of the embodiments of the second aspect or the third aspect of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0041] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can be obtained by the drawings without creative labor for those skilled in the art.

[0042] FIG. 1 is a structural schematic diagram of a power utilization device provided by some embodiments of the present application.

[0043] FIG. 2 is a structural schematic diagram of a battery pack provided by some embodiments of the present application.

[0044] FIG. 3 is a structural schematic diagram of a battery module provided by some embodiments of the present application.

[0045] FIG. 4 is a structural schematic diagram of a battery monomer provided by some embodiments of the present application.

[0046] FIG. 5 is a structural schematic diagram of an electrode assembly of a battery monomer provided by some embodiments of the present application.

[0047] FIG. 6 is a structural schematic diagram of a first pole piece of a battery cell according to some embodiments of the present application;

[0048] FIG. 7 is a structural schematic diagram of a first pole piece of a battery cell according to some other embodiments of the present application;

[0049] FIG. 8 is a structural schematic diagram of a first pole piece of a battery cell according to yet some other embodiments of the present application;

[0050] FIG. 9 is a structural schematic diagram of a first pole piece of a battery cell according to yet some other embodiments of the present application;

[0051] FIG. 10 is a structural schematic diagram of a first pole piece of a battery cell according to yet some other embodiments of the present application;

[0052] FIG. 11 is a structural schematic diagram of a first pole piece of a battery cell according to yet some other embodiments of the present application;

[0053] FIG. 12 is a structural schematic diagram of a first pole piece of a battery cell according to yet some other embodiments of the present application;

[0054] FIG. 13 is a structural schematic diagram of a second pole piece of a battery cell according to some embodiments of the present application;

[0055] FIG. 14 is a structural schematic diagram of a second pole piece of a battery cell according to some other embodiments of the present application;

[0056] FIG. 15 is a structural schematic diagram of a battery cell according to some other embodiments of the present application;

[0057] FIG. 16 is a structural schematic diagram of a battery cell according to yet some other embodiments of the present application;

[0058] FIG. 17 is a structural schematic diagram of a negative pole piece of a battery cell according to some embodiments of the present application;

[0059] FIG. 18 is a structural schematic diagram of an electrode assembly of a battery cell according to some embodiments of the present application.

[0060] The accompanying drawings are not necessarily drawn to scale.

[0061] 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

[0062] 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.

[0063] 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.

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

[0065] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0066] 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.

[0067] In this application, "multiple" means two or more (including two).

[0068] 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.

[0069] The battery cell can be a lithium-ion battery, a sodium-lithium-ion battery, etc., but this application does not limit this.

[0070] 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.

[0071] In view of the above problems, the embodiments of this application improve the cycle performance and reliability 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 is beneficial to improve energy density with a thinner coating thickness.

[0072] The negative electrode sheet contains silicon, which is beneficial for thin coating. Active ions such as lithium ions can migrate rapidly in the negative electrode sheet. With the addition of an appropriate amount of chain carboxylic acid ester solvent, the migration rate of lithium ions in the electrolyte can be improved, thereby improving the liquid phase transport rate of lithium ions and thus improving the fast charging capability of the battery cell.

[0073] However, silicon-containing anode active materials are more prone to side reactions with the electrolyte, leading to increased gas production. In contrast, the chain carboxylic acid ester solvent in this embodiment has a mass content of less than or equal to 35%, which allows active ions, such as lithium ions, to migrate rapidly, thereby mitigating the side reactions between the anode active material and the electrolyte and reducing gas production. The electrolyte also includes additives, which can repair the solid electrolyte interphase (SEI) film on the anode side, further mitigating the side reactions between the anode active material and the electrolyte and improving cycle performance. Moreover, the SEI film has relatively low impedance, which is beneficial for further improving the fast charging performance of the battery cell.

[0074] Therefore, the embodiments of this application can comprehensively improve the cycle performance and fast charging capability of battery cells under high energy density, and are beneficial to improving the cycle performance of battery cells under fast charging.

[0075] The battery cell described in this application is applicable to various battery devices and electrical appliances that use battery cells.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] In some implementations, a battery cell assembly is typically formed by arranging multiple battery cells.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] As shown in Figure 3, the battery module 6 includes multiple battery cells 7.

[0090] 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.

[0091] 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:

[0092] Charge from 20% SOC to 25% SOC at a constant current of 8.00C;

[0093] Charge from 25% SOC to 30% SOC at a constant current of 8.00C;

[0094] Charge from 30% SOC to 35% SOC at a constant current of 7.50C;

[0095] Charge from 35% SOC to 40% SOC at a constant current of 6.87C;

[0096] Charge from 40% SOC to 45% SOC at a constant current of 6.38C;

[0097] Charge from 45% SOC to 50% SOC at a constant current of 5.95C;

[0098] Charge from 50% SOC to 55% SOC at a constant current of 5.53C;

[0099] Charge from 55% SOC to 60% SOC at a constant current of 5.14C;

[0100] Charge from 60% SOC to 65% SOC at a constant current of 4.76C;

[0101] Charge from 65% SOC to 70% SOC at a constant current of 4.36C;

[0102] Charge from 70% SOC to 75% SOC at a constant current of 3.94C;

[0103] Charge from 75% SOC to 80% SOC at a constant current of 3.57C.

[0104] 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.

[0105] As shown in Figures 4 and 5, in some embodiments, the battery cell 7 includes an electrode assembly 10 and a housing assembly 20.

[0106] The housing assembly 20 has a receiving cavity for accommodating the electrode assembly 10 and the electrolyte.

[0107] In some embodiments, housing assembly 20 includes a housing and a terminal assembly disposed on the housing.

[0108] 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.

[0109] 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, etc.

[0110] 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.

[0111] 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 be provided one or more times.

[0112] 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.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] As an example, both the first electrode 11 and the second electrode 12 are folded to form multiple stacked folded segments.

[0119] As an example, multiple separators 13 can be provided, respectively disposed between any adjacent first electrode 11 or second electrode 12.

[0120] As an example, the spacer 13 can be continuously arranged between any adjacent first electrode 11 or second electrode 12 by folding or rolling.

[0121] 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.

[0122] In some embodiments, both the first electrode tab 11 and the second electrode tab 12 include a coating portion and an electrode ear portion. The coating portion is coated with an active material layer. The electrode ear portion is provided on at least one side of the coating portion along a first direction, and is not coated with the active material layer. The first direction is parallel to the length direction Z of the battery cell 7, or the first direction is parallel to the width direction Y of the battery cell 7.

