Battery cell, battery device, and electric device

Abstract

A battery cell, a battery device, and an electrical device are disclosed. The battery cell includes multiple positive electrode plates and multiple negative electrode plates, as well as an electrolyte. The multiple positive electrode plates and multiple negative electrode plates are stacked along the thickness direction of the battery cell. Each positive electrode plate 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 dimension of the positive electrode film layer along the length direction of the battery cell is 200 mm to 600 mm. The electrolyte includes an organic solvent, which includes a carboxylic acid ester solvent. The mass content of the carboxylic acid ester solvent in the electrolyte is 3% to 70%. The high-temperature cycle performance of the battery cell can be further improved.

Description

Battery cells, battery packs and electrical devices Technical Field

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

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

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

[0004] In a first aspect, embodiments of this application propose a battery cell, which includes a plurality of positive electrode plates and a plurality of negative electrode plates, as well as an electrolyte. The plurality of positive electrode plates and the plurality of negative electrode plates are stacked along the thickness direction of the battery cell. The positive electrode plate 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 dimension of the positive electrode film layer along the length direction of the battery cell is 200 mm to 600 mm. The electrolyte includes an organic solvent, which includes a carboxylic acid ester solvent. The mass content of the carboxylic acid ester solvent in the electrolyte is 3% to 70%.

[0005] Therefore, when the dimensions of the positive electrode film layer along the length of the battery cell in the embodiments of this application meet the above-mentioned range, the electrolyte includes a carboxylic acid ester solvent with high conductivity. The electrolyte can quickly wet the positive electrode sheet, which is beneficial to the rapid migration of lithium ions in the positive electrode film layer. Lithium ions can also migrate rapidly in the electrolyte, accelerating the rate at which lithium ions migrate from the positive electrode active material to the negative electrode active material through the electrolyte, improving the liquid phase transport capability of lithium ions and the transport capability between the solid and liquid phases. Furthermore, the mass content of the carboxylic acid ester solvent in the electrolyte will not be too high, which can reduce the side reactions at the negative electrode interface and reduce the amount of gas generated at high temperature, thereby improving the high-temperature cycle performance of the battery cell under fast charging.

[0006] In some embodiments, the electrolyte has a conductivity of 9 mS / cm to 18 mS / cm at room temperature; optionally, the electrolyte has a conductivity of 11 mS / cm to 18 mS / cm at room temperature. The high migration rate of lithium ions in this electrolyte further reduces the internal resistance of the battery cell, thereby reducing heat generation and minimizing high-temperature gas generation caused by heat accumulation, thus improving the high-temperature cycling performance of the battery cell under fast charging.

[0007] In some embodiments, the mass content of carboxylic acid ester solvent in the electrolyte is 10% to 30%. When the mass content of carboxylic acid ester solvent is within the above range, it can improve the conductivity of the electrolyte; and it can alleviate the side reactions on the negative electrode side, effectively reduce the gas production of the battery cell, and improve the high-temperature cycle performance of the battery cell under fast charging.

[0008] In some embodiments, the carboxylic acid ester solvent includes cyclic carboxylic acid esters, which include one or more of γ-butyrolactone, γ-valerolactone, and δ-valerolactone. The aforementioned material has low viscosity, which improves its wettability on the electrode and enhances high-temperature cycling performance under fast charging.

[0009] In some embodiments, the carboxylic acid ester solvent includes chain carboxylic acid esters, which include one or more of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, propyl propionate, and butyl propionate. The aforementioned materials have low viscosity, which improves the wetting ability of the electrode and enhances high-temperature cycling performance under fast charging.

[0010] In some embodiments, the organic solvent also includes carbonate solvents, including one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. The use of a mixture of carbonate solvents and carboxylic acid ester solvents can improve the stability of the electrolyte and reduce its high-temperature gas production.

[0011] In some embodiments, the carbonate solvent includes dimethyl carbonate, which has a mass content of 10% to 30% in the electrolyte; the material has a low viscosity, which can improve the wetting ability of the electrode and improve the high-temperature cycling performance under fast charging.

[0012] In some embodiments, the carbonate solvent includes dimethyl carbonate, and the mass ratio of dimethyl carbonate in the electrolyte to the mass content of the carboxylic acid ester solvent in the electrolyte is 1 to 7. When the mass contents of dimethyl carbonate and carboxylic acid ester solvent meet the above conditions, the stability of the electrolyte can be improved, its high-temperature gas production can be reduced, and the high-temperature cycling performance under fast charging can be improved.

[0013] In some embodiments, the electrolyte further includes one or more of fluorinated cyclic carbonates and vinylene carbonate. Fluorinated cyclic carbonates can form a lithium fluoride (LiF)-rich interfacial film on the negative electrode surface, which can alleviate the volume expansion of the negative electrode active material, improve its lifespan, and enhance high-temperature cycling performance. Vinylene carbonate forms a more compact interfacial film on the negative electrode surface, more effectively protecting the negative electrode active material, reducing the degree of side reactions at the negative electrode interface, and improving high-temperature cycling performance.

[0014] In some embodiments, the fluorocyclic carbonate includes at least one of monofluoroethylene carbonate, difluoroethylene carbonate, and trifluoropropylene carbonate.

[0015] In some embodiments, the mass content of the fluorocyclic carbonate is from 0.5% to 20% based on the mass of the electrolyte. When the mass content of the fluorocyclic carbonate is within the above range, it can form an excellent interfacial film, providing excellent protection for the negative electrode and improving high-temperature cycling performance.

[0016] In some embodiments, the mass content of vinylene carbonate is 0.1% to 3% based on the mass of the electrolyte. Vinylene carbonate participates in the formation of the negative electrode interface film, which can form an excellent interface film, providing excellent protection for the negative electrode and improving high-temperature cycling performance.

[0017] In some embodiments, the electrolyte further includes a lithium salt, comprising lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate, wherein the mass ratio of lithium bis(fluorosulfonyl)imide to lithium hexafluorophosphate is 0.3 to 1.2 based on the mass of the electrolyte. When the mass ratio of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide in the embodiments of this application satisfies the above range, on the one hand, the hydrofluoric acid content can be reduced, mitigating the side reactions at the negative electrode interface and reducing the amount of gas generated during high-temperature storage; on the other hand, the appropriate organic component content of the interfacial film formed at the negative electrode interface also reduces the amount of gas generated during high-temperature storage.

[0018] In some embodiments, the lithium bis(fluorosulfonyl)imide content is 2% to 11% by mass, based on the mass of the electrolyte. When the lithium bis(fluorosulfonyl)imide content is within the above range, the hydrofluoric acid content can be reduced, the negative electrode interface side reaction can be mitigated, the gas generation during high-temperature storage can be reduced, and the high-temperature cycle life of the battery cell can be improved.

[0019] In some embodiments, the lithium hexafluorophosphate content is between 3% and 14% by mass, depending on the mass of the electrolyte. When the lithium hexafluorophosphate content is within this range, the electrolyte conductivity is relatively high, which is beneficial for lithium-ion migration and improves the fast-charging performance of the battery cells.

[0020] In some embodiments, the positive electrode film has a length of 400 mm to 600 mm along the length of the battery cell. When the positive electrode film meets the above conditions, it works in conjunction with the electrolyte to allow the electrolyte to quickly wet the positive electrode film, resulting in uniform charging throughout the positive electrode film. This reduces the risk of localized side reactions on the negative electrode side and improves the cycle performance of the battery cell.

[0021] In some embodiments, the single-sided coating weight of the positive electrode film is 250 mg / 1540.25 mm. 2 Up to 300mg / 1540.25mm 2 When the single-sided coating weight of the positive electrode film is within the above range, the heat generation per unit area of ​​the positive electrode sheet will not be too large, and it can simultaneously improve the energy density and charging rate performance of the battery cell, while preventing excessive heat accumulation within the battery cell system, reducing the risk of electrolyte decomposition at high temperatures, and improving the cycle performance of the battery cell.

[0022] In some embodiments, the compaction density of the positive electrode film layer in a single battery cell at 0% charge is 2.2 g / cm³. 3 Up to 2.85 g / cm 3 When the compaction density of the positive electrode film is within the above range, the thickness of the positive electrode film will not be too thick, which is beneficial for the rapid charging of the battery cell; moreover, the particle packing of the positive electrode active material will not be too dense, reducing the risk of particle crushing and improving the high-temperature cycle performance of the battery cell.

[0023] In some implementations, the lithium-containing phosphate includes lithium iron phosphate, which has excellent cycle performance and can improve the cycle performance of individual battery cells.

[0024] In some embodiments, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The negative electrode film layer includes a negative electrode active material, which may be a carbon-based material. The single-sided coating weight of the negative electrode film layer is 80 mg / 1540.25 mm. 2 Up to 150mg / 1540.25mm 2 When the single-sided coating weight of the negative electrode film meets the above range, it is beneficial to improve the energy density of the battery cell, and the migration rate of active ions in the negative electrode film is faster, which is beneficial to improve the fast charging capability of the battery cell.

[0025] In some embodiments, the compaction density of the negative electrode film layer in a single battery cell at 0% charge is 1.1 g / cm³. 3 Up to 1.7 g / cm 3When the compaction density of the negative electrode film is within the above range, the thickness of the negative electrode film will not be too thick, which is beneficial for the rapid charging of the battery cell; moreover, the particle packing of the negative electrode active material will not be too dense, reducing the risk of particle crushing and improving the high-temperature cycle performance of the battery cell.

[0026] In some embodiments, the negative electrode active material also includes silicon-based materials, which can improve energy density and facilitate thinning of the negative electrode film, thereby increasing the migration rate of lithium ions.

[0027] In some embodiments, the silicon content of the silicon element in the negative electrode active material is between 0.3% and 15% by mass. Within the above mass content range, the silicon-based material can improve the energy density and is beneficial for thinning the negative electrode film, thereby increasing the migration rate of lithium ions.

[0028] In some embodiments, the negative electrode film layer includes a first region and a second region. The first region is a region of the negative electrode film layer that is close to the negative electrode current collector along its own thickness direction, and the thickness of the first region is 1 / 3 of the thickness of the negative electrode film layer. The second region is a region of the negative electrode film layer that is away from the negative electrode current collector along its thickness direction, and the thickness of the second region is 1 / 3 of the thickness of the negative electrode film layer. In a cross-section of the negative electrode film layer parallel to the thickness direction, the void ratio of a single carbon-based material located in the first region is smaller than the void ratio of a single carbon-based material located in the second region.

