Battery cells, battery devices and power-consuming devices

Abstract

The present application discloses a battery cell, a battery device and an electric device. The positive electrode active material of the positive electrode sheet of the battery cell includes a lithium-containing phosphate with an olivine structure, and the single-sided coating weight of the positive electrode film layer is 180mg / 1540.25mm 2 Up to 380mg / 1540.25mm 2 The negative electrode sheet includes a negative electrode film layer, the negative electrode film layer includes a negative electrode active material, the negative electrode active material includes a silicon-based material, and the mass content of silicon element is 0.3% to 10.0% based on the mass of the negative electrode active material; the electrolyte includes a first additive, the first additive includes at least one of vinylene carbonate and an ethylene carbonate derivative, and the mass content of the first additive is 1% to 12% based on the total mass of the electrolyte; the battery cell is 100% charged, and the compaction density of the positive electrode film layer is 2.50g / cm 3 ~2.80g / cm 3 .

Description

[0001] This application claims priority to PCT international application PCT / CN2024 / 125833, entitled “Batteries and Electrical Devices,” filed on October 18, 2024, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to a battery cell, a battery device and an electrical device. Background Art

[0003] Lithium-ion batteries, with their high capacity and long lifespan, are widely used in electronic devices such as mobile phones, laptops, electric bicycles, electric cars, electric aircraft, electric ships, and power tools. With the development of lithium-ion battery applications, higher requirements are being placed on lithium-ion battery performance, such as fast charging performance and energy density. Summary of the Invention

[0004] In view of the above problems, the present application provides a battery cell, a battery device and an electrical device, which can improve the energy density of the battery cell while also taking into account good cycle performance and fast charging performance (referred to as fast charging performance).

[0005] In a first aspect, the present application provides a battery cell, comprising an electrode assembly and an electrolyte, wherein the electrode assembly comprises a positive electrode sheet, a negative electrode sheet, and a separator, wherein the separator is located between the positive electrode sheet and the negative electrode sheet.

[0006] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one side of the positive electrode current collector. The positive electrode film layer includes a positive electrode active material. The positive electrode active material includes a lithium-containing phosphate with an olivine structure.

[0007] The single-sided coating weight of the positive electrode film is 180mg / 1540.25mm 2 ~380mg / 1540.25mm 2 ;

[0008] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one side of the negative electrode current collector, the negative electrode film layer includes a negative electrode active material, the negative electrode active material includes a silicon-based material, and the mass content of silicon element is 0.3% to 10.0% based on the mass of the negative electrode active material;

[0009] The electrolyte includes a first additive, the first additive includes at least one of vinylene carbonate and an ethylene carbonate derivative, and the mass content of the first additive is 1% to 12% based on the total mass of the electrolyte.

[0010] Among them, the ethylene carbonate derivatives include compounds shown in formula I,

[0011] Formula I

[0012] R1, R2, R3, and R4 each independently include any one of a hydrogen atom, a halogen atom, a C1-C5 alkyl group, and a C1-C5 halogenated alkyl group, and R1, R2, R3, and R4 are not hydrogen atoms at the same time.

[0013] In the present application, the positive electrode active material of the battery cell comprises an olivine-structured lithium phosphate having excellent structural stability. By matching the positive electrode film layer with a high coating weight with the negative electrode film layer containing a certain amount of silicon element, the fast charging performance of the battery cell can be effectively improved while ensuring that the energy density of the battery cell is improved; at the same time, the electrolyte of the battery cell contains a first additive of vinylene carbonate and / or ethylene carbonate derivatives, and the mass content of the first additive is controlled within an appropriate range, so that a SEI film with moderate thickness, enhanced flexibility and stability can be formed at the silicon-containing negative electrode interface, ensuring that the silicon-containing negative electrode interface has both good stability and low impedance, thereby achieving a battery cell with high energy density, excellent fast charging performance and good cycle performance.

[0014] In summary, the present application can achieve a balance between fast charging performance, cycle performance and energy density of the battery cell by synergistically controlling the single-sided coating weight of the positive electrode film layer, the mass content of the silicon element in the negative electrode active material, the positive electrode active material containing olivine structure lithium phosphate, and the type and mass content of additives in the electrolyte within an appropriate range.

[0015] In any embodiment, the mass content of silicon is 0.3% to 6.0% based on the mass of the negative electrode active material.

[0016] The mass content of silicon in silicon-based materials is within an appropriate range, which can increase the energy density of battery cells while reducing the impact of excessive silicon on the cycle performance of battery cells, thus taking into account both the energy density and cycle performance of battery cells.

[0017] In any embodiment, at least one of R1, R2, R3, and R4 contains a fluorine atom.

[0018] The ethylene carbonate derivative in which at least one of R1, R2, R3, and R4 is a fluorine atom is easy to open the ring, forming a SEI film containing more organic matter on the surface of the negative electrode, which is beneficial to improving the flexibility of the overall SEI film, achieving the purpose of improving the stability of the interface between the SEI film and the negative electrode during the cycle, and improving the cycle performance of the battery cell.

[0019] In any embodiment, the ethylene carbonate derivative includes one or more of fluoroethylene carbonate, difluoroethylene carbonate, and trifluoromethylethylene carbonate.

[0020] Suitable ethylene carbonate derivative additives can form a SEI film containing more organic matter on the negative electrode side, which is beneficial to improving the flexibility of the overall SEI film, achieving the purpose of improving the stability of the SEI film and the negative electrode interface during the cycle, and improving the cycle performance of the battery cell. At the same time, the SEI film formed with the participation of fluoroethylene carbonate, difluoroethylene carbonate, and trifluoromethylethylene carbonate has low impedance, which is also beneficial to improving the fast charging performance of the battery cell.

[0021] In any embodiment, the battery cell satisfies the following relationship: 0.025≤A / B≤6, optionally 0.035≤A / B≤2.5,

[0022] Wherein A is the mass content of silicon element, based on the mass of negative electrode active material; B is the mass content of the first additive, based on the total mass of electrolyte.

[0023] The ratio of the mass content of silicon in the negative electrode active material to the mass content of the first additive in the electrolyte is within an appropriate range. Through the synergistic effect of the silicon in the negative electrode and the first additive, the energy density of the battery cell can be improved while taking into account the cycle performance of the battery cell.

[0024] In any embodiment, based on the mass of the negative electrode active material, the mass content of silicon in the negative electrode active material is 0.3% to 3%;

[0025] Based on the total mass of the electrolyte, the mass content of the first additive is 2% to 7.5%.

[0026] In a system with a relatively low silicon content, the damage to the SEI film during the battery cell cycle is relatively small. By controlling the mass content of the first additive within an appropriate range, an SEI film of appropriate thickness is formed. While improving the stability of the interface between the SEI film and the negative electrode and improving the cycle performance of the battery cell, it can also achieve low impedance at the negative electrode interface, which is beneficial to improving the fast charging performance of the battery cell and is more suitable for use scenarios with higher requirements for the cycle performance and fast charging performance of the battery cell.

[0027] In any embodiment, based on the mass of the negative electrode active material, the mass content of silicon in the negative electrode active material is greater than 3% and less than or equal to 6%;

[0028] Based on the total mass of the electrolyte, the mass content of the first additive is 3% to 10%.

[0029] In a system with a relatively high silicon content, the damage to the SEI film during the battery cell cycle is relatively serious. By controlling the mass content of the first additive within an appropriate range and forming an SEI film of appropriate thickness, the stability of the interface between the SEI film and the negative electrode and the cycle performance of the battery cell can be improved. This is more suitable for use scenarios with higher requirements for the cycle performance and energy density of the battery cell.

[0030] In any embodiment, the olivine-structured lithium-containing phosphate comprises:

[0031] A lithium phosphate matrix, and

[0032] The coating layer is located on at least a portion of the surface of the lithium-containing phosphate matrix and contains carbon. The olivine-structured lithium-containing phosphate includes a carbon coating layer, which can improve the material's electrical conductivity and facilitate the fast-charging performance of the battery cell.

[0033] In any embodiment, the mass content of carbon element is 0.8% to 2.3% based on the mass of the lithium-containing phosphate with an olivine structure.

[0034] By controlling the mass content of carbon elements in the coating layer within an appropriate range, the conductivity of the material and the fast charging performance of the battery can be improved while taking into account the gram capacity of the material, the fast charging performance and energy density of the battery cell.

[0035] In any embodiment, the battery cell satisfies the following relationship: 0.08≤C / B≤1.15,

[0036] Wherein, C is the mass content of carbon element, which is based on the mass of lithium-containing phosphate with olivine structure;

[0037] B is the mass content of the first additive, based on the total mass of the electrolyte.

[0038] Controlling the mass content of carbon elements in the olivine-structured lithium-containing phosphate and the mass content of the first additive in the electrolyte within an appropriate range can improve the conductivity of the material, improve the fast charging performance of the battery cell, while also improving the cycle stability of the material and the cycle performance of the battery cell.

[0039] In any embodiment, the coating layer further comprises Li 3-d1 Fe 2-d1 M3 d1 (PO m1 ) n1 of substances,

[0040] Among them, 0≤d1≤1, 3≤m1≤5, 2≤n1≤4;

[0041] M3 includes one or more of Ti, Zr, Hf, Ge, and Sn. Optionally, M3 has a valence of +4.

[0042] The coating layer includes Li 3-d1 Fe 2-d1 M3 d1 (PO m1 ) n1 The material has excellent ion conductivity, can significantly increase the transmission rate of lithium ion deintercalation / lithium insertion of the material, improve the ion conductivity of the overall material, and is beneficial to improving the fast charging performance of the battery.

[0043] In any embodiment, the lithium phosphate matrix comprises a lithium phosphate having the general formula Li x1 A y1 Me a1 M b1 P 1-c1 X c1 Y z1 Compounds

[0044] Among them, 0.5≤x1≤1.3, 0≤y1≤1.3, 0.9≤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;

[0045] Wherein, 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 S, Si, Cl, B, C, N and P; and Y includes at least one of O and F.

[0046] In any embodiment, the lithium phosphate matrix includes one or more of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium nickel phosphate, lithium cobalt phosphate and modified forms of any of the foregoing substances, wherein the modified form includes one or more of doping modification and coating modification.

[0047] In any embodiment, the powder compaction density of the positive electrode active material at 30,000 N is 2.43 g / cm 3 ~2.85g / cm 3 , optional 2.48g / cm 3 ~2.80g / cm 3 .

[0048] When the powder compaction density of the positive electrode active material at 30,000N is within the above range, the energy density of the battery cell can be improved. Moreover, since the positive electrode active material in the positive electrode film layer can be stacked more densely and the contact resistance between particles is smaller, the resistance of the electrode sheet can be further reduced, which is also beneficial to improving the fast charging performance of the battery cell.

[0049] In any embodiment, the battery cell has a compacted density of 2.50 g / cm3 at 100% state of charge. 3 ~2.80g / cm 3 .

[0050] The compaction density of the positive electrode film layer is within a suitable range, and the battery cell has a high energy density.

[0051] In any embodiment, the negative electrode active material includes a carbon-based material, and the carbon-based material includes graphite.

[0052] Graphite has good conductivity and cycle stability, which is beneficial to improving the fast charging performance and cycle performance of battery cells.

[0053] In any embodiment, the graphite includes composite graphite particles, which include graphite particles and a carbon coating layer coated on the surface of the graphite particles. The graphite particles include secondary particles, and the carbon coating layer includes amorphous carbon.

[0054] The secondary particles have excellent ion transport properties, which are beneficial to the embedding and extraction of lithium ions and the improvement of the ion conductivity of the material. In addition, the carbon coating layer includes amorphous carbon, which can improve the conductivity of the composite graphite particles. The secondary particles in the inner core and the amorphous carbon coating layer jointly improve the electronic and ion conductivity of the material, which helps to improve the fast charging performance of the battery cell.

[0055] In any embodiment, the composite graphite particles satisfy at least one of the following conditions:

[0056] (1) Based on the total mass of the composite graphite particles, the mass content of amorphous carbon is 2% to 5%;

[0057] (2) The powder resistivity of the composite graphite particles is 0.005Ω•cm-0.04Ω•cm.

[0058] Controlling the mass content of amorphous carbon in composite graphite particles within an appropriate range can improve the conductivity of the material and enhance the fast-charging performance of the battery.

[0059] The powder resistivity of the composite graphite particles is small, and the composite graphite particles have excellent conductivity, which is beneficial to improving the fast charging performance of the battery cell.

[0060] In any embodiment, the first negative electrode film layer and the second negative electrode film layer, the first negative electrode film layer is disposed between the current collector and the second negative electrode film layer, and both the first negative electrode film layer and the second negative electrode film layer include the composite graphite particles.

[0061] In any embodiment, the volume average particle size Dv50 of the composite graphite particles in the first negative electrode film layer is greater than or equal to the volume average particle size Dv50 of the composite graphite particles in the second negative electrode film layer.

[0062] During the rapid charging process of the battery cell, the overpotential of the second negative electrode film layer away from the current collector is usually higher. The bottleneck in the negative electrode film layer that affects the fast charging performance of the battery cell mainly lies in the second negative electrode film layer. The present application controls the particle size of the composite graphite particles in the second negative electrode film layer to be relatively smaller, which can shorten the transmission path of lithium ions, improve the lithium ion transmission performance of the second negative electrode film layer, and improve the fast charging performance of the battery cell.

