Secondary battery and electric device

Abstract

A negative pole piece in the secondary battery comprises a negative current collector and a negative film layer, the negative film layer is arranged on at least one side of the negative current collector, the negative film layer comprises a negative active material, the negative active material comprises first graphite, and the Dv50 particle size of the first graphite is 2.2-7.7 [mu] m; the electrolyte comprises an organic solvent and an organic additive, the organic solvent comprises a first solvent, the first solvent comprises cyclic carbonate, and the mass content of the first solvent is 25%-40% based on the total mass of the organic solvent; the organic additives comprise a first additive and a second additive, the first additive comprises vinylene carbonate, the second additive comprises an ethylene carbonate derivative, based on the total mass of the electrolyte, the mass percent of the first additive in the electrolyte is 2%-10%, and the mass percent of the second additive in the electrolyte is 0.3%-6%.

Description

[0001] This application claims the priority of PCT International Application PCT / CN2024 / 102539 titled "Secondary Battery and Electrical Device" filed on June 28, 2024, the entire content of which is incorporated herein by reference. Technical Field

[0002] This application relates to the field of battery technologies, and particularly to a secondary battery and an electrical device. Background Art

[0003] The statements herein only provide background information related to this application and do not necessarily constitute prior art.

[0004] In recent years, with the rapid development of secondary batteries such as lithium-ion batteries, secondary batteries are widely used in energy storage power systems such as hydroelectric, thermal, wind, and solar power stations, as well as in multiple fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. As the application scope of secondary batteries becomes wider and wider, the demand for the fast charging performance of secondary batteries has gradually increased. However, it is currently difficult to balance the fast charging performance and the cycling performance. Therefore, how to enable secondary batteries to balance better fast charging performance and cycling performance has become an urgent problem to be solved. Summary of the Invention

[0005] This application provides a secondary battery and an electrical device, which have good fast charging performance, normal temperature cycling performance, and high temperature cycling performance.

[0006] In a first aspect of this application, a secondary battery is provided, including: a positive electrode tab, the positive electrode tab includes a positive current collector and a positive electrode film layer, the positive electrode film layer is disposed on at least one side of the positive current collector, and the positive electrode film layer includes a positive active material; a negative electrode tab, the negative electrode tab includes a negative current collector and a negative electrode film layer, the negative electrode film layer is disposed on at least one side of the negative current collector, the negative electrode film layer includes a negative active material, the negative active material includes a first graphite, and the Dv50 particle size of the first graphite is 2.2 μm to 7.7 μm; and an electrolyte, the electrolyte includes an organic solvent and an organic additive, the organic solvent includes a first solvent, the first solvent includes a cyclic carbonate, and based on the total mass of the organic solvent, the mass content of the first solvent is 25% to 40%; the organic additive includes a first additive and a second additive, the first additive includes vinylene carbonate, the second additive includes a vinyl carbonate derivative, and based on the total mass of the electrolyte, the mass percentage of the first additive in the electrolyte is 2% to 10%, and the mass percentage of the second additive in the electrolyte is 0.3% to 6%.

[0007] Therefore, the negative electrode active material of the secondary battery includes the first graphite with the smaller particle size. The negative electrode sheet containing the first graphite can improve the fast charging performance of the battery. However, the surface defects of the small particle size graphite are relatively many, the reaction activity is strong, and the consumption of the electrolyte is relatively fast. In addition, the temperature rise of the battery cell is relatively high under fast charging conditions, and the stability of the electrolyte is affected, which further makes it difficult to improve the cycle performance of the battery. Therefore, by improving the first solvent, the first additive, and the second additive and their contents in the above electrolyte, the electrolyte has good thermal stability, and a stable interface film is formed on the surface of the negative electrode sheet, thereby reducing the electrolyte consumption rate and the direct current internal resistance DCR of the battery, and further improving the cycle performance and fast charging performance of the secondary battery. In this way, the secondary battery can take into account good fast charging performance, normal temperature cycle performance, and high temperature cycle performance.

[0008] In any embodiment of the present application, the structure of the ethylene carbonate derivative is as follows: , R 1 and R 2 each independently includes any one of a hydrogen element, a halogen element, an alkyl group with 1 to 5 carbon atoms, and a halogenated alkyl group with 1 to 5 carbon atoms, and R 1 and R 2 are not simultaneously hydrogen elements. These second additives have good film-forming properties, electrical conductivity, and stability, and can improve the fast charging performance and cycle performance of the battery, especially the normal temperature cycle performance.

[0009] In any embodiment of the present application, the ethylene carbonate derivative includes at least one of fluorinated ethylene carbonate, difluorinated ethylene carbonate, and trifluoromethyl ethylene carbonate.

[0010] In any embodiment of the present application, the cyclic carbonate includes at least one of ethylene carbonate and propylene carbonate.

[0011] In any embodiment of the present application, based on the total mass of the organic solvent, the mass content of the first solvent is 30% - 40%. Controlling the mass content of the first solvent in the organic solvent within this range can make the battery have better cycle performance.

[0012] In any embodiment of the present application, based on the total mass of the electrolyte, the mass content of the first additive is 3% - 8%, and / or the mass content of the second additive is 1.5% - 5%. Controlling the mass content of the first additive and / or the second additive in the electrolyte within this optional range can make the battery have better cycle performance.

[0013] In any embodiment of the present application, the total mass content of the first additive and the second additive in the electrolyte is 3% to 12%, and may be optionally 3.5% to 9%. Controlling the total mass of the first additive and the second additive within the above range can further improve the problem that small-particle-size graphite has strong activity and a faster consumption rate of additives during cycling, resulting in a decline in cycling performance, thereby improving the cycling performance of the battery.

[0014] In any embodiment of the present application, the mass of the electrolyte per unit battery rated capacity of 1 Ah of the secondary battery is 2.2 g to 2.95 g.

[0015] In any embodiment of the present application, the mass of the electrolyte per unit battery rated capacity of 1 Ah of the secondary battery is 2.2 g to 2.65 g, and the total mass content of the first additive and the second additive in the electrolyte is 5% to 9%; Alternatively, the mass of the electrolyte per unit battery rated capacity of 1 Ah of the secondary battery is > 2.65 g and ≤ 2.95 g, and the total mass content of the first additive and the second additive in the electrolyte is 3.5% to 6.5%.

[0016] In any embodiment of the present application, the powder compaction density of the positive electrode active material under 30,000 N ≥ 2.43 g / cm 3 , and may be optionally 2.48 g / cm 3 ~2.85 g / cm 3 .

[0017] In any embodiment of the present application, the positive electrode active material includes at least one of lithium-containing phosphates with an olivine structure and derivatives.

[0018] In any embodiment of the present application, the positive electrode active material includes: a core part, including at least one of lithium-containing phosphates with an olivine structure and derivatives thereof; and an ion-conducting layer, the ion-conducting layer covering the surface of the core part, and the ion-conducting layer includes at least one element among Fe, C, Ti, Zr, Hf, Ge, and Sn.

[0019] By coating the surface of the core part with an ion-conducting layer, the conductivity of the lithium-containing phosphates with an olivine structure and derivatives thereof can be improved, the powder resistivity of the material can be reduced, and it is beneficial to the migration rate of lithium ions, improving the fast charging ability of the battery and reducing the heat generation of the battery cell.

[0020] In any embodiment of the present application, the lithium-containing phosphates with an olivine structure and derivatives thereof include a general formula of Li x1 A1 y1 M1 a1M2 b1 P 1-c1 X c1 Q1 z1 A compound of b1 P 1-c1 X c1 Q1 z1 , wherein 0.5 ≤ x1 ≤ 1.3, 0 ≤ y1 ≤ 1.3, and 0.9 ≤ x1 + y1 ≤ 1.3; 0.9 ≤ a1 ≤ 1.5, 0 ≤ b1 ≤ 0.5, and 0.9 ≤ a1 + b1 ≤ 1.5; 0 ≤ c1 ≤ 0.5; 3 ≤ z1 ≤ 5; A1 includes at least one of Na, K, and Mg; M1 includes at least one of Mn, Fe, Co, and Ni; M2 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; Q1 includes at least one of O and F. The olivine-structured lithium-containing phosphate has excellent cycling stability, which is beneficial to improving the cycling performance of the battery cell.

[0021] In any embodiment of the present application, the olivine-structured lithium-containing phosphate and its derivatives include at least one of lithium iron phosphate, lithium manganese phosphate, lithium nickel phosphate, and lithium cobalt phosphate.

[0022] In any embodiment of the present application, the ion-conducting layer includes a fast ion conductor with the chemical formula Li 3-b Fe 2-b M3 b (PO m ) n , where M3 includes at least one element of +4-valent Ti, Zr, Hf, Ge, and Sn, 0 ≤ b ≤ 1, 3 ≤ m ≤ 5, and 2 ≤ n ≤ 4.

[0023] In any embodiment of the present application, the fast ion conductor includes at least one of lithium iron titanium phosphate, lithium iron zirconium phosphate, and lithium iron tin phosphate. Coating the surface of the core with a fast ion conductor containing a NASICON structure can significantly improve the transmission rate of lithium ions during multiple deintercalation / insertion at the positive electrode end, improve the ionic conductivity of the positive electrode active material, improve the fast charging ability of the battery cell, and in addition, can also improve the specific capacity and the energy density of the corresponding battery cell.

[0024] In any embodiment of the present application, at least one of the following conditions is satisfied: (1) The tap density of the positive electrode sheet is 2.5 g / cm 3 ~ 2.8 g / cm 3 ; (2) The mass percentage of carbon in the positive electrode active material is 1% - 2%; (3) The powder resistivity range R of the positive electrode active material satisfies R ≤ 20 Ω•cm, and optionally R ≤ 11 Ω•cm; (4) The volume average particle size of the positive electrode active material satisfies: 1 µm ≤ Dv50 ≤ 2 µm, 0.4 µm ≤ Dv10 ≤ 0.7 µm.

[0025] In any embodiment of the present application, the positive electrode film layer further includes a lithium supplement agent, and the lithium supplement agent includes at least one of a ternary lithium supplement material, lithium phosphate, lithium hydrogen phosphate, lithium sulfate, lithium sulfite, lithium molybdate, lithium nickelate, lithium ferrate, lithium oxalate, lithium titanate, lithium tetraborate, lithium metasilicate, lithium manganate, lithium tartrate, and lithium citrate. The lithium supplement agent can supplement lithium ions to the positive electrode film layer, make up for the irreversible loss of lithium ions in the system, and improve the capacity, thereby improving the energy density of the battery cell.

[0026] In any embodiment of the present application, the ternary lithium supplement material includes Li x2 A2 y2 Ni a2 Co b2 Mn c2 M4 (1-a2-b2-c2) Q2 z2 , where 0 < x2 ≤ 2.1, 0 ≤ y2 ≤ 2.1; 0 ≤ a2 ≤ 1, 0 ≤ b2 ≤ 1, 0 ≤ c2 ≤ 1, and 0.1 ≤ a2 + b2 + c2 ≤ 1; 1.8 ≤ z2 ≤ 3.5; A2 includes at least one of Na, K, and Mg; M4 includes at least one of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; Q2 includes at least one of O and F.

[0027] In any embodiment of the present application, the positive electrode tab further includes a positive electrode conductive layer, the positive electrode conductive layer is disposed between the positive electrode current collector and at least one side of the positive electrode film layer, the positive electrode conductive layer includes a conductive agent, and the conductive agent includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0028] In any embodiment of the present application, the thickness of the positive electrode conductive layer is 0.5 µm to 2 µm.

[0029] In any embodiment of the present application, the positive electrode conductive layer includes a binder, and the binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and fluorinated acrylate resins; Optionally, in the positive electrode conductive layer, the mass content of the conductive agent is 30% to 50%, and the mass content of the binder is 50% to 70%.

[0030] In any embodiment of the present application, after the secondary battery is charged to 100% SOC at a charging rate of 0.33C, the tap density of the negative electrode sheet is 1.15 g / cm 3 ~1.46 g / cm 3 , optionally 1.15 g / cm 3 ~1.36 g / cm 3 .

[0031] In any embodiment of the present application, after the secondary battery is charged to 100% SOC at a charging rate of 0.33C, the tap density of the negative electrode sheet is 1.15 - 1.26 g / cm 3 , and the mass content of the first additive in the electrolyte is 3% to 8%.

[0032] In any embodiment of the present application, at least one of the following conditions is satisfied: (1) The mass content of the second additive in the electrolyte is 0.5% to 3%; (2) The mass content of the first solvent in the organic solvent is 30% to 40%.

[0033] In any embodiment of the present application, after the secondary battery is charged to 100% SOC at a charging rate of 0.33C, the tap density of the negative electrode sheet is >1.26 g / cm 3 and ≤1.36 g / cm 3 , and the mass content of the first additive in the electrolyte is 2.5% to 6.5%.

[0034] In any embodiment of the present application, at least one of the following conditions is satisfied: (1) The mass content of the second additive in the electrolyte is 1% to 4%; (2) The mass content of the first solvent in the organic solvent is 25% to 38%.

[0035] In any embodiment of the present application, the electrolyte further includes a second solvent, and the second solvent includes at least one of a linear carbonate, a carboxylic acid ester, an ether, a nitrile, and a sulfone.

[0036] In any embodiment of the present application, the second solvent includes a carboxylic acid ester; optionally, the carboxylic acid ester includes at least one of methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and methyl butyrate.

[0037] In any embodiment of the present application, the charging time of the secondary battery from 10% SOC to 80% SOC at 30 °C is 6 min to 15 min, the mass content of the carboxylic ester in the organic solvent is 20% to 75%, and the total mass content of the first additive and the second additive in the electrolyte is 2% to 9%.

[0038] In any embodiment of the present application, in the electrolyte, the mass content of the first additive is 1.5% to 7%, and the mass content of the second additive is 0.5% to 4%.

[0039] In any embodiment of the present application, the electrolyte includes a lithium salt, and the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, fluorosulfonylimide salt, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(oxalato)borate, lithium difluorobis(oxalato)phosphate, and lithium tetrafluorooxalate phosphate.

[0040] In any embodiment of the present application, the concentration of the lithium salt in the electrolyte is 0.7 mol / L to 1.5 mol / L.

[0041] In any embodiment of the present application, the lithium salt includes at least one of LiFSI and LiPF 6 and the lithium salt satisfies at least one of the following conditions: (1) The concentration of LiFSI is 0.2 mol / L to 0.5 mol / L; (2) The concentration of LiPF 6 is 0.5 mol / L to 1.3 mol / L; (3) The lithium salt includes LiFSI and LiPF 6 and the concentration ratio of LiFSI to LiPF 6 is (2 to 5):10.

[0042] In any embodiment of the present application, the negative electrode tab further includes a negative electrode conductive layer, the negative electrode conductive layer is disposed 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, and the conductive agent includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0043] In any embodiment of the present application, the thickness of the negative electrode conductive layer is 0.5 μm to 2 μm.

[0044] In any embodiment of the present application, the negative electrode conductive layer includes a binder, and the binder includes at least one of styrene-butadiene rubber, water-soluble unsaturated resin, water-based acrylic resin, polyvinyl alcohol, sodium alginate, and carboxymethyl chitosan.