[0029] Therefore, in the embodiments of this application, the void ratio of a single carbon-based material in the first region is less than or equal to the void ratio of a single carbon-based material in the second region, which is more conducive to the diffusion of lithium ions in the first region, improves the transmission rate, and thus facilitates the rapid charging of battery cells.

[0030] In some embodiments, 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. In the embodiments of this application, the particle size in the second region is relatively small, which can shorten the solid-phase transport path of lithium ions, improve fast charging performance, and improve the problem of lithium deposition on the surface of the negative electrode.

[0031] In some embodiments, when 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 average particle size of the carbon-based material in the first region is 12 μm to 21 μm. When the average particle size of the carbon-based material in the first region is within the above range, the cycle life can be improved and there is basically no adverse effect on the fast charging performance.

[0032] In some embodiments, where 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 average particle size of the carbon-based material in the second region is between 9 μm and 17 μm. When the average particle size of the carbon-based material is within this range, it is beneficial to improve the fast-charging capability of the battery cell and enhance the stability of the material.

[0033] In some embodiments, where 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 carbon-based material in the first region includes artificial graphite and / or natural graphite.

[0034] In some embodiments, where 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 carbon-based material in the second region includes artificial graphite.

[0035] In some embodiments, the average particle size of the carbon-based material in the second region is larger than that in the first region. The relatively larger average particle size of the carbon-based material in the second region results in higher pressure resistance during film fabrication, which is beneficial for improving particle density.

[0036] In some embodiments, where the average particle size of the carbon-based material in the second region is greater than that in the first region, the average particle size of the carbon-based material in the first region is between 9 μm and 17 μm. When the average particle size of the carbon-based material in the first region is within this range, cycle life can be improved.

[0037] In some embodiments, where the average particle size of the carbon-based material in the second region is greater than that in the first region, the average particle size of the carbon-based material in the second region is 12 μm to 21 μm. When the average particle size of the carbon-based material in the second region is within the above range, cycle life can be improved.

[0038] In some embodiments, where the average particle size of the carbon-based material in the second region is greater than that in the first region, the carbon-based material in the second region includes artificial graphite and / or natural graphite.

[0039] In some embodiments, where the average particle size of the carbon-based material in the second region is greater than the average particle size of the carbon-based material in the first region, the carbon-based material in the first region includes artificial graphite.

[0040] In some embodiments, the negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer. The first negative electrode film layer is disposed on the surface of the negative electrode current collector, and the negative electrode active material of the first negative electrode film layer includes a carbon-based material. The second negative electrode film layer is connected to the side of the first negative electrode film layer opposite to the negative electrode current collector, and the negative electrode active material of the second negative electrode film layer also includes a carbon-based material. At least one of the negative electrode active materials of the first and second negative electrode film layers includes a silicon-based material. This dual-layer configuration is beneficial for simultaneously improving the fast charging capability and energy density of the battery cell.

[0041] Secondly, embodiments of this application also propose a battery device, including a battery cell of any embodiment of the first aspect of this application.

[0042] Thirdly, embodiments of this application also propose an electrical device, which includes a battery device as described in any of the embodiments of the second or third aspects of this application. Attached Figure Description

[0043] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0044] Figure 1 is a schematic diagram of the structure of an electrical device provided in some embodiments of this application.

[0045] Figure 2 is a schematic diagram of the structure of a battery pack provided in some embodiments of this application;

[0046] Figure 3 is a schematic diagram of the structure of a battery module provided in some embodiments of this application;

[0047] Figure 4 is a schematic diagram of the structure of a battery cell provided in some embodiments of this application;

[0048] Figure 5 is a schematic diagram of the structure of the electrode assembly of a battery cell provided in some embodiments of this application;

[0049] Figure 6 is a schematic diagram of the structure of the negative electrode sheet of a battery cell provided in some embodiments of this application.

[0050] The accompanying drawings may not be drawn to scale.

[0051] The reference numerals in the attached drawings are explained as follows: X, thickness 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, positive electrode plate; 12, negative electrode plate; 121, negative electrode film; 122, negative electrode current collector; 1211, first negative electrode film; 1212, second negative electrode film; 121a, first region; 121b, second region; 121c, third region; 13, separator; 20, outer casing assembly; 21, housing; 22, end cap; 23, electrode terminal. Detailed Implementation

[0052] 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.

[0053] 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.

[0054] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions. Unless otherwise specified, all technical features and optional technical features of this application can be combined to form new technical solutions. Unless otherwise specified, all steps of this application can be performed sequentially or randomly, preferably sequentially. For example, if a 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 it is mentioned that the method may also include step (c), it means that step (c) can 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.

[0055] In this application, "multiple" means two or more (including two).

[0056] With the rapid development of the battery industry, the performance requirements for battery cells are gradually increasing. For example, the requirements for fast charging capability and high-temperature cycle life of battery cells are gradually increasing. However, it is difficult to improve fast charging capability and high-temperature cycle life at the same time. Therefore, the high-temperature cycle life of battery cells under fast charging is limited.

[0057] In view of the above problems, the embodiments of this application improve the high-temperature cycle life of individual battery cells under fast charging by synergistically regulating the positive electrode and electrolyte; specifically,

[0058] Increasing the length of the positive electrode film layer of a battery cell can increase the loading of active materials, thereby improving the energy density of the battery cell. However, increasing the length of the positive electrode film layer also means increasing the length of the positive electrode, which reduces the wetting ability of the electrolyte along the length of the positive electrode, hindering the fast charging of the battery cell. This application addresses this by adapting a suitable electrolyte to the longer positive electrode, including a carboxylic acid ester solvent, which enhances the wetting ability of the electrolyte on the positive electrode film layer, thus improving the transport performance of lithium ions between the solid and liquid phases. Simultaneously, the electrolyte of this application also improves the transport of lithium ions in the liquid phase, strengthening the transport rate of lithium ions from the positive active material through the electrolyte to the negative active material in the battery cell, effectively improving the fast charging capability of the battery cell. Furthermore, the mass content of the carboxylic acid ester solvent in the electrolyte is not excessively high, which reduces side reactions at the negative electrode interface and reduces high-temperature gas generation, thereby improving the high-temperature cycle life of the battery cell.

[0059] The battery cell described in this application is applicable to various battery devices and electrical appliances that use battery cells.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] In some implementations, a battery cell assembly is typically formed by arranging multiple battery cells. 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.

[0066] 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 within the housing 5. As an example, the battery cell assemblies can also be housed within the housing 5 by directly fixing multiple battery cells to the housing 5.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] As shown in Figure 3, the battery module 6 includes multiple battery cells 7.

[0072] As shown in Figures 4 and 5, in some embodiments, the battery cell 7 includes an electrode assembly 10 and a housing assembly 20. The housing assembly 20 has a receiving cavity for housing the electrode assembly 10 and the electrolyte.

[0073] In some embodiments, the housing assembly 20 includes a housing and electrode terminals 23 disposed on the housing.

[0074] 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.

[0075] 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.

[0076] In some embodiments, the housing includes an end cap 22 and a housing 21, the housing 21 having an opening, and the end cap 22 covering the opening. The housing 21 may have one or more openings. The end cap 22 may also have one or more.

[0077] 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.

[0078] Electrode terminal 23 can be disposed on housing 21 or on end cover 22. Electrode terminal 23 is electrically connected to the tab of electrode plate. Electrode terminal 23 can be directly connected to the tab or indirectly connected to the tab through current collector.

[0079] The electrode assembly 10 can be a wound structure, a stacked structure, or a hybrid structure of wound and stacked.

[0080] In some embodiments, the electrode assembly 10 is a wound structure. The positive electrode 11 and the negative electrode 12 are wound into a wound structure.

[0081] In some embodiments, the electrode assembly 10 has a stacked structure.

[0082] As an example, multiple positive electrode plates 11 and multiple negative electrode plates 12 can be set, and multiple positive electrode plates 11 and multiple negative electrode plates 12 can be stacked alternately.

[0083] As an example, multiple positive electrode plates 11 can be provided, and multiple negative electrode plates 12 can be folded to form multiple stacked folded segments, with a positive electrode plate 11 sandwiched between adjacent folded segments.

[0084] As an example, both the positive electrode 11 and the negative electrode 12 are folded to form multiple stacked folded segments.

[0085] As an example, multiple separators 13 can be provided, respectively disposed between any adjacent positive electrode 11 or negative electrode 12.

[0086] As an example, the separator 13 can be continuously arranged between any adjacent positive electrode 11 or negative electrode 12 by folding or rolling.

[0087] In some embodiments, the electrode assembly 10 may be cylindrical, flat, or polygonal in shape.

[0088] In some embodiments, the electrode assembly 10 is provided with tabs that can conduct current from the electrode assembly 10. The tabs include a positive tab and a negative tab. The electrode assembly 10 can adopt a wound structure or a stacked structure, and the stacked structure is preferable to improve the energy density of the battery cell 7.

[0089] In some embodiments, the battery cell 7 includes an electrode assembly 10, which includes a plurality of positive electrode plates 11 and a plurality of negative electrode plates 12. The plurality of positive electrode plates 11 and the plurality of negative electrode plates 12 are stacked along the thickness direction of the battery cell 7. The positive electrode plate 11 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 lithium phosphate. The dimension of the positive electrode film layer along the length direction of the battery cell 7 is 200 mm to 600 mm. The electrolyte includes an organic solvent, which includes a carboxylic acid ester solvent. The mass content of the carboxylic acid ester solvent in the electrolyte is 3% to 70%.

[0090] The positive electrode film layer has a dimension of 200 mm or more along the length of the battery cell 7, which allows the positive electrode film layer to carry more positive electrode active material and makes the energy density of the battery cell 7 relatively high.

[0091] The positive electrode active material includes lithium phosphate, which has relatively poor conductivity. As the size of the positive electrode film layer along the length of the battery cell 7 increases, the electron transport resistance becomes a limiting factor for fast charging. Therefore, in the embodiments of this application, the size of the positive electrode film layer along the length of the battery cell 7 is limited to less than or equal to 600 mm, so that the electron transport path is not too long, which is beneficial to the fast charging of the battery cell.

[0092] In fast charging systems, lithium ions are transported at a relatively high rate. The electrolyte in this embodiment also includes a carboxylic acid ester solvent with high conductivity. When its mass content is greater than or equal to 3%, the electrolyte can quickly wet the positive electrode sheet, which is beneficial for the rapid migration of lithium ions in the positive electrode film. Lithium ions can also migrate rapidly in the electrolyte, accelerating the rate at which lithium ions migrate from the positive electrode active material to the negative electrode active material through the electrolyte, thus improving the liquid phase transport capability and the transport capability between the solid and liquid phases. Furthermore, the mass content of the carboxylic acid ester solvent in the electrolyte is not too high, less than or equal to 70%, which can reduce the side reactions at the negative electrode interface and reduce the high-temperature gas generation, thereby improving the high-temperature cycle life of the battery cell.

