Battery cell, battery device, and electric device

Abstract

A battery cell, a battery device, and an electric device. The battery cell comprises an electrode assembly and an electrolyte. The electrode assembly comprises a positive electrode sheet and a negative electrode sheet. The positive electrode sheet comprises a lithium-containing phosphate having an olivine structure. The negative electrode sheet comprises graphite particles. The electrolyte comprises a carboxylic ester solvent and a first additive. The thickness of a single-sided negative electrode film layer is 50 μm to 75 μm. The volume average particle size of the graphite particles is 8.5 μm to 13.5 μm. On the basis of the mass of the electrolyte, the mass content of the carboxylic ester solvent is 8% to 60%, the total mass content of the first additive is 3% to 10%, and the first additive comprises 1,3-propane sultone having a mass content greater than or equal to 0, an ethylene carbonate derivative having a mass content greater than or equal to 0, and vinylene carbonate having a mass content greater than or equal to 3%. The battery cell has improved fast charging performance and cycle performance at high energy density.

Description

Battery cells, battery packs and electrical devices Technical Field

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

[0002] Battery cells possess characteristics such as high capacity and long lifespan, making them widely used in electronic devices such as mobile phones, laptops, electric vehicles, electric cars, electric aircraft, electric ships, and power tools. With the development of lithium-ion battery applications, higher demands are being placed on the performance of battery cells, such as their fast-charging performance at high energy densities, cycle performance, and reliability. Summary of the Invention

[0003] This application provides a battery cell, a battery device, and an electrical device that can improve the fast charging performance, cycle performance, and reliability of the battery cell at high energy density.

[0004] In a first aspect, this application proposes a battery cell, which includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode and a negative electrode. The positive electrode includes a positive current collector and a positive electrode film disposed on at least one side of the positive current collector, the positive electrode film comprising a lithium phosphate with an olivine structure. The negative electrode includes a negative current collector and a negative electrode film disposed on at least one side of the negative current collector, the negative electrode film comprising graphite particles. The electrolyte includes a carboxylic acid ester solvent and a first additive, wherein the thickness of the negative electrode film on one side is... The graphite particles have a volume average diameter of 8.5 μm to 13.5 μm, ranging from 50 μm to 75 μm; the carboxylic acid ester solvent has a mass content of 8% to 60% based on the mass of the electrolyte; the first additive has a total mass content of 3% to 10% based on the mass of the electrolyte, and the first additive includes 1,3-propanesulfonic acid lactone (≥0% by mass), ethylene carbonate derivatives (≥0% by mass), and vinylene carbonate (≥3% by mass), wherein the ethylene carbonate derivatives include compounds represented by Formula A.

[0005] In Formula A, Q1, Q2, Q3 and Q4 each independently include any one of hydrogen atoms, halogen atoms, C1 to C5 alkyl groups, or C1 to C5 haloalkyl groups, and Q1, Q2, Q3 and Q4 are not all hydrogen atoms at the same time.

[0006] Therefore, in this embodiment, the thickness of the negative electrode film layer, within an appropriate range, enables the battery cell to have a relatively high energy density. The electrolyte includes an appropriate mass content of carboxylic acid ester solvent, which can reduce the viscosity of the electrolyte and increase the migration rate of lithium ions in the electrolyte. The relatively small volume average particle size of the graphite particles results in a shorter solid-phase migration path for lithium ions within the graphite particles, thereby increasing the migration rate of lithium ions in both the liquid and solid phases and improving the fast charging capability of the battery cell. The carboxylic acid ester solvent content is not too high, and the volume average particle size of the graphite particles is not too small, mitigating side reactions. On the other hand, the thickness of the negative electrode film layer is not too high, reducing the viscosity of the graphite particles. The amount of graphite particles coated helps mitigate side reactions. Furthermore, a first additive, including vinylene carbonate, is added to the electrolyte. Vinylene carbonate and carboxylic acid ester solvents have similar reaction potentials and compete for reaction. Vinylene carbonate can participate in the formation of a dense solid electrolyte interphase (SEI) film containing organic components on the negative electrode side, making it difficult for carboxylic acid ester solvents to penetrate the SEI film to the graphite particles. This mitigates the side reactions between carboxylic acid ester solvents and graphite particles, reducing gas production. Moreover, because the first additive is present in an appropriate amount, the film impedance formed on the negative electrode side will not be excessive, and it will not significantly degrade fast-charging performance. Therefore, the embodiments of this application can improve the fast-charging capability, cycle performance, and reliability of battery cells at high energy densities.

[0007] In some embodiments, the first additive has a mass content of 3.5% to 8%, which can further improve the fast charging capability and cycle performance of the battery cell at high energy density, as well as its reliability in use.

[0008] In some embodiments, the mass content of vinylene carbonate in the electrolyte is 3% to 8%. When the mass content of vinylene carbonate is within the above range, a dense SEI film can be formed on the negative electrode side, and the impedance of the SEI film is relatively low, which can reduce the side reactions on the negative electrode side and improve the cycle performance and fast charging capability of the battery cell at high energy density.

[0009] In some embodiments, the mass content of 1,3-propanesulfonate lactone in the electrolyte is 0 to 0.5%, optionally 0.05% to 0.5%. When the mass content of 1,3-propanesulfonate lactone is within the above range, the impedance of the formed SEI film will not be too high, which can reduce impedance while alleviating side reactions and improve the fast charging performance and high-temperature cycling performance of the battery cell at high energy density.

[0010] In some embodiments, the ethylene carbonate derivative is present in the electrolyte at a mass content of 0 to 3.5%, optionally 0.5% to 1.5%. The ethylene carbonate derivative preferentially forms a film, optimizes the composition of the SEI film, reduces the impedance of the SEI film, and effectively improves the fast charging performance and cycle performance of the battery cell at high energy density.

[0011] In some embodiments, at least one of Q1, Q2, Q3, and Q4 includes a halogen atom or a C1 to C5 haloalkyl group. When the ethylene carbonate derivative includes a fluorine atom, the ethylene carbonate derivative can form a film rich in F and Li on the negative electrode side, which, while protecting the negative electrode active material, results in a lower film impedance, thus more effectively improving the high-temperature cycling performance and fast-charging performance of the battery cell at high energy densities.

[0012] In some embodiments, the ethylene carbonate derivative includes at least one of the compounds shown in Formula A-1 to Formula A-3.

[0013] The aforementioned materials can further improve the high-temperature cycling performance and fast charging performance of individual battery cells under high energy density.

[0014] In some embodiments, the carboxylic acid ester solvent includes compounds represented by Formula I.

[0015] In formula I,

[0016] R1 includes a hydrogen atom, a C1 to C5 alkyl group, or a C1 to C5 haloalkyl group.

[0017] R2 includes C1 to C5 alkyl or C1 to C5 haloalkyl.

[0018] The aforementioned chain-like carboxylic acid ester solvents have low viscosity, which improves the fast charging capability of battery cells at high energy densities and reduces the risk of lithium plating during fast charging, thereby improving the reliability of battery cells.

[0019] In some embodiments, the carboxylic acid ester solvent includes one or more compounds of formula I-1 to formula I-12.

[0020] The aforementioned materials can further improve the fast charging performance of individual battery cells at high energy densities.

[0021] In some embodiments, the electrolyte further includes a carbonate solvent, wherein the carbonate solvent comprises 18% to 70% by mass. The aforementioned amount of carbonate solvent can further improve the conductivity of the electrolyte at room temperature, which is beneficial for lithium-ion migration and enhances the fast charging capability of the battery cell at high energy densities.

[0022] In some embodiments, the carbonate solvent includes cyclic carbonates, which include one or more of ethylene carbonate, propylene carbonate, and butene carbonate; the above materials can further improve the fast charging performance of battery cells at high energy densities.

[0023] In some embodiments, the carbonate solvent includes chain carbonates, such as one or more of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. These materials can further improve the fast-charging performance of individual battery cells at high energy densities.

[0024] In some embodiments, the electrolyte includes a sulfur-containing additive at a mass content of 0 to 2%. Optionally, the sulfur-containing additive has a mass content of 0.5% to 2%, and the sulfur-containing additive includes one or more of vinyl sulfate, vinyl disulfate, butene sulfite, vinyl sulfite, and methylene disulfonate. The sulfur-containing additive and the first additive work together to participate in film formation, which can optimize the film composition of the SEI film. The sulfur-containing additive can participate in the formation of an inorganic-rich SEI film, and the inorganic matter can improve the high-temperature stability and high-voltage stability of the SEI film, thereby improving the high-temperature cycle performance of the battery cell.

[0025] In some embodiments, the electrolyte includes a lithium salt additive at a mass content of 0 to 1%. Optionally, the lithium salt additive has a mass content of 0.2% to 1%, and the lithium salt additive includes one or more of lithium difluorophosphate, lithium difluorooxalate borate, lithium tetrafluoroborate, and lithium bis(oxalate borate). The salt additive and the first additive work together to participate in film formation, which can optimize the film composition of the SEI film. The lithium salt additive can participate in the formation of an inorganic-rich SEI film, and the inorganic matter can improve the high-temperature stability and high-voltage stability of the SEI film, thereby improving the high-temperature cycle performance of the battery cell.

[0026] In some embodiments, the thickness of the single-sided negative electrode film is 50 μm to 65 μm. When the thickness of the single-sided negative electrode film is within this range, the lithium ion transport path is shorter, which is beneficial to improving the fast charging performance of the battery cell, thereby improving the high-temperature cycle performance and fast charging performance of the battery cell at high energy density.

[0027] In some embodiments, the volume average particle size of the graphite particles is between 9.5 μm and 13 μm. The relatively small volume average particle size of the graphite particles results in a shorter solid-phase migration path for lithium ions, which can improve the fast charging capability of the battery cell.

[0028] In some embodiments, the graphite particles include graphite bulk particles and a negative electrode coating layer covering the surface of the graphite bulk particles. The graphite bulk particles include secondary particles, and the negative electrode coating layer includes carbon elements. The graphite bulk particles include secondary particles, resulting in more lithium-ion migration paths within the graphite bulk particles and shorter migration paths in the primary particles, which can improve the lithium-ion migration rate. The negative electrode coating layer has more end faces and defects, increasing the number of sites for lithium-ion insertion and extraction, thus improving the conductivity of the negative electrode coating layer. This reduces the internal resistance of the negative electrode sheet, lowers the heat generation of the battery cell, and improves the fast charging performance and high-temperature cycling performance of the battery cell at high energy densities.

[0029] In some embodiments, the graphite bulk particles include at least one of artificial graphite and natural graphite.

[0030] In some embodiments, the carbon content of the negative electrode coating is 2% to 5% based on the total mass of graphite particles. When the carbon content of the electrode coating is within the above range, the internal resistance of the negative electrode sheet can be further reduced, the heat generation of the battery cell can be reduced, and the high-temperature cycle performance of the battery cell under high energy density can be improved.

[0031] In some embodiments, the negative electrode film layer further includes a silicon-based material, wherein the silicon content of the silicon element in the negative electrode film layer is 0.3% to 5% by mass. When the silicon content in the silicon-based material is within the above range, it can increase the capacity of the negative electrode active material, thereby improving the energy density of the battery cell.

[0032] In some embodiments, the powder compaction density of the negative electrode active material at 20000 N is 1.4 g / cm³. 3 Up to 1.8 g / cm 3 When the powder compaction density of the negative electrode active material at 20000N is within the above range, it can improve the energy density of the battery cell. Furthermore, since the negative electrode active material in the negative electrode film layer can be stacked more tightly, the contact resistance between particles is smaller, which can further reduce the resistance of the electrode sheet, thereby reducing heat generation and improving the high-temperature cycle performance of the battery cell at high energy density.

[0033] In some embodiments, the compaction density of the negative electrode film layer in a single battery cell at 0% charge is 1.30 g / cm³. 3 Up to 1.55 g / cm 3 When the compaction density of the negative electrode film is within the above range, it is beneficial to improve the energy density of the battery cell. Furthermore, since the negative electrode active material in the negative electrode film is densely packed, the contact resistance between particles is small, which can further reduce the resistance of the electrode, thereby reducing heat generation. This can reduce the amount of gas generated by the decomposition of carboxylic acid ester solvents due to heat accumulation and improve the high-temperature cycle performance of the battery cell.

[0034] In some embodiments, the single-sided coating weight of the negative electrode film is 90 mg / 1540.25 mm. 2 Up to 140mg / 1540.25mm 2 When the single-sided coating weight of the negative electrode film is within the above range, the heat generation per unit area of ​​the negative electrode sheet will not be too large, and it can also improve the high-temperature cycle performance of the battery cell under high energy density.

[0035] In some embodiments, the negative electrode further includes a negative electrode conductive layer located between the negative electrode current collector and the negative electrode film layer. The negative electrode conductive layer includes a negative electrode conductive agent, which may be one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The negative electrode conductive layer can further improve the conductivity of the negative electrode and reduce the heat generation of the negative electrode, thereby reducing the heat generation of the battery cell and improving the fast charging performance and high-temperature cycling performance of the battery cell.

[0036] In some embodiments, the thickness of the negative electrode conductive layer is from 0.5 μm to 2 μm. When the thickness of the negative electrode conductive layer is within the above range, the conductivity of the negative electrode sheet can be further improved, the heat generation of the negative electrode sheet can be reduced, thereby reducing the heat generation of the battery cell, and at the same time, the energy density of the battery cell can be improved.

[0037] In some embodiments, the thickness of the positive electrode film on one side is 50 μm to 65 μm. When the thickness of the positive electrode film on one side is within the above range, the thickness of the positive electrode film is relatively thin, resulting in a shorter lithium ion transport path, which is beneficial to improving the fast charging performance of the battery cell.

[0038] In some embodiments, the positive and negative electrode sheets are stacked along the thickness direction of the battery cell, and the dimension of the positive electrode film layer along the length direction of the battery cell is 200 mm to 650 mm. When the dimension of the positive electrode film layer along the length direction of the battery cell is within the above range, the coating amount of the positive electrode film layer is relatively large, which is beneficial to improving the energy density of the battery cell; moreover, the electron transport path is not too long, which is beneficial to improving the fast charging capability of the battery cell.

[0039] In some embodiments, the olivine-structured lithium phosphate includes phosphate particles and a positive electrode coating layer. The positive electrode coating layer is located on at least a portion of the surface of the phosphate particles and contains carbon elements. By coating the phosphate particles with the positive electrode coating layer, the conductivity of the olivine-structured lithium phosphate can be improved, which is beneficial to the migration rate of lithium ions, enhances the fast charging capability of the battery, reduces the heat generation of the battery cell, and improves the high-temperature cycle performance of the battery cell.

[0040] In some embodiments, the carbon content of the lithium phosphate based on the olivine structure is 0.8% to 2.3% by mass. When the carbon content is within the above range, the conductivity of the lithium phosphate with the olivine structure can be significantly improved, which is beneficial to improving the ionic and electronic conductivity of the lithium phosphate with the olivine structure, and can improve the rapid charging capability of the battery cell at high energy density.

[0041] In some embodiments, the positive electrode coating layer further includes one or more elements of Fe, Ti, Zr, Hf, Ge, and Sn. Materials containing these elements can improve the ionic conductivity of the positive electrode active material, enhance the fast-charging capability of the battery cell, and further increase the specific capacity and energy density of the corresponding battery cell.

[0042] In some embodiments, the phosphate particles include one or more of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium nickel phosphate, and lithium cobalt phosphate. These materials exhibit excellent cycle stability and can improve the cycle performance of individual battery cells.

[0043] In some embodiments, lithium phosphates include those with the general formula Li x1 A y1 Me a1 M b1 P 1-c1 X c1 Y z1 The compound, wherein 0.5≤x1≤1.3, 0≤y1≤1.3, 0.5≤x1+y1≤1.3, 0.9≤a1≤1.5, 0≤b1≤0.5, 0.9≤a1+b1≤1.5, 0≤c1≤0.5, 3≤z1≤5, A includes at least one of Na, K, and Mg; Me includes at least one of Mn, Fe, Co, and Ni; M includes at least one of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X includes at least one of Cl, C, and N; and Y includes at least one of O and F. The above materials exhibit excellent cycle stability and can improve the cycle performance of battery cells.

[0044] In some embodiments, the powder compaction density of the positive electrode active material at 30000 N is 2.43 g / cm³. 3 Up to 2.85 g / cm 3When the powder compaction density of the positive electrode active material at 30000N is within the above range, it can improve the energy density of the battery cell. Furthermore, since the positive electrode active material in the positive electrode film layer can be stacked more tightly, the contact resistance between particles is smaller, which can further reduce the resistance of the electrode sheet, thereby reducing heat generation and improving the high-temperature cycle performance and fast charging performance of the battery cell at high energy density.

[0045] In some embodiments, the compaction density of the positive electrode film layer is 2.46 g / cm³ when the battery cell is at 0% SOC. 3 Up to 2.80 g / cm 3 When the compaction density of the positive electrode film is within the above range, it is beneficial to improve the energy density of the battery cell. Furthermore, since the positive electrode active material in the positive electrode film is packed more tightly, the contact resistance between particles is smaller, which can further reduce the resistance of the electrode sheet, thereby reducing heat generation under fast charging and improving the high-temperature cycle performance and fast charging performance of the battery cell under high energy density.

[0046] In some embodiments, the single-sided coating weight of the positive electrode film is 200 mg / 1540.25 mm. 2 Up to 350mg / 1540.25mm 2 When the single-sided coating weight of the positive electrode film is within the above range, the heat generation per unit area of ​​the positive electrode sheet will not be too large, thus improving the high-temperature cycle performance and fast charging performance of the battery cell under high energy density.

[0047] In some embodiments, the positive electrode further includes a positive conductive layer located between the positive current collector and the positive electrode film layer. The positive conductive layer includes a positive conductive agent, which may be one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The positive conductive layer can further improve the conductivity of the positive electrode and reduce the heat generation of the positive electrode, thereby reducing the heat generation of the individual battery cells.

[0048] In some embodiments, the thickness of the positive electrode conductive layer is from 0.5 μm to 2 μm. When the thickness of the positive electrode conductive layer is within the above range, the conductivity of the positive electrode sheet can be further improved, the heat generation of the positive electrode sheet can be reduced, thereby reducing the heat generation of the battery cell and improving the high-temperature cycling performance of the battery cell at high energy density.

[0049] In some embodiments, the electrode assembly further includes a separator located between the positive and negative electrode plates. The separator includes a base film with a thickness of 4 μm to 12 μm and / or a porosity of 20% to 70%. When the base film meets the above range, it can enhance the migration ability of lithium ions in the separator, further reduce the internal resistance of the battery cell, thereby reducing heat generation and improving the fast charging performance and high-temperature cycling performance of the battery cell at high energy density.