[0063] In any embodiment, the volume average particle size Dv50 of the composite graphite particles in the first negative electrode film layer is 8.5 μm to 14.8 μm, and / or

[0064] The volume average particle size Dv50 of the composite graphite particles in the second negative electrode film layer is 7.8 μm to 12.8 μm.

[0065] Controlling the particle size of the composite graphite particles in the first negative electrode film layer and / or the second negative electrode film layer within a suitable range can shorten the transmission path of lithium ions in the negative electrode film layer and improve the fast charging performance of the battery cell.

[0066] In any embodiment, based on the total thickness of the first negative electrode film layer and the second negative electrode film layer, the thickness of the second negative electrode film layer accounts for 30% to 70%.

[0067] The thickness ratio of the second negative electrode film layer is within an appropriate range, which can take into account the contribution of the second negative electrode film layer to the fast charging performance of the battery and the contribution of the first negative electrode film layer to the energy density of the battery, thereby obtaining a battery cell with excellent fast charging performance and high energy density.

[0068] In any embodiment, the negative electrode plate further includes a negative electrode conductive layer, which is located between the negative electrode current collector and the negative electrode film layer on at least one side, and the negative electrode conductive layer includes a 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.

[0069] By providing a negative electrode conductive layer containing a conductive agent between the current collector and the negative electrode film layer, the conductivity of the negative electrode plate can be improved and the fast charging performance of the battery cell can be improved.

[0070] In any embodiment, the thickness of the negative electrode conductive layer is 0.5 μm to 2 μm.

[0071] By controlling the thickness of the negative electrode conductive layer within an appropriate range, both the fast charging performance and the energy density of the battery cell can be taken into account.

[0072] In any embodiment, the battery cell has a negative electrode film with a compact density of 1.15 g / cm at 100% state of charge. 3 ~1.45g / cm 3 , and / or,

[0073] The single-sided coating weight of the negative electrode film is 70mg / 1540.25mm 2 ~135mg / 1540.25mm 2 .

[0074] The single-sided coating weight or compaction density of the negative electrode film layer is within an appropriate range, which is beneficial to improving the fast charging performance of the battery cell.

[0075] In any embodiment, the electrolyte further comprises an organic solvent, and the organic solvent comprises one or more of a first organic solvent and a second organic solvent.

[0076] Wherein, the first organic solvent includes at least one of a cyclic carbonate and a chain carbonate, and can be a cyclic carbonate;

[0077] The second organic solvent includes R5-COO-R6,

[0078] Wherein, R5 includes any one of a hydrogen atom, a halogen atom, a C1-C5 alkyl group, and a C1-C5 halogenated alkyl group, and R6 includes any one of a C1-C5 alkyl group and a C1-C5 halogenated alkyl group.

[0079] The first organic solvent of cyclic carbonate and chain carbonate has a relatively high dielectric constant and excellent ionic conductivity, which is beneficial to improving the conductivity of the electrolyte. The second organic solvent has a low viscosity, which is beneficial to improving the conductivity of the electrolyte. The electrolyte contains the first organic solvent and / or the second organic solvent, which is beneficial to improving the migration of lithium ions and improving the fast charging performance of the battery cell.

[0080] In any embodiment, the cyclic carbonate comprises one or more of ethylene carbonate, propylene carbonate, and butylene carbonate; and / or,

[0081] The chain carbonate includes one or more of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; and / or,

[0082] The second organic solvent includes one or more of methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, and ethyl butyrate.

[0083] In any embodiment, the mass content of the first organic solvent is 20% to 72% based on the total mass of the electrolyte.

[0084] The first organic solvent containing a suitable content of cyclic carbonate or chain carbonate can further improve the conductivity of the electrolyte, facilitate the migration of lithium ions, and improve the fast charging performance of the battery cell.

[0085] In any embodiment, the electrolyte further includes a second additive, and the second additive includes one or more of a sulfur-containing additive and a lithium salt additive.

[0086] Sulfur-containing additives and lithium salt additives can improve the interfacial film performance on the positive electrode side and / or the negative electrode side, improve the interfacial chemistry between the positive electrode and / or the negative electrode and the electrolyte, and improve the fast charging performance and cycle performance of the battery.

[0087] In any embodiment, the sulfur-containing additive includes one or more of vinyl sulfate, vinyl disulfate, butylene sulfite, 1,3-propane sultone, vinyl sulfite, and methylene disulfonate; and / or,

[0088] The lithium salt additive includes one or more of lithium difluorophosphate, lithium difluorooxalatoborate, lithium tetrafluoroborate, and lithium bis(oxalatoborate).

[0089] In any embodiment, the electrolyte further includes a lithium salt, and the lithium salt includes one or both of a fluorine-containing sulfonyl imide salt and lithium hexafluorophosphate.

[0090] Fluorinated sulfonyl imide salts and lithium hexafluorophosphate are easy to dissociate, which is beneficial to the rapid migration of lithium ions and the improvement of the fast charging performance of battery cells. Fluorinated sulfonyl imide salts and lithium hexafluorophosphate are relatively stable in the electrolyte system and can improve the cycle performance of battery cells.

[0091] In any embodiment, the fluorine-containing sulfonyl imide salt includes one or both of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide.

[0092] In any embodiment, the lithium salt includes lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate, and the ratio of the molar concentration of lithium bis(fluorosulfonyl)imide to the molar concentration of lithium hexafluorophosphate is 0.2 to 1.0.

[0093] In any embodiment, the molar concentration of lithium bis(fluorosulfonyl)imide is 0.2 mol / L to 0.5 mol / L, and the molar concentration of lithium hexafluorophosphate is 0.5 mol / L to 1.2 mol / L.

[0094] In any embodiment, the isolation film satisfies at least one of the following conditions:

[0095] (1) The thickness of the isolation film is 4μm~12μm, and can be selected from 5μm~9μm;

[0096] (2) The porosity of the isolation membrane is 20%~70%, and can be optionally 35%~60%.

[0097] When the thickness of the isolation membrane is within an appropriate range, the migration path of lithium ions in the isolation membrane is shorter, which can reduce the internal resistance of the battery cell and improve the fast charging performance of the battery cell.

[0098] When the porosity of the separator is within an appropriate range, the migration rate of lithium ions in the separator can be increased, the internal resistance of the battery cell can be reduced, and the fast charging performance of the battery cell can be improved.

[0099] In any embodiment, the battery cell is configured to charge from 10% state of charge to 80% state of charge within a range of 5 minutes to 10.5 minutes.

[0100] The battery cell has a fast charging speed and has excellent fast charging performance.

[0101] In any embodiment, the volume energy density of the battery cell is 395Wh / L to 530Wh / L.

[0102] In a second aspect, the present application provides a battery device comprising the battery cell of the first aspect.

[0103] In any embodiment, the battery device is configured to charge from a 10% state of charge to an 80% state of charge within a range of 5 minutes to 10.5 minutes.

[0104] The battery device has a fast charging speed and an excellent fast charging performance.

[0105] In a third aspect, the present application provides an electrical device comprising the battery device of the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0106] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0107] Figure 1 is a schematic diagram of a battery cell according to an embodiment of the present application;

[0108] Figure 2 yes Figure 1 An exploded view of a battery cell according to an embodiment of the present application is shown;

[0109] Figure 3 is a schematic diagram of a battery module according to one embodiment of the present application;

[0110] Figure 4 is a schematic diagram of a battery pack according to one embodiment of the present application;

[0111] Figure 5 yes Figure 4 An exploded view of a battery pack according to an embodiment of the present application is shown;

[0112] Figure 6 FIG2 is a schematic diagram of an electrical device using a battery cell according to an embodiment of the present application as a power source.

[0113] Description of reference numerals:

[0114] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 cover plate. DETAILED DESCRIPTION

[0115] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0116] The battery, battery injection method, electrolyte, preparation method thereof, and electrical device of the present application are described in detail below with appropriate reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of substantially identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. In addition, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0117] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0118] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0119] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0120] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0121] With the continuous expansion of the application field of lithium-ion batteries, higher requirements are also put forward for their energy density and fast charging performance. In order to improve the energy density of the battery, the coating surface density of the positive and negative electrode films is generally increased. However, as the coating surface density of the positive and negative electrode films increases, the migration path of lithium ions becomes longer, the internal resistance of the battery is larger, and the fast charging performance of the battery is affected. In particular, the high coating surface density of the negative electrode film will seriously affect the fast charging performance of the battery cell. It is difficult to achieve both the energy density and fast charging performance of the battery cell by simply adjusting the coating weight of the positive and negative electrodes.

[0122] In view of the above problems, this application rationally designs the battery cell system to achieve a balance between energy density and fast charging performance. Specifically, by rationally matching the coating surface density of the positive electrode sheet, the silicon content of the negative electrode material and the additives in the electrolyte, while improving the energy density, it can also take into account the fast charging performance and cycle performance of the battery.

[0123] [Battery Cell]

[0124] The battery cell includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator. The separator is located between the positive electrode sheet and the negative electrode sheet.

[0125] The positive electrode plate includes a positive electrode current collector and a positive electrode film layer provided on at least one side of the positive electrode current collector, the positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes a lithium-containing phosphate with an olivine structure.

[0126] The single-sided coating weight of the positive electrode film layer is 180 mg / 1540.25 mm 2 Up to 380mg / 1540.25mm 2 ;

[0127] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer provided on at least one side of the negative electrode current collector, the negative electrode film layer includes a negative electrode active material, the negative electrode active material includes a silicon-based material, and the mass content of the silicon element is 0.3% to 10.0% based on the mass of the negative electrode active material;

[0128] The electrolyte includes a first additive, wherein the first additive includes at least one of vinylene carbonate and an ethylene carbonate derivative, and the mass content of the first additive is 1% to 12% based on the total mass of the electrolyte.

[0129] Wherein, the ethylene carbonate derivative includes the compound shown in formula I,

[0130] Formula I

[0131] R1, R2, R3, and R4 each independently include any one of a hydrogen atom, a halogen atom, a C1-C5 alkyl group, and a C1-C5 halogenated alkyl group, and R1, R2, R3, and R4 are not hydrogen atoms at the same time.

[0132] In some embodiments, the single-sided coating weight of the positive electrode film layer is 180 mg / 1540.25 mm 2 ~380mg / 1540.25mm 2 For example, the coating weight of the positive electrode film on one side is 180 mg / 1540.25 mm 2 、190mg / 1540.25mm 2 , 200mg / 1540.25mm 2 、210mg / 1540.25mm 2 、220mg / 1540.25mm 2 、230mg / 1540.25mm 2 、240mg / 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 / 1540.25mm 2 、320mg / 1540.25mm 2 、330mg / 1540.25mm 2 、340mg / 1540.25mm 2 、350mg / 1540.25mm 2 、360mg / 1540.25mm 2 、370mg / 1540.25mm 2 、380mg / 1540.25mm 2 Or a range consisting of any two of the above values.

[0133] In the embodiments of the present application, the single-sided coating density of the positive electrode film layer of a battery cell can be measured using the following method: For example, take a single-sided coated positive electrode sheet (if it is a double-sided coated sheet, the positive electrode film layer on one side can be wiped off first), punch it into small discs with an area of ​​S1, weigh it, record it as M1, and measure its thickness H1. Then, wipe off the positive electrode film layer of the weighed positive electrode sheet, weigh the positive electrode current collector, record it as M0, and measure its thickness H0. The single-sided coating weight of the positive electrode film layer = (weight of the positive electrode sheet M1 - weight of the positive electrode current collector M0) / S1.

[0134] In the embodiment of the present application, the silicon-based material may include at least one of elemental silicon, silicon oxide, silicon-carbon compound, silicon-nitrogen compound and silicon alloy material. The elemental silicon, silicon oxide, silicon-carbon compound, silicon-nitrogen compound and silicon alloy material here can refer to silicon-based materials or the form of silicon element in the negative electrode sheet of the battery after formation. The silicon oxide SiO x , 0<x≤2 is because the combination of silicon atoms and oxygen atoms in the negative electrode film layer is diverse, which can be SiO, SiO 1.2 , or at least one of SiO2 and other possible silicon oxides. The silicon-carbon composite here can refer to the form of silicon in the negative electrode of the battery after formation. The silicon-carbon composite can also be a silicon-carbon composite generated by certain chemical reactions between silicon and carbon in the battery cell. The silicon-carbon composite can also be formed by a physical mixture of silicon and carbon, for example, the carbon includes a porous skeleton, and the silicon is located in the pores of the porous skeleton or on the surface of the porous skeleton. The silicon-carbon composite can also be a carbon layer coated on the surface of the silicon.

[0135] In some embodiments, the mass content of silicon is 0.3% to 10.0% based on the mass of the negative electrode active material. For example, the mass content of silicon 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%, 5.2%, 5.5%, 5.8%, 6%, 6.2%, 6.5%, 6.8%, 7%, 7.2%, 7.5%, 7.8%, 8%, 8.2%, 8.5%, 8.8%, 9%, 9.2%, 9.5%, 9.8%, 10%, or a range consisting of any two of the above values.

