Secondary batteries and electrical devices

Abstract

The present application relates to a secondary battery and an electrical device, wherein a negative electrode plate in the secondary battery includes a negative electrode current collector and a negative electrode film layer, the negative electrode film layer is arranged on at least one side of the negative electrode current collector, the negative electrode film layer includes a negative electrode active material, the negative electrode active material includes a first graphite, and the Dv50 particle size of the first graphite is 2.2μm~7.7μm; 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 the mass content of the first solvent is 25%~40% based on the total mass of the organic solvent; the organic additive includes a first additive and a second additive, the first additive includes vinylene carbonate, and the second additive includes an ethylene carbonate derivative, and the mass percentage of the first additive in the electrolyte is 2%~10% based on the total mass of the electrolyte, and the mass percentage of the second additive in the electrolyte is 0.3%~6%.

Description

[0001] This application claims priority to PCT international application PCT / CN2024 / 102539, entitled “Secondary Batteries and Electrical Devices,” filed on June 28, 2024, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of battery technology, and in particular to a secondary battery and an electrical device. Background Art

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

[0004] In recent years, with the rapid development of secondary batteries such as lithium-ion batteries, they have been widely used in energy storage systems such as hydropower, thermal, wind, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. As the application range of secondary batteries becomes increasingly broad, the demand for fast-charging performance of secondary batteries is gradually increasing. However, it is currently difficult to achieve a balance between fast-charging performance and cycle performance. Therefore, how to ensure that secondary batteries have good fast-charging performance and cycle performance has become an urgent problem that needs to be solved. Summary of the Invention

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

[0006] In a first aspect of the present application, a secondary battery is provided, comprising:

[0007] 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 being disposed on at least one side of the positive electrode current collector, the positive electrode film layer comprising a positive electrode active material;

[0008] A negative electrode plate, the negative electrode plate 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 first graphite having a Dv50 particle size of 2.2 μm to 7.7 μm; and

[0009] 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 the mass content of the first solvent based on the total mass of the organic solvent is 25% to 40%; the organic additive comprising a first additive and a second additive, the first additive comprising vinylene carbonate, and the second additive comprising an 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%.

[0010] Therefore, the negative electrode active material of the above-mentioned secondary battery includes the above-mentioned first graphite with a smaller particle size. The negative electrode plate containing the first graphite can improve the fast charging performance of the battery. However, the small-particle graphite has more surface defects, stronger reaction activity, and consumes the electrolyte faster. In addition, the temperature rise of the battery cell is higher under fast charging conditions, which affects the stability of the electrolyte, and thus makes it difficult to improve the cycle performance of the battery. Therefore, by improving the first solvent, the first additive and the second additive in the above-mentioned electrolyte and their content, the electrolyte has good thermal stability, and a stable interface film is formed on the surface of the negative electrode plate, thereby reducing the electrolyte consumption rate and the DC internal resistance DCR of the battery, thereby improving the cycle performance and fast charging performance of the secondary battery. In this way, the above-mentioned secondary battery can take into account good fast charging performance, normal temperature cycle performance and high temperature cycle performance.

[0011] In any embodiment of the present application, the structure of the ethylene carbonate derivative is as follows:

[0012] , R1 and R2 each independently include any one of hydrogen, a halogen, a C1-C5 alkyl group, and a C1-C5 halogenated alkyl group, and R1 and R2 cannot both be hydrogen. These second additives have excellent film-forming properties, electrical conductivity, and stability, and can improve the battery's fast-charging and cycling performance, particularly room-temperature cycling performance.

[0013] In any embodiment of the present application, the ethylene carbonate derivative includes at least one of fluoroethylene carbonate, difluoroethylene carbonate and trifluoromethylethylene carbonate.

[0014] In any embodiment of the present application, the cyclic carbonate includes at least one of ethylene carbonate and propylene carbonate.

[0015] In any embodiment of the present application, the mass content of the first solvent is 30% to 40% based on the total mass of the organic solvent. Controlling the mass content of the first solvent in the organic solvent within this range can enable the battery to have better cycle performance.

[0016] In any embodiment of the present application, 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%. Controlling the mass content of the first additive and / or the second additive in the electrolyte within this optional range can enable the battery to have better cycle performance.

[0017] 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 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 of small-particle graphite being highly active and consuming the additive more quickly during cycling, resulting in a drop in cycling performance, thereby improving the cycling performance of the battery.

[0018] In any embodiment of the present application, 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.

[0019] In any embodiment of the present application, the mass of the electrolyte at a unit cell rated capacity of the secondary battery of 1 Ah 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%;

[0020] 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%.

[0021] In any embodiment of the present application, the powder compaction density of the positive electrode active material at 30000N is ≥2.43g / cm 3 , optional 2.48g / cm 3 ~2.85 g / cm 3 .

[0022] In any embodiment of the present application, the positive electrode active material includes at least one of an olivine-structured lithium-containing phosphate and its derivatives.

[0023] In any embodiment of the present application, the positive electrode active material includes:

[0024] a core portion comprising at least one of an olivine-structured lithium-containing phosphate and a derivative thereof; and

[0025] An ion-conducting layer is coated on the surface of the core portion, and the lithium-ion-conducting layer includes at least one element selected from the group consisting of Fe, C, Ti, Zr, Hf, Ge, and Sn.

[0026] By coating the core with an ion-conducting layer, the conductivity of the olivine-structured lithium-containing phosphate and its derivatives can be improved, the powder resistivity of the material can be reduced, and the migration rate of lithium ions can be promoted, thereby improving the fast charging capability of the battery and reducing the heat generation of the battery cell.

[0027] In any embodiment 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 z1 Compounds 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 comprises at least one of Na, K, and Mg; M1 comprises at least one of Mn, Fe, Co, and Ni; M2 comprises 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 comprises at least one of S, Si, Cl, B, C, N, and P; and Q1 comprises at least one of O and F. Olivine-structured lithium-containing phosphates have excellent cycling stability, which is beneficial for improving the cycling performance of battery cells.

[0028] 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.

[0029] In any embodiment of the present application, the ion-conducting layer comprises 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.

[0030] In any embodiment of the present application, the fast ion conductor comprises at least one of lithium iron titanium phosphate, lithium iron zirconium phosphate, and lithium iron tin phosphate. Coating the core surface with a fast ion conductor comprising a NASICON structure can significantly increase the rate of lithium ion transport during multiple lithium deintercalation and insertion at the positive terminal, improve the ionic conductivity of the positive electrode active material, enhance the rapid charging capability of the battery cell, and further increase the specific capacity and energy density of the corresponding battery cell.

[0031] In any embodiment of the present application, at least one of the following conditions is met:

[0032] (1) The compaction density of the positive electrode sheet is 2.5g / cm 3 ~2.8g / cm 3 ;

[0033] (2) The mass percentage of carbon in the positive electrode active material is 1% to 2%;

[0034] (3) The powder resistivity range of the positive electrode active material is R≤20Ω•cm, and optionally R≤11Ω•cm;

[0035] (4) The volume average particle size of the positive electrode active material satisfies: 1µm≤Dv50≤2µm, 0.4µm≤Dv10≤0.7µm.

[0036] In any embodiment of the present application, the positive electrode film layer further includes a lithium replenisher, and the lithium replenisher includes at least one of a ternary lithium replenisher 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. The lithium replenisher can replenish lithium ions to the positive electrode film layer, compensating for irreversible lithium ion loss in the system, increasing capacity, and thereby increasing the energy density of the battery cell.

[0037] 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 , 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.

[0038] In any embodiment of the present application, the positive electrode plate further includes a positive electrode conductive layer, which is arranged between the positive electrode current collector and the positive electrode film layer on at least one side, and the positive 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.

[0039] In any embodiment of the present application, the thickness of the positive electrode conductive layer is 0.5 μm to 2 μm.

[0040] 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 fluorine-containing acrylic resin;

[0041] 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%.

[0042] In any embodiment of the present application, the compaction density of the negative electrode sheet after the secondary battery is charged to 100% SOC at a charging rate of 0.33C is 1.15 g / cm 3 ~1.46g / cm 3 , optional 1.15g / cm 3 ~1.36g / cm 3 .

[0043] In any embodiment of the present application, the compaction density of the negative electrode sheet of the secondary battery after being charged to 100% SOC at a charging rate of 0.33C is 1.15-1.26 g / cm 3 , the mass content of the first additive in the electrolyte is 3%~8%.

[0044] In any embodiment of the present application, at least one of the following conditions is met:

[0045] (1) The mass content of the second additive in the electrolyte is 0.5% to 3%;

[0046] (2) The mass content of the first solvent in the organic solvent is 30% to 40%.

[0047] In any embodiment of the present application, the compaction density of the negative electrode sheet of the secondary battery after being charged to 100% SOC at a charging rate of 0.33C is greater than 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%.

[0048] In any embodiment of the present application, at least one of the following conditions is met:

[0049] (1) The mass content of the second additive in the electrolyte is 1% to 4%;

[0050] (2) The mass content of the first solvent in the organic solvent is 25% to 38%.

[0051] In any embodiment of the present application, the electrolyte further includes a second solvent, and the second solvent includes at least one of linear carbonate, carboxylate, ether, nitrile and sulfone.

[0052] In any embodiment of the present application, the second solvent includes a carboxylate; optionally, the carboxylate includes at least one of methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate and methyl butyrate.

[0053] 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 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 2% to 9%.

[0054] 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%.

[0055] 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, fluorine-containing sulfonyl imide salts, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate and lithium tetrafluorooxalatophosphate.

[0056] 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.

[0057] In any embodiment of the present application, the lithium salt includes at least one of LiFSI and LiPF6, and the lithium salt satisfies at least one of the following conditions:

[0058] (1) The concentration of LiFSI is 0.2 mol / L to 0.5 mol / L;

[0059] (2) The concentration of LiPF6 is 0.5 mol / L~1.3 mol / L;

[0060] (3) The lithium salt includes LiFSI and LiPF6, and the concentration ratio of the LiFSI to the LiPF6 is (2~5):10.

[0061] In any embodiment of the present application, the negative electrode plate further 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.

[0062] In any embodiment of the present application, the thickness of the negative electrode conductive layer is 0.5 μm to 2 μm.

[0063] 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, a water-soluble unsaturated resin, a water-based acrylic resin, polyvinyl alcohol, sodium alginate, and carboxymethyl chitosan.

[0064] In any embodiment of the present application, 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%.

[0065] In any embodiment of the present application, 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.

[0066] In any embodiment of the present application, the negative electrode film layer includes only one negative electrode active layer, the negative electrode active layer contains the first graphite, the Dv50 particle size of the first graphite is 4.2μm~7.2μm, and the Dv50 particle size of the second graphite is 7.8μm~14.8μm.