[0050] In some embodiments, the separator further includes a functional layer disposed on at least one side of the base membrane. The functional layer includes a first functional layer and a second functional layer. The first functional layer is located on one side of the base membrane and includes first inorganic particles. The second functional layer is located on the other side of the base membrane and includes composite particles. The composite particles include second inorganic particles and a plurality of non-fluoropolymer particles. The second inorganic particles are attached to the surface of the non-fluoropolymer particles and / or dispersed within the non-fluoropolymer particles. The first and second functional layers have good heat resistance, which can improve the heat resistance of the separator.

[0051] In some embodiments, the non-fluoropolymer particles include acrylate copolymers. Acrylate copolymers have excellent adhesion properties and high adhesion stability to the base film.

[0052] In some embodiments, the first inorganic particles include one or more of silicon oxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide; the first inorganic particles have good heat resistance, which is beneficial to improving the heat resistance and compressive modulus of the composite particles.

[0053] In some embodiments, the average particle size of the second inorganic particles is between 5 nm and 100 nm. When the average particle size of the first inorganic particles is within the above range, it is beneficial to improve the heat resistance and compressive modulus of the composite particles.

[0054] In some embodiments, the second inorganic particles include one or more of silicon oxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide. The second inorganic particles have good heat resistance, which is beneficial to improving the heat resistance and compressive modulus of the composite particles.

[0055] In some embodiments, the average particle size of the second inorganic particles is between 5 nm and 100 nm. When the average particle size of the second inorganic particles is within the above range, it is beneficial to improve the heat resistance and compressive modulus of the composite particles.

[0056] In some embodiments, the positive electrode and the negative electrode are stacked along the thickness direction of the battery cell; the electrode assembly also includes a positive electrode tab and a negative electrode tab, the positive electrode tab being connected to at least one side of the positive current collector along the length direction of the battery cell, and the negative electrode tab being connected to at least one side of the negative current collector along the length direction of the battery cell; along the length direction of the battery cell, the size of the negative electrode film is larger than the size of the positive electrode film, and the size difference between the negative electrode film and the positive electrode film is OH1; along the width direction of the battery cell, the size of the negative electrode film is larger than the size of the positive electrode film, and the size difference between the negative electrode film and the positive electrode film is OH2, wherein OH1 is greater than OH2.

[0057] Therefore, in this embodiment, OH1 is set to be greater than OH2, which makes the lithium ion receiving capacity of the negative electrode film layer in the length direction stronger. In particular, it can improve the lithium ion receiving capacity of the negative electrode film layer near the negative electrode tab, reduce the risk of lithium plating, and improve the reliability of the battery cell.

[0058] In some embodiments, OH1 is 1.0 mm to 4.0 mm; and / or OH2 is 1.0 mm to 3.0 mm. When a battery cell meets the above conditions, the risk of lithium plating can be reduced and the reliability of the battery cell can be improved.

[0059] In some embodiments, the battery cell further includes at least one positive terminal, and the current-passing area of ​​all positive terminals on the same side of the positive current collector is 150 mm². 2 Up to 1000mm 2 When the current-carrying area of ​​the positive terminal meets the above range, the current-carrying capacity is strong, which can reduce internal resistance and heat generation, and is conducive to improving the fast charging performance and high-temperature cycling performance of the battery cell at high energy density.

[0060] In some embodiments, the battery cell further includes at least one negative terminal, and the current-passing area of ​​all negative terminals on the same side of the negative current collector is 150 mm². 2 Up to 1000mm 2 When the current-carrying area of ​​the negative terminal meets the above range, the current-carrying capacity is stronger, which can reduce internal resistance and heat generation, and is beneficial to improving the fast charging performance and high-temperature cycling performance of the battery cell at high energy density.

[0061] In some embodiments, the battery cell includes a housing that contains electrode components and electrolyte, and the housing thickness is 0.1 mm to 0.5 mm. A housing thickness within this range results in higher mechanical strength, improving the reliability and cycle performance of the battery cell. Furthermore, the housing occupies less space, allowing for more internal space, which is beneficial for increasing the energy density of the battery cell.

[0062] Secondly, this application proposes a battery device comprising a plurality of battery cells according to any embodiment of the first aspect of this application.

[0063] In some implementations, the charging time for the battery device from 10% to 80% state of charge is 5 to 15 minutes. A faster charging speed improves the device's fast-charging capability.

[0064] Thirdly, this application proposes an electrical device, which includes the battery device according to any embodiment of the second aspect of this application. Attached Figure Description

[0065] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0066] Figure 1 is a schematic diagram of the structure of a battery cell provided in some embodiments of this application.

[0067] Figure 2 is an exploded schematic diagram of a battery cell provided in some embodiments of this application.

[0068] Figure 3 is a schematic diagram of the electrode assembly of a battery cell provided in some embodiments of this application.

[0069] Figure 4 is a schematic diagram of the structure of the positive electrode sheet of a battery cell provided in some embodiments of this application.

[0070] Figure 5 is a schematic diagram of the structure of the positive electrode sheet of a battery cell provided in some other embodiments of this application.

[0071] Figure 6 is a schematic diagram of the structure of the negative electrode sheet of a battery cell provided in some embodiments of this application.

[0072] Figure 7 is a schematic diagram of the structure of the negative electrode sheet of a battery cell provided in some other embodiments of this application.

[0073] Figure 8 is a top view of the electrode assembly of a battery cell provided in some embodiments of this application.

[0074] Figure 9 is a schematic diagram of the structure of a battery module provided in some embodiments of this application.

[0075] Figure 10 is a schematic diagram of the structure of a battery pack provided in some embodiments of this application.

[0076] Figure 11 is a schematic diagram of the structure of an electrical device provided in some embodiments of this application.

[0077] The accompanying drawings may not be drawn to scale.

[0078] The reference numerals in the attached drawings are explained as follows: 1. Electrical device; 2. Battery pack; 3. Controller; 4. Motor; 5. Housing; 5a. First housing section; 5b. Second housing section; 5c. Receiving space; 6. Battery module; 7. Battery cell; 10. Electrode assembly; 11. Positive electrode plate; 111. Positive electrode tab; 112. Positive current collector; 113. Positive electrode film; 12. Negative electrode plate; 121. Negative electrode tab; 122. Negative current collector; 123. Negative electrode film; 13. Separator; 14. Main body; 20. Outer shell; 21. Housing; 22. End cap; 31. Positive terminal; 32. Negative terminal. Detailed Implementation

[0079] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the battery cell, battery device, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0080] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a specific parameter, it is also expected that ranges of 60 to 110 and 80 to 120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise stated, the numerical range "a to b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0 to 5" means that all real numbers between "0 and 5" have been listed in this article; "0 to 5" is just a shortened representation of these numerical combinations. In addition, when a parameter is stated as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0081] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0082] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0083] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0084] A battery cell includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode and a negative electrode. The negative electrode includes a negative electrode active material. At the negative electrode interface, the negative electrode active material and the electrolyte may undergo side reactions, which deteriorate the cycle. As the charging rate of the battery cell increases, the side reactions at the negative electrode interface are further aggravated, which further deteriorates the cycle and is not conducive to fast charging.

[0085] In view of the above problems, the embodiments of this application rationally design the system of the battery cell, which can take into account both the improvement of the cycle performance and fast charging capability of the high energy density battery cell; specifically, the thickness of the negative electrode film layer within an appropriate range can make the energy density of the battery cell relatively high, the positive electrode active material includes lithium phosphate with olivine structure, and the negative electrode active material includes graphite particles. The above material system has excellent cycle stability.

[0086] During charging, active ions, such as lithium ions, migrate from the positive electrode to the negative electrode via the electrolyte. The electrolyte contains an appropriate amount of carboxylic acid ester solvent, which reduces the viscosity of the electrolyte and increases the migration rate of lithium ions in the electrolyte. The relatively small volume average particle size of graphite particles results in a shorter solid-phase migration path for lithium ions, which can improve the migration rate of lithium ions in both the liquid and solid phases, thereby improving the fast charging capability of the battery cell. Due to the low viscosity and better fluidity of the electrolyte, it is more conducive to the rapid wetting of the electrode. Under fast charging conditions, local lithium deposition is less likely to occur on the surface of the negative electrode, which can improve the reliability of the battery cell.

[0087] However, due to the more severe side reactions between carboxylic acid ester solvents and graphite particles under fast charging, gas production is aggravated. The embodiments of this application limit the amount of carboxylic acid ester solvent to a certain level and the volume average particle size of graphite particles to a certain level to alleviate the side reactions. On the other hand, the thickness of the negative electrode film layer is not too high to reduce the amount of graphite particles coated and alleviate the side reactions. Furthermore, a first additive is added to the electrolyte. The first additive includes vinylene carbonate. The reaction potential of vinylene carbonate and carboxylic acid ester solvent are close, and there is a competitive reaction between vinylene carbonate and carboxylic acid ester solvent. Vinylene carbonate can participate in the formation of a dense solid electrolyte interphase (SEI) film containing organic components on the negative electrode side, making it difficult for carboxylic acid ester solvent to penetrate the SEI film to the graphite particles. This alleviates the side reactions between carboxylic acid ester solvent and graphite particles and reduces gas production. Moreover, since the first additive is within an appropriate content, the film impedance formed on the negative electrode side will not be too high and will not significantly degrade the fast charging performance.

[0088] Therefore, the embodiments of this application can improve the fast charging capability, cycle performance, and reliability of battery cells at high energy density.

[0089] battery cell

[0090] In one aspect, this application proposes a single battery cell.

[0091] A single battery cell includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode and a negative electrode. The positive electrode includes a positive current collector and a positive electrode film disposed on at least one side of the positive current collector. The positive electrode film includes a positive active material, which includes a lithium phosphate with an olivine structure. The negative electrode includes a negative current collector and a negative electrode film disposed on at least one side of the negative current collector. The negative electrode film includes a negative active material, which includes graphite particles. The electrolyte includes an organic solvent and a first additive.

[0092] The thickness of the single-sided negative electrode film is 50 μm to 75 μm, and the volume average particle size of the graphite particles is 8.5 μm to 13.5 μm.

[0093] Organic solvents include carboxylic acid ester additives, with the carboxylic acid ester solvents comprising 8% to 60% of the electrolyte by mass.

[0094] Based on the mass of the electrolyte, the total mass content of the first additive is 3% to 10%. The first additive includes 1,3-propanesulfonic acid lactone with a mass content of ≥0, ethylene carbonate derivative with a mass content of ≥0, and vinylene carbonate with a mass content of ≥3%. The ethylene carbonate derivative includes compounds represented by Formula A.

[0095] In Formula A, Q1, Q2, Q3 and Q4 each independently include any one of hydrogen atoms, halogen atoms, C1 to C5 alkyl groups, or C1 to C5 haloalkyl groups, and Q1, Q2, Q3 and Q4 are not all hydrogen atoms at the same time.

[0096] The thickness of the single-sided negative electrode film is greater than or equal to 50 μm, which can make the energy density of the battery cell relatively high; the positive electrode active material includes lithium phosphate with olivine structure, and the negative electrode active material includes graphite particles. The above material system has excellent cycle stability.

[0097] During charging, active ions, such as lithium ions, migrate from the positive electrode to the negative electrode via the electrolyte. The electrolyte contains carboxylic acid ester solvents with a mass content of ≥8%, which reduces the viscosity of the electrolyte and increases the migration rate of lithium ions in the electrolyte. The relatively small volume average particle size of graphite particles, for example, ≥13.5μm, results in a shorter solid-phase migration path for lithium ions in the graphite particles, which can improve the migration rate of lithium ions in both the liquid and solid phases, thereby improving the fast charging capability of the battery cell. Due to the low viscosity and better fluidity of the electrolyte, it is more conducive to the rapid wetting of the electrode. Under fast charging conditions, local lithium deposition is less likely to occur on the surface of the negative electrode, which can improve the reliability of the battery cell.

[0098] However, under fast charging, the side reactions between carboxylic acid ester solvents and graphite particles are more severe, leading to increased gas production. The embodiments of this application, on the one hand, limit the carboxylic acid ester solvent content to less than or equal to 60%, and the volume average particle size of the graphite particles to greater than or equal to 8.5 μm, ensuring that the active area of ​​the graphite particles is not excessively large, thus mitigating the side reactions. On the other hand, the thickness of the negative electrode film is reduced, making the thickness of the negative electrode film on one side less than or equal to 75 μm, reducing the amount of graphite particles coated and decreasing the total amount participating in the reaction, thereby mitigating the side reactions. Furthermore, a first additive, including vinylene carbonate, is added to the electrolyte. Vinylene carbonate has a similar reaction potential to the carboxylic acid ester solvent and competes with it for reaction. Vinylene carbonate can participate in the formation of a dense SEI film containing organic components on the negative electrode side, making it difficult for the carboxylic acid ester solvent to penetrate the SEI film to the graphite particles, thereby mitigating the side reactions between the carboxylic acid ester solvent and graphite particles, reducing gas production, and improving high-temperature cycling performance. Moreover, since the first additive is within an appropriate content, the film impedance formed on the negative electrode side will not be excessive, and it will not significantly degrade the fast charging performance.

[0099] Therefore, the embodiments of this application can improve the fast charging capability, cycle performance, and reliability of battery cells at high energy density.

[0100] Electrolyte

[0101] A battery cell includes an electrolyte. During the charging and discharging process of a battery cell, active ions, such as lithium ions, are inserted and extracted back and forth between the positive and negative electrode plates. The electrolyte plays a role in conducting these active ions between the positive and negative electrode plates.

[0102] Electrolytes consist of organic solvents and electrolyte salts.

[0103] The organic solvent includes carboxylic acid ester solvents, which constitute 8% to 60% of the electrolyte by mass. For example, the mass content of the carboxylic acid ester solvent is 8%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, or any combination of two of these values. When the mass content of the carboxylic acid ester solvent is greater than or equal to 8%, the viscosity of the electrolyte system is relatively low, which is beneficial for lithium-ion migration; when the mass content of the carboxylic acid ester solvent is less than or equal to 60%, the side reactions between the carboxylic acid ester solvent and the negative electrode active material are relatively few, which is beneficial for improving cycle performance.

[0104] In some embodiments, the carboxylic acid ester solvent may include at least one of linear carboxylic acid ester solvents and cyclic carboxylic acid ester solvents, preferably linear carboxylic acid ester solvents. Linear carboxylic acid ester solvents have lower viscosity, which can further improve the migration rate of lithium ions and enhance the fast charging capability of the battery cell.

[0105] Because chain carboxylic acid ester solvents have lower viscosity and better fluidity, they are more conducive to rapid wetting of the electrode sheets. Under fast charging conditions, local lithium plating is less likely to occur on the surface of the negative electrode sheet, thus improving the reliability of the battery cell.

[0106] For example, carboxylic acid ester solvents include compounds represented by Formula I.

[0107] In formula I,

[0108] R1 includes a hydrogen atom, a C1 to C5 alkyl group, or a C1 to C5 haloalkyl group.

[0109] R2 includes C1 to C5 alkyl or C1 to C5 haloalkyl.

[0110] The aforementioned chain-like carboxylic acid ester solvents have low viscosity, which improves the fast charging capability of battery cells at high energy densities and reduces the risk of lithium plating during fast charging, thereby improving the reliability of battery cells.

[0111] Optionally, R1 includes a hydrogen atom, a C1 to C3 alkyl group, or a C1 to C3 haloalkyl group. More optionally, R1 includes a hydrogen atom, a C1 to C2 alkyl group, or a C1 to C2 haloalkyl group.

[0112] Optionally, R2 comprises a C1 to C3 alkyl group or a C1 to C3 haloalkyl group. More optionally, R2 comprises a C1 to C2 alkyl group or a C1 to C2 haloalkyl group.

[0113] In the above embodiments, the halogenated alkyl group includes one or more of fluoroalkyl, chloroalkyl, bromoalkyl and iodoalkyl groups, and optionally, the halogenated alkyl group includes fluoroalkyl.

[0114] For example, carboxylic acid ester solvents include one or more compounds of formula I-1 to formula I-12.

[0115] The aforementioned materials can further improve the fast charging performance of individual battery cells at high energy densities.

[0116] In some embodiments, the organic solvent further includes carbonate solvents, wherein the carbonate solvent comprises 18% to 70% by mass in the electrolyte. Exemplarily, the carbonate solvent comprises 18%, 20%, 25%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 40%, 45%, 48%, 50%, 55%, 60%, 65%, 70% by mass, or any combination of two of the above values. The carbonate solvent at the aforementioned mass contents can further improve the conductivity of the electrolyte at room temperature, which is beneficial for lithium-ion migration and enhances the fast charging capability of the battery cell at high energy density.

[0117] Optionally, the carbonate solvent includes at least one of cyclic carbonates and chain carbonates.

[0118] For example, cyclic carbonates include one or more of ethylene carbonate, propylene carbonate, and butene carbonate. These materials can further improve the fast-charging performance of individual battery cells at high energy densities.

[0119] For example, the chain carbonate includes one or more of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. The above materials can further improve the fast-charging performance of battery cells at high energy densities.

[0120] In the embodiments of this application, the electrolyte further includes additives, including a first additive, which includes 1,3-propanesulfonate lactone with a mass content ≥0, ethylene carbonate derivative with a mass content ≥0, and vinylene carbonate with a mass content ≥3.

[0121] In the embodiments of this application, the total mass content of the first additive is 3% to 10%, for example, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, or any range of two of the above values.

[0122] When the mass content of the first additive is less than 3%, the film formed on the negative electrode side is relatively thin, which is not conducive to the protection of the negative electrode active material. As the mass content of the first additive increases, the film formation effect on the negative electrode side is better, which can play a better protective role for the negative electrode active material, reduce the risk of carboxylic acid ester solvents penetrating the SEI film and entering the negative electrode film layer, reduce side reactions on the negative electrode side, reduce gas production, and improve high-temperature cycle performance. However, as the mass content of the first additive further increases, the impedance of the SEI film formed on the negative electrode side is high, which is not conducive to fast charging. Therefore, the mass content of the first additive in the embodiments of this application is controlled at 3% to 10%, which can balance the improvement of the cycle performance and fast charging performance of the battery cell at high energy density. Optionally, the mass content of the first additive is 3.5% to 8%, which can further improve the cycle performance and fast charging performance of the battery cell at high energy density. Optionally, the mass content of the first additive in the freshly prepared electrolyte is 3.5% to 8%. The freshly prepared electrolyte can be understood as the electrolyte that has not yet participated in the formation process.

[0123] The first additive includes vinylene carbonate with a mass content of ≥3%, in other words, vinylene carbonate is an essential component of the electrolyte.

[0124] When the mass content of 1,3-propanesulfonic acid lactone is 0 and the mass content of ethylene carbonate derivative is 0, the first additive may consist only of vinylene carbonate, and the mass content of vinylene carbonate may be 3% to 10%.