[0136] The qualitative and quantitative properties of each substance or element in this application can be detected using appropriate equipment and methods known to those skilled in the art. The relevant detection methods can refer to domestic and international detection standards, domestic and international enterprise standards, etc., and those skilled in the art can also adapt certain detection steps / instrument parameters, etc. from the perspective of detection accuracy to obtain more accurate detection results. A single detection method can be used for qualitative or quantitative determination, or several detection methods can be used in combination for qualitative or quantitative determination.

[0137] For example, the mass content of silicon in the negative electrode film layer has a well-known meaning in the art and can be detected using equipment and methods well-known in the art. For example, the negative electrode plate is placed in a solvent such as water for immersion, the negative electrode active material is separated from the negative electrode current collector, and the various substances in the negative electrode film layer are obtained by filtration. The test sample is used as a test sample, and the test sample is analyzed by an ICAP7400 model inductively coupled plasma-emission spectrometer of Thermo Fisher Scientific Company of the United States, referring to the GB / T30902-2014 standard to obtain the silicon content.

[0138] In some embodiments, based on the total mass of the electrolyte, the mass content of the first additive is 1% to 12%. For example, the mass content of the first additive is 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12% or a range consisting of any two of the above values.

[0139] The type and content of the first additive in the electrolyte can be determined by testing the electrolyte using methods known to those skilled in the art. For example, the composition of the electrolyte can be measured using liquid chromatography, ultraviolet spectrophotometry, ultraviolet-visible spectrophotometry, or the like. For example, an ion chromatograph (IC) is used to test the inorganic content of the electrolyte. A fixed amount of electrolyte solution (with a dilution concentration in the middle of the standard curve) is weighed and diluted to 100 mL with ultrapure water. The ion chromatograph is then automatically sampled and tested. The inorganic ion chromatogram is tested. The corresponding inorganic species are aligned based on the peak position in the chromatogram, and the corresponding inorganic ion content percentage is calculated based on the peak area. The free electrolyte solution was diluted 3 to 10 times with acetonitrile to obtain the electrolyte dilution to be tested. The electrolyte dilution was placed in the instrument for full scan qualitative analysis using a GC-MS 3100 organic component gas chromatograph. The injection port temperature was 250°C and the scan range was 35μm to 270μm. After the test, the total ion current chromatogram of each organic compound was obtained. The corresponding organic compound type was compared based on the chromatogram peak position, and the corresponding content percentage of each organic compound was calculated based on the peak area. The mass of the first additive obtained by dividing the mass of the electrolyte sample was used as the mass content of the first additive in the electrolyte of the battery cell. It can be understood that the mass content of the first additive in the electrolyte of the battery cell is slightly lower than the mass content of the first additive added to the electrolyte of the battery cell.

[0140] Herein, the term "halogen atom" includes one or more of a fluorine atom, a chlorine atom, a bromine atom and an iodine atom.

[0141] As used herein, the term "C1-C5 alkyl" refers to a straight or branched hydrocarbon chain radical consisting solely of carbon and hydrogen atoms, with no unsaturation present, having from one to five carbon atoms, and attached to the remainder of the molecule by a single bond. Examples include, but are not limited to, methyl, ethyl, propyl, isopropyl, 2-methyl-1-propyl, 2-methyl-2-propyl, 2-methyl-1-butyl, 3-methyl-1-butyl, 2-methyl-3-butyl, 2,2-dimethyl-1-propyl, 2-methyl-1-pentyl, butyl, isobutyl, tert-butyl, pentyl, isopentyl, and neopentyl.

[0142] As used herein, the term "C1-C5 haloalkyl" refers to a C1-C5 alkyl group in which at least one hydrogen atom is replaced by a halogen atom, including but not limited to: -CF3, -CF2CH2, -CF2CH2CH3, -CF2CF2CH2CH3, and -CF2CH2CH2CH2CH3.

[0143] This application matches a positive electrode film layer with a high coating weight with a negative electrode film layer containing silicon elements, which can reduce the coating weight of the negative electrode film layer while improving the energy density of the battery cell, thereby improving the fast charging performance of the battery cell. At the same time, the mass content of the silicon element in the negative electrode film layer is controlled within an appropriate range, which can improve the energy density of the battery cell while taking into account the cycle performance of the battery cell. However, when silicon-containing materials are introduced into the negative electrode active material, the silicon material has a large volume expansion and contraction during the charge and discharge process of the battery cell, and the SEI film on the negative electrode side is easily destroyed, exposing a fresh interface. The electrolyte continues to undergo a reduction reaction at the interface, consuming the electrolyte and active lithium, affecting the cycle and storage performance of the battery cell. To address this problem, the present application adds a first additive of vinylene carbonate and / or vinylene carbonate derivatives to the electrolyte. Vinylene carbonate and vinylene carbonate derivatives can participate in the formation of an SEI film on the negative electrode side in priority to other components in the electrolyte, and the organic matter content in the film formed by vinylene carbonate and vinylene carbonate derivatives is relatively high, which is beneficial to improving the overall flexibility of the SEI film, improving the stability of the SEI film and the negative electrode interface during the cycle, reducing the reaction between the negative electrode active material and the electrolyte, reducing the consumption of lithium ions, and improving the cycle performance and storage performance of the battery cell. In addition, by controlling the mass content of the first additive within an appropriate range, it is possible to improve the flexibility and stability of the SEI film while controlling the thickness of the SEI film within an appropriate range, thereby achieving stability and low impedance of the negative electrode interface at the same time, and taking into account the cycle performance and fast charging performance of the battery cell. In addition, the positive electrode active material includes a lithium-containing phosphate with an olivine structure, which has excellent structural stability and improves the cycle performance of the battery cell.

[0144] In summary, the present application can achieve a balance between fast charging performance, cycle performance and energy density of the battery cell by synergistically controlling the single-sided coating weight of the positive electrode film layer, the mass content of silicon in the negative electrode active material, the positive electrode active material containing olivine structure lithium phosphate, and the type and mass content of additives in the electrolyte within an appropriate range.

[0145] [Negative electrode]

[0146] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector and comprising a negative electrode active material. For example, the negative electrode current collector has two opposing surfaces in the thickness direction of the negative electrode current collector, and the negative electrode film layer is disposed on either or both of the two opposing surfaces of the negative electrode current collector.

[0147] In some embodiments, based on the mass of the negative electrode active material, the mass content of silicon element is 0.3%~6.0%, which can be optionally 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%, 5.2%, 5.5%, 5.8%, 6% or a range consisting of any two of the above values.

[0148] The mass content of silicon in silicon-based materials is within an appropriate range, which can increase the energy density of battery cells while reducing the impact of excessive silicon on the cycle performance of battery cells, thus taking into account both the energy density and cycle performance of battery cells.

[0149] In some embodiments, the battery cell satisfies the following relationship: 0.025≤A / B≤6, optionally 0.035≤A / B≤2.5,

[0150] Wherein A is the mass content of the silicon element, based on the mass of the negative electrode active material; B is the mass content of the first additive, based on the total mass of the electrolyte.

[0151] In some embodiments, the value of A / B can be selected as 0.025, 0.030, 0.035, 0.040, 0.045, 0.050, 0.1, 0.2, 0.3, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, or a range consisting of any two of the above values.

[0152] The ratio of the mass content of silicon in the negative electrode active material to the mass content of the first additive in the electrolyte is within an appropriate range. Through the synergistic effect of the silicon in the negative electrode active material and the first additive, the energy density of the battery cell can be improved while taking into account the cycle performance of the battery cell.

[0153] In some embodiments, based on the mass of the negative electrode active material, the mass content of the silicon element is 0.3% to 3%;

[0154] Based on the total mass of the electrolyte, the mass content of the first additive is 2% to 7.5%.

[0155] In some embodiments, the mass content of silicon in the negative electrode active material may be 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, or a range consisting of any two of the above values;

[0156] The mass content of the first additive in the electrolyte may be 2%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7%, 7.5% or a range consisting of any two of the above values.

[0157] In a system with a relatively low silicon content, the damage to the SEI film during the battery cell cycle is relatively small. By controlling the mass content of the first additive within an appropriate range, an SEI film of appropriate thickness is formed. While improving the stability of the interface between the SEI film and the negative electrode and improving the cycle performance of the battery cell, it can also achieve low impedance at the negative electrode interface, which is beneficial to improving the fast charging performance of the battery cell and is more suitable for use scenarios with higher requirements for the cycle performance and fast charging performance of the battery cell.

[0158] In some embodiments, based on the mass of the negative electrode active material, the mass content of silicon is greater than 3% and less than or equal to 6%;

[0159] Based on the total mass of the electrolyte, the mass content of the first additive is 3% to 10%.

[0160] In some embodiments, the mass content of silicon in the negative electrode active material may be 3.1%, 3.5%, 3.8%, 4.0%, 4.2%, 4.5%, 4.8%, 5%, 5.2%, 5.5%, 5.8%, 6%, or a range consisting of any two of the above values;

[0161] The mass content of the first additive in the electrolyte may be 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7%, 7.5%, 8.0%, 8.5%, 9.0%, 9.5%, 10.0% or a range consisting of any two of the above values.

[0162] In a system with a relatively high silicon content, the damage to the SEI film during the battery cell cycle is relatively serious. By controlling the mass content of the first additive within an appropriate range and forming an SEI film of appropriate thickness, the stability of the interface between the SEI film and the negative electrode and the cycle performance of the battery cell can be improved. This is more suitable for use scenarios with higher requirements for the cycle performance and energy density of the battery cell.

[0163] In some embodiments, the negative electrode active material includes a carbon-based material, and the carbon-based material includes graphite.

[0164] Graphite has good conductivity and cycle stability, which is beneficial to improving the fast charging performance and cycle performance of battery cells.

[0165] In some embodiments, based on the mass of the negative electrode active material, the mass proportion of the carbon-based material may be greater than or equal to 80% and less than 100%.

[0166] In some embodiments, the graphite includes composite graphite particles, wherein the composite graphite particles include graphite particles and a carbon coating layer coated on the surface of the graphite particles, the graphite particles include secondary particles, and the carbon coating layer includes amorphous carbon.

[0167] Secondary particles are particles formed by the aggregation of two or more primary particles.

[0168] In this article, amorphous carbon refers to a transitional carbon material with a very low degree of graphitization and crystallization, nearly amorphous (or lacking a fixed shape and periodic structural regularity). In this application, amorphous carbon refers to the product of carbonization of an organic carbon source, which has a large number of end faces and defects and a high number of lithium ion sites.

[0169] Secondary particles can increase the migration rate of lithium ions, improve the transmission performance of lithium ions, facilitate the embedding and extraction of lithium ions, and help improve the ion conductivity of the material. In addition, the carbon coating layer includes amorphous carbon, which can improve the conductivity of the composite graphite particles. The secondary particles in the inner core and the amorphous carbon coating layer jointly improve the electronic and ion conductivity of the material, which helps to improve the fast charging performance of the battery cell.

[0170] In an embodiment of the present application, the composite graphite particles can be prepared by methods known in the art. For example, the preparation method includes: providing graphite body particles (which can be artificial graphite) and an organic carbon source, mixing the two, and forming a carbon coating layer on at least a portion of the surface of the graphite body particles after carbonization treatment to obtain the composite graphite particles in the embodiment.

[0171] Optionally, the organic carbon source includes one or more of coal tar, petroleum tar, phenolic resin, and coconut shell. Further, the organic carbon source includes petroleum tar. Optionally, the softening point of the coal tar or petroleum tar is below 250°C.

[0172] Optionally, the carbonization temperature is 700° C. to 1800° C. Optionally, the carbonization temperature is 1000° C. to 1300° C. Within a suitable carbonization temperature range, the organic carbon source can be carbonized and a coating layer comprising amorphous carbon can be formed on at least a portion of the surface of the graphite particles. Optionally, the carbonization time is 1 hour to 6 hours.

[0173] In some embodiments, the mass content of the amorphous carbon is 2% to 5% based on the total mass of the composite graphite particles, and can be optionally 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or a range consisting of any two of the above values.

[0174] Controlling the mass content of amorphous carbon in composite graphite particles within an appropriate range can improve the conductivity of the material and enhance the fast-charging performance of the battery.

[0175] In some embodiments, the powder resistivity of the composite graphite particles is 0.005Ω•cm-0.04Ω•cm, which can be 0.01Ω•cm, 0.015Ω•cm, 0.020Ω•cm, 0.025Ω•cm, 0.03Ω•cm, 0.04Ω•cm, or a range consisting of any two of the above values.

[0176] In the embodiments of the present application, the powder resistivity of the material is well known in the art and can be tested using methods and equipment well known in the art, for example, using a PRCD1100 powder resistivity meter according to the test standard GB / T30835-2014.

[0177] The powder resistivity of the composite graphite particles is small, and the composite graphite particles have excellent conductivity, which is beneficial to improving the fast charging performance of the battery cell.

[0178] In the embodiment of the present 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. Optionally, the negative electrode film layer includes at least two film layers.