[0067] 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, it is 3:7 to 5:5.

[0068] 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% to 8%; or

[0069] 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%.

[0070] 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 stacked sequentially 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 7.8 μm~14.8 μm.

[0071] 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, it is 3:7 to 7:3.

[0072] In any embodiment of the present application, at least one of the following conditions is met:

[0073] (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; optionally 4:6 to 6:4;

[0074] (2) The mass content of the first graphite in the second negative electrode active layer is 20% to 70%; alternatively, 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%; 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 10%;

[0075] (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; optionally, the Dv50 particle size of the graphite in the first negative electrode active layer is 5.8 μm to 12.8 μm, optionally 7.8 μm to 12.8 μm; optionally, the Dv50 particle size of the graphite in the second negative electrode active layer is 2.2 μm to 7.7 μm, optionally 4.2 μm to 7.2 μm.

[0076] In any embodiment of the present application, the artificial graphite includes graphite body particles and a coating layer, the graphite body particles include secondary particles formed by aggregation of multiple primary particles, the coating layer is coated on the surface of the body particles, and the coating layer includes amorphous carbon.

[0077] In any embodiment of the present application, at least one of the following conditions is met:

[0078] (1) Based on the total mass of the artificial graphite, the mass content of the amorphous carbon is 2% to 5%;

[0079] (2) The powder resistivity of the artificial graphite is ≤0.04Ω•cm.

[0080] In any embodiment of the present application, the charge capacity of the first graphite at a rate of 0.1C in a button cell is ≥350 mAh / g, and can be selected from 350 mAh / g to 440 mAh / g.

[0081] 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 a silicon oxide 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%~10%, and can be optionally 1%~6%.

[0082] In any embodiment of the present application, the separator includes a porous base membrane and a functional layer disposed on at least one side of the porous base membrane.

[0083] In any embodiment of the present application, at least one of the following conditions is met:

[0084] (1) The thickness of the porous base membrane is ≤12 μm, and can be ≤9 μm;

[0085] (2) The porosity of the porous base membrane is 20% to 70%, and can be optionally 35% to 60%.

[0086] In any embodiment of the present application, 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, and 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.

[0087] In any embodiment of the present application, at least one of the following conditions is met:

[0088] (1) The non-fluorinated polymer particles include acrylic polymer particles;

[0089] (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.

[0090] A second aspect of the present application provides an electrical device comprising the secondary battery of the first aspect of the present application.

[0091] 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 description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0092] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the conventional technology, the following briefly introduces the drawings required for use in the embodiments or the conventional technology descriptions. Obviously, the drawings described below are merely embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the disclosed drawings without any creative work.

[0093] Figure 1 This is a schematic diagram of a battery cell according to one embodiment of the present application.

[0094] Figure 2 yes Figure 1 FIG. 1 is an exploded view of a battery cell according to an embodiment of the present application.

[0095] Figure 3 Schematic diagram of a battery module according to one embodiment of the present application.

[0096] Figure 4 Schematic diagram of a battery pack according to one embodiment of the present application.

[0097] Figure 5 yes Figure 4 An exploded view of a battery pack according to an embodiment of the present application is shown.

[0098] Figure 6 FIG. 1 is a schematic diagram of an electrical device using a secondary battery according to an embodiment of the present application as a power source.

[0099] Description of reference numerals:

[0100] 1. Battery pack; 2. Upper box; 3. Lower box; 4. Battery module; 5. Battery cell; 51. Housing; 52. Electrode assembly; 53. Cover; 6. Electrical device. DETAILED DESCRIPTION

[0101] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0102] " scope " disclosed in the present application can be limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and any end value can be included or not included independently, and can be arbitrarily combined, that is, any lower limit can form a scope with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 listed, and if the maximum range value 3,4 and 5 are also listed, then the following scope can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is merely an abbreviation for a combination of these values. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when a parameter is expressed as an integer selected from "2-10", this is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0103] In this application, "a plurality of" or "a plurality of" refers to a number greater than or equal to 2 unless otherwise specified. For example, "one or more" means one or more than or equal to two.

[0104] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0105] References to "embodiments" herein mean that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment or implementation of the present application. The appearance of such phrases in various locations in the specification does not necessarily refer to the same embodiment, nor does it necessarily refer to independent or alternative embodiments that are mutually exclusive with other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments. References to "implementations" herein have a similar understanding.

[0106] It will be appreciated by those skilled in the art that, in the methods of various embodiments or examples, the order in which the steps are written does not imply a strict order of execution and does not constitute any limitation on the implementation process, and the detailed order of execution of each step should be determined by its function and possible inherent logic. Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0107] In this application, open technical features or technical solutions described with words such as "contain," "include," and "includes" do not exclude additional members beyond the listed members unless otherwise specified, and can be regarded as providing both closed features or solutions consisting of the listed members and open features or solutions that include additional members beyond the listed members. For example, if A includes a1, a2, and a3, it may or may not include other members unless otherwise specified. This can be regarded as providing both the feature or solution of "A consists of a1, a2, and a3" and the feature or solution of "A includes not only a1, a2, and a3, but also other members."

[0108] In this 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.

[0109] In this application, the terms "optionally," "optional," and "optional" are optional and refer to either option being present or absent. If a technical solution contains multiple "options," each option is considered independent unless otherwise specified and there are no conflicts or constraints.

[0110] One embodiment of the present application provides a secondary battery, including a positive electrode sheet, a negative electrode sheet, and an electrolyte.

[0111] The positive electrode sheet includes 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 includes a positive electrode active material.

[0112] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer, wherein the negative electrode film layer is arranged on at least one side of the negative electrode current collector, the negative electrode film layer includes a negative electrode active material, and the negative electrode active material includes a first graphite, and the Dv50 particle size of the first graphite is 2.2μm~7.7μm.

[0113] The electrolyte includes an organic solvent and an organic additive. The organic solvent includes a first solvent. The first solvent includes a cyclic carbonate (EC), and the mass content of the first solvent is 25% to 40% based on the total mass of the organic solvent. The organic additive includes a first additive and a second additive. The first additive includes vinylene carbonate (VC), and the second additive includes an 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%.

[0114] Therefore, the negative electrode active material of the above-mentioned secondary battery includes the above-mentioned first graphite with a smaller particle size, so the negative electrode plate containing the first graphite can improve the fast charging performance of the battery. However, the small-particle graphite has more surface defects, stronger reaction activity, and consumes the electrolyte faster. In addition, the temperature rise of the battery cell is higher under fast charging conditions, which affects the stability of the electrolyte, and thus makes it difficult to improve the cycle performance of the battery. Therefore, by improving the first solvent, the first additive and the second additive in the above-mentioned electrolyte and their content, the electrolyte has good thermal stability, and a stable interface film is formed on the surface of the negative electrode plate, thereby reducing the electrolyte consumption rate and the DC internal resistance DCR of the battery, thereby improving the cycle performance and fast charging performance of the secondary battery. In this way, the above-mentioned secondary battery can take into account good fast charging performance, normal temperature cycle performance and high temperature cycle performance.

[0115] The first solvent includes a cyclic carbonate, which has a high dielectric constant and good film-forming properties. If the first solvent content in the electrolyte is too low, the electrolyte's inherent stability deteriorates, resulting in reduced conductivity. However, if the first solvent content is too high, the electrolyte's viscosity and melting point increase, which will also deteriorate the electrolyte's conductivity and the battery's kinetics, leading to poor cycling performance. Therefore, when the first solvent content is within the above range, the electrolyte can have good thermal stability and suitable conductivity.

[0116] The above-mentioned first additive includes vinylene carbonate (VC), and the second additive includes an ethylene carbonate derivative. The first additive and the second additive can participate in interfacial film formation. If the content of the first additive and the second additive is too low, the first solvent will participate too much in film formation, destroying the stability of the electrolyte, thereby accelerating the electrolyte consumption rate and deteriorating the battery's cycle performance and storage life; as the content of the first additive increases, the high-temperature cycle life of the battery is improved, but if the content of the first additive is too high, it will deteriorate the battery's kinetic window and DC internal resistance DCR, thereby causing cycle performance to deteriorate and being unfavorable for improving fast charging performance; as the content of the second additive increases, the battery's room temperature cycle life and fast charging performance are improved, but if the content of the second additive is too high, the battery's high-temperature performance deteriorates and the high-temperature cycle life decreases. Therefore, when the first additive and the second additive are each within the above-mentioned range, the electrolyte achieves a balance between film formation stability and battery kinetics.

[0117] Thus, by regulating the first solvent content within the aforementioned range, the electrolyte's thermal stability can be improved and its conductivity within an appropriate range. Simultaneously, regulating the first and second additives within the aforementioned ranges allows the electrolyte to achieve a balance between battery dynamics and film-forming stability, thereby reducing electrolyte consumption and improving the battery's room-temperature and high-temperature cycling performance and storage life. Furthermore, the battery also exhibits a lower DC internal resistance (DCR) while maintaining good fast-charging performance. This electrolyte is suitable for use in negative electrode plates and battery systems containing the aforementioned smaller-particle-size first graphite, enabling secondary batteries to achieve high fast-charging performance, room-temperature cycling performance, and high-temperature cycling performance.

[0118] electrolyte

[0119] 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).

[0120] 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%, or 40%. Furthermore, the mass content of the first solvent in the organic solvent is 25% to 38% or 30% to 40%, or within a range consisting of any of the above values as end values, and similarly hereinafter. Controlling the mass content of the first solvent in the organic solvent within this range can result in a battery having better cycle performance.

[0121] 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%, or 10%. Furthermore, the mass content of the first additive in the electrolyte is 3% to 8%. Furthermore, the first additive is vinylene carbonate (VC). Controlling the mass content of the first additive in the electrolyte within this selectable range can improve battery cycling performance, particularly high-temperature cycling performance.

[0122] In some embodiments of the present application, the structure of the ethylene carbonate derivative in the second additive is as follows:

[0123] , R1 and R2 each independently include any one of hydrogen, halogen, C1~C5 alkyl and C1~C5 haloalkyl, and R1 and R2 are not hydrogen at the same time. Furthermore, the halogen element includes at least one of fluorine, chlorine and bromine, and the C1~C5 alkyl and C1~C5 haloalkyl include but are not limited to at least one of halogenated or non-halogenated methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl and their isomers. 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 room temperature cycle performance.

[0124] Furthermore, the ethylene carbonate derivative includes at least one of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC) and trifluoromethylethylene carbonate.

[0125] 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%, or 6%. Furthermore, the mass content of the second additive in the electrolyte is 1.5% to 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 cycle performance, particularly room temperature cycling performance.