[0045] In any embodiment of the present application, in the negative electrode conductive layer, the mass content of the conductive agent is 20% - 40%, and the mass content of the binder is 60% - 80%.

[0046] In any embodiment of the present application, the negative electrode film layer includes at least one negative electrode active layer, and at least one negative electrode active layer includes the first graphite.

[0047] In any embodiment of the present application, the negative electrode film layer only includes one negative electrode active layer, the negative electrode active layer contains the first graphite, the Dv50 particle size of the first graphite is 4.2 μm - 7.2 μm, and the Dv50 particle size of the second graphite is 7.8 μm - 14.8 μm.

[0048] In any embodiment of the present application, the mass ratio of the first graphite to the second graphite is 2:8 to 6:4; optionally 3:7 to 5:5.

[0049] In any embodiment of the present application, the mass content of the first graphite in the negative electrode active layer is ≥20% and <50%, and the total mass content of the first additive and the second additive in the electrolyte is 3% - 8%; or, the mass content of the first graphite in the negative electrode active layer is 50% - 70%, and the total mass content of the first additive and the second additive in the electrolyte is 4% - 10%.

[0050] In any embodiment of the present application, the negative electrode film layer includes a first negative electrode active layer and a second negative electrode active layer which are sequentially stacked on the same side of the negative electrode current collector. The first negative electrode active layer includes at least one of artificial graphite and natural graphite. The second negative electrode active layer includes the first graphite and the third graphite. The first graphite includes artificial graphite, and the Dv50 particle size of the third graphite is 7.8 μm - 14.8 μm.

[0051] In any embodiment of the present application, in the second negative electrode active layer, the mass ratio of the first graphite to the third graphite is 2:8 to 8:2; optionally 3:7 to 7:3.

[0052] In any embodiment of the present application, at least one of the following conditions is satisfied: (1) The ratio of the total amount of the negative electrode active materials in the second negative electrode active layer to that in the first negative electrode active layer is 3:7 to 7:3; optionally 4:6 to 6:4; (2) The mass content of the first graphite in the second negative electrode active layer is 20% - 70%; optionally, the mass content of the first graphite in the second negative electrode active layer is ≥20% and <50%, and the total mass content of the first additive and the second additive in the electrolyte is 3% - 7%; or, the mass content of the first graphite in the second negative electrode active layer is 50% - 70%, and the total mass content of the first additive and the second additive in the electrolyte is 3.5% - 10%; (3) The Dv50 particle size of the graphite in the first negative electrode active layer ≥ the Dv50 particle size of the first graphite in the second negative electrode active layer; optionally, the Dv50 particle size of the graphite in the first negative electrode active layer is 5.8μm - 12.8μm, optionally 7.8μm - 12.8μm; optionally, the Dv50 particle size of the graphite in the second negative electrode active layer is 2.2μm - 7.7μm, optionally 4.2μm - 7.2μm.

[0053] In any embodiment of the present application, the artificial graphite includes a graphite body particle and a coating layer, the graphite body particle includes secondary particles aggregated by a plurality of primary particles, the coating layer is coated on the surface of the body particle, and the coating layer includes amorphous carbon.

[0054] In any embodiment of the present application, at least one of the following conditions is satisfied: (1) Based on the total mass of the artificial graphite, the mass content of the amorphous carbon is 2% - 5%; (2) The powder resistivity of the artificial graphite ≤0.04Ω•cm.

[0055] In any embodiment of the present application, the charging specific capacity of the first graphite in the coin cell at a rate of 0.1C ≥350mAh / g, optionally 350 mAh / g - 440 mAh / g.

[0056] In any embodiment of the present application, the negative electrode active material further includes a silicon-based material, and the silicon-based material includes at least one of silicon oxide and silicon-carbon composite; the mass content of silicon element in the silicon-based material in the negative electrode active material is 0.3% - 10%, optionally 1% - 6%.

[0057] In any embodiment of the present application, the separator includes a porous base film and a functional layer provided on at least one side of the porous base film.

[0058] In any embodiment of the present application, at least one of the following conditions is satisfied: (1) The thickness of the porous base film ≤12μm, optionally ≤9μm; (2) The porosity of the porous base film is 20% - 70%, and may be optionally 35% - 60%.

[0059] In any embodiment of the present application, the separator membrane includes a first functional layer and a second functional layer provided on both sides of the porous base film. The first functional layer includes first inorganic particles, and the second functional layer includes composite particles. The composite particles include second inorganic particles and non-fluoropolymer particles, and the second inorganic particles are attached to the surface of the non-fluoropolymer particles and / or dispersed inside the non-fluoropolymer particles.

[0060] In any embodiment of the present application, at least one of the following conditions is satisfied: (1) The non-fluoropolymer particles include acrylate polymer particles; (2) The first functional layer is located between the negative electrode sheet and the porous base film, and the second functional layer is located between the positive electrode sheet and the porous base film.

[0061] The second aspect of the present application provides an electrical device, including the secondary battery of the first aspect of the present application.

[0062] The details of one or more embodiments of the present application are set forth in the following drawings and description. Other features, objects, and advantages of the present application will become apparent from the specification, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] In order to more clearly illustrate the technical solutions in the embodiments of the present application or in the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained according to the disclosed drawings without creative efforts.

[0064] Figure 1 It is a schematic diagram of a battery cell according to an embodiment of the present application.

[0065] Figure 2 is Figure 1 The exploded view of the battery cell according to an embodiment of the present application shown.

[0066] Figure 3 It is a schematic diagram of a battery module according to an embodiment of the present application.

[0067] Figure 4 It is a schematic diagram of a battery pack according to an embodiment of the present application.

[0068] Figure 5 is Figure 4 The exploded view of the battery pack according to an embodiment of the present application shown.

[0069] Figure 6 It is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of the present application.

[0070] Description of reference numerals: 1. Battery pack; 2. Upper box body; 3. Lower box body; 4. Battery module; 5. Battery cell; 51. Housing; 52. Electrode assembly; 53. Cover plate; 6. Electrical device. Specific embodiments

[0071] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0072] The "range" disclosed in the present application can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a specific range. The range defined in this way can include or not include the end values. Any end value can be independently included or not included, and can be combined arbitrarily, 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, ranges of 60-110 and 80-120 are also contemplated. In addition, if the minimum range values of 1 and 2 are listed, and if the maximum range values of 3, 4, and 5 are also listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present application, unless otherwise stated, the numerical range "a-b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been fully listed herein, and "0-5" is only an abbreviated representation of these numerical combinations. In addition, when it is stated that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when it is stated that a certain parameter is an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0073] In the present application, the terms "a plurality of", "a variety of", etc., unless otherwise specified, refer to a quantity greater than 2 or equal to 2. For example, "one or more" means one or greater than or equal to two.

[0074] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0075] As used herein, the mention of "embodiment" means that the specific features, structures, or characteristics described in connection with the embodiment can be included in at least one embodiment or implementation of the present application. The phrase may not necessarily refer to the same embodiment each time it appears in the specification, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. Those skilled in the art will explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments. The same understanding applies to the "implementation" mentioned herein.

[0076] Those skilled in the art will understand that in the methods of each embodiment or implementation, the written order of each step does not mean a strict execution order that constitutes any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present application can be carried out sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out sequentially, or steps (b) and (a) carried out sequentially. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or steps (a), (c), and (b), or steps (c), (a), and (b), etc.

[0077] In the present application, in an open technical feature or technical solution described by words such as "containing", "comprising", "including", etc., unless otherwise specified, additional members other than the listed members are not excluded, and it can be regarded as providing both a closed feature or solution composed of the listed members and an open feature or solution that further includes additional members outside the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or may not include additional members, and it can be regarded as providing both a feature or solution of "A is composed of a1, a2, and a3" and a feature or solution of "A not only includes a1, a2, and a3, but also includes other members".

[0078] In the present application, unless otherwise specified, A (such as B) means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0079] In the present application, "optionally", "optional", and "option" mean having or not having, that is, either one selected from two parallel options of "having" or "not having". If "optional" appears multiple times in a technical solution, without special instructions, and without contradictions or mutual constraints, each "optional" is independent of each other.

[0080] An embodiment of the present application provides a secondary battery, including a positive electrode plate, a negative electrode plate, and an electrolyte.

[0081] The positive electrode plate includes a positive current collector and a positive electrode film layer. The positive electrode film layer is disposed on at least one side of the positive current collector, and the positive electrode film layer includes a positive active material.

[0082] The negative electrode plate includes a negative current collector and a negative electrode film layer. The negative electrode film layer is disposed on at least one side of the negative current collector, the negative electrode film layer includes a negative active material, the negative active material includes a first graphite, and the Dv50 particle size of the first graphite is 2.2 μm to 7.7 μm.

[0083] The electrolyte includes an organic solvent and an organic additive. The organic solvent includes a first solvent. The first solvent includes cyclic carbonate (EC). Based on the total mass of the organic solvent, the mass content of the first solvent is 25% to 40%. The organic additive includes a first additive and a second additive. The first additive includes vinylene carbonate (VC), and the second additive includes a ethylene carbonate derivative. Based on the total mass of the electrolyte, the mass percentage of the first additive in the electrolyte is 2% to 10%, and the mass percentage of the second additive in the electrolyte is 0.3% to 6%.

[0084] Thus, the negative active material of the above secondary battery includes the first graphite with the above smaller particle size. Therefore, the negative electrode plate containing the first graphite can improve the fast charging performance of the battery. However, the surface defects of the small particle size graphite are more, the reaction activity is stronger, and the consumption of the electrolyte is faster. In addition, the temperature rise of the battery cell is higher under fast charging, and the stability of the electrolyte is affected, which further leads to difficulty in improving the cycle performance of the battery. Therefore, by improving the first solvent, the first additive, the second additive, and their contents in the above electrolyte, the electrolyte has good thermal stability, and a stable interface film is formed on the surface of the negative electrode plate, so as to reduce the electrolyte consumption rate and the DC internal resistance DCR of the battery, and further improve the cycle performance and fast charging performance of the secondary battery. In this way, the above secondary battery can take into account better fast charging performance, normal temperature cycle performance, and high temperature cycle performance.

[0085] The above-mentioned first solvent includes cyclic carbonates. Cyclic carbonates have a relatively high dielectric constant and good film-forming performance. If the content of the first solvent in the electrolyte is too low, the self-stability of the electrolyte deteriorates, resulting in a decrease in conductivity. However, if the content of the first solvent is too high, the viscosity and melting point of the electrolyte increase, which will also deteriorate the conductivity of the electrolyte and the kinetic performance of the battery, thus leading to the deterioration of the cycling performance. Therefore, when the first solvent is within the above content range, the electrolyte can have good thermal stability and appropriate conductivity.

[0086] The above-mentioned first additive includes vinylene carbonate (VC), and the second additive includes ethylene carbonate derivatives. The first additive and the second additive can participate in the formation of the interface film. If the contents of the first additive and the second additive are too low, the first solvent will participate in the film formation excessively, destroying the stability of the electrolyte, and then accelerating the electrolyte consumption rate and deteriorating the cycling performance and storage life of the battery. As the content of the first additive increases, the high-temperature cycling life of the battery improves. However, if the content of the first additive is too high, it will deteriorate the battery kinetic window and the direct current internal resistance DCR, thus leading to the deterioration of the cycling performance and being unfavorable for the improvement of the fast charging performance. As the content of the second additive increases, the normal-temperature cycling life and the fast charging performance of the battery are improved. However, if the content of the second additive is too high, the high-temperature performance of the battery deteriorates and the high-temperature cycling life decreases. Therefore, when the first additive and the second additive are each within the above range, the electrolyte can achieve a balance between film-forming stability and battery kinetics.

[0087] Therefore, by controlling the first solvent within the above content range in the above-mentioned electrolyte, the thermal stability of the electrolyte can be improved and the conductivity of the electrolyte can be within an appropriate range. At the same time, by controlling the first additive and the second additive each within the above range, the electrolyte can achieve a balance between battery kinetics and film-forming stability, thereby reducing the electrolyte consumption rate, improving the normal-temperature and high-temperature cycling performance and storage life of the battery cell. In addition, the battery also has a relatively low direct current internal resistance DCR and good fast charging performance. This electrolyte can be applied to the negative electrode sheet including the above-mentioned first graphite with a smaller particle size and the battery system, enabling the secondary battery to have both high fast charging performance, normal-temperature cycling performance and high-temperature cycling performance.

[0088] Electrolyte In some embodiments of the present application, the cyclic carbonate in the first solvent includes at least one of ethylene carbonate (EC) and propylene carbonate (PC).

[0089] As an example, the mass content of the first solvent in the organic solvent can be, but is not limited to, 25%, 28%, 30%, 32%, 35%, 38%, 40%. Further, the mass content of the first solvent in the organic solvent is 25% - 38% or 30% - 40%, or within the range formed by any of the above point values as the end values. The same applies hereinafter. Controlling the mass content of the first solvent in the organic solvent within this range can make the battery have better cycling performance.

[0090] As an example, the mass content of the first additive in the electrolyte can be, but is not limited to, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%. Further, the mass content of the first additive in the electrolyte is 3% - 8%. Further, the first additive is vinylene carbonate (VC). Controlling the mass content of the first additive in the electrolyte within this optional range can make the battery have better cycling performance, especially high-temperature cycling performance.

[0091] In some embodiments of the present application, the structure of the ethylene carbonate derivative in the second additive is as follows: , R 1 and R 2 each independently includes any one of a hydrogen element, a halogen element, an alkyl group with 1 - 5 carbon atoms, and a halogenated alkyl group with 1 - 5 carbon atoms, and R 1 and R 2 are not simultaneously hydrogen elements. Further, the halogen element includes at least one of a fluorine element, a chlorine element, and a bromine element, and the alkyl group with 1 - 5 carbon atoms and the halogenated alkyl group with 1 - 5 carbon atoms include, but are not limited to, at least one of halogenated or unhalogenated methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl and its isomers. These second additives have good film-forming properties, electrical conductivity and stability, and can improve the fast charging performance and cycling performance of the battery, especially room-temperature cycling performance.

[0092] Further, the above ethylene carbonate derivative includes at least one of fluorinated ethylene carbonate (FEC), difluoroethylene carbonate (DFEC), and trifluoromethyl carbonate.

[0093] As an example, the mass content of the second additive in the electrolyte can be, but is not limited to, 0.3%, 0.4%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%. Further, the mass content of the second additive in the electrolyte is 1.5% - 5%. Controlling the mass content of the second additive in the electrolyte within this optional range can enable the battery to have better fast charging performance and cycling performance, especially room temperature cycling performance.

[0094] In some embodiments of the present application, the total mass content of the first additive and the second additive is 3% - 12%. As an example, the total mass content can be 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 11%, 12%. Further, the total mass content of the first additive and the second additive is 3.5% - 9%. Controlling the total mass of the first additive and the second additive within the above range can further improve the problem that small particle size graphite has strong activity and a faster consumption rate of additives during cycling, resulting in a decline in cycling performance, thereby enhancing the cycling performance of the battery.