[0125] Specifically, taking the case where the mass content of ethylene carbonate derivative is 0 as an example,

[0126] It can be that the freshly prepared electrolyte does not contain ethylene carbonate derivatives.

[0127] Alternatively, the electrolyte obtained after disassembling the battery cell may not contain ethylene carbonate derivatives. This could be because the freshly prepared electrolyte did not contain ethylene carbonate derivatives, or because a small amount of ethylene carbonate derivatives were added but participated in the SEI film formation reaction during the battery cell formation process, resulting in a ethylene carbonate derivative content of 0 during the detection process. Optionally, the freshly prepared electrolyte may include ethylene carbonate derivatives.

[0128] Furthermore, regarding the addition of certain substances, such as additives, to the electrolyte, the content of additives in the battery cell electrolyte is related to formation, different battery life cycles, or different battery storage states, due to the additives' role in film formation on the surface of active materials. Therefore, the additive content in freshly prepared electrolyte may differ from that in electrolyte obtained from reverse-engineered battery cells. However, those skilled in the art can determine the approximate range of the relevant substance content in the corresponding fresh electrolyte based on the battery cell's performance level (e.g., cycle count) and residual content. Similarly, those skilled in the art can also determine the approximate range of the content in non-freshly prepared (i.e., reverse-engineered) electrolytes based on the additive content in freshly prepared electrolytes, considering the battery cell's performance requirements and storage environment.

[0129] Therefore, the additive content mentioned in the technical solution of this application can be the content of additives actively added to fresh electrolyte, or the content of residual additives detected by reverse detection based on the actual battery state.

[0130] In some embodiments, the mass content of vinylene carbonate in the electrolyte is 3% to 8%, for example, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, or any combination of two of the above values. When the mass content of vinylene carbonate is within the above range, a dense SEI film containing organic components can be formed on the negative electrode side, and the SEI film has relatively low impedance, which can reduce side reactions on the negative electrode side and improve the cycle performance and fast charging capability of the battery cell at high energy density. Optionally, the mass content of vinylene carbonate in the electrolyte is 3% to 6%.

[0131] The first additive may include 1,3-propanesulfonate lactone with a mass content greater than 0, or the first additive may include a vinyl carbonate derivative with a mass content greater than 0, or the first additive may include 1,3-propanesulfonate lactone and a vinyl carbonate derivative.

[0132] 1,3-propanesulfonic acid lactone, ethylene carbonate derivatives and vinylene carbonate combine to form a dense film with relatively low impedance, reducing gas production and improving the cycle performance and fast charging performance of individual cells at high energy densities.

[0133] In some embodiments, the mass content of 1,3-propanesulfonate lactone in the electrolyte is 0 to 0.5%, for example, 0, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, or any combination of two of the above values. Optionally, the mass content of 1,3-propanesulfonate lactone in the electrolyte is 0.05% to 0.5%.

[0134] When the mass content of 1,3-propanesulfonate is 0, it means that 1,3-propanesulfonate may not be added to the freshly prepared electrolyte, or that the electrolyte obtained after disassembling a battery cell does not contain 1,3-propanesulfonate. Generally speaking, because 1,3-propanesulfonate is consumed in small amounts during the film-forming process, the mass content of 1,3-propanesulfonate in the freshly prepared electrolyte is slightly higher than the mass content in the electrolyte after disassembly.

[0135] Both 1,3-propanesulfonic acid lactone and vinylene carbonate can form a dense SEI film on the negative electrode side, which can effectively mitigate the risk of carboxylic acid ester solvents penetrating the SEI film and reacting with the negative electrode active material.

[0136] When the mass content of 1,3-propanesulfonic acid lactone is greater than 0 and less than or equal to 0.5%, the impedance of the formed SEI film will not be too high. It can reduce the impedance while alleviating side reactions and improve the fast charging performance and high-temperature cycling performance of the battery cell at high energy density.

[0137] For example, the mass content of 1,3-propanesulfonate lactone in the electrolyte is 0.05% to 0.5%; and the mass content of vinylene carbonate in the electrolyte is 3% to 6%.

[0138] In some embodiments, the ethylene carbonate derivative is present in the electrolyte at a mass content of 0 to 3.5%, for example, 0, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, or any combination of two of the above values. Optionally, the ethylene carbonate derivative is present in the electrolyte at a mass content of 0.5% to 1.5%.

[0139] Optionally, the freshly prepared electrolyte includes ethylene carbonate derivatives, and the mass content of ethylene carbonate derivatives in the freshly prepared electrolyte is greater than 0. Ethylene carbonate derivatives preferentially form films. After adding a certain amount of ethylene carbonate derivatives to the freshly prepared electrolyte, due to the large consumption of ethylene carbonate derivatives during the film-forming stage, the ethylene carbonate derivatives may not be detectable in the battery cells obtained after disassembly.

[0140] Ethylene carbonate continuously participates in the formation of the SEI film during the cycling process of battery cells, mitigating the risk of carboxylic acid ester solvents penetrating the SEI film. However, the organic component content of this SEI film is relatively high, resulting in relatively high impedance of the SEI film. Ethylene carbonate derivatives can preferentially form films, optimize the composition of the SEI film, reduce the impedance of the SEI film, and effectively improve the fast charging performance and cycle performance of battery cells at high energy densities.

[0141] For example, the mass content of vinylene carbonate in the electrolyte is 3% to 6%; the mass content of vinylene carbonate derivatives in the electrolyte is 0.5% to 1.5%.

[0142] For example, the mass content of 1,3-propanesulfonic acid lactone in the electrolyte is 0.05% to 0.5%; the mass content of vinylene carbonate in the electrolyte is 3% to 6%; and the mass content of vinylene carbonate in the electrolyte is 0.5% to 1.5%.

[0143] Under fast charging, the three types of substances mentioned above work together to form the SEI film. The SEI film can be strengthened by the low content of 1,3-propanesulfonate lactone, and the vinylene carbonate can further strengthen the film formation, reduce the risk of carboxylic acid ester solvents penetrating the SEI film, and improve the high-temperature cycle performance of the battery cell. An appropriate content of ethylene carbonate derivative can reduce the film-forming resistance and improve the fast charging performance. Moreover, the mass content of ethylene carbonate derivative is not too high, which can reduce the risk of high-temperature decomposition and further improve the high-temperature cycle performance of the battery cell. Thus, the fast charging performance and high-temperature cycle performance of the battery cell at high energy density are improved.

[0144] In the embodiments of this application, ethylene carbonate derivatives refer to ethylene carbonate in which at least one hydrogen atom is substituted, and the substituent group can be one, two, three or four, etc.

[0145] For example, ethylene carbonate derivatives include compounds represented by formula A.

[0146] In Formula A, Q1, Q2, Q3 and Q4 each independently include any one of hydrogen atoms, halogen atoms, C1 to C5 alkyl groups, or C1 to C5 haloalkyl groups, and Q1, Q2, Q3 and Q4 are not all hydrogen atoms at the same time.

[0147] Q1, Q2, Q3, and Q4 are not all hydrogen atoms at the same time. In other words, at least one of Q1, Q2, Q3, and Q4 includes a halogen atom, a C1 to C5 alkyl group, or a C1 to C5 haloalkyl group.

[0148] For example, one of Q1, Q2, Q3, and Q4 includes a halogen atom, a C1 to C5 alkyl group, or a C1 to C5 haloalkyl group, and the remainder are hydrogen atoms.

[0149] For example, at least two of Q1, Q2, Q3, and Q4 include a halogen atom, a C1 to C5 alkyl group, or a C1 to C5 haloalkyl group.

[0150] For example, at least three of Q1, Q2, Q3, and Q4 include halogen atoms, C1 to C5 alkyl groups, or C1 to C5 haloalkyl groups.

[0151] For example, Q1, Q2, Q3, and Q4 each independently include a halogen atom, a C1 to C5 alkyl group, or a C1 to C5 haloalkyl group.

[0152] Optionally, at least one of Q1, Q2, Q3, and Q4 includes a halogen atom or a C1 to C5 haloalkyl group. The halogen atom includes a fluorine atom, a bromine atom, or a chlorine atom, and may be a fluorine atom. The C1 to C5 haloalkyl group includes a C1 to C5 fluoroalkyl group, a C1 to C5 bromoalkyl group, or a C1 to C5 chloroalkyl group, and may be a fluorine atom. For example, the C1 to C5 fluoroalkyl group includes fluoromethyl, fluoroethyl, fluoropropyl, fluorobutyl, or fluoropentyl.

[0153] When ethylene carbonate derivatives include fluorine atoms, they can form a film rich in F and Li on the negative electrode side. This film can protect the negative electrode active material while reducing the impedance of the film, thus more effectively improving the high-temperature cycling performance and fast charging performance of the battery cell at high energy density.

[0154] For example, ethylene carbonate derivatives include at least one of the compounds shown in formula A-1 to formula A-6.

[0155] The aforementioned materials can further improve the high-temperature cycling performance and fast charging performance of individual battery cells under high energy density.

[0156] Optionally, the ethylene carbonate derivative includes at least one of the compounds shown in Formula A-1 to Formula A-3, and further optionally, the ethylene carbonate derivative includes the compound shown in Formula A-1.

[0157] In some embodiments, the electrolyte further includes a second additive with a mass content greater than or equal to 0, the second additive including at least one of a sulfur-containing additive and a lithium salt additive.

[0158] For example, sulfur-containing additives include one or more of vinyl sulfate DTD, vinyl disulfate 2-DTD, butylene sulfite BS, vinyl sulfite ES, and methylene disulfonate MMDS.

[0159] For example, lithium salt additives include one or more of lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium tetrafluoroborate (LiBF4), and lithium dioxalate borate (LiBOB).

[0160] In some embodiments, the electrolyte includes a sulfur-containing additive at a mass content of 0 to 2%, optionally at a mass content of 0.5% to 2%. The sulfur-containing additive and the first additive work together to participate in film formation, which can optimize the film composition of the SEI film. The sulfur-containing additive can participate in the formation of an SEI film rich in inorganic substances, which can improve the high-temperature stability and high-voltage stability of the SEI film and improve the high-temperature cycle performance of the battery cell.

[0161] For example, the sulfur-containing additive has a mass content of 0 to 2% in the electrolyte, such as 0, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 2%, or any combination of two of the above values.

[0162] In some embodiments, the electrolyte includes a lithium salt additive at a mass content of 0 to 1%, optionally at a mass content of 0.2% to 1%. The lithium salt additive and the first additive work together to participate in film formation, which can optimize the film composition of the SEI film. The lithium salt additive can participate in the formation of an inorganic-rich SEI film, and the inorganic matter can improve the high-temperature stability and high-pressure stability of the SEI film, thereby improving the high-temperature cycle performance of the battery cell.

[0163] For example, the lithium salt additive has a mass content of 0 to 1% in the electrolyte, such as 0, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, or any combination of two of the above values.

[0164] When the mass content of the second additive is 0, it means that the second additive can be omitted from the freshly prepared electrolyte, or that the second additive cannot be detected in the electrolyte obtained after disassembling the battery cell when the amount of the second additive is small.

[0165] In some embodiments, the electrolyte salt includes a lithium salt, specifically lithium hexafluorophosphate (LiPF6). Optionally, the electrolyte may also include a fluorosulfonylimide lithium salt, which can improve the cycle performance of the battery cell.

[0166] Optionally, the lithium fluorosulfonylimide includes one or more of lithium bisfluorosulfonylimide (LiFSI) and lithium bistrifluoromethanesulfonate (LiTFSI).

[0167] In some embodiments, the lithium salt content is 10% to 16% by mass.

[0168] In the embodiments of this application, the types and contents of inorganic components / lithium salts in the electrolyte are known in the art and can be detected using equipment and methods known in the art. For example, the inorganic components / lithium salts in the electrolyte can be qualitatively or quantitatively analyzed by ion chromatography analysis method according to standard JY / T020-1996 "General Rules for Ion Chromatography Analysis". In the embodiments of this application, freshly prepared electrolyte can be used as a sample, the free electrolyte of a fresh battery can be used as a sample, or a fully discharged battery cell can be disassembled in reverse (discharged to the discharge cutoff voltage so that the charge state of the battery cell is about 0% SOC) and the free electrolyte obtained from the battery cell can be used as a sample for detection by ion chromatography analysis method.

[0169] In the embodiments of this application, the types and contents of organic components in the electrolyte are known in the art and can be detected using equipment and methods known in the art. For example, the organic components of the electrolyte can be qualitatively and quantitatively analyzed by gas chromatography using GB / T9722-2006 "General Rules for Gas Chromatography of Chemical Reagents".

[0170] [Negative electrode plate]

[0171] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector and comprising a negative electrode active material. For example, the negative current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative current collector.

[0172] In this embodiment, the thickness of the single-sided negative electrode film is from 50 μm to 75 μm, for example, 50 μm, 51 μm, 52 μm, 53 μm, 54 μm, 55 μm, 56 μm, 57 μm, 58 μm, 59 μm, 60 μm, 61 μm, 62 μm, 63 μm, 64 μm, 65 μm, 66 μm, 67 μm, 68 μm, 69 μm, 70 μm, 71 μm, 72 μm, 73 μm, 74 μm, 75 μm, or any range of two of the above values. Optionally, the thickness of the single-sided negative electrode film is from 50 μm to 65 μm.

[0173] When the thickness of the single-sided negative electrode film is within the above range, the thickness of the negative electrode film is moderate. While improving the energy density of the battery cell, it reduces the amount of negative electrode active material added to the negative electrode film, which can effectively reduce the total amount of side reactions, thereby reducing gas production and improving the high-temperature cycle performance of the battery cell. Moreover, the lithium ion transport path is shorter, which is beneficial to improving the fast charging performance of the battery cell, thereby improving the high-temperature cycle performance and fast charging performance of the battery cell at high energy density.

[0174] In the embodiments of this application, the thickness of the single-sided negative electrode film layer has a meaning known in the art. For example, it can be detected using equipment and methods known in the art. For example, a battery cell that has been completely discharged (discharged to the discharge cutoff voltage so that the charge state of the battery cell is about 0% SOC) can be disassembled in reverse. The negative electrode sheet obtained from the battery cell is used as a sample, and the thickness of the negative electrode sheet is measured with a micrometer. Then, the negative electrode film layer on the surface of the negative electrode current collector is washed away with a solvent, and the thickness of the negative electrode current collector is measured with a micrometer. When the negative electrode film layer is coated on one side, the thickness of the negative electrode sheet minus the thickness of the negative electrode current collector is the thickness of the negative electrode film layer. Or, when the negative electrode film layer is coated on both sides, the thickness of the negative electrode sheet minus the thickness of the negative electrode current collector is the total thickness of the negative electrode film layer on both sides, and the total thickness of the negative electrode film layer on both sides divided by 2 is the thickness of the single-sided negative electrode film layer.

[0175] The upper limit voltage for charging and the lower limit voltage for discharging a single battery cell vary depending on the positive electrode active material. For example, when the phosphate material includes lithium iron phosphate, the upper limit voltage for charging can be 3.65V and the lower limit voltage for discharging can be 2.0V. Similarly, when the phosphate material includes lithium manganese iron phosphate, the upper limit voltage for charging can be 4.2V and the lower limit voltage for discharging can be 2.0V. The following explanation uses a charging upper limit voltage of 3.65V and a discharging lower limit voltage of 2.0V as an example to illustrate the state of a single battery cell: In this embodiment, the 100% state of charge (SOC) and 0% state of charge (SOC) of a single battery cell are defined as follows:

[0176] The battery cell is charged at a constant current charging rate of 0.33C to the upper limit of the charging voltage, and then charged at a constant voltage to 0.05C, which corresponds to the 100% SOC state of the battery cell. The battery cell is then discharged at a constant current discharging rate of 0.33C to the cutoff voltage, which corresponds to the 0% SOC state of the battery cell.

[0177] In the embodiments of this application, the negative electrode film layer includes at least one film layer, which can be a single film layer or at least two film layers. The negative electrode film layer can include two film layers, three film layers, four film layers, or even more film layers.

[0178] In this application, the negative electrode active material includes a carbon-based material, which includes graphite particles. Graphite particles have high cycle stability and can improve the cycle performance of the battery cell. The positive electrode active material of this application is mainly a lithium phosphate system with an olivine structure, and the negative electrode active material is mainly a carbon-based material system. The combination of the two results in excellent cycle performance of the battery cell.

[0179] The volume average particle size (Dv50) of the graphite particles is from 8.5 μm to 13.5 μm, for example, 8.5 μm, 9 μm, 9.5 μm, 9.8 μm, 10 μm, 10.2 μm, 10.5 μm, 10.8 μm, 11 μm, 11.2 μm, 11.5 μm, 11.8 μm, 12 μm, 12.2 μm, 12.5 μm, 12.8 μm, 13 μm, 13.5 μm, or any range of two of the above values. Optionally, the volume average particle size (Dv50) of the graphite particles is from 9.5 μm to 13 μm.

[0180] The relatively small volume-average particle size of graphite particles results in a shorter solid-phase migration path for lithium ions, which can improve the fast charging capability of battery cells. However, under fast charging conditions, the side reactions between small-diameter graphite particles and carboxylic acid ester solvents in the electrolyte are quite intense. The electrolyte is further supplemented with a first additive, which can preferentially form a film on the negative electrode side, providing excellent protection for the negative electrode active material, reducing the risk of side reactions on the negative electrode side, and improving the cycle performance of battery cells.

[0181] In the embodiments of this application, the volume average particle size Dv50 of the material refers to the particle size corresponding to 50% of the volume distribution. It can be detected using equipment and methods known in the art. For example, the negative electrode active material can be used as a sample, and the Dv50 of the particles can be tested using a Mastersizer 2000E laser particle size analyzer according to the test standard GB / T 19077-2016.

[0182] In some embodiments, the graphite particles include graphite bulk particles and a negative electrode coating layer. The graphite bulk particles include secondary particles, which in turn include multiple primary particles. The negative electrode coating layer coats the surface of the graphite bulk particles and comprises carbon elements. The carbon in the negative electrode coating layer is mainly amorphous carbon, which refers to transitional carbon materials with a very low degree of graphitization and crystallization, exhibiting an approximately amorphous morphology (or lacking a fixed shape and periodic structural regularity). In this application, amorphous carbon refers to the product after carbonization treatment of an organic carbon source.

[0183] The graphite bulk particles include secondary particles. There are multiple migration paths for lithium ions in the graphite bulk particles, and the migration paths in the primary particles are shorter, which can improve the migration rate of lithium ions. The negative electrode coating has more end faces and defects, which increases the number of sites where lithium ions can be inserted or extracted. This makes the conductivity of the negative electrode coating better, which can reduce the internal resistance of the negative electrode sheet, reduce the heat generation of the battery cell, and improve the fast charging performance and high-temperature cycling performance of the battery cell at high energy density.