[0126] In some embodiments of the present application, the total mass content of the first additive and the second additive is 3% to 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%, or 12%. Furthermore, the total mass content of the first additive and the second additive is 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 graphite is highly active and consumes additives faster during the cycle, resulting in a drop in cycle performance, thereby improving the cycle performance of the battery.

[0127] In some embodiments of the present application, the electrolyte further includes a second solvent. Furthermore, the second solvent includes at least one of a linear carbonate, a carboxylate, an ether, a nitrile, and a sulfone. The second solvent, together with the first solvent, serves as a solvent to lower the melting point and viscosity of the electrolyte system and improve the lithium ion transport performance of the electrolyte.

[0128] Furthermore, 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).

[0129] Furthermore, the carboxylic acid ester 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 a carboxylic acid ester. Furthermore, the second solvent includes both a carboxylic acid ester and a linear carbonate.

[0130] Furthermore, the ether includes but is not limited to at least one of diethyl ether and 1,2-dimethoxyethane (DME, also known as ethylene glycol dimethyl ether).

[0131] Furthermore, the nitrile includes but is not limited to acetonitrile (AN).

[0132] Furthermore, the sulfone includes but is not limited to at least one of sulfolane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0133] Furthermore, the mass content of the second solvent in the organic solvent is 20% to 75%; this mass content may be 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 73%, or 75%. Furthermore, the mass content of the carboxylate in the organic solvent is 30% to 60%, or 30% to 75%. In one specific example, the second solvent is a carboxylate.

[0134] In some embodiments of the present application, the electrolyte further includes an electrolyte salt, and the concentration of the electrolyte salt in the electrolyte is 0.1 mol / L to 2 mol / L. As an example, the concentration of the electrolyte salt in the electrolyte 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, or 2 mol / L; further, it can be 0.6 mol / L to 1.3 mol / L, or within a range consisting of any two of the above values as end values.

[0135] In some embodiments of the present application, the electrolyte salt includes a lithium salt, and the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS, CF3SO2Li), lithium difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorodioxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0136] Optionally, the concentration of the lithium salt in the electrolyte is 0.7 mol / L to 1.5 mol / L. Optionally, the lithium salt includes at least one of a fluorine-containing sulfonyl imide salt and LiPF6. More preferably, the fluorine-containing sulfonyl imide salt includes at least one of LiFSI and LiTFSI.

[0137] Furthermore, the lithium salt includes at least one of LiFSI and LiPF6. Furthermore, the concentration of LiFSI in the electrolyte is 0.2mol / L~0.5mol / L; further, the concentration of LiPF6 in the electrolyte is 0.5mol / L~1.3mol / L. Furthermore, the lithium salt includes LiFSI and LiPF6, and the molar ratio of LiFSI and LiPF6 is (2~5):10. Lithium bis(fluorosulfonyl)imide LiFSI has good conductivity and heat resistance, and is not easily hydrolyzed at high temperatures. It 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, above 200°C, LiFSI will decompose and generate heat, deteriorating the safety margin of the battery cell. Therefore, adding LiPF6 as a lithium salt can also effectively improve the safety performance of the battery.

[0138] In some embodiments of the present application, the mass of the electrolyte at a unit cell rated capacity of 1Ah of the secondary battery is 2.2g~2.95g. As an example, it can be 2.2g, 2.3g, 2.4g, 2.5g, 2.6g, 2.65g, 2.7g, 2.8g, 2.9g, or 2.95g. Further, it can be 2.2g~2.65g or 2.65g~2.95g. The above-mentioned electrolyte of the present application is particularly suitable for batteries with a low filling coefficient system. The consumption rate of the electrolyte is low and the kinetics are better, so the cycle performance of batteries with a low filling coefficient system can be improved.

[0139] Furthermore, the mass of the electrolyte at a unit cell rated capacity of 1Ah of the secondary battery is 2.2g~2.65g, and the total mass content of the first additive and the second additive in the electrolyte is 5%~9%. The mass of the electrolyte at a unit cell rated capacity of 1Ah of the secondary battery is relatively small. How can the cycle performance of the battery with a low filling coefficient system be improved by appropriately increasing the total mass content of the first additive and the second additive? As an example, the mass of the electrolyte at a unit cell rated capacity of 1Ah of the secondary battery can be 2.2g, 2.3g, 2.4g, 2.5g, 2.6g, 2.65g, or a range consisting 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 a range consisting of any two of the above values.

[0140] Alternatively, the mass of the electrolyte at a unit cell rated capacity of the secondary battery of 1Ah is greater than 2.65g and less than or equal to 2.95g, and the total mass content of the first additive and the second additive in the electrolyte is 3.5% to 6.5%. The mass of the electrolyte at a unit cell rated capacity of the secondary battery of 1Ah is relatively large, and the total mass content of the first additive and the second additive can be appropriately reduced, thereby balancing cost and battery cycle performance. As an example, the mass of the electrolyte at a unit cell rated capacity of the secondary battery of 1Ah can be 2.68g, 2.7g, 2.8g, 2.9g, 2.95g, or a range consisting 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 consisting of any two of the above values.

[0141] The test method for the electrolyte mass of a secondary battery per unit cell rated capacity of 1Ah is as follows: ① Take the battery and weigh its mass M0; ② Disassemble the battery, pour out the free electrolyte, and remove the electrode, separator, mechanical parts, and adhesive tape; ③ Use dimethyl carbonate (DMC) to soak and clean the electrode, separator, mechanical parts, and adhesive tape for 24 hours, repeating the cleaning process at least three times; ④ After cleaning, place the electrode, separator, mechanical parts, and adhesive tape in an oven until completely dry; ⑤ Weigh the electrode, separator, mechanical parts, and adhesive tape, and record their mass as M1; ⑥ The electrolyte mass per unit cell rated capacity of the secondary battery of 1Ah = (M0 - M1) / a. a = the rated capacity of the secondary battery, in Ah.

[0142] As a non-limiting example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0143] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. 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 base layer. The composite current collector may be obtained by forming a metal material on a polymer material substrate. Non-limiting examples of the metal material in the positive electrode current collector may include at least one of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymer material base material in the positive electrode current collector may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), and the like.

[0144] In some embodiments, the thickness of the positive electrode current collector is 10 μm to 15 μm, optionally 12 μm to 15 μm. For example, the thickness of the positive electrode 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 consisting of any two of the above values.

[0145] When the thickness of the positive electrode current collector is within the above range, the positive electrode current collector has a relatively excellent current flow capacity and can enable the battery cell to have a higher energy density.

[0146] In the embodiment of the present application, the thickness of the positive electrode film layer and the positive electrode current collector has a meaning well known in the art and can be detected by equipment 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 electrode current collector is removed, and the thickness of the positive electrode 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 electrode 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 electrode current collector) / 2.

[0147] The positive electrode film layer is typically formed by coating a positive electrode slurry onto a positive electrode current collector, drying it, and cold pressing it. The positive electrode slurry is typically formed by dispersing the positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring them uniformly. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP).

[0148] The positive electrode sheet does not exclude other additional functional layers in addition to 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 electrode current collector and the positive electrode film layer and disposed on the surface of the positive electrode current collector. In other embodiments, the positive electrode sheet of the embodiments of the present application further includes a protective layer covering the surface of the positive electrode film layer.

[0149] The positive electrode active material can be a positive electrode active material for batteries known in the art. In some embodiments, the powder compaction density of the positive electrode active material at 30,000 N is ≥ 2.43 g / cm 3 , optional 2.48g / cm 3 ~2.85 g / cm 3 Furthermore, the powder compaction density of the positive electrode active material at 30000N is 2.5g / cm 3 ~2.8g / cm 3 .

[0150] The use of the positive electrode active material with a higher powder compaction density can increase the compaction density of the positive electrode sheet, thereby improving the energy density of the battery.

[0151] As an example, the powder compaction density of the positive electrode active material in the positive electrode sheet at 30000N can be 2.43g / cm 3 , 2.45g / cm 3 , 2.5g / cm 3 , 2.55g / cm 3 , 2.6g / cm 3 , 2.65g / cm 3 , 2.7g / cm 3 , 2.75g / cm 3 , 2.8g / cm3 , 2.85g / cm 3 .

[0152] As a non-limiting example, the positive electrode active material may include at least one of the following materials: a phosphate-based positive electrode material, a lithium transition metal oxide, and modified compounds thereof, wherein the phosphate-based positive electrode material includes at least one of an olivine-structured lithium-containing phosphate and its derivatives.

[0153] Furthermore, the positive electrode active material includes at least one of an olivine-structured lithium-containing phosphate and its derivatives. Lithium-containing phosphates and their derivatives have smaller particle sizes, larger specific surface areas, and are more susceptible to water absorption. Consequently, electrolyte hydrolysis in these battery systems is more severe, generating more HF during hydrolysis. Consequently, electrolyte consumption is a significant issue. Using these electrolytes can leverage their slower electrolyte consumption rate, thereby improving the cycle performance of these batteries. Furthermore, they can leverage the advantages of lithium-containing phosphates and their derivatives, such as high energy density, long cycle life, and excellent safety.

[0154] 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 z1 Compounds 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 comprises at least one of Na, K, and Mg; M1 comprises at least one of Mn, Fe, Co, and Ni; M2 comprises 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 comprises at least one of S, Si, Cl, B, C, N, and P; and Q1 comprises at least one of O and F. Olivine-structured lithium-containing phosphates have excellent cycling stability, which is beneficial for improving the cycling performance of battery cells.

[0155] Furthermore, Li x1 A1 y1 M1 a1 M2 b1 P 1-c1 X c1 Q1 z1The compound includes at least one of lithium iron phosphate (LiFePO4), lithium manganese phosphate (LiMnPO4), lithium nickel phosphate (LiNiPO4) and lithium cobalt phosphate (LiCoPO4), and may also be a doped compound of these compounds.

[0156] The olivine-structured lithium-containing phosphate 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 portion and an ion-conducting layer. The core portion includes at least one of the olivine-structured lithium-containing phosphate and its derivatives, and the ion-conducting layer is coated on the surface of the core portion. The lithium-ion-conducting layer includes at least one element selected from Fe, C, Ti, Zr, Hf, Ge, and Sn.

[0157] By coating the core with an ion-conducting layer, the conductivity of the olivine-structured lithium-containing phosphate and its derivatives can be improved, the powder resistivity of the material can be reduced, and the migration rate of lithium ions can be promoted, thereby improving the fast charging capability of the battery and reducing the heat generation of the battery cell.

[0158] Furthermore, 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.