[0093] Negative electrode sheet

[0094] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector and comprising a negative electrode active material. For example, the negative current collector has two surfaces opposite each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative current collector.

[0095] The upper limit voltage for charging and the lower limit voltage for discharging a single battery cell vary depending on the positive electrode active material. For example, when the phosphate material includes lithium iron phosphate, the upper limit voltage for charging can be 3.65V and the lower limit voltage for discharging can be 2.0V, or the upper limit voltage for charging can be 3.8V and the lower limit voltage for discharging can be 2.0V. Another example is when the phosphate material includes lithium manganese iron phosphate, the upper limit voltage for charging can be 4.3V and the lower limit voltage for discharging can be 2.0V. Taking a charging upper limit voltage of 3.8V and a discharging lower limit voltage of 2.0V as an example, the state of a single battery cell will be described as follows: In this embodiment, the 100% state of charge (SOC) and the 0% state of charge (SOC) of a single battery cell are defined as follows...

[0096] The battery cell is charged at a constant current charging rate of 0.33C to the upper limit of the charging voltage, and then charged at a constant voltage to 0.05C, which corresponds to the 100% SOC state of the battery cell. The battery cell is then discharged at a constant current discharging rate of 0.33C to the cutoff voltage, which corresponds to the 0% SOC state of the battery cell.

[0097] In some embodiments, the compaction density of the negative electrode film layer at 0% state of charge (SOC) of the battery cell is 1.1 g / cm³. 3 Up to 1.7 g / cm 3 For example, the compaction density of the negative electrode film layer of a single battery cell at 0% charge is 1.10 g / cm³. 3 1.12 g / cm 3 1.14 g / cm 3 1.16 g / cm 3 1.18 g / cm 3 1.20g / cm 3 1.22g / cm 3 1.24 g / cm 3 1.26 g / cm 3 1.28g / cm 3 1.3g / cm 3 1.32g / cm 3 1.35g / cm 3 1.40g / cm 3 1.45g / cm 3 1.50g / cm 3 1.55g / cm 3 1.60g / cm3 1.65g / cm 3 1.66 g / cm 3 1.68g / cm 3 1.70g / cm 3 Or a range consisting of any two of the above values.

[0098] When the compaction density of the negative electrode film is within the above range, the thickness of the negative electrode film will not be too thick, which is beneficial for the rapid charging of the battery cell; moreover, the particle packing of the negative electrode active material will not be too dense, reducing the risk of particle crushing and improving the high-temperature cycle performance of the battery cell.

[0099] In some embodiments, the single-sided coating weight of the negative electrode film is 80 mg / 1540.25 mm. 2 Up to 150mg / 1540.25mm 2 For example, the single-sided coating weight of the negative electrode film is 80 mg / 1540.25 mm. 2 85mg / 1540.25mm 2 90mg / 1540.25mm 2 95mg / 1540.25mm 2 100mg / 1540.25mm 2 105mg / 1540.25mm 2 110mg / 1540.25mm 2 115mg / 1540.25mm 2 120mg / 1540.25mm 2 120mg / 1540.25mm 2 122mg / 1540.25mm 2 125mg / 1540.25mm 2 128mg / 1540.25mm 2 130mg / 1540.25mm 2 132mg / 1540.25mm 2 135mg / 1540.25mm 2 137mg / 1540.25mm 2 140mg / 1540.25mm 2 145mg / 1540.25mm 2 150mg / 1540.25mm 2 155mg / 1540.25mm 2 160mg / 1540.25mm 2 165mg / 1540.25mm2 170mg / 1540.25mm 2 175mg / 1540.25mm 2 180mg / 1540.25mm 2 Or a range consisting of any two of the above values.

[0100] When the single-sided coating weight of the negative electrode film meets the above range, its combination with an appropriate mass content of silicon element is beneficial to improving the energy density of the battery cell. The active ions migrate faster in the negative electrode film, which is beneficial to improving the fast charging capability of the battery cell.

[0101] In this embodiment, the compaction density of the negative electrode film layer at 0% State of Charge (SOC) of a battery cell is a well-known concept in the art. That is, the negative electrode sheet is disassembled from the battery cell at 0% SOC, and the compaction density of the negative electrode film layer is measured. For example, a single-sided coated negative electrode sheet (if double-sided coated, the negative electrode film layer on one side can be wiped off first) is taken, cut into small circular pieces with an area of ​​S1, weighed, and recorded as M1, and its thickness H1 is measured. Then, the negative electrode film layer of the weighed negative electrode sheet is wiped off, the weight of the negative current collector is weighed and recorded as M0, and its thickness H0 is measured. The single-sided coating weight of the negative electrode film layer = (weight of the negative electrode sheet M1 - weight of the negative current collector M0) / S1, the thickness of the negative electrode film layer = thickness of the negative electrode sheet H1 - thickness of the negative current collector H0, and the compaction density of the negative electrode film layer = single-sided coating weight of the negative electrode film layer / thickness of the negative electrode film layer.

[0102] In some embodiments, the negative electrode active material includes a silicon-based material. Optionally, the silicon-based material may include elemental silicon, silicon-carbon composites, or silicon oxide (SiO2). x At least one of (0 < x ≤ 2). The above materials can improve the capacity of the negative electrode active material, which is beneficial to reducing the coating thickness of the negative electrode film and shortening the migration path of lithium ions.

[0103] In some implementations, the specific surface area of ​​the silicon-based material is 1 m². 2 / g to 4m 2 / g, for example, 1m 2 / g, 1.2m 2 / g, 1.4m 2 / g, 1.5m 2 / g, 1.6m 2 / g, 1.8m 2 / g、2m 2 / g, 2.2m 2 / g, 2.4m 2 / g, 2.5m 2 / g, 2.6m 2 / g, 2.8m2 / g、3m 2 / g, 3.2m 2 / g, 3.4m 2 / g, 3.5m 2 / g, 3.6m 2 / g, 3.8m 2 / g、4m 2 / g or a range consisting of any two of the above values.

[0104] When the specific surface area of ​​silicon-based materials is within the above range, it can provide suitable insertion sites for lithium ions, thereby improving fast charging capability. Under fast charging conditions, it can also alleviate side reactions between silicon-based materials and electrolytes, reduce high-temperature gas generation, and improve the cycle performance of battery cells.

[0105] In the embodiments of this application, the specific surface area of ​​the material has a meaning known in the art and can be detected using equipment and methods known in the art. For example, it can be detected according to the testing standard GB / T 19587-2017. The negative electrode sheet in the battery cell can be disassembled to obtain the relevant material as a sample, and the specific surface area can be tested using the Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, Inc.

[0106] In some embodiments, the silicon-based material is in particulate form with an average particle size of 4 μm to 12 μm, such as 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, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, or any range of two of the above values.

[0107] When the average particle size of silicon-based materials is within the above range, it can alleviate the side reactions between silicon-based materials and electrolytes, improve high-temperature cycling performance, and provide appropriate insertion sites for lithium ions, thereby enhancing fast charging capability.

[0108] In some embodiments, the negative electrode active material includes a carbon-based material, which has high cycle stability and can improve the high-temperature cycle performance of the battery cell.

[0109] Optionally, the carbon-based material includes at least one of artificial graphite and natural graphite.

[0110] In some embodiments, the negative electrode active material may include, in addition to the aforementioned carbon-based materials and optionally silicon-based materials, at least one of tin-based materials and lithium titanate. Tin-based materials may include at least one of elemental tin, tin oxides, and tin alloys.

[0111] The qualitative and quantitative analysis of each substance or element in this application can be performed using suitable equipment and methods known to those skilled in the art. Relevant testing methods can be referenced from domestic and international testing standards and enterprise standards. Furthermore, those skilled in the art can adaptively modify certain testing steps / instrument parameters from the perspective of testing accuracy to obtain more accurate results. One testing method can be used for qualitative or quantitative analysis, or several testing methods can be used in combination for qualitative or quantitative determination.

[0112] For example, this application can combine the general rules of X-ray diffraction analysis in JIS / K0131-1996 to perform X-ray powder diffraction tests and qualitative analysis on negative electrode sheets or negative electrode active materials.

[0113] Artificial graphite and natural graphite can be distinguished by SEM cross-sectional images taken by scanning electron microscope (SEM). Natural graphite has gaps between the sheet-like structures in its SEM cross-section, while artificial graphite has a dense structure with no obvious gaps. Alternatively, they can be distinguished by XRD patterns obtained by X-ray diffraction. Natural graphite has obvious 2H and 3R phases in its XRD pattern, while artificial graphite only has the 2H phase in its XRD pattern.

[0114] As shown in Figure 6, in this embodiment of the application, the negative electrode film layer 121 of the negative electrode sheet 12 includes at least one film layer, which can be a single film layer or at least two film layers. Optionally, the negative electrode film layer 121 includes at least two film layers.

[0115] When the negative electrode film layer 121 is a single layer, the negative electrode active material in the negative electrode film layer 121 includes carbon-based materials and optional silicon-based materials.

[0116] When the negative electrode film 121 employs at least two film layers, the negative electrode active material in the negative electrode film 121 includes carbon-based materials and optionally silicon-based materials. The negative electrode film 121 may include two, three, four, or even more film layers.

[0117] In some embodiments, the negative electrode film 121 includes a first negative electrode film 1211 and a second negative electrode film 1212. The first negative electrode film 1211 is disposed on the surface of the negative electrode current collector 122, and the negative electrode active material of the first negative electrode film 1211 includes a carbon-based material. The second negative electrode film 1212 is connected to the side of the first negative electrode film 1211 facing away from the negative electrode current collector 122, and the negative electrode active material of the second negative electrode film 1212 also includes a carbon-based material. The interface between the first negative electrode film 1211 and the second negative electrode film 1212 may be regular or irregular, optionally irregular; or there may be no obvious interface between the first negative electrode film 1211 and the second negative electrode film 1212.

[0118] The negative electrode film layer 121 includes at least two film layers. Layered coating is beneficial to improving both the fast charging performance and cycle life of the battery cell.

[0119] In some embodiments, at least one of the first negative electrode film 1211 and the second negative electrode film 1212 comprises a silicon-based material.

[0120] Optionally, the first negative electrode film layer 1211 may also include a silicon-based material.

[0121] Optionally, the second negative electrode film 1212 may also include a silicon-based material.

