Battery cell, battery device, and electric device

Abstract

The present application discloses a battery cell, a battery device, and an electric device. The battery cell comprises an electrode assembly and an electrolyte solution; the electrode assembly comprises a positive electrode sheet and a negative electrode sheet; the positive electrode sheet comprises a positive electrode film layer; the positive electrode film layer comprises a positive electrode active material; the positive electrode active material comprises an olivine-structured lithium-containing phosphate; the single-sided coating weight of the positive electrode film layer is 180 mg / 1540.25 mm2 to 380 mg / 1540.25 mm2; the negative electrode sheet comprises a negative electrode film layer; the negative electrode film layer comprises a negative electrode active material; the negative electrode active material comprises a silicon-based material; based on the mass of the negative electrode active material, the mass content of a silicon element is 0.3%-10.0%; the electrolyte solution comprises a first additive; the first additive comprises at least one of vinylene carbonate and an ethylene carbonate derivative; and based on the total mass of the electrolyte solution, the mass content of the first additive is 1%-12%.

Description

Battery cells, battery packs and electrical devices Technical Field

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

[0002] Lithium-ion batteries are widely used in electronic devices such as mobile phones, laptops, electric vehicles, electric cars, electric airplanes, electric ships, and power tools due to their high capacity and long lifespan. With the development of lithium-ion battery applications, higher demands are being placed on their performance, such as fast charging capabilities and energy density.

[0003] Summary of the Invention

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

[0005] In a first aspect, this application provides a battery cell, including an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a negative electrode, and a separator, with the separator located between the positive and negative electrode.

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

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

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

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

[0010] Among them, ethylene carbonate derivatives include compounds represented by Formula I.

[0011] R1, R2, R3, and R4 each independently include any one of hydrogen atoms, halogen atoms, C1-C5 alkyl groups, and C1-C5 haloalkyl groups, and R1, R2, R3, and R4 are not all hydrogen atoms at the same time.

[0012] In this application, the positive electrode active material of the battery cell contains lithium phosphate with an olivine structure, which has 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, the energy density of the battery cell can be increased while effectively improving the fast charging performance of the battery cell. At the same time, the electrolyte of the battery cell contains a first additive of vinylene carbonate and / or ethylene carbonate derivative, and the mass content of the first additive is controlled within an appropriate range. This allows the formation of an SEI film with moderate thickness, enhanced flexibility and stability at the silicon-containing negative electrode interface, ensuring that the silicon-containing negative electrode interface has both good stability and low impedance. Thus, the battery cell achieves high energy density, excellent fast charging performance and good cycle performance.

[0013] In summary, by synergistically controlling the single-sided coating weight of the positive electrode film, the mass content of silicon in the negative electrode active material, the lithium phosphate containing olivine structure in the positive electrode active material, and the types and mass content of additives in the electrolyte within a suitable range, this application can achieve a balance between the fast charging performance, cycle performance, and energy density of the battery cell.

[0014] In any embodiment, based on the mass of the negative electrode active material, the mass content of silicon element is 0.3% to 6.0%.

[0015] When the mass content of silicon in silicon-based materials is within a suitable range, it can improve the energy density of individual battery cells while reducing the impact of excessive silicon on the cycle performance of individual battery cells, thus balancing the energy density and cycle performance of individual battery cells.

[0016] In any embodiment, at least one of R1, R2, R3, and R4 contains fluorine atoms.

[0017] Ethylene carbonate derivatives in which at least one of R1, R2, R3, and R4 is a fluorine atom are easy to open rings, forming an SEI film containing more organic matter on the negative electrode surface. This helps to improve the overall flexibility of the SEI film, thereby improving the stability of the SEI film and the negative electrode interface during cycling and enhancing the cycle performance of the battery cell.

[0018] In any embodiment, the ethylene carbonate derivative includes one or more of fluoroethylene carbonate, difluoroethylene carbonate, and trifluoromethylethylene carbonate.

[0019] Suitable ethylene carbonate derivative additives can form an SEI film containing more organic matter on the negative electrode side, which is beneficial to improve the overall flexibility of the SEI film and achieve the purpose of improving the stability of the SEI film and the negative electrode interface during cycling, thereby improving the cycle performance of the battery cell. At the same time, the SEI film formed by fluoroethylene carbonate, difluoroethylene carbonate, and trifluoromethyl ethylene carbonate has low impedance, which is also beneficial to improving the fast charging performance of the battery cell.

[0020] In any embodiment, the battery cell satisfies the following relationship: 0.025≤A / B≤6, which can be optionally 0.035≤A / B≤2.5.

[0021] Where A is the mass content of silicon, 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.

[0022] When 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 a suitable range, the synergistic effect of silicon and the first additive in the negative electrode can improve the energy density of the battery cell while also taking into account the cycle performance of the battery cell.

[0023] 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%;

[0024] Based on the total mass of the electrolyte, the mass content of the first additive is 2% to 7.5%.

[0025] In systems with relatively low silicon content, the damage to the SEI film during battery cell cycling is relatively small. By controlling the mass content of the first additive within a suitable range, an SEI film of appropriate thickness can be formed. This not only improves the stability of the SEI film and the negative electrode interface and enhances the cycle performance of the battery cell, but also achieves low impedance at the negative electrode interface. This is beneficial for improving the fast-charging performance of the battery cell and is more suitable for application scenarios with higher requirements for the cycle performance and fast-charging performance of the battery cell.

[0026] 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%.

[0027] Based on the total mass of the electrolyte, the mass content of the first additive is 3% to 10%.

[0028] In systems with relatively high silicon content, the SEI film is more severely damaged during battery cell cycling. By controlling the mass content of the first additive within a suitable range, an SEI film of appropriate thickness can be formed, thereby improving the stability of the SEI film and the negative electrode interface and enhancing the cycle performance of the battery cell. This approach is more suitable for application scenarios with higher requirements for the cycle performance and energy density of battery cells.

[0029] In any embodiment, the lithium phosphate with an olivine structure includes:

[0030] Lithium phosphate matrix, and

[0031] A coating layer, located on at least a portion of the surface of a lithium phosphate matrix, comprises carbon elements. The olivine-structured lithium phosphate, including the carbon coating layer, improves the material's conductivity, which is beneficial for enhancing the fast-charging performance of individual battery cells.

[0032] In any embodiment, the mass content of carbon element in the lithium phosphate based on the olivine structure is 0.8% to 2.3%.

[0033] By controlling the carbon content in the coating layer within a suitable range, the conductivity of the material can be improved, the fast-charging performance of the battery can be enhanced, and the specific capacity of the material, as well as the fast-charging performance and energy density of the battery cells, can also be taken into account.

[0034] In any embodiment, the battery cell satisfies the following relationship: 0.08 ≤ C / B ≤ 1.15.

[0035] Wherein, C represents the mass content of carbon, based on the mass of lithium phosphate containing olivine structure;

[0036] B represents the mass content of the first additive, based on the total mass of the electrolyte.

[0037] By controlling the mass content of carbon in lithium phosphate containing olivine structure and the mass content of the first additive in electrolyte within a suitable range, it is possible to improve the conductivity of the material, enhance the fast-charging performance of the battery cell, improve the cycle stability of the material, and improve the cycle performance of the battery cell.

[0038] In any embodiment, the coating layer further includes Li 3-d1 Fe 2-d1 M3 d1 (PO m1 ) n1 The substance,

[0039] Where, 0≤d1≤1, 3≤m1≤5, 2≤n1≤4;

[0040] M3 includes one or more of Ti, Zr, Hf, Ge, and Sn, and optionally, M3 is +4 valence.

[0041] The coating layer includes Li 3-d1 Fe 2-d1 M3 d1 (PO m1 ) n1 This substance possesses excellent ion-conductivity, which can significantly improve the lithium-ion deintercalation / intercalation transport rate of the material, enhance the overall ion-conductivity of the material, and improve the fast-charging performance of the battery.

[0042] In any embodiment, the lithium phosphate matrix includes the general formula Li x1 A y1 Me a1 M b1 P 1-c1 X c1 Y z1 compounds,

[0043] Wherein, 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;

[0044] 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.

[0045] 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 forms include one or more of doping modification and coating modification.

[0046] In any embodiment, the compacted density of the positive electrode active material at 30000 N is 2.43 g / cm³. 3 ~2.85g / cm 3 The option is 2.48g / cm³. 3 ~2.80g / cm 3 .

[0047] When the powder compaction density of the positive electrode active material at 30000N is within the above range, it can improve the energy density of the battery cell. Furthermore, since the positive electrode active material in the positive electrode film can be stacked more tightly, the contact resistance between particles is smaller, which can further reduce the resistance of the electrode sheet and also help improve the fast charging performance of the battery cell.

[0048] In any embodiment, the compaction density of the positive electrode film layer when the battery cell is at 100% charge is 2.50 g / cm³. 3 ~2.80g / cm 3 .

[0049] When the compaction density of the positive electrode film is within a suitable range, the battery cell has a high energy density.

[0050] In any embodiment, the negative electrode active material includes a carbon-based material, which includes graphite.

[0051] Graphite has good electrical conductivity and cycle stability, which is beneficial to improving the fast charging performance and cycle performance of battery cells.

[0052] In any embodiment, the graphite includes composite graphite particles, which include graphite bulk particles and a carbon coating layer covering the surface of the graphite bulk particles. The graphite bulk particles include secondary particles, and the carbon coating layer includes amorphous carbon.

[0053] Secondary particles have excellent ion transport properties, which are beneficial for lithium ion insertion and extraction and improve the ion conductivity of the material. In addition, the carbon coating layer includes amorphous carbon, which can improve the conductivity of composite graphite particles. The secondary particles in the core and the amorphous carbon coating layer together improve the conductivity of the material's electron and ion conduction properties, which helps to improve the fast charging performance of the battery cell.

[0054] In any embodiment, the composite graphite particles satisfy at least one of the following conditions:

[0055] (1) Based on the total mass of the composite graphite particles, the mass content of amorphous carbon is 2% to 5%;

[0056] (2) The resistivity of the composite graphite particles is 0.005Ω·cm-0.04Ω·cm.

[0057] Controlling the mass content of amorphous carbon in composite graphite particles within a suitable range can improve the conductivity of the material and enhance the fast-charging performance of the battery.

[0058] Composite graphite particles have low powder resistivity and excellent conductivity, which is beneficial for improving the fast charging performance of individual battery cells.

[0059] In any embodiment, there is a first negative electrode film layer and a second negative electrode film layer, wherein 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.

[0060] 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.

[0061] During the fast charging process of a battery cell, the overpotential of the second negative electrode film layer, which is far from the current collector, is usually higher. The bottleneck affecting the fast charging performance of the battery cell is mainly the second negative electrode film layer. This 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 lithium ion transport path, improve the lithium ion transport performance of the second negative electrode film layer, and improve the fast charging performance of the battery cell.

[0062] 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,

[0063] 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.

[0064] Controlling the particle size of the composite graphite particles in the first and / or second negative electrode film layers within a suitable range can shorten the lithium ion transport path in the negative electrode film layers and improve the fast charging performance of the battery cells.

[0065] 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%.

[0066] When the thickness ratio of the second negative electrode film is within a suitable range, it can balance the contribution of the second negative electrode film to the battery's fast charging performance and the contribution of the first negative electrode film to the battery's energy density, thus obtaining a battery cell with excellent fast charging performance and high energy density.