[0123] In the embodiments of the present application, the first direction, the second direction, and the thickness direction X of the battery cell 7 are perpendicular to each other pairwise.

[0124] When the first direction is parallel to the length direction Z of the battery cell 7, the dimension of the component in this direction can be regarded as the length of the component. For example, the dimension of the coating portion along the first direction is the length of the coating portion. In this case, the second direction is parallel to the width direction Y of the battery cell 7.

[0125] When the first direction is parallel to the width direction Y of the battery cell 7, the dimension of the component in this direction can be regarded as the width of the component. For example, the dimension of the coating portion along the first direction is the width of the coating portion. In this case, the second direction is parallel to the length of the battery cell 7.

[0126] To illustrate the present application more clearly, the electrode ear portion of the first electrode tab 11 is defined as the first electrode ear 111, and the coating portion of the first electrode tab 11 is defined as the first coating portion 112. The electrode ear portion of the second electrode tab 12 is defined as the second electrode ear 121, and the coating portion of the second electrode tab 12 is defined as the second coating portion 122. The electrode terminal that is of the same electric property as and electrically connected to the first electrode ear 111 is the above-mentioned first electrode terminal 31, and the electrode terminal that is of the same electric property as and electrically connected to the second electrode ear 121 is the above-mentioned second electrode terminal 32.

[0127] The polarities of the first electrode tab 11 and the second electrode tab 12 are opposite. When the first electrode tab 11 is a positive electrode tab, the second electrode tab 12 is a negative electrode tab. The first coating portion 112 is a positive electrode coating portion, the first electrode ear 111 is a positive electrode ear, the first electrode terminal 31 is a positive terminal, the second coating portion 122 is a negative electrode coating portion, the second electrode ear 121 is a negative electrode ear, and the second electrode terminal 32 is a negative terminal.

[0128] Or when the first electrode tab 11 is a negative electrode tab, the second electrode tab 12 is a positive electrode tab. The first coating portion 112 is a negative electrode coating portion, the first electrode ear 111 is a negative electrode ear, the first electrode terminal 31 is a negative terminal, the second coating portion 122 is a positive electrode coating portion, the second electrode ear 121 is a positive electrode ear, and the second electrode terminal 32 is a positive terminal.

[0129] The coating part includes a current collector part and a film layer provided on the current collector part and containing active materials. For example, the positive electrode coating part includes a positive electrode current collector part and a positive electrode film layer provided on the positive electrode current collector part and containing positive electrode active materials. Another example is that the negative electrode coating part includes a negative electrode current collector part and a negative electrode film layer provided on the negative electrode current collector part and containing negative electrode active materials.

[0130] As shown in FIGS. 6 to 8, in some embodiments, in the first electrode sheet 11, the tab part is provided on at least one side of the coating part along the first direction, and the first electrode sheet 11 satisfies that n*W1 / W2 is 0.2 to 1.0;

[0131] n represents the number of all tab parts on the same side of the coating part;

[0132] W1 represents the average size of the tab part along the second direction;

[0133] W2 represents the size of the coating part along the second direction, and the second direction, the first direction, and the thickness direction X are perpendicular to each other in pairs.

[0134] Exemplarily, 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 composed of any two of the above values. Optionally, n*W1 / W2 is 0.5 to 1.0.

[0135] When n*W1 / W2 satisfies the above range, the current-carrying area of the tab part is relatively large, which is beneficial to improving the fast charging performance of the battery cell 7.

[0136] W1 represents the average size of the first tab 111 along the second direction.

[0137] When the first tab 111 has a special-shaped structure, for example, along the first direction, the size of the first tab 111 along the second direction gradually increases. In this case, the sizes of the first tab 111 at multiple positions along the second direction can be measured, and thus the average size of the first tab 111 along the second direction can be calculated. Of course, the sizes of the first tab 111 at each position along the second direction can be the same value. In this case, this value can be used as the average size of the first tab 111.

[0138] The first tab 111 can be one or more. For example, n is 1 to 4. When there are multiple first tabs 111, after measuring the average sizes of each first tab 111 respectively, the average size of the first tab 111 can be calculated by adding up the average sizes and dividing by the number of the first tabs 111.

[0139] The first tab 111 and the first coating portion 112 are connected. The first tab 111 includes a first end 1111 connected to the first coating portion 112. When n*W1 / W2 satisfies 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 portion 112 is relatively large, the current-carrying capacity of the first tab 111 is strong, and the fast charging performance and cycling performance of the battery cell 7 can be improved.

[0140] Optionally, the current collector portion of the first tab 111 and the first coating portion 112 is an integral structure, so that the internal resistance of the first electrode sheet 11 is low, and the cycling performance of the battery cell 7 can be further improved.

[0141] In some embodiments, the first electrode sheet 11 includes at least one first tab 111, for example, including 1 to 4 first tabs 111. Optionally, the first electrode sheet 11 includes at least two first tabs 111, and may be four first tabs 111.

[0142] 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.

[0143] As shown in FIGS. 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 kind of setting is beneficial to increasing the occupied space of the electrode assembly 10, thereby improving the energy density of the battery cell 7. In FIG. 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 FIG. 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. Of course, the dimensions of each first tab 111 can also be slightly different. In FIG. 8, n is 1, and n*W1 / W2 is 1.

[0144] As shown in FIG. 9, for example, when the first electrode sheet 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.

[0145] Optionally, when a plurality of 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.; it may be four. This kind of setting is beneficial to the uniform distribution of electrons in the first electrode sheet 11 and is beneficial to improving the fast charging performance.

[0146] Optionally, the distance between two adjacent first tab 111 in 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 a range composed of any two of the above values. In FIG. 9, Z1 represents the distance between two adjacent first tab 111 in the length direction Z.

[0147] When the distance between two adjacent first tab 111 in the length direction Z satisfies the above range, it is beneficial to the uniform distribution of current in the current collecting part and beneficial to improving the fast charging performance.

[0148] In some other embodiments, the first pole piece 11 includes one or more first tabs 111; one or more first tabs 111 are provided on at least one side of the first coating part 112 in the length direction Z.

[0149] As shown in FIG. 10, for example, one or more first tabs 111 are provided on one side of the first coating part 112 in the length direction Z. In this case, it can be understood that all the first tabs 111 are provided on the same side of the first coating part 112 in the length direction Z.