[0184] For example, the graphite bulk particles include at least one of artificial graphite and natural graphite, optionally artificial graphite.

[0185] Optionally, based on the mass of the graphite particles, the carbon content of the negative electrode coating layer is 2% to 5% by mass. For example, the carbon content of the negative electrode coating layer is 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any combination of two of the above values.

[0186] When the carbon content of the negative electrode coating is within the above range, it can further reduce the internal resistance of the negative electrode sheet, reduce the heat generation of the battery cell, and improve the high-temperature cycle performance of the battery cell under high energy density.

[0187] In the embodiments of this application, the graphite particles can be prepared using methods known in the art. Taking artificial graphite as an example, the preparation method includes: providing artificial graphite and an organic carbon source, mixing the two, and then carbonizing them to form a negative electrode coating layer on at least a portion of the surface of the artificial graphite particles.

[0188] Optionally, the organic carbon source includes one or more of coal tar pitch, petroleum asphalt, phenolic resin, and coconut shell. Further optionally, the organic carbon source includes petroleum asphalt. Optionally, the softening point of coal tar pitch or petroleum asphalt is below 250°C.

[0189] Optionally, the carbonization temperature is between 700°C and 1800°C. Optionally, the carbonization temperature is between 1000°C and 1300°C. Within a suitable range, the carbonization temperature allows the organic carbon source to be carbonized, forming a negative electrode coating layer containing amorphous carbon on at least a portion of the surface of the artificial graphite.

[0190] Optionally, the carbonization treatment time is 1 hour to 6 hours.

[0191] In some embodiments, the carbon-based material may further include natural graphite. Specifically, the carbon-based material may include graphite particles, or it may include both graphite particles and natural graphite. Optionally, the carbon-based material is graphite particles.

[0192] In some embodiments, the negative electrode active material may include silicon-based materials in addition to graphite particles. The introduction of silicon-based materials can increase the capacity of the negative electrode active material and improve the energy density of the battery cell.

[0193] Optionally, based on the mass of the negative electrode film, the mass content of silicon element in the silicon-based material is 0.3% to 5.0%, optionally 1% to 5%. Exemplarily, the mass content of silicon element in the silicon-based material is 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.8%, 5%, or a range of any two of the above values.

[0194] When the mass content of silicon in silicon-based materials is within the above range, it can improve the capacity of the negative electrode active material, thereby improving the energy density of the battery cell.

[0195] Optionally, the silicon-based material may include at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy.

[0196] In some embodiments, the negative electrode active material may include, in addition to the aforementioned carbon-based materials and optionally silicon-based materials, at least one of tin-based materials and lithium titanate. Tin-based materials may include at least one of elemental tin, tin oxides, and tin alloys.

[0197] The qualitative and quantitative analysis of each substance or element in this application can be performed using suitable equipment and methods known to those skilled in the art. Relevant testing methods can be referenced from domestic and international testing standards and enterprise standards. Furthermore, those skilled in the art can adaptively modify certain testing steps / instrument parameters from the perspective of testing accuracy to obtain more accurate results. One testing method can be used for qualitative or quantitative analysis, or several testing methods can be used in combination for qualitative or quantitative determination.

[0198] For example, this application can combine the general rules of X-ray diffraction analysis in JIS / K0131-1996 to perform X-ray powder diffraction tests and qualitative analysis on negative electrode sheets or negative electrode active materials.

[0199] Artificial graphite and natural graphite can be distinguished by SEM cross-sectional images taken by scanning electron microscope (SEM). Natural graphite has gaps between the sheet-like structures in its SEM cross-section, while artificial graphite has a dense structure with no obvious gaps. Alternatively, they can be distinguished by XRD patterns obtained by X-ray diffraction. Natural graphite has obvious 2H and 3R phases in its XRD pattern, while artificial graphite only has the 2H phase in its XRD pattern.

[0200] In some embodiments, the compacted density of the negative electrode active material powder under a pressure of 20,000 N is 1.4 g / cm³. 3 Up to 1.8 g / cm 3 For example, the compacted density of the negative electrode active material powder under a pressure of 20000N is 1.4 g / cm³. 3 1.5g / cm 3 1.55g / cm 3 1.6g / cm 3 1.65g / cm 3 1.7g / cm 3 1.75g / cm 3 1.8g / cm 3 Or a range consisting of any two of the above values.

[0201] When the powder compaction density of the negative electrode active material at 20000N is within the above range, it can improve the energy density of the battery cell. Furthermore, since the negative electrode active material in the negative electrode film layer can be stacked more tightly, the contact resistance between particles is smaller, which can further reduce the resistance of the electrode sheet, thereby reducing heat generation and improving the high-temperature cycle performance of the battery cell at high energy density.

[0202] In this application, the powder compaction density of the material has a meaning known in the art and can be tested using methods and equipment known in the art, according to the testing standard GB / T24533-2009. As an example, a certain amount of negative electrode active material is taken as a sample and added to a UTM7305 electronic pressure testing machine with a base area of ​​1.327 cm². 2 In the mold, the pressure is increased to 2000 kg (equivalent to 20000 N), held for 30 s, then depressurized and held for 10 s. The compaction density of the negative electrode active material under a force of 20000 N is then recorded and calculated.

[0203] In some embodiments, the compaction density of the negative electrode film layer in a single battery cell at 0% charge is 1.30 g / cm³. 3 Up to 1.55 g / cm 3 For example, the compaction density of the negative electrode film layer of a single battery cell at 0% charge is 1.30 g / cm³. 3 1.32g / cm 3 1.35g / cm 3 1.40g / cm 3 1.45g / cm 3 1.50g / cm 3 1.55g / cm 3 Or a range consisting of any two of the above values.

[0204] When the compaction density of the negative electrode film is within the above range, it is beneficial to improve the energy density of the battery cell. Furthermore, since the negative electrode active material in the negative electrode film is packed more tightly, the contact resistance between particles is smaller, which can further reduce the resistance of the electrode, thereby reducing heat generation. This can reduce the amount of gas generated by the decomposition of carboxylic acid ester solvents due to heat accumulation and improve the high-temperature cycle performance of the battery cell.

[0205] In the embodiments of this application, the compaction density of the negative electrode film layer of a single battery cell under 0% charge state has a meaning known in the art and can be detected using equipment and methods known in the art, such as the compaction density test method of the positive electrode film layer described above.

[0206] In some embodiments, the single-sided coating weight of the negative electrode film is 90 mg / 1540.25 mm. 2 Up to 140mg / 1540.25mm 2 For example, the single-sided coating weight of the negative electrode film is 90 mg / 1540.25 mm. 2 92mg / 1540.25mm 2 95mg / 1540.25mm 2 96mg / 1540.25mm2 100mg / 1540.25mm 2 102mg / 1540.25mm 2 104mg / 1540.25mm 2 105mg / 1540.25mm 2 108mg / 1540.25mm 2 110mg / 1540.25mm 2 112mg / 1540.25mm 2 114mg / 1540.25mm 2 115mg / 1540.25mm 2 116mg / 1540.25mm 2 118mg / 1540.25mm 2 120mg / 1540.25mm 2 122mg / 1540.25mm 2 125mg / 1540.25mm 2 128mg / 1540.25mm 2 130mg / 1540.25mm 2 132mg / 1540.25mm 2 135mg / 1540.25mm 2 137mg / 1540.25mm 2 140mg / 1540.25mm 2 Or a range consisting of any two of the above values.

[0207] When the single-sided coating weight of the negative electrode film is within the above range, the heat generation per unit area of ​​the negative electrode sheet will not be too large, and it can also improve the high-temperature cycle performance of the battery cell under high energy density.

[0208] In this embodiment, the single-sided coating weight of the negative electrode film has a meaning known in the art and can be detected using equipment and methods known in the art. The negative electrode sheet is disassembled from a battery cell at 0% state of charge (SOC), and the compaction density of the negative electrode film is measured. For example, a single-sided coated negative electrode sheet (if it is a double-sided coated sheet, the negative electrode film layer on one side can be wiped off first) is cut into a small circular piece with an area of ​​S1, weighed, and recorded as M1, and its thickness H1 is measured. Then, the negative electrode film layer of the weighed negative electrode sheet is wiped off, the weight of the negative current collector is weighed and recorded as M0, and its thickness H0 is measured. The single-sided coating weight of the negative electrode film = (weight of the negative electrode sheet M1 - weight of the negative current collector M0) / S1, the thickness of the negative electrode film = thickness of the negative electrode sheet H1 - thickness of the negative current collector H0, and the compaction density of the negative electrode film = single-sided coating weight of the negative electrode film / thickness of the negative electrode film.

[0209] In some embodiments, the negative electrode film layer further includes a negative electrode binder, which includes at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). In some embodiments, the mass content of the negative electrode binder is ≤5% based on the total weight of the negative electrode film layer.

[0210] In some embodiments, the negative electrode film layer may optionally include a negative electrode conductive agent. This application does not impose particular limitations on the type of negative electrode conductive agent. As an example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass content of the negative electrode conductive agent is ≤5% based on the total weight of the negative electrode film layer.

[0211] In some embodiments, the negative electrode film layer may optionally include other additives. As examples, other additives may include thickeners, dispersants, etc., such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, etc. In some embodiments, the mass content of other additives is ≤2% based on the total weight of the negative electrode film layer.

[0212] In some embodiments, the negative current collector may be a metal foil or a composite current collector. Examples of metal foils include at least one foil made of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. A composite current collector may include a polymer base material and a metal material layer formed on at least one surface of the polymer base material. As an example, the metal material layer may include at least one of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer base material may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0213] The negative electrode film is typically formed by coating a negative electrode slurry onto the negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is usually formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0214] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of the present application further includes a negative electrode conductive layer sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector. In other embodiments, the negative electrode sheet of the present application further includes a protective layer covering the surface of the negative electrode film layer.

[0215] In some embodiments, the negative electrode sheet further includes a negative electrode conductive layer, which is located between the negative electrode film layer and the negative electrode current collector. The negative electrode conductive layer can further improve the conductivity of the negative electrode sheet, reduce the heat generation of the negative electrode sheet, thereby reducing the heat generation of the battery cell and improving the fast charging performance and high-temperature cycle performance of the battery cell.

[0216] In some embodiments, the thickness of the negative electrode conductive layer is from 0.5 μm to 2 μm. For example, the thickness of the negative electrode conductive layer can be 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, 1.6 μm, 1.8 μm, 2 μm, or any combination of two of the above values.

[0217] When the thickness of the negative electrode conductive layer is within the above range, the conductivity of the negative electrode sheet can be further improved, the heat generation of the negative electrode sheet can be reduced, thereby reducing the heat generation of the battery cell, and the energy density of the battery cell can also be improved.

[0218] In the embodiments of this application, the thickness of the negative electrode conductive layer has a meaning known in the art and can be detected using equipment and methods known in the art, such as performing a tomographic scan on the negative electrode sheet to directly measure the thickness of the negative electrode conductive layer.

[0219] In some embodiments, the negative electrode conductive layer includes one or more of a negative electrode conductive agent and a negative electrode binder. The negative electrode conductive agent in the negative electrode conductive layer can improve the conductivity of the negative electrode conductive layer, thereby improving the conductivity of the negative electrode sheet and reducing the heat generation of the battery cell. The negative electrode binder in the negative electrode conductive layer can improve the bonding performance between the negative electrode current collector and the negative electrode film layer, thereby improving the structural stability of the negative electrode sheet.

[0220] In some embodiments, the negative electrode conductive layer may optionally include other additives. As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc.

[0221] Optionally, the negative electrode conductive agent in the negative electrode conductive layer has a mass content of 20% to 40%. For example, the mass content of the negative electrode conductive agent is 20%, 25%, 30%, 35%, 40%, or any combination of two of the above values.

[0222] For example, the negative electrode conductive agent of the negative electrode conductive layer includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0223] Optionally, the negative electrode binder in the negative electrode conductive layer has a mass content of 60% to 80% in the negative electrode conductive layer. For example, 60%, 65%, 70%, 75%, 80%, or any combination of two of the above values.

[0224] For example, the negative electrode binder of the negative electrode conductive layer includes one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin, polyvinyl alcohol, sodium alginate, and carboxymethyl chitosan.

[0225] [Positive electrode plate]

[0226] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector and comprising a positive electrode active material. For example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0227] In some implementations, the thickness of the single-sided positive electrode film is 50 μm to 65 μm, for example, 50 μm, 55 μm, 60 μm, 65 μm or any combination of two of the above values.

[0228] When the thickness of the positive electrode film on one side is within the above range, the thickness of the positive electrode film is relatively thin, resulting in a shorter lithium ion transport path, which is beneficial to improving the fast charging performance of the battery cell.

[0229] In the embodiments of this application, the thickness of the single-sided positive electrode film layer has a meaning known in the art and can be detected using equipment and methods known in the art, such as the thickness detection method of the negative electrode film layer.

[0230] The electrode assembly in this application embodiment can be a wound electrode assembly or a stacked electrode assembly, and can be selected as a stacked electrode assembly.

[0231] When the electrode assembly has a wound structure, the positive electrode and the negative electrode are wound in the same direction.

[0232] When the electrode assembly has a stacked structure, there are multiple positive and negative electrode sheets, which are stacked along the thickness direction of the battery cell.

[0233] In some embodiments, the dimension of the positive electrode film layer along the length of the battery cell is 200 mm to 650 mm, such as 200 mm, 250 mm, 300 mm, 350 mm, 400 mm, 450 mm, 500 mm, 550 mm, 600 mm, 650 mm, or any combination of two of the above values. For example, when the electrode assembly has a stacked structure, the dimension of the positive electrode film layer along the length of the battery cell is 200 mm to 650 mm. This dimension along the length of the battery cell can be understood as the length of the positive electrode film layer, i.e., the length of the positive electrode film layer is 200 mm to 650 mm.

[0234] When the dimensions of the positive electrode film along the length of the battery cell are within the above range, the coating amount of the positive electrode film is relatively large, which is beneficial to improving the energy density of the battery cell; moreover, the electron transport path will not be too long, which is beneficial to improving the fast charging capability of the battery cell.

[0235] Carboxylic acid ester solvents have low viscosity and a mass content of 8% to 60%, which allows them to quickly wet the electrode along its length. This results in a more uniform reaction along the length of the electrode and reduces the likelihood of lithium plating when active ions migrate to the negative electrode, thus improving the reliability of the battery cell.

[0236] In this embodiment of the application, the lithium phosphate with olivine structure can be phosphate particles or a material obtained by coating and modifying them. For example, the lithium phosphate with olivine structure includes phosphate particles and a positive electrode coating layer. The positive electrode coating layer coats at least part of the surface of the phosphate particles and contains carbon elements.

[0237] Phosphate particles, by coating the surface with a positive electrode coating layer, can improve the conductivity of lithium phosphate with olivine structure, which is beneficial to the migration rate of lithium ions, improve the fast charging capability of the battery, reduce the heat generation of the battery cell, and improve the high-temperature cycle performance of the battery cell.

[0238] Examples of phosphate particles include, but are not limited to, one or more of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium nickel phosphate, and lithium cobalt phosphate. The above materials exhibit excellent cycle stability and can improve the cycle performance of individual battery cells.

[0239] In some embodiments, lithium phosphates include those with the general formula Li x1 A y1 Me a1 M b1 P 1-c1 X c1 Y z1 The compound, wherein 0.5≤x1≤1.3, 0≤y1≤1.3, 0.5≤x1+y1≤1.3, 0.9≤a1≤1.5, 0≤b1≤0.5, 0.9≤a1+b1≤1.5, 0≤c1≤0.5, 3≤z1≤5, A includes at least one of Na, K and Mg; Me includes at least one of Mn, Fe, Co and Ni; M includes at least one of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La and Ce; X includes at least one of Cl, C, N and P; Y includes at least one of O and F.

[0240] Phosphate particles exhibit excellent cycle stability, which is beneficial for improving the cycle performance of individual battery cells.

[0241] For example, phosphate particles include one or more of LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4. During the charging and discharging process, active ions such as Li are de-intercalated and consumed in a single battery cell, resulting in different molar contents of Li in different discharged states. In the examples of positive electrode active materials such as LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4, the molar contents of Li represent the initial state of the material, i.e., the state before feeding. When the positive electrode active material is applied to the battery system, the molar contents of Li may change after charge-discharge cycles. In the embodiments of this application, the molar contents of oxygen (O) in the examples of positive electrode active materials such as LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4 are only theoretical values. Lattice oxygen release can cause changes in the molar contents of oxygen (O). In reality, the molar contents of oxygen (O) may fluctuate, and all of the above situations are within the scope of protection of this application.

[0242] In some embodiments, the carbon content in the olivine-structured lithium phosphate is from 0.8% to 2.3% by mass. Exemplarily, the carbon content in the olivine-structured lithium phosphate is 0.8%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.3%, or a range consisting of any two of the above values.

[0243] Carbon mainly exists in the positive electrode coating layer in the form of a carbon coating layer. The carbon coating layer is loose and porous, which is beneficial to increasing the specific surface area of ​​the material, making it more conducive to the effective contact between the electrolyte and phosphate particles, and facilitating the transport of lithium ions at the phase interface. In addition, when the mass content of carbon is within the above range, it can significantly improve the conductivity of lithium phosphate with olivine structure, which is beneficial to improving the ionic and electronic conductivity of lithium phosphate with olivine structure, and can improve the rapid charging capability of battery cells at high energy density.

[0244] In some embodiments, the positive electrode coating layer further includes one or more elements of Fe, Ti, Zr, Hf, Ge, and Sn.

[0245] In some embodiments, the positive electrode coating layer includes materials of the general formula Li. 3-d1 Fe 2-d1 M3 d1 (PO m1 ) n1 The compounds wherein 0≤d1≤1, 3≤m1≤5, 2≤n1≤4, and M3 includes one or more of Ti, Zr, Hf, Ge, and Sn.

[0246] Li 3-d1 Fe 2-d1 M3 d1 (PO m1 ) n1 The compounds are fast ion conductors with a NASICON structure, such as one or more of lithium iron phosphate (Li2FeTi(PO4)3), lithium zirconium iron phosphate (Li2FeZr(PO4)3), and lithium tin iron phosphate (Li2FeSn(PO4)3).

[0247] Fast ion conductors with a NASICON structure are materials with ultrafast ion conduction capabilities, possessing abundant three-dimensional lithium-ion diffusion and transport channels. They exhibit advantages such as high ion conduction efficiency and strong structural stability during multiple lithium delithiation and lithium intercalation processes. Coating the surface of phosphate particles with fast ion conductors containing a NASICON structure can significantly improve the lithium-ion transport rate during multiple lithium delithiation / intercalation at the positive electrode, enhance the ionic conductivity of the positive electrode active material, improve the fast charging capability of the battery cell, and further increase the specific capacity and energy density of the corresponding battery cell.