[0067] In any embodiment, the negative electrode sheet further includes a negative electrode conductive layer, which is located between the negative electrode current collector and at least one side of the negative electrode film layer. 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.

[0068] By setting a negative electrode conductive layer containing a conductive agent between the current collector and the negative electrode film, the conductivity of the negative electrode sheet can be improved, thereby enhancing the fast-charging performance of the battery cell.

[0069] In any embodiment, the thickness of the negative electrode conductive layer is 0.5 μm to 2 μm.

[0070] By controlling the thickness of the negative electrode conductive layer within a suitable range, both the fast-charging performance and energy density of the battery cell can be balanced.

[0071] In any embodiment, when the battery cell is at 100% charge, the compaction density of the negative electrode film is 1.15 g / cm³. 3 ~1.45g / cm 3 , and / or

[0072] The single-sided coating weight of the negative electrode film is 70 mg / 1540.25 mm. 2 ~135mg / 1540.25mm 2 .

[0073] When the single-sided coating weight or compaction density of the negative electrode film is within a suitable range, it is beneficial to improve the fast charging performance of the battery cell.

[0074] In any embodiment, the electrolyte further includes an organic solvent, which includes one or more of a first organic solvent and a second organic solvent.

[0075] The first organic solvent includes at least one of cyclic carbonate and chain carbonate, and may be a cyclic carbonate.

[0076] The second organic solvent includes R5-COO-R6.

[0077] R5 includes any one of hydrogen atoms, halogen atoms, C1-C5 alkyl groups, and C1-C5 haloalkyl groups, and R6 includes any one of C1-C5 alkyl groups and C1-C5 haloalkyl groups.

[0078] The first organic solvent of cyclic carbonates and chain carbonates 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 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 cells.

[0079] In any embodiment, the cyclic carbonate includes one or more of ethylene carbonate, propylene carbonate, and butene carbonate; and / or,

[0080] Chain carbonates include one or more of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; and / or,

[0081] The second organic solvent includes one or more of methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, methyl butyrate, and ethyl butyrate.

[0082] In any embodiment, the mass content of the first organic solvent is 20% to 72% based on the total mass of the electrolyte.

[0083] The appropriate amount of cyclic carbonates and chain carbonates as the first organic solvent can further improve the conductivity of the electrolyte, which is beneficial to the migration of lithium ions and improves the fast charging performance of the battery cells.

[0084] In any embodiment, the electrolyte further includes a second additive, which includes one or more of sulfur-containing additives and lithium salt additives.

[0085] Sulfur-containing additives and lithium salt additives can improve the interfacial film performance of the positive and / or negative electrode sides, improve the interfacial chemistry between the positive and / or negative electrode and the electrolyte, and enhance the fast charging performance and cycle performance of the battery.

[0086] In any embodiment, the sulfur-containing additive includes one or more of vinyl sulfate, vinyl disulfate, butenyl sulfite, 1,3-propanesulfonate lactone, vinyl sulfite, and methylene disulfonate; and / or,

[0087] Lithium salt additives include one or more of lithium difluorophosphate, lithium difluorooxalate borate, lithium tetrafluoroborate, and lithium dioxalate borate.

[0088] In any embodiment, the electrolyte further includes a lithium salt, which includes one or both of fluorosulfonyl imide salt and lithium hexafluorophosphate.

[0089] Fluorosulfonyl imide salts and lithium hexafluorophosphate are easily dissociated, which is beneficial for the rapid migration of lithium ions and improves the fast-charging performance of battery cells. In addition, fluorosulfonyl imide salts and lithium hexafluorophosphate are relatively stable in the electrolyte system, which can improve the cycle performance of battery cells.

[0090] In any embodiment, the fluorosulfonyl imide salt includes one or both of lithium bisfluorosulfonyl imide and lithium bistrifluoromethanesulfonate imide.

[0091] In any embodiment, the lithium salt comprises lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate, wherein the molar concentration ratio of lithium bis(fluorosulfonyl)imide to lithium hexafluorophosphate is 0.2 to 1.0.

[0092] 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.

[0093] In any embodiment, the separator membrane satisfies at least one of the following conditions:

[0094] (1) The thickness of the isolation membrane is 4μm to 12μm, and can be selected as 5μm to 9μm;

[0095] (2) The porosity of the isolation membrane is 20% to 70%, and can be selected as 35% to 60%.

[0096] When the thickness of the separator is within a suitable range, the migration path of lithium ions in the separator is shorter, which can reduce the internal resistance of the battery cell and improve the fast charging performance of the battery cell.

[0097] When the porosity of the separator is within a suitable range, it can increase the migration rate of lithium ions in the separator, reduce the internal resistance of the battery cell, and improve the fast charging performance of the battery cell.

[0098] In any embodiment, the battery cell is configured to charge from 10% state of charge to 80% state of charge in a time of 5 min to 10.5 min.

[0099] The battery cells charge quickly, exhibiting excellent fast-charging performance.

[0100] In any embodiment, the volumetric energy density of the battery cell is 395Wh / L to 530Wh / L.

[0101] Secondly, this application provides a battery device including the battery cell of the first aspect.

[0102] In any embodiment, the battery device is configured to charge from 10% state of charge to 80% state of charge in a time of 5 min to 10.5 min.

[0103] The battery device charges quickly and has excellent fast-charging performance.

[0104] Thirdly, this application provides an electrical device, including the battery device of the second aspect. Attached Figure Description

[0105] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0106] Figure 1 is a schematic diagram of a battery cell according to an embodiment of this application;

[0107] Figure 2 is an exploded view of a battery cell according to an embodiment of this application shown in Figure 1;

[0108] Figure 3 is a schematic diagram of a battery module according to an embodiment of this application;

[0109] Figure 4 is a schematic diagram of a battery pack according to an embodiment of this application;

[0110] Figure 5 is an exploded view of the battery pack of one embodiment of this application shown in Figure 4;

[0111] Figure 6 is a schematic diagram of an electrical device in which a single battery cell is used as a power source according to an embodiment of this application.

[0112] Explanation of reference numerals in the attached figures:

[0113] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Casing; 52 Electrode assembly; 53 Cover plate. Detailed Implementation

[0114] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0115] The following detailed description, with appropriate reference to the accompanying drawings, discloses the battery, battery filling method, electrolyte, preparation method thereof, and electrical device of this application. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0116] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0117] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0118] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0119] Unless otherwise specified, all steps in this 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 it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0120] As the application fields of lithium-ion batteries continue to expand, higher demands are being placed on their energy density and fast-charging performance. To improve battery energy density, the coating density of the positive and negative electrode films is typically increased. However, with increased coating density, the migration path of lithium ions becomes longer, resulting in higher internal resistance and impacting fast-charging performance. In particular, a high coating density of the negative electrode film severely affects the fast-charging performance of individual battery cells. Simply adjusting the coating weight of the positive and negative electrodes is insufficient to achieve a balance between energy density and fast-charging performance in a single battery cell.

[0121] In view of the above problems, this application makes a reasonable design of the battery cell system to achieve a balance between energy density and fast charging performance. Specifically, by reasonably matching the coating density of the positive electrode sheet, the silicon content of the negative electrode material and the additives in the electrolyte, the energy density can be improved while also taking into account the battery's fast charging performance and cycle performance.

[0122] [Battery cell]

[0123] A single battery cell includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a negative electrode, and a separator, with the separator located between the positive and negative electrode.

[0124] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector. The positive electrode film layer includes a positive electrode active material, which includes a lithium phosphate with an olivine structure.

[0125] The single-sided coating weight of the positive electrode film is 180 mg / 1540.25 mm. 2 Up to 380mg / 1540.25mm 2 ;

[0126] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The negative electrode film layer includes a negative electrode active material, which includes a silicon-based material. Based on the mass of the negative electrode active material, the mass content of silicon element is 0.3% to 10.0%.

[0127] The electrolyte includes a first additive, which includes at least one selected from vinylene carbonate and ethylene carbonate derivatives. Based on the total mass of the electrolyte, the mass content of the first additive is 1% to 12%.

[0128] The ethylene carbonate derivatives include compounds represented by Formula I.

[0129] R1, R2, R3, and R4 each independently include any one of hydrogen atoms, halogen atoms, C1-C5 alkyl groups, and C1-C5 haloalkyl groups, and R1, R2, R3, and R4 are not all hydrogen atoms at the same time.

[0130] In some embodiments, the single-sided coating weight of the positive electrode film is 180 mg / 1540.25 mm. 2 ~380mg / 1540.25mm 2 For example, the single-sided coating weight of the positive electrode film 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.

[0131] In this embodiment, the areal density of the positive electrode film layer on one side of the battery cell can be detected by the following method: For example, take a positive electrode sheet with a single-sided coating (if it is a double-sided coated sheet, the positive electrode film layer on one side can be wiped off first), cut it into a small circular piece with an area of ​​S1, weigh it, record its weight as M1, and measure its thickness H1. Then, wipe off the positive electrode film layer of the weighed positive electrode sheet, weigh the positive current collector, record its weight as M0, and measure its thickness H0. The single-sided coating weight of the positive electrode film layer = (weight of the positive electrode sheet M1 - weight of the positive current collector M0) / S1.

[0132] In embodiments of this application, the silicon-based material may include at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. Here, elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy can refer to either silicon-based materials or the form in which silicon exists in the negative electrode of a battery after formation. Here, silicon oxide (SiO2) is used. x The condition 0 < x ≤ 2 is because the silicon atoms and oxygen atoms in the negative electrode film can combine in various ways, such as SiO2, SiO2, etc. 1.2 At least one of SiO2 or other possible silicon oxides. Here, silicon-carbon composite can refer to the form in which silicon exists in the negative electrode of a battery after formation. Silicon-carbon composite can also be a silicon-carbon composite formed by certain chemical reactions between silicon and carbon within a single battery cell. It can also be formed by a physical mixture of elemental silicon and elemental carbon, for example, where elemental carbon includes a porous framework, and elemental silicon is located in the pores of the porous framework or on its surface. Silicon-carbon composite can also be formed by coating a carbon layer onto the surface of elemental silicon.

[0133] In some embodiments, the mass content of silicon element is 0.3% to 10.0% based on the mass of the negative electrode active material. Exemplarily, the mass content of silicon element 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 of any two of the above values.

[0134] The qualitative and quantitative analysis of each substance or element in this application can be performed using suitable equipment and methods known to those skilled in the art. Relevant testing methods can be referenced from domestic and international testing standards and enterprise standards. Furthermore, those skilled in the art can adaptively modify certain testing steps / instrument parameters from the perspective of testing accuracy to obtain more accurate results. One testing method can be used for qualitative or quantitative analysis, or several testing methods can be used in combination for qualitative or quantitative determination.

[0135] For example, the mass content of silicon in the negative electrode film is a well-known concept in the art and can be detected using well-known equipment and methods. For instance, the negative electrode sheet can be immersed in a solvent such as water to separate the negative electrode active material from the negative electrode current collector. The various substances in the negative electrode film can be obtained by filtration and used as a test sample. The silicon content can be obtained by using an ICAP7400 inductively coupled plasma atomic emission spectrometer from Thermo Fisher Scientific, USA, in accordance with the GB / T30902-2014 standard.

