Battery cell and preparation method therefor, lithium battery, and electrical device

Abstract

A battery cell and a preparation method therefor, a lithium battery, and an electrical device. The battery cell comprises a positive electrode sheet, a negative electrode sheet, and an electrolyte. The negative electrode sheet comprises a negative electrode current collector, and a negative electrode active layer provided on at least one surface of the negative electrode current collector. The negative electrode active layer comprises a negative electrode active material and a first binder, the Young's modulus of the first binder being from 1.40 GPa to 1.70 GPa. The described configuration helps to reduce the amount of volume expansion of a lithium battery, and helps to prolong the cycle life of the lithium battery.

Description

Battery cells and their preparation methods, lithium batteries, electrical devices

[0001] Cross-references to related applications

[0002] This application claims priority to Chinese Patent Application No. 202411745491.2, filed on November 29, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of battery technology, and in particular to battery cells and their preparation methods, lithium batteries, and electrical devices. Background Technology

[0004] Lithium-ion batteries are widely used in wireless communication, transportation, aerospace and other fields due to their advantages such as high energy density, long cycle life, low self-discharge rate, fast charging capability and wide operating temperature range. With the continuous progress and development of technology, lithium-ion batteries will continue to play an important role and drive innovation in energy storage technology.

[0005] For lithium batteries, cycle life is a key factor affecting their development. Summary of the Invention

[0006] This application provides a battery cell and its preparation method, a lithium battery, and an electrical device to improve the cycle life of the battery cell.

[0007] To solve the above-mentioned technical problems, the first aspect of this application provides a battery cell including a positive electrode, a negative electrode, and an electrolyte; the negative electrode includes a negative current collector and a negative active layer disposed on at least one surface of the negative current collector; the negative active layer includes a negative active material and a first binder, wherein the Young's modulus of the first binder is 1.40 GPa-1.7 GPa.

[0008] In this embodiment, a first binder with a Young's modulus of 1.40 GPa to 1.7 GPa is selected. Under the same stress, the deformation of the first binder is small, which can provide strong resistance to deformation during the bonding process. The binder with a high Young's modulus can "frame" the particles in the electrode, which can, to a certain extent, slow down the volume expansion caused by lithium ion insertion into the active material and the volume shrinkage caused by lithium ion extraction from the active material during cycling. This maintains close contact between material particles, improves the cohesion of the electrode, reduces the probability of material particles falling off in the negative electrode active layer, and reduces the risk of the negative electrode breaking. This is beneficial to maintaining the structural stability of the negative electrode, reducing the volume expansion of the battery cell, and extending the cycle life of the lithium battery.

[0009] In one embodiment, based on the mass of the negative electrode active layer, the mass content of the first binder is 0.2%-3%.

[0010] By setting the amount of the first binder as described above, the amount of the first binder is appropriate, maintaining a large proportion of the negative electrode active material in the negative electrode active layer, maintaining a high capacity of the negative electrode sheet, and at the same time, the amount of the first binder can keep the negative electrode active material and other materials tightly bonded to the negative electrode current collector, limiting the expansion or contraction of the negative electrode active layer material to a certain extent, maintaining the structural stability of the negative electrode sheet, and helping to extend the cycle life of the lithium battery.

[0011] In one embodiment, the first binder includes at least one of hydroxyl and carboxyl groups.

[0012] By setting the first binder to include at least one of hydroxyl and carboxyl groups, the hydroxyl and carboxyl groups can form hydrogen bonds. The formation of hydrogen bonds between molecules promotes physical cross-linking between molecules, giving the first binder the characteristic of rapid self-healing, reducing the swelling of the negative electrode active layer, and mitigating the capacity loss caused by the swelling of the negative electrode sheet, which is beneficial to extending the cycle life of lithium batteries.

[0013] In one embodiment, the first binder includes at least one of polyacrylic acid, polyamide-imide, polyethylene oxide, polytetrafluoroethylene, crosslinked polyacrylic acid-polybenzimidazole, polyvinylidene fluoride-polytetrafluoroethylene block copolymer, and carboxymethyl chitosan.

[0014] By selecting the above-mentioned materials as the first binder, the negative electrode active material and other materials can be tightly bonded together with the negative electrode current collector, which to a certain extent restricts the expansion or contraction of the negative electrode active layer material, reduces the probability of material particles falling off in the negative electrode active layer, maintains the structural stability of the negative electrode sheet, and helps to extend the cycle life of lithium batteries.

[0015] In one embodiment, the first adhesive comprises at least one of polyacrylic acid, cross-linked polyacrylic acid-polybenzimidazole, polyethylene oxide, and carboxymethyl chitosan.

[0016] By using the above-mentioned materials as the first binder, the first binder includes at least one of hydroxyl and carboxyl groups. Hydroxyl and carboxyl groups can form hydrogen bonds. The formation of hydrogen bonds between molecules promotes physical cross-linking between molecules, giving the first binder the characteristic of rapid self-healing, reducing the swelling of the negative electrode active layer, alleviating the capacity loss caused by the swelling of the negative electrode sheet, and helping to extend the cycle life of the lithium battery.

[0017] In one embodiment, the negative electrode active layer further includes a second binder, the second binder having a Young's modulus less than that of the first binder.

[0018] By setting the negative electrode active layer including a first binder and a second binder, the first binder provides strong mechanical support, reducing the possibility of excessive deformation or even cracking of the negative electrode sheet due to material volume expansion; the second binder provides good flexibility, improving the flexibility of the electrode sheet and reducing the possibility of electrode sheet breakage; the combination of the first binder and the second binder maintains the overall structural strength of the negative electrode sheet while maintaining the structural stability of the negative electrode sheet, which is beneficial to extending the cycle life of lithium battery.

[0019] In one embodiment, based on the mass of the negative electrode active layer, the mass content of the second binder is 0.3%-2%.

[0020] By adjusting the amount of the second binder as described above, the first and second binders work together to maintain the overall structural strength of the negative electrode sheet while enabling the binder system to better adapt to volume changes in the negative electrode material, maintain the structural stability of the negative electrode sheet, and thus extend the cycle life of the lithium battery.

[0021] In one embodiment, the second adhesive includes at least one of styrene-butadiene rubber and sodium carboxymethyl cellulose.

[0022] By selecting the above-mentioned materials as the second binder, the second binder can provide better flexibility and can deform appropriately with the change of material volume of the negative electrode sheet, reduce the generation of internal stress, maintain the structural stability of the negative electrode sheet, and help extend the cycle life of the lithium battery.

[0023] In one embodiment, the negative electrode active material includes artificial graphite; based on the mass of the negative electrode active layer, the mass percentage of artificial graphite is greater than or equal to 80% and less than or equal to 97.5%.

[0024] Compared to natural graphite, artificial graphite has fewer defects; using artificial graphite as a negative electrode active material is beneficial for improving battery cycle life. Artificial graphite has good compatibility with the electrolyte, which facilitates the formation of a well-formed SEI film between the negative electrode and the electrolyte, resulting in a good cycle life for the lithium battery. By setting the mass percentage of artificial graphite in the negative electrode active layer to be greater than or equal to 80% and less than or equal to 97.5%, the negative electrode can store more lithium ions, increasing the energy density and performance of the lithium battery.

[0025] In one embodiment, the artificial graphite includes bulk particles and a coating layer on the surface of the bulk particles, the coating layer comprising amorphous carbon.

[0026] By coating amorphous carbon onto the surface of artificial graphite, the amorphous carbon can promote the formation of a more stable and thinner SEI film. Amorphous carbon acts as a barrier, reducing direct contact and side reactions between artificial graphite and the electrolyte, helping to maintain the integrity and stability of the artificial graphite structure and extending the lifespan of lithium-ion batteries. Compared to artificial graphite, amorphous carbon has a greater number of surface defects, which increases the number of sites for the insertion and extraction of active ions in the negative electrode active material, allowing active ions to diffuse more quickly within the particles and improving the performance of lithium-ion batteries.

[0027] In one embodiment, based on the total mass of artificial graphite, the mass percentage of amorphous carbon is greater than or equal to 0.5% and less than or equal to 10%.

[0028] By setting the mass percentage of amorphous carbon within the above range, the amount of amorphous carbon coating on the surface of artificial graphite is more suitable, which can improve the conductivity of artificial graphite, maintain the integrity and stability of the artificial graphite structure, and at the same time, the internal resistance of the battery is more suitable, which is conducive to improving the energy density, cycle stability and cycle life of lithium batteries.

[0029] In one embodiment, the degree of graphitization of the artificial graphite is greater than or equal to 90% and less than or equal to 97%.

[0030] The above-mentioned graphitization degree of artificial graphite has a highly ordered layered structure. Using artificial graphite with the above-mentioned graphitization degree is beneficial to reduce its volume expansion during charging and discharging, thereby improving the cycle life of lithium batteries.

[0031] In one embodiment, the disorder R value of the artificial graphite is greater than or equal to 0.04 and less than or equal to 0.6.

[0032] By setting the disorder R value of artificial graphite within the above range, it is beneficial to reduce its volume expansion during charging and discharging, reduce the stress generated by the volume expansion and contraction of the material, thereby reducing the risk of material pulverization and shedding, and helping to maintain the structural integrity of the negative electrode sheet. At the same time, with the disorder R value of artificial graphite within the above range, the defects in artificial graphite are more suitable. These defects can provide more channels and sites for lithium ion transport, making the diffusion of lithium ions in the electrode material easier and helping to improve the cycle life of the battery.

[0033] In one embodiment, the negative electrode active material has a 0.1C CC specific capacity greater than or equal to 350 mAh / g and less than or equal to 360 mAh / g.

[0034] By setting the negative electrode active material to a specific capacity of 0.1C CC as described above, the negative electrode active material exhibits good lithium-ion insertion and extraction efficiency, as well as relatively stable electrochemical performance, low lithium consumption, reduced side reaction gas production, and reduced volume expansion of the lithium battery, which is beneficial to extending the cycle life of the lithium battery.

[0035] In one embodiment, the negative electrode active layer includes a first sub-active layer disposed on the surface of the negative electrode current collector and a second sub-active layer disposed on the side of the first sub-active layer away from the negative electrode current collector; the Dv50 of the negative electrode active material of the first sub-active layer is greater than the Dv50 of the negative electrode active material of the second sub-active layer.

[0036] By setting the Dv50 of the negative electrode active material in the first sub-active layer to be greater than that in the second sub-active layer, that is, using a negative electrode active material with a larger particle size near the negative electrode current collector and a negative electrode active material with a smaller particle size near the electrolyte, the negative electrode active material near the electrolyte has a larger specific surface area, which can shorten the migration path of lithium ions, reduce diffusion resistance, and facilitate charging. At the same time, it helps to reduce the expansion and contraction of the negative electrode material, thereby extending the cycle life of the lithium battery.

[0037] In one embodiment, the Dv50 of the negative electrode active material in the first sub-active layer is greater than or equal to 11 μm and less than or equal to 20 μm; the Dv50 of the negative electrode active material in the second sub-active layer is greater than or equal to 7 μm and less than or equal to 16 μm.

[0038] By setting the Dv50 of the negative electrode active material in the first sub-active layer and the Dv50 of the negative electrode active material in the second sub-active layer as described above, the lithium-ion migration path can be shortened, the diffusion resistance can be reduced, and the expansion and contraction of the negative electrode material can be reduced, thereby extending the cycle life of the lithium battery.

[0039] In one embodiment, the Dv50 of the negative electrode active material in the first sub-active layer is greater than or equal to 12.5 μm and less than or equal to 18.5 μm; the Dv50 of the negative electrode active material in the second sub-active layer is greater than or equal to 8.5 μm and less than or equal to 15.5 μm.

[0040] By setting the Dv50 of the negative electrode active material in the first sub-active layer and the Dv50 of the negative electrode active material in the second sub-active layer as described above, the lithium-ion migration path can be shortened, the diffusion resistance can be reduced, and the expansion and contraction of the negative electrode material can be reduced, thereby extending the cycle life of the lithium battery.

[0041] In one embodiment, the thickness of the negative electrode active layer is 100μm-150μm.

[0042] The embodiments of this application select a negative electrode active layer with a thickness range of the above-mentioned range. The thickness is appropriate, and more active material can be loaded on a negative electrode current collector of a given area, which is beneficial to improving the energy density of the battery. During the charging and discharging process, the stress change of the battery during the charging and discharging process can be reduced. The negative electrode active layer structure is relatively stable and has a low rebound rate, which is beneficial to maintaining a long cycle life.

[0043] In one embodiment, the positive electrode includes a positive current collector and a positive active layer disposed on at least one surface of the positive current collector; the positive active layer includes a positive active material, which includes a lithium phosphate material with the general chemical formula LiFe. 1-x M x PO4, wherein M includes at least one of Mg, Ti, Cu, and Nb, and 0.05 ≤ x ≤ 0.30.