[0122] For example, the first negative electrode film 1211 includes a carbon-based material and a silicon-based material, and the second negative electrode film 1212 includes a carbon-based material and a silicon-based material. Alternatively, the first negative electrode film 1211 includes a carbon-based material and a silicon-based material, and the second negative electrode film 1212 includes a carbon-based material. Alternatively, the first negative electrode film 1211 includes a carbon-based material, and the second negative electrode film 1212 includes a carbon-based material and a silicon-based material.

[0123] When both the first negative electrode film layer 1211 and the second negative electrode film layer 1212 contain silicon-based materials, it is more beneficial to improve the energy density of the battery cell. When the first negative electrode film layer 1211 contains silicon-based materials but the second negative electrode film layer 1212 does not, the second negative electrode film layer 1212 can alleviate the volume expansion of the first negative electrode film layer 1211, reduce the side reactions between the negative electrode film layer 121 and the electrolyte, and improve high-temperature cycle performance.

[0124] When the negative electrode film layer 121 uses at least two film layers, the cross-sectional shape of the negative electrode film layer 121 along the thickness direction X can be the same or similar, or of course different.

[0125] Along the thickness direction X of the negative electrode film layer 121, the negative electrode film layer 121 is divided into three regions, namely the first region 121a, the third region 121c, and the second region 121b. The first region 121a is the region of the negative electrode film layer 121 that is close to the negative electrode current collector 122 along the thickness direction X, and the thickness of the first region 121a is 1 / 3 of the thickness of the negative electrode film layer 121. The second region 121b is the region of the negative electrode film layer 121 that is away from the negative electrode current collector 122 along the thickness direction X, and the thickness of the second region 121b is 1 / 3 of the thickness of the negative electrode film layer 121.

[0126] The cross-sectional shapes of the first region 121a and the second region 121b can be the same or similar, or they can be different. The cross-sectional shapes of the first region 121a and the third region 121c can be the same or similar, or they can be different. The cross-sectional shapes of the second region 121b and the third region 121c can be the same or similar, or they can be different.

[0127] There may or may not be a clear layer interface between the first region 121a, the second region 121b, and the third region 121c. For example, the first negative electrode film layer 1211 includes the first region 121a, the second negative electrode film layer 1212 includes the second region 121b, and the third region 121c may be a part of the first negative electrode film layer 1211, or the third region 121c may be a part of the second negative electrode film layer 1212, or the third region 121c may be a part of both the first negative electrode film layer 1211 and the second negative electrode film layer 1212.

[0128] In some embodiments, in a cross-section of the negative electrode film layer 121 parallel to the thickness direction X, the porosity of a single carbon-based material located in the first region 121a is greater than or equal to the porosity of a single carbon-based material located in the second region 121b. Optionally, the porosity of a single carbon-based material located in the first region 121a is less than the porosity of a single carbon-based material located in the second region 121b.

[0129] The carbon-based material is granular with internal voids. Along the cross-section of the negative electrode film layer 121 parallel to the thickness direction X, the percentage of void area to the total cross-sectional area of ​​the carbon-based material is the void ratio of a single carbon-based material.

[0130] During the charging process of a single battery cell, lithium ions diffuse from the second region 121b to the first region 121a. The porosity of a single carbon-based material in the first region 121a is less than or equal to the porosity of a single carbon-based material in the second region 121b, which is more conducive to the diffusion of lithium ions in the first region 121a, improves the transmission rate, and thus facilitates the rapid charging of the battery cell.

[0131] Optionally, the average particle size of the carbon-based material in the first region 121a can be greater than or equal to the average particle size of the carbon-based material in the second region 121b. More preferably, the average particle size of the carbon-based material in the first region 121a can be greater than the average particle size of the carbon-based material in the second region 121b, which facilitates the rapid migration of lithium ions from the second region 121b to the first region 121a, 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 121a can be smaller than the average particle size of the carbon-based material in the second region 121b.

[0132] Optionally, the average particle size of the carbon-based material of the first negative electrode film layer 1211 can be greater than or equal to the average particle size of the carbon-based material of the second negative electrode film layer 1212. More preferably, the average particle size of the carbon-based material of the first negative electrode film layer 1211 can be greater than the average particle size of the carbon-based material of the second negative electrode film layer 1212.

[0133] The difference in particle size between the first negative electrode film layer 1211 and the second negative electrode film layer 1212 can improve the fast charging performance of the battery cell. Specifically, during fast charging, the overpotential of the second negative electrode film layer 1212 is usually high, and the bottleneck of fast charging is mainly the second negative electrode film layer 1212. However, in the embodiment of this application, the particle size of the second negative electrode film layer 1212 is relatively small, which can shorten the solid phase transport path of lithium ions, improve the fast charging performance, and improve the problem of lithium deposition on the surface of the negative electrode sheet 12.

[0134] Optionally, the average particle size of the carbon-based material in the first region 121a is between 12 μm and 21 μm, for example, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm, 17.5 μm, 18 μm, 18.5 μm, 19 μm, 19.5 μm, 20 μm, 20.5 μm, 21 μm, or any combination of two of the above values. When the average particle size of the carbon-based material in the first region 121a is within the above range, it can improve cycle life and has virtually no adverse effect on fast charging performance.

[0135] Optionally, the average particle size of the carbon-based material in the first negative electrode film 1211 is between 12 μm and 21 μm. When the average particle size of the carbon-based material in the first negative electrode film 1211 is within the above range, it can improve cycle life and has virtually no adverse effect on fast charging performance.

[0136] Optionally, the average particle size of the carbon-based material in the second region 121b is from 9 μm to 17 μm, for example, 9 μm, 9.5 μm, 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, 16.5 μm, 17 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 1212 is within the above range, it is beneficial to improve the fast charging capability of the battery cell and enhance the stability of the material.

[0137] Optionally, the average particle size of the carbon-based material in the second negative electrode film 1212 is between 9 μm and 17 μm. When the average particle size of the carbon-based material in the second negative electrode film 1212 is within the above range, the solid-phase transport path of lithium ions can be shortened, thereby improving fast charging performance and material stability.

[0138] For example, the carbon-based material of the first region 121a includes artificial graphite and natural graphite, and the carbon-based material of the second region 121b includes artificial graphite. For instance, the negative electrode active material of the first region 121a includes silicon-based material, artificial graphite and natural graphite, and the negative electrode active material of the second region 121b includes silicon-based material and artificial graphite.

[0139] For example, the carbon-based material of the first negative electrode film layer 1211 includes artificial graphite and natural graphite, and the carbon-based material of the second negative electrode film layer 1212 includes artificial graphite. For instance, the negative electrode active material of the first negative electrode film layer 1211 includes silicon-based material, artificial graphite and natural graphite, and the negative electrode active material of the second negative electrode film layer 1212 includes silicon-based material and artificial graphite.

[0140] In other embodiments, in a cross section of the negative electrode film layer 121 parallel to the thickness direction X, the void ratio of a single carbon-based material located in the first region 121a is smaller than the void ratio of a single carbon-based material located in the second region 121b.

[0141] During the charging process of a single battery cell, lithium ions diffuse from the second region 121b to the first region 121a. The second region 121b has a larger proportion of voids in the individual carbon-based material, which is conducive to the rapid transport of lithium ions from the second region 121b to the first region 121a, thus facilitating the rapid charging of the battery cell.

[0142] Optionally, the average particle size of the carbon-based material in the first region 121a can be smaller than the average particle size of the carbon-based material in the second region 121b. The relatively larger average particle size of the carbon-based material in the second region 121b results in higher pressure resistance during film preparation, which is beneficial for improving particle density. Conversely, the relatively smaller average particle size of the carbon-based material in the first region 121a enables rapid lithium-ion migration, 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 121a can be greater than or equal to the average particle size of the carbon-based material in the second region 121b.

[0143] Optionally, the average particle size of the carbon-based material in the first region 121a is from 9 μm to 17 μm, for example, 9 μm, 9.5 μm, 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, 16.5 μm, 17 μm or any range of two of the above values.

[0144] Optionally, the carbon-based material of the first negative electrode film 1211 has an average particle size of 9 μm to 17 μm.

[0145] Optionally, the average particle size of the carbon-based material in the second region 121b is from 12 μm to 21 μm, for example, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm, 17.5 μm, 18 μm, 18.5 μm, 19 μm, 19.5 μm, 20 μm, 20.5 μm, 21 μm or any range of two of the above values.

[0146] Optionally, the carbon-based material of the second negative electrode film 1212 has an average particle size of 12 μm to 21 μm.

[0147] For example, the carbon-based material of the second region 121b includes artificial graphite and natural graphite, and the carbon-based material of the first region 121a includes artificial graphite. Optionally, the negative electrode active material also includes a silicon-based material. For example, the negative electrode active material of the second region 121b includes a silicon-based material, artificial graphite, and natural graphite, and the negative electrode active material of the first region 121a includes a silicon-based material and artificial graphite.

[0148] For example, the carbon-based material of the second negative electrode film 1212 includes artificial graphite and natural graphite, and the carbon-based material of the first negative electrode film 1211 includes artificial graphite. Optionally, the negative electrode active material further includes a silicon-based material. For example, the negative electrode active material of the second negative electrode film 1212 includes silicon-based materials, artificial graphite, and natural graphite, and the negative electrode active material of the first negative electrode film 1211 includes silicon-based materials and artificial graphite.

[0149] In the embodiments of this application, the average particle size of the active material in the first region 121a and the second region 121b can be detected by the following equipment and method: the negative electrode sheet 12 is used as a sample, and a scanning electron microscope (SEM) is used to take a cross-sectional image along the thickness direction X of the negative electrode film layer 121 to obtain an SEM cross-sectional image. The particle size of the active material in the SEM cross-section is counted, and the average particle size of the active material is calculated based on the counted number.

[0150] 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 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 negative electrode conductive agent is ≤5% based on the total weight of the negative electrode film layer.

[0151] 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.

[0152] 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.

[0153] In some embodiments, the negative electrode 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. The composite current collector may include a polymer substrate and a metal material layer formed on at least one surface of the polymer substrate. 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 substrate may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0154] The negative electrode film is typically formed by coating a negative electrode slurry onto a 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.

[0155] 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 this 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 this application further includes a protective layer covering the surface of the negative electrode film layer.

[0156] Positive electrode sheet

[0157] In some implementations, the battery cell also includes a positive electrode.

[0158] 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 active material. For example, the positive current collector has two surfaces opposite each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0159] In some embodiments, the dimension of the positive electrode film layer along the length of the positive electrode sheet is 200 mm to 600 mm, for example, 200 mm, 250 mm, 300 mm, 350 mm, 400 mm, 450 mm, 500 mm, 550 mm, 600 mm, or any range of two of the above values. Optionally, the dimension of the positive electrode film layer along the length of the positive electrode sheet is 400 mm to 600 mm.