[0136] In some embodiments, the mass content of the first additive is 1% to 12% based on the total mass of the electrolyte. For example, the mass content of the first additive is 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12% or any combination of two of the above values.

[0137] The type and content of the first additive in the electrolyte can be obtained by detecting the electrolyte using methods known to those skilled in the art. For example, the composition of the electrolyte can be determined by liquid chromatography, ultraviolet spectrophotometry, ultraviolet-visible spectrophotometry, etc. For instance, using an ion chromatograph (IC) to test the inorganic content in the electrolyte, a quantitative amount of electrolyte (with a dilution concentration at the midpoint of the standard curve) is weighed and diluted to 100 mL with ultrapure water. The ion chromatogram is automatically injected to detect the inorganic ions. The chromatogram peak positions are compared to the corresponding inorganic ion types, and the percentage of the corresponding inorganic ion content is calculated based on the peak area. The above-mentioned free electrolyte was diluted 3 to 10 times with acetonitrile to obtain the diluted electrolyte solution to be tested. Using a GC-MS 3100 organic component gas chromatograph, the diluted electrolyte solution was subjected to full-scan qualitative analysis. The injection port temperature was 250℃, and the scan range was 35μm to 270μm. After the test, total ion current chromatograms of each organic compound were obtained. The peak positions were compared to identify the corresponding organic compounds, and the percentage content of each organic compound was calculated based on the peak area. The mass content of the first additive in the electrolyte of the battery cell was calculated by dividing the calculated mass of the first additive by the mass of the electrolyte sample. 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.

[0138] In this document, the term "halogen atom" includes one or more of fluorine, chlorine, bromine, and iodine atoms.

[0139] In this document, the term "C1-C5 alkyl" refers to a straight-chain or branched hydrocarbon chain group consisting only of carbon and hydrogen atoms, without any unsaturation, having one to five carbon atoms, and attached to the rest of the molecule by single bonds. 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.

[0140] In this document, 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.

[0141] This application achieves this by matching a high-weight positive electrode film with a silicon-containing negative electrode film, thereby increasing the energy density of the battery cell while reducing the coating weight of the negative electrode film, thus improving the fast-charging performance of the battery cell. Simultaneously, by controlling the silicon content in the negative electrode film within a suitable range, the energy density of the battery cell is improved while maintaining its cycle performance. However, introducing silicon into the negative electrode active material results in significant volume expansion and contraction of the silicon material during battery cell charging and discharging. This can easily damage the SEI film on the negative electrode side, exposing a fresh interface. The electrolyte then continues to undergo reduction reactions at the interface, consuming electrolyte and active lithium, thus affecting the cycle and storage performance of the battery cell. To address this issue, this application introduces a first additive, vinylene carbonate and / or ethylene carbonate derivatives, into the electrolyte. Vinylene carbonate and ethylene carbonate derivatives preferentially participate in the formation of the SEI film on the negative electrode side, taking precedence over other components in the electrolyte. Furthermore, the film formed by vinylene carbonate and ethylene carbonate derivatives has a high organic content, which improves the overall flexibility of the SEI film, enhances the stability of the SEI film-negative electrode interface during cycling, reduces the reaction between the negative electrode active material and the electrolyte, reduces lithium-ion consumption, and improves the cycle performance and storage performance of the battery cell. Additionally, controlling the mass content of the first additive within a suitable range improves the flexibility and stability of the SEI film while also controlling its thickness within an appropriate range, thereby simultaneously achieving stability and low impedance at the negative electrode interface, balancing the cycle performance and fast-charging performance of the battery cell. Moreover, the positive electrode active material contains lithium phosphate with an olivine structure, which exhibits excellent structural stability and enhances the cycle performance of the battery cell.

[0142] In summary, this application achieves a balance between fast-charging performance, cycle performance, and energy density of a single battery cell by synergistically controlling the single-sided coating weight of the positive electrode film, the mass content of silicon in the negative electrode active material, the lithium phosphate containing olivine structure in the positive electrode active material, and the types and mass content of additives in the electrolyte within a suitable range.

[0143] [Negative electrode plate]

[0144] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector and comprising a negative electrode active material. For example, the negative current collector has two surfaces opposite each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative current collector.

[0145] In some embodiments, based on the mass of the negative electrode active material, the mass content of silicon element is 0.3% to 6.0%, and can be selected as 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 any combination of two of the above values.

[0146] When the mass content of silicon in silicon-based materials is within a suitable range, it can improve the energy density of individual battery cells while reducing the impact of excessive silicon on the cycle performance of individual battery cells, thus balancing the energy density and cycle performance of individual battery cells.

[0147] In some embodiments, the battery cell satisfies the following relationship: 0.025 ≤ A / B ≤ 6, which can be optionally 0.035 ≤ A / B ≤ 2.5.

[0148] Where A is the mass content of 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.

[0149] In some implementations, 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 of any two of the above values.

[0150] When 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 a suitable range, the synergistic effect of silicon in the negative electrode active material and the first additive can improve the energy density of the battery cell while also taking into account the cycle performance of the battery cell.

[0151] In some embodiments, based on the mass of the negative electrode active material, the mass content of silicon is 0.3% to 3%;

[0152] Based on the total mass of the electrolyte, the mass content of the first additive is 2% to 7.5%.

[0153] In some embodiments, the mass content of silicon in the negative electrode active material can be selected as 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, or any combination of two of the above values;

[0154] The mass content of the first additive in the electrolyte can be selected as 2%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7%, 7.5%, or any range of two of the above values.

[0155] In systems with relatively low silicon content, the damage to the SEI film during battery cell cycling is relatively small. By controlling the mass content of the first additive within a suitable range, an SEI film of appropriate thickness can be formed. This not only improves the stability of the SEI film and the negative electrode interface and enhances the cycle performance of the battery cell, but also achieves low impedance at the negative electrode interface. This is beneficial for improving the fast-charging performance of the battery cell and is more suitable for application scenarios with higher requirements for the cycle performance and fast-charging performance of the battery cell.

[0156] In some embodiments, based on the mass of the negative electrode active material, the mass content of silicon element is greater than 3% and less than or equal to 6%;

[0157] Based on the total mass of the electrolyte, the mass content of the first additive is 3% to 10%.

[0158] In some embodiments, the mass content of silicon in the negative electrode active material can be selected as 3.1%, 3.5%, 3.8%, 4.0%, 4.2%, 4.5%, 4.8%, 5%, 5.2%, 5.5%, 5.8%, 6%, or any range of two of the above values;

[0159] The mass content of the first additive in the electrolyte can be selected as 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 any range of two of the above values.

[0160] In systems with relatively high silicon content, the SEI film is more severely damaged during battery cell cycling. By controlling the mass content of the first additive within a suitable range, an SEI film of appropriate thickness can be formed, thereby improving the stability of the SEI film and the negative electrode interface and enhancing the cycle performance of the battery cell. This approach is more suitable for application scenarios with higher requirements for the cycle performance and energy density of battery cells.

[0161] In some embodiments, the negative electrode active material includes a carbon-based material, which includes graphite.

[0162] Graphite has good electrical conductivity and cycle stability, which is beneficial to improving the fast charging performance and cycle performance of battery cells.

[0163] In some implementations, based on the mass of the negative electrode active material, the mass percentage of carbon-based material can be greater than or equal to 80% and less than 100%.

[0164] In some embodiments, graphite includes composite graphite particles, which include graphite bulk particles and a carbon coating layer covering the surface of the graphite bulk particles. The graphite bulk particles include secondary particles, and the carbon coating layer includes amorphous carbon.

[0165] Secondary particles are particles formed by the aggregation of two or more primary particles.

[0166] In this paper, amorphous carbon refers to transitional carbon materials with very low graphitization and crystallization, exhibiting an approximately amorphous morphology (or lacking a fixed shape and periodic structural regularity). In this application, amorphous carbon refers to the product of carbonization treatment of organic carbon sources, which has numerous end faces and defects, and a large number of lithium ion sites.

[0167] Secondary particles can enhance the migration rate of lithium ions and improve the transport performance of lithium ions, which is beneficial for the insertion and extraction of lithium ions and improves the ionic conductivity of the material. In addition, the carbon coating layer, including amorphous carbon, can improve the conductivity of composite graphite particles. The secondary particles in the core and the amorphous carbon coating layer together improve the conductivity of the material's electron and ion conduction properties, which helps to improve the fast charging performance of the battery cell.

[0168] In the embodiments of this application, the composite graphite particles can be prepared using methods known in the art. For example, the preparation method includes: providing graphite bulk particles (which may be artificial graphite) and an organic carbon source, mixing the two, and then performing a carbonization treatment to form a carbon coating layer on at least a portion of the surface of the graphite bulk particles, thereby obtaining the composite graphite particles in the embodiments.

[0169] Optionally, the organic carbon source includes one or more of coal tar pitch, petroleum asphalt, phenolic resin, and coconut shell. More preferably, the organic carbon source includes petroleum asphalt. Optionally, the softening point of the coal tar pitch or petroleum asphalt is below 250°C.

[0170] Optionally, the carbonization temperature is between 700°C and 1800°C. Optionally, the carbonization temperature is between 1000°C and 1300°C. Within a suitable range, the carbonization temperature allows the organic carbon source to carbonize and form a coating layer containing amorphous carbon on at least a portion of the surface of the graphite bulk particles. Optionally, the carbonization time is between 1 hour and 6 hours.

[0171] In some embodiments, based on the total mass of the composite graphite particles, the mass content of the amorphous carbon is 2% to 5%, which can be selected as 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any combination of two of the above values.

[0172] Controlling the mass content of amorphous carbon in composite graphite particles within a suitable range can improve the conductivity of the material and enhance the fast-charging performance of the battery.

[0173] In some embodiments, the powder resistivity of the composite graphite particles is 0.005 Ω·cm to 0.04 Ω·cm, and can be selected as 0.01 Ω·cm, 0.015 Ω·cm, 0.020 Ω·cm, 0.025 Ω·cm, 0.03 Ω·cm, 0.04 Ω·cm, or any combination of two of the above values.

[0174] In the embodiments of this application, the powder resistivity of the material has a well-known meaning in the art and can be tested using methods and equipment well-known in the art, such as using a PRCD1100 powder resistivity meter according to the test standard GB / T30835-2014.

[0175] Composite graphite particles have low powder resistivity and excellent conductivity, which is beneficial for improving the fast charging performance of individual battery cells.

[0176] In the embodiments of this application, the negative electrode film layer includes at least one film layer, which can be a single film layer or at least two film layers. Optionally, the negative electrode film layer includes at least two film layers.

[0177] When a single-layer negative electrode film is used, the negative electrode active material in the negative electrode film includes graphite and silicon-based materials. Optionally, the negative electrode active material includes composite graphite particles and silicon-based materials. When a single-layer film is used, the volume average particle size Dv50 of the composite graphite particles is 8.2 μm to 13.5 μm. For example, 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.

[0178] When the negative electrode film layer comprises at least two layers, the negative electrode active material in the negative electrode film layer includes graphite and silicon-based materials. Optionally, the negative electrode active material includes composite graphite particles and silicon-based materials. The silicon-based material may 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 may 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 may include two, three, four, or even more film layers.