[0248] The carbon element and the fast ion conductor can be layered. For example, the carbon element can be an independent carbon coating layer, and the fast ion conductor can be an independent fast ion conductor layer. The carbon coating layer can be applied to the surface of the phosphate particles, and the fast ion conductor layer can be located on the surface of the carbon coating layer, i.e., the fast ion conductor layer is located on the side of the carbon coating layer away from the phosphate particles. Alternatively, the fast ion conductor layer can be applied to the surface of the phosphate particles, and the carbon coating layer can be located on the surface of the fast ion conductor layer, i.e., the carbon coating layer is located on the side of the fast ion conductor layer away from the phosphate particles. Of course, the carbon element and the fast ion conductor can also be layered together.

[0249] Optionally, the carbon coating layer can be formed by carbonizing an organic carbon source (e.g., glucose, polyethylene glycol, etc.) onto the surface of the fast ion conductor layer. The carbon coating layer can partially or completely cover the fast ion conductor layer. The carbon coating layer can significantly improve the electronic conductivity of phosphate particles, compensating for the poor electronic conductivity of phosphate particles and increasing the energy density of the battery cell.

[0250] The positive electrode active material of this application uses lithium phosphate as a substrate, fully leveraging the advantages of lithium phosphate such as low cost, high reliability, and good cycle stability. Simultaneously, it utilizes the positive electrode coating layers (fast ion conductor layer and carbon coating layer) to overcome the drawbacks of poor electronic and ionic conductivity. Battery cells prepared using the positive electrode active material of this application can improve the energy density of battery cells while maintaining excellent cycle performance.

[0251] In this embodiment, the elemental content in the positive electrode active material is defined in a way known in the art and can be detected using equipment and methods known in the art. For example, referring to EPA 6010D-2014, it can be tested by inductively coupled plasma atomic emission spectrometry (ICP-OES, instrument model: Thermo ICAP7400). After discharging the battery cell to 0% state of charge (SOC), the positive electrode sheet is disassembled, cleaned and dried with DMC, and then calcined at high temperature to remove impurities. 0.4g of the positive electrode active material is weighed and 10ml (50% concentration) of aqua regia is added. Then it is placed on a plate at 180°C for 30min. After digestion on the plate, the volume is adjusted to 100mL, and quantitative testing is performed using the standard curve method.

[0252] In some embodiments, the compacted density of the positive electrode active material at 30000 N is 2.43 g / cm³. 3 Up to 2.85 g / cm 3 .

[0253] For example, the compacted density of the positive electrode active material at 30000N is 2.43 g / cm³. 3 2.47 g / cm 3 2.48 g / cm 3 2.49 g / cm 3 2.5g / cm 3 2.51g / cm 3 2.55g / cm 3 2.58g / cm 3 2.60g / cm 3 2.65g / cm 3 2.68g / cm 3 2.70 g / cm 3 2.72 g / cm 3 2.75g / cm 3 2.78g / cm 3 2.80g / cm 3 2.85g / cm 3 Or a range consisting of any two of the above values.

[0254] When the powder compaction density of the positive electrode active material at 30000N is within the above range, it can improve the energy density of the battery cell. Furthermore, since the positive electrode active material in the positive electrode film layer can be stacked more tightly, the contact resistance between particles is smaller, which can further reduce the resistance of the electrode sheet, thereby reducing heat generation and improving the high-temperature cycle performance and fast charging performance of the battery cell at high energy density.

[0255] In the embodiments of this application, the powder compaction density of the material has a meaning known in the art and can be tested using methods and equipment known in the art, according to the testing standard GB / T24533-2009. For example, a certain amount of positive electrode active material is taken as a sample and added to a UTM7305 electronic pressure testing machine with a bottom area of ​​1.327 cm². 2 In the mold, the pressure is increased to 3000 kg (equivalent to 30000 N), held for 30 s, then depressurized and held for 10 s. The compaction density of the positive electrode active material under a force of 30000 N is then recorded and calculated.

[0256] In some embodiments, the compaction density of the positive electrode film layer at 0% state of charge (SOC) of the battery cell is 2.46 g / cm³. 3 Up to 2.80 g / cm 3 For example, at 0% state of charge (SOC), the compaction density of the positive electrode film in a single battery cell is 2.46 g / cm³. 3 2.50g / cm 3 2.52g / cm 3 2.55g / cm 3 2.56 g / cm 3 2.57g / cm 3 2.58g / cm 3 2.60g / cm 3 2.62 g / cm 3 2.65g / cm 3 2.68g / cm 3 2.70 g / cm 3 2.75g / cm 3 2.80g / cm 3 Or a range consisting of any two of the above values.

[0257] When the compaction density of the positive electrode film is within the above range, it is beneficial to improve the energy density of the battery cell. Furthermore, since the positive electrode active material in the positive electrode film is packed more tightly, the contact resistance between particles is smaller, which can further reduce the resistance of the electrode sheet, thereby reducing heat generation under fast charging and improving the high-temperature cycle performance and fast charging performance of the battery cell under high energy density.

[0258] In some embodiments, the single-sided coating weight of the positive electrode film is 200 mg / 1540.25 mm. 2 Up to 350mg / 1540.25mm 2 For example, 200mg / 1540.25mm², 210mg / 1540.25mm², 220mg / 1540.25mm², 230mg / 1540.25mm² 2240mg / 1540.25mm 2 250mg / 1540.25mm 2 260mg / 1540.25mm 2 270mg / 1540.25mm 2 280mg / 1540.25mm 2 290mg / 1540.25mm 2 300mg / 1540.25mm 2 , 310mg / 1540.25mm2, 320mg / 1540.25mm2, 330mg / 1540.25mm 2 340mg / 1540.25mm 2 350mg / 1540.25mm 2 Or a range consisting of any two of the above values.

[0259] When the single-sided coating weight of the positive electrode film is within the above range, the heat generation per unit area of ​​the positive electrode sheet will not be too large, thus improving the high-temperature cycle performance and fast charging performance of the battery cell under high energy density.

[0260] In this embodiment, the compaction density of the positive electrode film layer of a single battery cell at 0% State of Charge (SOC) can be detected by the following method: The positive electrode sheet of the single battery cell at 0% SOC is disassembled, and the compaction density of the positive electrode film layer is measured. For example, a single-sided coated positive electrode sheet (if it is a double-sided coated sheet, the positive electrode film layer on one side can be wiped off first) is taken, cut into small circular pieces with an area of ​​S1, weighed, and recorded as M1, and its thickness H1 is measured. Then, the positive electrode film layer of the weighed positive electrode sheet is wiped off, the weight of the positive current collector is weighed and recorded as M0, and its thickness H0 is measured. The single-sided coating weight of the positive electrode film layer = (weight of the positive electrode sheet M1 - weight of the positive current collector M0) / S1, the thickness of the positive electrode film layer = thickness of the positive electrode sheet H1 - thickness of the positive current collector H0, and the compaction density of the positive electrode film layer = single-sided coating weight of the positive electrode film layer / thickness of the positive electrode film layer.

[0261] In some embodiments, the positive electrode film layer may optionally include a positive electrode conductive agent. This application does not impose particular limitations on the type of positive electrode conductive agent. As an example, the positive electrode conductive agent includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass content of the positive electrode conductive agent is ≤5% based on the mass of the positive electrode film layer.

[0262] In some embodiments, the positive electrode film layer may optionally include a positive electrode binder. This application does not impose particular limitations on the type of positive electrode binder. As an example, the positive electrode binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and fluorinated acrylate resins. In some embodiments, the mass content of the positive electrode binder is ≤5% based on the mass of the positive electrode film layer.

[0263] In some embodiments, the positive current collector may be a metal foil or a composite current collector. Examples of metal foils include at least one foil made of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. A composite current collector may include a polymer base material and a metal material layer formed on at least one surface of the polymer base material. As an example, the metal material layer may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer base material may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0264] The positive electrode film is typically formed by coating a positive electrode slurry onto the positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is usually formed by dispersing the positive electrode active material, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP), but is not limited to it.

[0265] The positive electrode sheet does not exclude other additional functional layers besides the positive electrode film layer. For example, in some embodiments, the positive electrode sheet of the present application further includes a positive electrode conductive layer sandwiched between the positive electrode current collector and the positive electrode film layer and disposed on the surface of the positive electrode current collector. In other embodiments, the positive electrode sheet of the present application further includes a protective layer covering the surface of the positive electrode film layer.

[0266] In some embodiments, the positive electrode further includes a positive conductive layer located between the positive electrode film and the positive current collector. The positive conductive layer can further improve the conductivity of the positive electrode and reduce the heat generation of the positive electrode, thereby reducing the heat generation of the battery cell.

[0267] In some embodiments, the thickness of the positive electrode conductive layer is from 0.5 μm to 2 μm. For example, the thickness of the positive electrode conductive layer can be 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, 1.6 μm, 1.8 μm, 2 μm, or any combination of two of the above values.

[0268] When the thickness of the positive electrode conductive layer is within the above range, the conductivity of the positive electrode sheet can be further improved, the heat generation of the positive electrode sheet can be reduced, thereby reducing the heat generation of the battery cell and improving the fast charging performance and high-temperature cycling performance of the battery cell under high energy density.

[0269] In the embodiments of this application, the thickness of the positive electrode conductive layer has a meaning known in the art and can be detected using equipment and methods known in the art, such as performing a tomographic scan on the positive electrode sheet to directly measure the thickness of the positive electrode conductive layer.

[0270] In some embodiments, the positive conductive layer includes one or more of a positive conductive agent and a positive binder.

[0271] Optionally, the mass content of the positive electrode conductive agent in the positive electrode conductive layer is 30% to 50%. For example, the mass content of the positive electrode conductive agent is 30%, 35%, 40%, 45%, 50%, or any combination of two of the above values.

[0272] For example, the positive electrode conductive agent in the positive electrode conductive layer includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The positive electrode conductive agent in the positive electrode conductive layer can improve the conductivity of the positive electrode conductive layer, thereby improving the conductivity of the positive electrode sheet and reducing the heat generation of the battery cell.

[0273] Optionally, the positive electrode binder has a mass content of 50% to 70% in the positive electrode conductive layer. For example, 50%, 60%, 65%, 70%, or any combination of two of the above values.

[0274] For example, the positive electrode binder of the positive electrode conductive layer includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, a terpolymer of vinylidene fluoride-tetrafluoroethylene-propylene, a terpolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, a tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and fluorinated acrylate resins. The positive electrode binder of the positive electrode conductive layer can improve the adhesion between the positive electrode current collector and the positive electrode film layer, thereby improving the structural stability of the positive electrode sheet.

[0275] [Isolation membrane]

[0276] In this embodiment, the separator is disposed between the positive electrode and the negative electrode to isolate the positive electrode and the negative electrode.

[0277] In this embodiment, the separator includes a porous base membrane.

[0278] In some embodiments, the base film includes at least one of glass fiber, nonwoven fabric, and polyolefin. The base film can be a single-layer film or a multi-layer composite film, without particular limitation. When the base film is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0279] Optionally, the polyolefin includes at least one of polyethylene, polypropylene, and polyvinylidene fluoride.

[0280] In some embodiments, the porosity of the base membrane is 20% to 70%, optionally 35% to 60%. Exemplarily, the porosity of the base membrane is 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or any range of two of the above values.

[0281] When the porosity of the base film in the embodiments of this application is within the above-mentioned range, it can enhance the migration ability of lithium ions in the separator, further reduce the internal resistance of the battery cell, thereby reducing heat generation and improving the fast charging performance and high-temperature cycling performance of the battery cell at high energy density.

[0282] In this embodiment, porosity refers to the percentage of the volume of the pores in the base membrane of the separator to the total volume of the base membrane. Porosity can be tested according to the standard GB / T 36363-2018 "Polyolefin Separators for Battery Cells". It should be noted that the actual testing process may differ slightly from the standard due to differences in testing instruments, testing errors, and to minimize the impact on porosity testing, in order to obtain more accurate test values.

[0283] In some embodiments, the thickness of the base film is from 4 μm to 12 μm, optionally from 6 μm to 9 μm. Exemplarily, the thickness of the base film is 4 μm, 5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, or a range consisting of any two of the above values.

[0284] When the thickness of the base film is within the above range, the migration path of lithium ions in the base film is shorter, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation and improving the fast charging performance and high-temperature cycling performance of the battery cell at high energy density.

[0285] In this embodiment, the separator can be a base film. Optionally, the separator further includes a functional layer disposed on at least one side of the base film. The functional layer may include inorganic particles to improve the heat resistance of the separator. Optionally, the functional layer is disposed on both sides of the base film.

[0286] In some embodiments, the functional layer includes a first functional layer and a second functional layer. The first functional layer is located on one side of the base film and includes first inorganic particles. The second functional layer is located on the other side of the base film and includes composite particles. The composite particles include second inorganic particles and a plurality of non-fluoropolymer particles. The second inorganic particles are attached to the surface of the non-fluoropolymer particles and / or dispersed inside the non-fluoropolymer particles.

[0287] The first and second functional layers have good heat resistance, which can improve the heat resistance of the separator.

[0288] Optionally, the first functional layer may include an adhesive, optionally including at least one of a fluorinated adhesive or a polyacrylic adhesive, such as polyvinylidene fluoride.

[0289] Optionally, the first inorganic particles include one or more of silicon oxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide. These first inorganic particles can improve the heat resistance of the first functional layer.

[0290] Optionally, the average particle size of the first inorganic particles is 5 nm to 100 nm, optionally 10 nm to 100 nm, or optionally 5 nm to 20 nm. For example, the average particle size of the second inorganic particles is 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, or any combination of two of the above values. When the average particle size of the first inorganic particles is within the above range, it is beneficial to improve the heat resistance and compressive modulus of the composite particles.

[0291] In the embodiments of this application, the thickness of the base film has a meaning known in the art and can be detected using known meanings and equipment. For example, a newly prepared separator can be taken as a sample, or a battery cell that has been completely discharged (discharged to the lower limit cutoff voltage so that the battery's state of charge is about 0% SOC) can be disassembled in reverse, the separator can be obtained from the battery cell, and the separator can be dried and used as a sample. The separator can be cut with an ion beam cutter to form a cross section, and then the thickness of the separator and its various layers can be measured using a scanning electron microscope.

[0292] In the second functional layer, the non-fluorinated polymer particles refer to polymers that are non-fluorinated polymers. For example, non-fluorinated polymer particles include acrylate copolymers. Optionally, acrylate copolymers include acrylate-acrylonitrile-acrylamide-propylene copolymers. Acrylate copolymers have excellent adhesion properties and high adhesion stability to the base film. The molar ratio of each monomer in the copolymer can be arbitrary, for example, a molar ratio of 35%:30%:15%:20%, or 40%, 20%, 10%, 30%, or 45%, 15%, 20%, 20%, etc.

[0293] The second inorganic particle in the composite particles prevents the non-fluoropolymer particles from sticking together due to the high-temperature treatment during granulation. This creates porosity within the composite particles, facilitating lithium-ion transport and enhancing the ion-conductivity of the separator. Furthermore, the second inorganic particle increases the compressive modulus of the composite particles, reducing their deformation during charging and discharging, resulting in a more stable separator structure and improved kinetic performance of the battery cells, as well as faster charging performance. Optionally, compared to the first functional layer, the second functional layer is positioned closer to the negative electrode. Because the composite particles are less prone to deformation, the separator exerts minimal pressure or other side effects on the negative electrode, ensuring stable kinetic performance of the negative electrode. Correspondingly, the first functional layer is positioned closer to the positive electrode.

[0294] Optionally, the second inorganic particles include one or more of silicon oxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide; optionally, the second inorganic particles include silicon oxide. The aforementioned second inorganic particles can improve the heat resistance of the second functional layer and can combine with non-fluoropolymers to form composite particles, further improving the cycle stability and kinetic performance of the separator, and improving the cycle performance and fast-charging performance of the battery cells.

[0295] The average particle size of the second inorganic particles is 5 nm to 100 nm, optionally 10 nm to 100 nm, or optionally 5 nm to 20 nm. For example, the average particle size of the second inorganic particles is 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, or any combination of two of the above values. When the average particle size of the second inorganic particles is within the above range, it is beneficial to improve the heat resistance and compressive modulus of the composite particles.

[0296] In the embodiments of this application, the average particle size of the second inorganic particles has a meaning known in the art and can be detected using equipment and methods known in the art. For example, after obtaining the separator membrane and drying it as a sample, the separator membrane is cut with an ion beam cutter to form a cross-section. Subsequently, the particle size of the second inorganic particles in the separator membrane is measured using a scanning electron microscope. The particle size of multiple, for example, 50, second inorganic particles is measured, and their average value is calculated as the average particle size of the second inorganic particles.

[0297] In some implementations, the positive electrode, separator, and negative electrode can be fabricated into an electrode assembly using a winding process and / or a stacking process.

[0298] Figures 1 and 2 show schematic diagrams of the structure of a single battery cell.

[0299] In some embodiments, the battery cell 7 may include a housing 20.

[0300] The outer casing 20 can be of various shapes, such as a cylinder or a cuboid. The shape of the outer casing 20 can be determined according to the specific shape of the electrode assembly 10. For example, if the electrode assembly 10 is a cylindrical structure, the outer casing 20 can be a cylindrical structure. If the electrode assembly 10 is a cuboid structure, the outer casing 20 can be a cuboid structure. Optionally, the electrode assembly 10 can be a cuboid structure.

[0301] The outer casing 20 can be made of various materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, etc., and this application embodiment does not impose any special limitations on this. Optionally, the inner wall of the outer casing 20 may also include an insulating layer, which can separate the outer casing 20 from the electrode assembly 10. The material of the insulating layer can be selected from materials commonly used in the art, and is not particularly limited here.

[0302] The electrode assembly 10 housed within the housing 20 may be one or more.

[0303] In some embodiments, the housing 20 includes a housing 21 and an end cap 22, the housing 21 having an opening and the end cap 22 closing the opening, the housing 21 containing the electrode assembly 10 and the electrolyte.

[0304] In some embodiments, the casing 21 is made of steel, which has high mechanical strength, is not easily deformed, and can improve the reliability and cycle performance of the battery cells. Optionally, steel is the material with the highest mass percentage in the casing 21.