[0159] Exemplarily, the fast ion conductor is a material having a NASICON structure, such as one or more of lithium iron titanium phosphate Li2FeTi(PO4)3, lithium iron zirconium phosphate Li2FeZr(PO4)3, and lithium iron tin phosphate Li2FeSn(PO4)3.

[0160] Fast ion conductors with a NASICON structure are materials with ultrafast ion conduction capabilities. They possess abundant three-dimensional lithium ion diffusion and transport channels, offering advantages such as high ion conduction efficiency and strong structural stability during multiple lithium stripping and insertion processes. Coating a fast ion conductor with a NASICON structure on the core surface can significantly increase the lithium ion transport rate during multiple stripping and insertion processes at the positive electrode, improving the ionic conductivity of the positive electrode active material, and enhancing the rapid charging capability of the battery cell. Furthermore, it can increase the specific capacity and the energy density of the corresponding battery cell.

[0161] In some embodiments, the ion-conducting layer further includes carbon to further improve the material.

[0162] The carbon element and the fast ion conductor can be arranged in layers. For example, the carbon element serves as a separate carbon coating layer, and the fast ion conductor serves as a separate fast ion conductor layer. The carbon coating layer can be coated on the surface of the core, with the fast ion conductor layer located on the surface of the carbon coating layer, i.e., the fast ion conductor layer is located on the side of the carbon coating layer facing away from the core. Alternatively, the fast ion conductor layer can be coated on the surface of the core, with the carbon coating layer located on the surface of the fast ion conductor layer, i.e., the carbon coating layer is located on the side of the fast ion conductor layer facing away from the core. Of course, the carbon element and the fast ion conductor can also be arranged in the same layer.

[0163] Optionally, a carbon coating layer can be formed from an organic carbon source, such as glucose or polyethylene glycol, and coated onto the surface of the fast ion conductor layer through a carbonization process. The carbon coating layer can partially or completely cover the fast ion conductor layer. The carbon coating layer can significantly improve the electronic conductivity of the core, compensating for the core's poor electronic conductivity and increasing the energy density of the battery cell.

[0164] Specifically, the provision of the carbon coating layer enables the positive electrode active material of the present application to have the following advantages:

[0165] The carbon coating layer in the positive electrode active material of the present application provides a suitable channel for the transmission of electrons, which can significantly improve the conduction rate of electrons in multiple lithium delithiation and lithium insertion processes, improve the electronic conductivity of lithium-containing phosphates, improve the charging capacity of the corresponding battery cells, and also improve the energy density.

[0166] The carbon coating layer of the positive electrode active material of the present application is loose and porous, which enables the electrolyte to be in 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 capacity of the battery cell.

[0167] Coating a carbon coating layer on the surface of the lithium-containing phosphate can not only improve the conductivity of the lithium-containing phosphate, but also improve the structural stability of the positive electrode active material, effectively preventing the iron dissolution of the positive electrode active material during long-term storage and cyclic use of the battery cell, thereby ensuring the cycle life of the battery cell.

[0168] The cathode active material of this application, based on a lithium-containing phosphate, fully leverages the advantages of lithium-containing phosphates: low cost, high reliability, and good cycling stability. It also utilizes an ion-conducting layer (a fast ion conductor layer and a carbon coating layer) to address their poor electronic and ionic conductivity. Battery cells prepared with this cathode active material exhibit significantly improved energy density while maintaining excellent cycling performance.

[0169] In some embodiments, the mass content of carbon in the positive electrode active material is 1% to 2%. For 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, thereby improving the fast charging performance of the battery. It is understandable that the carbon element can come from, but is not limited to, a coated carbon layer. As an example, the surface of an olivine-structured lithium-containing phosphate and its derivatives is coated with a carbon coating layer.

[0170] In some embodiments, the powder resistivity of the positive electrode active material is ≤20Ω•cm, thereby further improving the conductivity of the positive electrode active material and thereby enhancing the fast charging performance of the battery. As an example, the powder resistivity of the positive electrode active material can be 20Ω•cm, 15Ω•cm, 10Ω•cm, 8Ω•cm, 5Ω•cm, etc., and optionally ≤11Ω•cm.

[0171] In some embodiments, the volume average particle size of the positive electrode active material satisfies the following conditions: 1µm ≤ Dv50 ≤ 2µm, and 0.4µm ≤ Dv10 ≤ 0.7µm, thereby further improving the fast charging and power performance of the battery. For example, the Dv50 particle size of the positive electrode active material can be 1µm, 1.5µm, or 2µm. For example, the volume average particle size Dv10 of the positive electrode active material can be 0.4µm, 0.5µm, 0.6µm, or 0.7µm.

[0172] Herein, Dv50 and Dv10 are well-known in the art and can be measured using methods known in the art. For example, they can be measured using a laser particle size analyzer (e.g., Malvern Master Size 3000). Dv50 represents the particle size at which the cumulative volume percentage of particles, starting from the smallest particle size, reaches 50%, based on the particle size volume distribution. Dv10 represents the particle size at which the cumulative volume percentage of particles, starting from the smallest particle size, reaches 10%, based on the particle size volume distribution.

[0173] Particle size and volume distribution can be determined by the following method: Add an appropriate amount of the sample to be tested to a clean beaker and thoroughly sonicate to ensure complete dispersion. The test instrument is a Malvern 2000 (USA). The sample is poured into the injection tower and then circulated with the solution into the test optical system. The particles are illuminated by a laser beam, and the energy distribution of the scattered light is measured to determine the particle size distribution (shading degree: 8%-12%). A particle size and volume distribution graph is then plotted based on the test data.

[0174] In some embodiments, the positive electrode film layer further includes a lithium replenisher. Furthermore, the lithium replenisher includes at least one of a ternary lithium replenisher 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. The lithium replenisher can replenish lithium ions in the positive electrode film layer, compensating for irreversible lithium ion loss within the system, increasing capacity, and thereby improving the energy density of the battery cell.

[0175] Furthermore, 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.

[0176] Furthermore, 0.9≤x2+y2≤2.1.

[0177] For example, the ternary material includes LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), LiNi 0.80 Co 0.15 Al 0.05 At least one of O2.

[0178] The lithium replenisher can be located in the same layer as the positive electrode active material, or in different layers. When the lithium replenisher and the positive electrode active material are located in different layers, the lithium replenisher can be located in the lithium replenisher layer, and the positive electrode active material can be located in the positive electrode active material layer. In other words, the positive electrode film layer includes a lithium replenisher layer and a positive electrode active material layer. The positive electrode active material layer can be arranged on at least one side of the positive electrode current collector, and the lithium replenisher layer can be located between the positive electrode active material layer and the positive electrode current collector. Alternatively, the lithium replenisher layer can be arranged on at least one side of the positive electrode current collector, and the positive electrode active material layer can be located between the lithium replenisher layer and the positive electrode current collector. Optionally, the lithium replenisher layer can be located between the positive electrode active material layer and the positive electrode current collector.

[0179] In some embodiments, the mass content of the positive electrode active material in the positive electrode film layer is 80% to 98%. As an example, the mass content may be 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 96%, or 98%. Furthermore, the mass content of the positive electrode active material in the positive electrode film layer may be 90% to 98%.

[0180] In some embodiments, the positive electrode film layer may also optionally include a binder. As non-limiting examples, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorinated acrylate resin. In some embodiments, the binder content is ≤5% by weight based on the total weight of the positive electrode film layer.

[0181] In some embodiments, the positive electrode film layer may further include a conductive agent. As non-limiting examples, 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, the conductive agent comprises ≤5% by weight based on the total weight of the positive electrode film layer.

[0182] In some embodiments, the positive electrode sheet can be prepared by dispersing the components for preparing the positive electrode sheet, 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 side of a positive electrode current collector, and performing drying, cold pressing, and other processes to obtain the positive electrode sheet. The solvent can be selected from, but not limited to, any of the aforementioned embodiments, such as N-methylpyrrolidone (NMP). The positive electrode slurry can be coated on a single surface of the positive electrode current collector or on both surfaces of the positive electrode current collector.

[0183] In some embodiments, the positive electrode sheet further includes a positive conductive layer, which is disposed between the positive current collector and the positive electrode film layer on at least one side. The positive conductive layer includes a conductive agent. The positive conductive layer can also be formed by first coating the surface of the positive current collector with a corresponding slurry, then coating the above-mentioned positive electrode slurry, and drying to form the positive electrode sheet. The positive conductive layer can enhance the bonding strength between the positive electrode film layer and the positive current collector, as well as the overall conductivity of the positive electrode sheet, thereby improving the electron transfer rate.

[0184] Furthermore, 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 sheet and reducing the heat generation of the battery.

[0185] Furthermore, the thickness of the positive electrode conductive layer is 0.5 μm to 2 μm, and as examples, 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, the conductivity of the positive electrode sheet can be further improved while also increasing the energy density of the battery cell.

[0186] Furthermore, the positive electrode conductive layer also includes a binder. The binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and a fluorinated acrylic resin. The binder in the positive electrode conductive layer can improve the bonding between the positive electrode current collector and the positive electrode film, thereby enhancing the structural stability of the positive electrode sheet.

[0187] Optionally, in the positive electrode conductive layer, the weight content of the conductive agent is 30% to 50%, and as examples, it can be 30%, 35%, 40%, 45%, or 50%. Optionally, in the positive electrode conductive layer, the weight content of the binder is 50% to 70%, and as examples, it can be 50%, 55%, 60%, 65%, or 70%. In some examples, the positive electrode conductive layer is composed of the conductive agent and the binder.

[0188] Negative electrode

[0189] As a non-limiting example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0190] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be obtained by forming a metal material on a polymer substrate. Non-limiting examples of the metal material in the negative electrode current collector may include at least one of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymer substrate in the negative electrode current collector may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), and the like.

[0191] In some embodiments, the compact density of the negative electrode sheet after the secondary battery is charged to 100% SOC at a charge rate of 0.33C is 1.15 g / cm 3 ~1.46g / cm 3 , optional 1.15g / cm 3 ~1.36g / cm 3 . Thus, the above-mentioned negative electrode sheet still has a high compaction density after being fully charged. For example, after the secondary battery is charged to 100% SOC at a charge rate of 0.33C, the compaction density of the negative electrode sheet is 1.15g / cm 3 , 1.18g / cm 3 , 1.20g / cm 3 , 1.22g / cm 3 , 1.25g / cm 3 , 1.28g / cm 3 , 1.3g / cm 3 , 1.32g / cm 3 , 1.35g / cm 3 , 1.36g / cm 3 , 1.38g / cm 3 , 1.4g / cm 3 , 1.42g / cm 3 , 1.45g / cm 3 , 1.46g / cm 3 or a range consisting 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. Furthermore, because the negative electrode active material in the negative electrode film layer is densely packed, the contact resistance between particles is low, which can further reduce the resistance of the electrode sheet and thus reduce heat generation.