[0150] As shown in FIGS. 11 and 12, for example, when the first pole piece 11 includes a plurality of first tabs 111, the plurality of first tabs 111 are respectively provided on both sides of the first coating part 112 in the length direction Z.

[0151] Optionally, the plurality of first tabs 111 are respectively provided on both sides of the first coating part 112 in the length direction Z. This setting can shorten the transmission path of electrons in the first pole piece 11 and is beneficial to improving the fast charging performance. For example, two first tabs 111 are located on one side of the first coating part 112 in the length direction Z, and the other two first tabs 111 are located on the other side of the first coating part 112 in the length direction Z.

[0152] Optionally, when the plurality of first tabs 111 are respectively provided on at least one side of the first coating part 112 in the length direction Z, there are at least two first tabs 111 on the same side of the first coating part 112 in the length direction Z, such as two, three, four, five, six, etc. This setting is beneficial to the uniform distribution of electrons in the first pole piece 11 and is beneficial to improving the fast charging performance.

[0153] Optionally, the distance between two adjacent first tabs 111 in 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 a range composed of any two of the above values.

[0154] As shown in FIG. 13, in some embodiments, in the second electrode tab 12, the tab portion is disposed on at least one side of the coating portion in the first direction, and the second electrode tab 12 satisfies: m*W3 / W4 is 0.2 to 1.0;

[0155] m represents the number of all tab portions on the same side of the coating portion;

[0156] W3 represents the average dimension of the tab portion in the second direction;

[0157] W4 represents the dimension of the coating portion in the second direction.

[0158] Exemplarily, 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 composed of any two of the above values. Optionally, m*W3 / W4 is 0.5 to 1.0.

[0159] When m*W3 / W4 satisfies the above range, the current-carrying area of the second tab 121 is relatively large, which is beneficial to improving the fast charging performance of the battery cell 7.

[0160] W3 represents the average dimension of the second tab 121 in the second direction. The second tab 121 can be one or more. For example, m is 1 to 4. When there are multiple second tabs 121, the average dimension can be calculated by measuring the dimensions of each second tab 121 with a micrometer.

[0161] The second tab 121 is connected to the second coating portion 122. The second tab 121 includes a second end 1211 connected to the second coating portion 122. When n*W3 / W4 satisfies 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 portion 122 is relatively large, the current-carrying capacity of the second tab 121 is strong, and the fast charging performance and cycling performance of the battery cell 7 can be improved.

[0162] Optionally, the current collector portion of the second tab 121 and the second coating portion 122 is an integral structure, so that the internal resistance of the second electrode tab 12 is low, and the fast charging performance and cycling performance of the battery cell 7 can be further improved.

[0163] In some embodiments, the second electrode tab 12 includes at least one second tab 121, optionally at least two second tabs 121, and optionally four second tabs 121.

[0164] 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 the 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 tab 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.

[0165] 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 kind of arrangement is beneficial to increase the occupied space of the electrode assembly 10, thereby improving the energy density of the battery cell 7.

[0166] Optionally, when a plurality of second tabs 121 are disposed on at least one side of the coating portion along the width direction Y, there are at least two second tabs 121 on the same side of the second coating portion 122 along the width direction Y, such as two, three, four, five, six, etc.; preferably four. This kind of arrangement is beneficial to the uniform distribution of electrons in the second electrode tab 12 and is beneficial to improving the fast charging performance.

[0167] Optionally, the distance between two adjacent second tabs 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 the range composed of any two of the above values.

[0168] As shown in FIG. 14, in some other embodiments, the second electrode tab 12 includes one or more second tabs 121; 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, one or more second tabs 121 are disposed on one side of the second coating portion 122 along the length direction Z. In this case, it can be understood that all the second tabs 121 are disposed on the same side of the second coating portion 122 along the length direction Z. Or for example, when the second electrode tab 12 includes a plurality of second tabs 121, the plurality of second tabs 121 are respectively disposed on both sides of the second coating portion 122 along the length direction Z.

[0169] Optionally, the plurality of second tabs 121 are respectively disposed on both sides of the second coating portion 122 along the length direction Z. This kind of arrangement can shorten the transmission path of electrons in the second electrode tab 12 and is beneficial to improving the fast charging performance.

[0170] Optionally, when multiple second tabs 121 are disposed on at least one side of the second coating portion 122 along the length direction Z, there are at least two second tabs 121 on the same side of the second coating portion 122 along the length direction Z, such as two, three, four, five, six, etc. This setting is beneficial to the uniform distribution of electrons in the second electrode sheet 12 and is beneficial to improving the fast charging performance.

[0171] Optionally, the distance between two adjacent second tabs 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 the range composed of any two of the above values.

[0172] As shown in FIG. 15, in some embodiments, the terminal assembly may be disposed on the housing 21, or the terminal assembly is disposed on the end cap 22.

[0173] The terminal assembly includes a first electrode terminal 31 and a second electrode terminal 32. The first electrode terminal 31 is connected to the first tab 111, and the second electrode terminal 32 is connected to the second tab 121.

[0174] Exemplarily, 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 are disposed on the end cap 22. Optionally, the first electrode terminal 31 and the second electrode terminal 32 are disposed on the end cap 22.

[0175] On the same end cap 22, the first electrode terminal 31 and the second electrode terminal 32 may be disposed simultaneously. For example, there is one end cap 22, and the first electrode terminal 31 and the second electrode terminal 32 are disposed at intervals on the end cap 22. Another example is that there are two end caps 22, the two end caps 22 are disposed opposite to each other, and the first electrode terminal 31 and the second electrode terminal 32 are disposed on each end cap 22.

[0176] The first electrode terminal 31 and the second electrode terminal 32 are respectively disposed on different end caps 22. For example, there are two end caps 22, the two end caps 22 are disposed opposite to each other, the first electrode terminal 31 is disposed on one end cap 22, and the second electrode terminal 32 is disposed on the other end cap 22.

[0177] In some embodiments, the first electrode terminal 31 is at least one, and may be optionally at least two, such as two, three or four, etc.

[0178] 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.

[0179] As shown in FIG. 15, for example, all the first electrode terminals 31 are disposed on one side of the electrode assembly 10 along the length direction Z.

[0180] 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.

[0181] 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.

[0182] 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.

[0183] 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.

[0184] 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.

[0185] 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.

[0186] 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.

[0187] 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.

[0188] 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.