[0179] When the negative electrode film layer adopts a single-layer film layer, the negative electrode active material in the negative electrode film layer includes graphite and a silicon-based material. Optionally, the negative electrode active material includes composite graphite particles and a silicon-based material. When a single-layer film layer is adopted, the volume average particle size Dv50 of the composite graphite particles is 8.2 μm to 13.5 μm. Exemplarily, the volume average particle size Dv50 of the composite graphite particles is 8.2 μm, 8.5 μm, 8.8 μm, 9 μm, 9.2 μm, 9.5 μm, 9.8 μm, 10 μm, 10.2 μm, 10.5 μm, 10.8 μm, 11 μm, or a range consisting of any two of the above values.

[0180] When the negative electrode film layer uses at least two film layers, the negative electrode active material in the negative electrode film layer includes graphite and a silicon-based material. Optionally, the negative electrode active material includes composite graphite particles and a silicon-based material. The silicon-based material can be located in one of the at least two film layers, or in at least two of the at least two film layers. The composite graphite particles can be located in one of the at least two film layers, or in at least two of the 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.

[0181] In some embodiments, the negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer, the first negative electrode film layer is located between the current collector and the second negative electrode film layer, the silicon-based material can be located in the first negative electrode film layer and / or the second negative electrode film layer, and the composite graphite particles can be located in the first negative electrode film layer and / or the second negative electrode film layer.

[0182] The interface between the first negative electrode film layer and the second negative electrode film layer may be regular or irregular, and may optionally be irregular.

[0183] The negative electrode film comprises at least two layers, and layered coating can improve the fast-charging performance of the battery cell. In particular, when the first and second negative electrode film layers are differentiated, this can create a pore difference in the negative electrode film layers, reducing the tortuosity of lithium-ion transport and improving the fast-charging performance of the battery cell.

[0184] In some embodiments, both the first negative electrode film layer and the second negative electrode film layer include composite graphite particles.

[0185] The first negative electrode film layer and the second negative electrode film layer both include composite graphite particles, which can improve the fast charging performance of the battery cell.

[0186] In some embodiments, the volume average particle size Dv50 of the composite graphite particles in the first negative electrode film layer is greater than or equal to the volume average particle size Dv50 of the composite graphite particles in the second negative electrode film layer.

[0187] In the embodiment of the present application, the volume average particle size Dv50 of the material refers to the particle size corresponding to 50% in the volume distribution, which can be detected using equipment and methods known in the art. For example, the positive electrode active material is used as a sample and the Dv50 of the particles is tested by a Mastersizer 2000E laser particle size analyzer according to the test standard GB / T19077-2016.

[0188] During the rapid charging process of the battery cell, the overpotential of the second negative electrode film layer away from the current collector is usually higher. The bottleneck in the negative electrode film layer that affects the fast charging performance of the battery cell mainly lies in the second negative electrode film layer. The present application controls the particle size of the composite graphite particles in the second negative electrode film layer to be relatively smaller, which can shorten the transmission path of lithium ions, improve the lithium ion transmission performance of the second negative electrode film layer, and improve the fast charging performance of the battery cell.

[0189] In some embodiments, the volume average particle size Dv50 of the composite graphite particles in the first negative electrode film layer is 8.5 μm~14.8 μm, which can be 8.5 μm, 9.0 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 14.8 μm or a range consisting of any two of the above values.

[0190] In some embodiments, the volume average particle size Dv50 of the composite graphite particles in the second negative electrode film layer is 7.8 μm to 12.8 μm, which can be selected from 7.8 μm, 8.0 μm, 8.5 μm, 9.0 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 12.8 μm or a range consisting of any two of the above values.

[0191] Controlling the particle size of the graphite particles in the first negative electrode film layer and / or the second negative electrode film layer within a suitable range can, on the one hand, shorten the solid-phase transmission path of lithium ions and improve the fast charging performance; on the other hand, the material is not easily agglomerated during the preparation process, which can improve the stability of the material; on still another hand, the combination of the negative electrode active material in the second negative electrode film layer and the negative electrode active material in the first negative electrode film layer within the above-mentioned volume average particle size range is conducive to constructing a gradient pore difference between the second negative electrode film layer and the first negative electrode film layer, reducing the tortuosity of lithium ion transmission, and improving the fast charging performance of the battery cell.

[0192] In some embodiments, based on the total thickness of the first negative electrode film layer and the second negative electrode film layer, the thickness of the second negative electrode film layer accounts for 30% to 70%, which can be optionally 30%, 40%, 50%, 60%, 70% or a range consisting of any two of the above values.

[0193] The thickness ratio of the second negative electrode film layer is within an appropriate range. By adjusting the thickness ratio of the first negative electrode film layer and the second negative electrode film layer, the gradient pore difference between the upper and lower layers can be further increased, the tortuosity of lithium ion transmission can be reduced, and the fast charging performance of the battery cell can be improved.

[0194] In some embodiments, when the battery cell is at 100% state of charge, the thickness of the first negative electrode film layer is 15 μm to 65 μm, for example, 15 μm, 17 μm, 18 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 57 μm, 58 μm, 60 μm, 61 μm, 62 μm, 63 μm, 64 μm, 65 μm, or a range consisting of any two of the above values.

[0195] When the thickness of the first negative electrode film layer is within the above range, the gradient pore difference between the first negative electrode film layer and the second negative electrode film layer can be increased, the tortuosity of lithium ion transmission can be reduced, and the fast charging performance of the battery cell can be improved.

[0196] In some embodiments, at 100% state of charge, the second negative electrode film layer has a thickness of 15 μm to 65 μm, such as 15 μm, 17 μm, 18 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 57 μm, 58 μm, 60 μm, 61 μm, 62 μm, 63 μm, 64 μm, 65 μm, or a range consisting of any two of the foregoing values. When the thickness of the second negative electrode film layer is within the foregoing range, the gradient porosity difference between the first negative electrode film layer and the second negative electrode film layer can be increased, thereby reducing the tortuosity of lithium ion transport and improving the fast charging performance of the battery cell.

[0197] In an embodiment of the present application, the test steps for the first negative electrode film layer and the second negative electrode film layer of the battery cell at 100% charge state are as follows: charge the battery cell to 3.65V at a constant current of 0.33C, and then continue to charge to 0.05C under a constant voltage condition of 3.65V, and stop charging. At this time, the battery state is 100% charge state, and the negative electrode plate of the battery cell at 100% charge state is disassembled, and a cross-section in the thickness direction of the middle area of ​​the negative electrode plate is observed using a tomographic scanning electron microscope. The first negative electrode film layer and the second negative electrode film layer are distinguished according to the interface between the two areas, and the thickness of the two areas are measured respectively. For example, the thickness of 10 positions of the first negative electrode film layer is measured respectively, and the average value thereof is calculated as the average value of the first negative electrode film layer, and the thickness of 10 positions of the second negative electrode film layer is measured, and the average value thereof is calculated as the average value of the second negative electrode film layer.

[0198] In some embodiments, the negative electrode film layer may further optionally include a negative electrode conductive agent. The present application does not particularly limit the type of the negative electrode conductive agent. For 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.

[0199] 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.

[0200] In some embodiments, the negative electrode film layer may further include a negative electrode binder.

[0201] In some embodiments, the negative electrode binder includes one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, aqueous acrylic resin, polyvinyl alcohol, sodium alginate, and carboxymethyl chitosan.

[0202] In some embodiments, the mass content of the negative electrode binder is ≤5% based on the total weight of the negative electrode film layer.

[0203] In some embodiments, the negative electrode film layer may optionally include other additives, such as thickeners, dispersants, and the like, for example, sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, and the like.

[0204] In some embodiments, based on the total weight of the negative electrode film layer, the mass content of other additives is ≤2%.

[0205] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. Examples of metal foils include at least one of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base layer. For example, the metal layer may include at least one of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. For example, the polymer base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0206] The negative electrode film layer is typically formed by coating the negative electrode slurry onto the negative electrode current collector, drying it, and cold pressing it. The negative electrode slurry is typically formed by dispersing the negative electrode active material, an optional conductive agent, an optional binder, and other optional additives in a solvent and stirring them uniformly. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0207] The negative electrode sheet does not exclude other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of the embodiments of the present application further includes a negative 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 embodiments of the present application further includes a protective layer covering the surface of the negative electrode film layer.

[0208] In some embodiments, the negative electrode plate further includes a negative electrode conductive layer, wherein the negative electrode conductive layer is located between the negative electrode current collector and the negative electrode film layer on at least one side, and the negative electrode conductive layer includes a conductive agent, wherein the conductive agent includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0209] By providing a negative electrode conductive layer containing a conductive agent between the current collector and the negative electrode film layer, the conductivity of the negative electrode plate can be improved and the fast charging performance of the battery cell can be improved.

[0210] In some embodiments, the thickness of the negative electrode conductive layer is 0.5 μm to 2 μm, and 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 a range consisting of any two of the above values.

[0211] In the embodiment of the present application, the thickness of the negative electrode conductive layer has a well-known meaning in the art and can be detected using equipment and methods well-known in the art. Reference can be made to the test method for the first negative electrode film layer or the second negative electrode film layer mentioned above.

[0212] By controlling the thickness of the negative electrode conductive layer within an appropriate range, both the fast charging performance and the energy density of the battery cell can be taken into account.

[0213] In some embodiments, the negative electrode conductive layer includes a negative electrode conductive layer binder.

[0214] The binder in the negative electrode conductive layer can improve the bonding performance between the negative electrode current collector and the negative electrode film layer, and improve the structural stability of the negative electrode sheet.

[0215] In some embodiments, the negative electrode conductive layer binder 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.

[0216] In some embodiments, the battery cell has a compaction density of the negative electrode film layer of 1.15 g / cm at 100% state of charge. 3 ~1.45g / cm 3 For example, the compaction density of the negative electrode film layer of the battery cell at 100% state of charge is 1.15 g / cm 3 , 1.18g / cm 3 , 1.20g / cm 3 , 1.22g / cm 3 , 1.25g / cm 3 , 1.28g / cm 3 , 1.3g / cm 3 , 1.32g / cm 3 , 1.35g / cm 3 , 1.36g / cm 3 , 1.38g / cm 3 , 1.4g / cm 3 , 1.42g / cm 3 , 1.45g / cm 3 Or a range consisting of any two of the above values.

[0217] In the embodiments of the present application, the compaction density of the negative electrode film layer of a battery cell at 100% state of charge (SOC) can be tested using the following method: charge the battery cell to 3.65V at a constant current of 0.33C, then continue charging at a constant voltage of 3.65V to 0.05C, and then stop charging. At this point, the battery is at 100% state of charge. Disassemble the negative electrode sheet from the battery cell at 100% state of charge (SOC), and measure the compaction density of the negative electrode film layer. Take 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), punch it into a small disc with an area of ​​S1, weigh it, record it as M1, and measure its thickness H1. Then wipe off the negative electrode film layer of the weighed negative electrode sheet, weigh the negative electrode current collector, record it as M0, and measure its thickness H0. The single-sided coating weight of the negative electrode film layer = (the weight of the negative electrode plate M1 - the weight of the negative electrode current collector M0) / S1, the thickness of the negative electrode film layer = the thickness of the negative electrode plate H1 - the thickness of the negative electrode current collector H0, the compaction density of the negative electrode film layer = the single-sided coating weight of the negative electrode film layer / the thickness of the negative electrode film layer.

[0218] The compaction density of the negative electrode film layer is within an appropriate range, which is beneficial to improving the fast charging performance of the battery cell.

[0219] In some embodiments, the single-sided coating weight of the negative electrode film layer is 70 mg / 1540.25 mm 2 ~135mg / 1540.25mm 2 For example, the coating weight of the negative electrode film on one side is 70 mg / 1540.25 mm 2 、75mg / 1540.25mm 2 、80mg / 1540.25mm 2 、85mg / 1540.25mm 2 、90mg / 1540.25mm 2 、92mg / 1540.25mm 2 、95mg / 1540.25mm 2 、96mg / 1540.25mm 2 、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 Or a range consisting of any two of the above values.

[0220] The single-sided coating weight of the negative electrode film layer is within an appropriate range, which is beneficial to improving the fast charging performance of the battery cell.

[0221] [Positive electrode]

[0222] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector and comprising a positive electrode active material. For example, the positive electrode current collector may have two opposing surfaces in its thickness direction, and the positive electrode film layer may be disposed on either or both of the two opposing surfaces of the positive electrode current collector.

[0223] In some embodiments, the mass proportion of the lithium-containing phosphate with an olivine structure in the positive electrode active material may be greater than or equal to 80% and less than or equal to 100%, and the positive electrode active material of the present application may be considered to be a lithium-containing phosphate system with an olivine structure. When the mass proportion of the lithium-containing phosphate with an olivine structure is less than 100%, the positive electrode active material may also include a commonly used positive electrode active material, for example, it may include but is not limited to at least one of lithium-containing transition metal oxides. Examples of lithium-containing transition metal oxides may include but are not limited to at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds.

[0224] In some embodiments, the mass proportion of the lithium-containing phosphate with an olivine structure in the positive electrode active material is 100%.