[0192] In the embodiment of the present application, the compaction density of the negative electrode sheet after the secondary battery is charged to 100% SOC at a charging rate of 0.33C has a meaning commonly known in the art, that is, the positive electrode sheet is disassembled from the battery cell charged to 100% SOC at a charging rate of 0.33C, and the compaction density of the positive electrode film layer is measured.

[0193] In the embodiment of the present application, 100% SOC is defined as follows:

[0194] The battery cell was charged at a constant current rate of 0.33C to the upper limit voltage of the battery, and then charged at a constant voltage rate of 0.05C, corresponding to a state of 100% SOC of the battery cell. Correspondingly, the battery cell was discharged at a constant current rate of 0.33C to the cut-off voltage, corresponding to a state of 0% SOC of the battery cell.

[0195] Due to the different types of positive electrode active materials in the battery, the full charge cut-off voltage may also be different. For example, the upper limit voltage of battery charging can be 3.65V or 3.8V; the battery discharge cut-off voltage can be 2.5V or 2.0V. Taking the positive electrode active material in the positive electrode plate as an example, the above secondary battery is charged to 3.65V at a charging rate of 0.33C, and then charged to 0.05C at a constant voltage (that is, charged to 100% SOC at a charging rate of 0.33C). The compaction density of the negative electrode plate is 1.15g / cm 3 ~1.46g / cm 3 .

[0196] In some embodiments, the compaction density of the negative electrode sheet after cold pressing is 1.5 g / cm 3 ~1.7g / cm 3 , optional 1.55g / cm 3 ~1.65g / cm 3 The compaction density of the negative electrode after cold pressing refers to the compaction density of the negative electrode after cold pressing and before assembly into a battery.

[0197] In some embodiments, the secondary battery is charged to 100% SOC at a charge rate of 0.33C, and the compaction density of the negative electrode sheet is 1.15-1.26 g / cm 3 ; At the same time, the mass content of the first additive in the electrolyte is 3%~8%.

[0198] The lower the full-charge density of the negative electrode sheet, the greater the rebound thickness or the lower the initial density, and the stronger the graphite activity. Therefore, more electrolyte is consumed, and more additives need to be added to the electrolyte to enhance the stability of the negative electrode sheet's interfacial film and improve the battery's cycling performance. Therefore, there is a matching relationship between the compaction density of the negative electrode sheet and the mass content of the first additive in the electrolyte. When the secondary battery is charged to 100% SOC at a charge rate of 0.33C, the compaction density of the negative electrode sheet is within the above range, and the mass content of the first additive in the electrolyte is 3% to 8%, which can simultaneously achieve a better balance between high fast-charging performance and cycling performance.

[0199] The second additive in the electrolyte has a low film-forming impedance, which can improve the dynamic performance of the battery and thus improve the battery ID fast charging performance, but its content should not be too high to further improve the battery cycle performance. Therefore, there is a matching relationship between the compaction density of the negative electrode sheet and the mass content of the second additive in the electrolyte. Furthermore, when the secondary battery is charged to 100% SOC at a charge rate of 0.33C, the compaction density of the negative electrode sheet is between 1.15 and 1.26 g / cm 3 , the mass content of the second additive in the electrolyte is 0.5%~3%.

[0200] Furthermore, when the secondary battery is charged to 100% SOC at a charge rate of 0.33C, the compaction density of the negative electrode sheet 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%.

[0201] Furthermore, when the secondary battery is charged to 100% SOC at a charge rate of 0.33C, the compaction density of the negative electrode sheet is 1.15-1.26 g / cm 3 The mass of the electrolyte of the secondary battery per unit cell at a rated capacity of 1Ah is 2.5g~3.0g.

[0202] In some embodiments, the compaction density of the negative electrode sheet of the secondary battery after being charged to 100% SOC at a charge rate of 0.33C is greater than 1.26 g / cm 3 and ≤1.36g / cm 3 The mass content of the first additive in the electrolyte is 2.5% to 6.5%. When the secondary battery is charged to 100% SOC at a charge rate of 0.33C, the compaction density of the negative electrode sheet is within the above range. The mass content of the first additive in the electrolyte is 2.5% to 6.5%, which can simultaneously achieve high fast-charging performance and cycle performance.

[0203] Furthermore, when the secondary battery is charged to 100% SOC at a charge rate of 0.33C, the compaction density of the negative electrode sheet is greater than 1.26 g / cm 3 and ≤1.36g / cm 3 The mass content of the second additive in the electrolyte is 1% to 4%. Furthermore, the mass content of the first solvent in the organic solvent of the electrolyte is 25% to 38%.

[0204] Furthermore, when the secondary battery is charged to 100% SOC at a charge rate of 0.33C, the compaction density of the negative electrode sheet is greater than 1.26 g / cm 3 and ≤1.36g / cm 3 The mass of the electrolyte of the secondary battery per unit cell at a rated capacity of 1Ah is 2.2g~2.8g.

[0205] In some embodiments, the charging time of the secondary battery from 10% SOC to 80% SOC at 30°C is 6 minutes to 15 minutes, 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 2% to 9%. In this way, on the basis of using high-pressure dense graphite to provide a higher energy density, the battery is also a fast-charging type battery. By adding the above-mentioned content of carboxylic acid ester to the electrolyte and increasing the amount of the first additive and the second additive, the secondary battery has higher energy density, fast charging performance and cycle performance. Furthermore, 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%.

[0206] In some embodiments, the charging process of the secondary battery from 10% state of charge to 80% state of charge 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, for example, 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 consisting of any two of the above values.

[0207] The secondary battery includes multiple charging steps from a 10% state of charge to a 40% state of charge. For any charging step, it can be charged at any rate between 5C and 10C. The charging rate corresponding to each charging step can be any value of 5C, 5.5C, 6C, 6.5C, 7C, 7.5C, 8C, 8.5C, 9C, 9.5C, 10C, or a value in the range of any two of the above values.

[0208] The secondary battery also includes multiple charging steps from a 40% state of charge to an 80% state of charge, the charging rate of any charging step is less than the charging rate of any charging step from a 10% state of charge to a 40% state of charge, and the charging rate of the step of charging to an 80% state of charge is any value between 2.5C and 5C, for example, it can be 2.7C.

[0209] For example, the charging process of the secondary battery from 10% to 80% can be performed as follows:

[0210] Charge from 10% SOC to 15% SOC at 5.0C constant current;

[0211] Charge from 15% SOC to 20% SOC at 5.0C constant current;

[0212] Charge from 20% SOC to 25% SOC at 5.0C constant current;

[0213] Charge from 25% SOC to 30% SOC at 5.0C constant current;

[0214] Charge from 30% SOC to 35% SOC at 5.0C constant current;

[0215] Charge from 35% SOC to 40% SOC at 5.0C constant current;

[0216] Charge from 40% SOC to 45% SOC at 4.6C constant current;

[0217] Charge from 45% SOC to 50% SOC at 4.3C constant current;

[0218] Charge from 50% SOC to 55% SOC at 4.0C constant current;

[0219] Charge from 55% SOC to 60% SOC at 3.7C constant current;

[0220] Charge from 60% SOC to 65% SOC at 3.4C constant current;

[0221] Charge from 65% SOC to 70% SOC at 3.1C constant current;

[0222] Charge from 70% SOC to 75% SOC at 2.9C constant current;

[0223] Charge from 75% SOC to 80% SOC at 2.7C constant current.

[0224] In some embodiments, the charging time of the secondary battery from 10% state of charge to 80% state of charge is 6 min to 15 min. Exemplarily, the charging time of the secondary battery from 10% state of charge to 80% state of charge 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 a range consisting of any two of the above values.

[0225] In some embodiments, the negative electrode plate further includes a negative electrode conductive layer disposed between the negative electrode current collector and at least one of the negative electrode film layers. The negative electrode conductive layer can enhance the overall conductivity of the negative electrode plate, thereby increasing the electron transfer rate.

[0226] 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, then coating the negative electrode slurry, and drying to form the negative electrode sheet. Furthermore, 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.

[0227] Optionally, the thickness of the negative electrode conductive layer is 0.5 μm to 2 μm, for example, 0.5 μm, 1 μm, 1.5 μm, 2 μm, or a range consisting of any two of these values. When the thickness of the negative electrode conductive layer is within this range, the conductivity of the negative electrode sheet can be further improved, thereby reducing heat generation in the negative electrode sheet, thereby reducing heat generation in the battery cell; while also increasing the energy density of the battery cell.

[0228] In some embodiments, the negative electrode conductive layer includes a binder comprising at least one of styrene-butadiene rubber (SBR), a water-soluble unsaturated resin, a 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 and the negative electrode current collector, as well as the overall conductivity of the negative electrode sheet, thereby improving the electron transfer rate.

[0229] Optionally, in the negative electrode conductive layer, the weight content of the conductive agent is 20% to 40%, and illustratively, it can be 20%, 25%, 30%, 35%, 40%, or a range consisting of any two of the above values. Optionally, in the negative electrode conductive layer, the weight content of the binder is 60% to 80%, and illustratively, it can be 60%, 65%, 70%, 75%, 80%, or a range consisting of any two of the above values.

[0230] In some embodiments, the negative electrode film layer may further include a binder. The binder may 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).

[0231] In some embodiments, the negative electrode film layer may further include a conductive agent, which may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0232] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0233] In some embodiments, the negative electrode sheet can be prepared by dispersing the aforementioned components for preparing the negative electrode sheet, such as the negative electrode active material, conductive agent, binder, and any other components, in a solvent (a non-limiting example of the solvent is deionized water) to form a negative electrode slurry; coating the negative electrode slurry on at least one side of a negative electrode current collector, and performing drying, cold pressing, and other processes to obtain the negative electrode sheet. The negative electrode current collector surface coated with the negative electrode slurry can be a single surface of the negative electrode current collector or both surfaces of the negative electrode current collector.

[0234] Furthermore, the first graphite comprises at least one of artificial graphite and natural graphite. Furthermore, artificial graphite has fewer surface active sites and consumes the first solvent and first additive in the electrolyte at a lower rate, thereby meeting the battery's long life requirements. Furthermore, the graphite has a discharge capacity of 358 mAh / g or less. Within this range, the graphite exhibits suitable activity, which helps reduce electrolyte consumption and improves the battery's cycle performance.

[0235] The first graphite may have a Dv50 particle size of 2.2 μm to 7.7 μm. For example, the first graphite may 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 consisting of any two of the foregoing values. Furthermore, the first graphite may have a Dv50 particle size of 2.2 μm to 7 μm.