[0189] 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.

[0190] 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.

[0191] 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.

[0192] 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.

[0193] 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.

[0194] 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.

[0195] 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.

[0196] In some embodiments, the battery cell 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 active material, which includes a lithium phosphate. 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 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 electrolyte includes an organic solvent and additives. The organic solvent includes a chain carboxylic acid ester solvent, which has a mass content of 5% to 35% in the electrolyte. The additives include one or more of carbonate additives, sulfur-containing additives, and lithium salt additives, which have a mass content of 0.5% to 10% in the electrolyte.

[0197] The mass content of silicon in the negative electrode active material is greater than or equal to 0.3%, which is beneficial to improve the energy density with a thinner coating thickness.

[0198] Active ions, such as lithium ions, have a shorter migration path in the negative electrode film, allowing them to migrate rapidly within the negative electrode sheet. Furthermore, the electrolyte contains at least 5% chain carboxylic acid ester solvents, which increases the migration rate of lithium ions in the electrolyte, thereby improving the liquid phase transport rate of lithium ions and thus enhancing the fast charging capability of the battery cell.

[0199] However, with the increase of silicon content and chain carboxylic acid ester solvent content, the interfacial reaction between silicon-based materials and electrolyte intensifies, gas production increases, and may damage the SEI film on the negative electrode side. Therefore, the embodiments of this application further control the silicon content to be less than or equal to 10% and the chain carboxylic acid ester solvent content in the electrolyte to be less than or equal to 35%, so as to alleviate the interfacial side reaction between the negative electrode active material and electrolyte, reduce gas production, and improve the cycle performance of the battery cell.

[0200] Furthermore, the electrolyte also includes additives. When the mass content of the additives is greater than or equal to 0.5%, the additives can repair the SEI film on the negative electrode side. When the mass content of the additives is less than or equal to 10%, the resulting SEI film has relatively low impedance, which can effectively improve the fast charging capability of the battery cell.

[0201] Therefore, the embodiments of the present application can improve the cycle performance and fast charging ability of battery cells at high energy density, and are beneficial to the improvement of cycle performance under fast charging.

[0202] Negative electrode sheet

[0203] The negative electrode sheet includes a negative electrode current collector portion and a negative electrode film layer provided on at least one side of the negative electrode current collector portion and including a negative electrode active material. For example, the negative electrode current collector portion has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is provided on either one or both of the two opposite surfaces of the negative electrode current collector portion.

[0204] The upper charge cut-off voltage and the lower discharge cut-off voltage of the battery cell vary depending on the positive electrode active material. For example, when the phosphate material includes lithium iron phosphate, the upper charge cut-off voltage can be 3.65V and the lower discharge cut-off voltage can be 2.0V, or the upper charge cut-off voltage can be 3.8V and the lower discharge cut-off voltage can be 2.0V; for another example, when the phosphate material includes lithium manganese iron phosphate, the upper charge cut-off voltage can be 4.3V and the lower discharge cut-off voltage can be 2.0V. Next, taking the upper charge cut-off voltage of 3.8V and the lower discharge cut-off voltage of 2.0V as an example, the state of the battery cell will be described: In the embodiments of the present application, the 100% state of charge (SOC) and 0% state of charge (SOC) of the battery cell are defined as follows.

[0205] The battery cell is charged at a constant current charging rate of 0.05C to the upper charge cut-off voltage, corresponding to the state of 100% SOC of the battery cell, and the battery cell is discharged at a constant current discharge rate of 0.05C to the cut-off voltage, corresponding to the state of 0% SOC of the battery cell.

[0206] In some embodiments, when the battery cell is in the state of 100% state of charge (SOC), the compaction density of the negative electrode film layer is 1.5 g / cm 3 to 1.7 g / cm 3 . Exemplarily, the compaction density of the negative electrode film layer when the battery cell is in the state of 100% state of charge is 1.50 g / cm 3 [[ID=二十一]]1.55 g / cm [[ID=二十二]] 3 [[ID=二十三]]1.60 g / cm [[ID=二十四]] 3 [[ID=二十五]]1.65 g / cm [[ID=二十六]] 3 [[ID=二十七]]1.66 g / cm [[ID=二十八]] 3 [[ID=二十九]]1.68 g / cm [[ID=三十]] 3 [[ID=三十一]]1.70 g / cm [[ID=三十二]] 3 [[ID=三十三]]or the range composed of any two of the above values. [[ID=三十四]] [[ID=三十五]]

[0207] When the compaction density of the negative electrode film layer is within the above range, it is beneficial to improve the energy density of the battery cell; and because the negative electrode active materials in the negative electrode film layer are stacked relatively tightly, the contact resistance between particles is small, which can further reduce the resistance of the electrode sheet, thereby reducing heat generation and improving the cycle performance. Therefore, by adjusting the compaction density of the negative electrode film layer to a reasonable range, the battery cell can improve its fast charging ability and cycle performance at high energy density.

[0208] In some embodiments, the single-sided coating weight of the negative electrode film layer is 70 mg / 1540.25 mm 2 to 175 mg / 1540.25 mm 2 Exemplarily, the single-sided coating weight of the negative electrode film layer is 70 mg / 1540.25 mm 2 、80 mg / 1540.25 mm 2 、85 mg / 1540.25 mm 2 、90 mg / 1540.25 mm 2 、95 mg / 1540.25 mm 2 、100 mg / 1540.25 mm 2 、105 mg / 1540.25 mm 2 、110 mg / 1540.25 mm 2 、115 mg / 1540.25 mm 2 、120 mg / 1540.25 mm 2 、120 mg / 1540.25 mm 2 、122 mg / 1540.25 mm 2 、125 mg / 1540.25 mm 2 、128 mg / 1540.25 mm 2 、130 mg / 1540.25 mm 2 、140 mg / 1540.25 mm 2 、150 mg / 1540.25 mm 2 、160 mg / 1540.25 mm 2 、170 mg / 1540.25 mm 2 、175 mg / 1540.25 mm 2 or a range composed of any two of the above values. Optionally, the single-sided coating weight of the negative electrode film layer is 95 mg / 1540.25 mm 2 to 142 mg / 1540.25 mm 2 .

[0209] When the single-sided coating weight of the negative electrode film layer meets the above range, in combination with silicon elements with an appropriate mass content, it is beneficial to improve the energy density of the battery cell. Moreover, the migration rate of active ions in the negative electrode film layer is relatively fast, which is beneficial to reducing the polarization phenomenon under high-rate charging and is beneficial to improving the fast charging ability of the battery cell at a high energy density.