[0095] In some embodiments of the present application, the electrolyte further includes a second solvent. Further, the second solvent includes at least one of linear carbonates, carboxylates, ethers, nitriles, and sulfones. The second solvent and the first solvent together serve as solvents, and their function is to lower the melting point and viscosity of the electrolyte system and improve the lithium ion transport performance of the electrolyte.

[0096] Further, the linear carbonate includes at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC).

[0097] Further, the carboxylate includes at least one of methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate, methyl propionate, ethyl propionate (EP), propyl propionate, methyl butyrate, ethyl butyrate, and 1,4 - butyrolactone. In some examples, the second solvent includes carboxylates. Further, the second solvent includes both carboxylates and linear carbonates at the same time.

[0098] Further, the ether includes at least one of, but is not limited to, diethyl ether and 1,2 - dimethoxyethane (DME, also known as ethylene glycol dimethyl ether).

[0099] Further, the nitrile includes, but is not limited to, acetonitrile (AN).

[0100] Further, the sulfone includes at least one of, but is not limited to, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0101] Further, the mass content of the second solvent in the organic solvent is 20% to 75%; this mass content can be 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 73%, 75%. Further, the mass content of the carboxylic acid ester in the organic solvent is 30% to 60%, 30% to 75%. In a specific example, the second solvent is a carboxylic acid ester.

[0102] In some embodiments of the present application, the electrolyte solution further includes an electrolyte salt, and the concentration of the electrolyte salt in the electrolyte solution is 0.1 mol / L to 2 mol / L. As an example, the concentration of the electrolyte salt in the electrolyte solution can be 0.1 mol / L, 0.2 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.5 mol / L, 1.6 mol / L, 1.8 mol / L, 2 mol / L; further, it can be 0.6 mol / L to 1.3 mol / L, or within the range formed by any two of the above point values as the end values.

[0103] In some embodiments of the present application, the electrolyte salt includes a lithium salt, and the lithium salt includes lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ), lithium hexafluoroarsenate (LiAsF 6 ), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS, CF 3 SO 2 Li), lithium difluorophosphate (LiPO 2 F 2 ), lithium difluorooxalate borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium difluoro bis(oxalato)phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP) at least one of them.

[0104] Optionally, the concentration of the lithium salt in the electrolyte solution is 0.7 mol / L to 1.5 mol / L. Optionally, the lithium salt includes at least one of a fluorosulfonylimide salt and LiPF 6 Among them. More optionally, the fluorosulfonylimide salt includes at least one of LiFSI and LiTFSI.

[0105] Further, the lithium salt includes LiFSI and LiPF 6At least one of them. Further, the concentration of LiFSI in the electrolyte is 0.2 mol / L to 0.5 mol / L; further, the concentration of LiPF 6 in the electrolyte is 0.5 mol / L to 1.3 mol / L. Further, the lithium salt includes LiFSI and LiPF 6 , LiFSI and LiPF 6 The molar ratio of is (2 to 5):10. Lithium bis(fluorosulfonyl)imide LiFSI has good conductivity and heat resistance, and is not easily hydrolyzed at high temperatures, and is particularly suitable for the fast charging system with a large temperature rise in this application; however, when the temperature is too high, for example, when it reaches above 200 °C, LiFSI will decompose and generate heat, deteriorating the safety margin of the battery cell. Therefore, LiPF 6 is added as the lithium salt together, which also effectively improves the safety performance of the battery.

[0106] In some embodiments of the present application, the mass of the electrolyte per unit battery rated capacity of 1 Ah of the secondary battery is 2.2 g to 2.95 g. As an example, it can be 2.2 g, 2.3 g, 2.4 g, 2.5 g, 2.6 g, 2.65 g, 2.7 g, 2.8 g, 2.9 g, 2.95 g. Further, it can be 2.2 g to 2.65 g or 2.65 g to 2.95 g. The above electrolyte of the present application is particularly suitable for batteries in a low injection coefficient system. The consumption rate of this electrolyte is low and the kinetics is better, so the cycle performance of the batteries in the low injection coefficient system can be improved.

[0107] Further, the mass of the electrolyte per unit battery rated capacity of 1 Ah of the secondary battery is 2.2 g to 2.65 g, and the total mass content of the first additive and the second additive in the electrolyte is 5% to 9%. The mass of the electrolyte per unit battery rated capacity of 1 Ah of the secondary battery is small. By appropriately increasing the total mass content of the first additive and the second additive, the cycle performance of the batteries in the low injection coefficient system can be improved. Among them, as an example, the mass of the electrolyte per unit battery rated capacity of 1 Ah of the secondary battery can be 2.2 g, 2.3 g, 2.4 g, 2.5 g, 2.6 g, 2.65 g or the range composed of any two of the above values, and the total mass content of the first additive and the second additive in the electrolyte can be 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9% or the range composed of any two of the above values.

[0108] Alternatively, the mass of the electrolyte at a unit cell rated capacity of 1 Ah of the secondary battery is > 2.65 g and ≤ 2.95 g, and the total mass content of the first additive and the second additive in the electrolyte is 3.5% - 6.5%. When the mass of the electrolyte at a unit cell rated capacity of 1 Ah of the secondary battery is relatively large, the total mass content of the first additive and the second additive can be appropriately reduced, so as to balance the cost and the cycle performance of the battery. Among them, as an example, the mass of the electrolyte at a unit cell rated capacity of 1 Ah of the secondary battery can be 2.68 g, 2.7 g, 2.8 g, 2.9 g, 2.95 g, or a range composed of any two of the above values, and the total mass content of the first additive and the second additive in the electrolyte can be 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, or a range composed of any two of the above values.

[0109] The test method for the mass of the electrolyte at a unit cell rated capacity of 1 Ah of the secondary battery is as follows: ① Take the battery and weigh the mass M of the battery. 0 ; ② Disassemble the battery, pour out the free electrolyte, and take out the electrode sheet, separator, mechanical parts, and adhesive tape; ③ Immerse and clean the electrode sheet, separator, mechanical parts, and adhesive tape with dimethyl carbonate (DMC) respectively for 24 h, and wash repeatedly more than 3 times; ④ After the cleaning is completed, place the electrode sheet, separator, mechanical parts, and adhesive tape in an oven until completely dried; ⑤ Weigh the electrode sheet, separator, mechanical parts, and adhesive tape, and record the mass as M. 1 ; ⑥ The mass of the electrolyte at a unit cell rated capacity of 1 Ah of the secondary battery = (M 0 - M 1 ) / a. a = the battery rated capacity of the secondary battery, in units of Ah.

[0110] As a non-limiting example, the positive current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0111] In some embodiments, the positive current collector can be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector can include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be obtained by forming a metal material on a polymer material substrate. In the positive current collector, non-limiting examples of the metal material can include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc. In the positive current collector, non-limiting examples of the polymer material substrate can include at least one of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE), etc.

[0112] In some embodiments, the thickness of the positive current collector is from 10 μm to 15 μm, and optionally from 12 μm to 15 μm. Exemplarily, the thickness of the positive current collector is 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm or a range composed of any two of the above values.

[0113] When the thickness of the positive current collector is within the above range, the current-carrying capacity of the positive current collector is relatively excellent, and it can enable the battery cell to have a high energy density.

[0114] In the embodiments of the present application, the thicknesses of the positive electrode film layer and the positive current collector have meanings well-known in the art, and can be detected by devices and methods well-known in the art. For example, the thickness of the positive electrode sheet is measured with a micrometer, the film layer on the surface of the positive current collector is removed, and the thickness of the positive current collector is measured with a micrometer. When the positive electrode film layer is coated on one side, the thickness of the positive electrode film layer is the thickness of the positive electrode sheet minus the thickness of the positive current collector; when the positive electrode film layer is coated on both sides, the thickness of the positive electrode film layer is (the thickness of the positive electrode sheet minus the thickness of the positive current collector) / 2.

[0115] The positive electrode film layer is usually formed by coating a positive electrode slurry on a positive current collector and then drying and cold pressing. The positive electrode slurry is usually formed by dispersing a positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring evenly. The solvent can be N-methylpyrrolidone (NMP), but is not limited thereto.

[0116] The positive electrode sheet does not exclude other additional functional layers besides the positive electrode film layer. For example, in some embodiments, the positive electrode sheet of the embodiments of the present application further includes a positive electrode conductive layer sandwiched between the positive current collector and the positive electrode film layer and disposed on the surface of the positive current collector. In other embodiments, the positive electrode sheet of the embodiments of the present application further includes a protective layer covering the surface of the positive electrode film layer.

[0117] The positive electrode active material can be a positive electrode active material well-known in the art for batteries. In some of these embodiments, the powder compaction density of the positive electrode active material under 30,000 N ≥ 2.43 g / cm 3 , and optionally 2.48 g / cm 3 ~2.85 g / cm 3 . Further, the powder compaction density of the positive electrode active material under 30,000 N is 2.5 g / cm 3 ~2.8 g / cm 3 .

[0118] Using the positive electrode active material with such a high powder compaction density can increase the compaction density of the positive electrode sheet, thereby improving the energy density of the battery.

[0119] As an example, the powder tap density of the positive active material in the positive electrode sheet under 30,000 N can be 2.43 g / cm 3 、2.45 g / cm 3 、2.5 g / cm 3 、2.55 g / cm 3 、2.6 g / cm 3 、2.65 g / cm 3 、2.7 g / cm 3 、2.75 g / cm 3 、2.8 g / cm 3 、2.85 g / cm 3 。

[0120] As a non-limiting example, the positive active material may include at least one of the following materials: phosphate-based positive electrode materials, lithium transition metal oxides, and their respective modified compounds. Among them, the phosphate-based positive electrode materials include at least one of olivine-structured lithium-containing phosphates and their derivatives.

[0121] Furthermore, the positive active material includes at least one of olivine-structured lithium-containing phosphates and their derivatives. The lithium-containing phosphate and its derivative-based positive active materials have a smaller particle size and a larger specific surface area, and are prone to water absorption. Therefore, the hydrolysis of the electrolyte in this system of batteries is more serious, and thus more HF is generated by hydrolysis. Therefore, the problem of electrolyte consumption is more prominent. Using the above electrolyte can help to exert its advantage of a slower electrolyte consumption rate, thereby improving the cycle performance of such batteries. At the same time, it is beneficial to exert the advantages of large energy density, long cycle life, and good safety performance of lithium-containing phosphates and their derivatives.

[0122] In some embodiments of the present application, the olivine-structured lithium-containing phosphate and its derivatives include the general formula Li x1 A1 y1 M1 a1 M2 b1 P 1-c1 X c1 Q1 z1Compounds, wherein 0.5 ≤ x1 ≤ 1.3, 0 ≤ y1 ≤ 1.3, and 0.9 ≤ x1 + y1 ≤ 1.3; 0.9 ≤ a1 ≤ 1.5, 0 ≤ b1 ≤ 0.5, and 0.9 ≤ a1 + b1 ≤ 1.5; 0 ≤ c1 ≤ 0.5; 3 ≤ z1 ≤ 5; A1 includes at least one of Na, K, and Mg; M1 includes at least one of Mn, Fe, Co, and Ni; M2 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; Q1 includes at least one of O and F. The lithium-containing phosphate with olivine structure has excellent cycle stability, which is beneficial to improving the cycle performance of single cells.

[0123] Furthermore, Li x1 A1 y1 M1 a1 M2 b1 P 1-c1 X c1 Q1 z1 The compounds of include lithium iron phosphate (LiFePO 4 ), lithium manganese phosphate (LiMnPO 4 ), lithium nickel phosphate (LiNiPO 4 ), and lithium cobalt phosphate (LiCoPO 4 ), and may also be doped compounds of these compounds.

[0124] The lithium-containing phosphate with olivine structure and its derivatives may or may not contain a coating layer. In some embodiments of the present application, the positive electrode active material includes a core and an ion-conducting layer. The core includes at least one of the lithium-containing phosphate with olivine structure and its derivatives, and the ion-conducting layer coats the surface of the core. The ion-conducting layer includes at least one element of Fe, C, Ti, Zr, Hf, Ge, and Sn.

[0125] By coating the surface of the core with the ion-conducting layer, the conductivity of the lithium-containing phosphate with olivine structure and its derivatives can be improved, the powder resistivity of the material can be reduced, the migration rate of lithium ions is facilitated, the fast charging ability of the battery can be improved, and the heat generation of the single cell can be reduced.

[0126] Furthermore, the ion-conducting layer includes a chemical formula of Li 3-b Fe 2-b M3 b (PO m ) nThe fast ion conductor M3 includes at least one element of Ti, Zr, Hf, Ge and Sn with a valence of +4, 0≤b≤1, 3≤m≤5, 2≤n≤4.

[0127] Exemplarily, the fast ion conductor is a material having a NASICON structure, for example, lithium iron titanium phosphate Li 2 FeTi(PO 4 ) 3 、Lithium Zirconium Iron Phosphate Li 2 FeZr(PO 4 ) 3 、Lithium iron tin phosphate Li 2 FeSn(PO 4 ) 3 One or more of .

[0128] Fast ion conductors with NASICON structures are materials with ultrafast ion conduction capabilities, rich three-dimensional lithium ion diffusion and transmission channels, and have the advantages of high ion conduction efficiency and strong structural stability during multiple lithium stripping and insertion processes. Coating the surface of the core with a fast ion conductor containing a NASICON structure can significantly increase the transmission rate of lithium ions in multiple lithium stripping / insertion at the positive terminal, improve the ionic conductivity of the positive electrode active material, and improve the fast charging capability of the battery cell. In addition, it can also increase the gram capacity and the energy density of the corresponding battery cell.

[0129] In some embodiments, the ion-conducting layer further includes carbon to further improve the material.

[0130] The carbon element and the fast ion conductor can be arranged in layers, for example, the carbon element is used as an independent carbon coating layer, and the fast ion conductor is used as an independent fast ion conductor layer. The carbon coating layer can be coated on the surface of the core portion, and the fast ion conductor layer is located on the surface of the carbon coating layer, that is, the fast ion conductor layer is located on the side of the carbon coating layer away from the core portion; or the fast ion conductor layer can be coated on the surface of the core portion, and the carbon coating layer is located on the surface of the fast ion conductor layer, that is, the carbon coating layer is located on the side of the fast ion conductor layer away from the core portion. Of course, the carbon element and the fast ion conductor can also be arranged in the same layer.

[0131] Optionally, the carbon coating layer can be made of an organic carbon source, such as glucose, polyethylene glycol, etc., and coated on the surface of the fast ion conductor layer through a carbonization process. The carbon coating layer can partially coat the fast ion conductor layer, or it can completely coat the fast ion conductor layer. The provision of the carbon coating layer can significantly improve the electronic conductivity of the core, make up for the defect of poor electronic conductivity of the core, and improve the energy density of the battery cell. Specifically, the provision of the carbon coating layer enables the positive electrode active material of the present application to have the following advantages: The carbon coating layer in the positive electrode active material of this application provides a suitable channel for the transmission of electrons, which can significantly improve the conduction rate of electrons during multiple de-lithiation and intercalation processes, enhance the electronic conductivity of lithium-containing phosphate, improve the charging ability of the corresponding battery monomer, and also increase the energy density.