[0044] By doping lithium iron phosphate with at least one element selected from Mg, Ti, Cu, and Nb, more conductive channels are formed, enhancing electron mobility. Simultaneously, the crystal structure of lithium iron phosphate is strengthened, reducing volume changes caused by phase transitions during charging and discharging, improving structural stability, and thus extending cycle life and maintaining high energy density. By setting the mass proportion of metal-doped lithium iron phosphate in the positive electrode active layer to be greater than or equal to 80%, the positive electrode active material achieves both high energy density and structural stability, thereby improving the energy density of the lithium battery and maintaining a long cycle life.

[0045] In one implementation, 0.1 ≤ x ≤ 0.2.

[0046] By setting the doping amount x of the doping element to 0.1≤x≤0.2, the doping element can fully exert its role, improve the structural stability of lithium iron phosphate, reduce the amount of iron leaching, and help extend the cycle life.

[0047] In one embodiment, the Dv50 of the positive electrode active material is greater than or equal to 0.6 μm and less than or equal to 2.2 μm.

[0048] The Dv50 of the positive electrode active material is within the above range. The positive electrode active material has good structural stability, which is beneficial to improving the energy density of lithium batteries and extending the cycle life of lithium batteries.

[0049] In one embodiment, the Dv50 of the positive electrode active material is greater than or equal to 1 μm and less than or equal to 1.6 μm.

[0050] The Dv50 of the positive electrode active material is within the above range. The positive electrode active material has good structural stability, which is beneficial to improving the energy density of lithium batteries and extending the cycle life of lithium batteries.

[0051] In one embodiment, the positive electrode active material has a first delithiation capacity of ≥145 mAh / g at 0.1C.

[0052] This application uses the aforementioned positive electrode active material with specific capacity on a substrate doped with metal elements in lithium iron phosphate, maintaining a high energy density and a relatively stable structure, which is beneficial to improving the performance of lithium batteries.

[0053] In one embodiment, the positive electrode active material has a first delithiation capacity of less than or equal to 147 mAh / g at 0.1C.

[0054] This application uses the above-mentioned positive electrode active material with specific capacity to maintain a high energy density of the positive electrode active material, which is beneficial to the lithium battery having a high energy density and improving the performance of the lithium battery.

[0055] In one embodiment, the coating weight of the positive electrode active layer is greater than or equal to 260 mg / 1540.25 mm. 2 And less than or equal to 330mg / 1540.25mm 2 .

[0056] The embodiments of this application employ a positive electrode active layer within the aforementioned coating weight range, which is beneficial for improving the energy density of lithium batteries and extending cycle life.

[0057] In one embodiment, the compaction density of the positive electrode active layer is greater than or equal to 2.3 g / cc and less than or equal to 2.7 g / cc.

[0058] The positive electrode active layer with a compaction density within the above-mentioned range is used in the embodiments of this application, which is beneficial to enable the lithium battery to have a higher energy density and a longer cycle life.

[0059] In one embodiment, the compaction density of the positive electrode active layer is greater than or equal to 2.4 g / cc and less than or equal to 2.6 g / cc.

[0060] The positive electrode active layer with a compaction density within the above-mentioned range is used in the embodiments of this application, which is beneficial to enable the lithium battery to have a higher energy density and a longer cycle life.

[0061] In one embodiment, the thickness of the positive electrode active layer is 70 μm-100 μm.

[0062] The embodiments of this application select a positive electrode active layer with a thickness range of the above-mentioned range. The thickness is appropriate, and more active material can be loaded on a positive electrode current collector of a given area, which is beneficial to improving the energy density of the battery. During the charging and discharging process, the stress change of the battery during the charging and discharging process can be reduced, and the positive electrode active layer structure is relatively stable, which is beneficial to maintaining a long cycle life.

[0063] In one embodiment, the conductivity of the electrolyte is 7 mS / cm to 13 mS / cm.

[0064] By setting the conductivity of the electrolyte within the above range, it is beneficial to improve the transport capacity of lithium ions in the electrolyte, which helps to form a stable solid electrolyte interface (SEI) film. This can prevent direct contact between the electrolyte and the negative electrode material, reduce the decomposition reaction of the electrolyte, and thus suppress gas generation, thereby improving the cycle life of the lithium-ion battery.

[0065] In one embodiment, the conductivity of the electrolyte is 7 mS / cm to 10 mS / cm.

[0066] By setting the conductivity of the electrolyte within the above range, lithium ions can be kept to have a faster transport capacity in the electrolyte, which helps to form a stable solid electrolyte interface (SEI) film. This can prevent direct contact between the electrolyte and the negative electrode material, reduce the decomposition reaction of the electrolyte, and thus suppress gas generation, thereby improving the cycle life of the lithium-ion battery.

[0067] In one embodiment, the water content of the electrolyte is less than or equal to 200 ppm.

[0068] By setting the water content in the electrolyte to less than or equal to 200 ppm, the reaction between water and lithium salt to generate hydrofluoric acid can be reduced, thereby reducing the damage of hydrofluoric acid to active materials or SEI film and helping to maintain a longer cycle life of lithium batteries.

[0069] In one embodiment, the electrolyte includes a first solvent, which includes at least one of vinyl acetate, methyl acetate, dimethyl carbonate, ethyl propionate, and propyl propionate.

[0070] The embodiments of this application use a first solvent including one or more of ethyl acetate, methyl acetate, propyl propionate, ethyl propionate, and dimethyl carbonate. The resulting electrolyte has high conductivity, which helps to improve the migration speed of lithium ions, facilitates effective contact between the active material and the electrolyte, and is beneficial to improving the kinetic performance and cycle life of lithium-ion batteries.

[0071] In one embodiment, the first solvent accounts for less than or equal to 20% of the mass of the electrolyte.

[0072] The embodiments of this application, by adjusting the proportion of the first solvent in the electrolyte, achieve a suitable amount of the first solvent, which is beneficial to charging and cycle life; by leveraging the synergistic effect of the multi-component electrolyte, it is beneficial to improve the film-forming stability of the electrolyte at the negative electrode, enabling the lithium-ion battery to have good cycle stability over a wide temperature range and improving the cycle life of the lithium-ion battery.

[0073] In one embodiment, the electrolyte includes an additive, which includes at least one of vinylene carbonate, 1,3-propenesulfonate lactone, fluoroethylene carbonate, methylbenzenesulfonyl isocyanate, and 1-(trimethylsilyl)-1H-benzotriazole.

[0074] By selecting the above materials as additives, they can remove water and acid, reduce the water content in the electrolyte, and neutralize the acid produced by the side reactions of lithium salts or other components, which helps to extend the cycle life of lithium batteries.

[0075] In one embodiment, the additive accounts for 0.05% to 2% of the mass of the electrolyte.

[0076] By setting the mass ratio of additives in the electrolyte within the above range, the water and acid content in the electrolyte can be effectively reduced, which is beneficial to extending the cycle life of lithium batteries.

[0077] In one embodiment, the additive accounts for 0.1% to 0.8% of the mass of the electrolyte.

[0078] By setting the mass ratio of additives in the electrolyte within the above range, the water and acid content in the electrolyte can be effectively reduced, which is beneficial to extending the cycle life of lithium batteries.

[0079] In one embodiment, the electrolyte includes a lithium salt with a concentration greater than or equal to 0.7 mol / L and less than or equal to 1.2 mol / L.

[0080] The embodiments of this application, by employing lithium salts of the above concentration, are beneficial for improving the film-forming stability of the electrolyte at the negative electrode, regulating the conductivity of the electrolyte, enhancing the migration rate of lithium ions, and improving the cycle life of lithium-ion batteries.

[0081] In one embodiment, the electrolyte includes a lithium salt with a concentration greater than or equal to 0.8 mol / L and less than or equal to 1 mol / L.

[0082] The embodiments of this application, by employing lithium salts of the above concentration, are beneficial for improving the film-forming stability of the electrolyte at the negative electrode, regulating the conductivity of the electrolyte, enhancing the migration rate of lithium ions, and improving the cycle life of lithium-ion batteries.

[0083] A second aspect of this application provides a method for preparing a battery cell, comprising: sequentially stacking a negative electrode sheet, a separator, and a positive electrode sheet to form a cell assembly; placing the cell assembly in a housing; and injecting an electrolyte into the housing and sealing it to form a battery cell; wherein the negative electrode sheet includes a negative current collector and a negative active layer disposed on at least one surface of the negative current collector; the negative active layer includes a negative active material and a first binder, wherein the Young's modulus of the first binder is 1.40 GPa-1.7 GPa.

[0084] In this embodiment, a first binder with a Young's modulus of 1.40 GPa to 1.7 GPa is selected. The binder with a high Young's modulus can "frame" the particles in the electrode, which can, to a certain extent, mitigate the volume expansion caused by lithium ion insertion into the active material and the volume shrinkage caused by lithium ion extraction from the active material during cycling. This maintains close contact between material particles, improves the cohesive force of the electrode, reduces the probability of material particles falling off from the negative electrode active layer, and reduces the risk of the negative electrode breaking. This is beneficial for maintaining the structural stability of the negative electrode, reducing the volume expansion of the battery cell, and extending the cycle life of the lithium battery.

[0085] In one embodiment, the method for preparing the negative electrode sheet includes: forming a negative electrode active layer on at least one side of a negative electrode current collector to form a first semi-finished product; drying and compacting the first semi-finished product to form a second semi-finished product; and heat-treating the second semi-finished product to obtain a negative electrode sheet, wherein the thickness of the negative electrode sheet is greater than the thickness of the second semi-finished product.

[0086] In the negative electrode preparation method provided in this application embodiment, the pre-rebound of the negative electrode is achieved by heat-treating the second semi-finished product after drying and compaction. This effectively improves the rebound of the negative electrode during cycling, thereby improving the expansion force. It is beneficial to maintain a certain gap between the positive and negative electrode during battery cycling, reducing the possibility of compression between the positive and negative electrode. Maintaining a certain gap between the positive and negative electrode maintains good wettability of the electrolyte on the positive and negative electrode, reducing the possibility of lithium plating, and is conducive to achieving a long life of lithium battery.

[0087] In one embodiment, the difference between the thickness of the negative electrode sheet and the thickness of the second semi-finished product is 4% to 15% of the thickness of the second semi-finished product.

[0088] By pre-rebounding the negative electrode sheet within the aforementioned range, the rebound of the negative electrode sheet during cycling is effectively improved, the expansion force is effectively reduced, and the lithium battery has a longer cycle life.

[0089] In one embodiment, the difference between the thickness of the negative electrode sheet and the thickness of the second semi-finished product is 7% to 10% of the thickness of the second semi-finished product.

[0090] By pre-rebounding the negative electrode sheet within the aforementioned range, the rebound of the negative electrode sheet during cycling is effectively improved, the expansion force is effectively reduced, and the lithium battery has a longer cycle life.

[0091] In one embodiment, the heat treatment temperature is 140°C to 220°C; and / or, the heat treatment time is 30s to 120s.

[0092] By setting the heat treatment temperature and time to the above range, the second semi-finished product can expand under the action of this temperature, achieving the effect of pre-rebound.

[0093] In one embodiment, the heat treatment temperature is 160°C to 180°C; and / or the heat treatment time is 40s to 90s.

[0094] By setting the heat treatment temperature and time to the above range, the second semi-finished product can expand under the action of this temperature, achieving the effect of pre-rebound.

[0095] A third aspect of this application provides a lithium battery comprising a cell according to any of the above-described embodiments or a cell prepared by a method thereof. The lithium battery possesses at least the same advantages as the aforementioned cell.

[0096] A fourth aspect of this application provides an electrical device comprising a battery cell according to any of the preceding claims, a battery cell prepared by any of the preceding claims, or a lithium battery as described above. The electrical device has at least the same advantages as the aforementioned battery cell.

[0097] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0098] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0099] Figure 1 is a schematic diagram of the vehicle structure provided in an embodiment of this application;

[0100] Figure 2 is a schematic diagram of the exploded structure of a lithium battery provided in an embodiment of this application;

[0101] Figure 3 is a schematic diagram of the exploded structure of a battery cell provided in an embodiment of this application;

[0102] Figure 4 is a schematic flowchart of the method for preparing a battery cell provided in an embodiment of this application;

[0103] Figure 5 is a flowchart illustrating the method for preparing the negative electrode sheet provided in the embodiments of this application. Detailed Implementation

[0104] To make the objectives, technical solutions, and effects of this application clearer and more explicit, the embodiments of the technical solutions of this application will be described in detail below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of this application, and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0105] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0106] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces), unless otherwise explicitly specified.

[0107] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0108] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0109] Quantities, ratios, and other numerical values ​​are presented in range format in this document. It should be understood that this range format is for convenience and brevity and should be interpreted flexibly to include not only numerical values ​​explicitly specified as range limits, but also all individual numerical values ​​or subranges covered within the range, as if each numerical value and subrange were explicitly specified.