[0179] 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 being located between the current collector and the second negative electrode film layer, silicon-based material being located in the first negative electrode film layer and / or the second negative electrode film layer, and composite graphite particles being located in the first negative electrode film layer and / or the second negative electrode film layer.

[0180] The interface between the first negative electrode film and the second negative electrode film can be regular or irregular, and can optionally be irregular.

[0181] The negative electrode film consists of at least two layers, and layered coating is beneficial for improving the fast charging performance of the battery cell. In particular, when there are differences between the first and second negative electrode films, it can create porosity differences in the negative electrode films, reduce the tortuosity of lithium-ion transport, and improve the fast charging performance of the battery cell.

[0182] In some embodiments, both the first negative electrode film layer and the second negative electrode film layer include composite graphite particles.

[0183] Both the first and second negative electrode films contain composite graphite particles, which can improve the fast charging performance of the battery cells.

[0184] 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.

[0185] In the embodiments of this application, the volume average particle size Dv50 of the material refers to the particle size corresponding to 50% of the volume distribution. It can be detected using equipment and methods known in the art. For example, the positive electrode active material is used as a sample, and the Dv50 of the particles is tested using a Mastersizer2000E laser particle size analyzer according to the test standard GB / T19077-2016.

[0186] During the fast charging process of a battery cell, the overpotential of the second negative electrode film layer, which is far from the current collector, is usually higher. The bottleneck affecting the fast charging performance of the battery cell is mainly the second negative electrode film layer. This 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 lithium ion transport path, improve the lithium ion transport performance of the second negative electrode film layer, and improve the fast charging performance of the battery cell.

[0187] 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 to 14.8 μm, and can be selected as 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 any range of two of the above values.

[0188] 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, and can be selected as 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 any combination of two of the above values.

[0189] Controlling the particle size of graphite particles in the first and / or second negative electrode film layers within a suitable range can shorten the solid-phase transport path of lithium ions and improve fast charging performance. On the other hand, the material is less prone to agglomeration during preparation, which can improve the stability of the material. Furthermore, the combination of the negative electrode active material in the second negative electrode film layer and the negative electrode active material in the first negative electrode film layer within the aforementioned volume average particle size range is beneficial for constructing a gradient porosity difference between the second and first negative electrode film layers, reducing the tortuosity of lithium ion transport, and improving the fast charging performance of the battery cell.

[0190] In some embodiments, based on the total thickness of the first negative electrode film and the second negative electrode film, the thickness of the second negative electrode film accounts for 30% to 70%, and can be selected as 30%, 40%, 50%, 60%, 70%, or any combination of two of the above values.

[0191] By adjusting the thickness ratio of the first and second negative electrode layers within a suitable range, the gradient porosity difference between the upper and lower layers can be further increased, the tortuosity of lithium-ion transport can be reduced, and the fast charging performance of the battery cell can be improved.

[0192] In some embodiments, when the battery cell is in a 100% charged state, the thickness of the first negative electrode film 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 any range of two of the above values.

[0193] When the thickness of the first negative electrode film is within the above range, it can increase the gradient porosity difference between the first negative electrode film and the second negative electrode film, reduce the tortuosity of lithium-ion transport, and improve the fast charging performance of the battery cell.

[0194] In some embodiments, when the battery cell is at 100% charge, the thickness of the second negative electrode film is between 15 μm and 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 any combination of two of the above values. When the thickness of the second negative electrode film is within the above range, the gradient porosity difference between the first and second negative electrode films can be increased, reducing the tortuosity of lithium-ion transport and improving the fast-charging performance of the battery cell.

[0195] In this embodiment, the testing steps for the first and second negative electrode films when the battery cell is in a 100% charged state are as follows: the battery cell is charged to 3.65V with a constant current of 0.33C, and then charged to 0.05C under a constant voltage of 3.65V. Charging is then stopped, at which point the battery is in a 100% charged state. The negative electrode sheet is disassembled from the battery cell in a 100% charged state. The cross-section of the thickness direction of the middle region of the negative electrode sheet is observed using a scanning electron microscope. The two regions are distinguished according to the interface between the first and second negative electrode films, and their thicknesses are measured respectively. For example, the thickness of the first negative electrode film is measured at 10 locations, and its average value is calculated as the average value of the first negative electrode film. The thickness of the second negative electrode film is measured at 10 locations, and its average value is calculated as the average value of the second negative electrode film.

[0196] In some embodiments, the negative electrode film layer may optionally include a negative electrode conductive agent. This application does not impose any particular limitation on the type of negative electrode conductive agent. As an example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0197] In some implementations, the mass content of the negative electrode conductive agent is ≤5% based on the total weight of the negative electrode film.

[0198] In some embodiments, the negative electrode film layer may optionally include a negative electrode binder.

[0199] In some embodiments, the negative electrode binder includes one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resin, polyvinyl alcohol, sodium alginate, and carboxymethyl chitosan.

[0200] In some implementations, the mass content of the negative electrode binder is ≤5% based on the total weight of the negative electrode film.

[0201] In some embodiments, the negative electrode film may optionally include other additives. As examples, other additives may include thickeners, dispersants, etc., such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, etc.

[0202] In some implementations, the mass content of other additives is ≤2% based on the total weight of the negative electrode film.

[0203] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. Examples of metal foils include at least one foil selected from copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material layer may include at least one selected from copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymeric material substrate may include at least one selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0204] The negative electrode film is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is usually formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0205] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of this application further includes a negative electrode conductive layer sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector. In other embodiments, the negative electrode sheet of this application further includes a protective layer covering the surface of the negative electrode film layer.

[0206] In some embodiments, the negative electrode sheet further includes a negative electrode conductive layer, which is located between the negative electrode current collector and the negative electrode film layer 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, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0207] By setting a negative electrode conductive layer containing a conductive agent between the current collector and the negative electrode film, the conductivity of the negative electrode sheet can be improved, thereby enhancing the fast-charging performance of the battery cell.

[0208] In some embodiments, the thickness of the negative electrode conductive layer is 0.5 μm to 2 μm, and can be selected as 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, 1.6 μm, 1.8 μm, 2 μm or any combination of two of the above values.

[0209] In the embodiments of this application, the thickness of the negative electrode conductive layer has a meaning known in the art and can be detected using equipment and methods known in the art. The test methods for the first negative electrode film layer or the second negative electrode film layer mentioned above can be referred to.

[0210] By controlling the thickness of the negative electrode conductive layer within a suitable range, both the fast-charging performance and energy density of the battery cell can be balanced.

[0211] In some embodiments, the negative electrode conductive layer includes a negative electrode conductive layer adhesive.

[0212] 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, thereby improving the structural stability of the negative electrode sheet.

[0213] 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.

[0214] In some embodiments, when the battery cell is at 100% charge, the compaction density of the negative electrode film is 1.15 g / cm³. 3 ~1.45g / cm 3 For example, the compaction density of the negative electrode film layer of a single battery cell at 100% charge is 1.15 g / cm³. 3 1.18 g / 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 1.36 g / 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.

[0215] In this embodiment, the compaction density of the negative electrode film layer of a single battery cell at 100% State of Charge (SOC) can be detected by the following method: The battery cell is charged to 3.65V with a constant current of 0.33C, and then charged to 0.05C under a constant voltage of 3.65V. Charging is then stopped. At this point, the battery is at 100% SOC. The negative electrode sheet is disassembled from the battery cell at 100% SOC, and the compaction density of the negative electrode film layer is measured. A single-sided coated negative electrode sheet (if double-sided coated, the negative electrode film layer on one side can be wiped off first) is taken, cut into small circular pieces with an area of ​​S1, weighed, and recorded as M1, and its thickness H1 is measured. Then, the negative electrode film layer of the weighed negative electrode sheet is wiped off, the weight of the negative current collector is weighed and recorded as M0, and its thickness H0 is measured. The single-sided coating weight of the negative electrode film = (weight of the negative electrode sheet M1 - weight of the negative electrode current collector M0) / S1, the thickness of the negative electrode film = the thickness of the negative electrode sheet H1 - the thickness of the negative electrode current collector H0, and the compaction density of the negative electrode film = the single-sided coating weight of the negative electrode film / the thickness of the negative electrode film.

[0216] A suitable compaction density of the negative electrode film layer is beneficial for improving the fast charging performance of individual battery cells.

[0217] In some embodiments, the single-sided coating weight of the negative electrode film is 70 mg / 1540.25 mm. 2 ~135mg / 1540.25mm 2 For example, the single-sided coating weight of the negative electrode film 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 2115mg / 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.

[0218] A suitable single-sided coating weight of the negative electrode film is beneficial for improving the fast-charging performance of the battery cell.

[0219] [Positive electrode plate]

[0220] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector and comprising a positive electrode active material. For example, the positive current collector has two surfaces opposite each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0221] In some embodiments, the mass percentage of olivine-structured lithium phosphate in the positive electrode active material can be greater than or equal to 80% and less than or equal to 100%, and the positive electrode active material of this application can be considered as an olivine-structured lithium phosphate system. When the mass percentage of olivine-structured lithium phosphate is less than 100%, the positive electrode active material may also include commonly used positive electrode active materials, such as, but not limited to, at least one of lithium transition metal oxides. Examples of lithium transition metal oxides 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.

[0222] In some embodiments, the lithium phosphate with an olivine structure in the positive electrode active material accounts for 100% by mass.

[0223] In some embodiments, the lithium phosphate with the olivine structure includes:

[0224] Lithium phosphate matrix, and

[0225] A coating layer located on at least a portion of the surface of the lithium phosphate matrix, the coating layer comprising carbon.

[0226] The olivine-structured lithium phosphate includes a carbon coating layer. The carbon coating layer is loose and porous, which helps to increase the specific surface area of ​​the material, facilitates effective contact between the electrolyte and phosphate particles, promotes the transport of lithium ions at the phase interface, improves the conductivity of the material, and enhances the fast-charging performance of the battery cell.

[0227] In some embodiments, the lithium phosphate matrix includes materials with the general formula Li. x1 A y1 Me a1 M b1 P 1-c1 X c1 Y z1 compounds,

[0228] Wherein, 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;

[0229] 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.

[0230] In some implementations, 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 of any two of the above values.

[0231] In some implementations, 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 of any two of the above values.

[0232] In some implementations, x1+y1 can be selected as 0.9, 1.0, 1.1, 1.2, 1.3 or a range of any two of the above values.

[0233] In some implementations, a1 can be selected as 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5 or a range of any two of the above values.

[0234] In some implementations, b1 can be selected as 0, 0.1, 0.2, 0.3, 0.4, 0.5 or a range of any two of the above values.

[0235] In some implementations, a1+b1 can be selected as 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5 or a range of any two of the above values.

[0236] In some implementations, c1 can be selected as 0, 0.1, 0.2, 0.3, 0.4, 0.5 or a range of any two of the above values.

[0237] In some implementations, z1 can be selected as 3.0, 3.5, 4.0, 4.5, 5.0 or a range of any two of the above values.

[0238] Lithium phosphates with an olivine structure exhibit good cycle stability, which is beneficial for improving the cycle performance of individual battery cells.

[0239] In some embodiments, the lithium-containing 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, wherein the modified forms include one or more of doping modification and coating modification.