[0132] The carbon coating layer of the positive electrode active material of this application is loose and porous, enabling the electrolyte to come into full and effective contact with the lithium-containing phosphate, thereby increasing the transmission rate of lithium ions at the phase interface and improving the charging ability of the battery monomer.

[0133] Coating a layer of carbon coating on the surface of lithium-containing phosphate can not only improve the conductivity of lithium-containing phosphate but also enhance the structural stability of the positive electrode active material, effectively preventing the iron dissolution phenomenon of the positive electrode active material during long-term storage and cyclic use of the battery monomer, thus ensuring the cycle life of the battery monomer.

[0134] The positive electrode active material of this application uses lithium-containing phosphate as the base material, giving full play to the advantages of low cost, high reliability in use, and good cycle stability of lithium-containing phosphate. At the same time, the ion-conducting layer (fast ion conductor layer and carbon coating layer) is used to solve the disadvantages of poor electronic conductivity and ion conductivity. The battery monomer prepared from the positive electrode active material of this application has a significantly improved energy density on the premise of excellent cycle performance.

[0135] In some embodiments, the mass content of carbon in the positive electrode active material is 1% - 2%. As an example, it can be 1%, 1.5%, or 2%. Controlling the mass content of carbon in the positive electrode active material within this range can further improve the conductivity of the positive electrode active material and thus enhance the fast charging performance of the battery. It is understandable that the carbon element can come from, but is not limited to, the carbon coating layer. As an example, the surface of lithium-containing phosphate with an olivine structure and its derivatives is coated with a carbon coating layer.

[0136] In some embodiments, the powder resistivity of the positive electrode active material is ≤20 Ω•cm, which further improves the conductivity of the positive electrode active material and thus enhances the fast charging performance of the battery. As an example, the powder resistivity of the positive electrode active material can be 20 Ω•cm, 15 Ω•cm, 10 Ω•cm, 8 Ω•cm, 5 Ω•cm, etc., and optionally ≤11 Ω•cm.

[0137] In some embodiments, the volume average particle size of the positive electrode active material satisfies: 1 µm ≤ Dv50 ≤ 2 µm, 0.4 µm ≤ Dv10 ≤ 0.7 µm, which further improves the fast charging and power performance of the battery. As an example, the Dv50 particle size of the positive electrode active material can be 1 µm, 1.5 µm, or 2 µm. As an example, the volume average particle size Dv10 of the positive electrode active material can be 0.4 µm, 0.5 µm, 0.6 µm, or 0.7 µm.

[0138] In this text, Dv50 and Dv10 have meanings well-known in the art and can be tested using methods known in the art. For example, they can be measured using a laser particle size analyzer (such as Malvern Master Size 3000). Among them, Dv50 represents the particle size corresponding to when the cumulative volume distribution percentage of particles reaches 50% starting from the smaller particle size according to the particle size volume distribution. Dv10 represents the particle size corresponding to when the cumulative volume distribution percentage of particles reaches 10% starting from the smaller particle size according to the particle size volume distribution.

[0139] The particle size volume distribution can be obtained through the following method: Take a clean beaker, add an appropriate amount of the sample to be tested, and ultrasonicate it sufficiently to ensure complete dispersion of the sample. The test instrument is Malvern 2000 from the United States. After the sample is poured into the injection tower, it circulates with the solution to the test optical path system. When the particles are irradiated by the laser beam, the particle size distribution characteristics of the particles can be obtained by receiving and measuring the energy distribution of the scattered light (light obscuration: 8% - 12%). Draw the particle size volume distribution diagram based on the test data.

[0140] In some of these embodiments, the positive electrode film layer further includes a lithium supplementing agent. Further, the lithium supplementing agent includes at least one of ternary lithium supplementing materials, lithium phosphate, lithium hydrogen phosphate, lithium sulfate, lithium sulfite, lithium molybdate, lithium nickelate, lithium ferrate, lithium oxalate, lithium titanate, lithium tetraborate, lithium metasilicate, lithium manganite, lithium tartrate, and lithium citrate. The lithium supplementing agent can supplement lithium ions for the positive electrode film layer, make up for the irreversible lithium ion loss in the system, and improve the capacity, thereby improving the energy density of the battery cell.

[0141] Further, the ternary lithium supplementing material includes Li x2 A2 y2 Ni a2 Co b2 Mn c2 M4 (1-a2-b2-c2) Q2 z2 , where 0 < x2 ≤ 2.1, 0 ≤ y2 ≤ 2.1; 0 ≤ a2 ≤ 1, 0 ≤ b2 ≤ 1, 0 ≤ c2 ≤ 1, and 0.1 ≤ a2 + b2 + c2 ≤ 1; 1.8 ≤ z2 ≤ 3.5; A2 includes at least one of Na, K, and Mg; M4 includes at least one of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; Q2 includes at least one of O and F.

[0142] Even further, 0.9 ≤ x2 + y2 ≤ 2.1.

[0143] Exemplarily, the ternary material includes LiNi 1 / 3Co 1 / 3 Mn 1 / 3 O 2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), LiNi 0.80 Co 0.15 Al 0.05 O 2 at least one of

[0144] The lithium supplement agent can be in the same layer as the positive electrode active material or in different layers. When the lithium supplement agent and the positive electrode active material are in different layers, the lithium supplement agent can be in the lithium supplement layer and the positive electrode active material can be in the positive electrode active material layer. In other words, the positive electrode film layer includes a lithium supplement layer and a positive electrode active material layer. The positive electrode active material layer can be disposed on at least one side of the positive electrode current collector, and the lithium supplement layer can be located between the positive electrode active material layer and the positive electrode current collector. Alternatively, the lithium supplement layer can be disposed on at least one side of the positive electrode current collector, and the positive electrode active material layer can be located between the lithium supplement layer and the positive electrode current collector. Optionally, the lithium supplement layer can be located between the positive electrode active material layer and the positive electrode current collector.

[0145] In some embodiments, in the positive electrode film layer, the mass content of the positive electrode active material is 80% - 98%. As an example, the mass content can be 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 96%, 98%. Further, in the positive electrode film layer, the mass content of the positive electrode active material can be 90% - 98%.

[0146] In some embodiments, the positive electrode film layer may optionally further include a binder. As a non - restrictive example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride - tetrafluoroethylene - propylene terpolymer, vinylidene fluoride - hexafluoropropylene - tetrafluoroethylene terpolymer, tetrafluoroethylene - hexafluoropropylene copolymer, and fluorinated acrylate resin. In some embodiments, based on the total mass of the positive electrode film layer, the mass content of the binder is ≤5%.

[0147] In some of these embodiments, the positive electrode film layer may further optionally include a conductive agent. As a non-limiting example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, based on the total mass of the positive electrode film layer, the mass content of the conductive agent is ≤5%.

[0148] In some of these embodiments, the positive electrode plate can be prepared in the following manner: dispersing the above components for preparing the positive electrode plate, such as the positive electrode active material, conductive agent, binder, and any other components, in a solvent to form a positive electrode slurry; coating the positive electrode slurry on at least one surface of the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode plate can be obtained. The type of the solvent can be selected from, but not limited to, any one of the foregoing embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode current collector on which the positive electrode slurry is coated can be a single surface of the positive electrode current collector or two surfaces of the positive electrode current collector.

[0149] In some of these embodiments, the positive electrode plate further includes a positive electrode conductive layer, and the positive electrode conductive layer is disposed between the positive electrode current collector and at least one side of the positive electrode film layer. The positive electrode conductive layer includes a conductive agent. The positive electrode conductive layer can also be formed by first coating a corresponding slurry on the surface of the positive electrode current collector, and then coating the above positive electrode slurry and drying. The positive electrode conductive layer can improve the adhesion between the positive electrode film layer and the positive electrode current collector and the overall conductivity of the positive electrode plate, which is beneficial to improving the electron transfer rate.

[0150] Further, the conductive agent includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The conductive agent in the positive electrode conductive layer can improve the conductivity of the positive electrode conductive layer, thereby improving the conductivity of the positive electrode plate and reducing the heat generation of the battery.

[0151] Further, the thickness of the positive electrode conductive layer is 0.5 μm to 2 μm. As an example, it can be 0.5 μm, 1 μm, 1.5 μm, or 2 μm. When the thickness of the positive electrode conductive layer is within the above range, it can further improve the conductive performance of the positive electrode plate and can also take into account the improvement of the energy density of the battery cell.

[0152] Further, the positive electrode conductive layer further includes a binder. Further, the binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and fluorinated acrylate resins. The binder in the positive electrode conductive layer can improve the adhesion between the positive electrode current collector and the positive electrode film layer and enhance the structural stability of the positive electrode plate.

[0153] Optionally, in the positive electrode conductive layer, the mass content of the conductive agent is 30% to 50%, which can be 30%, 35%, 40%, 45%, 50% as examples; optionally, in the positive electrode conductive layer, the mass content of the binder is 50% to 70%, which can be 50%, 55%, 60%, 65%, 70%. In some examples, the positive electrode conductive layer is composed of a conductive agent and a binder.

[0154] Negative electrode tab As a non-limiting example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0155] In some of these embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be obtained by forming a metal material on the polymer material substrate. In the negative electrode current collector, non-limiting examples of the metal material may include at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. In the negative electrode current collector, non-limiting examples of the polymer material substrate may include at least one of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0156] In some of these embodiments, after the secondary battery is charged to 100% SOC at a charging rate of 0.33C, the tap density of the negative electrode tab is 1.15 g / cm 3 ~1.46 g / cm 3 , and can be 1.15 g / cm 3 ~1.36 g / cm 3 . Thus, the above negative electrode tab still has a relatively high tap density after full charge. Exemplarily, after the secondary battery is charged to 100% SOC at a charging rate of 0.33C, the tap density of the negative electrode tab is 1.15 g / cm 3 , 1.18 g / cm 3 , 1.20 g / cm 3 , 1.22 g / cm 3 , 1.25 g / cm 3 , 1.28 g / cm 3 , 1.3 g / cm 3 , 1.32 g / cm 3 , 1.35 g / cm 3 , 1.36 g / cm 3 , 1.38 g / cm 3 , 1.4 g / cm3 , 1.42 g / cm 3 , 1.45 g / cm 3 , 1.46 g / cm 3 Or a range composed of any two of the above values. When the compaction density of the negative electrode film layer is within the above range, it is beneficial to improve the energy density of the battery cell; and since the negative electrode active material in the negative electrode film layer is stacked relatively tightly, the contact resistance between particles is small, which can further reduce the resistance of the electrode sheet, thereby reducing heat generation.

[0157] In the embodiments of the present application, the compaction density of the negative electrode sheet after charging the secondary battery at a charging rate of 0.33C to 100% SOC has the meaning well known in the art, that is, the positive electrode sheet is disassembled from the battery cell charged to 100% state of charge (SOC) at a charging rate of 0.33C, and the compaction density of the positive electrode film layer is measured.

[0158] In the embodiments of the present application, 100% SOC is defined as follows: The battery cell is charged at a constant current charging rate of 0.33C to the upper limit voltage of the battery, and then charged at a constant voltage to 0.05C, corresponding to the state of 100% SOC of the battery cell. Correspondingly, the battery cell is discharged at a constant current discharge rate of 0.33C to the cut-off voltage, corresponding to the state of 0% SOC of the battery cell.

[0159] Due to the different types of positive electrode active materials in the battery, the cut-off voltage for full charge may also be different. Exemplarily, the upper limit voltage for battery charging can be 3.65V, 3.8V; the cut-off voltage for battery discharge can be 2.5V, 2.0V. Taking the positive electrode active material in the positive electrode sheet as lithium iron phosphate as an example, the compaction density of the negative electrode sheet after charging the above secondary battery at a charging rate of 0.33C to 3.65V and then charging at a constant voltage to 0.05C (i.e., after charging at a charging rate of 0.33C to 100% SOC) is 1.15 g / cm 3 ~1.46 g / cm 3 .

[0160] In some of the embodiments, the compaction density of the above negative electrode sheet after cold pressing is 1.5 g / cm 3 ~1.7 g / cm 3 , and can be optionally 1.55 g / cm 3 ~1.65 g / cm 3 . The compaction density of the negative electrode sheet after cold pressing refers to the compaction density of the negative electrode sheet before being assembled into a battery after cold pressing and forming.

[0161] In some of the embodiments, the compaction density of the negative electrode sheet of the secondary battery after charging at a charging rate of 0.33C to 100% SOC is 1.15~1.26 g / cm 3; Meanwhile, the mass content of the first additive in the electrolyte is 3% - 8%.

[0162] The lower the full charge compaction density of the negative electrode plate, the greater the rebound thickness or the lower the initial compaction density, and the stronger the graphite activity. Therefore, more electrolyte is required to be consumed, and more additives need to be added to the electrolyte to enhance the interfacial film stability of the negative electrode plate and improve the cycle performance of the battery. Therefore, there is a matching relationship between the compaction density of the negative electrode plate and the mass content of the first additive in the electrolyte. Thus, when the secondary battery is charged to 100% SOC at a charging rate of 0.33C, if the compaction density of the negative electrode plate is within the above range and the mass content of the first additive in the electrolyte is 3% - 8%, the battery can better balance high fast charging performance and cycle performance.

[0163] The second additive in the electrolyte has a lower film formation impedance, which can improve the kinetic performance of the battery and thus enhance the ID fast charging performance of the battery. However, its content should not be too much to further improve the cycle performance of the battery. Therefore, there is a matching relationship between the compaction density of the negative electrode plate and the mass content of the second additive in the electrolyte. Further, when the secondary battery is charged to 100% SOC at a charging rate of 0.33C and the compaction density of the negative electrode plate is 1.15 - 1.26 g / cm 3 , the mass content of the second additive in the electrolyte is 0.5% - 3%.

[0164] Further, when the secondary battery is charged to 100% SOC at a charging rate of 0.33C and the compaction density of the negative electrode plate is 1.15 - 1.26 g / cm 3 , the mass content of the first solvent in the organic solvent of the electrolyte is 30% - 40%.

[0165] Further, when the secondary battery is charged to 100% SOC at a charging rate of 0.33C and the compaction density of the negative electrode plate is 1.15 - 1.26 g / cm 3 , the mass of the electrolyte per unit battery rated capacity of 1 Ah of the secondary battery is 2.5 g - 3.0 g.

[0166] In some embodiments, when the secondary battery is charged to 100% SOC at a charging rate of 0.33C, the compaction density of the negative electrode plate is > 1.26 g / cm 3 and ≤ 1.36 g / cm 3 , and the mass content of the first additive in the electrolyte is 2.5% - 6.5%. Thus, when the secondary battery is charged to 100% SOC at a charging rate of 0.33C and the compaction density of the negative electrode plate is within the above range and the mass content of the first additive in the electrolyte is 2.5% - 6.5%, the battery can better balance high fast charging performance and cycle performance.