[0236] In some embodiments, 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.

[0237] In one embodiment, the negative electrode film layer includes only one negative electrode active layer, which contains the first graphite and the second graphite. The first graphite has a Dv50 particle size of 4.2μm to 7.2μm, and the second graphite has a Dv50 particle size of 7.8μm to 14.8μm. The first graphite has a smaller particle size range and a lower compaction density. In addition, it is more active in reacting with the electrolyte, thus affecting the battery's energy density, cycle performance, and storage performance. To further improve the battery's energy density, cycle performance, and storage performance, the larger second graphite is added to the negative electrode active layer.

[0238] 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 consisting of any two of the above values.

[0239] 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, the mass ratio can be 2:8, 3:7, 4:6, 5:5, 6:4 or a range consisting of any two of the above values.

[0240] Furthermore, the mass content of the first graphite in the negative electrode active layer in which it is located is 20%~70%. As an example, the mass content of the first graphite in the negative electrode active layer in which it is located is 20%, 25%, 30%, 35%, 40%, 45%, 48%, 50%, 55%, 60%, 65%, 70% or a range consisting of any two of the above values.

[0241] Furthermore, the total mass content of the first graphite and the second graphite in the negative electrode active layer in which they are located is 30% to 98%. As an example, the 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 consisting of any two of the above values.

[0242] Optionally, the mass content of the first graphite in the negative electrode active layer is ≥20% and <50%, and as an example it can be 20%, 25%, 30%, 35%, 40%, 45%, 48%, and the total mass content of the first additive and the second additive in the electrolyte is 3% to 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 consisting of any two of the above values. There is a matching relationship between the content of the first graphite and the content of the additive in the electrolyte. Through the above setting, 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 cycle performance of the battery.

[0243] Optionally, the mass content of the first graphite in the negative electrode active layer is 50% to 70%, as an example, it can be 50%, 55%, 60%, 65%, 70% or a range consisting of any two of the above values, and the total mass content of the first additive and the second additive in the electrolyte is 4% to 10%, 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 consisting 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. 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 cycle performance of the battery.

[0244] In another embodiment, the negative electrode film layer includes a first negative electrode active layer and a second negative electrode active layer stacked sequentially 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 the artificial graphite and the natural graphite, and the second negative electrode active layer includes a first graphite and a third graphite, the first graphite includes the artificial graphite, and the Dv50 particle size of the third graphite is 7.8μm~14.8μm. Artificial graphite has fewer surface active sites and a lower consumption rate of the first solvent and the first additive in the electrolyte. The first graphite is arranged in the upper second negative electrode active layer, and a larger particle size third graphite is added to the second negative electrode active layer to further improve the energy density, cycle performance, and storage performance of the battery.

[0245] 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; optionally 3:7 to 7:3. As an example, the mass ratio can be 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, or a range consisting of any two of the above values.

[0246] Furthermore, the mass content of the first graphite in the second negative electrode active layer is 20% to 70%. As an example, the mass content of the first graphite in the negative electrode active layer is 20%, 25%, 30%, 35%, 40%, 45%, 48%, 50%, 55%, 60%, 65%, 70% or a range consisting of any two of the above values.

[0247] Optionally, the mass content of the first graphite in the second negative electrode active layer is ≥20% and <50%, and as an example it can be 20%, 25%, 30%, 35%, 40%, 45%, 48%, and the total mass content of the first additive and the second additive in the electrolyte is 3% to 7%. 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% or a range consisting of any two of the above values. There is a matching relationship between the content of the first graphite and the content of the additive in the electrolyte. Through the above setting, 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 cycle performance of the battery.

[0248] Optionally, the mass content of the first graphite in the second negative electrode active layer is 50% to 70%, and as an example, it can be 50%, 55%, 60%, 65%, 70% or a range consisting 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% to 8%. As an example, 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%, and 8%. The higher the content of the first graphite, the more additives need to be added to 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 cycle performance of the battery.

[0249] Furthermore, 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. Still further, the Dv50 particle size of the graphite in the first negative electrode active layer is > 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 is reduced, the contact area between the negative electrode active material particles is increased, the conductive channels and bridges are increased, and the active area that can participate in the reaction is increased, thereby significantly improving the specific capacity and fast charging performance of the battery; and the addition of graphite with a larger particle size in the lower first negative electrode active layer causes the pores in the first negative electrode active layer to be larger and have better electrolyte infiltration performance, which can further help improve the fast charging performance and cycle performance of the battery.

[0250] Furthermore, 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 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 consisting of any two of the above values.

[0251] Furthermore, the Dv50 particle size of the first graphite in the second negative electrode active layer is 2.2 μm to 7.7 μm, and can be optionally 4.2 μm to 7.2 μm.

[0252] Furthermore, the thickness of the second negative electrode active layer accounts for 30% to 70% of the total thickness of the first negative electrode active layer and the second negative electrode active layer, for example, it can be 30%, 40%, 50%, 60%, 70% or a range consisting of any two of the above values.

[0253] 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, and then performing drying, cold pressing and other processes.

[0254] In some embodiments, the artificial graphite comprises graphite particles and a coating layer, wherein the graphite particles comprise secondary particles formed by the aggregation of multiple primary particles. The coating layer coats the surface of the graphite particles and comprises amorphous carbon. Amorphous carbon refers to a transitional carbon material with a very low degree of graphite crystallization, nearly an amorphous form (or lacking a fixed shape and periodic structural regularity). In this application, amorphous carbon refers to the product of carbonization of an organic carbon source.

[0255] The graphite main particles include secondary particles, so there are more migration paths for lithium ions in artificial graphite, and the migration paths in primary particles are shorter, which can increase the migration rate of lithium ions; the amorphous carbon layer has more end faces and defects, which increases the number of sites that can insert and remove lithium ions, making the conductivity of the amorphous carbon layer better, which can reduce the internal resistance of the negative electrode plate and reduce the heat generation of the battery cell.

[0256] Furthermore, 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 consisting of any two of the foregoing values.

[0257] When the mass content of the amorphous carbon layer is within the above range, the internal resistance of the negative electrode plate can be further reduced, and the heat generation of the battery cell can be reduced.

[0258] In the embodiment of the present application, artificial graphite can be prepared by methods known in the art. For example, the preparation method includes: providing graphite particles and an organic carbon source, mixing the two, and forming an amorphous carbon layer on at least a portion of the surface of the graphite particles after carbonization.

[0259] Optionally, the organic carbon source includes one or more of coal tar, petroleum tar, phenolic resin, and coconut shell. Further, the organic carbon source includes petroleum tar. Optionally, the softening point of the coal tar or petroleum tar is below 250°C.

[0260] Optionally, the carbonization temperature is 700° C. to 1800° C. Optionally, the carbonization temperature is 1000° C. to 1300° C. When the carbonization 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 a portion of the surface of the artificial graphite.

[0261] Optionally, the carbonization treatment time is 1 hour to 6 hours.

[0262] Furthermore, the powder resistivity of the artificial graphite is ≤0.04Ω•cm.

[0263] In some embodiments, the charge capacity of graphite at a rate of 0.1C in a button cell is ≥350 mAh / g, and can be selected from 350 mAh / g to 440 mAh / g.

[0264] In some embodiments, the negative electrode active material may include not only the graphite mentioned above but also a silicon-based material. The introduction of the silicon-based material can increase the capacity of the negative electrode active material and improve the energy density of the battery cell.

[0265] Further, the silicon-based material may include at least one of a silicon-oxygen compound and a silicon-carbon composite.

[0266] Furthermore, the mass content of silicon in the silicon-based material in the negative electrode active material is 0.3% to 10%, optionally 1% to 6%. For example, the mass content of silicon 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 a range consisting of any two of the above values.

[0267] The qualitative and quantitative properties of each substance or element in this application can be detected using appropriate equipment and methods known to those skilled in the art. The relevant detection methods can refer to domestic and international detection standards, domestic and international enterprise standards, etc., and those skilled in the art can also adapt certain detection steps / instrument parameters, etc. from the perspective of detection accuracy to obtain more accurate detection results. A single detection method can be used for qualitative or quantitative determination, or several detection methods can be used in combination for qualitative or quantitative determination.

[0268] Isolation film

[0269] In some embodiments, the secondary battery further includes a separator, which is disposed between the positive electrode and the negative electrode to prevent a short circuit between the positive and negative electrodes while allowing ions to pass through.

[0270] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0271] This application does not specifically limit the type of isolation membrane; any known porous structure isolation membrane with good chemical and mechanical stability can be used. The isolation membrane can be a single-layer film or a multi-layer composite film, without specific limitations. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different, without specific limitations. In some embodiments, the thickness of the isolation membrane is 6μm to 40μm, and can optionally be 12μm to 20μm.

[0272] In some embodiments, the separator includes a porous base membrane and a functional layer disposed on at least one side of the porous base membrane.

[0273] Furthermore, the porous base membrane may be made of at least one of glass fiber, non-woven fabric, and polyolefin. Optionally, the polyolefin includes at least one of polyethylene, polypropylene, and polyvinylidene fluoride.

[0274] Furthermore, the thickness of the porous base film is ≤12 μm, optionally ≤9 μm, and optionally 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.

[0275] In the embodiment of the present application, when the porosity of the separator 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.

[0276] In the embodiments of this application, porosity refers to the percentage of the pore volume within the separator to the total volume of the separator. Porosity can be tested in accordance with the standard GB / T 36363-2018, "Polyolefin Separators for Battery Cells." It should be noted that the actual testing process may vary slightly from the standard to obtain a more accurate test value, depending on instrument differences, test errors, and to minimize the impact of porosity on the test.

[0277] Furthermore, the porosity of the porous base membrane is 20% to 70%, and can be 35% to 60%. For example, the porosity of the base membrane is 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or a range consisting of any two of the above values.

[0278] When the thickness of the porous base membrane is within the above range, the migration path of lithium ions in the base membrane is shorter, which can further reduce the internal resistance of the battery cell and thus reduce heat generation.

[0279] In an embodiment of the present application, the isolation membrane may be a base membrane; optionally, the isolation membrane further includes a functional layer disposed on at least one side of the base membrane, the functional layer may include inorganic particles to enhance the heat resistance of the isolation membrane. Optionally, the functional layer is disposed on both sides of the base membrane.

[0280] 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 inside the non-fluoropolymer particles.

[0281] The first functional layer and the second functional layer have good heat resistance, which can improve the heat resistance of the isolation film.

[0282] Optionally, the first functional layer may include a binder, optionally including at least one of a fluorine-containing binder or a polyacrylic binder, such as polyvinylidene fluoride.

[0283] 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 first inorganic particles can improve the heat resistance of the first functional layer.