[0305] Optionally, the thickness of the casing 21 is 0.1 mm to 0.5 mm, and optionally 0.2 mm to 0.35 mm. For example, the thickness of the casing 21 is 0.1 mm, 0.15 mm, 0.2 mm, 0.25 mm, 0.3 mm, 0.35 mm, 0.4 mm, 0.45 mm, 0.5 mm, or any combination of two of the above values. When the thickness of the casing 21 is within the above range, the mechanical strength of the casing 21 is high, which can improve the reliability and cycle performance of the battery cell 7. Furthermore, the casing 21 occupies less space, and the internal space of the casing 21 is larger, which is beneficial to improving the energy density of the battery cell 7.

[0306] The following explanation will take the electrode assembly 10, which has a stacked structure, as an example.

[0307] As shown in Figures 2 and 3, the electrode assembly 10 includes a main body 14, a positive electrode tab 111, and a negative electrode tab 121, which protrude from the main body 14. The positive electrode tab 111 and the negative electrode tab 121 are used to draw out the current from the main body 14.

[0308] The portion of the positive electrode 11 without an active material layer is the positive electrode tab 111. The active material coated on the positive current collector 112 of the positive electrode 11 constitutes the positive electrode film layer 113. The positive electrode film layer 113 and the positive current collector 112 coated with active material are part of the main body 14.

[0309] The portion of the negative electrode sheet 12 that is not coated with an active material layer is the negative electrode tab 121. The active material coated on the negative electrode current collector 122 of the negative electrode sheet 12 constitutes the negative electrode film layer 123. The negative electrode film layer 123 and the negative electrode current collector 122 coated with active material are part of the main body 14.

[0310] The main body 14 may also include a separator 13, which is located between the positive electrode 11 and the negative electrode 12.

[0311] The positive electrode tab 111 and the negative electrode tab 121 can extend from the same side of the main body 14, or they can extend from opposite sides respectively.

[0312] In some embodiments, the positive electrode tab 111 is connected to at least one side of the positive current collector 112 along the length direction Z of the battery cell 7, and the negative electrode tab 121 is connected to at least one side of the negative current collector 122 along the length direction Z of the battery cell.

[0313] As shown in Figure 4, for example, the positive electrode tab 111 is connected to the positive current collector 112 on one side along the length direction Z of the battery cell 7.

[0314] As shown in Figure 5, for example, the positive electrode tab 111 is connected to both sides of the positive current collector 112 along the length direction Z of the battery cell 7.

[0315] As shown in Figure 6, for example, the negative electrode tab 121 is connected to the negative electrode current collector 122 on one side along the length direction Z of the battery cell 7.

[0316] As shown in Figure 7, for example, the negative electrode tab 121 is connected to both sides of the negative electrode current collector 122 along the length direction Z of the battery cell 7.

[0317] As shown in Figure 8, in some embodiments, the positive electrode tab 111 is connected to at least one side of the positive current collector 112 along the length direction Z, and the negative electrode tab 121 is connected to at least one side of the negative current collector 122 along the length direction Z. Along the length direction Z of the battery cell 7, the size of the negative electrode film layer 123 is larger than the size of the positive electrode film layer 113, and the size difference between the negative electrode film layer 123 and the positive electrode film layer 113 is OH1. Along the width direction Y of the battery cell 7, the size of the negative electrode film layer 123 is larger than the size of the positive electrode film layer 113, and the size difference between the negative electrode film layer 123 and the positive electrode film layer 113 is OH2, where OH1 is greater than OH2.

[0318] The negative electrode tab 121 is located on at least one side of the negative electrode current collector 122 along the length direction Z. The current density in the connection area between the negative electrode tab 121 and the negative electrode current collector 122 increases sharply, making it more prone to problems such as lithium plating. However, in the embodiment of this application, OH1 is set to be greater than OH2, which makes the ability of the negative electrode film layer 123 to receive lithium ions in the length direction Z stronger. In particular, it can improve the ability of the negative electrode film layer 123 to receive lithium ions in the area near the negative electrode tab 121, reduce the risk of lithium plating, and improve the reliability of the battery cell 7.

[0319] For example, OH1 is 1.0 mm to 4.0 mm, such as 1.0 mm, 1.2 mm, 1.5 mm, 1.8 mm, 2 mm, 2.2 mm, 2.5 mm, 2.8 mm, 3.0 mm, 3.5 mm, 4.0 mm, or any combination of two of the above values. Along the length direction Z, the negative electrode film layer 123 extends beyond the positive electrode film layer 113 on both sides, exceeding OH1 / 2 on each side, that is, half the size of OH1, as shown in Figure 8.

[0320] For example, OH2 is 1.0 mm to 3.0 mm, such as 1 mm, 1.2 mm, 1.5 mm, 1.8 mm, 2 mm, 2.2 mm, 2.5 mm, 2.8 mm, 3.0 mm, or any combination of two of the above values. Along the width direction Y, the negative electrode film layer 123 extends beyond the positive electrode film layer 113 on both sides, exceeding OH2 / 2 on each side, that is, half the size of OH2, as shown in Figure 8.

[0321] In other embodiments, the positive electrode tab 111 is connected to at least one side of the positive current collector 112 along the width direction Y, and the negative electrode tab 121 is connected to at least one side of the negative current collector 122 along the width direction Y.

[0322] Optionally, the number of positive electrode tabs 111 located on the same side of the main body 14 is at least one, and optionally at least two. At least two positive electrode tabs 111 can increase the current carrying capacity of the positive electrode tabs 111.

[0323] Optionally, the number of negative electrode tabs 121 located on the same side of the main body 14 is at least one, and optionally at least two. At least two negative electrode tabs 121 can increase the current carrying capacity of the negative electrode tabs 121.

[0324] In some embodiments, the battery cell 7 also includes a positive terminal 31, which is disposed on the housing 20 and may be disposed on the housing 21 or the end cap 22.

[0325] The positive terminal 31 is electrically connected to the positive electrode tab 111. Optionally, the positive terminal 31 and the positive electrode tab 111 are welded together. The positive terminal 31 and the positive electrode tab 111 can be connected by an adapter, or they can be connected without an adapter. Optionally, the positive terminal 31 and the positive electrode tab 111 are directly welded together without an adapter, which can reduce the resistance at the connection point and help reduce the overall internal resistance of the battery cell 7.

[0326] In some embodiments, the battery cell 7 also includes a negative terminal 32, which is disposed on the housing 20, and may be disposed on the housing 21 or the end cap 22.

[0327] The negative terminal 32 is electrically connected to the negative electrode tab 121. Optionally, the negative terminal 32 and the negative electrode tab 121 are welded together. The negative terminal 32 and the negative electrode tab 121 can be connected by an adapter, or they can be connected without an adapter. Optionally, the negative terminal 32 and the negative electrode tab 121 are directly welded together without an adapter, which can reduce the resistance at the connection point and help reduce the overall internal resistance of the battery cell 7.

[0328] Optionally, the number of positive terminals 31 located on the same side of the main body 14 is at least one, and optionally at least two. At least two positive terminals 31 can increase the current carrying capacity of the positive terminals 31.

[0329] Alternatively, the flow area of ​​the single-sided positive terminal 31 is 150 mm². 2 Up to 1000mm 2 200mm is optional 2 Up to 1000mm 2The current-carrying area of ​​a single positive terminal 31 refers to the sum of the current-carrying areas of all positive terminals 31 located on the same side of the main body 14. The current-carrying area of ​​a positive terminal 31 can be understood as the cross-sectional area of ​​the positive terminal 31, which is perpendicular to the thickness direction of the end cap 22. When the current-carrying area of ​​a single positive terminal 31 meets the above range, the current-carrying capacity is strong, which can reduce internal resistance and heat generation, and is beneficial to improving the fast charging performance and high-temperature cycling performance of the battery cell 7 at high energy density.

[0330] For example, the flow area of ​​the single-sided positive terminal 31 can be 150 mm². 2 200mm 2 210mm 2 250mm 2 280mm 2 300mm 2 320mm 2 350mm 2 380mm 2 400mm 2 450mm 2 500mm 2 550mm 2 600mm 2 650mm 2 700mm 2 750mm 2 800mm 2 850mm 2 900mm 2 950mm 2 1000mm 2 Or a range consisting of any two of the above values.

[0331] Optionally, the number of negative terminals 32 located on the same side of the main body 14 is at least one, and optionally at least two. At least two negative terminals 32 can increase the current carrying capacity of the negative terminals 32.

[0332] Alternatively, the flow area of ​​the single-sided negative terminal 32 is 150 mm². 2 Up to 1000mm 2 200mm is optional 2 Up to 1000mm 2The current-carrying area of ​​a single negative terminal 32 refers to the sum of the current-carrying areas of all negative terminals 32 located on the same side of the main body 14. The current-carrying area of ​​a negative terminal 32 can be understood as the cross-sectional area of ​​the negative terminal 32, which is perpendicular to the thickness direction of the end cap 22. When the current-carrying area of ​​a single negative terminal 32 meets the above range, the current-carrying capacity is strong, which can reduce internal resistance and heat generation, and is beneficial to improving the fast charging performance and high-temperature cycling performance of the battery cell 7 at high energy density.

[0333] For example, the flow area of ​​the single-sided negative terminal 32 can be 150 mm². 2 200mm 2 210mm 2 250mm 2 280mm 2 300mm 2 320mm 2 350mm 2 380mm 2 400mm 2 450mm 2 500mm 2 550mm 2 600mm 2 650mm 2 700mm 2 750mm 2 800mm 2 850mm 2 900mm 2 950mm 2 1000mm 2 Or a range consisting of any two of the above values.

[0334] As shown in Figure 9, the battery cell 7 of the present application embodiment can be assembled into a battery module 6. The number of battery cells 7 contained in the battery module 6 can be one or more, and the specific number can be adjusted according to the application and capacity of the battery module 6.

[0335] If there are multiple battery cells 7, they can be connected in series, parallel, or in a mixed configuration. A mixed configuration means that some battery cells 7 are connected in series while others are connected in parallel. Multiple battery cells 7 can be directly connected in series, parallel, or in a mixed configuration, and then the entire assembly of these battery cells 7 is housed within the housing of the battery module 6. Alternatively, multiple battery cells 7 can first be connected in series, parallel, or in a mixed configuration to form the battery module 6, and then the multiple battery modules 6 can be connected in series, parallel, or in a mixed configuration to form a whole, which is then housed within the housing. Optionally, the battery module 6 may also include a housing with a accommodating space, within which multiple battery cells 7 are housed.

[0336] Multiple battery cells 7 of the battery module 6 can be electrically connected through a busbar to achieve parallel, series, or mixed connection of the multiple battery cells 7 of the battery module 6. There can be one or more busbars, and each busbar is used to electrically connect at least two battery cells 7.

[0337] As shown in Figure 10, in some embodiments, the battery module 6 can also be assembled into a battery pack 2, and the number of battery modules 6 contained in the battery pack 2 can be adjusted according to the application and capacity of the battery pack. The battery device described herein can be a battery module 6, a battery pack 2, or a battery cell 7, with the battery cell 7 being the smallest unit constituting the battery device.

[0338] The battery pack 2 may include a housing 5 and a plurality of battery modules 6 disposed in the housing 5. The housing 5 includes a first housing portion 5a and a second housing portion 5b, and the housing 5 has a receiving space 5c. The first housing portion 5a is used to cover the second housing portion 5b and form a closed space for receiving the battery modules 6. The plurality of battery modules 6 can be arranged in the housing 5 in any manner.

[0339] The first housing portion 5a and the second housing portion 5b overlap each other, and together they define a receiving space 5c for accommodating a single battery cell. The second housing portion 5b can be a hollow structure with one open end, and the first housing portion 5a can be a plate-like structure. The first housing portion 5a covers the open side of the second housing portion 5b to form a housing 5 with the receiving space 5c. Alternatively, both the first housing portion 5a and the second housing portion 5b can be hollow structures with one open side, with the open side of the first housing portion 5a covering the open side of the second housing portion 5b to form a housing 5 with the receiving space 5c. Of course, the first housing portion 5a and the second housing portion 5b can be of various shapes, such as cylinders, cuboids, etc.

[0340] To improve the sealing performance after the first housing part 5a and the second housing part 5b are connected, a sealing element, such as sealant or sealing ring, can also be provided between the first housing part 5a and the second housing part 5b.

[0341] Assuming that the first box section 5a covers the top of the second box section 5b, the first box section 5a can also be called the upper box cover, and the second box section 5b can also be called the lower box.

[0342] In some embodiments, during the charging process of the battery pack 2 or any individual battery cell comprising the battery pack 2 from 0% state of charge (SOC) to 100% state of charge (SOC), the ambient temperature of the external environment in which the battery pack 2 is located is 30°C.

[0343] In some embodiments, during the charging process of the battery pack 2 or any individual battery cell comprising the battery pack 2 from 10% state of charge (SOC) to 80% SOC, the ambient temperature of the external environment in which the battery pack 2 is located is 30°C.

[0344] In some embodiments, the charging process of the battery pack 2 or any individual battery cell comprising the battery pack 2 from 10% state of charge to 80% state of charge includes multiple charging steps. The difference between the maximum state of charge of any charging step and the maximum state of charge of its adjacent charging step is less than or equal to 5% state of charge, such as 1% state of charge, 1.5% state of charge, 2% state of charge, 2.5% state of charge, 3% state of charge, 3.5% state of charge, 4% state of charge, 4.5% state of charge, 5% state of charge, or any range of any two of the above values.

[0345] The battery pack 2 or any individual battery cell comprising the battery pack 2 includes multiple charging steps from 10% state of charge to 40% state of charge. For any charging step, the battery can be charged at any rate between 4C and 10C. The charging rate corresponding to each charging step can be any value of 4C, 5C, 5.5C, 6C, 6.5C, 7C, 7.5C, 8C, 8.5C, 9C, 9.5C, or 10C, or a value within a range of any two of the above values.

[0346] For example, the charging steps from 10% to 80% for the battery pack 2 or any individual battery cell comprising the battery pack 2 can be performed as follows:

[0347] Charge from 10% SOC to 15% SOC at a constant current of 5.0C.

[0348] Charge from 15% SOC to 20% SOC at a constant current of 5.0C.

[0349] Charge from 20% SOC to 25% SOC at a constant current of 5.0C.

[0350] Charge from 25% SOC to 30% SOC at a constant current of 5.0C.

[0351] Charge from 30% SOC to 35% SOC at a constant current of 5.0C.

[0352] Charge from 35% SOC to 40% SOC at a constant current of 5.0C.

[0353] Charge from 40% SOC to 45% SOC at a constant current of 4.6C.

[0354] Charge from 45% SOC to 50% SOC at a constant current of 4.3C.

[0355] Charge from 50% SOC to 55% SOC at a constant current of 4.0C.

[0356] Charge from 55% SOC to 60% SOC at a constant current of 3.7C.

[0357] Charge from 60% SOC to 65% SOC at a constant current of 3.4C.

[0358] Charge from 65% SOC to 70% SOC at a constant current of 3.1C.

[0359] Charge from 70% SOC to 75% SOC at a constant current of 2.9C.

[0360] Charge from 75% SOC to 80% SOC at a constant current of 2.7C.

[0361] In some embodiments, the charging time for the battery pack 2 or any individual battery cell comprising the battery pack 2 from 10% state of charge to 80% state of charge is 5 min to 15 min, and the ambient temperature of the battery pack 2 at 10% state of charge is room temperature, for example, 30°C. Exemplarily, the charging time for the battery pack 2 from 10% state of charge to 80% state of charge is 15 min, 14 min, 13 min, 12 min, 11 min, 10 min, 9.5 min, 9 min, 8.5 min, 8 min, 7.5 min, 7 min, 6.5 min, 6 min, 5.5 min, 5 min, or a range of any two of the above values.

[0362] Electrical appliances

[0363] The second aspect of this application provides an electrical device, which includes a battery device as described in this application, such as a battery cell, battery module, or battery pack. The battery cell, battery module, or battery pack can be the power source of the electrical device or the energy storage unit of the electrical device. The electrical device can be a vehicle, mobile phone, portable device, laptop computer, ship, spacecraft, electric toy, and power tool, etc. Vehicles can be gasoline-powered vehicles, natural gas-powered vehicles, or new energy vehicles; new energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc.; spacecraft include airplanes, rockets, space shuttles, and spacecraft, etc.; electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc.; power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, etc. This application does not impose any special limitations on the above-described electrical device.

[0364] Electrical devices can be equipped with individual battery cells, battery modules, or battery packs depending on their usage requirements.

[0365] Figure 11 is a schematic diagram of an example electrical device 1. This electrical device 1 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of this electrical device 1, a battery pack or battery module can be used.

[0366] The electrical device 1 is equipped with a battery pack 2, which can be located at the bottom, head, or tail of the electrical device 1. The battery pack 2 can be used to supply power to the electrical device 1. For example, the battery pack 2 can serve as the operating power source for the electrical device 1, and can also serve as the driving power source for the electrical device 1, replacing or partially replacing fuel oil or natural gas to provide driving power for the electrical device 1.

[0367] Electrical device 1 may also include controller 3 and motor 4. Controller 3 is used to control battery pack 2 to supply power to motor 4, for example, to meet the power needs of electrical device 1 during startup, navigation and driving.

[0368] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0369] The following charging methods can be selected for the charging process of electrical devices:

[0370] Charge from 10% SOC to 15% SOC at a constant current of 5.0C.

[0371] Charge from 15% SOC to 20% SOC at a constant current of 5.0C.

[0372] Charge from 20% SOC to 25% SOC at a constant current of 5.0C.

[0373] Charge from 25% SOC to 30% SOC at a constant current of 5.0C.

[0374] Charge from 30% SOC to 35% SOC at a constant current of 5.0C.

[0375] Charge from 35% SOC to 40% SOC at a constant current of 5.0C.

[0376] Charge from 40% SOC to 45% SOC at a constant current of 4.6C.

[0377] Charge from 45% SOC to 50% SOC at a constant current of 4.3C.

[0378] Charge from 50% SOC to 55% SOC at a constant current of 4.0C.

[0379] Charge from 55% SOC to 60% SOC at a constant current of 3.7C.

[0380] Charge from 60% SOC to 65% SOC at a constant current of 3.4C.

[0381] Charge from 65% SOC to 70% SOC at a constant current of 3.1C.

[0382] Charge from 70% SOC to 75% SOC at a constant current of 2.9C.

[0383] Charge from 75% SOC to 80% SOC at a constant current of 2.7C.

[0384] In some embodiments, the charging time for the electrical device from 10% state of charge to 80% state of charge is 5 to 15 minutes, and the ambient temperature of the battery pack 2 at 10% state of charge is room temperature, for example, 30°C. Exemplarily, the charging time for the battery pack 2 from 10% state of charge to 80% state of charge is 15 minutes, 14 minutes, 13 minutes, 12 minutes, 11 minutes, 10 minutes, 9.5 minutes, 9 minutes, 8.5 minutes, 8 minutes, 7.5 minutes, 7 minutes, 6.5 minutes, 6 minutes, 5.5 minutes, 5 minutes, or a range of any two of the above values.