[0240] During the charging and discharging process, active ions such as Li undergo insertion / extraction and consumption in a single battery cell. The molar content of Li varies depending on the discharge state of the cell. This relates to the positive electrode active materials LiFePO4, LiMnPO4, and LiFe... 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, i.e., the state before feeding. When the positive electrode active material is used in a battery system, the molar content of Li may change after charge-discharge cycles. In the embodiments of this application, the positive electrode active materials LiFePO4, LiMnPO4, LiNiPO4, and LiFe... 1-x Mn x In the examples of PO4 (0 < x < 1), LiCoPO4, etc., the molar content of oxygen is only a theoretical state value. The release of oxygen from the crystal lattice will cause the molar content of oxygen to change, and the actual molar content of oxygen will fluctuate. All of the above situations are within the scope of protection of this application.

[0241] In some embodiments, based on the mass of the lithium phosphate containing the olivine structure, the mass content of the carbon element is 0.8% to 2.3%, and can be selected as 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, 2.2%, 2.3%, or a range of any two of the above values.

[0242] The carbon content in materials is usually measured by infrared absorption, such as by infrared carbon-sulfur instruments, or by indirect carbon determination methods. The latter can be found in the national standard GB / T 3521-2008 (pages 3-4 of "Methods for Chemical Analysis of Graphite").

[0243] By controlling the carbon content in the coating layer within a suitable range, the conductivity of the material can be improved, the fast-charging performance of the battery can be enhanced, and the specific capacity of the material, as well as the fast-charging performance and energy density of the battery cells, can also be taken into account.

[0244] In some implementations, the battery cell satisfies the following relationship: 0.08 ≤ C / B ≤ 1.15.

[0245] Wherein, C is the mass content of carbon element, based on the mass of lithium phosphate containing the olivine structure;

[0246] B represents the mass content of the first additive, based on the total mass of the electrolyte.

[0247] In some implementations, 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 of any two of the above values.

[0248] As mentioned earlier, the carbon in the carbon coating layer can improve the effective contact between the electrolyte and phosphate particles, thereby enhancing the conductivity of the material. However, while the porous carbon coating layer improves the wetting performance of the electrolyte, it can also lead to side reactions between the phosphate particles and the electrolyte, consuming lithium ions and affecting the cycle performance of the battery cell. The first additive in the electrolyte helps to form a CEI film 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 cycle performance of the battery cell.

[0249] This application controls the mass content of carbon in the lithium phosphate containing olivine structure and the mass content of the first additive within a suitable range. Through the synergistic effect of the two, it can improve the conductivity of the material, enhance the fast charging performance of the battery cell, and also take into account the cycle stability of the material and the cycle performance of the battery.

[0250] In some embodiments, the coating layer also includes Li 3-d1 Fe 2-d1 M3 d1 (PO m1 ) n1 The substance,

[0251] Where 0≤d1≤1, 0≤m1≤5, 0≤n1≤4;

[0252] M3 includes one or more elements selected from Ti, Zr, Hf, Ge, and Sn. Optionally, M3 has a +4 valence.

[0253] In some embodiments, the coating layer further includes one or more of Li2FeTi(PO4)3, Li2FeZr(PO4)3, and Li2FeSn(PO4)3.

[0254] In some implementations, carbon and Li 3-d1 Fe 2-d1 M3 d1 (PO m1 ) n1 Substances can be layered, for example, carbon can be used as an independent carbon coating layer, and Li 3-d1 Fe 2-d1 M3 d1 (PO m1 ) n1 The material can act as an independent fast ion conductor layer. The carbon coating can be applied to the surface of the phosphate particles, with the fast ion conductor layer located on the surface of the carbon coating layer (i.e., on the side of the carbon coating layer facing away from the phosphate particles). Alternatively, the fast ion conductor layer can be applied to the surface of the phosphate particles, with the carbon coating layer located on the surface of the fast ion conductor layer (i.e., on the side of the fast ion conductor layer facing away from the phosphate particles). Of course, carbon and Li... 3-d1 Fe 2-d1 M3 d1 (PO m1 ) n1 The same material can also be placed on the same layer.

[0255] The coating layer includes Li 3-d1 Fe 2-d1 M3 d1 (PO m1 ) n1 It has excellent ion conductivity, which, together with the carbon element in the coating layer that has excellent conductivity, improves the conductivity and ion conductivity of the material, which is beneficial to improving the fast charging performance of the battery.

[0256] In this embodiment, the elemental content in the positive electrode active material has a meaning known in the art and can be detected using equipment and methods known in the art. For example, referring to EPA6010D-2014, it can be tested by inductively coupled plasma atomic emission spectrometry (ICP-OES, instrument model: Thermo ICAP7400). After discharging the battery cell to 0% state of charge (SOC), the positive electrode sheet is disassembled, cleaned and dried with DMC, and then calcined at high temperature to remove impurities. 0.4g of the positive electrode active material is weighed and 10ml (50% concentration) of aqua regia is added. Then it is placed on a plate at 180℃ for 30min. After digestion on the plate, the volume is adjusted to 100mL, and quantitative testing is performed using the standard curve method.

[0257] In some embodiments, the powder compaction density of the positive electrode active material at 30000N is 2.43 g / cm³. 3 ~2.85g / cm 3 The option is 2.43 g / cm³. 3 2.44 g / cm 3 2.45g / cm 3 2.46 g / cm 3、 2.47g / cm 3 2.48 g / cm 3 2.49 g / cm 3 2.5g / cm 3 2.51g / cm 3 2.55g / cm 3 2.58g / cm 3 2.60g / cm 3 2.65g / cm 3 2.68g / cm 3 2.70 g / cm 3 2.72 g / cm 3 2.75g / cm 3 2.78g / cm 3 2.80g / cm 3 2.85g / cm 3 Or a range consisting of any two of the above values.

[0258] When the powder compaction density of the positive electrode active material at 30000N is within the above range, it can improve the energy density of the battery cell. Furthermore, since the positive electrode active material in the positive electrode film can be stacked more tightly, the contact resistance between particles is smaller, which can further reduce the resistance of the electrode sheet and also help improve the fast charging performance of the battery cell.

[0259] In the embodiments of this application, the powder compaction density of the material has a meaning known in the art and can be tested using methods and equipment known in the art, according to the testing standard GB / T24533-2009. For example, a certain amount of positive electrode active material is taken as a sample and added to a UTM7305 electronic pressure testing machine with a bottom area of ​​1.327 cm². 2 In the mold, the pressure is increased to 3000 kg (equivalent to 30000 N), held for 30 s, then depressurized and held for 10 s. The compaction density of the positive electrode active material under a force of 30000 N is then recorded and calculated.

[0260] In some embodiments, the compaction density of the positive electrode film layer is 2.50 g / cm³ when the battery cell is at 100% charge. 3 ~2.80g / cm 3 2.50g / cm³ is an option. 3 2.55g / cm 3 2.60g / cm 3 2.65g / cm 3 2.70 g / cm 3 2.75g / cm 3 2.80g / cm 3 Or a range consisting of any two of the above values.

[0261] In the embodiments of this application, the compaction density of the positive electrode film layer of a single battery cell under 100% charge state has a well-known meaning in the art and can be detected using well-known equipment and methods in the art. The detection method is as described above for the compaction density test method of the negative electrode film layer.

[0262] When the compaction density of the positive electrode film is within a suitable range, the battery cell has a high energy density.

[0263] In some embodiments, the positive electrode film layer may optionally include a positive electrode conductive agent. This application does not impose particular limitations on the type of positive electrode conductive agent. As an example, the positive electrode conductive agent includes at least one selected from superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass content of the positive electrode conductive agent is ≤5% based on the mass of the positive electrode film layer.

[0264] In some embodiments, the positive electrode film layer may optionally include a positive electrode binder. This application does not impose particular limitations on the type of positive electrode binder. As an example, the positive electrode binder may include at least one selected from polyvinylidene fluoride, polytetrafluoroethylene, a terpolymer of vinylidene fluoride-tetrafluoroethylene-propylene, a terpolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, a tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and fluorinated acrylate resins. In some embodiments, the mass content of the positive electrode binder is ≤5% based on the mass of the positive electrode film layer.

[0265] In some embodiments, the positive current collector may be a metal foil or a composite current collector. Examples of metal foils include at least one foil selected from aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material layer may include at least one selected from aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymeric material substrate may include at least one selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0266] The positive electrode film layer is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is typically formed by dispersing positive electrode active material, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP), but is not limited to it. The positive electrode sheet does not exclude other additional functional layers besides the positive electrode film layer. For example, in some embodiments, the positive electrode sheet of this application further includes a positive electrode conductive layer sandwiched between the positive electrode current collector and the positive electrode film layer and disposed on the surface of the positive electrode current collector. In other embodiments, the positive electrode sheet of this application further includes a protective layer covering the surface of the positive electrode film layer.

[0267] Electrolyte

[0268] During the charging and discharging process of a single battery cell, active ions such as lithium ions are inserted and extracted back and forth between the positive and negative electrode plates, and the electrolyte plays the role of conducting active ions between the positive and negative electrode plates.

[0269] In this embodiment, the electrolyte includes a first additive, which includes at least one of vinylene carbonate and ethylene carbonate derivatives. Based on the total mass of the electrolyte, the mass content of the first additive is 1% to 12%.

[0270] The ethylene carbonate derivatives include compounds represented by Formula I.

[0271] R1, R2, R3, and R4 each independently include any one of hydrogen atoms, halogen atoms, C1-C5 alkyl groups, and C1-C5 haloalkyl groups, and R1, R2, R3, and R4 are not all hydrogen atoms at the same time.

[0272] Adding vinylene carbonate and / or ethylene carbonate derivatives as a first additive to the electrolyte allows vinylene carbonate and ethylene carbonate derivatives to preferentially participate in the formation of the SEI film on the negative electrode side, prioritizing other components in the electrolyte. Furthermore, the high organic content in the film formed by vinylene carbonate and ethylene carbonate derivatives improves the overall flexibility of the SEI film, enhances the stability of the SEI film-negative electrode interface during cycling, reduces the reaction between the negative electrode active material and the electrolyte, decreases lithium-ion consumption, and improves the cycle performance and storage performance of the battery cell. Additionally, controlling the mass content of the first additive within a suitable range improves the flexibility and stability of the SEI film while also controlling its thickness within a suitable range, thereby simultaneously achieving stability and low impedance at the negative electrode interface, balancing the cycle performance and fast-charging performance of the battery cell.

[0273] In some embodiments, at least one of R1, R2, R3, and R4 contains fluorine atoms.

[0274] Ethylene carbonate derivatives in which at least one of R1, R2, R3, and R4 is a fluorine atom are easy to open rings, forming an SEI film containing more organic matter on the negative electrode surface. This helps to improve the overall flexibility of the SEI film, thereby improving the stability of the SEI film and the negative electrode interface during cycling and enhancing the cycle performance of the battery cell.

[0275] In some embodiments, the ethylene carbonate derivative includes one or more of fluoroethylene carbonate, difluoroethylene carbonate, and trifluoromethylethylene carbonate.

[0276] Suitable ethylene carbonate derivative additives can form an SEI film containing a large amount of organic matter on the negative electrode side, which can improve the overall flexibility of the SEI film and achieve the purpose of improving the stability of the SEI film and negative electrode interface during cycling, thereby improving the cycle performance of the battery cell. At the same time, the SEI film formed by fluoroethylene carbonate, difluoroethylene carbonate, and trifluoromethyl ethylene carbonate has low impedance, which is also beneficial to improving the fast charging performance of the battery cell.