[0210] In the embodiments of the present application, the compaction density of the negative electrode film layer of the battery cell in the 100% state of charge (SOC) is a well-known meaning in the art. That is, the negative electrode plate of the battery cell in the 100% state of charge (SOC) is disassembled, and the compaction density of the negative electrode film layer is measured. For example, a single-sided coated negative electrode plate (if it is a double-sided coated plate, one side of the negative electrode film layer can be wiped off first) is punched into small round pieces with an area of S1, weighed, recorded as M1, and its thickness H1 is measured. Then, the negative electrode film layer of the weighed negative electrode plate is wiped off, and the weight of the negative electrode current collector is weighed, recorded as M0, and its thickness H0 is measured. The single-sided coating weight of the negative electrode film layer = (the weight M1 of the negative electrode plate - the weight M0 of the negative electrode current collector) / S1, the thickness of the negative electrode film layer = the thickness H1 of the negative electrode plate - the thickness H0 of the negative electrode current collector, and the compaction density of the negative electrode film layer = the single-sided coating weight of the negative electrode film layer / the thickness of the negative electrode film layer.

[0211] In some embodiments, the charging specific capacity of the negative electrode active material is 350 mAh / g to 540 mAh / g. Exemplarily, the charging specific capacity of the negative electrode active material is any one of 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 composed of any two of the above values.

[0212] When the charging specific capacity of the negative electrode active material is within the above range, the energy density of the battery cell is relatively high.

[0213] In the embodiments of the present application, the specific capacity per gram of the active material has the meaning well-known in the art, and can be tested by the equipment and methods well-known in the art. The test method for the first Coulomb efficiency and the first discharge specific capacity in Appendix G of the national standard GB / T 24533-2019 can be adopted to test the charging specific capacity per gram of the negative active material at a rate of 0.1C in a half-button cell. Using metallic lithium as the negative electrode and the sample electrode sheet containing the above materials as the positive electrode, a half-button cell is assembled. Under the condition of 23°C ± 2°C, the half-button cell is placed on a battery tester or other test equipment with the same performance, and the discharge capacity is obtained through charge and discharge at a rate of 0.1C. Then, the capacity is divided by the mass of the active material of the electrode sheet to obtain the charging specific capacity parameter.

[0214] In some embodiments, the negative active material includes silicon-based materials. Optionally, the silicon-based materials may include at least one of elemental silicon, silicon-carbon composites, and silicon oxides SiO x (0 < x ≤ 2). For example, the silicon-carbon composite can be silicon carbide.

[0215] In some embodiments, the mass content of silicon element in the silicon-based material in the negative electrode film layer is 0.3% to 10%, such as 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 the range composed of any two of the above values. Optionally, the mass content of silicon element in the silicon-based material in the negative electrode film layer is 3% to 6%.

[0216] When the mass content of silicon element is within the above range, the capacity of the negative active material can be improved, which is beneficial to increasing the energy density of the battery cell; moreover, during the charge and discharge process, the volume expansion of silicon element 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.

[0217] In some embodiments, the negative active material includes carbon-based materials. The carbon-based materials have high cycle stability and can improve the cycle performance of the battery cell.

[0218] Optionally, the carbon-based materials include at least one of artificial graphite and natural graphite.

[0219] In some embodiments, in addition to the above-mentioned carbon-based materials and optionally silicon-based materials, the negative active material may further include at least one of tin-based materials and lithium titanate. The tin-based materials may include at least one of elemental tin, tin oxides, and tin alloy materials.

[0220] The qualitative and quantitative analysis of various substances or elements in this application can be detected by suitable equipment and methods known to those skilled in the art. Relevant detection methods can refer to domestic and foreign detection standards, domestic and foreign enterprise standards, etc. And those skilled in the art can also adaptively change certain detection steps / instrument parameters from the perspective of detection accuracy, etc., to obtain more accurate detection results. One detection method can be used for qualitative or quantitative analysis, or several detection methods can be used in combination for qualitative or quantitative determination.

[0221] For example, this application can combine the general rules of X-ray diffraction analysis method in JIS / K0131-1996 to conduct X-ray powder diffraction test and qualitative analysis on the negative electrode sheet or negative electrode active material.

[0222] Artificial graphite and natural graphite can be distinguished by the SEM cross-sectional view taken by scanning electron microscope (SEM). There are voids between flaky structures in the SEM cross-sectional view of natural graphite, while the SEM cross-sectional view of artificial graphite is dense and has no obvious gaps. Or they can be distinguished by the XRD spectrum obtained by X-ray diffraction method. There are obvious 2H phase and 3R phase in the XRD spectrum of natural graphite, while only 2H phase exists in the XRD spectrum of artificial graphite.

[0223] As shown in FIG. 17, in the embodiment of this application, the negative electrode film layer 141 of the negative electrode sheet 14 includes at least one layer of film layer, which can be a single-layer film layer or at least two-layer film layers. Optionally, the negative electrode film layer 141 includes at least two-layer film layers.

[0224] When the negative electrode film layer 141 adopts a single-layer film layer, the negative electrode active material in the negative electrode film layer 141 includes a carbon-based material and an optional silicon-based material.

[0225] When the negative electrode film layer 141 adopts at least two-layer film layers, the negative electrode active material in the negative electrode film layer 141 includes a carbon-based material and an optional silicon-based material. The negative electrode film layer 141 can include two-layer film layers, three-layer film layers, four-layer film layers, or even more film layers.

[0226] In some embodiments, the negative electrode film layer 141 includes a first negative electrode film layer 1411 and a second negative electrode film layer 1412. The first negative electrode film layer 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 layer 1411 includes a carbon-based material. The second negative electrode film layer 1412 is connected to the side of the first negative electrode film layer 1411 facing away from the negative electrode current collector 142, and the negative electrode active material of the second negative electrode film layer 1412 includes a carbon-based material. The interface between the first negative electrode film layer 1411 and the second negative electrode film layer 1412 can be regular or irregular. Optionally, it is irregular; or there is no obvious interface between the first negative electrode film layer 1411 and the second negative electrode film layer 1412.

[0227] 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.

[0228] 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.

[0229] Optionally, the first negative electrode film layer 1411 may also include a silicon-based material.