[0160] When the electrode assembly has a stacked structure, the length direction of the positive electrode sheet is parallel to the length direction 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 positive electrode sheet is parallel to the width direction 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.

[0161] For example, the positive electrode film has a length dimension of 200 mm to 600 mm; the electrolyte includes an organic solvent, including carboxylic acid ester solvents, and the electrolyte has a conductivity of 9 mS / cm to 18 mS / cm at room temperature. The length of the positive electrode film, combined with the electrolyte's conductivity, is beneficial for improving the liquid phase transport rate of lithium ions, enhancing kinetic performance, and increasing the fast-charging capability of the battery cell. Furthermore, because carboxylic acid ester solvents have low viscosity, they can uniformly wet all parts of the positive electrode film, resulting in a uniform charging degree throughout the positive electrode film. The lithium ions released from the positive electrode film are evenly distributed on the negative electrode side, reducing the risk of localized side reactions on the negative electrode side and improving high-temperature cycling performance under fast charging.

[0162] Optionally, when the length of the positive electrode film is greater than or equal to 200 mm and less than 400 mm, the electrolyte includes an organic solvent, including carboxylic acid ester solvents, and the conductivity of the electrolyte at room temperature is 9 mS / cm to 18 mS / cm. The length of the positive electrode film, combined with the electrolyte's conductivity as described above, is beneficial for improving high-temperature cycling performance under fast charging.

[0163] Optionally, the positive electrode film has a length dimension of 400 mm to 600 mm; the electrolyte includes an organic solvent, including carboxylic acid ester solvents, and the electrolyte has a conductivity of 11 mS / cm to 18 mS / cm at room temperature. The relatively long length of the positive electrode film, combined with the electrolyte of the aforementioned conductivity, is beneficial for improving high-temperature cycling performance under fast charging.

[0164] Optionally, the positive electrode film layer has a length dimension of 400 mm to 600 mm; the electrolyte includes an organic solvent, including carboxylic acid ester solvents, with the carboxylic acid ester solvent having a mass content of 3% to 70%, optionally 10% to 30%. The aforementioned mass content of carboxylic acid ester solvent results in a relatively low viscosity of the electrolyte, which facilitates rapid wetting of the positive electrode film layer, ensuring uniform charge and discharge performance throughout the positive electrode film layer, reducing the risk of lithium deposition on the negative electrode side, and improving the cycle life of the battery cell.

[0165] In some embodiments, the compaction density of the positive electrode film layer at 0% state of charge (SOC) of the battery cell is 2.20 g / cm³. 3 Up to 2.85 g / cm 3 For example, at 0% state of charge (SOC), the compaction density of the positive electrode film layer in a single battery cell is 2.20 g / cm³. 3 2.25g / cm 3 2.30g / cm 3 2.32 g / cm 3 2.35g / cm 3 2.38g / cm 3 2.40 g / cm 3 2.42 g / cm 3 2.45g / cm 3 2.48 g / cm 3 2.50g / cm 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 2.85g / cm 3 Or a range consisting of any two of the above values.

[0166] When the compaction density of the positive electrode film is within the above range, it is beneficial to improve the energy density of the battery cell. Furthermore, since the positive active material of the positive electrode film is packed more densely, the contact resistance between particles is smaller, which can further reduce the resistance of the electrode, thereby reducing heat generation under fast charging, reducing high-temperature gas generation, and improving high-temperature cycle performance, especially the high-temperature cycle performance under fast charging system.

[0167] In some embodiments, the single-sided coating weight of the positive electrode film is 250 mg / 1540.25 mm. 2 Up to 300mg / 1540.25mm 2 For example, the single-sided coating weight of the positive electrode film is 250 mg / 1540.25 mm. 2 260mg / 1540.25mm 2 270mg / 1540.25mm 2 280mg / 1540.25mm 2 290mg / 1540.25mm 2 300mg / 1540.25mm 2 Or a range consisting of any two of the above values.

[0168] 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, and it can simultaneously improve the energy density and charging rate performance of the battery cell, while preventing excessive heat accumulation within the battery cell system, reducing the risk of electrolyte decomposition at high temperatures, and improving the cycle performance of the battery cell.

[0169] In this embodiment, the compaction density of the positive electrode film layer at 0% State of Charge (SOC) of a single battery cell is a well-known concept in the art. This means disassembling the battery cell at 0% SOC to separate the positive electrode sheet and measuring the compaction density of the positive electrode film layer. For example, take a single-sided coated positive electrode sheet (if it is a double-sided coated sheet, the positive electrode film layer on one side can be wiped off first), cut it into a small circular piece with an area of ​​S1, weigh it, record its weight as M1, and measure its thickness H1. Then wipe off the positive electrode film layer of the weighed positive electrode sheet, weigh the positive current collector, record its weight as M0, and measure its thickness H0. The single-sided coating weight of the positive electrode film layer = (weight of the positive electrode sheet M1 - weight of the positive current collector M0) / S1, the thickness of the positive electrode film layer = thickness of the positive electrode sheet H1 - thickness of the positive current collector H0, and the compaction density of the positive electrode film layer = single-sided coating weight of the positive electrode film layer / thickness of the positive electrode film layer.

[0170] In some embodiments, the positive electrode active material includes one or more of lithium-containing transition metal oxides and lithium-containing phosphates. Optionally, the positive electrode active material includes lithium-containing phosphates. The lithium-containing phosphate can have an olivine structure, which is structurally stable during charge and discharge and can improve the cycle life of the battery cell.

[0171] 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.

[0172] In some embodiments, the positive electrode film layer also includes a carbon-containing material, which is a carbon-containing conductive material. The aforementioned material can improve the conductivity of the positive electrode film layer, which is beneficial to improving the fast charging performance of the battery cell.

[0173] Optionally, the carbon content of the positive electrode film is from 0.8% to 3.5% by mass, for example, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, or any range of two of the above values. Optionally, the carbon content of the positive electrode film is from 1.3% to 3.0% by mass.

[0174] For example, carbon-containing materials may include carbon nanotubes, which can act as conductive agents in the positive electrode film to improve the conductivity of the positive electrode film.

[0175] For example, the lithium phosphate with olivine structure can be an unmodified lithium phosphate such as lithium iron phosphate, or a material obtained by coating modification, such as a carbon-containing material 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.

[0176] 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 high-temperature cycle performance of battery cells.

[0177] 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.

[0178] 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.

[0179] In some embodiments, the lithium phosphate is in the form of particles, which includes a plurality of first phosphate particles and a plurality of second phosphate particles. The longest diameter of the first phosphate particles is greater than or equal to a preset longest diameter, such as 1 μm, and the longest diameter of the second phosphate particles is less than 1 μm. It can be understood that particles with a longest diameter greater than or equal to 1 μm belong to the first phosphate particles, and particles with a longest diameter less than 1 μm belong to the second phosphate particles.

[0180] The longest diameter of the first phosphate particle is greater than that of the second phosphate particle. The average longest diameter of the first phosphate particle is 1 μm to 5 μm, and the average longest diameter of the second phosphate particle is 0.1 μm to 0.5 μm.

[0181] For example, the average longest diameter of the first phosphate particle is 1 μm to 5 μm, such as 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm or any range of two of the above values.

[0182] For example, the average longest diameter of the second phosphate particles is 0.1 μm to 0.5 μm, such as 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm or any combination of two of the above values.

[0183] When lithium phosphates meet the above conditions, their longest diameter is relatively small, the lithium ion insertion / extraction path in lithium phosphates is short, and the heat generation is low; moreover, the particle size of the above lithium phosphates is not too small, and they will not agglomerate during the processing and preparation process, which makes the performance of lithium phosphates stable; thus, it is beneficial to improve the high-temperature cycle performance of battery cells.

[0184] In some embodiments, the mass content of the second phosphate particles in the lithium phosphate is 80% to 95%, for example, 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, or any combination of two of the above values. A mass content of the second phosphate particles within an appropriate range, such as 80% to 95%, can further reduce heat generation, decrease heat generation within the battery cell system, reduce the risk of electrolyte component decomposition due to heat accumulation, and improve the high-temperature cycle performance of the battery cell.

[0185] In some embodiments, the positive electrode film layer also includes a lithium replenishing agent, which includes lithium element. During the charging process of the battery cell, the lithium ions are released to compensate for lithium loss, which is beneficial to improving the capacity characteristics and high-temperature cycle performance of the battery cell.

[0186] In some embodiments, the lithium supplement includes at least one of lithium ferrite, lithium nickel oxide, and lithium cobalt oxide.

[0187] In some embodiments, the lithium replenishing agent is in particulate form with an average longest diameter of 9 μm to 13 μm, such as 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm or any combination thereof.

[0188] In some embodiments, the lithium replenishing agent is in particulate form with an average shortest diameter of 5 μm to 9 μm, such as 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm or any combination thereof.

[0189] In this embodiment, the positive electrode sheet is cut along its thickness direction to expose the cross-section of the positive electrode film layer. This can also be understood as a cross-section of the positive electrode film layer along its own thickness direction. By performing scanning electron microscopy (SEM) testing on the cross-section of the positive electrode film layer, the longest and shortest diameters of the lithium supplement particles and the longest diameter of the lithium phosphate-containing particles are determined. For example, the "longest diameter" of a particle refers to the longest straight line passing through the center point of the particle and extending to the outer periphery of the particle. The "shortest diameter" of a particle refers to the shortest straight line passing through the center point of the particle and extending to the outer periphery of the particle.

[0190] In a cross-section of the positive electrode film along its thickness direction, the longest diameter of multiple, for example, 10, lithium supplements is counted, and their average value is calculated as the average longest diameter; the shortest diameter of multiple, for example, 10, lithium supplements is counted, and their average value is calculated as the average shortest diameter.

[0191] In a cross-section along the thickness direction of the positive electrode film, the longest diameter of multiple, for example, 50 lithium phosphate particles is counted. Particles with a longest diameter greater than or equal to 1 μm are classified as first phosphate particles, and particles with a longest diameter less than 1 μm are classified as second phosphate particles. The average of the longest diameters of all first phosphate particles is calculated as the average longest diameter of the first phosphate particles, and the average of the longest diameters of all second phosphate particles is calculated as the average longest diameter of the second phosphate particles.

[0192] In some embodiments, the mass percentage of the lithium replenishing agent, based on the total mass of the positive electrode film, is 0.5% to 3%, for example, 0.5%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, 2.5%, 3.0%, or any combination thereof. When using a lithium replenishing agent within the above mass range, the stability of the lithium replenishing agent can be effectively improved, while also exhibiting a good oxygen release effect.