[0277] In some embodiments, the electrolyte further includes an organic solvent, which includes one or more of a first organic solvent and a second organic solvent.

[0278] The first organic solvent includes at least one of cyclic carbonates and chain carbonates, and may be a cyclic carbonate.

[0279] The second organic solvent includes R5-COO-R6.

[0280] R5 includes any one of hydrogen atoms, halogen atoms, C1-C5 alkyl groups, and C1-C5 haloalkyl groups, and R6 includes any one of C1-C5 alkyl groups and C1-C5 haloalkyl groups.

[0281] The first organic solvent of cyclic carbonates and chain carbonates 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 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 cells.

[0282] In some embodiments, the cyclic carbonate includes one or more of ethylene carbonate, propylene carbonate, and butene carbonate.

[0283] In some embodiments, the chain carbonate includes one or more of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0284] In some embodiments, the second organic solvent includes one or more of methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, methyl butyrate, and ethyl butyrate.

[0285] In some embodiments, based on the total mass of the electrolyte, the mass content of the first organic solvent is 20% to 72%, and can be selected as 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 72%, or any combination of two of the above values.

[0286] The appropriate amount of cyclic carbonates and chain carbonates as the first organic solvent can further improve the conductivity of the electrolyte, which is beneficial to the migration of lithium ions and improves the fast charging performance of the battery cells.

[0287] The type and quality of solvents in the electrolyte can be obtained by methods known to those skilled in the art. For example, the composition of the electrolyte can be determined by liquid chromatography, ultraviolet spectrophotometry, or ultraviolet-visible spectrophotometry. For instance, a battery cell is disassembled, and free electrolyte is obtained from it. The free electrolyte in the battery cell is diluted 3 to 10 times with acetonitrile to obtain a diluted electrolyte solution to be tested. Using a GC-MS 3100 organic component gas chromatograph, the above diluted electrolyte solution is placed in the instrument for full-scan qualitative analysis. The injection port temperature is 250°C, and the scan range is 35 μm to 270 μm. After the test, a total ion chromatogram of each organic compound is obtained. The peak positions are compared with the corresponding organic compounds, and the percentage content of each organic compound is calculated based on the peak area.

[0288] In some embodiments, the electrolyte further includes a second additive, which includes one or more of sulfur-containing additives and lithium salt additives.

[0289] Additives refer to components with low content in electrolytes, generally accounting for no more than 10% of the electrolyte by mass. They are characterized by their strong targeting and small dosage, and can significantly optimize a certain aspect of battery performance without changing the production process.

[0290] Sulfur-containing additives and lithium salt additives can improve the interfacial film performance of the positive and / or negative electrode sides, improve the interfacial chemistry between the positive and / or negative electrode and the electrolyte, and enhance the fast charging performance and cycle performance of the battery.

[0291] In some embodiments, the sulfur-containing additive includes one or more of vinyl sulfate, vinyl disulfate, butene sulfite, 1,3-propanesulfonate lactone, vinyl sulfite, and methylene disulfonate.

[0292] In some embodiments, the lithium salt additive includes one or more of lithium difluorophosphate, lithium difluorooxalate borate, lithium tetrafluoroborate, and lithium dioxalate borate.

[0293] In some embodiments, the electrolyte further includes a lithium salt, which includes one or both of fluorosulfonyl imide salt and lithium hexafluorophosphate.

[0294] Fluorosulfonyl imide salts and lithium hexafluorophosphate are easily dissociated, which is beneficial for the rapid migration of lithium ions and improves the fast-charging performance of battery cells. In addition, fluorosulfonyl imide salts and lithium hexafluorophosphate are relatively stable in the electrolyte system, which can improve the cycle performance of battery cells.

[0295] In some embodiments, the fluorosulfonyl imide salt includes one or both of lithium bisfluorosulfonyl imide and lithium bistrifluoromethanesulfonate imide.

[0296] In some embodiments, the lithium salt comprises lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate, wherein the molar concentration ratio of the lithium bis(fluorosulfonyl)imide to the molar concentration of the lithium hexafluorophosphate is 0.2 to 1.0, and may be selected from 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0 or any combination of two of the above values.

[0297] In some embodiments, the molar concentration of the lithium bis(fluorosulfonyl)imide is 0.2 mol / L to 0.5 mol / L, and can be selected as 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 any combination of two of the above values;

[0298] The molar concentration of lithium hexafluorophosphate is 0.5 mol / L to 1.2 mol / L, and can be selected from 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 any combination of two of the above values.

[0299] [Isolation membrane]

[0300] The electrode assembly includes a separator membrane disposed between the positive and negative electrodes.

[0301] This application does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0302] As an example, the main material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and ceramic. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation. The separator can be a single component located between the positive and negative electrodes, or it can be attached to the surfaces of the positive and negative electrodes. An inorganic particle coating, an organic particle coating, or an organic / inorganic composite coating can also be applied to the surface of the separator.

[0303] In some embodiments, the thickness of the isolation membrane is 4μm to 12μm, and can be selected as 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm or any combination of two of the above values.

[0304] In the embodiments of this application, the thickness of the separator is defined in the sense of a known concept in the art. It can be tested using known concepts and equipment in the art. For example, a newly prepared separator can be used as a sample, or a battery cell that has been fully discharged (discharged to the lower limit cutoff voltage so that the battery's state of charge is about 0% SOC) can be disassembled in reverse. The separator can be obtained from the battery cell, dried, and used as a sample. The separator can be cut with an ion beam cutter to form a cross-section. Subsequently, the thickness of the separator can be measured using a scanning electron microscope.

[0305] When the thickness of the separator is within a suitable range, the migration path of lithium ions in the separator is shorter, which can reduce the internal resistance of the battery cell and improve the fast charging performance of the battery cell.

[0306] In some embodiments, the porosity of the isolation membrane is 20% to 70%, and can be selected as 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or any combination of two of the above values.

[0307] In this embodiment, porosity refers to the percentage of the volume of the pores in the separator to the total volume of the separator. Porosity can be tested according to the standard GB / T36363-2018 "Polyolefin Separators for Battery Cells". It should be noted that the actual testing process may differ slightly from the standard due to differences in testing instruments, testing errors, and to minimize the impact on porosity testing, in order to obtain more accurate test values.

[0308] When the porosity of the separator is within a suitable range, it can increase the migration rate of lithium ions in the separator, reduce the internal resistance of the battery cell, and improve the fast charging performance of the battery cell.

[0309] In some embodiments, the battery cell is configured to charge from 10% state of charge to 80% state of charge in a time of 5 min to 10.5 min, which may be selected as 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, 10.5 min or any combination of two of the above values.

[0310] In some implementations, the charging process of a single battery cell from 10% state of charge to 80% state of charge includes multiple charging steps. The difference between the maximum state of charge in any of the multiple charging steps and the maximum state of charge in its adjacent charging step is less than or equal to 5% state of charge, such as 1% state of charge, 1.5% state of charge, 2% state of charge, 2.5% state of charge, 3% state of charge, 3.5% state of charge, 4% state of charge, 4.5% state of charge, 5% state of charge, or any point value within a range of any two of the above values.

[0311] The charging process for a single battery cell from 10% to 40% state of charge involves multiple charging steps. For any charging step, the battery 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, or 10C, or a value within a range of any two of the above values.

[0312] The charging process from 40% to 80% state of charge for a single battery cell also includes multiple charging steps. The charging rate of any one of the charging steps is less than the charging rate of any one of the charging steps from 10% to 40% state of charge, and the charging rate of the step to 80% state of charge is any value from 2.5C to 7C.

[0313] For example, the charging process of a single battery cell from 10% state of charge to 80% state of charge can be performed as follows:

[0314] Charge from 10% SOC to 15% SOC at a constant current of 7.0C;

[0315] Charge from 15% SOC to 20% SOC at a constant current of 7.0C;

[0316] Charge from 20% SOC to 25% SOC at a constant current of 7.0C;

[0317] Charge from 25% SOC to 30% SOC at a constant current of 6.6C;

[0318] Charge from 30% SOC to 35% SOC at a constant current of 6.2C;

[0319] Charge from 35% SOC to 40% SOC at a constant current of 5.7C;

[0320] Charge from 40% SOC to 45% SOC at a constant current of 5.2C;

[0321] Charge from 45% SOC to 50% SOC at a constant current of 4.8C;

[0322] Charge from 50% SOC to 55% SOC at a constant current of 4.6C;

[0323] Charge from 55% SOC to 60% SOC at a constant current of 4.4C;

[0324] Charge from 60% SOC to 65% SOC at a constant current of 4.2C;

[0325] Charge from 65% SOC to 70% SOC at a constant current of 3.9C;

[0326] Charge from 70% SOC to 75% SOC at a constant current of 3.5C;

[0327] Charge from 75% SOC to 80% SOC at a constant current of 3.0C.

[0328] The battery cells charge quickly, exhibiting excellent fast-charging performance.

[0329] In some embodiments, the volumetric energy density of the battery cell is 395Wh / L to 530Wh / L, and can be selected from 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 any two of the above values.

[0330] The volumetric energy density of the battery cells is relatively high.

[0331] In the embodiments of this application, the volumetric energy density of a single battery cell has a meaning known in the art and can be detected using equipment and methods known in the art. For example, taking a battery charging upper limit voltage of 3.65V and a battery discharge cutoff voltage of 2.0V as an example, the battery cell is placed at 25°C and charged to 3.65V with a constant current of 0.33C, then charged to 0.05C with a constant voltage, and discharged to 2.0V with 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 using calipers (generally calculated based on the battery casing dimensions, excluding the height of the electrode terminals and the insulating film outside the casing). The volume of the single battery cell V0 is calculated in L. The volumetric energy density of the battery cell VED = (A0 × discharge plateau voltage) / V0 in Wh / L.

[0332] [Battery Device]

[0333] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0334] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0335] In some implementations, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging of the battery cell can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0336] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 shows a square battery cell 5 as an example.

[0337] In some embodiments, referring to FIG2, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. The positive electrode sheet, negative electrode sheet, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0338] In some implementations, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0339] Figure 3 shows a battery module 4 as an example. Referring to Figure 3, in the battery module 4, multiple battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple battery cells 5 can be fixed in place using fasteners.

[0340] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0341] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0342] Figures 4 and 5 show a battery pack 1 as an example. Referring to Figures 4 and 5, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper box 2 and a lower box 3, with the upper box 2 covering the lower box 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0343] In addition, this application also provides an electrical device, which includes at least one of the battery cell, battery module, or battery pack provided in this application. The battery cell, battery module, or battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is 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 and satellites, energy storage systems, etc.

[0344] As an electrical device, you can choose individual battery cells, battery modules, or battery packs according to your usage requirements.

[0345] Figure 6 shows an example of an electrical device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the individual battery cells, a battery pack or battery module can be used.

[0346] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0347] I. Preparation method of the embodiment

[0348] The following embodiments describe the contents disclosed in this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of the embodiments of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0349] Example 1

[0350] (1) Preparation of positive electrode sheet

[0351] The positive electrode includes a positive current collector, a positive conductive layer on the positive current collector, and a positive film layer. The positive current collector is an aluminum foil with a thickness of 13μm.