[0230] Optionally, the second negative electrode film 1412 may also include a silicon-based material.

[0231] 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.

[0232] 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.

[0233] 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.

[0234] 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.

[0235] 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.

[0236] 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.

[0237] 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.

[0238] 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.

[0239] 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.

[0240] 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.

[0241] 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.

[0242] 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.

[0243] 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.

[0244] 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.

[0245] 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.

[0246] 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.

[0247] 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.

[0248] 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.

[0249] 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.

[0250] 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.

[0251] 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.

[0252] 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.

[0253] 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.

[0254] 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).

[0255] 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.

[0256] 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.

[0257] 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.

[0258] 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.

[0259] Positive electrode sheet

[0260] In some implementations, the battery cell also includes a positive electrode.

[0261] 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.

[0262] 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.

[0263] In some embodiments, the dimension of the positive electrode film layer along the length of the positive electrode sheet is 265 mm to 655 mm.

[0264] In some embodiments, 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 and energy density of the battery cell at high energy density.

[0265] 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.

[0266] 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.

[0267] 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.

[0268] 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 reliability 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.

[0269] 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.

[0270] 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.

[0271] 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.

[0272] 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.

[0273] 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.

[0274] 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.

[0275] 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.

[0276] 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.

[0277] 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.

[0278] 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.

[0279] 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.

[0280] 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.

[0281] 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.

[0282] 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 3 2.55g / 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.

[0283] 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.

[0284] 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 .

[0285] 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.

[0286] 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.

[0287] 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.

[0288] 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.

[0289] 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.

[0290] 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.

[0291] 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.

[0292] 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.

[0293] 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 zThe 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.

[0294] 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.

[0295] 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.

[0296] 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.

[0297] 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.

[0298] 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.

[0299] 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.

[0300] 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.

[0301] 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.

[0302] 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 sheet 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 the sample is dried, the volume average particle size Dv50 of the particles is tested using a Mastersizer 2000E laser particle size analyzer according to the test standard GB / T 19077-2016.

[0303] 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.

[0304] 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.

[0305] 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).

[0306] 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.

[0307] 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.

[0308] 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.

[0309] 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.

[0310] Electrolyte

[0311] 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.

[0312] 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.

[0313] 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.

[0314] 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.

[0315] 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.

[0316] 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.

[0317] 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.

[0318] 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.

[0319] 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.

[0320] 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.

[0321] In some embodiments, the organic solvent includes chain carboxylic acid ester solvents.

[0322] 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%.

[0323] 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 SEI film on the anode side, and improve the fast charging capability and cycle performance of the battery cell.

[0324] In some embodiments, the chain carboxylic acid ester solvent includes compounds represented by Formula I.

[0325] In formula I,

[0326] R1 includes a hydrogen atom, a C1 to C5 alkyl group, or a C1 to C5 haloalkyl group.

[0327] R2 includes C1 to C5 alkyl or C1 to C5 haloalkyl.

[0328] The aforementioned chain-like carboxylic acid ester solvents have high conductivity, which is beneficial for improving the fast charging capability of battery cells.

[0329] 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.

[0330] 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.

[0331] 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.

[0332] For example, the chain carboxylic acid ester solvent includes one or more compounds of formula I-1 to formula I-8.

[0333] In some embodiments, the organic solvent includes carbonate solvents.

[0334] 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.

[0335] 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.

[0336] 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.

[0337] For example, carbonate solvents include one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0338] 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.

[0339] 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.

[0340] For example, lithium fluorosulfonylimide includes one or more of lithium trifluorosulfonylimide and lithium difluorosulfonylimide, optionally lithium difluorosulfonylimide.

[0341] 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%.

[0342] 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%.

[0343] 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.

[0344] 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 SEI film formed at the negative electrode interface is appropriate, which can also reduce the gas production at high temperature storage and improve the cycle performance.

[0345] 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 performance of the SEI film on the negative electrode side, resulting in a more stable SEI film with relatively low impedance, which is beneficial for improving the fast-charging performance of the battery cell and enhancing cycle performance.

[0346] 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%.

[0347] The additives mentioned above can effectively improve the performance of the SEI film on the negative electrode side, which is beneficial to improving the fast charging performance of the battery cells and improving cycle performance.

[0348] 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.

[0349] Fluorinated ethylene carbonate can form a lithium fluoride (LiF)-rich SEI film 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.

[0350] The combined use of fluoroethylene carbonate and vinylene carbonate results in a denser SEI 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.

[0351] 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.

[0352] Optionally, the lithium salt additives include one or more of lithium difluorophosphate, lithium difluorooxalate borate, lithium tetrafluoroborate, and lithium dioxalate borate.

[0353] 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.

[0354] 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".

[0355] 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%.

[0356] 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%.

[0357] Isolation component

[0358] In some embodiments, the electrode assembly further includes a spacer disposed between the positive electrode and the negative electrode.

[0359] 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.

[0360] 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.

[0361] 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.

[0362] 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.

[0363] 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.

[0364] Example

[0365] 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.

[0366] Example 1

[0367] 1. Preparation of positive electrode sheet

[0368] 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.

[0369] 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.

[0370] 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.

[0371] The volume average particle size Dv50 of the positive electrode additive is 9.5 μm.

[0372] The single-sided coating weight of the positive electrode film is 284 mg / 1540.25 mm. 2 .

[0373] The length of the positive electrode film is 592 mm.

[0374] 2. Preparation of negative electrode sheet

[0375] 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.

[0376] 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.

[0377] The single-sided coating weight of the negative electrode film is 135 mg / 1540.25 mm. 2 .

[0378] 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.

[0379] The first 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 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, and the average particle size of artificial graphite is 13 μm.

[0380] 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.

[0381] 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.

[0382] 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.

[0383] The charge capacity of the negative electrode active material is 420mAh / g.

[0384] 3. Isolation components

[0385] The separator includes a base film, which is a 7μm polyethylene film layer with a porosity of 42%.

[0386] 4. Preparation of electrolyte

[0387] 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.

[0388] 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.

[0389] Based on the mass of the electrolyte, the additive contains 2.5% vinylene carbonate (VC) by mass.

[0390] The lithium salt comprises 10% lithium hexafluorophosphate (LiPF6) and 4% lithium difluorosulfonylimide.

[0391] 5. Preparation of battery cells

[0392] 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 .

[0393] Comparative Example 1-1

[0394] 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.