[0110] Unless otherwise specified, all steps of this application may be performed sequentially, randomly, or in parallel, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially, or steps (a) and (b) may be performed simultaneously in parallel. For example, the method may also include step (c), indicating that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or steps (a), (c), and (b), or steps (c), (a), and (b), etc.

[0111] With the rapid development of modern technology, lithium batteries, as a highly efficient and portable energy storage device, have been widely used in many fields, such as consumer electronics (mobile phones, laptops, etc.), electric vehicles, and renewable energy storage systems. However, the cycle life of lithium batteries has always been one of the key factors limiting their further widespread application and performance improvement.

[0112] Therefore, embodiments of this application provide a battery cell and its preparation method, a lithium battery, and an electrical device. The battery cell includes a negative electrode sheet, which includes a negative current collector and a negative active layer disposed on at least one surface of the negative current collector. The negative active layer includes a negative active material and a first binder, wherein the Young's modulus of the first binder is 1.40 GPa-1.7 GPa. Embodiments of this application, by controlling the first binder, reduce the volume expansion of the lithium battery, improve the structural stability of the negative electrode sheet, and thus extend the cycle life of the lithium battery.

[0113] The technical solutions described in the embodiments of this application are applicable to various electrical devices that use lithium batteries, such as mobile phones, portable devices, laptops, electric vehicles, electric toys, power tools, vehicles, ships, and spacecraft. For example, spacecraft include airplanes, rockets, space shuttles, and spacecraft.

[0114] For ease of explanation, the following embodiments will be described using a vehicle 1000 as an example of an electrical device according to an embodiment of this application.

[0115] Please refer to Figure 1, which is a structural schematic diagram of a vehicle provided in an embodiment of this application.

[0116] Vehicle 1000 can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. A lithium battery 100 is installed inside vehicle 1000, which can be located at the bottom, front, or rear of vehicle 1000. The lithium battery 100 can be used to power vehicle 1000; for example, it can serve as the operating power source for vehicle 1000. Vehicle 1000 may also include a controller 200 and a motor 300. The controller 200 controls the lithium battery 100 to supply power to the motor 300, for example, to meet the power needs of vehicle 1000 during starting, navigation, and driving.

[0117] In some embodiments of this application, the lithium battery 100 can not only serve as the operating power source for the vehicle 1000, but also as the driving power source for the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0118] Please refer to Figure 2, which is an exploded structural diagram of a lithium battery provided in an embodiment of this application.

[0119] The lithium battery 100 includes a housing 10 and a battery cell 20, with the battery cell 20 housed within the housing 10. The housing 10 provides space for the battery cell 20 and can have various structures.

[0120] In some embodiments, the housing 10 may include a first portion 11 and a second portion 12, which overlap each other, and together define a receiving space for accommodating the battery cell 20. The second portion 12 may be a hollow structure with one open end, and the first portion 11 may be a plate-like structure, with the first portion 11 covering the open side of the second portion 12 so that the first portion 11 and the second portion 12 together define the receiving space; alternatively, the first portion 11 and the second portion 12 may both be hollow structures with one open side, with the open side of the first portion 11 covering the open side of the second portion 12. Of course, the housing 10 formed by the first portion 11 and the second portion 12 can be of various shapes, such as a cylinder, a cuboid, etc.

[0121] In the lithium battery 100, there can be multiple battery cells 20. These multiple battery cells 20 can be connected in series, parallel, or in a mixed manner. A mixed connection means that multiple battery cells 20 are connected in both series and parallel. Multiple battery cells 20 can be directly connected in series, parallel, or in a mixed manner, and then the whole assembly of multiple battery cells 20 is housed in the housing 10. Alternatively, the lithium battery 100 can also be composed of multiple battery cells 20 first connected in series, parallel, or in a mixed manner to form a battery module, and then multiple battery modules are connected in series, parallel, or in a mixed manner to form a whole, which is then housed in the housing 10.

[0122] The lithium battery 100 may also include other structures, for example, the lithium battery 100 may also include a busbar for realizing electrical connection between multiple battery cells 20.

[0123] Among them, the battery cell 20 can be in the form of a cylinder, a flat shape, a cuboid, or other shapes.

[0124] Please refer to Figure 3, which is an exploded structural diagram of a battery cell provided in an embodiment of this application.

[0125] A battery cell 20 refers to the smallest unit that makes up a lithium battery 100. A battery cell 20 includes an end cap 21, a housing 22, a cell assembly 23, and other functional components.

[0126] End cap 21 refers to a component that covers the opening of housing 22 to isolate the internal environment of battery cell 20 from the external environment. The shape of end cap 21 can be adapted to the shape of housing 22 to fit it. Optionally, end cap 21 can be made of a material with certain hardness and strength (such as aluminum alloy), so that end cap 21 is not easily deformed under pressure and impact, giving battery cell 20 higher structural strength and improved safety performance. Functional components such as electrode terminals 21a can be provided on end cap 21. Electrode terminals 21a can be used for electrical connection with cell assembly 23 to output or input electrical energy to battery cell 20. In some embodiments, end cap 21 can also be provided with a pressure relief mechanism for releasing internal pressure when the internal pressure or temperature of battery cell 20 reaches a threshold. The material of end cap 21 can also be various, including but not limited to copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc. In some embodiments, an insulating element may be provided on the inner side of the end cap 21. The insulating element can be used to isolate the electrical connection components within the housing 22 from the end cap 21 to reduce the risk of short circuits. For example, the insulating element may be made of plastic, rubber, etc.

[0127] The housing 22 is a component used to cooperate with the end cap 21 to form the internal environment of the battery cell 20. This internal environment can accommodate the cell assembly 23, electrolyte, and other components. The housing 22 and the end cap 21 can be independent components. An opening can be provided on the housing 22, and the end cap 21 closes the opening to form the internal environment of the battery cell 20. Alternatively, the end cap 21 and the housing 22 can be integrated. Specifically, the end cap 21 and the housing 22 can form a common connecting surface before other components are inserted into the housing. When it is necessary to encapsulate the interior of the housing 22, the end cap 21 closes the housing 22. The housing 22 can be of various shapes and sizes, such as cuboid, cylindrical, hexagonal prism, etc. Specifically, the shape of the housing 22 can be determined according to the specific shape and size of the cell assembly 23. The housing 22 can be made of various materials, including but not limited to copper, iron, aluminum, stainless steel, aluminum alloy, and plastic.

[0128] The cell assembly 23 is the component in the battery cell 20 where the electrochemical reaction occurs. The casing 22 may contain one or more cell assemblies 23. The cell assembly 23 is mainly formed by winding or stacking positive and negative electrode plates, and typically a separator is provided between the positive and negative electrode plates. The portions of the positive and negative electrode plates containing active material constitute the main body of the cell assembly 23, while the portions of the positive and negative electrode plates without active material each constitute a tab. The positive and negative tabs may be located together at one end of the main body or separately at both ends of the main body. During the charging and discharging process of the battery cell 20, the positive and negative active materials react with the electrolyte, and the tabs connect to the electrode terminals to form a current loop.

[0129] It should be noted that the electrolyte of the battery cell 20 in the above embodiments can also be referred to as a liquid electrolyte. In other embodiments, the battery cell 20 may also include a solid electrolyte or a semi-solid electrolyte; in this case, the battery cell 20 does not need to be provided with a separator.

[0130] In this embodiment, the negative electrode sheet includes a negative current collector and a negative active layer disposed on at least one surface of the negative current collector; the negative active layer includes a negative active material and a first binder, wherein the Young's modulus of the first binder is 1.40 GPa-1.7 GPa.

[0131] The Young's modulus of the first binder reflects the material's resistance to elastic deformation. The Young's modulus of the first binder can be obtained through nanoindentation testing. The testing method for the Young's modulus of the first binder is as follows: 1) Sample preparation: Prepare the first binder material into a sample suitable for nanoindentation testing, ensuring the sample surface is flat and smooth. 2) Sample installation: Install the sample on the sample stage of the nanoindentation testing instrument, ensuring the sample is firmly fixed. 3) Indenter selection: Berkovich indenter. 4) Test parameter settings: Maximum load 500 mN; loading speed 0.1 mN / s; holding time 30 s. 5) Testing: Start the nanoindentation testing instrument and conduct the test according to the set parameters. During the test, the instrument will automatically record the load and displacement data. 6) Data analysis: After the test, import the recorded data into data analysis software for analysis and processing to obtain the Young's modulus of the material.

[0132] The Young's modulus of the first binder can be 1.40 GPa, 1.42 GPa, 1.44 GPa, 1.46 GPa, 1.48 GPa, 1.5 GPa, 1.52 GPa, 1.54 GPa, 1.56 GPa, 1.58 GPa, 1.6 GPa, 1.62 GPa, 1.7 GPa, etc., or it can be a range of any two of the above values, such as 1.42 GPa-1.56 GPa, 1.48 GPa-1.54 GPa, 1.42 GPa-1.62 GPa, etc.

[0133] In this embodiment, a first binder with a Young's modulus of 1.40 GPa to 1.7 GPa is selected. Under the same stress, the deformation of the first binder is small, which can provide strong resistance to deformation during the bonding process. The binder with a high Young's modulus can "frame" the particles in the electrode, which can, to a certain extent, slow down the volume expansion caused by lithium ion insertion into the active material and the volume shrinkage caused by lithium ion extraction from the active material during cycling. This maintains close contact between material particles, improves the cohesion of the electrode, reduces the probability of material particles falling off in the negative electrode active layer, and reduces the risk of the negative electrode breaking. This is beneficial to maintaining the structural stability of the negative electrode, reducing the volume expansion of the battery cell, and extending the cycle life of the lithium battery.

[0134] When the Young's modulus of the first binder is less than 1.40 GPa, the first binder cannot effectively mitigate the volume expansion caused by lithium ion insertion into the active material during cycling; when the Young's modulus of the first binder is greater than 1.7 GPa, the formed electrode is more brittle and prone to the problem of material particles falling off from the negative electrode active layer, which is not conducive to improving the cycle life of the battery cell.

[0135] In one embodiment, based on the mass of the negative electrode active layer, the mass content of the first binder is 0.2%-3%.

[0136] The amount of the first binder can be 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.5%, 2%, 2.4%, 2.6%, 3% of the mass of the negative electrode active layer, or it can be a range of any two of the above values, such as 0.2%-1.0%, 0.7%-2.4%, etc.

[0137] By setting the amount of the first binder as described above, the amount of the first binder is appropriate, maintaining a large proportion of the negative electrode active material in the negative electrode active layer, maintaining a high capacity of the negative electrode sheet, and at the same time, the amount of the first binder can keep the negative electrode active material and other materials tightly bonded to the negative electrode current collector, limiting the expansion or contraction of the negative electrode active layer material to a certain extent, maintaining the structural stability of the negative electrode sheet, and helping to extend the cycle life of the lithium battery.

[0138] In one embodiment, the first adhesive includes at least one of hydroxyl and carboxyl groups. Optionally, the first adhesive includes at least one of polyacrylic acid (PAA) and cross-linked polyacrylic acid-polybenzimidazole (PAA-PBI), wherein PAA and PAA-PBI include carboxyl groups. Optionally, the first adhesive includes polyethylene oxide (PEO, with the structural formula H-(-OCH2CH2-)). n At least one of polyethylene oxide (PEG) and carboxymethyl chitosan, wherein PEG and carboxymethyl chitosan include hydroxyl groups.

[0139] By incorporating at least one of hydroxyl and carboxyl groups into the first binder, hydrogen bonds can be formed between molecules, promoting physical cross-linking. Hydrogen bonds are a relatively weak intermolecular force; compared to chemical bonds, they are easier to break and reform. Hydrogen-bonded molecular chains can move relatively to some extent. When the binder develops microcracks or damage, the hydroxyl and / or carboxyl groups on the surrounding molecular chains can rapidly move and rearrange due to their dynamic hydrogen bond interactions, tending to fill the cracks and reform hydrogen bonds, thus repairing the damage and achieving self-healing. In other words, the first binder has rapid self-healing properties. Due to the physical cross-linking effect of hydrogen bonds, the molecular chains of the first binder are fixed in certain positions, forming a relatively stable three-dimensional network structure. When solvent molecules attempt to enter the interior of the first binder, they need to overcome the binding force of the hydrogen bonds. Compared to the case without physical cross-linking, the swelling process is hindered, thereby reducing the swelling of the negative electrode active layer. This can mitigate the capacity loss caused by the swelling of the negative electrode sheet and help extend the cycle life of the lithium battery.