[0167] Further, when the secondary battery is charged at a charging rate of 0.33C to 100% SOC, the tap density of the negative electrode plate is > 1.26 g / cm 3 and ≤ 1.36 g / cm 3 , and the mass content of the second additive in the electrolyte is 1% - 4%. Further, the mass content of the first solvent in the organic solvent of the electrolyte is 25% - 38%.

[0168] Further, when the secondary battery is charged at a charging rate of 0.33C to 100% SOC, the tap density of the negative electrode plate is > 1.26 g / cm 3 and ≤ 1.36 g / cm 3 , and the mass of the electrolyte per unit battery rated capacity of 1 Ah of the secondary battery is 2.2 g - 2.8 g.

[0169] In some embodiments, the charging time of the secondary battery from 10% SOC to 80% SOC at 30°C is 6 min - 15 min, the mass content of the carboxylic acid ester in the organic solvent is 20% - 75%, and the total mass content of the first additive and the second additive in the electrolyte is 2% - 9%. Thus, on the basis of using high-tap-density graphite to provide a high energy density, the battery is also a fast-charging type battery. By adding the carboxylic acid ester in the electrolyte in the above content and increasing the dosages of the first additive and the second additive, the secondary battery has both high energy density, fast-charging performance, and cycling performance. Further, in the electrolyte, the mass content of the first additive is 1.5% - 7%, and the mass content of the second additive is 0.5% - 4%.

[0170] In some embodiments, during the charging process of the secondary battery from 10% state of charge to 80% state of charge, it includes multiple charging steps, and the difference between the maximum state of charge of any charging step and the maximum state of charge of its adjacent charging step is less than or equal to 5% state of charge, such as 1% state of charge, 1.5% state of charge, 2% state of charge, 2.5% state of charge, 3% state of charge, 3.5% state of charge, 4% state of charge, 4.5% state of charge, 5% state of charge, or a range composed of any two of the above values.

[0171] The secondary battery from 10% state of charge to 40% state of charge includes multiple charging steps. For any charging step, it can be charged at any rate between 5C and 10C, and the charging rate corresponding to each charging step can be any value among 5C, 5.5C, 6C, 6.5C, 7C, 7.5C, 8C, 8.5C, 9C, 9.5C, 10C, or a value within the range composed of any two of the above values.

[0172] The secondary battery also includes multiple charging steps from 40% state of charge (SOC) to 80% SOC. The charging rate of any charging step is less than that of any charging step from 10% SOC to 40% SOC, and the charging rate of the step of charging to 80% SOC is any value from 2.5C to 5C. For example, it can be 2.7C.

[0173] Exemplarily, the charging steps of the secondary battery from 10% to 80% can be carried out as follows: Constant current charge from 10% SOC to 15% SOC at 5.0C; Constant current charge from 15% SOC to 20% SOC at 5.0C; Constant current charge from 20% SOC to 25% SOC at 5.0C; Constant current charge from 25% SOC to 30% SOC at 5.0C; Constant current charge from 30% SOC to 35% SOC at 5.0C; Constant current charge from 35% SOC to 40% SOC at 5.0C; Constant current charge from 40% SOC to 45% SOC at 4.6C; Constant current charge from 45% SOC to 50% SOC at 4.3C; Constant current charge from 50% SOC to 55% SOC at 4.0C; Constant current charge from 55% SOC to 60% SOC at 3.7C; Constant current charge from 60% SOC to 65% SOC at 3.4C; Constant current charge from 65% SOC to 70% SOC at 3.1C; Constant current charge from 70% SOC to 75% SOC at 2.9C; Constant current charge from 75% SOC to 80% SOC at 2.7C.

[0174] In some embodiments, the charging time of the secondary battery from 10% SOC to 80% SOC is 6 min to 15 min. Exemplarily, the charging time of the secondary battery from 10% SOC to 80% SOC is 6 min, 6.5 min, 7 min, 7.5 min, 8 min, 8.5 min, 9 min, 9.5 min, 10 min, 10.5 min, 11 min, 11.5 min, 12 min, 12.5 min, 13 min, 14 min, 14.5 min, 15 min, or the range composed of any two of the above values.

[0175] In some of these embodiments, the negative electrode tab further includes a negative electrode conductive layer disposed between the negative electrode current collector and at least one side of the negative electrode film layer. The negative electrode conductive layer can enhance the overall conductivity of the negative electrode tab, which is beneficial to improving the electron transfer rate.

[0176] The negative electrode conductive layer includes a conductive agent. The negative electrode conductive layer can also be formed by first coating the surface of the negative electrode current collector with a corresponding slurry and then coating the above-mentioned negative electrode slurry, followed by drying. Further, the conductive agent in the negative electrode conductive layer includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0177] Optionally, the thickness of the negative electrode conductive layer is 0.5 μm to 2 μm. As an example, it can be 0.5 μm, 1 μm, 1.5 μm, 2 μm, or a range composed of any two of the above values. When the thickness of the negative electrode conductive layer is within the above range, it can further enhance the conductivity of the negative electrode tab, reduce the heat generation of the negative electrode tab, thereby reducing the heat generation of the battery cell; and it can also take into account the improvement of the energy density of the battery cell.

[0178] In some of these embodiments, the negative electrode conductive layer includes a binder, and the binder includes at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin, water-based acrylic resin, polyvinyl alcohol, sodium alginate, and carboxymethyl chitosan. The negative electrode conductive layer can enhance the adhesion between the negative electrode film layer and the negative electrode current collector and the overall conductivity of the negative electrode tab, which is beneficial to improving the electron transfer rate.

[0179] Optionally, in the negative electrode conductive layer, the mass content of the conductive agent is 20% to 40%. Exemplarily, it can be 20%, 25%, 30%, 35%, 40%, or a range composed of any two of the above values. Optionally, in the negative electrode conductive layer, the mass content of the binder is 60% to 80%. Exemplarily, it can be 60%, 65%, 70%, 75%, 80%, or a range composed of any two of the above values.

[0180] In some of these embodiments, the negative electrode film layer may further optionally include a binder. The binder can include at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0181] In some of these embodiments, the negative electrode film layer may further optionally include a conductive agent. The conductive agent can include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0182] In some of these embodiments, the negative electrode film layer may further optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)), etc.

[0183] In some of these embodiments, the negative electrode tab can be prepared in the following manner: Dispersing the above-mentioned components for preparing the negative electrode tab, such as the negative electrode active material, conductive agent, binder, and any other components, in a solvent (non-limiting examples of the solvent include deionized water) to form a negative electrode slurry; Coating the negative electrode slurry on at least one surface of the negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode tab can be obtained. The surface of the negative electrode current collector on which the negative electrode slurry is coated can be a single surface of the negative electrode current collector or two surfaces of the negative electrode current collector.

[0184] Further, the first graphite includes at least one of artificial graphite and natural graphite. Further, artificial graphite is used for the graphite. The artificial graphite has fewer active sites on the surface and a lower consumption rate of the first solvent and the first additive in the electrolyte, which can meet the requirements of the long life of the battery. Further, the discharge specific capacity of the graphite ≤ 358 mAh / g. When the graphite specific capacity is within this range, the activity of the graphite is appropriate, which is beneficial to reducing the consumption rate of the electrolyte and thus improving the cycle performance of the battery.

[0185] The Dv50 particle size of the above-mentioned first graphite is 2.2 μm to 7.7 μm. As an example, it can be 2.2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.2 μm, 4.5 μm, 5 μm, 5.5 μm, 5.8 μm, 6 μm, 6.5 μm, 7 μm, 7.2 μm, 7.5 μm, 7.7 μm or a range composed of any two of the above values. Further, the Dv50 particle size of the first graphite can be 2.2 μm to 7 μm.

[0186] In some of these embodiments, the negative electrode film layer includes at least one negative electrode active layer, and at least one negative electrode active layer includes the first graphite.

[0187] In one of the embodiments, the negative electrode film layer only includes one negative electrode active layer. The negative electrode active layer contains the first graphite and the second graphite. The Dv50 particle size of the first graphite is 4.2 μm to 7.2 μm, and the Dv50 particle size of the second graphite is 7.8 μm to 14.8 μm. The particle size range of the first graphite is smaller, the tap density is lower, and in addition, its activity in reacting with the electrolyte is stronger. Therefore, it affects the energy density, cycle performance, and storage performance of the battery. In order to further improve the energy density, cycle performance, and storage performance of the battery, the second graphite with a larger particle size is paired in the negative electrode active layer.

[0188] As an example, the Dv50 particle size of the second graphite can be 7.8μm, 8μm, 8.2μm, 8.5μm, 9μm, 9.2μm, 9.5μm, 9.6μm, 10μm, 10.2μm, 10.5μm, 10.6μm, 11μm, 11.8μm, 12μm, 12.5μm, 12.8μm, 13μm, 13.5μm, 13.7μm, 14μm, 14.2μm, 14.5μm, 14.8μm, or a range composed of any two of the above values.

[0189] Furthermore, the mass ratio of the first graphite to the second graphite is 2:8 to 6:4; optionally 3:7 to 5:5; as an example, this mass ratio can be 2:8, 3:7, 4:6, 5:5, 6:4, or a range composed of any two of the above values.

[0190] Furthermore, the mass content of the first graphite in the negative electrode active layer where it is located is 20% - 70%. As an example, the mass content of the first graphite in the negative electrode active layer where it is located is 20%, 25%, 30%, 35%, 40%, 45%, 48%, 50%, 55%, 60%, 65%, 70%, or a range composed of any two of the above values.

[0191] Furthermore, the total mass content of the first graphite and the second graphite in the negative electrode active layer where they are located is 30% - 98%. As an example, this total mass content can be 30%, 35%, 40%, 45%, 48%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 98%, or a range composed of any two of the above values.

[0192] Optionally, the mass content of the first graphite in the negative electrode active layer is ≥20% and <50%. As an example, it can be 20%, 25%, 30%, 35%, 40%, 45%, 48%. At the same time, the total mass content of the first additive and the second additive in the electrolyte is 3% - 8%. As an example, the total mass content of the first additive and the second additive can be 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, or a range composed of any two of the above values. There is a matching relationship between the content of the first graphite and the content of the additives in the electrolyte. Through the above settings, the content of the first graphite is more matched with the total mass content of the first additive and the second additive, which can effectively improve the fast charging performance and cycling performance of the battery.

[0193] Optionally, the mass content of the first graphite in the negative electrode active layer is 50% to 70%, and as an example, it can be 50%, 55%, 60%, 65%, 70% or a range composed of any two of the above values. At the same time, the total mass content of the first additive and the second additive in the electrolyte is 4% to 10%, and as an example, the total mass content of the first additive and the second additive can be 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5, 9%, 9.5%, 10% or a range composed of any two of the above values. The higher the content of the first graphite, the more additives need to be added to the electrolyte accordingly. In this way, the content of the first graphite is more matched with the total mass content of the first additive and the second additive, which can effectively improve the fast charging performance and cycling performance of the battery.

[0194] In another embodiment, the negative electrode film layer includes a first negative electrode active layer and a second negative electrode active layer that are sequentially stacked on the same side of the negative electrode current collector. The graphite includes at least one of artificial graphite and natural graphite. The graphite in the first negative electrode active layer includes at least one of artificial graphite and natural graphite. The second negative electrode active layer includes a first graphite and a third graphite. The first graphite includes artificial graphite, and the Dv50 particle size of the third graphite is 7.8 μm to 14.8 μm. The surface of artificial graphite has fewer active sites, and the consumption rate of the first solvent and the first additive in the electrolyte is lower. The first graphite is arranged in the upper second negative electrode active layer, and a third graphite with a larger particle size is added to the second negative electrode active layer, further improving the energy density, cycling performance and storage performance of the battery.

[0195] Optionally, in the second negative electrode active layer, the mass ratio of the first graphite to the third graphite is 2:8 to 8:2; it can be selected as 3:7 to 7:3. As an example, this mass ratio can be 2:8, 3:7, 4:6, 5:5, 6:4, 7:3 or a range composed of any two of the above values.

[0196] Furthermore, the mass content of the first graphite in the second negative electrode active layer is 20% to 70%, and as an example, the mass content of the first graphite in its corresponding negative electrode active layer is 20%, 25%, 30%, 35%, 40%, 45%, 48%, 50%, 55%, 60%, 65%, 70% or a range composed of any two of the above values.

[0197] Optionally, the mass content of the first graphite in the second negative electrode active layer is ≥20% and <50%, and as examples, it can be 20%, 25%, 30%, 35%, 40%, 45%, 48%. At the same time, the total mass content of the first additive and the second additive in the electrolyte is 3% - 7%, and as examples, the total mass content of the first additive and the second additive can be 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7% or a range composed of any two of the above values. There is a matching relationship between the content of the first graphite and the content of the additives in the electrolyte. Through the above settings, the content of the first graphite is more matched with the total mass content of the first additive and the second additive, which can effectively improve the fast charging performance and cycling performance of the battery.

[0198] Optionally, the mass content of the first graphite in the second negative electrode active layer is 50% - 70%, and as examples, it can be 50%, 55%, 60%, 65%, 70% or a range composed of any two of the above values. At the same time, the total mass content of the first additive and the second additive in the electrolyte is 3.5% - 8%, and as examples, the total mass content of the first additive and the second additive can be 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%. The higher the content of the first graphite, the more additives need to be added correspondingly in the electrolyte. In this way, the content of the first graphite is more matched with the total mass content of the first additive and the second additive, which can effectively improve the fast charging performance and cycling performance of the battery.

[0199] Furthermore, the Dv50 particle size of the graphite in the first negative electrode active layer ≥ the Dv50 particle size of the first graphite in the second negative electrode active layer. Even further, the Dv50 particle size of the graphite in the first negative electrode active layer > the Dv50 particle size of the graphite in the second negative electrode active layer. The first graphite is arranged in the upper second negative electrode active layer. Since the distance between the negative electrode active material particles in the upper second negative electrode active layer decreases, the contact area between the negative electrode active material particles increases, the conductive channels and bridges increase, and the active area capable of participating in the reaction increases, thus significantly improving the specific capacity and fast charging performance of the battery; while in the lower first negative electrode active layer, graphite with a larger particle size is added, and the pores in the first negative electrode active layer are larger, having better electrolyte infiltration performance. Therefore, it can further contribute to improving the fast charging performance and cycling performance of the battery.

[0200] Further, the Dv50 particle size of the graphite in the first negative electrode active layer is 5.8 μm to 12.8 μm, and may be optionally 7.8 μm to 12.8 μm. As an example, the Dv50 particle size of the graphite in the first negative electrode active layer may be 5.8 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 12 μm, 13 μm, 14 μm, 14.5 μm, 14.8 μm, 15 μm, 16 μm, 17 μm, 18 μm, 18.5 μm or a range composed of any two of the above values.

[0201] Further, the Dv50 particle size of the first graphite in the second negative electrode active layer is 2.2 μm to 7.7 μm, and may be optionally 4.2 μm to 7.2 μm.

[0202] Further, the proportion of the thickness of the second negative electrode active layer in the total thickness of the first negative electrode active layer and the second negative electrode active layer is 30% to 70%, for example, it may be 30%, 40%, 50%, 60%, 70% or a range composed of any two of the above values.