[0395] Comparative Examples 1-2

[0396] Battery cells were prepared using a method similar to that of Example 1, except that the mass content of silicon was adjusted.

[0397] Examples 2-1 to 2-3

[0398] Battery cells were prepared using a method similar to that of Example 1, except that the mass content of silicon was adjusted.

[0399] Examples 2-4

[0400] 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.

[0401] Example 3

[0402] Battery cells were prepared using a method similar to that of Example 1, except that the material of the silicon-based material was adjusted.

[0403] Performance testing

[0404] 1. DC resistance (DCR) test of individual battery cells

[0405] You can refer to the methods in GB / T 31467 "Performance Test Specification for High-Power Lithium-ion Power Batteries for HEVs".

[0406] 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%.

[0407] 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 ,

[0408] Where, 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.

[0409] 2. High-temperature cycle performance test of individual battery cells

[0410] At 60±5℃, the battery cells are charged at a constant current of 1C to the charging cutoff voltage, then charged at a constant voltage to the cutoff current of 0.05C, and then discharged at a constant current of 1C to the discharge cutoff voltage. This is one charge-discharge cycle.

[0411] 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.

[0412] 3. Room temperature cycle performance test of individual battery cells

[0413] At 25±5℃, the battery cells are charged with a constant current using Stercharge:

[0414] Charge from 0% SOC to 20% SOC at a constant current of 0.33C;

[0415] Charge from 20% SOC to 25% SOC at a constant current of 8C.

[0416] Charge from 25% SOC to 30% SOC at a constant current of 8C.

[0417] Charge from 30% SOC to 35% SOC at a constant current of 7.5C;

[0418] Charge from 35% SOC to 40% SOC at a constant current of 6.87C;

[0419] Charge from 40% SOC to 45% SOC at a constant current of 6.38C;

[0420] Charge from 45% SOC to 50% SOC at a constant current of 5.95C;

[0421] Charge from 50% SOC to 55% SOC at a constant current of 5.53C;

[0422] Charge from 55% SOC to 60% SOC at a constant current of 5.14C;

[0423] Charge from 60% SOC to 65% SOC at a constant current of 4.76C;

[0424] Charge from 65% SOC to 70% SOC at a constant current of 4.36C;

[0425] Charge from 70% SOC to 75% SOC at a constant current of 3.94C;

[0426] Charge from 75% SOC to 80% SOC at a constant current of 3.57C.

[0427] Charge from 80% SOC to 85% SOC using 2C constant current

[0428] Charge from 90% SOC to 95% SOC using a constant current of 1C.

[0429] Charge from 95% SOC to 98% SOC at a constant current of 0.5C.

[0430] Charge from 98% SOC to 100% SOC at a constant current of 0.25C.

[0431] The charging cutoff voltage is set at a constant current of 0.1C.

[0432] Then, constant current discharge is performed at 1C until the discharge cutoff voltage is reached, which constitutes one charge-discharge cycle.

[0433] 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.

[0434] 4. Fast charging time test of individual battery cells from 20% to 80% SOC

[0435] At 25±5℃, the battery cells are charged with a constant current using Stercharge:

[0436] Charge from 0% SOC to 20% SOC at a constant current of 0.33C;

[0437] Charge from 20% SOC to 25% SOC at a constant current of 8C.

[0438] Charge from 25% SOC to 30% SOC at a constant current of 8C.

[0439] Charge from 30% SOC to 35% SOC at a constant current of 7.5C;

[0440] Charge from 35% SOC to 40% SOC at a constant current of 6.87C;

[0441] Charge from 40% SOC to 45% SOC at a constant current of 6.38C;

[0442] Charge from 45% SOC to 50% SOC at a constant current of 5.95C;

[0443] Charge from 50% SOC to 55% SOC at a constant current of 5.53C;

[0444] Charge from 55% SOC to 60% SOC at a constant current of 5.14C;

[0445] Charge from 60% SOC to 65% SOC at a constant current of 4.76C;

[0446] Charge from 65% SOC to 70% SOC at a constant current of 4.36C;

[0447] Charge from 70% SOC to 75% SOC at a constant current of 3.94C;

[0448] Charge from 75% SOC to 80% SOC at a constant current of 3.57C.

[0449] The test results are shown in Table 1.

[0450] Table 1

[0451] Comparative Example 1-1 did not add silicon-based materials. At higher energy densities, 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.

[0452] The high amount of silicon-based material added in Comparative Examples 1-2 resulted in more severe side reactions on the negative electrode side, exacerbating gas production, especially at high temperatures, which worsened the cycle.

[0453] In this application, embodiments 2-1 to 2-4 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. This can effectively improve the volumetric energy density of the battery cell, effectively improve the cycle performance and fast charging performance of the battery cell under high energy density, and also help improve the cycle performance under fast charging conditions.

[0454] For example, in Examples 2-4, 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 involved in side reactions, thereby improving the cycle performance under fast charging conditions and high-temperature cycle performance.

[0455] As the mass content of silicon increases, the specific charging capacity of the negative electrode active material increases. For example, in Examples 2-3, the specific charging capacity of the negative electrode active material can reach 534 mAh / g.

[0456] 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.

[0457] Comparative Example 2-1 and Comparative Example 2-2

[0458] Battery cells were prepared using a method similar to that of Example 1, except that the composition of the electrolyte was adjusted.

[0459] Examples 4-1 and 4-2

[0460] Battery cells were prepared using a method similar to that of Example 1, except that the composition of the electrolyte was adjusted.

[0461] The test results are shown in Table 2.

[0462] Table 2

[0463] In Table 2,

[0464] In Comparative Example 2-1, 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.

[0465] In Comparative Example 2-2, the mass content of chain carboxylic acid ester solvents is relatively high, and the conductivity of the electrolyte is high, which is beneficial to reducing the DCR of the battery cells; however, the side reactions between the above solvents and the negative electrode active materials are more serious, gas production is aggravated, especially at high temperatures, which worsens the cycle.

[0466] 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.

[0467] Comparative Example 3-1 and Comparative Example 3-2

[0468] Battery cells were prepared using a method similar to that of Example 1, except that the composition of the electrolyte was adjusted.

[0469] Examples 5-1 to 5-5

[0470] Battery cells were prepared using a method similar to that of Example 1, except that the composition of the electrolyte was adjusted.

[0471] The test results are shown in Table 3.