[0352] The positive electrode conductive layer on the positive electrode current collector is a film formed by uniformly mixing the positive electrode conductive agent superconducting carbon, the positive electrode binder polyvinylidene fluoride (PVDF), and the solvent N-methylpyrrolidone (NMP), coating it on the surface of the current collector, and drying it. The thickness is 1 μm. The positive electrode conductive layer contains 40% positive electrode conductive agent by mass and 60% positive electrode binder by mass.

[0353] The positive electrode film layer comprises a film layer formed by uniformly coating a positive electrode slurry (solvent being N-methylpyrrolidone, NMP) onto the surface of a positive electrode conductive layer, followed by drying and cold pressing. The positive electrode film layer comprises positive electrode active material, binder polyvinylidene fluoride (PVDF), and conductive agent acetylene black in a weight ratio of 97:2:1.

[0354] The positive electrode active material includes lithium iron phosphate, which has a coating layer that coats the surface of the lithium iron phosphate particles. The coating layer includes lithium titanium iron phosphate (Li2FeTi(PO4)3) and carbon elements, with a carbon element mass content of 1.12%.

[0355] The single-sided coating weight of the positive electrode film is 250 mg / 1540.25 mm. 2 .

[0356] (2) Preparation of negative electrode sheet

[0357] The negative electrode sheet includes a negative current collector, a negative conductive layer on the negative current collector, and a negative film layer. The negative current collector is a copper foil with a thickness of 5μm.

[0358] The negative electrode conductive layer on the negative electrode current collector is a film formed by uniformly mixing the negative electrode conductive agent superconducting carbon, the negative electrode binder styrene-butadiene rubber SBR, the thickener sodium carboxymethyl cellulose (CMC-Na), and the solvent water, coating it on the surface of the negative electrode current collector, and drying it. The thickness is 1μm. The negative electrode conductive agent has a mass content of 35% in the negative electrode conductive layer, the negative electrode binder has a mass content of 60% in the negative electrode conductive layer, and the thickener has a mass content of 5% in the negative electrode conductive layer.

[0359] The negative electrode film layer comprises a film layer formed by uniformly coating a negative electrode slurry (with deionized water as the solvent) onto the surface of a negative electrode conductive layer, followed by drying and cold pressing.

[0360] The single-sided coating weight of the negative electrode film is 95 mg / 1540.25 mm. 2 .

[0361] 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.

[0362] The first negative electrode film layer comprises 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.

[0363] 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.

[0364] The thickness ratio of the first film layer to the second film layer is 50%:50%.

[0365] (3) Separating membrane

[0366] The separator includes a base membrane, which is a 7μm polyethylene film layer with a porosity of 42%.

[0367] (4) Preparation of electrolyte

[0368] The electrolyte comprises an organic solvent, a lithium salt, and a first additive and a second additive.

[0369] The organic solvents include 39.0% by mass of a chain carboxylic acid ester solvent (ethyl acetate) and 39.0% by mass of a carbonate solvent (27.3% by mass of ethylene carbonate EC and 11.7% by mass of dimethyl carbonate). The mass content of each component in the organic solvents is calculated based on the mass of the electrolyte.

[0370] 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 difluorooxalate borate LiDFOB in a mass ratio of 5:1:0.5:0.5.

[0371] The lithium salts consist of lithium bis(fluorosulfonyl)imide (LiFSI) at a mass content of 4.5% and lithium hexafluorophosphate (LiPF6) at a mass content of 10.5%, with the mass content of the lithium salts calculated based on the mass of the electrolyte.

[0372] (5) Preparation of battery cells

[0373] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation, thus obtaining an electrode assembly. The electrode assembly is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a battery cell is obtained.

[0374] Examples 2-5

[0375] Compared with Example 1, Examples 2-5 adjusted the single-sided coating weight of the positive electrode film and the mass content of silicon-carbon composite material in the first and second negative electrode films. Specific parameters are shown in Table 1.

[0376] Examples 6-9

[0377] Compared with Example 1, Examples 6-9 adjusted the mass content of ethylene carbonate, dimethyl carbonate, ethyl acetate, and the first additive in the electrolyte, as well as the mass content of silicon-carbon composite material in the first and second negative electrode layers. Specific parameters are shown in Table 1.

[0378] Examples 10-12

[0379] Compared with Example 1, the mass content of carbon in the lithium iron phosphate coating layer was adjusted in Examples 10-12. The specific parameters are shown in Table 1.

[0380] Example 13

[0381] Compared with Example 1, Example 13 adjusted the single-sided coating weight of the positive electrode film and the negative electrode film, as well as the mass content of ethylene carbonate, dimethyl carbonate, ethyl acetate, and the first additive in the electrolyte. Specific parameters are shown in Table 1.

[0382] Comparative Example 1

[0383] Compared with Example 1, Comparative Example 1 adjusted the single-sided coating weight of the positive electrode film and the negative electrode film, and the negative electrode film did not contain silicon-carbon composite material. For specific parameters, please refer to Table 1.

[0384] Comparative Example 2

[0385] Compared with Example 1, Comparative Example 2 adjusted the single-sided coating weight of the positive electrode film and the mass content of silicon-carbon composite material in the first and second negative electrode films. Specific parameters are shown in Table 1.

[0386] Comparative Examples 3-4

[0387] Compared with Example 1, Comparative Examples 3-4 adjusted the mass content of ethylene carbonate, dimethyl carbonate, ethyl acetate, and the first additive in the electrolyte. Specific parameters are shown in Table 1.

[0388] II. Performance Testing.

[0389] 1. The charging time for a single battery cell from 10% SOC to 80% SOC is as follows, and the specific charging steps are as follows:

[0390] Taking the battery cell of Example 1 as an example:

[0391] At 30°C, the battery cells are charged from a state of 10% SOC.

[0392] Charge from 10% SOC to 15% SOC at a constant current of 7.0C;

[0393] Charge from 15% SOC to 20% SOC at a constant current of 7.0C;

[0394] Charge from 20% SOC to 25% SOC at a constant current of 7.0C;

[0395] Charge from 25% SOC to 30% SOC at a constant current of 7.0C;

[0396] Charge from 30% SOC to 35% SOC at a constant current of 6.2C;

[0397] Charge from 35% SOC to 40% SOC at a constant current of 5.7C;

[0398] Charge from 40% SOC to 45% SOC at a constant current of 5.2C;

[0399] Charge from 45% SOC to 50% SOC at a constant current of 4.8C;

[0400] Charge from 50% SOC to 55% SOC at a constant current of 4.6C;

[0401] Charge from 55% SOC to 60% SOC at a constant current of 4.4C;

[0402] Charge from 60% SOC to 65% SOC at a constant current of 4.2C;

[0403] Charge from 65% SOC to 70% SOC at a constant current of 3.9C;

[0404] Charge from 70% SOC to 75% SOC at a constant current of 3.5C;

[0405] Charge from 75% SOC to 80% SOC at a constant current of 3.0C;

[0406] Record the total charging time.

[0407] The slight differences in charging time between 10% and 80% SOC for battery cells in different embodiments and comparative examples can be obtained by slightly adjusting the above charging rate. Overall, the charging rate gradually decreases from low SOC to high SOC. The specific charging rate for different SOC ranges is tested as follows: At 25°C, the battery cell is charged at a constant current of 1 / 3C to the charging cutoff voltage of 3.65V, then charged at a constant voltage to a current of 0.05C, left to stand for 5 minutes, and then discharged at a constant current of 1 / 3C to the discharge cutoff voltage of 2V. Its actual capacity is recorded as C. Then, the individual battery cells were sequentially charged 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 until the full battery charging cutoff voltage of 3.65V or the lithium plating potential of 0mV (whichever comes first). After each charge, the cells were discharged at 1C until the full battery discharge cutoff voltage of 2V. The SOC (State of Charge) was recorded at different charging rates until 10%, 15%, 20%, 25%, 30%...80%. The negative electrode potential corresponding to the state of charge (SOC) is plotted, and the rate-negative electrode potential curves under different SOC states are obtained after linear fitting. The charging rate corresponding to the 0mV lithium plating potential under different SOC states is obtained. This charging rate is the charging rate adopted in the corresponding SOC range during the above charging time test. Among them, the charging power of 7C from 10% SOC to 15% SOC is the maximum rate that the mechanical parts of the battery cell can withstand. For specific charging rates, please refer to Table 1 and Table 2.

[0408] Table 1

[0409] Table 2

[0410] 2. Capacity retention rate of individual battery cells after 1000 cycles at 30℃

[0411] At 30℃, the battery cell is charged from 0% SOC, charged to 100% SOC according to the rates corresponding to the different SOC values ​​listed below, and then charged at a constant current rate of 0.33C to 3.65V. After resting for 30 minutes, it is discharged at a constant current rate of 1C to 2.0V. This constitutes one charge-discharge cycle. The capacity C0 after the first cycle is recorded. The above charge-discharge cycle steps are repeated until 1000 cycles are completed. The capacity Cn after the 1000th cycle is recorded. The capacity retention rate of the battery after 1000 cycles at 30℃ is calculated as Cn / C0 × 100%. A higher capacity retention rate indicates better cycle performance of the battery cell. The charging process from 0% SOC to 100% SOC is as follows:

[0412] Taking the battery cell of Example 1 as an example:

[0413] Charge from 0% SOC to 10% SOC at a constant current of 1C.

[0414] Charge from 10% SOC to 15% SOC at a constant current of 7.0C;

[0415] Charge from 15% SOC to 20% SOC at a constant current of 7.0C;

[0416] Charge from 20% SOC to 25% SOC at a constant current of 7.0C;

[0417] Charge from 25% SOC to 30% SOC at a constant current of 7.0C;

[0418] Charge from 30% SOC to 35% SOC at a constant current of 6.2C;

[0419] Charge from 35% SOC to 40% SOC at a constant current of 5.7C;

[0420] Charge from 40% SOC to 45% SOC at a constant current of 5.2C;

[0421] Charge from 45% SOC to 50% SOC at a constant current of 4.8C;

[0422] Charge from 50% SOC to 55% SOC at a constant current of 4.6C;

[0423] Charge from 55% SOC to 60% SOC at a constant current of 4.4C;

[0424] Charge from 60% SOC to 65% SOC at a constant current of 4.2C;

[0425] Charge from 65% SOC to 70% SOC at a constant current of 3.9C;

[0426] Charge from 70% SOC to 75% SOC at a constant current of 3.5C;

[0427] Charge from 75% SOC to 80% SOC at a constant current of 3.0C;

[0428] Charge from 80% SOC to 100% SOC at a constant current of 0.33C.

[0429] The slight differences in charging time between 10% and 80% SOC for different embodiments and comparative examples of battery cells can be obtained by slightly adjusting the above charging rate. Overall, the charging rate gradually decreases from low SOC to high SOC. For specific charging rates, please refer to Table 1 and Table 2.

[0430] 3. The test procedure for the volumetric energy density (VED) of a single battery cell is as follows:

[0431] The battery cells of the examples and comparative examples were placed at 25°C and charged to 3.65V with a constant current of 0.33C, then charged to 0.05C with a constant voltage of 3.65V, and left to stand for 30 minutes; they were then discharged to 2.0V with a constant current of 0.33C, and the discharge capacity A0 was recorded at this time, in Ah; the length, width, and height of the battery cells were measured with calipers, and the volume of the battery cell V0 was calculated, in L; the volumetric energy density of the battery cell VED = (A0 × discharge plateau voltage) / V0, in Wh / L.