[0203] It can be understood that the first negative electrode active layer and the second negative electrode active layer can be obtained by sequentially laminating and coating two slurries respectively, and then through processes such as drying and cold pressing.

[0204] In some embodiments, the artificial graphite includes graphite body particles and a coating layer. The graphite body particles include secondary particles aggregated by a plurality of primary particles. The coating layer is coated on the surface of the body particles, and the coating layer includes amorphous carbon. Amorphous carbon refers to a transition carbon material with a very low degree of graphitization, approximately an amorphous form (or no fixed shape and periodic structural rules). In the present application, amorphous carbon refers to the product after carbonization treatment of an organic carbon source.

[0205] The graphite body particles include secondary particles. Therefore, there are more migration paths for lithium ions in the artificial graphite, and the migration path in the primary particles is shorter, which can improve the migration rate of lithium ions; the amorphous carbon layer has more end faces and defects, so that the number of sites capable of intercalating and deintercalating lithium ions is more, and the conductivity of the amorphous carbon layer is relatively excellent, which can reduce the internal resistance of the negative electrode sheet and reduce the heat generation of the battery cell.

[0206] Further, based on the total mass of the artificial graphite, the mass content of the amorphous carbon is 2% to 5%. Exemplarily, the mass content of the amorphous carbon layer is 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or a range composed of any two of the above values.

[0207] When the mass content of the amorphous carbon layer is within the above range, the internal resistance of the negative electrode sheet can be further reduced, and the heat generation of the battery cell can be reduced.

[0208] In the embodiments of the present application, artificial graphite can be prepared by methods well-known in the art. For example, the preparation method includes: providing graphite body particles and an organic carbon source, mixing the two, and after carbonization treatment, forming an amorphous carbon layer on at least part of the surface of the graphite body particles.

[0209] Optionally, the organic carbon source includes one or more of coal tar pitch, petroleum pitch, phenolic resin, and coconut shell. Further optionally, the organic carbon source includes petroleum pitch. Optionally, the softening point of the coal tar pitch and petroleum pitch is below 250°C.

[0210] Optionally, the carbonization treatment temperature is 700°C to 1800°C. Optionally, the carbonization treatment temperature is 1000°C to 1300°C. When the carbonization treatment temperature is within a suitable range, the organic carbon source can be carbonized, and a coating layer containing amorphous carbon can be formed on at least part of the surface of the artificial graphite.

[0211] Optionally, the carbonization treatment time is 1h to 6h.

[0212] Furthermore, the powder resistivity of the artificial graphite is ≤0.04Ω•cm.

[0213] In some of these embodiments, the charging specific capacity of the graphite in a coin cell at a 0.1C rate is ≥350mAh / g, optionally in the range of 350 mAh / g to 440 mAh / g.

[0214] In some of these embodiments, in addition to the above-mentioned graphite, the negative electrode active material may further include a silicon-based material. The introduction of the silicon-based material can improve the capacity of the negative electrode active material and increase the energy density of the battery cell.

[0215] Furthermore, the silicon-based material may include at least one of silicon oxides and silicon-carbon composites.

[0216] Furthermore, the mass content of silicon element in the silicon-based material in the negative electrode active material is 0.3% - 10%, and can be optionally 1% - 6%. Exemplarily, the mass content of silicon element in the silicon-based material is 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.8%, 5%, 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 the range composed of any two of the above values.

[0217] In this application, the qualitative and quantitative determination of each substance or each element can be detected by suitable equipment and methods known to those skilled in the art. The relevant detection methods can refer to domestic and foreign detection standards, domestic and foreign enterprise standards, etc. And those skilled in the art can also adaptively change some detection steps / instrument parameters, etc. from the perspective of detection accuracy to obtain more accurate detection results. One detection method can be used for qualitative or quantitative determination, or several detection methods can be used in combination for qualitative or quantitative determination.

[0218] Separator In some embodiments, the secondary battery further includes a separator. The separator is disposed between the positive electrode plate and the negative electrode plate, mainly playing a role in preventing short circuit between the positive and negative electrodes, and at the same time allowing ions to pass through.

[0219] In some embodiments, the positive electrode plate, the negative electrode plate and the separator can be made into an electrode assembly by a winding process or a stacking process.

[0220] This application has no particular limitation on the type of the separator, and any well-known porous structure separator with good chemical stability and mechanical stability can be selected. 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. In some embodiments, the thickness of the separator is 6μm - 40μm, and can be optionally 12μm - 20μm.

[0221] In some embodiments, the separator includes a porous base film and a functional layer disposed on at least one side of the porous base film.

[0222] Furthermore, the material of the porous base film can include at least one of glass fiber, non-woven fabric, and polyolefin. Optionally, the polyolefin includes at least one of polyethylene, polypropylene, and polyvinylidene fluoride.

[0223] Further, the thickness of the porous base film is ≤12 μm, and can be ≤9 μm, and can be 6 μm to 9 μm. Exemplarily, the thickness of the base film is 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, or a range consisting of any two of the above values.

[0224] When the porosity of the separator in the embodiment of the present application is within the above range, the migration ability of lithium ions in the separator can be improved, and the internal resistance of the battery cell can be further reduced, thereby reducing heat generation.

[0225] In the embodiments of the present application, porosity refers to the percentage of the pore volume in the separator to the total volume of the separator. The porosity can be tested in accordance with the standard GB / T 36363-2018 "Polyolefin separator for battery monomers". It should be noted that the actual test process can be slightly different from the standard test process according to the difference in test instruments, test errors, and in order to eliminate the test influence on porosity as much as possible, so as to obtain a more accurate test value.

[0226] Further, the porosity of the porous base film is 20% to 70%, and can be 35% to 60%. Exemplarily, the porosity of the base film is 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or a range consisting of any two of the above values.

[0227] When the thickness of the porous base film is within the above range, the migration path of lithium ions in the base film is shorter, which can further reduce the internal resistance of the battery cell and thus reduce heat generation.

[0228] In the embodiment of the present application, the isolation film may be a base film; optionally, the isolation film further comprises a functional layer disposed on at least one side of the base film, and the functional layer may comprise inorganic particles to improve the heat resistance of the isolation film. Optionally, the functional layer is disposed on both sides of the base film.

[0229] In some embodiments, the functional layer includes a first functional layer and a second functional layer, the first functional layer is located on one side of the base film, the first functional layer includes first inorganic particles, the second functional layer is located on the other side of the base film, the second functional layer includes composite particles, the composite particles include second inorganic particles and multiple non-fluoropolymer particles, the second inorganic particles are attached to the surface of the non-fluoropolymer particles and / or dispersed in the interior of the non-fluoropolymer particles.

[0230] The first functional layer and the second functional layer have good heat resistance and can improve the heat resistance of the isolation film.

[0231] Optionally, the first functional layer may include a binder, optionally including at least one of a fluorine-containing binder or a polyacrylic acid binder, such as polyvinylidene fluoride.

[0232] Optionally, the first inorganic particles include one or more of silicon oxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide. The above-mentioned first inorganic particles can improve the heat resistance of the first functional layer.

[0233] In the embodiments of the present application, the meaning of the thickness of the base film is the meaning well-known in the art, and it can be detected by using the meaning and equipment well-known in the art. For example, a newly prepared separator can be taken as a sample, or a battery cell that has been discharged (discharged to the lower cut-off voltage so that the charged state of the battery is about 0% SOC) can be disassembled in reverse, the separator is obtained from the battery cell, and the separator is dried and used as a sample. The separator is cut off with an ion beam cutter to form a cross-section; subsequently, a scanning electron microscope is used to measure the thickness of the cross-section of the separator and its respective layers.

[0234] The non-fluoropolymer particles in the second functional layer refer to polymers that are non-fluorinated polymers. For example, the non-fluoropolymer particles include acrylate copolymers. Optionally, the acrylate copolymers include acrylate-acrylonitrile-acrylamide-acrylonitrile copolymers. The acrylate copolymers have excellent adhesion properties and relatively high adhesion stability with the base film. The molar ratio of each monomer in the copolymer can be any ratio, such as a molar ratio of 35%:30%:15%:20%, or 40%, 20%, 10%, 30%, or 45%, 15%, 20%, 20%, etc.

[0235] The second inorganic particles in the composite particles make it difficult for the non-fluoropolymer particles to adhere to each other due to the high-temperature treatment during the granulation process, resulting in pores in the composite particles, which is beneficial to the transmission of lithium ions and improves the ionic conductivity of the separator; and the second inorganic particles can also increase the compression modulus of the composite particles. During charge and discharge, the composite particles are not easily deformed, making the structure of the separator more stable, which can improve the kinetic performance of the battery cell and enhance the fast charging performance. Optionally, compared with the first functional layer, the second functional layer is disposed closer to the negative electrode tab. Since the composite particles are not easily deformed, the separator basically does not cause side effects such as extrusion to the negative electrode tab, making the kinetic performance of the negative electrode tab stable. Correspondingly, the first functional layer is disposed closer to the positive electrode tab.

[0236] Optionally, the second inorganic particles include one or more of silica, alumina, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide; optionally, the second inorganic particles include silica. The above-mentioned second inorganic particles can improve the heat resistance of the second functional layer, and can form composite particles in cooperation with the non-fluoropolymer, further improving the cycle stability and kinetic performance of the separator membrane, and improving the cycle performance and fast charging performance of the battery cell.

[0237] The average particle size of the second inorganic particles is 5 nm to 100 nm, optionally 10 nm to 100 nm, optionally 5 nm to 20 nm. Exemplarily, the average particle size of the second inorganic particles is 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm or the range composed of any two of the above values. When the average particle size of the second inorganic particles is within the above range, it is beneficial to improve the heat resistance and compression modulus of the composite particles.

[0238] In the embodiments of the present application, the average particle size of the second inorganic particles has the meaning well known in the art, and can be detected by the equipment and methods well known in the art. For example, after obtaining the separator membrane and drying the separator membrane as a sample, use an ion beam cutter to cut the separator membrane to form a cross-section; subsequently, use a scanning electron microscope to measure the particle size of the second inorganic particles in the separator membrane, measure the particle sizes of multiple, such as 50, second inorganic particles, and calculate their average value as the average particle size of the second inorganic particles.

[0239] In some embodiments, the ionic conductivity of the separator membrane is 0.3 mS / cm to 0.6 mS / cm. Exemplarily, the ionic conductivity of the separator membrane is 0.3 mS / cm, 0.35 mS / cm, 0.4 mS / cm, 0.45 mS / cm, 0.5 mS / cm, 0.55 mS / cm, 0.6 mS / cm or the range composed of any two of the above values.

[0240] When the ionic conductivity of the separator membrane is within the above range, it can further improve the migration ability of lithium ions in the separator membrane and improve the fast charging performance of the battery cell.

[0241] In the embodiments of the present application, the ionic conductivity of the separator membrane has the meaning well known in the art, and can be detected by the equipment and methods well known in the art. For example, Prepare a test 2025-type button battery: In a vacuum glove box, place a lithium sheet in the battery negative electrode case, and add 150 μL of electrolyte. The electrolyte uses 1M LiPF 6In a solution with EC / EMC / DEC = 3 / 5 / 2 (mass ratio), then place the separator (with an area of 3.14 cm 2 , a thickness of 12 μm) to make it close to the lithium sheet, then add 25 μL of electrolyte, and finally place the positive electrode sheet (the positive electrode sheet can be the positive electrode sheet in Example 1) on it, and encapsulate. Take out the assembled button battery from the vacuum glove box and place it for 24 h for the next test.

[0242] Test: On an electrochemical workstation, test in the frequency range of 10 -1 ~10 6 Hz to obtain the separator resistance Rb, and calculate the ionic conductivity σ (unit: mS / cm) through the following formula, σ = L / (R b ×S) where: R b is the equivalent resistance, and L and S are the thickness and area of the separator to be measured, respectively.

[0243] The secondary battery includes at least one battery cell. The secondary battery can include 1 or more battery cells.

[0244] In the present application, unless otherwise specified, a "battery cell" refers to a basic unit capable of realizing the mutual conversion between chemical energy and electrical energy. Further, generally, it includes at least a positive electrode sheet, a negative electrode sheet, and an electrolyte. During the charge and discharge process of the battery, active ions are embedded and extracted back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting active ions between the positive electrode sheet and the negative electrode sheet.

[0245] The present application does not particularly limit the shape of the battery cell, and it can be cylindrical, square, or any other shape. For example, Figure 1 the shown secondary battery is a battery cell, which is an example of the battery cell 5 with a square structure.

[0246] In some of the embodiments, the battery cell 5 may include an outer package. The outer package can be used to encapsulate the above electrode assembly and electrolyte. In some of the embodiments, the outer package of the battery cell 5 can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the battery cell 5 can also be a soft package, such as a pouch soft package. The material of the soft package can be plastic. Further, non-limiting examples of the plastic can include at least one of polypropylene, polybutylene terephthalate, and polybutylene succinate, etc.

[0247] In some of the embodiments, refer to Figure 2, the outer package may include a housing 51 and a cover plate 53. Among them, the housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose to form a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode plate, the negative electrode plate and the separator can be formed into an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. The number of electrode assemblies 52 included in the battery cell 5 can be one or more, and those skilled in the art can select according to actual needs.

[0248] In some embodiments, the secondary battery may be a battery module or a battery pack. The battery module includes at least one battery cell. The number of battery cells included in the battery module can be one or more, and those skilled in the art can select a suitable number according to the application and capacity of the battery module.

[0249] Figure 3 The secondary battery shown is a battery module, which is a battery module 4 as an example. Refer to Figure 3 , in the battery module 4, a plurality of battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other way. Further, the plurality of battery cells 5 can be fixed by fasteners.

[0250] Optionally, the battery module 4 may further include a housing having a receiving space, and a plurality of battery cells 5 are received in the receiving space.

[0251] In some of these embodiments, the above battery module can also be assembled into a battery pack. The number of battery modules included in the battery pack can be one or more, and those skilled in the art can select a suitable number according to the application and capacity of the battery pack.

[0252] Figure 4 and Figure 5 and are shown as the secondary battery being a battery pack, which is a battery pack 1 as an example. Refer to Figure 4 and Figure 5 , in the battery pack 1, it may include a battery box and a plurality of battery modules 4 arranged in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can be covered on the lower box body 3 and form a closed space for receiving the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any way.

[0253] In addition, an embodiment of the present application further provides an electrical device, which includes the secondary battery provided by the present application. The secondary battery 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, electric vehicles, electric trains, ships, satellites, energy storage systems, etc. Among them, the mobile device may be, for example, a mobile phone, a laptop computer, etc.; the electric vehicle may be, for example, a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc., but is not limited to this.

[0254] As the electrical device, the secondary battery can be selected according to its usage requirements.

[0255] Figure 6 Shown is an electrical device 6 as an example. The electrical device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the electrical device for the secondary battery, a battery pack or a battery module can be used.

[0256] Another example of the device can be a mobile phone, a tablet computer, a laptop computer, etc. This device usually requires being thin and light, and the battery cell 5 can be used as the power source.

[0257] In order to make the technical problems, technical solutions, and beneficial effects solved by the present application clearer, the present application will be further described in detail below with reference to embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and in no way constitutes a limitation to the present application and its application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present application.