[0140] In one embodiment, the first adhesive includes at least one of polyacrylic acid (PAA), polyamide-imide (PAI), polyethylene oxide (PEO), polytetrafluoroethylene (PTFE), crosslinked polyacrylic acid-polybenzimidazole (PAA-PBI), polyvinylidene fluoride-polytetrafluoroethylene block copolymer (PVDF-PTFE copolymer), and carboxymethyl chitosan.

[0141] By selecting the above-mentioned materials as the first binder, the negative electrode active material and other materials can be tightly bonded together with the negative electrode current collector, which to a certain extent restricts the expansion or contraction of the negative electrode active layer material, reduces the probability of material particles falling off in the negative electrode active layer, maintains the structural stability of the negative electrode sheet, and helps to extend the cycle life of lithium batteries.

[0142] In one embodiment, the first adhesive comprises at least one of polyacrylic acid, cross-linked polyacrylic acid-polybenzimidazole, polyethylene oxide, and carboxymethyl chitosan.

[0143] By using the above-mentioned materials as the first binder, the first binder includes at least one of hydroxyl and carboxyl groups. Hydroxyl and carboxyl groups can form hydrogen bonds. The formation of hydrogen bonds between molecules promotes physical cross-linking between molecules, giving the first binder the characteristic of rapid self-healing, reducing the swelling of the negative electrode active layer, alleviating the capacity loss caused by the swelling of the negative electrode sheet, and helping to extend the cycle life of the lithium battery.

[0144] In one embodiment, the negative electrode active layer further includes a second binder; that is, the negative electrode active layer includes a first binder and a second binder, wherein the Young's modulus of the second binder is less than that of the first binder.

[0145] By setting the negative electrode active layer including a first binder and a second binder, the first binder provides strong mechanical support, reducing the possibility of excessive deformation or even cracking of the negative electrode sheet due to material volume expansion; the second binder provides good flexibility, improving the flexibility of the electrode sheet and reducing the possibility of electrode sheet breakage; the combination of the first binder and the second binder maintains the overall structural strength of the negative electrode sheet while maintaining the structural stability of the negative electrode sheet, which is beneficial to extending the cycle life of lithium battery.

[0146] In one embodiment, based on the mass of the negative electrode active layer, the mass content of the second binder is 0.3%-2%.

[0147] By setting the amount of the second binder as described above, the first and second binders work together to maintain the overall structural strength of the negative electrode sheet while allowing the binder system to better adapt to volume changes in the negative electrode material, maintaining the structural stability of the negative electrode sheet and thus extending the cycle life of the lithium battery. The amount of the second binder can be 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2% of the negative electrode active layer mass, or a range consisting of any two of the above values, such as 0.3%-1.5% or 0.4%-1%.

[0148] In one embodiment, the second adhesive includes at least one of styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC-Na).

[0149] By selecting the above-mentioned materials as the second binder, the second binder can provide better flexibility and can deform appropriately with the change of material volume of the negative electrode sheet, reduce the generation of internal stress, maintain the structural stability of the negative electrode sheet, and help extend the cycle life of the lithium battery.

[0150] In one embodiment, the negative electrode active material includes artificial graphite; based on the mass of the negative electrode active layer, the mass percentage of artificial graphite is greater than or equal to 80% and less than or equal to 97.5%.

[0151] Among them, artificial graphite refers to graphite materials obtained through organic carbonization followed by high-temperature graphitization treatment.

[0152] Compared to natural graphite, artificial graphite has fewer defects; using artificial graphite as a negative electrode active material is beneficial for improving battery cycle life. Artificial graphite has good compatibility with the electrolyte, which facilitates the formation of a well-formed SEI film between the negative electrode and the electrolyte, resulting in a good cycle life for the lithium battery. By setting the mass percentage of artificial graphite in the negative electrode active layer to be greater than or equal to 80% and less than or equal to 97.5%, the negative electrode can store a large number of lithium ions, improving the energy density and performance of the lithium battery. The mass percentage of artificial graphite in the negative electrode active layer can be 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 97%, 97.5%, or any range of two of these values, such as 80%–90% or 86%–97%.

[0153] In one embodiment, the artificial graphite includes bulk particles and a coating layer on the surface of the bulk particles, the coating layer comprising amorphous carbon.

[0154] By coating amorphous carbon onto the surface of artificial graphite, the amorphous carbon can promote the formation of a more stable and thinner SEI film. The amorphous carbon acts as a barrier, reducing direct contact and side reactions between the artificial graphite and the electrolyte, thus helping to maintain the integrity and stability of the artificial graphite structure and extending the lifespan of lithium batteries. Compared to artificial graphite, amorphous carbon has a larger interlayer spacing, allowing active ions to diffuse more quickly within the negative electrode active material particles, which is beneficial for improving the performance of lithium-ion batteries.

[0155] In one embodiment, based on the total mass of artificial graphite, the mass percentage of amorphous carbon is greater than or equal to 0.5% and less than or equal to 10%.

[0156] By setting the mass percentage of amorphous carbon within the aforementioned range, the amount of amorphous carbon coating on the surface of artificial graphite is optimal. This improves the conductivity of artificial graphite, maintains the integrity and stability of its structure, and results in a more suitable internal resistance for the battery, thus enhancing the energy density, cycle stability, and cycle life of the lithium battery. The mass percentage of amorphous carbon, based on the total mass of the artificial graphite coated with amorphous carbon, can be 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, etc., or a range consisting of any two of the above values, such as 1%–5% or 0.5%–6%.

[0157] In one embodiment, the degree of graphitization of the artificial graphite is greater than or equal to 90% and less than or equal to 97%.

[0158] Graphitization degree is an indicator of the extent to which carbon atoms form a close-packed hexagonal graphite crystal structure. The closer the lattice size of graphite is to the lattice constant of ideal graphite, the higher the graphitization degree. Graphitization degree can be measured using methods known in the art. For example, graphitization degree can be measured using an X-ray diffractometer (such as a Bruker D8 Discover). The measurement method can be referenced in JB / T 4220-2011. The interlayer spacing d002 of the (002) crystal planes of graphite is measured, and then the graphitization degree is calculated using the formula G = (0.344 - d002) / (0.344 - 0.3354), where G represents the graphitization degree.

[0159] The aforementioned graphitization degree of artificial graphite possesses a highly ordered layered structure. Using artificial graphite with this degree of graphitization helps reduce volume expansion during charging and discharging, thereby improving the cycle life of lithium batteries. The graphitization degree of artificial graphite can be 97%, 96.5%, 96%, 95%, 94%, 93%, 92%, 91%, 90%, or any range of two of these values, such as 92%–97% or 93%–96.5%.

[0160] In one embodiment, the disorder R value of the artificial graphite is greater than or equal to 0.04 and less than or equal to 0.6.

[0161] The R value is the ratio of the intensity of the D peak to the G peak in the Raman spectrum of artificial graphite, R = I D / I G R-value is used to characterize the disorder in the near-surface region of graphite materials. A larger R-value indicates a higher degree of disorder in the artificial graphite material; conversely, a smaller R-value indicates better regularity and higher order. The R-value can be characterized using Raman spectroscopy. The specific testing method is as follows: 1) Obtaining the Raman spectrum: First, it is necessary to obtain the spectral data of the sample using a Raman spectrometer; this usually involves irradiating the sample with a laser and collecting the scattered light. 2) Identifying the D and G peaks: In Raman spectroscopy, the D and G peaks are two key characteristic peaks; the D peak typically appears at approximately 1300 cm⁻¹. -1 The G peak is located near the lattice defects of carbon atoms in the material, particularly sp3 hybridized carbon atoms; the G peak is located at approximately 1580 cm⁻¹. -1 Nearby, this originates from the stretching vibrations of in-plane CC bonds formed by carbon atoms with sp2 hybrid orbitals. 3) Calculate the peak intensity ratio: Use spectral software or manually measure the intensities of the D and G peaks; typically, the maximum intensity value of each peak is chosen to represent the peak intensity. Then, calculate the ratio of the D peak intensity (ID) to the G peak intensity (IG), i.e., IG. D / I G .

[0162] By setting the disorder R value of artificial graphite within the above range, it is beneficial to reduce its volume expansion during charging and discharging, reduce the stress generated by the volume expansion and contraction of the material, thereby reducing the risk of material pulverization and shedding, and helping to maintain the structural integrity of the negative electrode sheet. At the same time, with the disorder R value of artificial graphite within the above range, the defects in artificial graphite are more suitable. These defects can provide more channels and sites for lithium ion transport, making the diffusion of lithium ions in the electrode material easier and helping to improve the cycle life of the battery.

[0163] The disorder R value of artificial graphite can be 0.6, 0.57, 0.52, 0.5, 0.48, 0.45, 0.4, 0.39, 0.35, 0.32, 0.3, 0.29, 0.25, 0.22, 0.2, 0.15, 0.12, 0.1, 0.05, 0.04, etc., or it can be a range of any two of the above values, such as 0.4 to 0.6, 0.2 to 0.5, etc.

[0164] In one embodiment, the negative electrode active material has a 0.1C CC specific capacity greater than or equal to 350 mAh / g and less than or equal to 360 mAh / g.

[0165] 0.1C CC specific capacity refers to the capacity per unit mass of electrode material obtained when the battery is charged or discharged at a current of 0.1 times the rated capacity of the battery under constant current charge-discharge (CC) conditions.

[0166] By setting the specific capacity of the negative electrode active material at 0.1C CC as described above, the negative electrode active material exhibits good lithium-ion insertion and extraction efficiency, relatively stable electrochemical performance, low lithium consumption, reduced side reaction gas production, and reduced volume expansion of the lithium battery, which is beneficial to extending the cycle life of the lithium battery. The specific capacity of the negative electrode active material at 0.1C CC can be 350mAh / g, 351mAh / g, 352mAh / g, 353mAh / g, 354mAh / g, 355mAh / g, 356mAh / g, 357mAh / g, 358mAh / g, 359mAh / g, 360mAh / g, etc., or it can be a range of any two of the above values, such as 350mAh / g~355mAh / g, 353mAh / g~358mAh / g, etc.

[0167] In one embodiment, the negative electrode active layer includes a first sub-active layer disposed on the surface of the negative electrode current collector and a second sub-active layer disposed on the side of the first sub-active layer away from the negative electrode current collector; the Dv50 of the negative electrode active material of the first sub-active layer is greater than the Dv50 of the negative electrode active material of the second sub-active layer.

[0168] The physical definition of Dv50 is the particle size corresponding to a cumulative volume distribution percentage of 50% in artificial graphite. Dv50 can be determined using a laser particle size analyzer (such as the Malvern Master Size 3000) in accordance with the standard GB / T19077.1-2016.

[0169] By setting the Dv50 of the negative electrode active material in the first sub-active layer to be greater than that in the second sub-active layer, that is, using a negative electrode active material with a larger particle size near the negative electrode current collector and a negative electrode active material with a smaller particle size near the electrolyte, the negative electrode active material near the electrolyte has a larger specific surface area, which can shorten the migration path of lithium ions, reduce diffusion resistance, and facilitate charging. At the same time, it helps to reduce the expansion and contraction of the negative electrode material, thereby extending the cycle life of the lithium battery.

[0170] Optionally, the negative electrode active material of the first sub-active layer includes artificial graphite, and the negative electrode active material of the second sub-active layer includes artificial graphite.

[0171] In one embodiment, the Dv50 of the negative electrode active material in the first sub-active layer is greater than or equal to 11 μm and less than or equal to 20 μm; the Dv50 of the negative electrode active material in the second sub-active layer is greater than or equal to 7 μm and less than or equal to 16 μm.

[0172] The Dv50 of the negative electrode active material in the first sub-active layer can be 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, etc., or it can be a range of any two of the above values, such as 12μm~19μm, 14μm~20μm, etc. The Dv50 of the negative electrode active material in the second sub-active layer can be 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, etc., or it can be a range of any two of the above values, such as 8μm~16μm, 9μm~13μm, etc.

[0173] By setting the Dv50 of the negative electrode active material in the first sub-active layer and the Dv50 of the negative electrode active material in the second sub-active layer as described above, the lithium-ion migration path can be shortened, the diffusion resistance can be reduced, and the expansion and contraction of the negative electrode material can be reduced, thereby extending the cycle life of the lithium battery.

[0174] In one embodiment, the Dv50 of the negative electrode active material in the first sub-active layer is greater than or equal to 12.5 μm and less than or equal to 18.5 μm; the Dv50 of the negative electrode active material in the second sub-active layer is greater than or equal to 8.5 μm and less than or equal to 15.5 μm.

[0175] The Dv50 of the negative electrode active material in the first sub-active layer can be 12.5μm, 13μm, 13.5μm, 14μm, 14.5μm, 15μm, 15.5μm, 16μm, 16.5μm, 17μm, 17.5μm, 18μm, 18.5μm, etc., or it can be a range of any two of the above values, such as 12.5μm~15μm, 13.5μm~17μm, etc. The Dv50 of the negative electrode active material in the second sub-active layer can be 8.5μm, 9μm, 9.5μm, 10μm, 10.5μm, 11μm, 11.5μm, 12μm, 12.5μm, 13μm, 13.5μm, 14μm, 14.5μm, 15μm, 15.5μm, etc., or it can be a range of any two of the above values, such as 9μm~13μm, 10μm~13.5μm, etc.