[0225] In some embodiments, the olivine-structured lithium-containing phosphate comprises:

[0226] A lithium phosphate matrix, and

[0227] The coating layer is located on at least a portion of the surface of the lithium-containing phosphate matrix, and the coating layer contains carbon elements.

[0228] The lithium-containing phosphate with an olivine structure includes a carbon coating layer. The carbon coating layer is loose and porous, which is beneficial to increasing the specific surface area of ​​the material, more conducive to effective contact between the electrolyte and the phosphate particles, and conducive to the transmission of lithium ions at the phase interface. It can improve the electrical conductivity of the material and is beneficial to improving the fast charging performance of the battery cell.

[0229] In some embodiments, the lithium-containing phosphate matrix comprises a general formula of Li x1 A y1 Me a1 M b1 P 1-c1 X c1 Y z1 Compounds

[0230] Among them, 0.5≤x1≤1.3, 0≤y1≤1.3, 0.9≤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;

[0231] Wherein, 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 S, Si, Cl, B, C, N and P; and Y includes at least one of O and F.

[0232] In some embodiments, x1 can be selected as 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, or a range consisting of any two of the above values.

[0233] In some embodiments, y1 can be selected as 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3 or a range consisting of any two of the above values.

[0234] In some embodiments, x1+y1 can be selected as 0.9, 1.0, 1.1, 1.2, 1.3, or a range consisting of any two of the above values.

[0235] In some embodiments, a1 can be selected as 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, or a range consisting of any two of the above values.

[0236] In some embodiments, b1 can be selected as 0, 0.1, 0.2, 0.3, 0.4, 0.5, or a range consisting of any two of the above values.

[0237] In some embodiments, a1+b1 can be selected as 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, or a range consisting of any two of the above values.

[0238] In some embodiments, c1 can be selected as 0, 0.1, 0.2, 0.3, 0.4, 0.5, or a range consisting of any two of the above values.

[0239] In some embodiments, z1 can be selected as 3.0, 3.5, 4.0, 4.5, 5.0 or a range consisting of any two of the above values.

[0240] Lithium-containing phosphates with an olivine structure have good cycle stability, which is beneficial to improving the cycle performance of battery cells.

[0241] In some embodiments, the lithium phosphate matrix includes one or more of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium nickel phosphate, lithium cobalt phosphate, and modified forms of any of the foregoing substances, wherein the modified form includes one or more of doping modification and coating modification.

[0242] During the charge and discharge process of battery cells, active ions such as Li are deintercalated and consumed. The molar content of Li in battery cells is different when they are discharged to different states. 1-x Mn x In the examples of PO4 (0 < x < 1), LiNiPO4, LiCoPO4, etc., the molar content of Li refers to the initial state of the material, that is, the state before adding the material. When the positive electrode active material is used in the battery system, the molar content of Li may change after charge and discharge cycles. In the embodiments of this application, the positive electrode active materials LiFePO4, LiMnPO4, LiNiPO4, LiFe 1-x Mn x In the examples of PO4 (0<x<1), LiCoPO4, etc., the molar content of oxygen is only a theoretical value. The release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual molar content of oxygen will fluctuate. The above situations are all within the scope of protection of this application.

[0243] In some embodiments, based on the mass of the olivine-structured lithium-containing phosphate, the mass content of the carbon element is 0.8%~2.3%, which can be optionally 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, 2.2%, 2.3% or a range consisting of any two of the above values.

[0244] The carbon content in materials is usually measured by infrared absorption, such as infrared carbon-sulfur instruments, or by indirect carbon determination methods. The latter can refer to the national standard GB / T 3521-2008 ("Chemical Analysis Methods of Graphite" on pages 3-4).

[0245] By controlling the mass content of carbon elements in the coating layer within an appropriate range, the conductivity of the material and the fast charging performance of the battery can be improved while taking into account the gram capacity of the material, the fast charging performance and energy density of the battery cell.

[0246] In some embodiments, the battery cells satisfy the following relationship: 0.08≤C / B≤1.15,

[0247] Wherein, C is the mass content of carbon element, which is based on the mass of the lithium-containing phosphate with olivine structure;

[0248] B is the mass content of the first additive, based on the total mass of the electrolyte.

[0249] In some embodiments, the value of C / B can be selected as 0.08, 0.10, 0.12, 0.15, 0.18, 0.2, 0.25, 0.30, 0.35, 0.40, 0.45, 0.5, 0.55, 0.60, 0.65, 0.70, 0.75, 0.8, 0.85, 0.90, 1.0, 1.05, 1.10, 1.15, or a range consisting of any two of the above values.

[0250] As mentioned above, the carbon element in the carbon coating can improve the effective contact between the electrolyte and the phosphate particles, improving the conductivity of the material. However, while the porous carbon coating improves the electrolyte's wettability, it also causes side reactions between the phosphate particles and the electrolyte, consuming lithium ions and affecting the battery's cycling performance. The first additive in the electrolyte helps form a CEI film layer on the positive electrode side, reducing the possibility of side reactions between the electrolyte and the positive electrode active material, improving the stability of the positive electrode interface, and enhancing the battery's cycling performance.

[0251] This application controls the mass content of carbon elements in the lithium-containing phosphate with an olivine structure and the mass content of the first additive within an appropriate range. Through the synergistic effect of the two, it can improve the conductivity of the material and enhance the fast charging performance of the battery cell while also taking into account the cycle stability of the material and the cycle performance of the battery.

[0252] In some embodiments, the coating layer further comprises Li 3-d1 Fe 2-d1 M3 d1 (PO m1 ) n1 of substances,

[0253] Among them, 0≤d1≤1, 0≤m1≤5, 0≤n1≤4;

[0254] M3 includes one or more elements selected from Ti, Zr, Hf, Ge, and Sn. Optionally, M3 has a valence of +4.

[0255] In some embodiments, the coating layer further includes one or more of Li2FeTi(PO4)3, Li2FeZr(PO4)3, and Li2FeSn(PO4)3.

[0256] In some embodiments, carbon and Li 3-d1 Fe 2-d1 M3 d1 (PO m1 ) n1 The materials can be layered, such as carbon as an independent carbon coating layer, Li 3-d1 Fe 2-d1 M3 d1 (PO m1 ) n1 The material can be used as an independent fast ion conductor layer, the carbon coating layer can be coated on the surface of the phosphate particles, and the fast ion conductor layer is located on the surface of the carbon coating layer, that is, 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 coated on the surface of the phosphate particles, and the carbon coating layer is located on the surface of the fast ion conductor layer, that is, the carbon coating layer is located on the side of the fast ion conductor layer away from the phosphate particles. Of course, carbon and Li 3-d1 Fe 2-d1 M3 d1 (PO m1 ) n1 The materials can also be set on the same layer.

[0257] The coating layer includes Li 3-d1 Fe 2-d1 M3 d1 (PO m1 ) n1 , which has excellent ion conductivity, and together with the carbon element with excellent conductivity in the coating layer, it improves the conductivity and ion conductivity of the material, which is beneficial to improving the fast charging performance of the battery.

[0258] In the embodiments of the present application, the content of elements in the positive electrode active material has a meaning known in the art and can be detected using equipment and methods known in the art, for example, with reference to EPA6010D-2014, by inductively coupled plasma atomic emission spectrometry, using plasma atomic emission (ICP-OES, instrument model: ThermoICAP7400) for determination. After the battery cell is discharged to 0% state of charge (SOC), the positive electrode sheet is disassembled, cleaned with DMC and dried.

[0259] After high-temperature calcination to remove impurities, 0.4g of the positive electrode active material was weighed and 10ml of 50% aqua regia was added. The mixture was then placed on a plate at 180°C for 30 minutes. After digestion on the plate, the volume was adjusted to 100ml and quantitative analysis was performed using the standard curve method.

[0260] In some embodiments, the powder compaction density of the positive electrode active material at 30,000 N is 2.43 g / cm 3 ~2.85g / cm 3 , optional 2.43g / cm 3 , 2.44g / cm 3 , 2.45g / cm 3 , 2.46g / cm 3、 2.47g / cm 3 , 2.48g / cm 3 , 2.49g / 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 , 2.70g / cm 3 , 2.72g / 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.

[0261] When the powder compaction density of the positive electrode active material at 30,000N is within the above range, the energy density of the battery cell can be improved. Moreover, since the positive electrode active material in the positive electrode film layer can be stacked more densely and the contact resistance between particles is smaller, the resistance of the electrode sheet can be further reduced, which is also beneficial to improving the fast charging performance of the battery cell.

[0262] In the embodiment of the present application, the powder compaction density of the material is a well-known meaning in the art and can be tested using methods and equipment known in the art. 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 cm 2 The mold was pressurized to 3000 kg (equivalent to 30000 N), maintained for 30 seconds, then released and maintained for 10 seconds, and then the powder compaction density of the positive electrode active material under a force of 30000 N was recorded and calculated.

[0263] In some embodiments, when the battery cell is at 100% state of charge, the compaction density of the positive electrode film layer is 2.50 g / cm 3 ~2.80g / cm 3 , optional 2.50g / cm 3 , 2.55g / cm 3 , 2.60g / cm 3 , 2.65g / cm 3 , 2.70g / cm 3 , 2.75g / cm 3 , 2.80g / cm 3 Or a range consisting of any two of the above values.

[0264] In the embodiment of the present application, the compaction density of the positive electrode film layer of the battery cell at 100% charge state has a meaning well known in the art and can be detected using equipment and methods well known in the art, and the detection method is the same as the compaction density test method of the negative electrode film layer mentioned above.

[0265] The compaction density of the positive electrode film layer is within a suitable range, and the battery cell has a high energy density.

[0266] In some embodiments, the positive electrode film layer may further optionally include a positive electrode conductive agent. The present application does not particularly limit the type of positive electrode conductive agent. For example, the positive 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 positive electrode conductive agent is ≤5% based on the mass of the positive electrode film layer.

[0267] In some embodiments, the positive electrode film layer may further optionally include a positive electrode binder. The embodiments of the present application do not particularly limit the type of positive electrode binder. As an example, the positive electrode binder may include at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and fluorine-containing acrylic resin. In some embodiments, based on the mass of the positive electrode film layer, the mass content of the positive electrode binder is ≤5%.

[0268] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. Examples of metal foils include at least one of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base layer. For example, the metal material of the metal layer may include at least one of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. For example, the polymer base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0269] The positive electrode film layer is usually formed by coating the positive electrode slurry on the positive electrode current collector, drying it, and cold pressing it. 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 them evenly. The solvent can be N-methylpyrrolidone (NMP), but is not limited to this. The positive electrode plate does not exclude other additional functional layers in addition to the positive electrode film layer. For example, in some embodiments, the positive electrode plate of the embodiment 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 arranged on the surface of the positive electrode current collector. In some other embodiments, the positive electrode plate of the embodiment of the present application further includes a protective layer covering the surface of the positive electrode film layer.

[0270] [Electrolyte]

[0271] During the charge and discharge process of a battery cell, active ions such as lithium ions are embedded and released back and forth between the positive electrode and the negative electrode, and the electrolyte plays the role of conducting active ions between the positive electrode and the negative electrode.

[0272] In an embodiment of the present application, the electrolyte includes a first additive, wherein the first additive includes at least one of vinylene carbonate and an ethylene carbonate derivative, and the mass content of the first additive is 1% to 12% based on the total mass of the electrolyte.

[0273] Wherein, the ethylene carbonate derivative includes the compound shown in formula I,

[0274] Formula I

[0275] R1, R2, R3, and R4 each independently include any one of a hydrogen atom, a halogen atom, a C1-C5 alkyl group, and a C1-C5 halogenated alkyl group, and R1, R2, R3, and R4 are not hydrogen atoms at the same time.

[0276] A first additive of vinylene carbonate and / or vinylene carbonate derivatives is added to the electrolyte. Vinylene carbonate and vinylene carbonate derivatives can participate in the formation of an SEI film on the negative electrode side in priority to other components in the electrolyte, and the organic matter content in the film formed by vinylene carbonate and vinylene carbonate derivatives is relatively high, which is beneficial to improving the overall flexibility of the SEI film, improving the stability of the SEI film and the negative electrode interface during the cycle, reducing the reaction between the negative electrode active material and the electrolyte, reducing the consumption of lithium ions, and improving the cycle performance and storage performance of the battery cell. In addition, controlling the mass content of the first additive within an appropriate range can improve the flexibility and stability of the SEI film while controlling the thickness of the SEI film within an appropriate range, thereby achieving the stability and low impedance of the negative electrode interface at the same time, and taking into account the cycle performance and fast charging performance of the battery cell.

[0277] In some embodiments, at least one of R1, R2, R3, and R4 comprises a fluorine atom.

[0278] The ethylene carbonate derivative in which at least one of R1, R2, R3, and R4 is a fluorine atom is easy to open the ring, forming a SEI film containing more organic matter on the surface of the negative electrode, which is beneficial to improving the flexibility of the overall SEI film, achieving the purpose of improving the stability of the interface between the SEI film and the negative electrode during the cycle, and improving the cycle performance of the battery cell.

[0279] In some embodiments, the ethylene carbonate derivative includes one or more of fluoroethylene carbonate, difluoroethylene carbonate, and trifluoromethylethylene carbonate.