[0258] For those not specifying specific techniques or conditions in the embodiments, the techniques or conditions described in the literature in the art or according to the product specifications are followed. For reagents or instruments not indicating the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0259] Embodiment 1 (1) Preparation of the positive electrode sheet: The positive electrode active material includes lithium iron phosphate and an ion-conducting layer, the ion-conducting layer is coated on the surface of the lithium iron phosphate, and the ion-conducting layer includes lithium iron titanium phosphate Li 2 FeTi(PO 4 ) 3 and amorphous carbon. The Dv50 of the positive electrode active material is 1.6 μm, and the Dv10 is 0.64 μm. The powder compaction density under 30000 N is 2.53 g / cm3 。

[0260] The positive current collector is an aluminum foil with a thickness of 10 μm, and a positive conductive layer is provided on the positive current collector. The positive conductive layer is formed by uniformly mixing conductive carbon SP, binder polyvinylidene fluoride (PVDF), and solvent N-methylpyrrolidone NMP and then coating it on the surface of the current collector, with a thickness of 1 μm.

[0261] Mix the positive active material lithium iron phosphate LiFePO 4 , binder polyvinylidene fluoride, and conductive agent acetylene black in a mass ratio of 97:2:1, and then add solvent N-methylpyrrolidone (NMP) and stir evenly to form a positive electrode paste; uniformly coat the positive electrode paste on the positive conductive layer of the positive current collector aluminum foil, and after drying and cold pressing, a positive electrode plate is obtained. The positive electrode plate includes a positive current collector and a positive conductive layer and a positive electrode film layer sequentially provided on the positive current collector.

[0262] Among them, based on the mass of the positive electrode film layer, the single-sided coating weight of the positive electrode plate is 300 mg / 1540.25 mm 2 ; the battery is charged at a charging rate of 0.33C until the compaction density of the positive electrode plate at 100% SOC is 2.63 g / cm 3 。

[0263] Among them, the battery is charged at a charging rate of 0.33C to 100% SOC in the following manner: charge the battery monomer at a constant current charging rate of 0.33C until the upper limit voltage of the battery (3.65V), and then charge at a constant voltage until 0.05C, corresponding to the state of 100% SOC of the battery monomer.

[0264] (2) Preparation of negative electrode plate: The preparation method of the double-layer structure negative electrode plate is as follows: The Dv50 particle sizes of the first graphite, the second graphite, and the third graphite are 5.8 μm, 9.6 μm, and 9.6 μm respectively.

[0265] The negative current collector is a copper foil with a thickness of 5 μm, and a negative conductive layer is provided on the negative current collector. The negative conductive agent is formed by uniformly mixing conductive carbon SP, binder SBR, dispersant CMC, and solvent water and then coating it on the surface of the current collector, with a thickness of 1 μm.

[0266] Mix the negative active material third graphite, conductive agent acetylene black, binder styrene-butadiene rubber, and thickener sodium carboxymethylcellulose in a mass ratio of 96:0.5:2.5:1, and then add solvent deionized water and stir evenly to form a first negative electrode paste.

[0267] The negative electrode active materials, the first graphite, the second graphite, the conductive agent acetylene black, the binder styrene butadiene rubber and the thickener sodium carboxymethyl cellulose were mixed in a mass ratio of 54.9:41.1:0.5:2.5:1, and then the solvent deionized water was added and stirred evenly to form a second negative electrode slurry.

[0268] The first negative electrode slurry is evenly coated on the negative electrode conductive layer of the negative electrode current collector copper foil and dried; the second negative electrode slurry is coated on the surface of the dried first negative electrode slurry, and the negative electrode sheet is obtained after drying and cold pressing. The negative electrode sheet includes a negative electrode current collector and a negative electrode conductive layer and a negative electrode film layer sequentially arranged on the negative electrode current collector. The negative electrode film layer includes a first negative electrode active layer and a second negative electrode active layer sequentially arranged on the negative electrode conductive layer.

[0269] Among them, based on the total mass of the negative electrode film layer, the single-sided coating weight of the negative electrode sheet is 138 mg / mm 2 ; The battery is charged at a charge rate of 0.33C to 100% SOC, and the compaction density of the positive electrode sheet is 1.2g / cm 3 ; Based on the total mass of the first graphite, the second graphite and the third graphite in the negative electrode film layer, the mass proportions of the first graphite, the second graphite and the third graphite are 40%, 30% and 30% respectively.

[0270] (3) Preparation of electrolyte: In an argon atmosphere glove box with a water content of less than 10 ppm, a first solvent ethylene carbonate (EC), a second solvent ethyl acetate (EA) and dimethyl carbonate (DMC) were uniformly mixed in a certain mass ratio to obtain an organic solvent, in which the mass contents of ethylene carbonate (EC), ethyl acetate (EA) and dimethyl carbonate (DMC) were 25%, 50% and 25%, respectively, as shown in Table 1; a certain mass of lithium hexafluorophosphate (LiPF 6 ) is a lithium salt, which is stirred thoroughly until it is completely dissolved. LiPF 6 The concentration is 1 mol / L. After returning to room temperature, add the first additive vinylene carbonate (VC) accounting for 6% of the total mass of the electrolyte and the second additive fluoroethylene carbonate (FEC) accounting for 4% of the total mass of the electrolyte, and mix them thoroughly to obtain the electrolyte. The mass b of the electrolyte at the rated capacity of the unit cell of the secondary battery of 1Ah is 2.65g, as shown in Table 1.

[0271] (4) Isolation film: The isolation film comprises a base film, which is a 7 μm polyethylene film layer with a porosity of 42%.

[0272] (5) Secondary battery preparation: Stack the positive electrode sheet, separator, and negative electrode sheet in sequence and wind them to obtain a wound electrode assembly; place the electrode assembly into a square aluminum outer package, dry it, inject electrolyte, and through processes such as encapsulation, standing, formation, aging, secondary encapsulation, and capacity measurement, a secondary battery is obtained.

[0273] The preparation methods of Examples 2 to 4 are similar to that of Example 1, except that: the mass content of the first solvent ethylene carbonate (EC) in the organic solvent is adjusted (the mass content of dimethyl carbonate (DMC) is adjusted accordingly), as shown in Table 1 specifically.

[0274] The preparation methods of Examples 5 to 8 are similar to that of Example 2, except that: the mass content of the first additive VC in the electrolyte is adjusted, as shown in Table 1 specifically.

[0275] The preparation methods of Examples 9 to 13 are similar to that of Example 2, except that: the mass content of the second additive FEC in the electrolyte is adjusted, as shown in Table 1 specifically.

[0276] The preparation method of Example 14 is similar to that of Example 2, except that: the type and content of the second solvent are adjusted, and at the same time, the single-sided coating weight of the active layers of the positive electrode sheet and the negative electrode sheet is adjusted.

[0277] As shown in Table 1 specifically.

[0278] The preparation methods of Examples 15 to 17 are similar to that of Example 2, except that: the type of the first graphite of the negative active material is adjusted, and its Dv50 parameter is different, as shown in Table 1 specifically.

[0279] The preparation methods of Examples 18 to 19 are similar to that of Example 10, except that: the injection coefficient of the electrolyte is adjusted, so the mass b of the electrolyte under the rated capacity of 1 Ah per unit cell of the secondary battery is different, and at the same time, the mass content of the first additive in the electrolyte is adjusted, as shown in Table 1 specifically.

[0280] Example 19 The preparation method is similar to that of Example 3, except that the negative electrode sheet is a single-layer structure, and its preparation method is as follows: Mix the first graphite, second graphite, conductive agent acetylene black, binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose of the negative active material according to a mass ratio of 38.4:57.6:0.5:2.5:1, and then add the solvent deionized water and stir evenly to form a negative electrode slurry; uniformly coat the negative electrode slurry on the negative electrode conductive layer of the negative electrode current collector copper foil, and through drying and cold pressing, a negative electrode sheet is obtained.

[0281] The negative electrode sheet includes a negative electrode current collector and a negative electrode conductive layer and a negative electrode active layer sequentially provided on the negative electrode current collector.

[0282] Among them, based on the total mass of the negative electrode active layer, the single-sided coating weight of the negative electrode sheet is 138 mg / mm 2 ; when the battery is charged at a charging rate of 0.33C to 100% SOC, the compaction density of the positive electrode sheet is 1.2 g / cm 3 ; based on the total mass of the first graphite and the second graphite in the negative electrode active layer, the mass percentages of the first graphite and the second graphite are 40% and 60% respectively.

[0283] The preparation methods of Comparative Examples 1 to 5 are similar to those of Example 3, except that: at least one of the mass content of ethylene carbonate (EC) in the organic solvent, the mass content of the first additive, and the mass content of the first additive in the electrolyte is adjusted, as shown in Table 1 specifically.

[0284] The following are performance tests.

[0285] (I) The test steps for the capacity retention rate of the battery cycling 1000 times at 60 °C are as follows: At 60 °C, the battery is charged at a constant current of 1C to the charging cut-off voltage of 3.65V respectively, left standing for 30 min, and then discharged at a constant current of 1C to 2.0V. This is one charge-discharge cycle, and the capacity C0 after the first cycle is recorded; repeat the above charge-discharge cycle steps until cycling 1000 times, and record the corresponding capacity Cn after the 1000th cycle. The capacity retention rate of the battery cycling 1000 times at 60 °C = Cn / C0×100%. The higher the capacity retention rate, the better the cycling performance of the battery.

[0286] (II) The test steps for the charging time T of the secondary battery charging from 10% SOC to 80% SOC at 30 °C are as follows: At an ambient temperature of 30 °C, the battery is charged from the state of 10% SOC, charged at a constant current of 5.0C from 10% SOC to 15% SOC; charged at a constant current of 5.0C from 15% SOC to 20% SOC; charged at a constant current of 5.0C from 20% SOC to 25% SOC; charged at a constant current of 5.0C from 25% SOC to 30% SOC; charged at a constant current of 5.0C from 30% SOC to 35% SOC; charged at a constant current of 5.0C from 35% SOC to 40% SOC; charged at a constant current of 4.6C from 40% SOC to 45% SOC; charged at a constant current of 4.3C from 45% SOC to 50% SOC; charged at a constant current of 4.0C from 50% SOC to 55% SOC; Charge from 55% SOC to 60% SOC at a constant current of 3.7C; Charge from 60% SOC to 65% SOC at a constant current of 3.4C; Charge from 65% SOC to 70% SOC at a constant current of 3.1C; Charge from 70% SOC to 75% SOC at a constant current of 2.9C; Charge from 75% SOC to 80% SOC at a constant current of 2.7C; Record the total charging time.

[0287] (III) The test steps for the capacity retention rate of the battery with 1000 cycles at 30°C are as follows: At 30°C, charge the battery starting from 10% SOC respectively, charge to 80% SOC at the corresponding rate according to the different SOCs above, then continue to charge at a constant current of 0.33C until 3.65V, let it stand for 30 min, and then discharge at a constant current of 1C to 2.0V. This is one charge-discharge cycle. Record the capacity C0 after the first cycle; repeat the above charge-discharge cycle steps until 1000 cycles, record the corresponding capacity Cn after the 1000th cycle, and obtain the capacity retention rate of the battery with 1000 cycles at 30°C = Cn / C0×100%. The higher the capacity retention rate, the better the cycle performance of the battery.

[0288] Partial parameters of each example and comparative example are shown in Table 1, where the contents are all mass contents, and the unit of the single-sided coating weight of the positive electrode and the negative electrode is mg / 1540.25mm 2 。

[0289] The above performance test results of each example and comparative example are shown in Table 2.

[0290] Table 1

[0291] Table 2

[0292] As can be seen from Tables 1-2 above, in Comparative Example 1, the content of the first additive is too high, and the room temperature cycle performance of the battery deteriorates; in Comparative Example 1, the content of the first additive is too low, and the high temperature cycle performance of the battery deteriorates, and the fast charging time is long, indicating that its fast charging performance is poor; in Comparative Example 3, the content of the second additive is too high, and the high temperature cycle performance of the battery deteriorates; in Comparative Example 4, the content of the second additive is too low, and the room temperature cycle performance of the battery decreases; in Comparative Example 5, the content of the first solvent is too low, the self-stability of the electrolyte becomes poor, resulting in a decrease in conductivity, making both the room temperature and high temperature cycle performances poor.

[0293] Each embodiment adjusts the composition and proportion of the electrolyte and makes it cooperate synergistically with the negative electrode sheet containing the first graphite with a smaller particle size, so that the prepared secondary battery can take into account good fast charging performance, normal temperature cycle performance and high temperature cycle performance. Among them, in Example 14, the second solvent in the electrolyte all adopts a carbonate solvent, and the conductivity of the electrolyte decreases, so the single-sided coating weight of the positive electrode sheet and the negative electrode sheet is reduced to improve the fast charging performance of the battery.

[0294] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of concise description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0295] The above-described embodiments only represent several implementation manners of the present application. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A secondary battery, characterized in that: include: A positive electrode sheet, the positive electrode sheet comprising a positive electrode current collector and a positive electrode film layer, the positive electrode film layer is arranged on at least one side of the positive electrode current collector, and the positive electrode film layer comprises a positive electrode active material; A negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode film layer, the negative electrode film layer being disposed on at least one side of the negative electrode current collector, the negative electrode film layer comprising a negative electrode active material, the negative electrode active material comprising a first graphite, and the Dv50 particle size of the first graphite being 2.2 μm to 7.7 μm; and An electrolyte, the electrolyte comprising an organic solvent and an organic additive, the organic solvent comprising a first solvent, the first solvent comprising a cyclic carbonate, and based on the total mass of the organic solvent, the mass content of the first solvent is 25%~40%; the organic additive comprises a first additive and a second additive, the first additive comprising vinylene carbonate, the second additive comprising a vinyl carbonate derivative, based on the total mass of the electrolyte, the mass percentage of the first additive in the electrolyte is 2%~10%, and the mass percentage of the second additive in the electrolyte is 0.3%~6%.

2. The secondary battery according to claim 1, wherein: The structure of the ethylene carbonate derivative is as follows: ， R1 and R2 each independently include any one of hydrogen, halogen, C1-C5 alkyl and C1-C5 halogenated alkyl, and R1 and R2 are not hydrogen at the same time.

3. The secondary battery according to claim 1 or 2, characterized in that: The ethylene carbonate derivative includes at least one of fluoroethylene carbonate, difluoroethylene carbonate and trifluoromethylethylene carbonate.

4. The secondary battery according to claim 1, wherein: The cyclic carbonate includes at least one of ethylene carbonate and propylene carbonate.

5. The secondary battery according to claim 1, wherein: Based on the total mass of the organic solvent, the mass content of the first solvent is 30% to 40%.

6. The secondary battery according to claim 1, wherein: Based on the total mass of the electrolyte, the mass content of the first additive is 3% to 8%, and / or the mass content of the second additive is 1.5% to 5%.

7. The secondary battery according to claim 1, wherein: The total mass content of the first additive and the second additive in the electrolyte is 3% to 12%.