[0176] By setting the Dv50 of the negative electrode active material in the first sub-active layer and the Dv50 of the negative electrode active material in the second sub-active layer as described above, the lithium-ion migration path can be shortened, the diffusion resistance can be reduced, and the expansion and contraction of the negative electrode material can be reduced, thereby extending the cycle life of the lithium battery.

[0177] In one embodiment, the thickness of the negative electrode active layer is 100μm-150μm.

[0178] The thickness of the negative electrode active layer refers to the vertical distance between the surface of the negative electrode active layer away from the negative electrode current collector and the surface of the negative electrode active layer close to the negative electrode current collector.

[0179] The embodiments of this application select a negative electrode active layer with a thickness range of the above-mentioned range. The thickness is appropriate, and more active material can be loaded on a negative electrode current collector of a given area, which is beneficial to improving the energy density of the battery. During the charging and discharging process, the stress change of the battery during the charging and discharging process can be reduced. The negative electrode active layer structure is relatively stable and has a low rebound rate, which is beneficial to maintaining a long cycle life.

[0180] The thickness of the negative electrode active layer can be 100μm, 110μm, 120μm, 130μm, 140μm, 150μm, etc., or it can be a range of any two of the above values, such as 110μm-130μm, 120μm-140μm, etc.

[0181] In one embodiment, the negative electrode active layer further includes a negative electrode thickener, which includes at least one of sodium carboxymethyl cellulose (CMC-Na) and lithium carboxymethyl cellulose (CMC-Li).

[0182] In one embodiment, the negative electrode active layer further includes a negative electrode conductive agent, which includes one or more of superconducting carbon, acetylene black, carbon black, carbon nanotubes, graphene, and carbon nanofibers.

[0183] In one embodiment, the negative electrode current collector may be a metal foil or a composite negative electrode current collector. Optionally, the metal foil may be made of aluminum, copper, nickel, titanium, silver, or their corresponding alloys. Optionally, the composite negative electrode current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite negative electrode current collector may be formed by forming a metal material on the polymer material substrate; the metal material may include at least one of aluminum, aluminum alloy, copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy; the polymer material may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0184] In one specific embodiment, the negative electrode active material, the first binder, the negative electrode thickener, the negative electrode conductive agent and any other components are dispersed in a solvent (e.g., deionized water), stirred in a dry environment to form a uniform negative electrode slurry, the negative electrode slurry is coated on the negative electrode current collector, and then dried and rolled to form a negative electrode sheet.

[0185] In one embodiment, the positive electrode includes a positive current collector and a positive active layer disposed on at least one surface of the positive current collector. The positive active layer includes a positive active material, which includes a lithium phosphate material with the general chemical formula LiFe. 1-x M x PO4, wherein M includes at least one of Mg, Ti, Cu, and Nb, and 0.05 ≤ x ≤ 0.3.

[0186] By doping lithium iron phosphate with at least one element selected from Mg, Ti, Cu, and Nb, more conductive channels are formed through metal doping, enhancing lithium-ion transport. At the same time, the crystal structure of lithium iron phosphate can be strengthened, reducing volume changes caused by phase transitions during charging and discharging, improving structural stability, which is beneficial for extending cycle life and maintaining high energy density.

[0187] By setting the doping amount x of at least one element selected from Mg, Ti, Cu, and Nb to 0.05 ≤ x ≤ 0.3, the doping element plays its role in improving the structural stability of lithium iron phosphate and thus extending its cycle life. The doping amount x can be 0.05, 0.052, 0.054, 0.056, 0.058, 0.06, 0.062, 0.064, 0.066, 0.068, 0.07, 0.072, 0.073, 0.075, 0.1, 0.15, 0.17, 0.2, 0.25, 0.28, 0.3, etc., or it can be a range of any two of the above values, such as 0.05-0.075, 0.05-0.1, 0.15-0.3, etc.

[0188] Furthermore, lithium iron phosphate doped with metal elements exhibits better structural stability, which can reduce iron leaching and thus decrease the Fe content on the negative electrode. It should be noted that the Fe content on the negative electrode can be analyzed using inductively coupled plasma optical emission spectrometry (ICP).

[0189] The mass ratio of lithium phosphate material in the positive electrode active layer is greater than or equal to 80%. The positive electrode active material has a relatively stable structure while having a high energy density, which is conducive to improving the energy density of lithium batteries and maintaining a long cycle life of lithium batteries.

[0190] The mass percentage of lithium phosphate material in the positive electrode active layer is 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98%, 99%, etc., or it can be a range of any two of the above values, such as 80%-90%, 86%-98%, etc.

[0191] It should be noted that, in this application, the metal elements doped in lithium iron phosphate and their doping amounts can be determined using methods known in the art. For example, they can be characterized by energy-dispersive X-ray spectroscopy (EDS) or X-ray photoelectron spectroscopy (XPS). EDS spectra can be used to determine whether LFP is uniformly doped with at least one element selected from Mg, Ti, Cu, and Nb. Similarly, fitting the corresponding elemental orbital maps using XPS can also determine whether a particular element has been successfully doped.

[0192] In one implementation, 0.1 ≤ x ≤ 0.2.

[0193] By setting the doping amount x of the dopant element to 0.1 ≤ x ≤ 0.2, the dopant element can fully exert its function, improve the structural stability of lithium iron phosphate, and help extend cycle life and maintain a high energy density. The doping amount x can be 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2, etc., or it can be a range of any two of the above values, such as 0.1~0.16, 0.13~0.19, etc.

[0194] In one embodiment, the Dv50 of the positive electrode active material is greater than or equal to 0.6 μm and less than or equal to 2.2 μm.

[0195] The physical definition of Dv50 is the particle size corresponding to a cumulative volume distribution percentage of 50% for the positive electrode active material. The Dv50 of the positive electrode active material can be determined using a laser particle size analyzer (such as Malvern Master Size 3000) in accordance with the standard GB / T19077.1-2016.

[0196] The Dv50 of the positive electrode active material falls within the range described above. This ensures the positive electrode active material exhibits good structural stability, which is beneficial for improving the energy density and extending the cycle life of lithium batteries. The Dv50 of the positive electrode active material can be 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1.0μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, 1.6μm, 1.7μm, 1.8μm, 1.9μm, 2.0μm, 2.1μm, 2.2μm, etc., or it can be a range consisting of any two of the above values, such as 0.6μm~1.4μm, 1.0μm~2.1μm, etc.

[0197] In one embodiment, the Dv50 of the positive electrode active material is greater than or equal to 1 μm and less than or equal to 1.6 μm.

[0198] The Dv50 of the positive electrode active material falls within the range described above. This provides the positive electrode active material with good structural stability, which is beneficial for improving the energy density and extending the cycle life of lithium batteries. The Dv50 of the positive electrode active material can be 1.0μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, 1.6μm, etc., or it can be a range consisting of any two of the above values, such as 1.0μm~1.3μm, 1.2μm~1.5μm, etc.

[0199] In one embodiment, the positive electrode active material has a first delithiation capacity of ≥145 mAh / g at 0.1C.

[0200] The first lithium delithiation capacity of the positive electrode active material at 0.1C refers to the following: the positive electrode active material is assembled into a lithium battery, the lithium battery is charged for the first time until the set cutoff voltage is reached, and then discharged at a rate of 0.1 times the theoretical capacity of the battery per hour, and the discharge curve is recorded until the discharge termination voltage is reached; the capacity during the first discharge process is the first lithium delithiation capacity at 0.1C.

[0201] This application uses the aforementioned positive electrode active material with specific capacity on a substrate doped with metal elements in lithium iron phosphate, maintaining a high energy density and a relatively stable structure, which is beneficial to improving the performance of lithium batteries.

[0202] In one embodiment, the positive electrode active material has a first delithiation capacity of less than or equal to 147 mAh / g at 0.1C.

[0203] This application uses the above-mentioned positive electrode active material with specific capacity to maintain a high energy density of the positive electrode active material, which is beneficial to the lithium battery having a high energy density and improving the performance of the lithium battery.

[0204] The initial lithium delithiation capacity of the positive electrode active material at 0.1C can be 145mAh / g, 145.5mAh / g, 146mAh / g, 146.5mAh / g, 147mAh / g, etc.; or it can be a range of any two of the above values, such as 145mAh / g-146mAh / g, 145.5mAh / g-147mAh / g, etc.

[0205] In one embodiment, the coating weight of the positive electrode active layer is greater than or equal to 260 mg / 1540.25 mm. 2 And less than or equal to 330mg / 1540.25mm 2 .

[0206] The coating weight of the positive electrode active layer refers to the weight of the material forming the positive electrode active layer per unit area coated on the positive electrode current collector, which can be expressed as mg / 1540.25mm². 2 The unit is (milligrams per 1540.25 mm²). The method for determining coating weight (CW) is as follows: A positive electrode sheet is used as the substrate for stamping to obtain a sheet with an area of ​​1540.25 mm². 2 The small discs are weighed using a balance to obtain their weight. The weight of the current collector portion of the small discs is then subtracted to obtain the coating weight of the positive electrode active layer.

[0207] The embodiments of this application employ a positive electrode active layer within the aforementioned coating weight range, which is beneficial for improving the energy density of lithium batteries and extending cycle life. The coating weight of the positive electrode active layer can be 260mg / 1540.25mm. 2 270mg / 1540.25mm 2 280mg / 1540.25mm 2 290mg / 1540.25mm 2 300mg / 1540.25mm 2 310mg / 1540.25mm 2 320mg / 1540.25mm 2 330mg / 1540.25mm 2 "etc." can also be a range consisting of any two of the above values, for example, 270mg / 1540.25mm. 2 ~310mg / 1540.25mm 2 280mg / 1540.25mm 2 ~330mg / 1540.25mm 2 wait.

[0208] In one embodiment, the compaction density of the positive electrode active layer is greater than or equal to 2.3 g / cc and less than or equal to 2.7 g / cc.

[0209] The compaction density of the positive electrode active layer refers to the weight per unit volume of the material forming the positive electrode active layer on the positive electrode current collector after compaction treatment. It is usually expressed in g / CC (grams per cubic centimeter). The compaction density of the positive electrode active layer reflects the degree of compaction of the material forming the positive electrode active layer. The specific test method for compaction density is as follows: 1) Punch the electrode sheet to obtain a circular sample, and measure the cross-sectional area A of the sample thickness. 2) Weigh the obtained sample mass m1, and measure the sample thickness d1. 3) Confirm the number of faces of the electrode sheet, which is 1 or 2. 4) Wash the sample with water to remove the active material, and obtain the substrate. 5) Weigh the obtained substrate mass m2, and measure the substrate thickness d2. 6) The compaction density of the electrode sheet = (m1-m2) / [(d1-d2)*A].

[0210] The positive electrode active layer with a compaction density within the aforementioned range, as used in the embodiments of this application, is beneficial for enabling lithium batteries to have higher energy density and longer cycle life. The compaction density of the positive electrode active layer can be 2.3 g / cc, 2.35 g / cc, 2.4 g / cc, 2.45 g / cc, 2.5 g / cc, 2.55 g / cc, 2.6 g / cc, 2.65 g / cc, 2.7 g / cc, etc., or it can be a range consisting of any two of the aforementioned values, such as 2.3 g / cc to 2.5 g / cc, 2.35 g / cc to 2.65 g / cc, etc.

[0211] In one embodiment, the compaction density of the positive electrode active layer is greater than or equal to 2.4 g / cc and less than or equal to 2.6 g / cc.

[0212] The positive electrode active layer with a compaction density within the aforementioned range, as used in the embodiments of this application, is beneficial for enabling lithium batteries to have higher energy density and longer cycle life. The compaction density of the positive electrode active layer can be 2.4 g / cc, 2.43 g / cc, 2.45 g / cc, 2.48 g / cc, 2.5 g / cc, 2.52 g / cc, 2.55 g / cc, 2.57 g / cc, 2.6 g / cc, etc., or it can be a range consisting of any two of the above values, such as 2.43 g / cc to 2.55 g / cc, 2.5 g / cc to 2.6 g / cc, etc.

[0213] In one embodiment, the thickness of the positive electrode active layer is 70 μm-100 μm.

[0214] The thickness of the positive electrode active layer refers to the vertical distance between the surface of the positive electrode active layer facing away from the positive electrode current collector and the surface of the positive electrode active layer facing towards the positive electrode current collector. Optionally, a positive electrode active layer is provided on one surface of the positive electrode current collector, and the thickness of the positive electrode active layer is 70μm-100μm. Optionally, positive electrode active layers are provided on two opposite surfaces of the positive electrode current collector, and the thicknesses of the positive electrode active layers formed on the two opposite surfaces of the positive electrode current collector are 70μm-100μm respectively.