[0280] Suitable ethylene carbonate derivative additives can form a SEI film containing a large amount of organic matter on the negative electrode side, which can improve the overall flexibility of the SEI film, thereby achieving the purpose of improving the stability of the SEI film and the negative electrode interface during the cycle, and improving the cycle performance of the battery cell. At the same time, the SEI film formed with the participation of fluoroethylene carbonate, difluoroethylene carbonate, and trifluoromethylethylene carbonate has low impedance, which is also beneficial to improving the fast charging performance of the battery cell.

[0281] In some embodiments, the electrolyte further comprises an organic solvent, wherein the organic solvent comprises one or more of a first organic solvent and a second organic solvent.

[0282] Wherein, the first organic solvent includes at least one of a cyclic carbonate and a chain carbonate, and can be a cyclic carbonate;

[0283] The second organic solvent includes R5-COO-R6,

[0284] Wherein, R5 includes any one of a hydrogen atom, a halogen atom, a C1-C5 alkyl group, and a C1-C5 halogenated alkyl group, and R6 includes any one of a C1-C5 alkyl group and a C1-C5 halogenated alkyl group.

[0285] The first organic solvent of cyclic carbonate and chain carbonate has a relatively high dielectric constant and excellent ionic conductivity, which is beneficial to improving the conductivity of the electrolyte. The second organic solvent has a low viscosity, which is beneficial to improving the conductivity of the electrolyte. The electrolyte contains the first organic solvent and / or the second organic solvent, which is beneficial to improving the migration of lithium ions and improving the fast charging performance of the battery cell.

[0286] In some embodiments, the cyclic carbonate includes one or more of ethylene carbonate, propylene carbonate, and butylene carbonate.

[0287] In some embodiments, the linear carbonate includes one or more of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0288] In some embodiments, the second organic solvent includes one or more of methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, and ethyl butyrate.

[0289] In some embodiments, based on the total mass of the electrolyte, the mass content of the first organic solvent is 20%~72%, which can be optionally 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 72% or a range consisting of any two of the above values.

[0290] The first organic solvent containing a suitable content of cyclic carbonate or chain carbonate can further improve the conductivity of the electrolyte, facilitate the migration of lithium ions, and improve the fast charging performance of the battery cell.

[0291] The type and quality of the solvent in the electrolyte can be obtained by testing the electrolyte by methods well known to those skilled in the art. For example, the composition of the electrolyte can be measured by liquid chromatography, ultraviolet spectrophotometry, ultraviolet-visible spectrophotometry, etc. For example, the battery cell is disassembled, and free electrolyte is obtained from the battery cell. The free electrolyte in the battery cell is diluted to 3 to 10 times with acetonitrile to obtain the electrolyte dilution to be tested. The above electrolyte dilution is placed in the instrument for full scan qualitative analysis using a GC-MS 3100 organic component gas chromatograph. The injection port temperature is 250°C, and the scanning range is: 35μm~270μm. After the test is completed, the total ion current chromatogram of each organic matter is obtained. The type of organic matter corresponding to the peak position of the chromatogram is compared, and the corresponding content percentage of each organic matter is calculated based on the peak area.

[0292] In some embodiments, the electrolyte further includes a second additive, and the second additive includes one or more of a sulfur-containing additive and a lithium salt additive.

[0293] Additives refer to components with low content in the electrolyte, which generally account for no more than 10% of the mass of the electrolyte. They are highly targeted and used in small amounts, and can significantly optimize the performance of a certain aspect of the battery without changing the production process.

[0294] Sulfur-containing additives and lithium salt additives can improve the interfacial film performance on the positive electrode side and / or the negative electrode side, improve the interfacial chemistry between the positive electrode and / or the negative electrode and the electrolyte, and improve the fast charging performance and cycle performance of the battery.

[0295] In some embodiments, the sulfur-containing additive includes one or more of vinyl sulfate, vinyl bissulfate, butylene sulfite, 1,3-propane sultone, vinyl sulfite, and methylene disulfonate.

[0296] In some embodiments, the lithium salt additive includes one or more of lithium difluorophosphate, lithium difluorooxalatoborate, lithium tetrafluoroborate, and lithium bis(oxalatoborate).

[0297] In some embodiments, the electrolyte further includes a lithium salt, and the lithium salt includes one or both of a fluorine-containing sulfonyl imide salt and lithium hexafluorophosphate.

[0298] Fluorinated sulfonyl imide salts and lithium hexafluorophosphate are easy to dissociate, which is beneficial to the rapid migration of lithium ions and the improvement of the fast charging performance of battery cells. Fluorinated sulfonyl imide salts and lithium hexafluorophosphate are relatively stable in the electrolyte system and can improve the cycle performance of battery cells.

[0299] In some embodiments, the fluorine-containing sulfonyl imide salt includes one or both of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide.

[0300] In some embodiments, the lithium salt includes lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate, and the ratio of the molar concentration of the lithium bis(fluorosulfonyl)imide to the molar concentration of the lithium hexafluorophosphate is 0.2-1.0, and can be optionally 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, or a range consisting of any two of the above values.

[0301] In some embodiments, the molar concentration of the lithium bis(fluorosulfonyl)imide is 0.2 mol / L to 0.5 mol / L, which can be 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.40 mol / L, 0.45 mol / L, 0.5 mol / L, or a range consisting of any two of the above values;

[0302] The molar concentration of lithium hexafluorophosphate is 0.5 mol / L to 1.2 mol / L, and can be 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.2 mol / L, or a range consisting of any two of the above values.

[0303] [Isolation film]

[0304] The electrode assembly includes a separator disposed between the positive electrode and the negative electrode.

[0305] The present application has no particular limitation on the type of isolation membrane, and any known isolation membrane with a porous structure having good chemical stability and mechanical stability can be selected.

[0306] As an example, the primary material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and ceramic. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation. The separator can be a separate component located between the positive and negative electrodes, or it can be attached to the surfaces of the positive and negative electrodes. The surface of the separator can also be coated with an inorganic particle coating, an organic particle coating, or an organic / inorganic composite coating.

[0307] In some embodiments, the thickness of the isolation film is 4 μm to 12 μm, and can be 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, or a range consisting of any two of the above values.

[0308] In the embodiments of the present application, the thickness of the isolation membrane has a meaning well known in the art, and can be detected using the meanings and equipment well known in the art. For example, a newly prepared isolation membrane can be taken as a sample, or a battery cell that has been discharged (discharged to the lower limit cut-off voltage so that the battery's charged state is approximately 0% SOC) can be reversely disassembled, the isolation membrane can be obtained from the battery cell and dried as a sample, the isolation membrane can be cut with an ion beam cutter to form a cross section, and then the thickness of the isolation membrane can be measured using a scanning electron microscope.

[0309] When the thickness of the isolation membrane is within an appropriate range, the migration path of lithium ions in the isolation membrane is shorter, which can reduce the internal resistance of the battery cell and improve the fast charging performance of the battery cell.

[0310] In some embodiments, the porosity of the isolation membrane is 20% to 70%, which can be 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70% or a range consisting of any two of the above values.

[0311] In the embodiments of this application, porosity refers to the percentage of the pore volume within the separator to the total volume of the separator. Porosity can be tested in accordance with the standard GB / T36363-2018, "Polyolefin Separators for Battery Cells." It should be noted that the actual testing process may vary slightly from the standard to obtain a more accurate test value, depending on instrument differences, test errors, and to minimize the impact of porosity testing.

[0312] When the porosity of the separator is within an appropriate range, the migration rate of lithium ions in the separator can be increased, the internal resistance of the battery cell can be reduced, and the fast charging performance of the battery cell can be improved.

[0313] In some embodiments, the battery cell is configured to have a charging time from 10% state of charge to 80% state of charge of 5 minutes to 10.5 minutes, which can be 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, 10.5 minutes, or a range consisting of any two of the above values.

[0314] In some embodiments, the charging process of the battery cell from 10% state of charge to 80% state of charge includes multiple charging steps, and the maximum state of charge of any charging step in the multiple charging steps is

[0315] The difference between the maximum state of charge in the state of charge and the maximum state of charge in the 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 point value in the range formed by any two of the above values.

[0316] The battery cell includes multiple charging steps from 10% state of charge to 40% state of charge. For any charging step, it can be charged at any rate between 5C and 10C. The charging rate corresponding to each charging step can be any value of 5C, 5.5C, 6C, 6.5C, 7C, 7.5C, 8C, 8.5C, 9C, 9.5C, 10C, or a value in the range of any two of the above values.

[0317] The battery cell also includes multiple charging steps from 40% state of charge to 80% state of charge, the charging rate of any charging step is less than the charging rate of any charging step from 10% state of charge to 40% state of charge, and the charging rate of the step to 80% state of charge is any value between 2.5C and 7C.

[0318] For example, the charging process of a battery cell from 10% state of charge to 80% state of charge may be performed as follows:

[0319] Charge from 10% SOC to 15% SOC at 7.0C constant current;

[0320] Charge from 15% SOC to 20% SOC at 7.0C constant current;

[0321] Charge from 20% SOC to 25% SOC at 7.0C constant current;

[0322] Charge from 25% SOC to 30% SOC at 6.6C constant current;

[0323] Charge from 30% SOC to 35% SOC at 6.2C constant current;

[0324] Charge from 35% SOC to 40% SOC at 5.7C constant current;

[0325] Charge from 40% SOC to 45% SOC at 5.2C constant current;

[0326] Charge from 45% SOC to 50% SOC at 4.8C constant current;

[0327] Charge from 50% SOC to 55% SOC at 4.6C constant current;

[0328] Charge from 55% SOC to 60% SOC at 4.4C constant current;

[0329] Charge from 60% SOC to 65% SOC at 4.2C constant current;

[0330] Charge from 65% SOC to 70% SOC at 3.9C constant current;

[0331] Charge from 70% SOC to 75% SOC at 3.5C constant current;

[0332] Charge from 75% SOC to 80% SOC at 3.0C constant current.

[0333] The battery cell has a fast charging speed and has excellent fast charging performance.

[0334] In some embodiments, the volume energy density of the battery cell is 395Wh / L~530Wh / L, which can be 395Wh / L, 400Wh / L, 410Wh / L, 420Wh / L, 430Wh / L, 440Wh / L, 450Wh / L, 460Wh / L, 470Wh / L, 480Wh / L, 490Wh / L, 500Wh / L, 510Wh / L, 520Wh / L, 530Wh / L or a range consisting of any two of the above values.

[0335] The volume energy density of battery cells is high.

[0336] In the embodiments of the present application, the volume energy density of a battery cell has a meaning well known in the art and can be detected using equipment and methods well known in the art. For example, taking a battery charging upper limit voltage of 3.65V and a battery discharge cut-off voltage of 2.0V as an example, the battery cell is placed at 25°C, charged to 3.65V at a constant current of 0.33C, then charged to 0.05C at a constant voltage, and discharged to 2.0V at a constant current of 0.33C. The discharge capacity A0 at this time is recorded in Ah. The length, width, and height of the battery cell are measured with a caliper (generally calculated based on the size of the battery casing, excluding the height of the electrode terminals and the insulating film outside the casing), and the volume V0 of the single cell is calculated in L. The volume energy density VED of the battery cell is VED=(A0×discharge platform voltage) / V0 in Wh / L.

[0337] [Battery device]

[0338] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0339] In some embodiments, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0340] In some embodiments, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the battery cell may be a soft shell, such as a pouch-type soft shell. The soft shell may be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0341] The present application has no particular restrictions on the shape of the battery cell, which can be cylindrical, square or any other shape. For example, Figure 1 The battery cell 5 is a square structure as an example.

[0342] In some embodiments, reference Figure 2 The outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the diaphragm can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0343] In some embodiments, a battery cell pool may be assembled into a battery module. The number of battery cells contained in the battery module may be one or more. The specific number may be selected by those skilled in the art based on the application and capacity of the battery module.

[0344] Figure 3 4 is an example of a battery module. Figure 3 In the battery module 4, the plurality of battery cells 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. The plurality of battery cells 5 may further be fixed by fasteners.

[0345] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0346] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0347] Figure 4 and Figure 5 The battery pack 1 is used as an example. Figure 4 and Figure 5The battery pack 1 may include a battery box and multiple battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner in the battery box.

[0348] In addition, the present application also provides an electrical device, which includes at least one of the battery cells, battery modules, or battery packs provided in the present application. The battery cells, battery modules, or battery packs can serve as power sources for the electrical device or as energy storage units for the electrical device. Electrical devices may include, but are not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc.

[0349] As an electrical device, a battery cell, battery module or battery pack can be selected according to its usage requirements.

[0350] Figure 6 This is an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the battery cells in this device, a battery pack or battery module can be used.

[0351] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be lightweight and thin, and may use a battery cell as a power source.

[0352] 1. Preparation method of embodiment

[0353] The following examples describe the disclosure of the present invention in more detail. These examples are intended for illustrative purposes only, as various modifications and variations within the scope of the disclosure of the present invention will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing, and the instruments used in the examples are commercially available.

[0354] Example 1

[0355] (1) Preparation of positive electrode

[0356] The positive electrode sheet includes a positive electrode current collector, a positive electrode conductive layer on the positive electrode current collector and a positive electrode film layer. The positive electrode current collector is an aluminum foil with a thickness of 13 μm.