[0385] Example

[0386] The following embodiments describe the contents disclosed in this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of the embodiments of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0387] Example 1

[0388] 1. Preparation of positive electrode sheet

[0389] The positive electrode includes a positive current collector, a positive electrode film layer, and a positive electrode conductive layer. The positive electrode film layer is disposed on both sides of the positive current collector, and the positive electrode conductive layer is located between the positive current collector and the positive electrode film layer. The positive current collector is an aluminum foil.

[0390] The positive electrode conductive layer on the positive electrode current collector is a film formed by uniformly mixing the positive electrode conductive agent superconducting carbon, the positive electrode binder polyvinylidene fluoride PVDF, and the solvent N-methylpyrrolidone NMP, coating it on the surface of the positive electrode current collector, and drying it. The thickness is 1μm. The mass content of the positive electrode conductive agent in the positive electrode conductive layer is 40%, and the mass content of the positive electrode binder is 60%.

[0391] The positive electrode film layer comprises a film layer formed by uniformly coating a positive electrode slurry (solvent being N-methylpyrrolidone NMP) onto the surface of a positive electrode conductive layer, followed by drying and cold pressing. The positive electrode film layer comprises a positive electrode active material, a binder of polyvinylidene fluoride (PVDF), and a conductive agent of acetylene black in a weight ratio of 97:2:1.

[0392] The positive electrode active material includes lithium iron phosphate particles and a positive electrode coating layer. The positive electrode coating layer is coated on the surface of the lithium iron phosphate particles. The positive electrode coating layer includes lithium titanium iron phosphate (Li2FeTi(PO4)3) and carbon, with a carbon content of 1.12% by mass.

[0393] The compacted density of the positive electrode active material at 30000N is 2.55 g / cm³. 3 .

[0394] The single-sided coating weight of the positive electrode film is 263 mg / 1540.25 mm. 2 .

[0395] The positive electrode film has a length of 610 mm and a width of 110 mm.

[0396] 2. Preparation of negative electrode sheet

[0397] The negative electrode includes a negative current collector, a negative electrode film layer, and a negative electrode conductive layer. The negative electrode film layer is disposed on both sides of the negative current collector, and the negative electrode conductive layer is located between the negative current collector and the negative electrode film layer. The negative current collector is a copper foil.

[0398] The negative electrode conductive layer on the negative electrode current collector is a film formed by uniformly mixing the negative electrode conductive agent superconducting carbon, the negative electrode binder styrene-butadiene rubber SBR, the thickener sodium carboxymethyl cellulose CMC-Na, and the solvent water, coating it on the surface of the negative electrode current collector, and drying it. The thickness is 1μm. The mass content of the negative electrode conductive agent in the negative electrode conductive layer is 35%, the mass content of the negative electrode binder in the negative electrode conductive layer is 60%, and the mass content of the thickener in the negative electrode conductive layer is 5%.

[0399] The negative electrode film layer comprises a film layer formed by uniformly coating a negative electrode slurry (with deionized water as the solvent) onto the surface of a negative electrode conductive layer, followed by drying and cold pressing.

[0400] The negative electrode film layer comprises negative electrode active material (96.5:0.5:2:1 by mass), conductive agent acetylene black, negative electrode binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose. The graphite particles consist of artificial graphite and a negative electrode coating layer, with the negative electrode coating layer covering the surface of the artificial graphite. The carbon content of the negative electrode coating layer is 3.5% by mass. The Dv50 of the graphite particles is 11.3 μm.

[0401] The compacted density of the negative electrode active material at 20000N is 1.6 g / cm³. 3 .

[0402] The single-sided coating weight of the negative electrode film is 120 mg / 1540.25 mm. 2 .

[0403] The negative electrode film is 4 mm longer than the positive electrode film, and its width is 3 mm wider than the positive electrode film. After being fabricated into a battery cell, the negative electrode film was tested by disassembling the cell at 0% SOC, and the thickness of the negative electrode film was found to be 55 μm.

[0404] 3. Separating membrane

[0405] The separator includes a base membrane and functional layers disposed on both sides of the base membrane. The base membrane includes a 7μm polyethylene membrane layer with a porosity of 42%.

[0406] The functional layer includes a first functional layer and a second functional layer. The first functional layer includes alumina particles and polyvinylidene fluoride binder. The first functional layer is a film layer formed by coating a first slurry onto one side of the base film, with a thickness of 1 μm and an average particle size of 10 nm for the alumina particles. The first slurry includes alumina particles and polyvinylidene fluoride binder.

[0407] The second functional layer is a composite particle formed by polyacrylate and calcium oxide particles dispersed on the polyacrylate. The second functional layer is a film layer formed by coating the second slurry on the other side of the base film with a thickness of 5 μm and an average particle size of 10 nm for the calcium oxide particles. The second slurry includes composite particles.

[0408] 4. Preparation of electrolyte

[0409] The electrolyte consists of organic solvents, lithium salts, and additives.

[0410] The components of each organic solvent are mixed, and lithium salt and additives are added to prepare an electrolyte.

[0411] The organic solvents include 39% by mass of chain carboxylic acid ester solvents (ethyl acetate), 27.3% by mass of ethylene carbonate EC, and 11.7% by mass of dimethyl carbonate. The mass content of each component in the organic solvents is calculated based on the mass of the electrolyte.

[0412] The additive has a mass content of 6%, which includes vinylene carbonate (VC), 1,3-propanesulfonic acid lactone, fluoroethylene carbonate (FEC), vinyl sulfite (ES), and lithium difluorooxalate borate (LiDFOB) in a mass ratio of 4:0.2:0.8:0.5:0.5.

[0413] The lithium salt includes lithium hexafluorophosphate (LiPF6) with a mass content of 16%, and the mass content of the lithium salt is calculated based on the mass of the electrolyte.

[0414] 5. Preparation of battery cells

[0415] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrode to obtain a stacked electrode assembly. The electrode assembly is placed in a housing, with the positive and negative terminals set on the housing. After baking, electrolyte is injected. After vacuum sealing, settling, formation, aging, placement in a storage chamber, and shaping, a battery cell is obtained.

[0416] The electrolyte injection coefficient of the battery cell is 2.9 g / Ah.

[0417] The compaction density of the positive electrode film layer of the battery cell at 0% SOC is 2.70 g / cm³. 3 The compaction density of the negative electrode film at 0% SOC is 1.41 g / cm³. 3 .

[0418] The outer shell is a rectangular aluminum shell, and the thickness of the shell corresponding to the largest surface area of ​​the rectangular structure is 0.5mm.

[0419] The current-carrying area of ​​the positive terminal on the same side is 640 mm². 2 The current-carrying area of ​​the negative terminal on the same side is 640 mm². 2 .

[0420] Examples 2-2 to 2-11

[0421] Battery cells were prepared using a method similar to that of Example 1. The difference from Example 1 was that the components and content of the first additive were adjusted. Specifically, the mass content of dimethyl carbonate was adjusted accordingly based on the adjustment of the first additive. For example, if the mass content of the first additive increased by 1% compared to Example 1, then the mass content of dimethyl carbonate decreased by 1% compared to Example 1. See Table 1 for details.

[0422] Example 3

[0423] Battery cells were prepared using a method similar to that of Example 1. The difference from Example 1 was that the material of the ethylene carbonate derivative was adjusted, as shown in Table 1.

[0424] Comparative Examples 1-1 to 1-3

[0425] Battery cells were prepared using a method similar to that of Example 1. The difference from Example 1 was that the components and content of the first additive were adjusted. Specifically, the mass content of dimethyl carbonate was adjusted accordingly based on the adjustment of the first additive. For example, if the mass content of the first additive increased by 1% compared to Example 1, then the mass content of dimethyl carbonate decreased by 1% compared to Example 1. See Table 1 for details.

[0426] Performance testing

[0427] 1. DC internal resistance (DCR) test of individual battery cells

[0428] You can refer to the methods in GB / T 31467 "Performance Test Specification for High-Power Lithium-ion Power Batteries for HEVs".

[0429] For example, at room temperature, charge a single battery cell to 3.65V with a constant current of 0.33C, then charge it to 0.05C with a constant voltage of 3.65V, let it stand for 30 minutes, and discharge it to 2.0V with a constant current of 0.33C. Record the discharge capacity A0 at this point in Ah. Then charge it to 0.5A0Ah with a constant current of 0.33C and adjust the SOC to 50%.

[0430] After placing the battery cell at -20℃ for 2 hours, it was discharged at a constant current of 1C for 10 seconds, and ΔU was recorded. 放电 ΔI 放 电 The discharge DCR data of lithium-ion batteries can be calculated using the following formula, R. 放电 =ΔU 放电 / ΔI 放电 ,

[0431] Wherein, ΔU 放电 ΔI represents the voltage change within 10 seconds of the start of discharge. 放电 This indicates the current value within 10 seconds of the start of discharge.

[0432] 2. Number of cycles required for a single battery cell to reach 70% SOH

[0433] At 60℃, the battery cells are charged at a constant current of 0.8C to the charging cutoff voltage of 3.6V, then charged at a constant current of 0.1C to the charging cutoff voltage of 3.65V, and allowed to rest for 30 minutes; then discharged at a constant current of 1C to 2.83V, and allowed to rest for 30 minutes. This constitutes one charge-discharge cycle. The above charge-discharge cycle steps are repeated until the cycle capacity retention rate (i.e., Cn / C0×100%) is 70%, and the number of cycles is recorded. The more cycles, the better the cycle performance of the battery cell.

[0434] 3. Lithium plating test of individual battery cells

[0435] At 30°C, each battery cell of each embodiment was cycled 200 times according to its respective charge-discharge strategy, and then fully charged to 100% SOC according to the corresponding charging strategy. The negative electrode was then disassembled, unfolded, and the cleavage region (grayish-white area) was observed and the cleavage area was measured. The degree of cleavage is as follows:

[0436] No lithium plating: lithium plating area < 0.05%.

[0437] Slight lithium plating: lithium plating area <2% and ≥0.05%.

[0438] Severe lithium plating: lithium plating area ≥2%.

[0439] The charging process for individual battery cells includes the following steps:

[0440] Charge from 0% SOC to 5% SOC at a constant current of 5.0C;

[0441] Charge from 5% SOC to 10% SOC at a constant current of 5.0C;

[0442] Charge from 10% SOC to 15% SOC at a constant current of 5.0C;

[0443] Charge from 15% SOC to 20% SOC at a constant current of 5.0C;

[0444] Charge from 20% SOC to 25% SOC at a constant current of 5.0C;

[0445] Charge from 25% SOC to 30% SOC at a constant current of 5.0C;

[0446] Charge from 30% SOC to 35% SOC at a constant current of 5.0C;

[0447] Charge from 35% SOC to 40% SOC at a constant current of 5.0C;

[0448] Charge from 40% SOC to 45% SOC at a constant current of 4.6C;

[0449] Charge from 45% SOC to 50% SOC at a constant current of 4.3C;

[0450] Charge from 50% SOC to 55% SOC at a constant current of 4.0C;

[0451] Charge from 55% SOC to 60% SOC at a constant current of 3.7C;

[0452] Charge from 60% SOC to 65% SOC at a constant current of 3.4C;

[0453] Charge from 65% SOC to 70% SOC at a constant current of 3.1C;

[0454] Charge from 70% SOC to 75% SOC at a constant current of 2.9C;

[0455] Charge from 75% SOC to 80% SOC at a constant current of 2.7C;

[0456] Charge from 80% SOC to 85% SOC at a constant current of 1.8C;

[0457] Charge from 85% SOC to 90% SOC at a constant current of 1.3C;

[0458] Charge from 90% SOC to 95% SOC at a constant current of 0.7C;

[0459] Charge from 95% SOC to 98% SOC at a constant current of 0.33C;

[0460] Charge from 98% SOC to 100% SOC at a constant current of 0.1C.

[0461] The cutoff voltage for the final charging step in the above charging process is 3.65V.

[0462] The discharge strategy is as follows: discharge at a constant current of 0.33C until the cutoff voltage, for example, 2.0V.

[0463] In the above-mentioned charge and discharge test of battery cells, the battery cells can be assembled in the battery device, and the required charge and discharge strategy can be controlled by the battery management system for testing.

[0464] The test results are shown in Table 1.

[0465] Table 1

[0466] In Table 1,

[0467] VC stands for vinylene carbonate;

[0468] PS stands for 1,3-propanesulfonyl lactone;

[0469] FEC stands for fluoroethylene carbonate or fluoroethylene carbonate.

[0470] DFEC stands for difluoroethylene carbonate.

[0471] The amount of the first additive in the electrolytes of Comparative Examples 1-1 and 1-3 was too low. For example, the amount of vinylene carbonate was too low, and the electrolytes of Comparative Examples 1-3 did not even contain vinylene carbonate. Although the impedance of the SEI film on the negative electrode side was relatively low, the relatively poor protective effect of the SEI film made it easy for carboxylic acid ester solvents to react with the negative electrode active material at high temperatures, which worsened the high-temperature cycle and may have triggered lithium plating.

[0472] The amount of the first additive in the electrolyte of Comparative Examples 1-2 was too high. For example, the amount of vinylene carbonate was too high. Vinylene carbonate can form a dense SEI film of organic components on the negative electrode side, which can alleviate the side reactions of carboxylic acid ester solvents and negative electrode active materials. However, due to the high impedance of the SEI film, it is not conducive to the rapid migration of lithium ions, so that the battery cells cannot be charged quickly.

[0473] In this embodiment, the amount of the first additive in the electrolyte is within an appropriate range, with a mass content of 3% to 10%. The reaction potentials of the vinylene carbonate and carboxylic acid ester solvents in the first additive are close, and they compete for reaction with the carboxylic acid ester solvents. The vinylene carbonate can participate in the formation of a dense SEI film on the negative electrode side, making it difficult for the carboxylic acid ester solvent to penetrate the SEI film to the graphite particles. This alleviates the side reaction between the carboxylic acid ester solvent and the graphite particles and reduces the amount of gas produced. Moreover, since the first additive is in an appropriate content, the film impedance formed on the negative electrode side is relatively small, which is beneficial to improving high-temperature cycling performance and reducing the risk of lithium plating.

[0474] Example 2-2: The electrolyte components were analyzed to obtain the data in Table 1. In this case, the battery cells had not yet undergone the formation process. After the electrolyte components were tested and analyzed, they were assembled into battery cells and then their performance was tested. It should be noted that Example 2-2 used the electrolyte of the unformed battery cells as a sample, and the mass content of each component in the first additive was calculated with the mass of the electrolyte as 100%.

[0475] Example 2-1 analyzed the free electrolyte in the battery cells after processing such as formation, aging, and storage, and obtained the data in Table 1. The composition of the fresh electrolyte of the battery cells is shown in Example 2-2. As can be seen from the data in Table 1, after the formation process, vinylene carbonate, 1,3-propanesulfonic acid lactone, and fluoroethylene carbonate are all consumed and participate in the film formation reaction of the SEI film on the negative electrode side, which can obtain an SEI film with relatively low impedance, improve the fast charging performance, high temperature cycle performance, and reliability of the battery cells.

[0476] It should be noted that in Example 2-1, the free electrolyte of the battery cell after processing such as formation was used as a sample, and the mass content of each component in the first additive was calculated with the mass of the electrolyte as 100%.

[0477] Examples 2-3 to 2-5 show that by controlling the mass content of vinylene carbonate, 1,3-propanesulfonic acid lactone, and fluoroethylene carbonate in the freshly prepared electrolyte, an SEI film with relatively low impedance can be obtained, which improves the fast charging performance, high-temperature cycling performance, and reliability of the battery cell.

[0478] Examples 2-6, 2-7, and 2-11, by controlling the mass content of 1,3-propanesulfonate lactone, show that increasing the mass content of 1,3-propanesulfonate lactone optimizes the composition of the SEI film, improves its protective effect, and enhances high-temperature cycling performance. However, the impedance of the SEI film also increases appropriately, which may slightly reduce the fast-charging performance of the battery cell. Therefore, the mass content of 1,3-propanesulfonate lactone is 0 to 0.5%, preferably 0.05% to 0.5%, to balance improving both the high-temperature cycling performance and fast-charging performance of the battery cell.

[0479] Examples 1, 2-8 to 2-11, by controlling the mass content of fluoroethylene carbonate, show that increasing the mass content of fluoroethylene carbonate optimizes the composition of the SEI film, reduces its impedance, facilitates rapid lithium-ion migration, and improves the fast-charging performance of the battery cell. However, at high temperatures, fluoroethylene carbonate exhibits poor stability and easily decomposes to produce acid, damaging the SEI film and worsening the protection of the negative electrode active material, potentially leading to a slight deterioration in high-temperature cycling performance. Therefore, the mass content of the ethylene carbonate derivative in the electrolyte is 0 to 3.5%, preferably 0.1% to 1.5%, and further preferably 0.5% to 1.5%, to balance the improvement of both high-temperature cycling performance and fast-charging performance of the battery cell.

[0480] Using ethylene carbonate derivatives of different materials, such as fluoroethylene carbonate and difluoroethylene carbonate, can effectively improve the high-temperature cycle performance and fast charging performance of battery cells.

[0481] Examples 4-1 and 4-2

[0482] Battery cells were prepared using a method similar to that of Example 1, except that the composition and mass content of the carboxylic acid ester solvent and the carbonate solvent were adjusted.

[0483] In Example 4-1, the content of ethylene carbonate was 3%, 1,3-propanesulfonic acid lactone was 0.5%, fluoroethylene carbonate (FEC) was 1.5%, and the mass content of the first additive was 5%.

[0484] In Example 4-2, the content of ethylene carbonate was 3%, 1,3-propanesulfonic acid lactone was 0.5%, fluoroethylene carbonate (FEC) was 1.5%, and the mass content of the first additive was 5%.

[0485] The details are shown in Table 2.

[0486] Example 5

[0487] Battery cells were prepared using a method similar to that in Example 1, except that the material of the carboxylic acid ester solvent and the mass content of the carbonate solvent were adjusted.

[0488] In Example 5, the content of ethylene carbonate was 6%, 1,3-propanesulfonic acid lactone was 0.5%, fluoroethylene carbonate (FEC) was 1.5%, and the mass content of the first additive was 8.0%.

[0489] The details are shown in Table 2.

[0490] Examples 6-1 to 6-3

[0491] Battery cells were prepared using a method similar to that of Example 1. The difference from Example 1 was that the composition and mass content of the second additive were adjusted. Specifically, the mass content of dimethyl carbonate was adjusted accordingly based on the additive. For example, if the mass content of the additive increased by 1% compared to Example 1, then the mass content of dimethyl carbonate decreased by 1% compared to Example 1. See Table 2 for details.