[0215] The embodiments of this application select a positive electrode active layer with a thickness within the aforementioned range. This suitable thickness allows for the loading of a larger amount of active material onto a given area of ​​positive electrode current collector, which is beneficial for improving the battery's energy density. During charging and discharging, it reduces stress changes in the battery, resulting in a more stable positive electrode active layer structure and contributing to a longer cycle life. The thickness of the positive electrode active layer can be 70μm, 72μm, 74μm, 76μm, 78μm, 80μm, 82μm, 85μm, 89μm, 90μm, 94μm, 95μm, 98μm, 100μm, etc., or it can be a range consisting of any two of the above values, such as 70μm-90μm, 76μm-95μm, etc.

[0216] In one embodiment, the positive electrode active layer further includes a positive electrode binder, which includes one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and copolymers of PVDF and PTFE.

[0217] In one embodiment, the positive electrode active layer further includes a positive electrode conductive agent, which includes one or more of superconducting carbon, acetylene black, carbon black, carbon nanotubes, graphene, and carbon nanofibers.

[0218] In one embodiment, the positive electrode current collector may be a metal foil or a composite positive electrode current collector. Optionally, the metal foil may be made of aluminum, copper, nickel, titanium, silver, or their corresponding alloys. Optionally, the composite positive electrode current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite positive electrode current collector may be formed by forming a metal material on a polymer material substrate; the metal material may include at least one of aluminum, aluminum alloy, copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy; the polymer material may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0219] In one specific embodiment, the positive electrode sheet is prepared by dispersing the positive active material, conductive agent, binder and any other components in a solvent (e.g., N-methylpyrrolidone NMP), stirring in a dry environment to form a uniform positive slurry, coating the positive slurry onto a positive current collector, and then drying and rolling to form a positive electrode sheet.

[0220] In one embodiment, the conductivity of the electrolyte is 7 mS / cm to 13 mS / cm.

[0221] Electrolyte conductivity refers to the ability of active ions to conduct within the electrolyte. Higher conductivity indicates greater conductivity of active ions, which is beneficial for improving the fast-charging performance of lithium-ion batteries. The conductivity of an electrolyte at 25°C can be tested using any known method. For example, a conductivity meter can be used to test the conductivity by inserting its electrodes into the electrolyte and applying a constant voltage. The conductivity meter measures the current flowing through the electrolyte and calculates the conductivity based on the voltage-to-current ratio.

[0222] By setting the electrolyte conductivity within the aforementioned range, it is beneficial to improve the transport capacity of lithium ions in the electrolyte, facilitate the formation of a stable solid electrolyte interphase (SEI) film, prevent direct contact between the electrolyte and the negative electrode material, reduce electrolyte decomposition reactions, and thus suppress gas generation, thereby improving the cycle life of the lithium-ion battery. The electrolyte conductivity can be 7 mS / cm, 8 mS / cm, 9 mS / cm, 10 mS / cm, 11 mS / cm, 12 mS / cm, 13 mS / cm, etc., or it can be a range of any two of the above values, such as 7 mS / cm~11 mS / cm, 9 mS / cm~12 mS / cm, etc.

[0223] In one embodiment, the conductivity of the electrolyte is 7 mS / cm to 10 mS / cm.

[0224] In this paper, electrolytes with suitable conductivity can be obtained by adjusting the solvent, lithium salt, or additives of the electrolyte.

[0225] By setting the electrolyte conductivity within the aforementioned range, lithium ions maintain a relatively fast transport capability within the electrolyte, which helps form a stable solid electrolyte interphase (SEI) film. This prevents direct contact between the electrolyte and the negative electrode material, reduces electrolyte decomposition reactions, and suppresses gas generation, thereby improving the cycle life of the lithium-ion battery. The electrolyte conductivity can be 7 mS / cm, 7.5 mS / cm, 8 mS / cm, 8.5 mS / cm, 9 mS / cm, 9.5 mS / cm, 10 mS / cm, etc., or it can be a range of any two of the above values, such as 7 mS / cm~9 mS / cm, 8 mS / cm~10 mS / cm, etc.

[0226] In one embodiment, the water content of the electrolyte is less than or equal to 200 ppm.

[0227] The method for testing the water content in the electrolyte is as follows: Place the Karl Fischer moisture analyzer in the glove box for equilibration for 30 minutes; weigh 3-5 g of sample using the subtraction method on an electronic balance (accurate reading to 0.001 g), and extract the sample with a syringe; inject the extracted sample into the titration cell through the injection port, stir thoroughly for 10 seconds, and then start the titration; after the titration is completed, input the sample mass and record the water content determination result in the sample.

[0228] By setting the water content in the electrolyte to be less than or equal to 200 ppm, the reaction between water and lithium salt to form hydrofluoric acid can be reduced. This reduces the damage of hydrofluoric acid to active materials or the SEI film, thus helping to maintain a longer cycle life for lithium batteries. The water content of the electrolyte can be 200 ppm, 180 ppm, 160 ppm, 140 ppm, 120 ppm, 100 ppm, 80 ppm, 60 ppm, etc., or it can be a range of any two of the above values, such as 180 ppm to 200 ppm, 80 ppm to 140 ppm, etc.

[0229] In one embodiment, the water content of the electrolyte is less than or equal to 100 ppm.

[0230] By setting the water content in the electrolyte to be less than or equal to 100 ppm, the reaction between water and lithium salt to form hydrofluoric acid can be reduced. This reduces the damage of hydrofluoric acid to active materials or the SEI film, thus helping to maintain a longer cycle life for lithium batteries. The water content of the electrolyte can be 100 ppm, 80 ppm, 60 ppm, 40 ppm, 20 ppm, or any range of two of the above values, such as 80 ppm to 100 ppm, 40 ppm to 80 ppm, etc.

[0231] In one embodiment, the electrolyte includes a first solvent, which includes at least one of vinyl acetate (EC), methyl acetate (MA), dimethyl carbonate (DMC), ethyl propionate (EP), and propyl propionate (PP).

[0232] Among them, vinyl acetate has a melting point of 35-38℃, a boiling point of 248℃, a dielectric constant of 90 c / vm at 20℃, and a viscosity of 1.9 mPa·s. Methyl acetate has a melting point of -98℃, a boiling point of 57.8℃, a dielectric constant of 6.68 at 20℃, and a viscosity of 0.39 mPa·s. Propyl propionate has a melting point of -75.9℃, a boiling point of 122.5℃, a dielectric constant of 4.7 c / vm at 20℃, and a viscosity of 0.68 mPa·s. Ethyl propionate has a melting point of -73.9℃, a boiling point of 99.1℃, a dielectric constant of 5.65 at 20℃, and a viscosity of 0.89 mPa·s. Dimethyl carbonate has a melting point of 4.6℃, a boiling point of 91℃, a dielectric constant of 3.1 c / vm, and a viscosity of 0.59 mPa·s.

[0233] The embodiments of this application use a first solvent including one or more of vinyl acetate, methyl acetate, propyl propionate, ethyl propionate, and dimethyl carbonate. The resulting electrolyte has high conductivity, which helps to improve the migration speed of lithium ions, facilitates effective contact between the active material and the electrolyte, and is beneficial to improving the kinetic performance and cycle life of lithium-ion batteries.

[0234] In this application, the components and their contents of the electrolyte can be determined according to methods known in the art. For example, they can be determined by gas chromatography, gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), nuclear magnetic resonance spectroscopy (NMR), inductively coupled plasma optical emission spectrometry (ICP-OES), etc.

[0235] In one embodiment, the first solvent accounts for less than or equal to 20% of the mass of the electrolyte.

[0236] Based on the total mass of the electrolyte, the mass percentage of the first solvent can be 0.1%, 0.2%, 0.5%, 1%, 1.1%, 1.2%, 1.5%, 2%, 2.1%, 2.2%, 2.5%, 3%, 3.1%, 3.2%, 3.5%, 4%, 4.1%, 4.2%, 4.5%, 5%, 5.1%, 5.2%, 5.5%, 6%, 6.1%, 6.2%, 6.5%, 7%, 7.1%, 7.2%, 7.5%, 8%, 8.1%, 8.2%, 8.5%, 9%, 9.1%, 9.2%, 9.5%, 10%, 10.1%, 10.2%, 10.5%, 11%, 11.1%, 11.2%, 11. 5%, 12%, 12.1%, 12.2%, 12.5%, 13%, 13.1%, 13.2%, 13.5%, 14%, 14.1%, 14.2%, 14.5%, 15%, 15.1%, 15.2%, 15.5%, 16%, 16.1%, 16.2%, 16.5%, 17%, 17.1%, 17.2%, 17.5%, 18%, 18.1%, 18.2%, 18.5%, 19%, 19.1%, 19.2%, 19.5%, 20%, etc., or any range of any two of the above values, for example, 1% to 5%, 3% to 8%, 5% to 10%, 8% to 15%, 10% to 20%, etc.

[0237] The embodiments of this application, by adjusting the proportion of the first solvent in the electrolyte, achieve a suitable amount of the first solvent, which is beneficial to charging and cycle life; by leveraging the synergistic effect of the multi-component electrolyte, it is beneficial to improve the film-forming stability of the electrolyte at the negative electrode, enabling the lithium-ion battery to have good cycle stability over a wide temperature range and improving the cycle life of the lithium-ion battery.

[0238] In one embodiment, the electrolyte further includes additives, including at least one of vinylene carbonate (VC), 1,3-propenesulfonyl lactone (PS), fluoroethylene carbonate (FEC), methylbenzenesulfonyl isocyanate (PTSI), and 1-(trimethylsilyl)-1H-benzotriazole (TMSBTA).

[0239] By selecting the above-mentioned additives, they can react chemically with HF and H2O or interact with hydrogen bonds to achieve the effects of removing acid and water, reducing the water content in the electrolyte, and neutralizing the acid produced by the side reactions of lithium salts or other components, which is beneficial to extending the cycle life of lithium batteries.

[0240] In one embodiment, the additive accounts for 0.05% to 2% of the mass of the electrolyte.

[0241] By setting the mass percentage of the additive in the electrolyte within the range mentioned above, the water and acid content in the electrolyte can be effectively reduced, which is beneficial for extending the cycle life of lithium batteries. The mass percentage of the additive in the electrolyte can be 0.05%, 0.07%, 0.09%, 0.1%, 0.12%, 0.14%, 0.16%, 0.18%, 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, etc., or it can be a range consisting of any two of the above values, such as 0.05% to 1%, 0.8% to 1.7%, etc.

[0242] In one embodiment, the additive accounts for 0.1% to 0.8% of the mass of the electrolyte.

[0243] By setting the mass percentage of the additive in the electrolyte within the range mentioned above, the water and acid content in the electrolyte can be effectively reduced, which is beneficial for extending the cycle life of lithium batteries. The mass percentage of the additive in the electrolyte can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, etc., or it can be a range of any two of the above values, such as 0.1%–0.6%, 0.3%–0.8%, etc.

[0244] In one embodiment, the electrolyte further includes a lithium salt with a concentration greater than or equal to 0.7 mol / L and less than or equal to 1.2 mol / L.

[0245] Lithium salts are compounds containing lithium ions that act as carriers of lithium ions in electrolytes, migrating between the positive and negative electrodes.

[0246] The embodiments of this application, by employing lithium salts of the aforementioned concentrations, are beneficial for improving the film-forming stability of the electrolyte at the negative electrode, regulating the conductivity of the electrolyte, enhancing the migration rate of lithium ions, and improving the cycle life of lithium-ion batteries. The concentration of the lithium salt in the electrolyte can be 0.7 mol / L, 0.75 mol / L, 0.8 mol / L, 0.85 mol / L, 0.9 mol / L, 0.95 mol / L, 1 mol / L, 1.1 mol / L, 1.2 mol / L, or any range of two of the above values, for example, 0.9 mol / L to 1.1 mol / L, 0.8 mol / L to 1.2 mol / L, etc.

[0247] In one embodiment, the electrolyte further includes a lithium salt with a concentration greater than or equal to 0.8 mol / L and less than or equal to 1 mol / L.

[0248] The embodiments of this application, by employing lithium salts of the aforementioned concentrations, are beneficial for improving the film-forming stability of the electrolyte at the negative electrode, regulating the conductivity of the electrolyte, enhancing the migration rate of lithium ions, and improving the cycle life of lithium-ion batteries. The concentration of the lithium salt in the electrolyte can be 0.8 mol / L, 0.82 mol / L, 0.85 mol / L, 0.88 mol / L, 0.9 mol / L, 0.93 mol / L, 0.95 mol / L, 0.99 mol / L, 1 mol / L, or any range of two of the above values, such as 0.9 mol / L to 1 mol / L, or 0.82 mol / L to 0.95 mol / L.