[0432] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0433] Each example and comparative example was prepared according to the above method, and various performance parameters were measured. The results are shown in the table below.

[0434] Table 3

[0435] Table 4

[0436] (The 863cls@60%SOH in Comparative Example 3 means that the capacity retention rate of the battery cell in Comparative Example 3 is only 60% after 863 cycles.)

[0437] Based on the above results, the battery cell in Examples 1-13 includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a negative electrode, and a separator. The separator is located between the positive and negative electrode. The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector. The positive electrode film layer includes a positive active material, which includes a lithium phosphate with an olivine structure. The single-sided coating weight of the positive electrode film layer is 180 mg / 1540.25 mm. 2 ~380mg / 1540.25mm 2 The negative electrode includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The negative electrode film layer includes a negative electrode active material, which includes a silicon-based material. Based on the mass of the negative electrode active material, the mass content of silicon element is 0.3%-10.0%. The electrolyte includes a first additive, which includes vinylene carbonate and / or fluoroethylene carbonate. The mass content of the first additive is 1%-12%.

[0438] As can be seen from the comparison between Examples 1-13 and Comparative Example 1, compared with simply adjusting the single-sided coating weight of the positive electrode film and the single-sided coating weight of the negative electrode film, this application can improve the energy density of the battery cell while taking into account the fast charging performance of the battery cell by adjusting the single-sided coating weight of the positive electrode film and the silicon-based element content in the negative electrode film.

[0439] As can be seen from the comparison between Examples 1-13 and Comparative Example 2, controlling the mass content of silicon element in silicon-based materials to be between 0.3% and 10.0% can improve the cycle performance and fast charging performance of battery cells.

[0440] As can be seen from the comparison between Examples 1-13 and Comparative Examples 3-4, controlling the mass content of the first additive to be between 1% and 12% can improve the cycle performance of the battery cell while also taking into account the fast charging performance of the battery cell.

[0441] A comparison of Examples 1-4 with Example 5 shows that the silicon content in the silicon-based material is 0.3%-6.0% by mass, which can further improve the cycle performance and fast charging performance of the battery cell.

[0442] As can be seen from Examples 1-3, 6-7, and 10-13, 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 cell has excellent cycle performance and fast charging performance.

[0443] As can be seen from Examples 4-5 and 8-9, 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 volumetric energy density.

[0444] As can be seen from Examples 1-13, the ratio of the mass content A of silicon element in the silicon-based material to the mass content B of the first additive is 0.025 to 6, and the battery cell has high energy density, excellent cycle performance and fast charging performance.

[0445] As can be seen from Examples 1 and 10-12, the mass content of carbon element in lithium carbonate based on olivine structure is 0.8% to 2.3%, and the battery cell has both excellent cycle performance and fast charging performance.

[0446] 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. 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 by, The system includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a negative electrode, and a separator, with the separator located between the positive and negative electrode. The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector. The positive electrode film layer includes a positive electrode active material, which includes a lithium phosphate with an olivine structure. The single-side coating weight of the positive electrode film layer is 180 mg / 1540.25 mm 2 to 380 mg / 1540.25 mm 2 ; The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The negative electrode film layer includes a negative electrode active material, which includes a silicon-based material. Based on the mass of the negative electrode active material, the mass content of silicon element is 0.3% to 10.0%. The electrolyte includes a first additive, which includes at least one selected from vinylene carbonate and ethylene carbonate derivatives. Based on the total mass of the electrolyte, the mass content of the first additive is 1% to 12%. The ethylene carbonate derivative includes a compound represented by Formula I, R1, R2, R3, and R4 each independently include any one of hydrogen atoms, halogen atoms, C1-C5 alkyl groups, and C1-C5 haloalkyl groups, and R1, R2, R3, and R4 are not all hydrogen atoms at the same time.

2. The battery cell of claim 1, wherein, Based on the mass of the negative electrode active material, the mass content of silicon element is 0.3% to 6.0%.

3. The battery cell according to claim 1 or 2, characterized in that, At least one of R1, R2, R3, and R4 contains a fluorine atom.

4. The battery cell according to any one of claims 1 to 3, characterized in that, The ethylene carbonate derivatives include one or more of fluoroethylene carbonate, difluoroethylene carbonate, and trifluoromethylethylene carbonate.

5. The battery cell according to any one of claims 1 to 4, characterized in that, The battery cell satisfies the following relationship: 0.025≤A / B≤6, which can be optionally 0.035≤A / B≤2.

5. Where A is the mass content of 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.

6. The battery cell according to any one of claims 1 to 5, characterized in that, Based on the mass of the negative electrode active material, the mass content of silicon element is 0.3% to 3%; Based on the total mass of the electrolyte, the mass content of the first additive is 2% to 7.5%.

7. The battery cell according to any one of claims 1 to 5, characterized in that, Based on the mass of the negative electrode active material, the mass content of silicon element 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 3% to 10%.

8. The battery cell of any one of claims 1 to 7, wherein, The lithium phosphate with the olivine structure includes: Lithium phosphate matrix, and A coating layer located on at least a portion of the surface of the lithium phosphate matrix, the coating layer comprising carbon.

9. The battery cell of claim 8, wherein, Based on the mass of the lithium phosphate containing the olivine structure, the carbon content is 0.8% to 2.3% by mass.

10. The battery cell according to claim 8 or 9, 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 phosphate containing the olivine structure; B represents the mass content of the first additive, based on the total mass of the electrolyte.

11. The battery cell of any one of claims 8 to 10, wherein, The cladding layer also comprises Li 3-d1 Fe 2-d1 M3 d1 (PO m1 ) n1 of the substance, Where 0≤d1≤1, 3≤m1≤5, 2≤n1≤4; M3 includes one or more of Ti, Zr, Hf, Ge, and Sn, and optionally, M3 is +4 valence.

12. The battery cell of any one of claims 8 to 11, wherein, The lithium-containing phosphate base includes a compound of the general formula Li x1 A y1 Me a1 M b1 P 1-c1 X c1 Y z1 of the compound, Wherein, 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.

13. The battery cell of any one of claims 8 to 12, wherein, The lithium-containing 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 aforementioned substances, wherein the modified forms include one or more of doping modification and coating modification.

14. The battery cell of any one of claims 1-13, wherein, The positive electrode active material has a powder compaction density of 2.43 g / cm 3 ~ 2.85 g / cm 3 , and can be 2.48 g / cm 3 ~ 2.80 g / cm 3 .

15. The battery cell of any one of claims 1 to 14, wherein, The compaction density of the positive electrode film layer is 2.50 g / cm 3 ~ 2.80 g / cm 3 .

16. The battery cell of any one of claims 1 to 15, wherein, The negative electrode active material includes a carbon-based material, and the carbon-based material includes graphite.

17. The battery cell of claim 16, wherein, The graphite includes composite graphite particles, which include graphite bulk particles and a carbon coating layer covering the surface of the graphite bulk particles. The graphite bulk particles include secondary particles, and the carbon coating layer includes amorphous carbon.

18. The battery cell of claim 16 or 17, wherein, The composite graphite particles satisfy 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 resistivity of the composite graphite particles is 0.005Ω·cm-0.04Ω·cm.

19. The battery cell of any one of claims 16-18, wherein, The negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer. The first negative electrode film layer is disposed between the current collector and the second negative electrode film layer. Both the first negative electrode film layer and the second negative electrode film layer include the composite graphite particles.

20. The battery cell of claim 19, wherein, 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.

21. The battery cell of claim 20, wherein, 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.

22. The battery cell of any one of claims 19-21, wherein, Based on the total thickness of the first negative electrode film and the second negative electrode film, the thickness of the second negative electrode film accounts for 30% to 70%.

23. The battery cell of any one of claims 1-22, wherein, The negative electrode sheet further includes a negative electrode conductive layer, which is located between the negative electrode current collector and at least one side of the negative electrode film layer. 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.

24. The battery cell of claim 23, wherein, The thickness of the negative electrode conductive layer is 0.5μm to 2μm.

25. The battery cell of any one of claims 1-24, wherein, The compacted density of the negative electrode film layer is 1.15 g / cm 3 ~ 1.45 g / cm 3 , and / or, The single-side coating weight of the negative electrode film layer is 70 mg / 1540.25 mm 2 to 135 mg / 1540.25 mm 2 .

26. The battery cell of any one of claims 1-25, wherein, The electrolyte further includes an organic solvent, which includes one or more of a first organic solvent and a second organic solvent. The first organic solvent includes at least one of cyclic carbonates and chain carbonates, and may be a cyclic carbonate. The second organic solvent includes R5-COO-R6. R5 includes hydrogen atoms, halogen atoms, C1-C5 alkyl groups, and C1-C5 haloalkyl groups. R6 includes any one of C1-C5 alkyl groups and C1-C5 haloalkyl groups.

27. The battery cell of claim 26, wherein, The cyclic carbonate includes one or more of ethylene carbonate, propylene carbonate, and butene 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, methyl butyrate, and ethyl butyrate.

28. The battery cell of claim 26 or 27, wherein, Based on the total mass of the electrolyte, the mass content of the first organic solvent is 20% to 72%.

29. The battery cell of any one of claims 1-28, wherein, The electrolyte also includes a second additive, which includes one or more of sulfur-containing additives and lithium salt additives.

30. The battery cell of claim 29, wherein, The sulfur-containing additive includes one or more of vinyl sulfate, vinyl disulfate, butenyl sulfite, 1,3-propanesulfonate lactone, vinyl sulfite, and methylene disulfonate; and / or, The lithium salt additives include one or more of lithium difluorophosphate, lithium difluorooxalate borate, lithium tetrafluoroborate, and lithium dioxalate borate.

31. The battery cell of any one of claims 1-30, wherein, The electrolyte also includes lithium salts, which include one or both of fluorosulfonyl imide salts and lithium hexafluorophosphate.

32. The battery cell of claim 31, wherein, The fluorosulfonyl imide salt includes one or both of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide.

33. The battery cell of claim 32, wherein, The lithium salt includes lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate, wherein the molar concentration ratio of lithium bis(fluorosulfonyl)imide to lithium hexafluorophosphate is 0.2 to 1.

0.

34. The battery cell of claim 33, wherein, The molar concentration of the lithium difluorosulfonylimide 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.

35. The battery cell of any one of claims 1-34, wherein, The isolation membrane satisfies at least one of the following conditions: (1) The thickness of the isolation membrane is 4μm to 12μm, and can be selected as 5μm to 9μm; (2) The porosity of the isolation membrane is 20% to 70%, and can be selected as 35% to 60%.

36. The battery cell of any one of claims 1-35, wherein, The battery cell is configured to take 5 to 10.5 minutes to charge from 10% to 80% state of charge.

37. The battery cell of any one of claims 1-36, wherein, The volumetric energy density of the battery cell is 395Wh / L to 530Wh / L.

38. A battery device comprising a battery cell according to any one of claims 1 to 37.

39. The battery device of claim 38, wherein, The battery device is configured to charge from 10% to 80% in 5 to 10.5 minutes.

40. An electrical device comprising the battery device as described in claim 38 or 39.

Images