8. The secondary battery according to claim 7, characterized in that The total mass content of the first additive and the second additive in the electrolyte is 3.5% to 9%.

9. The secondary battery according to claim 1, wherein: The mass of the electrolyte of the secondary battery at a unit cell rated capacity of 1 Ah is 2.2 g to 2.95 g.

10. The secondary battery according to claim 9, characterized in that The mass of the electrolyte of the secondary battery at a unit cell rated capacity of 1Ah is 2.2g-2.65g, and the total mass content of the first additive and the second additive in the electrolyte is 5%-9%; Alternatively, the mass of the electrolyte at a unit cell rated capacity of the secondary battery of 1 Ah is greater than 2.65 g and less than or equal to 2.95 g, and the total mass content of the first additive and the second additive in the electrolyte is 3.5% to 6.5%.

11. The secondary battery according to claim 1, wherein The powder compaction density of the positive electrode active material at 30000N is ≥2.43g / cm 3 .

12. The secondary battery according to claim 11, wherein: The powder compaction density of the positive electrode active material at 30000N is 2.48g / cm 3 ~2.85 g / cm 3 .

13. The secondary battery according to claim 11, wherein: The positive electrode active material includes at least one of an olivine-structured lithium-containing phosphate and a derivative thereof.

14. The secondary battery according to claim 13, characterized in that: The positive electrode active material comprises: a core portion comprising at least one of an olivine-structured lithium-containing phosphate and a derivative thereof; and An ion-conducting layer is coated on the surface of the core portion, and the ion-conducting layer includes at least one element selected from the group consisting of Fe, C, Ti, Zr, Hf, Ge and Sn.

15. The secondary battery according to claim 13 or 14, characterized in that: The olivine structured lithium-containing phosphate and its derivatives include a general formula of Li x1 A1 y1 M1 a1 M2 b1 P 1-c1 X c1 Q1 z1 A compound, wherein 0.5≤x1≤1.3, 0≤y1≤1.3, and 0.9≤x1+y1≤1.3; 0.9≤a1≤1.5, 0≤b1≤0.5, and 0.9≤a1+b1≤1.5; 0≤c1≤0.5; 3≤z1≤5; A1 includes at least one of Na, K and Mg; M1 includes at least one of Mn, Fe, Co and Ni; M2 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 and N, P; Q1 includes at least one of O and F.

16. The secondary battery according to claim 15, characterized in that: The olivine-structured lithium-containing phosphate and its derivatives include at least one of lithium iron phosphate, lithium manganese phosphate, lithium nickel phosphate and lithium cobalt phosphate.

17. The secondary battery according to claim 14, wherein: The ion-conducting layer includes a chemical formula of Li 3-b Fe 2- b M3 b (PO m ) n The fast ion conductor M3 includes at least one element of Ti, Zr, Hf, Ge and Sn with a valence of +4, 0≤b≤1, 3≤m≤5, 2≤n≤4.

18. The secondary battery according to claim 17, wherein: The fast ion conductor includes at least one of lithium iron titanium phosphate, lithium iron zirconium phosphate and lithium iron tin phosphate.

19. The secondary battery according to claim 1, wherein: At least one of the following conditions is met: (1) The compaction density of the positive electrode sheet is 2.5 g / cm 3 ~2.8g / cm 3 ; (2) The mass percentage of carbon in the positive electrode active material is 1% to 2%; (3) The powder resistivity range of the positive electrode active material is R≤20Ω•cm; (4) The volume average particle size of the positive electrode active material satisfies: 1µm≤Dv50≤2µm.

20. The secondary battery according to claim 19, wherein: At least one of the following conditions is met: (1) The powder resistivity range of the positive electrode active material is R≤11Ω•cm; (2) The volume average particle size of the positive electrode active material satisfies 0.4µm≤Dv10≤0.7µm.

21. The secondary battery according to claim 1, characterized in that: The positive electrode film layer also includes a lithium supplement agent, which includes at least one of a ternary lithium supplement material, lithium phosphate, lithium dihydrogen phosphate, lithium sulfate, lithium sulfite, lithium molybdate, lithium nickelate, lithium ferrite, lithium oxalate, lithium titanate, lithium tetraborate, lithium metasilicate, lithium metamanganate, lithium tartrate and trilithium citrate.

22. The secondary battery according to claim 21, characterized in that The ternary lithium supplement material includes Li x2 A2 y2 Ni a2 Co b2 Mn c2 M4 (1-a2-b2-c2) Q2 z2 , wherein 0<x2≤2.1, 0≤y2≤2.1; 0≤a2≤1, 0≤b2≤1, 0≤c2≤1, and 0.1≤a2+b2+c2≤1; 1.8≤z2≤3.5; A2 includes at least one of Na, K and Mg; M4 includes at least one of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La and Ce; Q2 includes at least one of O and F.

23. The secondary battery according to claim 1, characterized in that: The positive electrode plate also includes a positive electrode conductive layer, which is arranged between the positive electrode collector and the positive electrode film layer on at least one side. The positive electrode conductive layer includes a conductive agent, and the conductive agent includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

24. The secondary battery according to claim 23, characterized in that: The thickness of the positive electrode conductive layer is 0.5 μm to 2 μm.

25. The secondary battery according to claim 23 or 24, characterized in that: The positive electrode conductive layer includes a binder, and the binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid and fluorine-containing acrylic resin.

26. The secondary battery according to claim 25, characterized in that: In the positive electrode conductive layer, the mass content of the conductive agent is 30% to 50%, and the mass content of the binder is 50% to 70%.

27. The secondary battery according to claim 1, characterized in that: After the secondary battery is charged to 100% SOC at a charging rate of 0.33C, the compaction density of the negative electrode sheet is 1.15 g / cm 3 ~1.46g / cm 3 .

28. The secondary battery according to claim 27, characterized in that After the secondary battery is charged to 100% SOC at a charging rate of 0.33C, the compaction density of the negative electrode sheet is 1.15 g / cm 3 ~1.36g / cm 3 .

29. The secondary battery according to claim 27, wherein: After the secondary battery is charged to 100% SOC at a charging rate of 0.33C, the compaction density of the negative electrode sheet is 1.15 g / cm 3 ~1.26g / cm 3 , the mass content of the first additive in the electrolyte is 3%~8%.

30. The secondary battery according to claim 29, characterized in that At least one of the following conditions is met: (1) The mass content of the second additive in the electrolyte is 0.5% to 3%; (2) The mass content of the first solvent in the organic solvent is 30% to 40%.

31. The secondary battery according to claim 27, characterized in that: After the secondary battery is charged to 100% SOC at a charging rate of 0.33C, the compaction density of the negative electrode sheet is >1.26 g / cm 3 And ≤1.36g / cm 3 , the mass content of the first additive in the electrolyte is 2.5%~6.5%.

32. The secondary battery according to claim 31, characterized in that At least one of the following conditions is met: (1) The mass content of the second additive in the electrolyte is 1% to 4%; (2) The mass content of the first solvent in the organic solvent is 25% to 38%.

33. The secondary battery according to claim 1, characterized in that: The electrolyte further includes a second solvent, and the second solvent includes at least one of linear carbonate, carboxylate, ether, nitrile and sulfone.

34. The secondary battery according to claim 33, characterized in that: The second solvent includes a carboxylic acid ester.

35. The secondary battery according to claim 33, characterized in that: The carboxylic acid ester includes at least one of methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate and methyl butyrate.

36. The secondary battery according to claim 34, characterized in that The charging time of the secondary battery from 10% SOC to 80% SOC at 30° C. is 6 min to 15 min, the mass content of the carboxylic acid ester in the organic solvent is 20% to 75%, and the total mass content of the first additive and the second additive in the electrolyte is 3% to 9%.

37. The secondary battery according to claim 36, characterized in that In the electrolyte, the mass content of the first additive is 2% to 7%, and the mass content of the second additive is 0.5% to 4%.

38. The secondary battery according to claim 1, characterized in that: The electrolyte includes a lithium salt, and the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, fluorine-containing sulfonyl imide salts, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate and lithium tetrafluorooxalatophosphate.

39. The secondary battery according to claim 38, characterized in that The concentration of the lithium salt in the electrolyte is 0.7 mol / L to 1.5 mol / L.

40. The secondary battery according to claim 38 or 39, characterized in that: The lithium salt includes at least one of LiFSI and LiPF6, and the lithium salt satisfies at least one of the following conditions: (1) The concentration of LiFSI is 0.2 mol / L to 0.5 mol / L; (2) The concentration of LiPF6 is 0.5 mol / L~1.3 mol / L; (3) The lithium salt includes LiFSI and LiPF6, and the concentration ratio of the LiFSI to the LiPF6 is (2-5):

10.

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

42. The secondary battery according to claim 41, characterized in that The thickness of the negative electrode conductive layer is 0.5 μm to 2 μm.

43. The secondary battery according to claim 41 or 42, characterized in that: The negative electrode conductive layer includes a binder, and the binder includes at least one of styrene-butadiene rubber, a water-soluble unsaturated resin, a water-based acrylic resin, polyvinyl alcohol, sodium alginate, and carboxymethyl chitosan.

44. The secondary battery according to claim 43, characterized in that In the negative electrode conductive layer, the mass content of the conductive agent is 20% to 40%, and the mass content of the binder is 60% to 80%.

45. The secondary battery according to claim 1, characterized in that: The negative electrode film layer includes at least one negative electrode active layer, and the at least one negative electrode active layer includes the first graphite.

46. ​​The secondary battery according to claim 45, characterized in that The negative electrode film layer includes only one negative electrode active layer, and the negative electrode active layer contains the first graphite and the second graphite. The Dv50 particle size of the first graphite is 4.2 μm to 7.2 μm, and the Dv50 particle size of the second graphite is 7.8 μm to 14.8 μm.

47. The secondary battery according to claim 46, characterized in that The mass ratio of the first graphite to the second graphite is 2:8 to 6:

4.

48. The secondary battery according to claim 47, characterized in that The mass ratio of the first graphite to the second graphite is 3:7 to 5:

5.

49. The secondary battery according to claim 46 or 47, characterized in that: The mass content of the first graphite in the negative electrode active layer is ≥20% and <50%, and the total mass content of the first additive and the second additive in the electrolyte is 3% to 8%; Alternatively, the mass content of the first graphite in the negative electrode active layer is 50% to 70%, and the total mass content of the first additive and the second additive in the electrolyte is 4% to 10%.

50. The secondary battery according to claim 45, characterized in that The negative electrode film layer includes a first negative electrode active layer and a second negative electrode active layer stacked in sequence on the same side of the negative electrode current collector, the first negative electrode active layer includes at least one of artificial graphite and natural graphite, the second negative electrode active layer includes the first graphite and a third graphite, the first graphite includes artificial graphite, and the Dv50 particle size of the third graphite is 7.8μm~14.8μm.

51. The secondary battery according to claim 50, characterized in that In the second negative electrode active layer, a mass ratio of the first graphite to the third graphite is 2:8 to 8:

2.

52. The secondary battery according to claim 51, characterized in that In the second negative electrode active layer, a mass ratio of the first graphite to the third graphite is 3:7 to 7:

3.

53. The secondary battery according to claim 50 or 51, characterized in that: At least one of the following conditions is met: (1) the ratio of the total amount of negative electrode active material in the second negative electrode active layer to that in the first negative electrode active layer is 3:7 to 7:3; (2) The mass content of the first graphite in the second negative electrode active layer is 30% to 70%; or the mass content of the first graphite in the second negative electrode active layer is 50% to 70%, and the total mass content of the first additive and the second additive in the electrolyte is 3.5% to 8%; (3) The Dv50 particle size of the graphite in the first negative electrode active layer is ≥ the Dv50 particle size of the first graphite in the second negative electrode active layer.

54. The secondary battery according to claim 53, characterized in that At least one of the following conditions is met: (1) the ratio of the total amount of negative electrode active material in the second negative electrode active layer to that in the first negative electrode active layer is 4:6 to 6:4; (2) The mass content of the first graphite in the second negative electrode active layer is ≥20% and <50%, and the total mass content of the first additive and the second additive in the electrolyte is 3% to 7%; (3) The Dv50 particle size of the graphite in the first negative electrode active layer is 5.8 μm to 12.8 μm; the Dv50 particle size of the graphite in the second negative electrode active layer is 2.2 μm to 7.7 μm.

55. The secondary battery according to claim 54, characterized in that The Dv50 particle size of the graphite in the first negative electrode active layer is 7.8 μm to 12.8 μm; the Dv50 particle size of the graphite in the second negative electrode active layer is 4.2 μm to 7.2 μm.

56. The secondary battery according to claim 50, characterized in that The artificial graphite comprises graphite body particles and a coating layer, wherein the graphite body particles comprise secondary particles formed by aggregation of a plurality of primary particles, and the coating layer is coated on the surface of the body particles, and comprises amorphous carbon.

57. The secondary battery according to claim 56, characterized in that At least one of the following conditions is met: (1) Based on the total mass of the artificial graphite, the mass content of the amorphous carbon is 2% to 5%; (2) The powder resistivity of the artificial graphite is ≤0.04Ω•cm.

58. The secondary battery according to claim 1, characterized in that The charging capacity of the first graphite at a rate of 0.1C in a button cell is ≥350 mAh / g.

59. The secondary battery according to claim 58, characterized in that The charge capacity of the first graphite at a rate of 0.1C in a button cell is between 350 mAh / g and 440 mAh / g.

60. The secondary battery according to claim 1, characterized in that The negative electrode active material further includes a silicon-based material, and the silicon-based material includes at least one of a silicon-oxygen compound and a silicon-carbon composite; the mass content of silicon element in the silicon-based material in the negative electrode active material is 0.3% to 10%.

61. The secondary battery according to claim 60, characterized in that The mass content of silicon element in the silicon-based material in the negative electrode active material is 1% to 6%.

62. The secondary battery according to claim 1, characterized in that The separator includes a porous base film and a functional layer disposed on at least one side of the porous base film.

63. The secondary battery according to claim 62, characterized in that At least one of the following conditions is met: (1) The thickness of the porous base film is ≤12 μm; (2) The porosity of the porous base membrane is 20% to 70%.

64. The secondary battery according to claim 63, characterized in that At least one of the following conditions is met: (1) The thickness of the porous base film is ≤9 μm; (2) The porosity of the porous base membrane is 35% to 60%.

65. The secondary battery according to claim 62 or 63, characterized in that: The isolation membrane includes a first functional layer and a second functional layer arranged on both sides of the porous base membrane, the first functional layer includes first inorganic particles, the second functional layer includes composite particles, the composite particles include second inorganic particles and non-fluoropolymer particles, the second inorganic particles are attached to the surface of the non-fluoropolymer particles and / or dispersed inside the non-fluoropolymer particles.

66. The secondary battery according to claim 65, characterized in that At least one of the following conditions is met: (1) The non-fluorinated polymer particles include acrylic polymer particles; (2) The first functional layer is located between the negative electrode plate and the porous base film, and the second functional layer is located between the positive electrode plate and the porous base film.

67. An electrical device, characterized in that: A secondary battery comprising the secondary battery according to any one of claims 1 to 66.

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