[0249] In one embodiment, the lithium salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate, potassium difluorophosphate, lithium difluorooxalate borate (LiBF2(C2O4), LiDFOB), lithium bis(oxalate borate) (LiB(C2O4)2, LiBOB), potassium difluorooxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0250] Please refer to Figures 4 and 5. Figure 4 is a flowchart illustrating the method for preparing a battery cell according to an embodiment of this application, and Figure 5 is a flowchart illustrating the method for preparing a negative electrode sheet according to an embodiment of this application.

[0251] This application also provides a method for preparing a battery cell, which can be used to prepare the battery cell provided in the above embodiments. Specifically, the method for preparing the battery cell includes:

[0252] Step S01: A negative electrode sheet, a separator and a positive electrode sheet are sequentially stacked to form a battery cell assembly; wherein, the negative electrode sheet includes a negative current collector and a negative active layer disposed on at least one surface of the negative current collector; the negative active layer includes a negative active material and a first binder, wherein the Young's modulus of the first binder is 1.40 GPa-1.7 GPa.

[0253] Specifically, the steps for forming a battery cell assembly include: sequentially preparing a positive electrode sheet and a negative electrode sheet, alternately stacking the positive and negative electrode sheets, and setting a separator between the positive and negative electrode sheets to achieve the function of isolation, thereby obtaining a battery cell assembly, or the battery cell assembly can be obtained by winding.

[0254] Step S02: Place the battery cell assembly in the housing.

[0255] Specifically, the housing is a component used to form an internal environment that can accommodate the battery cell assembly. The shape of the housing can be determined according to the specific shape and size of the battery cell assembly. The housing can be made of various materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and this application embodiment does not impose any special limitations on this.

[0256] Step S03: Inject electrolyte into the casing and seal it to form a battery cell.

[0257] Specifically, the internal environment formed by the casing also serves to contain the electrolyte, which affects the performance of the lithium-ion battery. The electrolyte provides a path for lithium ions to move between the positive and negative electrode plates, promoting the charging and discharging process of the battery.

[0258] Electrolyte is injected into the casing and sealed to obtain a single battery cell. Multiple battery cells are integrated to form a battery module, which can provide higher voltage and capacity, and has specific output functions. The battery module is then installed in a battery housing, usually with the addition of a battery management system, to form a battery pack, which is typically provided to the user. Alternatively, multiple battery cells can be directly installed in a housing to form a battery pack.

[0259] In this embodiment, by selecting a first binder with a Young's modulus of 1.40 GPa-1.7 GPa, the negative electrode sheet can be provided with strong mechanical strength. This allows the negative electrode sheet to maintain a relatively firm bond between the negative electrode active material and other materials under greater pressure. The high cohesion of the negative electrode active layer reduces the probability of material particles falling off and the risk of the negative electrode sheet cracking, which is beneficial for maintaining the structural stability of the negative electrode sheet. In addition, selecting a first binder within the aforementioned Young's modulus range can, to a certain extent, limit the expansion or contraction of the material in the negative electrode active layer, which is beneficial for maintaining the dimensional and structural stability of the negative electrode sheet, reducing the volume expansion of the lithium battery, and extending the cycle life of the lithium battery.

[0260] In one embodiment, the method for preparing the negative electrode sheet includes:

[0261] Step S011: A negative electrode active layer is formed on at least one side of the negative electrode current collector to form a first semi-finished product.

[0262] Step S012: The first semi-finished product is dried and compacted to form the second semi-finished product.

[0263] Step S013: Heat-treat the second semi-finished product to obtain a negative electrode sheet, wherein the thickness of the negative electrode sheet is greater than the thickness of the second semi-finished product.

[0264] In the negative electrode preparation method provided in this application embodiment, the pre-rebound of the negative electrode is achieved by heat-treating the second semi-finished product after drying and compaction. This effectively improves the rebound of the negative electrode during cycling, thereby improving the expansion force. It is beneficial to maintain a certain gap between the positive and negative electrode during battery cycling, reducing the possibility of compression between the positive and negative electrode. Maintaining a certain gap between the positive and negative electrode maintains good wettability of the electrolyte on the positive and negative electrode, reducing the possibility of lithium plating, and is conducive to achieving a long life of lithium battery.

[0265] In one embodiment, the difference between the thickness of the negative electrode sheet and the thickness of the second semi-finished product is 4% to 15% of the thickness of the second semi-finished product.

[0266] By pre-rebounding the negative electrode sheet within the aforementioned range, the rebound of the negative electrode sheet during cycling is effectively improved, thus reducing expansion force and resulting in a longer cycle life for the lithium battery. The difference between the thickness of the negative electrode sheet and the thickness of the second semi-finished product can be 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15% of the thickness of the second semi-finished product, or it can be a range composed of any two of the above values, such as 6%–12% or 10%–15%.

[0267] In one embodiment, the difference between the thickness of the negative electrode sheet and the thickness of the second semi-finished product is 7% to 10% of the thickness of the second semi-finished product.

[0268] By pre-rebounding the negative electrode sheet within the aforementioned range, the rebound of the negative electrode sheet during cycling is effectively improved, thus reducing expansion force and resulting in a longer cycle life for the lithium battery. The difference between the thickness of the negative electrode sheet and the thickness of the second semi-finished product can be 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10% of the thickness of the second semi-finished product, or it can be a range of any two of the above values, such as 7%–9% or 7.5%–10%.

[0269] In one embodiment, in step S013, the heat treatment temperature is 140°C to 220°C; and / or, the heat treatment time is 30s to 120s.

[0270] By setting the heat treatment temperature and time within the aforementioned range, the second semi-finished product can expand under this temperature, achieving a pre-rebound effect. The heat treatment temperature can be 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, 220℃, etc., or any range of two of the above values, such as 160℃~200℃, 140℃~180℃, etc. The heat treatment time can be 30s, 40s, 50s, 60s, 70s, 80s, 90s, 100s, 110s, 120s, etc., or any range of two of the above values, such as 30s~100s, 50s~110s, etc.

[0271] In one embodiment, in step S013, the heat treatment temperature is 160°C to 180°C; and / or, the heat treatment time is 40s to 90s.

[0272] By setting the heat treatment temperature and time within the aforementioned range, the second semi-finished product can expand under this temperature, achieving a pre-expansion effect. The heat treatment temperature can be 160℃, 165℃, 170℃, 175℃, 180℃, etc., or any range of any two of the above values, such as 160℃~175℃, 165℃~180℃, etc. The heat treatment time can be 40s, 50s, 60s, 70s, 80s, 90s, etc., or any range of any two of the above values, such as 40s~80s, 60s~90s, etc.

[0273] In one specific embodiment, the negative electrode active layer includes a negative electrode active material and a first binder, the first binder having a Young's modulus of 1.42 GPa-1.62 GPa. During the preparation of the negative electrode sheet, the second semi-finished product undergoes heat treatment for pre-rebound. The electrolyte has a conductivity of 7 mS / cm to 13 mS / cm and a water content of less than or equal to 200 ppm. The pre-rebound of the negative electrode sheet before casing is achieved through the first binder and heat treatment process, and the water content and composition of the first solvent in the electrolyte are limited. These factors work together to achieve low rebound of the negative electrode sheet and low gas production in the electrolyte during battery use, improving the expansion force of the cell and extending the cycle life of the battery.

[0274] In one specific embodiment, the positive electrode active layer includes a positive electrode active material, which includes lithium iron phosphate doped with metal elements; the negative electrode active layer includes a negative electrode active material, which includes artificial graphite, the surface of which is coated with amorphous carbon; the conductivity of the electrolyte is 7 mS / cm to 13 mS / cm. Through the interaction of the doping elements and their content in the lithium iron phosphate, the carbon coating amount of the artificial graphite, the conductivity of the electrolyte, and the composition of the first solvent, the lithium battery maintains a high energy density and a long cycle life.

[0275] To make the technical problems, technical solutions, and beneficial effects solved by the embodiments of this application clearer, the following will provide a more detailed description in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0276] The preparation process of Example 1 is as follows:

[0277] (1) Preparation of positive electrode sheet:

[0278] (a) Obtain the positive current collector aluminum foil with a thickness of 15 μm.

[0279] (b) Undoped lithium iron phosphate (LiFePO4), polyvinylidene fluoride (PVDF) binder, and conductive carbon black (SP) conductive agent were added to a 30L mixing tank in a mass percentage ratio of 96:2:2. The mixture was stirred in a dry environment to form a homogeneous slurry, thus preparing the positive electrode active slurry. The Dv50 of the positive electrode active material was 1.4 μm. The positive electrode active slurry was then coated onto both surfaces of the positive electrode current collector aluminum foil to form a positive electrode active layer with a thickness of 90 μm.

[0280] (c) After drying and rolling, a positive electrode sheet is obtained.

[0281] (2) Preparation of negative electrode sheet:

[0282] (a) Obtain a copper foil for the negative electrode current collector with a thickness of 6 μm.

[0283] (b) A mixture of amorphous carbon-coated artificial graphite (a negative electrode active material), polyacrylic acid (PAA) as the first binder, styrene-butadiene rubber (SBR) as the second binder, sodium carboxymethyl cellulose (CMC-Na) as the second binder, and conductive agent (SP) in a weight percentage ratio of 97:0.5:0.5:1:1 is added to deionized water and stirred to form a homogeneous slurry, thus preparing the negative electrode active slurry. The first binder has a Young's modulus of 1.5 GPa, and the artificial graphite has a graphitization degree of 96.5%. The negative electrode active slurry is then coated onto a copper foil used as a negative electrode current collector to form a negative electrode active layer with a thickness of 122 μm.

[0284] (c) After drying and cold pressing, the second semi-finished product is obtained.

[0285] (d) The second semi-finished product is treated at 170°C for 90s to obtain the negative electrode sheet.

[0286] (3) Preparation of electrolyte:

[0287] Ethylene carbonate (EC) and dimethyl carbonate (EMC) were mixed at a volume ratio of 3:7 to obtain an organic solvent. LiPF6 was dissolved in the organic solvent to prepare a LiPF6 solution with a concentration of 1.15 mol / L. Additives vinylene carbonate (VC) and fluoroethylene carbonate (FEC) were added to bring the mass fraction to 1.5 wt%.

[0288] (4) Separating membrane:

[0289] A 12μm polyethylene film was used as the separator.

[0290] (5) Assembly:

[0291] The prepared negative electrode and positive electrode are stacked in sequence, with the separator placed between the positive and negative electrode to provide isolation. The cells are then wound to obtain a bare cell, which is then inserted into the battery casing. After drying, electrolyte is injected, and the lithium-ion battery (secondary battery) is obtained through vacuum sealing, settling, formation, and shaping processes.

[0292] Through the above steps (1) to (5), a lithium-ion battery is obtained.

[0293] The preparation process of the lithium batteries in Examples 1-14 is similar to that in Example 1, with the specific differences in parameters shown in Table 1. In Examples 1-3, the positive electrode active material is lithium iron phosphate without metal doping. The preparation process of the lithium battery in Example 15 is similar to that in Example 1, except that in the negative electrode preparation process, only the first binder, polyacrylic acid (PAA), is used, and the second binder, styrene-butadiene rubber (SBR), is not used. Other specific differences in parameters are shown in Table 1. The preparation process of the lithium batteries in Examples 16 and Comparative Examples 1-2 is similar to that in Example 1, except that step (d) in the negative electrode preparation process of Example 1 is not performed; step (c) is performed to complete the negative electrode preparation. The positive electrode active material in Comparative Examples 1-2 is lithium iron phosphate without metal doping.

[0294] The relevant parameter testing process for the embodiments and comparative examples of this application is as follows:

[0295] 1. Dv50 test.

[0296] Particle size distribution can be conveniently determined using a laser particle size analyzer, referring to GB / T 19077-2016 Laser Diffraction Method. The testing instrument can be the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0297] 2. Graphitization degree test.

[0298] The degree of graphitization can be measured using an X-ray diffractometer (such as a Bruker D8 Discover). The measurement method can be found in JB / T 4220-2011. The interlayer spacing d002 of the graphite (002) crystal planes is measured, and then the degree of graphitization is calculated using the formula G=(0.344-d002) / (0.344-0.3354), where G represents the degree of graphitization.

[0299] 3. Fe content test.

[0300] Accurately weigh 0.1000 g (accurate to ±0.0001 g) of the positive electrode coating sample, add 10 mL of dilute hydrochloric acid (1:1), and when the sample no longer dissolves, add 2 mL of nitric acid and heat at low temperature until the reaction is complete. After cooling, dilute to a 100 mL volumetric flask (solution A). Accurately transfer 10.00 mL of the diluted solution to a 100 mL volumetric flask, add 5 mL of concentrated hydrochloric acid, and dilute to volume for analysis (solution B). Test solution B using ICP.