[0357] The positive conductive layer on the positive current collector is a film layer formed by evenly mixing the positive electrode conductive agent superconducting carbon, the positive electrode binder polyvinylidene fluoride (PVDF) and the solvent N-methylpyrrolidone NMP, and then coating it on the current collector surface and drying it. The thickness is 1μm. The mass content of the positive electrode conductive agent in the positive conductive layer is 40%, and the mass content of the positive electrode binder is 60%.

[0358] The positive electrode film layer includes a positive electrode slurry (the solvent is N-methylpyrrolidone NMP) uniformly coated on the surface of the positive electrode conductive layer, and a film layer formed after drying and cold pressing. The positive electrode film layer includes a positive electrode active material, a binder polyvinylidene fluoride (PVDF) and a conductive agent acetylene black in a weight ratio of 97:2:1.

[0359] The positive electrode active material includes lithium iron phosphate, which has a coating layer. The coating layer is coated on the surface of the lithium iron phosphate particles. The coating layer includes lithium iron titanium phosphate Li2FeTi(PO4)3 and carbon element, and the mass content of the carbon element is 1.12%.

[0360] The single-sided coating weight of the positive electrode film is 250mg / 1540.25mm 2 .

[0361] (2) Preparation of negative electrode sheet

[0362] The negative electrode sheet includes a negative electrode current collector, a negative electrode conductive layer on the negative electrode current collector and a negative electrode film layer. The negative electrode current collector is a copper foil with a thickness of 5 μm.

[0363] The negative electrode conductive layer on the negative electrode current collector is a film layer formed by evenly 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, and then coating it on the surface of the negative electrode current collector and drying it. The thickness is 1 μm, 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%.

[0364] The negative electrode film layer includes a film layer formed by uniformly coating the negative electrode slurry (the solvent is deionized water) on the surface of the negative electrode conductive layer, drying, and cold pressing.

[0365] The single-sided coating weight of the negative electrode film is 95mg / 1540.25mm 2 .

[0366] The negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer. The first negative electrode film layer is located on the surface of the negative electrode conductive layer, and the second negative electrode film layer is located on the surface of the first negative electrode film layer.

[0367] The first negative electrode film layer includes composite graphite particles, silicon-carbon composite material, conductive agent acetylene black, binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose in a mass ratio of 91.5:5:0.5:2:1. The Dv50 of the composite graphite particles is 11.3 μm.

[0368] The second negative electrode film layer includes composite graphite particles, silicon-carbon composite material, conductive agent acetylene black, binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose in a mass ratio of 92.5:5:0.5:1:1. The Dv50 of the composite graphite particles is 11.3 μm.

[0369] The thickness ratio of the first film layer to the second film layer is 50%:50%.

[0370] (3) Isolation film

[0371] The isolation film includes a base film, which is a 7 μm polyethylene film layer with a porosity of 42%.

[0372] (4) Preparation of electrolyte

[0373] The electrolyte includes an organic solvent, a lithium salt, a first additive, and a second additive.

[0374] The organic solvent includes a chain carboxylate solvent (ethyl acetate) with a mass content of 39.0% and a carbonate solvent (ethylene carbonate EC with a mass content of 27.3% and dimethyl carbonate with a mass content of 11.7%) with a mass content of 39.0%. The mass content of each component in the organic solvent is calculated based on the mass of the electrolyte.

[0375] Based on the mass of the electrolyte, the total mass content of the first additive and the second additive is 7%, which includes vinylene carbonate VC, fluoroethylene carbonate FEC, vinyl sulfite ES and lithium difluorooxalatoborate LiDFOB in a mass ratio of 5:1:0.5:0.5.

[0376] The lithium salt includes lithium bis(fluorosulfonyl)imide LiFSI with a mass content of 4.5% and lithium hexafluorophosphate LiPF6 with a mass content of 10.5%. The mass content of the lithium salt is calculated based on the mass of the electrolyte.

[0377] (5) Preparation of battery cells

[0378] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive electrode sheet and the negative electrode sheet to serve as an isolation to obtain an electrode assembly. The electrode assembly is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum packaging, standing, forming, shaping and other processes, a battery cell is obtained.

[0379] Example 2-Example 5

[0380] Compared with Example 1, Examples 2-5 adjusted the single-sided coating weight of the positive electrode film layer and the mass content of the silicon-carbon composite material in the first negative electrode film layer and the second negative electrode film layer. For specific parameters, see Table 3 and Table 4.

[0381] Examples 6-9

[0382] Compared with Example 1, Examples 6-9 adjusted the mass contents of ethylene carbonate, dimethyl carbonate, ethyl acetate, and the first additive in the electrolyte and the mass contents of the silicon-carbon composite material in the first negative electrode film layer and the second negative electrode film layer in the negative electrode film layer. For specific parameters, see Table 3 and Table 4.

[0383] Examples 10-12

[0384] Compared with Example 1, the mass content of carbon in the lithium iron phosphate coating layer was adjusted in Examples 10-12. For specific parameters, see Table 3 and Table 4.

[0385] Example 13

[0386] Compared with Example 1, Example 13 adjusts the single-sided coating weight of the positive electrode film layer and the negative electrode film layer and the mass content of ethylene carbonate, dimethyl carbonate, ethyl acetate, and the first additive in the electrolyte. For specific parameters, see Table 3 and Table 4.

[0387] Comparative Example 1

[0388] Compared with Example 1, Comparative Example 1 adjusted the single-sided coating weight of the positive electrode film layer and the negative electrode film layer, and the negative electrode film layer did not contain the silicon-carbon composite material. For specific parameters, see Table 3 and Table 4.

[0389] Comparative Example 2

[0390] Compared with Example 1, Comparative Example 2 adjusted the single-sided coating weight of the positive electrode film layer and the mass content of the silicon-carbon composite material in the first negative electrode film layer and the second negative electrode film layer. For specific parameters, see Table 3 and Table 4.

[0391] Comparative Example 3-Comparative Example 4

[0392] Compared with Example 1, the mass contents of ethylene carbonate, dimethyl carbonate, ethyl acetate, and the first additive in the electrolyte were adjusted in Comparative Examples 3-4. For specific parameters, see Tables 3 and 4.

[0393] 2. Performance testing.

[0394] 1. The charging time of the battery cell from 10% SOC to 80% SOC is specifically charged in the following steps:

[0395] Take the battery cell of Example 1 as an example:

[0396] At 30°C, charge from 10% SOC of the battery cell.

[0397] Charge from 10% SOC to 15% SOC at 7.0C constant current;

[0398] Charge from 15% SOC to 20% SOC at 7.0C constant current;

[0399] Charge from 20% SOC to 25% SOC at 7.0C constant current;

[0400] Charge from 25% SOC to 30% SOC at 7.0C constant current;

[0401] Charge from 30% SOC to 35% SOC at 6.2C constant current;

[0402] Charge from 35% SOC to 40% SOC at 5.7C constant current;

[0403] Charge from 40% SOC to 45% SOC at 5.2C constant current;

[0404] Charge from 45% SOC to 50% SOC at 4.8C constant current;

[0405] Charge from 50% SOC to 55% SOC at 4.6C constant current;

[0406] Charge from 55% SOC to 60% SOC at 4.4C constant current;

[0407] Charge from 60% SOC to 65% SOC at 4.2C constant current;

[0408] Charge from 65% SOC to 70% SOC at 3.9C constant current;

[0409] Charge from 70% SOC to 75% SOC at 3.5C constant current;

[0410] Charge from 75% SOC to 80% SOC at 3.0C constant current;

[0411] Record the total charging time.

[0412] The slight difference in charging time between the battery cells of different embodiments and comparative examples at 10%~80% SOC can be obtained by slightly adjusting the above-mentioned charging rate. Overall, the charging rate gradually decreases from low SOC to high SOC. The specific charging rate adopted in different SOC ranges is tested as follows: at 25°C, the battery cell is charged at a constant current of 1 / 3C to a charging cut-off voltage of 3.65V, then charged at a constant voltage to a current of 0.05C, allowed to stand for 5 minutes, and then discharged at a constant current of 1 / 3C to a discharge cut-off voltage of 2V, and its actual capacity is recorded as C. Then charge the battery cells at a constant current of 0.5C, 1.0C, 1.5C, 2.0C, 2.5C, 3.0C, 3.5C, 4.0C, 4.5C, 5.0C, 5.5C, 6.0C, 6.5C, 7.0C, 7.5C, 8.0C, 8.5C, 9.0C, 9.5C, and 10.0C in sequence to the full battery charge cut-off voltage of 3.65V or the lithium plating potential of 0mV (whichever is reached first). After each charge, discharge at 1C to the full battery discharge cut-off voltage of 2V. Record the state of charge (SOC) at different charge rates to 10%, 15%, 20%, 25%, 30%...80%. The negative electrode potential corresponding to the state of charge (SOC) was calculated, and the rate-negative electrode potential curves under different SOC states were drawn. After linear fitting, the charge rate corresponding to the lithium deposition potential of 0mV under different SOC states was obtained. The charge rate is the charge rate adopted in the corresponding SOC range during the test of the above charging time. Among them, the charging power of 7C for charging from 10% SOC to 15% SOC is the maximum rate that the battery cell mechanical parts can withstand. For specific charge rates, please refer to Tables 1 and 2.

[0413] Table 1

[0414]

[0415] Table 2

[0416]

[0417] 2. Capacity retention of battery cells after 1000 cycles at 30°C

[0418] At 30°C, charge the battery cell from 0% SOC, charge it to 100% SOC at the rates corresponding to the following different SOCs, then continue charging it to 3.65V at a constant current of 0.33C, let it rest for 30 minutes, and then discharge it to 2.0V at a constant current of 1C. This is one charge and discharge cycle, and record the capacity C0 after the first cycle; repeat the above charge and discharge cycle steps until the cycle is 1000, and record the capacity Cn after the 1000th cycle. The capacity retention rate of the battery after 1000 cycles at 30°C is obtained as Cn / C0×100%. The higher the capacity retention rate, the better the cycle performance of the battery cell. The charging process from 0% SOC to 100% SOC is as follows:

[0419] Take the battery cell of Example 1 as an example:

[0420] Charge from 0% SOC to 10% SOC at 1C constant current;

[0421] Charge from 10% SOC to 15% SOC at 7.0C constant current;

[0422] Charge from 15% SOC to 20% SOC at 7.0C constant current;

[0423] Charge from 20% SOC to 25% SOC at 7.0C constant current;

[0424] Charge from 25% SOC to 30% SOC at 7.0C constant current;

[0425] Charge from 30% SOC to 35% SOC at 6.2C constant current;

[0426] Charge from 35% SOC to 40% SOC at 5.7C constant current;

[0427] Charge from 40% SOC to 45% SOC at 5.2C constant current;

[0428] Charge from 45% SOC to 50% SOC at 4.8C constant current;

[0429] Charge from 50% SOC to 55% SOC at 4.6C constant current;

[0430] Charge from 55% SOC to 60% SOC at 4.4C constant current;

[0431] Charge from 60% SOC to 65% SOC at 4.2C constant current;

[0432] Charge from 65% SOC to 70% SOC at 3.9C constant current;

[0433] Charge from 70% SOC to 75% SOC at 3.5C constant current;

[0434] Charge from 75% SOC to 80% SOC at 3.0C constant current;

[0435] Charge from 80% SOC to 100% SOC at a constant current of 0.33C.

[0436] The slight differences in charging time between the battery cells of different embodiments and comparative examples at 10% to 80% SOC can be achieved by slightly adjusting the above-mentioned charging rate. Overall, the charging rate gradually decreases from low SOC to high SOC. For specific charging rates, please refer to Tables 1 and 2.

[0437] 3. The volume energy density (VED) test steps of battery cells are as follows:

[0438] The battery cells of the embodiment and comparative example were placed at 25°C, charged at a constant current of 0.33C to 3.65V, then charged at a constant voltage of 3.65V to 0.05C, and allowed to stand for 30 minutes; discharged at a constant current of 0.33C to 2.0V, and the discharge capacity A0 at this time was recorded in Ah; the length, width, and height of the battery cells were measured with a caliper, and the volume V0 of the battery cells was calculated in L; the volume energy density of the battery cell, VED, was calculated as (A0×discharge platform voltage) / V0 in Wh / L.

[0439] 3. Analysis of test results of various embodiments and comparative examples

[0440] The examples and comparative examples were prepared according to the above method, and various performance parameters were measured. The results are shown in the table below.