[0492] Comparative Examples 2-1 to 2-2

[0493] Battery cells were prepared using a method similar to that of Example 1. The difference from Example 1 was that the composition and mass content of the carboxylic acid ester solvent and the carbonate solvent were adjusted. Specifically, the mass content of dimethyl carbonate was adjusted accordingly based on the addition of additives. For example, if the mass content of the additives increased by 1% compared to Example 1, then the mass content of dimethyl carbonate would decrease by 1% compared to Example 1. Details are shown in Table 2.

[0494] The test results are shown in Table 2.

[0495] Table 2

[0496] In Table 2, EA represents ethyl acetate; MA represents methyl acetate.

[0497] EC represents ethylene carbonate; DMC represents dimethyl carbonate.

[0498] ES stands for vinyl sulfite;

[0499] DTD stands for vinyl sulfate;

[0500] LiDFOB represents lithium difluorooxalate borate;

[0501] LiPO2F2 represents lithium difluorophosphate;

[0502] EC:27.3 indicates that the mass content of EC is 27.3%.

[0503] The meanings of the other examples are explained in the same way as above, and will not be repeated here.

[0504] The electrolyte in Comparative Example 2-1 has a relatively low mass content of carboxylic acid ester solvents, resulting in higher electrolyte viscosity and impedance. This also hinders rapid wetting of the electrode, leading to varying wettability at different points on the electrode and resulting in different degrees of electrode discharge. This may cause localized lithium plating on the negative electrode side and deteriorate the cycle.

[0505] The electrolyte in Comparative Example 2-2 has a relatively high mass content of carboxylic acid ester solvents, which results in lower electrolyte viscosity and lower impedance, which is beneficial for fast charging. However, at high temperatures, the side reactions between carboxylic acid ester solvents and negative electrode active materials are more severe, which deteriorates the high-temperature cycling performance and may lead to lithium deposition on the negative electrode side.

[0506] Because the carboxylic acid ester solvent in Example 4-1 has a relatively low mass content, the migration rate of lithium ions in the electrolyte is slow, resulting in a slight risk of lithium plating at a given current density. Increasing the mass content of the carboxylic acid ester solvent can reduce the viscosity of the electrolyte and improve the migration rate of lithium ions. Furthermore, when combined with an appropriate amount of the first additive, it can mitigate side reactions, improve high-temperature cycling, and reduce the risk of lithium plating.

[0507] Examples 4-1 and 4-2 of this application, by adjusting the mass content of carboxylic acid ester solvent within an appropriate range, such as 8% to 60%, can reduce the viscosity of the electrolyte and increase the migration rate of lithium ions in the electrolyte; and when combined with an appropriate amount of the first additive, it can alleviate side reactions, improve high-temperature cycling, and reduce the risk of lithium plating.

[0508] Carboxylic acid ester solvents, using different materials such as ethyl acetate and methyl acetate, can improve fast charging performance and high-temperature cycling performance. For example, the carboxylic acid ester solvent in Example 5 includes methyl acetate, which, combined with a high content of the first additive, can improve the film-forming performance of the SEI film while reducing the electrolyte viscosity, reducing the internal resistance of the battery cell, and improving the fast charging performance of the battery cell. Furthermore, since the SEI film can effectively protect the negative electrode active material, it can alleviate side reactions and improve high-temperature cycling performance. However, because ethyl acetate has a relatively high boiling point and relatively good stability at high temperatures, the high-temperature cycling performance of Example 1 is superior to that of Example 5.

[0509] Examples 6-1 to 6-3 use second additives of different materials, which can further optimize the composition of the SEI film, reduce the internal resistance of the battery cells, and improve the fast charging performance and high-temperature cycling performance of the battery cells.

[0510] Examples 7-1 and 7-2

[0511] Battery cells were prepared using a method similar to that of Example 1. The difference from Example 1 was that the thickness of the negative electrode film on one side was adjusted, as shown in Table 3.

[0512] Examples 8-1 and 8-2

[0513] Battery cells were prepared using a method similar to that in Example 1. The difference from Example 1 was that the volume average particle size of the graphite particles in the negative electrode film was adjusted, as shown in Table 3.

[0514] Example 9

[0515] Battery cells were prepared using a method similar to that in Example 1. The difference from Example 1 was that the composition of the negative electrode active material in the negative electrode film was adjusted. The negative electrode active material also included silicon oxide, a silicon-based material, and the mass content of silicon in the negative electrode film was 1.5%.

[0516] Comparative Example 3-1 and Comparative Example 3-2

[0517] Battery cells were prepared using a method similar to that of Example 1. The difference from Example 1 was that the thickness of the negative electrode film on one side was adjusted, as shown in Table 3.

[0518] Comparative Examples 3-3 and 3-4

[0519] Battery cells were prepared using a method similar to that in Example 1. The difference from Example 1 was that the volume average particle size of the graphite particles in the negative electrode film was adjusted, as shown in Table 3.

[0520] The test results are shown in Table 3.

[0521] Table 3

[0522] The thickness of the single-sided negative electrode film in Comparative Example 3-1 is relatively thin, resulting in a shorter lithium-ion transport path. This helps reduce the internal resistance of the battery cell and improve fast charging performance; however, the energy density of the battery cell is low, which may not meet the energy density requirements.

[0523] The thickness of the single-sided negative electrode film in Comparative Example 3-2 is relatively thick, and the energy density of the battery cell is relatively high. However, this results in a longer lithium-ion transport path and higher internal resistance of the battery cell, which is not conducive to fast charging and high-temperature cycling at high energy density.

[0524] The negative electrode film thicknesses of Examples 1, 7-1, and 7-2 are moderate, enabling the battery cell to balance high energy density and a short lithium-ion migration path, thus improving the fast-charging performance of the battery cell. Furthermore, the appropriate amounts of carboxylic acid ester solvents and the first additive effectively further improve the fast-charging performance and high-temperature cycling performance of the battery cell at high energy densities. Specifically, the energy density of Example 1 is 410 Wh / L.

[0525] The graphite particles in Comparative Example 3-3 have a relatively small volume average particle size, resulting in a shorter lithium-ion transport path in the solid phase, which is beneficial for improving the fast charging performance of the battery cells. However, the graphite particles have a relatively large number of active surfaces, which exacerbates side reactions and worsens high-temperature cycling.

[0526] The graphite particles in Comparative Examples 3-4 have a relatively large volume average particle size, relatively few active surfaces, relatively few side reactions, and excellent high-temperature cycling performance; however, the lithium ion transport path in the solid phase is relatively long, which is not conducive to the fast charging performance of the battery cells.

[0527] The graphite particles in Examples 8-1 and 8-2 have a moderate volume average particle size, which can shorten the lithium-ion solid-phase transport path while reducing the degree of side reactions, thus improving the fast charging capability and high-temperature cycling performance of the battery cells.

[0528] The negative electrode film layer of Example 9 also includes silicon element with a mass content of 1.5%. Silicon element can effectively improve the energy density of the battery cell; however, due to the large volume expansion of silicon-based materials during the charging and discharging process, the side reactions on the negative electrode side are more than those in Example 1, and the high-temperature cycling is slightly worse.

[0529] When the negative electrode film layer includes silicon-based materials under the preset high energy density, a relatively thin negative electrode film layer can be used, which can shorten the migration path of lithium ions and improve the fast charging capability.

[0530] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the present application, and that changes, substitutions and modifications can be made to the embodiments without departing from the spirit, principles and scope of the present application.

Claims

1. A battery cell, comprising an electrode assembly and an electrolyte, wherein the electrode assembly comprises a positive electrode and a negative electrode; The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector, the positive electrode film layer including a lithium phosphate with an olivine structure; The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector, the negative electrode film layer including graphite particles; The electrolyte comprises a carboxylic acid ester solvent and a first additive. in, The thickness of the negative electrode film layer on one side is 50 μm to 75 μm, and the volume average particle size of the graphite particles is 8.5 μm to 13.5 μm; Based on the mass of the electrolyte, the mass content of the carboxylic acid ester solvent is 8% to 60%. Based on the mass of the electrolyte, the total mass content of the first additive is 3% to 10%, and the first additive includes 1,3-propanesulfonic acid lactone with a mass content ≥0, ethylene carbonate derivative with a mass content ≥0, and vinylene carbonate with a mass content ≥3%, wherein the ethylene carbonate derivative includes compounds represented by Formula A. In Formula A, Q1, Q2, Q3 and Q4 each independently include any one of hydrogen atoms, halogen atoms, C1 to C5 alkyl groups, or C1 to C5 haloalkyl groups, and Q1, Q2, Q3 and Q4 are not all hydrogen atoms at the same time.

2. The battery cell according to claim 1, wherein, The mass content of the first additive is 3.5% to 8%.

3. The battery cell according to claim 1 or 2, wherein, The vinylene carbonate content in the electrolyte is 3% to 8% by mass.

4. The battery cell according to any one of claims 1 to 3, wherein, The 1,3-propanesulfonate lactone has a mass content of 0 to 0.5% in the electrolyte.

5. The battery cell according to claim 4, wherein, The 1,3-propanesulfonic acid lactone is present in the electrolyte at a mass content of 0.05% to 0.5%.

6. The battery cell according to any one of claims 1 to 5, wherein, The ethylene carbonate derivative has a mass content of 0 to 3.5% in the electrolyte.

7. The battery cell according to claim 6, wherein, The ethylene carbonate derivative is present in the electrolyte at a mass content of 0.5% to 1.5%.

8. The battery cell according to any one of claims 1 to 7, wherein, At least one of Q1, Q2, Q3 and Q4 includes a halogen atom or a C1 to C5 haloalkyl group.

9. The battery cell according to any one of claims 1 to 8, wherein, The ethylene carbonate derivatives include at least one compound represented by formula A-1 to formula A-3.

10. The battery cell according to any one of claims 1 to 9, wherein, The carboxylic acid ester solvents include compounds represented by Formula I. In formula I, R1 includes a hydrogen atom, a C1 to C5 alkyl group, or a C1 to C5 haloalkyl group. R2 includes C1 to C5 alkyl or C1 to C5 haloalkyl.

11. The battery cell according to claim 10, wherein, The carboxylic acid ester solvents include one or more of the compounds shown in Formula I-1 to Formula I-12.

12. The battery cell according to any one of claims 1 to 11, wherein, The electrolyte also includes a carbonate solvent, wherein the carbonate solvent comprises 18% to 70% by mass in the electrolyte.

13. The battery cell according to claim 12, wherein, The carbonate solvent includes cyclic carbonates, which include one or more of ethylene carbonate, propylene carbonate, and butenyl carbonate; and / or, The carbonate solvents include chain carbonates, which include one or more of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

14. The battery cell according to any one of claims 1 to 13, wherein, The electrolyte includes a sulfur-containing additive at a mass content of 0 to 2%, wherein the sulfur-containing additive includes one or more of vinyl sulfate, vinyl disulfate, butene sulfite, vinyl sulfite, and methylene disulfonate; and / or The electrolyte includes lithium salt additives in a mass content of 0 to 1%, wherein the lithium salt additives include one or more of lithium difluorophosphate, lithium difluorooxalate borate, lithium tetrafluoroborate, and lithium dioxalate borate.

15. The battery cell according to claim 14, wherein, The sulfur-containing additive has a mass content of 0.5% to 2%; and / or the lithium salt additive has a mass content of 0.2% to 1%.

16. The battery cell according to any one of claims 1 to 15, wherein, The thickness of the negative electrode film on one side is 50 μm to 65 μm.

17. The battery cell according to any one of claims 1 to 16, wherein, The graphite particles have a volume average particle size of 9.5 μm to 13 μm.

18. The battery cell according to any one of claims 1 to 17, wherein, The graphite particles include graphite body particles and a negative electrode coating layer covering the surface of the graphite body particles. The graphite body particles include secondary particles, and the negative electrode coating layer includes carbon elements.

19. The battery cell according to claim 18, wherein, The graphite bulk particles include at least one of artificial graphite and natural graphite.

20. The battery cell according to claim 18 or 19, wherein, Based on the total mass of the graphite particles, the carbon content of the negative electrode coating layer is 2% to 5% by mass.

21. The battery cell according to any one of claims 1 to 20, wherein, The negative electrode film layer also includes a silicon-based material, wherein the silicon content of the silicon element in the negative electrode film layer is 0.3% to 5% by mass.

22. The battery cell according to any one of claims 1 to 21, wherein, The compacted density of the negative electrode active material at 20000N is 1.4 g / cm³. 3 Up to 1.8 g / cm 3 .

23. The battery cell according to any one of claims 1 to 22, wherein, When the battery cell is at 0% charge, the compaction density of the negative electrode film is 1.30 g / cm³. 3 Up to 1.55 g / cm 3 , and / or The single-sided coating weight of the negative electrode film is 90 mg / 1540.25 mm. 2 Up to 140mg / 1540.25mm 2 .

24. The battery cell according to any one of claims 1 to 23, wherein, The negative electrode sheet further includes a negative electrode conductive layer, which is located between the negative electrode current collector and the negative electrode film layer. The negative electrode conductive layer includes a negative electrode conductive agent, which includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

25. The battery cell according to claim 24, wherein, The thickness of the negative electrode conductive layer is 0.5 μm to 2 μm.

26. The battery cell according to any one of claims 1 to 25, wherein, The thickness of the positive electrode film on one side is 50 μm to 65 μm.

27. The battery cell according to any one of claims 1 to 26, wherein, The positive electrode and the negative electrode are stacked along the thickness direction of the battery cell, and the positive electrode film has a dimension of 200mm to 650mm along the length direction of the battery cell.

28. The battery cell according to any one of claims 1 to 27, wherein, The lithium phosphate with the olivine structure includes: Phosphate particles, and A positive electrode coating layer is located on at least a portion of the surface of the phosphate particles, and the positive electrode coating layer contains carbon.

29. The battery cell according to claim 28, wherein, Based on the mass of the lithium phosphate containing the olivine structure, the carbon content is from 0.8% to 2.3% by mass.

30. The battery cell according to claim 28 or 29, wherein, The positive electrode coating layer also includes one or more elements such as Fe, Ti, Zr, Hf, Ge, and Sn.

31. The battery cell according to any one of claims 28 to 30, wherein, The phosphate particles include one or more of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium nickel phosphate, and lithium cobalt phosphate.

32. The battery cell according to any one of claims 1 to 31, wherein, The lithium-containing phosphate includes those with the general formula Li x1 A y1 Me a1 M b1 P 1-c1 X c1 Y z1 compounds, Wherein, 0.5≤x1≤1.3, 0≤y1≤1.3, 0.5≤x1+y1≤1.3, 0.9≤a1≤1.5, 0≤b1≤0.5, 0.9≤a1+b1≤1.5, 0≤c1≤0.5, 3≤z1≤5, A includes at least one of Na, K, and Mg; Me includes at least one of Mn, Fe, Co, and Ni; M includes at least one of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X includes at least one of Cl, C, and N; Y includes at least one of O and F.

33. The battery cell according to any one of claims 1 to 32, wherein, The compacted density of the positive electrode active material at 30000N is 2.43 g / cm³. 3 Up to 2.85 g / cm 3 .

34. The battery cell according to any one of claims 1 to 33, wherein, When the battery cell is at 0% SOC, the compaction density of the positive electrode film is 2.46 g / cm³. 3 Up to 2.80 g / cm 3 ; and / or The single-sided coating weight of the positive electrode film is 200 mg / 1540.25 mm. 2 Up to 350mg / 1540.25mm 2 .

35. The battery cell according to any one of claims 1 to 34, wherein, The positive electrode sheet further includes a positive conductive layer, which is located between the positive current collector and the positive film layer. The positive conductive layer includes a positive conductive agent, which includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

36. The battery cell according to claim 35, wherein, The thickness of the positive electrode conductive layer is 0.5 μm to 2 μm.

37. The battery cell according to any one of claims 1 to 36, wherein, The electrode assembly further includes a separator membrane located between the positive electrode and the negative electrode. The separator membrane includes a base film with a thickness of 4 μm to 12 μm and / or a porosity of 20% to 70%.

38. The battery cell according to claim 37, wherein, The isolation membrane further includes a functional layer disposed on at least one side of the base membrane, the functional layer comprising: A first functional layer is located on one side of the base film, and the first functional layer includes first inorganic particles. The second functional layer is located on the other side of the base film. The second functional layer includes composite particles, which include second inorganic particles and a plurality of non-fluoropolymer particles. The second inorganic particles are attached to the surface of the non-fluoropolymer particles and / or dispersed inside the non-fluoropolymer particles.

39. The battery cell according to claim 38, wherein, The non-fluoropolymer particles include acrylate copolymers.

40. The battery cell according to claim 38 or 39, wherein, The first inorganic particles include one or more of silicon oxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide; and / or the average particle size of the first inorganic particles is 5 nm to 100 nm.

41. The battery cell according to any one of claims 38 to 40, wherein, The second inorganic particles include one or more of silicon oxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide, and / or The average particle size of the second inorganic particle is 5 nm to 100 nm.

42. The battery cell according to any one of claims 1 to 41, wherein, The positive electrode and the negative electrode are stacked along the thickness direction of the battery cell; The electrode assembly further includes a positive electrode tab and a negative electrode tab, wherein the positive electrode tab is connected to at least one side of the positive current collector along the length direction of the battery cell, and the negative electrode tab is connected to at least one side of the negative current collector along the length direction of the battery cell. Along the length of the battery cell, the size of the negative electrode film is larger than the size of the positive electrode film, and the size difference between the negative electrode film and the positive electrode film is OH1; Along the width direction of the battery cell, the size of the negative electrode film is larger than the size of the positive electrode film, and the difference between the size of the negative electrode film and the size of the positive electrode film is OH2, wherein OH1 is greater than OH2.

43. The battery cell according to claim 42, wherein, OH1 is 1.0 mm to 4.0 mm; and / or OH2 is 1.0 mm to 3.0 mm.

44. The battery cell according to any one of claims 1 to 43, wherein the battery cell further comprises at least one positive terminal, and the current-passing area of ​​all the positive terminals located on the same side of the positive current collector is 150 mm². 2 Up to 1000mm 2 ; and / or The battery cell also includes at least one negative terminal, and the current-passing area of ​​all the negative terminals located on the same side of the negative current collector is 150 mm². 2 Up to 1000mm 2 .

45. The battery cell according to any one of claims 1 to 44, the battery cell comprising a housing that houses the electrode assembly and the electrolyte, the housing having a thickness of 0.1 mm to 0.5 mm.

46. ​​A battery device comprising a battery cell according to any one of claims 1 to 45.

47. The battery device according to claim 46, wherein, The battery device is configured to charge from 10% to 80% state of charge in 5 to 15 minutes.

48. An electrical device comprising the battery device as described in claim 46 or 47.

Images