[0284] In the embodiments of the present application, the thickness of the base film has a meaning well known in the art, and can be tested using the meanings and equipment well known in the art. For example, a newly prepared isolation membrane can be taken as a sample, or a battery cell that has been discharged (discharged to the lower cut-off voltage so that the battery's charged state is approximately 0% SOC) can be reversely disassembled, and the isolation membrane can be obtained from the battery cell. After drying the isolation membrane, it is used as a sample, and the isolation membrane is cut using 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 isolation membrane and its various layers.

[0285] The non-fluorinated polymer particles in the second functional layer refer to polymers that are non-fluorinated polymers. For example, the non-fluorinated polymer particles include an acrylic copolymer. Optionally, the acrylic copolymer includes an acrylate-acrylonitrile-acrylamide-propylene copolymer. Acrylic copolymers have excellent bonding properties and high bonding stability with the base film. The molar ratio of each monomer in the copolymer can be any ratio, such as 35%:30%:15%:20%, or 40%, 20%, 10%, 30%, or 45%, 15%, 20%, 20%, etc.

[0286] The second inorganic particles in the composite particles prevent the non-fluoropolymer particles from bonding due to the high-temperature treatment during the granulation process, resulting in pores in the composite particles, which is beneficial for the transmission of lithium ions and improves the ion conductivity of the separator. The second inorganic particles can also increase the compression modulus of the composite particles. During the charge and discharge process, the composite particles are less likely to deform, making the structure of the separator more stable, which can improve the dynamic performance of the battery cell and improve the fast charging performance. Optionally, compared to the first functional layer, the second functional layer is arranged closer to the negative electrode plate. Since the composite particles are less likely to deform, the separator will basically not cause side effects such as squeezing the negative electrode plate, which stabilizes the dynamic performance of the negative electrode plate. Accordingly, the first functional layer is arranged closer to the positive electrode plate.

[0287] Optionally, the second inorganic particles include one or more of silicon oxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide; optionally, the second inorganic particles include silicon oxide. These second inorganic particles can enhance the heat resistance of the second functional layer and, in combination with non-fluoropolymers, form composite particles that further improve the cycle stability and dynamic performance of the separator, and enhance the cycle performance and fast-charging performance of the battery cell.

[0288] 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 a range consisting 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.

[0289] In the embodiment of the present application, the average particle size of the second inorganic particles has a meaning well known in the art and can be detected using equipment and methods well known in the art. For example, after obtaining the isolation film and drying the isolation film as a sample, the isolation film is cut with an ion beam cutter to form a cross section; then, a scanning electron microscope is used to measure the particle size of the second inorganic particles in the isolation film, and the particle sizes of multiple, for example, 50, second inorganic particles are measured, and the average value is calculated as the average particle size of the second inorganic particles.

[0290] In some embodiments, the ionic conductivity of the separator is 0.3 mS / cm to 0.6 mS / cm. For example, the ionic conductivity of the separator 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 a range consisting of any two of the foregoing values.

[0291] When the ionic conductivity of the separator is within the above range, the migration ability of lithium ions in the separator can be further improved, thereby improving the fast charging performance of the battery cell.

[0292] In the embodiments of the present application, the ionic conductivity of the isolation membrane has a meaning known in the art and can be detected using equipment and methods known in the art, for example,

[0293] Preparation of 2025 button cells for testing: In a vacuum glove box, a lithium sheet was placed in the negative electrode shell of the battery, and 150 μL of electrolyte was added thereto. The electrolyte was a solution of 1M LiPF6 in EC / EMC / DEC = 3 / 5 / 2 (mass ratio). Then, an isolation membrane (area of 3.14 cm) was placed in the negative electrode shell of the battery. 2 , 12μm thick) to ensure close contact with the lithium sheet. 25μL of electrolyte was then added. Finally, a positive electrode sheet (the one described in Example 1 can be used) was placed on top and packaged. The assembled button cell was removed from the vacuum glove box and allowed to rest for 24 hours before the next test.

[0294] Test: On an electrochemical workstation, at 10 -1 ~10 6 The test is carried out in the frequency range of Hz to obtain the isolation membrane resistance Rb, and the ionic conductivity σ (unit: mS / cm) is calculated by the following formula:

[0295] σ=L / (R b ×S)

[0296] Where: R b is the equivalent resistance, L and S are the thickness and area of the isolation film to be measured respectively.

[0297] A secondary battery includes at least one battery cell. A secondary battery may include one or more battery cells.

[0298] In this application, unless otherwise specified, a "battery cell" refers to a basic unit that can achieve the mutual conversion of chemical energy and electrical energy. Further, generally speaking, it includes at least a positive electrode plate, a negative electrode plate, and an electrolyte. During the battery's charge and discharge process, active ions are embedded in and out of the positive and negative electrode plates. The electrolyte plays the role of conducting active ions between the positive and negative electrode plates.

[0299] The present application has no particular restrictions on the shape of the battery cell, which can be cylindrical, square or any other shape. For example, Figure 1 The secondary battery shown is a single battery cell, which is an example of a battery cell 5 having a square structure.

[0300] In some embodiments, the battery cell 5 may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte. In some embodiments, the outer packaging of the battery cell 5 may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell 5 may also be a soft shell, such as a pouch-type soft shell. The soft shell may be made of plastic. Non-limiting examples of plastic include at least one of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0301] In some of these embodiments, reference Figure 2 The outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to actual needs.

[0302] In some embodiments, the secondary battery may be a battery module or a battery pack. A battery module includes at least one battery cell. A battery module may contain one or more battery cells, and those skilled in the art may select an appropriate number based on the application and capacity of the battery module.

[0303] Figure 3 The secondary battery shown is a battery module, which is an example of a battery module 4. Figure 3 In the battery module 4, the plurality of battery cells 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. The plurality of battery cells 5 may further be fixed by fasteners.

[0304] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0305] In some embodiments, the battery modules may be assembled into a battery pack. The battery pack may contain one or more battery modules. Those skilled in the art may select an appropriate number based on the application and capacity of the battery pack.

[0306] Figure 4 and Figure 5 The secondary battery shown is a battery pack, which is an example of a battery pack 1. Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner in the battery box.

[0307] In addition, one embodiment of the present application further provides an electrical device, comprising the aforementioned secondary battery provided herein. The secondary battery can serve as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices, electric vehicles, electric trains, ships, satellites, energy storage systems, and the like. Examples of mobile devices include, but are not limited to, mobile phones and laptop computers; examples of electric vehicles include, but are not limited to, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, and electric trucks.

[0308] As an electrical device, a secondary battery can be selected according to its usage requirements.

[0309] Figure 6 The power consumption device 6 is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the power consumption device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module can be used.

[0310] As another example, the device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be light and thin, and may use a battery cell 5 as a power source.

[0311] In order to make the technical problems, technical solutions and beneficial effects solved by this application clearer, the application will be further described in detail below with reference to the embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present application and its applications. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0312] If no specific techniques or conditions are specified in the examples, the experiments were carried out according to the techniques or conditions described in the literature in the field or according to the product instructions. All reagents or instruments used without specifying the manufacturer are commercially available conventional products.

[0313] Example 1

[0314] (1) Preparation of positive electrode sheet:

[0315] 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 comprises lithium iron titanium phosphate (Li2FeTi(PO4)3) and amorphous carbon. The Dv50 of the positive electrode active material is 1.6μm and the Dv10 is 0.64μm. The powder compaction density at 30,000N is 2.53g / cm 3 .

[0316] The positive electrode current collector is a 10μm thick aluminum foil, on which a 1μm thick positive conductive layer is applied. This layer is formed by mixing conductive carbon SP, a binder called polyvinylidene fluoride (PVDF), and a solvent called N-methylpyrrolidone (NMP), and then coating the surface of the current collector.

[0317] The positive electrode active material, lithium iron phosphate (LiFePO4), the binder, polyvinylidene fluoride (PVDF), and the conductive agent, acetylene black, are mixed in a mass ratio of 97:2:1. N-methylpyrrolidone (NMP) solvent is then added and stirred evenly to form a positive electrode slurry. The slurry is evenly coated onto the positive conductive layer of the positive electrode current collector, aluminum foil, followed by drying and cold pressing to form a positive electrode sheet. A positive electrode sheet consists of a positive electrode current collector, a positive conductive layer, and a positive electrode film layer, which are sequentially disposed on the positive electrode current collector.

[0318] The coating weight of the positive electrode sheet on one side is 300mg / 1540.25mm, based on the mass of the positive electrode film layer. 2 The battery is charged at a charge rate of 0.33C to 100% SOC, and the compaction density of the positive electrode is 2.63g / cm 3 .

[0319] Among them, the battery is charged to 100% SOC at a charging rate of 0.33C as follows: the battery cell is charged to the battery upper limit voltage (3.65V) at a constant current charging rate of 0.33C, and then charged to 0.05C at a constant voltage, corresponding to the state of 100% SOC of the battery cell.

[0320] (2) Preparation of negative electrode sheet:

[0321] The preparation method of the double-layer structure negative electrode sheet is as follows:

[0322] 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.

[0323] The negative electrode current collector is a 5μm thick copper foil with a negative electrode conductive layer on the negative electrode current collector. The negative electrode conductive agent is formed by mixing conductive carbon SP, binder SBR, dispersant CMC and solvent water and then coating the current collector surface with a thickness of 1μm.

[0324] The negative electrode active material third graphite, the conductive agent acetylene black, the binder styrene butadiene rubber and the thickener sodium carboxymethyl cellulose were mixed in a mass ratio of 96:0.5:2.5:1, and then the solvent deionized water was added and stirred evenly to form a first negative electrode slurry.

[0325] 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 deionized water was added as a solvent and stirred evenly to form a second negative electrode slurry.

[0326] 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 then coated on the surface of the dried first negative electrode slurry, dried, and cold pressed to obtain a negative electrode sheet. The negative electrode sheet comprises a negative electrode current collector, a negative electrode conductive layer, and a negative electrode film layer, which are sequentially disposed on the negative electrode current collector. The negative electrode film layer comprises a first negative electrode active layer and a second negative electrode active layer, which are sequentially disposed on the negative electrode conductive layer.

[0327] Among them, based on the total mass of the negative electrode film layer, the single-side 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 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.