[0441] Table 3

[0442]

[0443] Table 4

[0444]

[0445] (863cls@60%SOH in Comparative Example 3 means that after 863 cycles of the battery cell in Comparative Example 3, the capacity retention rate is only 60%)

[0446] According to the above results, the battery cells in Examples 1-13 include an electrode assembly and an electrolyte, the electrode assembly includes a positive electrode sheet, a negative electrode sheet and a separator, the separator is located between the positive electrode sheet and the negative electrode sheet, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one side of the positive electrode current collector, the positive electrode film layer includes a positive electrode active material, the positive electrode active material includes an olivine-structured lithium-containing phosphate, and the single-sided coating weight of the positive electrode film layer is 180 mg / 1540.25 mm 2 ~380mg / 1540.25mm 2The negative electrode plate includes a negative electrode current collector and a negative electrode film layer arranged on at least one side of the negative electrode current collector, the negative electrode film layer includes a negative electrode active material, the negative electrode active material includes a silicon-based material, and the mass content of silicon element is 0.3%-10.0% based on the mass of the negative electrode active material; the electrolyte includes a first additive, the first additive includes vinylene carbonate and / or fluoroethylene carbonate, and the mass content of the first additive is 1%-12%.

[0447] From the comparison of Examples 1-13 and Comparative Example 1, it can be seen that compared with simply adjusting the single-sided coating weight of the positive electrode film layer and the single-sided coating weight of the negative electrode film layer, the present application adjusts the single-sided coating weight of the positive electrode film layer and the content of silicon-based elements in the negative electrode film layer, while taking into account the fast charging performance of the battery cell, it can improve the energy density of the battery cell.

[0448] From the comparison of Examples 1-13 and Comparative Example 2, it can be seen that controlling the mass content of silicon element in the silicon-based material to 0.3%~10.0% can improve the cycle performance and fast charging performance of the battery cell.

[0449] From the comparison of Examples 1-13 and Comparative Examples 3-4, it can be seen that controlling the mass content of the first additive to 1%-12% can improve the cycle performance of the battery cell while also taking into account the fast charging performance of the battery cell.

[0450] From the comparison between Examples 1-4 and Example 5, it can be seen that the mass content of silicon element in the silicon-based material is 0.3%-6.0%, which can further improve the cycle performance and fast charging performance of the battery cell.

[0451] From Examples 1-3, 6-7, and 10-13, it can be seen that the mass content of silicon in the negative electrode active material is 0.3% to 3%, the mass content of the first additive in the electrolyte is 2% to 7%, and the battery cells have excellent cycle performance and fast charging performance.

[0452] From Examples 4-5, 8-9, it can be seen that the mass content of silicon in the negative electrode active material is greater than 3% and less than or equal to 6%, the mass content of the first additive in the electrolyte is 3% to 10%, and the battery cell has a high volume energy density.

[0453] From Examples 1-13, it can be seen that the ratio of the mass content A of the silicon element in the silicon-based material to the mass content B of the first additive is 0.025-6, and the battery cell has high energy density, excellent cycle performance and fast charging performance.

[0454] As can be seen from Examples 1 and 10-12, the mass content of carbon element is 0.8% to 2.3% based on the mass of lithium-containing carbonate with olivine structure, and the battery cell has both excellent cycle performance and fast charging performance.

[0455] As can be seen from Examples 1 and 13, the electrolyte includes a first organic solvent of ethylene carbonate and dimethyl carbonate and a second organic solvent of ethyl acetate, and based on the total mass of the electrolyte, the mass content of the first organic solvent is 20% to 72%, and the battery cell has excellent cycle performance and fast charging performance.

Claims

1. A battery cell, characterized in that: The electrolyte comprises an electrode assembly and an electrolyte, wherein the electrode assembly comprises a positive electrode sheet, a negative electrode sheet and a separator, wherein the separator is located between the positive electrode sheet and the negative electrode sheet. The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one side of the positive electrode current collector, the positive electrode film layer includes a positive electrode active material, the positive electrode active material includes a lithium-containing phosphate with an olivine structure, the lithium-containing phosphate includes a lithium-containing phosphate matrix, and the lithium-containing phosphate matrix includes one or more of lithium iron phosphate and its doped and modified forms. The single-sided coating weight of the positive electrode film layer is 180 mg / 1540.25 mm 2 Up to 380mg / 1540.25mm 2 ; The negative electrode plate includes a negative electrode current collector and a negative electrode film layer provided on at least one side of the negative electrode current collector, the negative electrode film layer includes a negative electrode active material, and the negative electrode active material includes a silicon-based material; The electrolyte includes a first additive, wherein the first additive includes at least one of vinylene carbonate and an ethylene carbonate derivative, and the mass content of the first additive is 1% to 12% based on the total mass of the electrolyte. Wherein, the ethylene carbonate derivative includes the compound shown in formula I, Formula I R1, R2, R3, and R4 are each independently a hydrogen atom, a halogen atom, a C1-C5 alkyl group, and a C1-C5 halogenated alkyl group, and R1, R2, R3, and R4 are not hydrogen atoms at the same time. The battery cell is at 100% charge state, and the compaction density of the positive electrode film layer is 2.50 g / cm 3 ~2.80g / cm 3 , Based on the mass of the negative electrode active material, the mass content of silicon is 0.3% to 3%, and based on the total mass of the electrolyte, the mass content of the first additive is 2% to 7.5%; or Based on the mass of the negative electrode active material, the mass content of silicon is greater than 3% and less than or equal to 6%. Based on the total mass of the electrolyte, the mass content of the first additive is 8% to 10%.

2. The battery cell according to claim 1, wherein: At least one of R1, R2, R3, and R4 contains a fluorine atom.

3. The battery cell according to claim 1, wherein: The ethylene carbonate derivatives include one or more of fluoroethylene carbonate, difluoroethylene carbonate, and trifluoromethylethylene carbonate.

4. The battery cell according to claim 1, wherein: When the mass content of the silicon element is 0.3% to 3%, the battery cell satisfies the following relationship: 0.4≤A / B≤1.5, Wherein A is the mass content of the silicon element, based on the mass of the negative electrode active material; B is the mass content of the first additive, based on the total mass of the electrolyte.

5. The battery cell according to claim 1, characterized in that The olivine-structured lithium-containing phosphate further comprises The coating layer is located on at least a portion of the surface of the lithium-containing phosphate matrix, and the coating layer contains carbon elements.

6. The battery cell according to claim 5, characterized in that Based on the mass of the olivine-structured lithium-containing phosphate, the mass content of the carbon element is 0.8% to 2.3%.

7. The battery cell according to claim 5 or 6, characterized in that: The battery cell satisfies the following relationship: 0.08≤C / B≤1.15, Wherein, C is the mass content of the carbon element, based on the mass of the lithium-containing phosphate with an olivine structure; B is the mass content of the first additive, based on the total mass of the electrolyte.

8. The battery cell according to claim 5, characterized in that The coating layer also includes Li 3-d1 Fe 2-d1 M3 d1 (PO m1 ) n1 of substances, Among them, 0≤d1≤1, 3≤m1≤5, 2≤n1≤4; M3 includes one or more of Ti, Zr, Hf, Ge, and Sn.

9. The battery cell according to claim 8, characterized in that M3 has a valence of +4.

10. The battery cell according to claim 1, characterized in that The lithium-containing phosphate matrix includes a general formula of Li x1 A y1 Me a1 M b1 P 1-c1 X c1 Y z1 Compounds Among them, 0.5≤x1≤1.3, 0≤y1≤1.3, 0.9≤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; Wherein, 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 S, Si, Cl, B, C, N and P; and Y includes at least one of O and F.

11. The battery cell according to claim 1, characterized in that The powder compaction density of the positive electrode active material at 30000N is 2.43g / cm 3 ~2.85g / cm 3 .

12. The battery cell according to claim 11, characterized in that The powder compaction density of the positive electrode active material at 30000N is 2.48g / cm 3 ~2.80g / cm 3 .

13. The battery cell according to claim 1, characterized in that The negative electrode active material includes a carbon-based material, and the carbon-based material includes graphite.

14. The battery cell according to claim 13, characterized in that The graphite includes composite graphite particles, which include graphite particles and carbon coating layers coated on the surfaces of the graphite particles. The graphite particles include secondary particles, and the carbon coating layers include amorphous carbon.

15. The battery cell according to claim 14, characterized in that The composite graphite particles meet at least one of the following conditions: (1) Based on the total mass of the composite graphite particles, the mass content of the amorphous carbon is 2% to 5%; (2) The powder resistivity of the composite graphite particles is 0.005Ω•cm-0.04Ω•cm.

16. The battery cell according to claim 14, characterized in that The negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer, the first negative electrode film layer is arranged between the current collector and the second negative electrode film layer, and the first negative electrode film layer and the second negative electrode film layer both include the composite graphite particles.

17. The battery cell according to claim 16, characterized in that The volume average particle size Dv50 of the composite graphite particles in the first negative electrode film layer is greater than or equal to the volume average particle size Dv50 of the composite graphite particles in the second negative electrode film layer.

18. The battery cell according to claim 17, characterized in that The volume average particle size Dv50 of the composite graphite particles in the first negative electrode film layer is 8.5 μm to 14.8 μm, and / or The volume average particle size Dv50 of the composite graphite particles in the second negative electrode film layer is 7.8 μm to 12.8 μm.

19. The battery cell according to claim 16, characterized in that Based on the total thickness of the first negative electrode film layer and the second negative electrode film layer, the thickness of the second negative electrode film layer accounts for 30% to 70%.

20. The battery cell according to claim 1, characterized in that The negative electrode plate also includes a negative electrode conductive layer, which is located between the negative electrode current collector and the negative electrode film layer on at least one side. The negative electrode conductive layer includes a conductive agent, which includes one or more of superconducting carbon, conductive graphite, acetylene black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

21. The battery cell according to claim 20, characterized in that The thickness of the negative electrode conductive layer is 0.5 μm to 2 μm.

22. The battery cell according to claim 1, characterized in that The battery cell is at 100% charge state, and the compaction density of the negative electrode film layer is 1.15 g / cm 3 ~1.45g / cm 3 , and / or, The single-sided coating weight of the negative electrode film layer is 70 mg / 1540.25 mm 2 Up to 135mg / 1540.25mm 2 .

23. The battery cell according to claim 1, characterized in that The electrolyte further includes an organic solvent, and the organic solvent includes one or more of a first organic solvent and a second organic solvent. Wherein, the first organic solvent includes at least one of a cyclic carbonate and a chain carbonate; The second organic solvent includes R5-COO-R6, Wherein, R5 includes any one of a hydrogen atom, a halogen atom, a C1-C5 alkyl group, and a C1-C5 halogenated alkyl group, and R6 includes any one of a C1-C5 alkyl group and a C1-C5 halogenated alkyl group.

24. The battery cell according to claim 23, characterized in that The first organic solvent is a cyclic carbonate.

25. The battery cell according to claim 23, characterized in that The cyclic carbonate includes one or more of ethylene carbonate, propylene carbonate, and butylene carbonate; and / or, The chain carbonate includes one or more of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; and / or, The second organic solvent includes one or more of methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, and ethyl butyrate.

26. The battery cell according to claim 24 or 25, characterized in that: Based on the total mass of the electrolyte, the mass content of the first organic solvent is 20% to 72%.

27. The battery cell according to claim 1, characterized in that The electrolyte further includes a second additive, which includes one or more of a sulfur-containing additive and a lithium salt additive.

28. The battery cell according to claim 27, characterized in that The sulfur-containing additive includes one or more of vinyl sulfate, vinyl disulfate, butylene sulfite, 1,3-propane sultone, vinyl sulfite, and methylene disulfonate; and / or, The lithium salt additive includes one or more of lithium difluorophosphate, lithium difluorooxalatoborate, lithium tetrafluoroborate, and lithium bis(oxalatoborate).

29. The battery cell according to claim 1, characterized in that The electrolyte further includes a lithium salt, and the lithium salt includes one or both of a fluorine-containing sulfonyl imide salt and lithium hexafluorophosphate.

30. The battery cell according to claim 29, characterized in that The fluorine-containing sulfonyl imide salt includes one or both of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide.

31. The battery cell according to claim 30, characterized in that The lithium salt includes lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate, and the ratio of the molar concentration of the lithium bis(fluorosulfonyl)imide to the molar concentration of the lithium hexafluorophosphate is 0.2-1.

0.

32. The battery cell according to claim 31, characterized in that The molar concentration of the lithium bis(fluorosulfonyl)imide is 0.2 mol / L to 0.5 mol / L, and the molar concentration of the lithium hexafluorophosphate is 0.5 mol / L to 1.2 mol / L.

33. The battery cell according to claim 1, characterized in that The isolation film satisfies at least one of the following conditions: (1) The thickness of the isolation film is 4 μm to 12 μm; (2) The porosity of the isolation membrane is 20% to 70%.

34. The battery cell according to claim 33, characterized in that The isolation film satisfies at least one of the following conditions: (1) The thickness of the isolation film is 5 μm to 9 μm; (2) The porosity of the isolation membrane is 35% to 60%.

35. The battery cell according to claim 1, characterized in that The battery cells are configured such that a charging time from a 10% state of charge to an 80% state of charge is 5 minutes to 10.5 minutes.

36. The battery cell according to claim 1, characterized in that The volume energy density of the battery cell is 395Wh / L~530Wh / L.

37. A battery device, characterized in that: A battery cell comprising the battery cell according to any one of claims 1 to 36.

38. The battery device according to claim 37, characterized in that The battery device is configured to charge from a 10% state of charge to an 80% state of charge within a range of 5 minutes to 10.5 minutes.

39. An electrical device, characterized in that: A battery device comprising the battery device of claim 37 or 38.

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