[0193] 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.

[0194] Optionally, the positive electrode conductive agent includes carbon nanotubes, and the mass content of carbon nanotubes in the positive electrode film layer is 0.1% to 2%, for example, 0.1%, 0.3%, 0.5%, 0.7%, 0.9%, 1.1%, 1.3%, 1.5%, 1.7%, 1.9%, 2%, or any combination thereof. Optionally, the mass content of carbon nanotubes in the positive electrode film layer is 0.15% to 1.2%.

[0195] When the mass content of carbon nanotubes is within the above range, it is beneficial to improve the conductivity of the positive electrode film and improve the fast charging performance of the battery cell.

[0196] Optionally, the specific surface area of ​​the carbon nanotubes is 500 m². 2 / g to 2500m 2 / g, for example 500m 2 / g、700m 2 / g、900m 2 / g、1100m 2 / g、1300m 2 / g, 1500m 2 / g、1700m 2 / g、1900m 2 / g、2100m 2 / g、2300m 2 / g、2500m 2 / g or a range consisting of any two of the above.

[0197] When the specific surface area of ​​carbon nanotubes is within the above range, it is beneficial to improve electron conduction ability; and when combined with an appropriate amount of carbon nanotubes, the degree of side reaction can be reduced and high-temperature cycling performance can be improved.

[0198] Optionally, the diameter of the carbon nanotubes is from 0.5 nm to 20 nm, specifically 0.5 nm, 1.5 nm, 2.5 nm, 3.5 nm, 4.5 nm, 5.5 nm, 6.5 nm, 7.5 nm, 8.5 nm, 9.5 nm, 10.5 nm, 11.5 nm, 12.5 nm, 13.5 nm, 14.5 nm, 15.5 nm, 16.5 nm, 17.5 nm, 18.5 nm, 19.5 nm, 20 nm, or any combination of the above. Optionally, the diameter of the carbon nanotubes is from 0.5 nm to 7.5 nm.

[0199] When the diameter of carbon nanotubes is within the above range, the structure is relatively stable and has excellent electronic conductivity.

[0200] Carbon nanotubes can generally be considered as two-dimensional carbon materials rolled up. When the number of layers formed by the rolling is single, it is a single-walled carbon nanotube; when the rolling is multi-layered, it is a multi-walled carbon nanotube. The diameter of a carbon nanotube is the outer diameter of the carbon nanotube along a cross-section perpendicular to its own central axis.

[0201] 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.

[0202] 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. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. 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 polymeric material substrate may include at least one selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0203] The positive electrode film is typically formed by coating a positive electrode slurry onto a 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.

[0204] 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 this application further includes a positive conductive layer sandwiched between the positive current collector and the positive electrode film layer and disposed on the surface of the positive current collector. In other embodiments, the positive electrode sheet of this application further includes a protective layer covering the surface of the positive electrode film layer.

[0205] Electrolyte

[0206] 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.

[0207] In some embodiments, the electrolyte has a conductivity of 9 mS / cm to 18 mS / cm at room temperature. Exemplarily, the electrolyte conductivity at room temperature is 9 mS / cm, 9.5 mS / cm, 10 mS / cm, 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, 14 mS / cm, 14.5 mS / cm, 15 mS / cm, 15.5 mS / cm, 16 mS / cm, 16.5 mS / cm, 17 mS / cm, 17.5 mS / cm, 18 mS / cm, or any combination of two of the above values. Optionally, the electrolyte conductivity at room temperature is 11 mS / cm to 18 mS / cm.

[0208] 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, thereby reducing heat generation and reducing the amount of high-temperature gas generated due to heat accumulation, and improving the high-temperature cycle performance of the battery cell under fast charging.

[0209] 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.

[0210] In some embodiments, the organic solvent includes carboxylic acid ester solvents.

[0211] Optionally, the carboxylic acid ester solvent has a mass content of 3% to 70% in the electrolyte. Exemplarily, the mass content of the carboxylic acid ester solvent is 3%, 5%, 8%, 10%, 13%, 15%, 18%, 20%, 23%, 25%, 28%, 30%, 33%, 35%, 38%, 40%, 43%, 45%, 48%, 50%, 53%, 55%, 58%, 60%, 63%, 65%, 68%, 70%, or a range of any two of the above values. Optionally, the carboxylic acid ester solvent has a mass content of 10% to 30% in the electrolyte.

[0212] When the mass content of carboxylic acid ester solvents is within the above-mentioned range, it can improve the conductivity of the electrolyte; and the electrolyte is compatible with the silicon-containing anode, effectively mitigating side reactions on the anode side, reducing gas production in the battery cell, and improving the high-temperature cycle performance of the battery cell under fast charging. The carboxylic acid ester solvents at the above-mentioned mass content can also rapidly wet the cathode film, resulting in a more uniform charging state of the cathode film, reducing the risk of localized side reactions on the anode side, and further improving the high-temperature cycle performance of the battery cell under fast charging.

[0213] For example, the carboxylic acid ester solvent includes cyclic carboxylic acid esters, which include one or more of γ-butyrolactone, γ-valerolactone, and δ-valerolactone. The aforementioned material has low viscosity, which improves its wettability on the electrode and enhances high-temperature cycling performance under fast charging.

[0214] For example, the carboxylic acid ester solvent includes chain carboxylic acid esters, which include one or more of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, propyl propionate, and butyl propionate. The aforementioned materials have low viscosity, which improves the wetting ability of the electrode and enhances high-temperature cycling performance under fast charging.

[0215] In some embodiments, the organic solvent includes carbonate solvents.

[0216] Using a mixture of carbonate and carboxylic acid ester solvents can improve the stability of the electrolyte, reduce its high-temperature gas production, and help improve the high-temperature cycle life of battery cells.

[0217] For example, carbonate solvents include one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. Optionally, carbonate solvents include one or more of ethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate.

[0218] In some embodiments, the carbonate solvent includes dimethyl carbonate, which has a mass content in the electrolyte of 10% to 30%, for example 10%, 15%, 20%, 25%, 30%, or any combination of two of the above values.

[0219] When the mass content of dimethyl carbonate is within the above range, the viscosity of the electrolyte is lower, which is conducive to the rapid transport of lithium ions and improves the fast charging capability; it can also improve the wetting ability of the electrode and improve the high-temperature cycle performance under fast charging.

[0220] In some embodiments, the ratio of the mass content of dimethyl carbonate to the mass content of the carboxylic acid ester solvent is 1 to 7, based on the mass of the electrolyte, for example, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7 or any range of two of the above values.

[0221] When the ratio of the mass content of dimethyl carbonate to the mass content of carboxylic acid ester solvent is within the above range, it is beneficial to improve the fast charging capability and cycle performance of the battery cell.

[0222] In some embodiments, the electrolyte salt includes a lithium salt, which includes one or more of lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate. Optionally, the lithium salt includes lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate.

[0223] Lithium hexafluorophosphate may decompose to produce hydrofluoric acid (HF). The side reaction between hydrofluoric acid and the negative electrode, especially the silicon-containing negative electrode, may lead to increased gas production during high-temperature storage. The combined use of lithium hexafluorophosphate and lithium difluorosulfonylimide can reduce the hydrofluoric acid content, slow down the side reaction at the negative electrode interface, reduce the amount of gas produced during high-temperature storage, and help improve the high-temperature cycle life of the battery cells.

[0224] In some embodiments, the mass ratio of lithium difluorosulfonylimide to lithium hexafluorophosphate is 0.3 to 1.2, for example, 0.3, 0.5, 0.7, 0.9, 1.1, 1.2 or any combination of the two values ​​mentioned above, based on the mass of the electrolyte.

[0225] 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 amount of gas generated during 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 amount of gas generated during high-temperature storage and is conducive to improving the high-temperature cycle life of the battery cell.

[0226] For example, based on the mass of the electrolyte, the mass content of lithium difluorosulfonylimide is 2% to 11%, such as 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, or any combination of two of the above values. When the mass content of lithium difluorosulfonylimide is within the above range, the hydrofluoric acid content can be reduced, the side reactions at the negative electrode interface can be mitigated, the gas generation during high-temperature storage can be reduced, and the high-temperature cycle life of the battery cell can be improved.

[0227] For example, based on the mass of the electrolyte, the mass content of lithium hexafluorophosphate is 3% to 14%, such as 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, or any combination of two of the above values. When the mass content of lithium hexafluorophosphate is within the above range, the conductivity of the electrolyte is relatively high, which is beneficial to the migration of lithium ions and improves the fast charging performance of the battery cells.

[0228] In some embodiments, the electrolyte also contains additives, which may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature power performance.

[0229] In some embodiments, the additive comprises cyclic carbonate additives, such as one or more of fluorocyclic carbonates and vinylene carbonates; alternatively, the additive comprises fluorocyclic carbonates and vinylene carbonates.

[0230] Fluorinated cyclic carbonates 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 improve high-temperature cycling performance.

[0231] The combined use of fluorinated cyclic carbonates and vinylene carbonates results in a denser SEI film on the anode surface with lower impedance, which can more effectively protect silicon-containing anodes, reduce the degree of side reactions at the anode interface, and improve high-temperature cycling performance.

[0232] Optionally, the fluorocyclic carbonate includes at least one of monofluoroethylene carbonate, difluoroethylene carbonate, and trifluoropropylene carbonate.

[0233] Optionally, based on the mass of the electrolyte, the mass content of the fluorocyclic carbonate is from 0.5% to 20%, for example, 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%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, 15%, 15.5%, 16%, 16.5%, 17%, 17.5%, 18%, 18.5%, 19%, 19.5%, 20%, or any combination of two of the above values. A mass content of fluorocyclic carbonate within the above range is beneficial for improving cycle performance.

[0234] As an example, based on the mass of the electrolyte, the mass content of fluorinated cyclic carbonates is 0.5% to 10%; the mass content of silicon in the negative electrode active material of silicon-based materials is 0.3% to 7.5%.

[0235] When the mass content of silicon is relatively high, the volume expansion is relatively greater. When the mass content of fluorinated cyclic carbonates and the mass content of silicon meet the above conditions, the volume expansion of silicon can be more effectively mitigated, which can improve the lifespan of silicon-containing systems and improve high-temperature cycling performance.

[0236] As another example, based on the mass of the electrolyte, the mass content of fluorinated cyclic carbonates is greater than 10% and less than or equal to 20%, and the mass content of silicon in the negative electrode active material of silicon-based materials is greater than 7.5% and less than or equal to 15%.