[0472] Table 3

[0473] In Table 3,

[0474] VC stands for vinylene carbonate;

[0475] FEC stands for fluoroethylene carbonate;

[0476] PS stands for 1,3-propanesulfonate lactone;

[0477] VC:2 indicates that the mass content of vinylene carbonate in the electrolyte is 2%;

[0478] Other examples are explained in the same way as above, and will not be repeated here.

[0479] The negative electrode side reaction in Comparative Example 3-1 was more severe, which worsened the cycle; the additive content in Comparative Example 3-2 was too high, which resulted in a high SEI film impedance on the negative electrode side, which was not conducive to fast charging.

[0480] In the embodiments of this application, the additive has an appropriate mass content, which can form a dense SEI film on the negative electrode side. The film layer impedance is relatively low, which can alleviate interfacial side reactions, reduce gas production, and improve the fast charging capability and cycle performance of the battery cell at high energy density.

[0481] In Examples 5-1, 1, and 5-2, as the VC content of vinylene carbonate increases, the resulting SEI film becomes denser and provides better protection for the negative electrode side, effectively improving cycle performance. However, the film impedance increases accordingly, resulting in a decrease in fast charging performance.

[0482] Example 5-3 uses fluoroethylene carbonate (FEC) to protect the negative electrode side. FEC can form a SEI film with relatively low impedance on the negative electrode side, reducing the internal resistance of the battery cell and improving the fast charging capability of the battery cell. However, the SEI film formed by FEC has a weaker protective effect on the negative electrode active material than the SEI film formed by vinylene carbonate (VC). Compared with Example 1, Example 5-3 has a higher risk of side reactions on the negative electrode side and slightly worse cycle performance.

[0483] In Examples 5-4, the mixed use of vinylene carbonate (VC) and fluoroethylene carbonate (FEC) not only forms an excellent SEI film on the negative electrode side but also provides excellent protection for the negative electrode active material, improving cycle performance. It also reduces the impedance of the SEI film, improving the fast-charging performance of the battery cells. When using the same amounts of VC and FEC, the SEI film formed by VC and FEC exhibits slightly poorer protective performance and cycle performance; furthermore, FEC carries the risk of high-temperature decomposition, which may result in slightly poorer high-temperature cycle performance.

[0484] In Examples 5-5, the combination of vinylene carbonate (VC) and 1,3-propanesulfonic acid lactone not only forms an excellent SEI film on the negative electrode side, but also reduces impedance, improves the fast charging performance of the battery cell, and is beneficial to improving cycle performance under fast charging conditions.

[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 the embodiments can be changed, substituted and modified without departing from the spirit, principles and scope of the implementation of the present application.

Claims

1. 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 including lithium phosphate; 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 element in the silicon-based material has a mass content of 0.3% to 10% in the negative electrode film layer. as well as An electrolyte comprising a chain carboxylic acid ester solvent and additives, wherein the chain carboxylic acid ester solvent comprises 5% to 35% by mass in the electrolyte, and the additives comprise one or more of carbonate additives, sulfur-containing additives, and lithium salt additives, wherein the additives comprise 0.5% to 10% by mass in the electrolyte.

2. The battery cell according to claim 1, wherein, The silicon content of the silicon-based material in the negative electrode film layer is 3% to 6% by mass.

3. The battery cell according to claim 1 or 2, wherein, The silicon-based material includes one or more of silicon carbide and silicon oxide.

4. The battery cell according to any one of claims 1 to 3, 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.

5. The battery cell according to claim 4, 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.

6. The battery cell according to claim 4 or 5, 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.

7. The battery cell according to any one of claims 4 to 6, wherein, At least one of the first region and the second region comprises a silicon-based material.

8. The battery cell according to any one of claims 1 to 7, 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.

9. The battery cell according to any one of claims 1 to 8, wherein, The negative electrode film layer includes a negative electrode conductive agent, which includes one or more of conductive carbon and carbon nanotubes.

10. The battery cell according to claim 9, 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%.

11. The battery cell according to any one of claims 1 to 10, 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.

12. The battery cell according to any one of claims 1 to 11, wherein, The chain-like carboxylic acid ester solvent has a mass content of 8% to 20% in the electrolyte.

13. The battery cell according to any one of claims 1 to 12, 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.

14. The battery cell according to claim 13, wherein, The chain-like carboxylic acid ester solvents include one or more compounds from Formula I-1 to Formula I-8.

15. The battery cell according to any one of claims 1 to 14, wherein, The electrolyte also includes carbonate solvents, wherein the carbonate solvents constitute 65% to 75% of the electrolyte by mass.

16. The battery cell according to claim 15, wherein, The carbonate solvents include one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

17. The battery cell according to any one of claims 1 to 16, wherein, The additive is present in the electrolyte at a mass content of 2% to 6%.

18. The battery cell according to any one of claims 1 to 17, wherein, The carbonate additives include one or more of fluoroethylene carbonate and vinylene carbonate; and / or The sulfur-containing additive includes one or more of vinyl sulfate, vinyl disulfate, butenyl sulfite, 1,3-propanesulfonate lactone, vinyl sulfite, and methylene disulfonate; and / or The lithium salt additives include one or more of lithium difluorophosphate, lithium difluorooxalate borate, lithium tetrafluoroborate, and lithium dioxalate borate.

19. The battery cell according to any one of claims 1 to 18, wherein, The electrolyte also includes one or more of lithium fluorosulfonylimide and lithium hexafluorophosphate.

20. The battery cell according to claim 19, wherein, The lithium fluorinated sulfonyl imide includes one or more of lithium trifluorosulfonyl imide and lithium difluorosulfonyl imide.

21. The battery cell according to claim 19 or 20, wherein, The mass content of the lithium fluorosulfonyl imide and the lithium hexafluorophosphate in the electrolyte is greater than 0 and less than or equal to 18%.

22. The battery cell according to claim 21, wherein, The lithium fluorosulfonyl imide and the lithium hexafluorophosphate have a mass content of 4% to 16% in the electrolyte.

23. The battery cell according to any one of claims 1 to 22, wherein, The single-sided coating weight of the positive electrode film is 150 mg / 1540.25 mm. 2 Up to 370mg / 1540.25mm 2 ; and / or The single-sided coating weight of the negative electrode film is 80 mg / 1540.25 mm. 2 Up to 135mg / 1540.25mm 2 .

24. A battery device comprising a battery cell as claimed in any one of claims 1 to 23.

25. An electrical device comprising the battery device as described in claim 24.

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