[0301] 4. Negative electrode rebound rate test.

[0302] The difference between the thickness L0 of the negative electrode sheet before cycling and the thickness L1 of the negative electrode sheet after 500 cycles is denoted as L1-L0. The rebound rate is equal to the ratio of (L1-L0) to the thickness L0 of the negative electrode sheet before cycling. The thickness of the negative electrode sheet is measured using a micrometer.

[0303] 5. Cohesive force test of negative electrode sheet.

[0304] The cohesive force of the negative electrode sheet can be tested using equipment and methods known in the art. Specifically, the negative electrode sheet is cut into 20*100mm pieces. 2 Prepare test specimens of the required dimensions; adhere the test specimen to the side to be tested with double-sided tape and press it firmly with a pressure roller to ensure complete adhesion between the double-sided tape and the negative electrode film layer in the specimen; attach the other side of the double-sided tape to the stainless steel surface, bend one end of the specimen in the opposite direction at a bending angle of 180°; use a high-speed rail tensile testing machine, fix one end of the stainless steel to the lower clamp of the tensile testing machine, fix the bent end of the specimen to the upper clamp, adjust the specimen angle to ensure that the upper and lower ends are in a vertical position, and then stretch the specimen at a speed of 50 mm / min until the specimen is completely peeled off from the substrate, record the displacement and force during the process, and generally consider the force when the forces are balanced to be the cohesive force of the negative electrode film layer.

[0305] 6. Capacity retention rate test.

[0306] Method for determining the capacity retention rate of secondary batteries at 25℃: At 25℃, charge the battery to 3.8V with a constant current of 0.33C, then charge it to 0.05C with a constant voltage of 3.8V until the current drops to 0.05C, and then discharge it to 2.0V with a constant current of 0.33C. The discharge specific capacity of the first cycle (Cd1) is obtained. Repeat this charge-discharge cycle for 500 cycles to obtain the discharge specific capacity of the lithium-ion battery after 500 cycles, which is recorded as (Cdn).

[0307] Capacity retention rate = discharge specific capacity after 500 cycles / discharge specific capacity in the first cycle.

[0308] By comparing Examples 1-16 with Comparative Examples 1-2, it was found that by using a first binder with a Young's modulus of 1.40 GPa-1.7 GPa on the negative electrode sheet, the expansion or contraction of the negative electrode active layer material during battery cycling can be limited to a certain extent. The cohesive force of the negative electrode sheet is relatively large, which maintains the structural stability of the negative electrode sheet, improves the capacity retention rate after 500 cycles, and improves the cycle life of the battery.

[0309] By comparing Examples 5 and 16, pre-rebound treatment of the negative electrode sheet can reduce the rebound rate of the negative electrode sheet. By comparing Examples 1 and 4, using lithium iron phosphate doped with metal elements as the positive electrode active material reduces the Fe element content on the negative electrode sheet after 500 cycles at 60°C. By comparing Examples 1-16 and Comparative Examples 1-2, by controlling the Young's modulus of the first binder of the negative electrode sheet to 1.40 GPa-1.7 GPa, the doping element of lithium iron phosphate to be at least one of Mg, Cu, Nb, and Ti, and the doping amount, and by pre-rebound treatment of the negative electrode sheet, the capacity retention rate after 500 cycles can be improved, thus increasing the cycle life of the battery.

[0310] The above description is merely an embodiment of this application and does not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A battery cell, wherein, It includes positive electrode, negative electrode, and electrolyte; The negative electrode sheet includes a negative current collector and a negative active layer disposed on at least one surface of the negative current collector; the negative active layer includes a negative active material and a first binder, wherein the Young's modulus of the first binder is 1.40 GPa-1.7 GPa.

2. The battery cell according to claim 1, wherein, Based on the mass of the negative electrode active layer, the mass content of the first binder is 0.2%-3%.

3. The battery cell according to claim 1 or 2, wherein, The first adhesive includes at least one of hydroxyl and carboxyl groups.

4. The battery cell according to claim 1 or 2, wherein, The first adhesive includes at least one of polyacrylic acid, polyamide-imide, polyethylene oxide, polytetrafluoroethylene, crosslinked polyacrylic acid-polybenzimidazole, polyvinylidene fluoride-polytetrafluoroethylene block copolymer, and carboxymethyl chitosan.

5. The battery cell according to any one of claims 1 to 4, wherein, The first adhesive includes at least one of polyacrylic acid, cross-linked polyacrylic acid-polybenzimidazole, polyethylene oxide, and carboxymethyl chitosan.

6. The battery cell according to any one of claims 1 to 5, wherein, The negative electrode active layer further includes a second binder, the Young's modulus of which is less than that of the first binder.

7. The battery cell according to claim 6, wherein, Based on the mass of the negative electrode active layer, the mass content of the second binder is 0.3%-2%.

8. The battery cell according to claim 6 or 7, wherein, The second adhesive includes at least one of styrene-butadiene rubber and sodium carboxymethyl cellulose.

9. The battery cell according to any one of claims 1 to 8, wherein, The negative electrode active material includes artificial graphite; based on the mass of the negative electrode active layer, the mass percentage of the artificial graphite is greater than or equal to 80% and less than or equal to 97.5%.

10. The battery cell according to any one of claims 1 to 9, wherein, The artificial graphite comprises bulk particles and a coating layer on the surface of the bulk particles, the coating layer comprising amorphous carbon.

11. The battery cell according to claim 10, wherein, Based on the total mass of artificial graphite, the mass percentage of amorphous carbon is greater than or equal to 0.5% and less than or equal to 10%.

12. The battery cell according to any one of claims 9 to 11, wherein, The degree of graphitization of the artificial graphite is greater than or equal to 90% and less than or equal to 97%.

13. The battery cell according to any one of claims 9 to 12, wherein, The disorder R value of the artificial graphite is greater than or equal to 0.04 and less than or equal to 0.

6.

14. The battery cell according to any one of claims 1 to 13, wherein, The negative electrode active material has a specific capacity of greater than or equal to 350 mAh / g and less than or equal to 360 mAh / g at 0.1C CC.

15. The battery cell according to any one of claims 1 to 14, wherein, The negative electrode active layer includes a first sub-active layer disposed on the surface of the negative electrode current collector and a second sub-active layer disposed on the side of the first sub-active layer away from the negative electrode current collector; The Dv50 of the negative electrode active material in the first sub-active layer is greater than the Dv50 of the negative electrode active material in the second sub-active layer.

16. The battery cell according to claim 15, wherein, The Dv50 of the negative electrode active material in the first sub-active layer is greater than or equal to 11 μm and less than or equal to 20 μm; the Dv50 of the negative electrode active material in the second sub-active layer is greater than or equal to 7 μm and less than or equal to 16 μm.

17. The battery cell according to claim 15 or 16, wherein, The Dv50 of the negative electrode active material in the first sub-active layer is greater than or equal to 12.5 μm and less than or equal to 18.5 μm; the Dv50 of the negative electrode active material in the second sub-active layer is greater than or equal to 8.5 μm and less than or equal to 15.5 μm.

18. The battery cell according to any one of claims 1 to 17, wherein, The thickness of the negative electrode active layer is 100μm-150μm.

19. The battery cell according to any one of claims 1 to 18, wherein, The positive electrode sheet includes a positive current collector and a positive active layer disposed on at least one surface of the positive current collector; the positive active layer includes a positive active material, the positive active material including a lithium phosphate material, the general chemical formula of the lithium phosphate material being LiFe. 1-x M x PO4, wherein M includes at least one of Mg, Ti, Cu, and Nb, and 0.05 ≤ x ≤ 0.

30.

20. The battery cell according to claim 19, wherein, 0.1≤x≤0.2。 21. The battery cell according to any one of claims 19 or 20, wherein, The Dv50 of the positive electrode active material is greater than or equal to 0.6 μm and less than or equal to 2.2 μm.

22. The battery cell according to any one of claims 19 to 21, wherein, The Dv50 of the positive electrode active material is greater than or equal to 1 μm and less than or equal to 1.6 μm.

23. The battery cell according to any one of claims 19 to 22, wherein, The positive electrode active material has a first delithiation capacity of ≥145 mAh / g at 0.1C.

24. The battery cell according to any one of claims 19 to 23, wherein, The positive electrode active material has a first delithiation capacity of less than or equal to 147 mAh / g at 0.1C.

25. The battery cell according to any one of claims 19 to 24, wherein, The coating weight of the positive electrode active layer is greater than or equal to 260 mg / 1540.25 mm. 2 And less than or equal to 330mg / 1540.25mm 2 .

26. The battery cell according to any one of claims 19 to 25, wherein, The compaction density of the positive electrode active layer is greater than or equal to 2.3 g / cc and less than or equal to 2.7 g / cc.

27. The battery cell according to any one of claims 19 to 26, wherein, The compaction density of the positive electrode active layer is greater than or equal to 2.4 g / cc and less than or equal to 2.6 g / cc.

28. The battery cell according to any one of claims 19 to 27, wherein, The thickness of the positive electrode active layer is 70μm-100μm.

29. The battery cell according to any one of claims 1 to 28, wherein, The conductivity of the electrolyte is 7 mS / cm to 13 mS / cm.

30. The battery cell according to any one of claims 1 to 29, wherein, The conductivity of the electrolyte is 7 mS / cm to 10 mS / cm.

31. The battery cell according to any one of claims 1 to 30, wherein, The water content of the electrolyte is less than or equal to 200 ppm.

32. The battery cell according to any one of claims 1 to 31, wherein, The electrolyte includes a first solvent, which includes at least one of vinyl acetate, methyl acetate, dimethyl carbonate, ethyl propionate, and propyl propionate.

33. The battery cell according to claim 32, wherein, The first solvent accounts for less than or equal to 20% of the mass of the electrolyte.

34. The battery cell according to any one of claims 1 to 33, wherein, The electrolyte includes additives, which include at least one of vinylene carbonate, 1,3-propenesulfonate lactone, fluoroethylene carbonate, methylbenzenesulfonyl isocyanate, and 1-(trimethylsilyl)-1H-benzotriazole.

35. The battery cell according to claim 34, wherein, The additive accounts for 0.05% to 2% of the mass of the electrolyte.

36. The battery cell according to claim 34 or 35, wherein, The additive accounts for 0.1% to 0.8% of the mass of the electrolyte.

37. The battery cell according to any one of claims 1 to 36, wherein, The electrolyte includes a lithium salt, the concentration of which is greater than or equal to 0.7 mol / L and less than or equal to 1.2 mol / L.

38. The battery cell according to any one of claims 1 to 37, wherein, The electrolyte includes a lithium salt, the concentration of which is greater than or equal to 0.8 mol / L and less than or equal to 1 mol / L.

39. A method for preparing a single battery cell, wherein, include: A battery cell assembly is formed by sequentially stacking negative electrode plates, separator membranes, and positive electrode plates; The battery cell assembly is placed in the housing; as well as Electrolyte is injected into the casing and sealed to form a battery cell; The negative electrode sheet includes a negative current collector and a negative active layer disposed on at least one surface of the negative current collector; the negative active layer includes a negative active material and a first binder, wherein the Young's modulus of the first binder is 1.40 GPa-1.7 GPa.

40. The method for preparing a battery cell according to claim 39, wherein, The method for preparing the negative electrode sheet includes: A negative electrode active layer is provided on at least one side of the negative electrode current collector to form a first semi-finished product; The first semi-finished product is dried and compacted to form the second semi-finished product; The second semi-finished product is subjected to heat treatment to obtain a negative electrode sheet, wherein the thickness of the negative electrode sheet is greater than the thickness of the second semi-finished product.

41. The method for preparing a battery cell according to claim 40, wherein, The difference between the thickness of the negative electrode sheet and the thickness of the second semi-finished product is 4% to 15% of the thickness of the second semi-finished product.

42. The method for preparing a battery cell according to claim 40 or 41, wherein, The difference between the thickness of the negative electrode sheet and the thickness of the second semi-finished product is 7% to 10% of the thickness of the second semi-finished product.

43. The method for preparing a battery cell according to any one of claims 40 to 42, wherein, The heat treatment temperature is 140℃~220℃; and / or the heat treatment time is 30s~120s.

44. The method for preparing a battery cell according to any one of claims 40 to 43, wherein, The heat treatment temperature is 160℃~180℃; and / or the heat treatment time is 40s~90s.

45. A lithium battery, wherein, This includes battery cells prepared by any one of claims 1 to 38 or any one of claims 39 to 44.

46. ​​An electrical appliance, wherein, This includes battery cells as described in any one of claims 1 to 38, battery cells prepared by the method described in any one of claims 39 to 44, or lithium batteries as described in claim 45.

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