[0237] When the mass content of fluorinated cyclic carbonates and the mass content of silicon meet the above conditions, the volume expansion of silicon can be more effectively mitigated, the lifespan of silicon-containing systems can be improved, and the high-temperature cycling performance can be enhanced.

[0238] Optionally, based on the mass of the electrolyte, the mass content of vinylene carbonate is from 0.1% to 3%, for example, 0.1%, 0.5%, 0.6%, 1.0%, 1.1%, 1.5%, 1.6%, 2.0%, 2.1%, 2.5%, 2.6%, 3%, or any combination of two of the above values. The above-mentioned mass content of vinylene carbonate results in a more compact SEI film on the negative electrode surface, more effectively protecting the silicon-containing negative electrode, reducing the degree of side reactions at the negative electrode interface, and improving cycle performance.

[0239] The combined use of the aforementioned amounts of vinylene carbonate and fluorocyclic carbonate further optimizes the performance of the SEI film on the negative electrode surface, resulting in excellent density and low impedance. This more effectively protects the silicon-containing negative electrode, reduces the degree of side reactions at the negative electrode interface, and improves cycle performance.

[0240] 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.

[0241] 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".

[0242] In this embodiment, after quantitative and qualitative detection of each component in the electrolyte, the components are classified, and carboxylic acid ester solvents and carbonate solvents are included as components of organic solvents. The mass content of each component is calculated based on the mass of the electrolyte as 100%.

[0243] Fluorinated cyclic carbonates and vinylene carbonates were used as additives in the electrolyte. The mass content of each component was calculated based on the mass of the electrolyte as 100%.

[0244] Isolation component

[0245] In some embodiments, the electrode assembly further includes a spacer disposed between the positive electrode and the negative electrode.

[0246] 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.

[0247] 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.

[0248] In some embodiments, the separator is a solid electrolyte. The solid electrolyte is disposed between the positive and negative electrodes, serving both to transport ions and to isolate the positive and negative electrodes.

[0249] Example

[0250] 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.

[0251] Example 1

[0252] 1. Preparation of positive electrode sheet

[0253] 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 aluminum foil.

[0254] The positive electrode film layer comprises lithium phosphate, polyvinylidene fluoride (PVDF) binder, and acetylene black conductive agent in a mass ratio of 96:2:2. The positive electrode film layer is formed by uniformly coating the positive electrode slurry (solvent N-methylpyrrolidone NMP) on both sides of the positive electrode current collector, followed by drying and cold pressing.

[0255] Lithium-containing phosphates include lithium iron phosphate.

[0256] The single-sided coating weight of the positive electrode film is 280 mg / 1540.25 mm. 2 The length of the positive electrode film is 450 mm.

[0257] The lithium phosphate is sourced from Shenzhen Defang Nanotechnology Co., Ltd.

[0258] 2. Preparation of negative electrode sheet

[0259] 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 copper foil.

[0260] The negative electrode film is formed by uniformly coating the negative electrode slurry (solvent is deionized water) onto the surface of the negative electrode current collector, followed by drying and cold pressing.

[0261] 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.

[0262] The first negative electrode film layer comprises carbon-based material, silicon-based material silicon oxide, conductive agent acetylene black, negative electrode binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose in a mass ratio of 91.5:5:1:1.5:1. The carbon-based material of the first negative electrode film layer comprises artificial graphite and natural graphite in a mass ratio of 80%:20%, and the average particle size of the carbon-based material is 15 μm.

[0263] The second negative electrode film layer comprises carbon-based material, silicon-based material silicon oxide, conductive agent acetylene black, negative electrode binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose in a mass ratio of 91.5:5:1:1.5:1. The carbon-based material of the second negative electrode film layer includes artificial graphite, and the average particle size of the carbon-based material is 12 μm.

[0264] In this case, the silicon element in the negative electrode active material (including carbon-based materials and silicon-based materials) of the negative electrode film layer has a mass content of 2.5%.

[0265] The single-sided coating weight of the negative electrode film is 140 mg / 1540.25 mm. 2 .

[0266] The negative electrode active material comes from BTR New Materials Group Co., Ltd.

[0267] 3. Separating membrane

[0268] The separator includes a base membrane, which is a 7μm polyethylene film layer with a porosity of 42%.

[0269] 4. Preparation of electrolyte

[0270] The electrolyte comprises an organic solvent, a lithium salt, and additives. The components of the organic solvent are mixed thoroughly, and then the lithium salt and additives are added to prepare the electrolyte. The organic solvent comprises 25% chain carboxylic acid ester solvent (ethyl acetate EA) and 57% carbonate solvent (30% dimethyl carbonate DMC, 27% ethylene carbonate EC), with the mass content of each component in the organic solvent calculated based on the mass of the electrolyte. The lithium salt comprises 8% lithium hexafluorophosphate LiPF6 and 6% lithium bis(fluorosulfonyl)imide. The additives comprise 2% ethylene monofluorocarbonate FEC and 2% vinylene carbonate VC. The conductivity of the electrolyte is 14.2 mS / cm.

[0271] 5. Preparation of battery cells

[0272] The above-mentioned positive electrode sheet, separator, and negative electrode sheet are cut into sheets, with the positive electrode film layer of the positive electrode sheet having a length of 450 mm. These are stacked sequentially, with the separator positioned between the positive and negative electrode sheets to provide isolation, resulting in an electrode assembly. The electrode assembly is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping processes, a battery cell is obtained. The compaction density of the positive electrode film layer in the battery cell at 0% SOC is 2.6 g / cm³. 3 The compaction density of the negative electrode film at 0% SOC is 1.6 g / cm³. 3 .

[0273] Comparative Example 1-1 and Comparative Example 1-2

[0274] Battery cells were prepared using a method similar to that of Example 1, except that the composition and content of the electrolyte were adjusted.

[0275] Examples 2-1 to 2-9

[0276] Battery cells were prepared using a method similar to that of Example 1, except that the composition and content of the electrolyte were adjusted.

[0277] Performance testing

[0278] 1. High-temperature cycle performance test of individual battery cells

[0279] At 45±5℃, the battery cell is charged at a constant current of 2C to the upper limit of the cutoff voltage of 3.65V, then charged at a constant voltage to the cutoff current of 0.05C, and then discharged at a constant current of 2C to the discharge cutoff voltage of 2.5V. This constitutes one charge-discharge cycle. The discharge capacity of this cycle is recorded as the discharge capacity C1 of the battery cell in the first cycle.

[0280] Repeat the cyclic process for the same battery cell. After 800 cycles, record the discharge capacity Cn of the nth cycle. The cycle capacity retention rate of this battery cell = Cn / C1*100%. For accuracy, take the average of 5 parallel samples as the test result.

[0281] The test results are shown in Table 1.

[0282] Table 1

[0283] In Table 1,

[0284] EA stands for ethyl acetate;

[0285] MA represents methyl acetate;

[0286] EC stands for ethylene carbonate;

[0287] DMC stands for dimethyl carbonate;

[0288] EMC stands for ethyl methyl carbonate;

[0289] FEC stands for ethylene monofluorocarbonate;

[0290] EA:25 indicates that the mass content of EA is 25%;

[0291] EC:27 indicates that the mass content of EC is 27%.

[0292] The mass ratio of DMC to carboxylic acid ester solvents refers to the ratio of the mass content of dimethyl carbonate to the mass content of carboxylic acid ester solvents.

[0293] The mass ratio of lithium bis(fluorosulfonyl)imide to lithium hexafluorophosphate refers to the ratio of the mass content of lithium bis(fluorosulfonyl)imide to the mass content of lithium hexafluorophosphate.

[0294] The meanings of the other examples are explained in the same way as above, and will not be repeated here.

[0295] In Comparative Example 1-1, the mass content of carboxylic acid ester solvent was too low, resulting in poor wetting ability of the electrolyte on the electrode, uneven wetting of the electrode, which is not conducive to the rapid transport of lithium ions and the rapid charging of the battery cell.

[0296] In Comparative Examples 1-2, the mass content of carboxylic acid ester solvents was too high. Under fast charging conditions, the risk of side reactions and gas generation by carboxylic acid ester solvents on the negative electrode side was high, resulting in poor high-temperature cycle performance of the battery cells.

[0297] The mass content of the carboxylic acid ester solvent in the embodiments of this application is 3% to 70%. The electrolyte can quickly wet the electrode, and the performance of the electrode is uniform throughout, which is beneficial to improving the cycle performance of the battery cell under fast charging.

[0298] If the conductivity of the electrolyte is too low, it will hinder the rapid migration of lithium ions and make fast charging difficult. If the conductivity of the electrolyte in Comparative Examples 1-2 is too high, high-temperature gas production may be aggravated, which will hinder the improvement of cycling under fast charging conditions.

[0299] In this embodiment, lithium hexafluorophosphate and lithium difluorosulfonylimide are used in combination, for example, the mass content of lithium difluorosulfonylimide to the mass content of lithium hexafluorophosphate is 0.3 to 1.2, which can reduce the content of hydrofluoric acid, slow down the side reaction at the negative electrode interface, reduce the amount of gas generated during high-temperature storage, and help improve the high-temperature cycle life of the battery cell.

[0300] The fluorinated cyclic carbonate has a mass content of 0.5% to 20%. Fluorinated cyclic carbonate can form a lithium fluoride (LiF)-rich SEI film on the negative electrode surface, which can alleviate the volume expansion on the negative electrode side, improve the life of the negative electrode system, and improve cycle performance.

[0301] Comparative Example 2-1 and Comparative Example 2-2

[0302] Battery cells were prepared using a method similar to that of Example 1, except that the length of the positive electrode film and the coating weight on one side of the positive and negative electrode films were adjusted.

[0303] Examples 3-1 to 3-5

[0304] Battery cells were prepared using a method similar to that of Example 1, except that the length of the positive electrode film and the coating weight on one side of the positive and negative electrode films were adjusted.

[0305] Examples 3-6

[0306] Battery cells were prepared using a method similar to that of Example 1, except that the compaction density of the positive and negative electrode films was adjusted.

[0307] The test performance is shown in Table 2.

[0308] Table 2.

[0309] In Comparative Example 2-1, the size of the positive electrode film is relatively short. In order to meet the energy density requirements, the single-sided coating weight of the positive electrode film is high, which makes the lithium ion transport path longer, the internal resistance larger, and the cycle deterioration worse.

[0310] In Comparative Example 2-2, the positive electrode film is relatively long, resulting in a longer electron transport path, higher ohmic resistance, and higher heat generation. This makes the electrolyte prone to high-temperature gas generation due to heat accumulation, leading to poor high-temperature cycling performance under rapid conditions.

[0311] The size of the positive electrode film layer of the positive electrode sheet of the battery cell is within an appropriate range, so that the electron transport path is not too long. Combined with an appropriate range of coating weight and compaction density, the lithium ion transport path is also not too long, which can effectively improve the fast charging capability of the battery cell. Furthermore, with an electrolyte of appropriate composition, the side reactions at the negative electrode interface can be reduced, the amount of gas generated at high temperature can be reduced, thereby improving the high temperature cycle life of the battery cell.

[0312] Example 4

[0313] Battery cells were prepared using a method similar to that of Example 1, except that the particle size of the carbon-based material was adjusted. Specifically:

[0314] 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 copper foil.

[0315] The negative electrode film is formed by uniformly coating the negative electrode slurry (solvent is deionized water) onto the surface of the negative electrode current collector, followed by drying and cold pressing.

[0316] 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.

[0317] The carbon-based material of the first negative electrode film consists of artificial graphite and natural graphite in a mass ratio of 80%:20%, and the average particle size of the carbon-based material is 17μm.

[0318] The carbon-based material of the second negative electrode film includes artificial graphite, and the average particle size of the carbon-based material is 15 μm.

[0319] Example 5

[0320] Battery cells were prepared using a method similar to that of Example 1, except that the silicon content of the negative electrode active material was 5% by mass.

[0321] Example 6

[0322] The battery cells were prepared using a method similar to that of Example 1, except that the arrangement of the negative electrode film was adjusted. Specifically:

[0323] 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 copper foil.

[0324] The negative electrode film is formed by uniformly coating the negative electrode slurry (solvent is deionized water) onto the surface of the negative electrode current collector, followed by drying and cold pressing.

[0325] 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.

[0326] The first negative electrode film layer comprises carbon-based material, silicon-based material silicon oxide, conductive agent acetylene black, negative electrode binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose in a mass ratio of 91.5:5:1:1.5:1. The carbon-based material of the first negative electrode film layer includes artificial graphite, and the average particle size of the carbon-based material is 12 μm.

[0327] The second negative electrode film layer comprises carbon-based material, silicon-based material silicon oxide, conductive agent acetylene black, negative electrode binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose in a mass ratio of 91.5:5:1:1.5:1. The carbon-based material of the second negative electrode film layer comprises artificial graphite and natural graphite in a mass ratio of 80%:20%, and the average particle size of the carbon-based material is 15μm.

[0328] In this case, the silicon element in the negative electrode active material (including carbon-based materials and silicon-based materials) of the negative electrode film layer has a mass content of 2.5%.

[0329] Example 7

[0330] The battery cells were prepared using a method similar to that of Example 1, except that the arrangement of the negative electrode film was adjusted. Specifically:

[0331] 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 copper foil.

[0332] The negative electrode film is formed by uniformly coating the negative electrode slurry (solvent is deionized water) onto the surface of the negative electrode current collector, followed by drying and cold pressing.

[0333] The negative electrode film layer comprises carbon-based material, silicon-based material, conductive agent acetylene black, negative electrode binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose in a mass ratio of 91.5:5:1:1.5:1. The carbon-based material of the first negative electrode film layer includes artificial graphite, and the average particle size of the carbon-based material is 12 μm.

[0334] Table 3

[0335] Example 4: By controlling the average particle size of the carbon-based material, the average particle size of the carbon-based material in the first negative electrode film layer is larger than that in the second negative electrode film layer. This can shorten the solid-phase transport path of lithium ions, improve the fast charging capability, reduce the risk of lithium plating on the negative electrode side surface, and improve cycle performance.

[0336] Example 5 adjusts the silicon content of the silicon-based material, which is beneficial for improving the energy density of the battery cell. This solution is applicable to silicon-based materials of various materials, such as silicon-oxygen materials and silicon-carbon materials.

[0337] In Example 6, when the average particle size of the carbon-based material in the first negative electrode film is smaller than that in the second negative electrode film, a porosity difference in the negative electrode film can be created, thereby improving the fast charging capability.

[0338] Example 7 uses a single-layer negative electrode film, which can improve cycle performance to a certain extent, provided that its coating weight and other requirements are met.

[0339] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the implementation of the present application, and that changes, substitutions and modifications can be made to the embodiments without departing from the spirit, principles and scope of the implementation of the present application.

Claims

1. A single battery cell, comprising: An electrode assembly includes multiple positive electrode sheets and multiple negative electrode sheets, wherein the multiple positive electrode sheets and multiple negative electrode sheets are stacked along the thickness direction of the battery cell. Each positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector. The positive electrode film layer includes a positive electrode active material, which includes a lithium phosphate-containing material. The dimension of the positive electrode film layer along the length direction of the battery cell is 200 mm to 600 mm. The electrolyte includes an organic solvent, said organic solvent including carboxylic acid ester solvents, said carboxylic acid ester solvents having a mass content of 3% to 70% in the electrolyte.

2. The battery cell according to claim 1, wherein, The electrolyte has a conductivity of 9 mS / cm to 18 mS / cm at room temperature.

3. The battery cell according to claim 1 or 2, wherein, The electrolyte has a conductivity of 11 mS / cm to 18 mS / cm at room temperature.

4. The battery cell according to any one of claims 1 to 3, wherein, The carboxylic acid ester solvent has a mass content of 10% to 30% in the electrolyte.

5. The battery cell according to any one of claims 1 to 4, wherein, The carboxylic acid ester solvent includes cyclic carboxylic acid esters, which include one or more of γ-butyrolactone, γ-valerolactone, and δ-valerolactone; and / or The carboxylic acid ester solvent includes chain carboxylic acid esters, which include one or more of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, propyl propionate, and butyl propionate.

6. The battery cell according to any one of claims 1 to 5, wherein, The organic solvent includes carbonate solvents, which include one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

7. The battery cell according to claim 6, wherein, The carbonate solvents include dimethyl carbonate. The dimethyl carbonate content in the electrolyte is 10% to 30% by mass; and / or Based on the mass of the electrolyte, the ratio of the mass content of dimethyl carbonate to the mass content of the carboxylic acid ester solvent is 1 to 7.

8. The battery cell according to any one of claims 1 to 7, wherein, The electrolyte also includes one or more of fluoroethylene carbonate and vinylene carbonate.

9. The battery cell according to claim 8, wherein, Based on the mass of the electrolyte, the mass content of the fluoroethylene carbonate is from 0.5% to 20%. and / or Based on the mass of the electrolyte, the mass content of the vinylene carbonate is from 0.1% to 3%.

10. The battery cell according to any one of claims 1 to 9, wherein, The electrolyte also includes lithium salts, including lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate, wherein the mass ratio of the lithium bis(fluorosulfonyl)imide to the lithium hexafluorophosphate is 0.3 to 1.2 based on the mass of the electrolyte.

11. The battery cell according to claim 10, wherein, Based on the mass of the electrolyte, the lithium bis(fluorosulfonyl)imide content is 2% to 11% by mass; and / or Based on the mass of the electrolyte, the lithium hexafluorophosphate content is 3% to 14% by mass.

12. The battery cell according to any one of claims 1 to 11, wherein, The positive electrode film layer has a dimension of 400 mm to 600 mm along the length of the battery cell.

13. The battery cell according to any one of claims 1 to 12, wherein, The single-sided coating weight of the positive electrode film is 250 mg / 1540.25 mm. 2 Up to 300mg / 1540.25mm 2 .

14. The battery cell according to any one of claims 1 to 13, wherein, When the battery cell is at 0% charge, the compaction density of the positive electrode film is 2.2 g / cm³. 3 Up to 2.85 g / cm 3 .

15. The battery cell according to any one of claims 1 to 14, wherein, The lithium-containing phosphate includes lithium iron phosphate.

16. The battery cell according to any one of claims 1 to 15, wherein, The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The negative electrode film layer includes a negative electrode active material, which may be a carbon-based material. The single-sided coating weight of the negative electrode film layer is 80 mg / 1540.25 mm. 2 Up to 150mg / 1540.25mm 2 .

17. The battery cell according to claim 16, wherein, When the battery cell is at 0% charge, the compaction density of the negative electrode film is 1.1 g / cm³. 3 Up to 1.7 g / cm 3 .

18. The battery cell according to claim 16 or 17, wherein the negative electrode active material further comprises a silicon-based material, and the silicon element in the silicon-based material has a mass content of 0.3% to 15% in the negative electrode active material.

19. The battery cell according to claim 18, wherein, The silicon-based material includes one or more of elemental silicon, silicon-carbon composites, and silicon oxides.

20. The battery cell according to any one of claims 16 to 19, wherein, The negative electrode film layer includes: A first region is defined as the area of ​​the negative electrode film layer adjacent to the negative electrode current collector along its own thickness direction, and the thickness of the first region is 1 / 3 of the thickness of the negative electrode film layer; and The second region is the area of ​​the negative electrode film layer that faces away from the negative electrode current collector along the thickness direction, and the thickness of the second region is 1 / 3 of the thickness of the negative electrode film layer. In the cross-section of the negative electrode film layer parallel to the thickness direction, the void ratio of a single carbon-based material in the first region is smaller than that in the second region.

21. The battery cell according to claim 20, 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.

22. The battery cell according to claim 20 or 21, wherein, The average particle size of the carbon-based material in the first region is 12 μm to 21 μm; and / or The average particle size of the carbon-based material in the second region is 9 μm to 17 μm.

23. The battery cell according to any one of claims 20 to 22, wherein, The carbon-based material in the first region includes synthetic graphite and / or natural graphite; and / or The carbon-based material in the second region includes artificial graphite.

24. The battery cell according to claim 20, wherein, The average particle size of the carbon-based material in the second region is greater than that in the first region.

25. The battery cell according to claim 24, wherein, The average particle size of the carbon-based material in the first region is 9 μm to 17 μm; and / or The average particle size of the carbon-based material in the second region is 12 μm to 21 μm.

26. The battery cell according to claim 24 or 25, wherein, The carbon-based material in the second region includes synthetic graphite and / or natural graphite; and / or The carbon-based material in the first region includes artificial graphite.

27. The battery cell according to any one of claims 16 to 26, 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 negative electrode active material of the first negative electrode film layer includes a carbon-based material; 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, and the negative electrode active material of the second negative electrode film layer includes a carbon-based material. Wherein, at least one of the negative electrode active materials of the first negative electrode film layer and the second negative electrode film layer includes a silicon-based material.

28. A battery device comprising a battery cell as claimed in any one of claims 1 to 27.

29. An electrical device comprising the battery device as described in claim 28.

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