[0328] (3) Preparation of electrolyte:

[0329] In an argon atmosphere glove box with a water content of <10 ppm, a first solvent, ethylene carbonate (EC), a second solvent, ethyl acetate (EA), and dimethyl carbonate (DMC), were mixed uniformly in specific mass ratios to form an organic solvent. The mass proportions of ethylene carbonate (EC), ethyl acetate (EA), and dimethyl carbonate (DMC) in the organic solvent were 25%, 50%, and 25%, respectively, as shown in Table 1. A specific mass of lithium hexafluorophosphate (LiPF6) was slowly added as a lithium salt and stirred thoroughly until it was completely dissolved. The LiPF6 concentration in the electrolyte was 1 mol / L. After returning to room temperature, a first additive, vinylene carbonate (VC), accounting for 6% of the total mass of the electrolyte, and a second additive, fluoroethylene carbonate (FEC), accounting for 4% of the total mass of the electrolyte, were added and mixed thoroughly to form an electrolyte. The mass b of the electrolyte at a rated unit cell capacity of 1 Ah for the secondary battery was 2.65 g, as shown in Table 1.

[0330] (4) Isolation film:

[0331] The isolation film includes a base film, which is a 7 μm polyethylene film layer with a porosity of 42%.

[0332] (5) Secondary battery preparation:

[0333] The positive electrode sheet, separator, and negative electrode sheet are stacked and wound in sequence to obtain a wound electrode assembly; the electrode assembly is added to an outer square aluminum shell, dried, and then injected with electrolyte. After packaging, standing, formation, aging, secondary packaging, capacity and other processes, a secondary battery is obtained.

[0334] The preparation methods of Examples 2 to 4 are similar to those 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.

[0335] The preparation methods of Examples 5 to 8 are similar to those of Example 2, except that the mass content of the first additive VC in the electrolyte is adjusted, as shown in Table 1.

[0336] The preparation methods of Examples 9 to 13 are similar to those of Example 2, except that the mass content of the second additive FEC in the electrolyte is adjusted, as shown in Table 1.

[0337] 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 the single-sided coating weight of the active layer of the positive electrode sheet and the negative electrode sheet is adjusted.

[0338] The details are shown in Table 1.

[0339] The preparation methods of Examples 15 to 17 are similar to those of Example 2, except that the type of the first graphite as the negative electrode active material is adjusted, and the Dv50 parameters thereof are different, as shown in Table 1.

[0340] The preparation methods of Examples 18 to 19 are similar to those of Example 10, except that the injection coefficient of the electrolyte is adjusted, so the mass b of the electrolyte at the unit cell rated capacity of the secondary battery of 1 Ah is different, and the mass content of the first additive in the electrolyte is adjusted, as shown in Table 1.

[0341] Example 19

[0342] The preparation method is similar to that of Example 3, except that the negative electrode sheet is a single-layer structure. The preparation method is as follows:

[0343] The negative electrode active materials, first graphite, second graphite, conductive agent acetylene black, binder styrene-butadiene rubber and thickener sodium carboxymethyl cellulose are mixed in a mass ratio of 38.4:57.6:0.5:2.5:1, and then solvent deionized water is added and stirred evenly to form a negative electrode slurry; the negative electrode slurry is evenly coated on the negative electrode conductive layer of the negative electrode current collector copper foil, and after drying and cold pressing, a negative electrode sheet is obtained.

[0344] The negative electrode sheet includes a negative electrode current collector and a negative electrode conductive layer and a negative electrode active layer sequentially arranged on the negative electrode current collector.

[0345] The coating weight of the negative electrode sheet on one side is 138 mg / mm2 based on the total mass of the negative electrode active layer. 2 The battery is charged at a charge rate of 0.33C to 100% SOC, and the compaction density of the positive electrode is 1.2g / cm 3 ; Based on the total mass of the first graphite and the second graphite in the negative electrode active layer, the mass proportions of the first graphite and the second graphite are 40% and 60% respectively.

[0346] 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 first additive, and the mass content of the first additive in the electrolyte is adjusted, as shown in Table 1.

[0347] The following is a performance test.

[0348] (1) The test steps for the capacity retention rate of the battery after 1000 cycles at 60°C are as follows:

[0349] At 60°C, charge the battery at a constant current of 1C to a charge cutoff voltage of 3.65V, let it rest for 30 minutes, and then discharge it at a constant current of 1C to 2.0V. This constitutes one charge-discharge cycle, and record the capacity C0 after the first cycle. Repeat these charge-discharge cycles until 1000 cycles, and record the corresponding capacity Cn after the 1000th cycle. The capacity retention rate of the battery after 1000 cycles at 60°C is calculated as Cn / C0 × 100%. A higher capacity retention rate indicates better cycle performance.

[0350] (2) The test steps for the charging time T of a secondary battery from 10% SOC to 80% SOC at 30°C are as follows:

[0351] At an ambient temperature of 30°C, charge the battery from 10% SOC.

[0352] Charge from 10% SOC to 15% SOC at 5.0C constant current;

[0353] Charge from 15% SOC to 20% SOC at 5.0C constant current;

[0354] Charge from 20% SOC to 25% SOC at 5.0C constant current;

[0355] Charge from 25% SOC to 30% SOC at 5.0C constant current;

[0356] Charge from 30% SOC to 35% SOC at 5.0C constant current;

[0357] Charge from 35% SOC to 40% SOC at 5.0C constant current;

[0358] Charge from 40% SOC to 45% SOC at 4.6C constant current;

[0359] Charge from 45% SOC to 50% SOC at 4.3C constant current;

[0360] Charge from 50% SOC to 55% SOC at 4.0C constant current;

[0361] Charge from 55% SOC to 60% SOC at 3.7C constant current;

[0362] Charge from 60% SOC to 65% SOC at 3.4C constant current;

[0363] Charge from 65% SOC to 70% SOC at 3.1C constant current;

[0364] Charge from 70% SOC to 75% SOC at 2.9C constant current;

[0365] Charge from 75% SOC to 80% SOC at 2.7C constant current;

[0366] Record the total charging time.

[0367] (III) The test steps for the capacity retention rate of the battery after 1000 cycles at 30°C are as follows:

[0368] At 30°C, the battery was charged starting from 10% SOC, then charged to 80% SOC at the rates corresponding to the different SOCs described above. It was then charged to 3.65V at a constant current of 0.33C, allowed to rest for 30 minutes, and then discharged to 2.0V at a constant current of 1C. This constituted one charge-discharge cycle, and the capacity after the first cycle, C0, was recorded. Repeat the above charge-discharge cycle steps until 1000 cycles were completed, and the capacity after the 1000th cycle, Cn, was recorded. The capacity retention rate of the battery after 1000 cycles at 30°C was calculated as Cn / C0 × 100%. A higher capacity retention rate indicates better cycle performance.

[0369] Some parameters of each embodiment and comparative example are shown in Table 1, where the contents are all in mass content, and the unit of the single-side coating weight of the positive electrode and the negative electrode is mg / 1540.25mm 2 .

[0370] The above performance test results of each embodiment and comparative example are shown in Table 2.

[0371] Table 1

[0372]

[0373] Table 2

[0374]

[0375] It can be seen from Tables 1 to 2 above that the content of the first additive in Comparative Example 1 is too high, and the room temperature cycle performance of the battery deteriorates; the content of the first additive in Comparative Example 1 is too low, the high temperature cycle performance of the battery deteriorates, and the fast charging time is long, indicating that its fast charging performance is poor; the content of the second additive in Comparative Example 3 is too high, and the high temperature cycle performance of the battery deteriorates; the content of the second additive in Comparative Example 4 is too low, and the room temperature cycle performance of the battery decreases; the content of the first solvent in Comparative Example 5 is too low, the self-stability of the electrolyte deteriorates, resulting in a decrease in conductivity, resulting in poor room temperature and high temperature cycle performance.

[0376] By adjusting the composition and ratio of the electrolyte and synergizing it with a negative electrode sheet containing a first graphite having a smaller particle size, each embodiment achieves a secondary battery that achieves good fast-charging performance, room-temperature cycling performance, and high-temperature cycling performance. In Example 14, the second solvent in the electrolyte is a carbonate solvent, which reduces the conductivity of the electrolyte and thus reduces the coating weight on each side of the positive and negative electrode sheets, thereby improving the battery's fast-charging performance.

[0377] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0378] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, and these modifications and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by 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 being disposed on at least one side of the positive electrode current collector, the positive electrode film layer comprising a positive electrode active material; A negative electrode plate, the negative electrode plate 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 first graphite having a Dv50 particle size of 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 the mass content of the first solvent based on the total mass of the organic solvent is 25% to 40%; the organic additive comprising a first additive and a second additive, the first additive comprising vinylene carbonate, and the second additive comprising an ethylene carbonate derivative, and the mass percentage of the first additive in the electrolyte based on the total mass of the electrolyte is 2% to 10%, and the mass percentage of the second additive in the electrolyte is 0.3% to 6%. 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.

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, wherein: 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, wherein 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 2.65 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 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%.

10. The secondary battery according to claim 1, wherein The powder compaction density of the positive electrode active material at 30,000 N is ≥ 2.43 g / cm 3 .

11. The secondary battery according to claim 10, wherein The powder compaction density of the positive electrode active material at 30000N is 2.48g / cm 3 ~2.85 g / cm 3 .

12. The secondary battery according to claim 10, wherein The positive electrode active material includes at least one of an olivine-structured lithium-containing phosphate and a derivative thereof.

13. The secondary battery according to claim 12, wherein The positive electrode active material includes: 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.

14. The secondary battery according to claim 12 or 13, wherein: 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 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, N, and P; and Q1 includes at least one of O and F.

15. The secondary battery according to claim 14, wherein 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.

16. The secondary battery according to claim 13, 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.

17. The secondary battery according to claim 16, wherein The fast ion conductor includes at least one of lithium iron titanium phosphate, lithium iron zirconium phosphate and lithium iron tin phosphate.

18. 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 2.5g / 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.

19. The secondary battery according to claim 18, 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 0.4 μm ≤ Dv10 ≤ 0.7 μm.

20. The secondary battery according to claim 1, wherein 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.

21. The secondary battery according to claim 20, wherein 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.

22. The secondary battery according to claim 1, wherein The positive electrode plate also includes a positive electrode conductive layer, which is arranged between the positive electrode current 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.

23. The secondary battery according to claim 22, wherein The thickness of the positive electrode conductive layer is 0.5 μm to 2 μm.

24. The secondary battery according to claim 22 or 23, wherein: 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.

25. The secondary battery according to claim 24, wherein 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%.

26. The secondary battery according to claim 1, wherein The compaction density of the negative electrode sheet of the secondary battery after being charged to 100% SOC at a charging rate of 0.33C is 1.15 g / cm 3 ~1.46g / cm 3 .

27. The secondary battery according to claim 26, wherein The compaction density of the negative electrode sheet of the secondary battery after being charged to 100% SOC at a charging rate of 0.33C is 1.15 g / cm 3 ~1.36g / cm 3 .

28. The secondary battery according to claim 26, wherein After the secondary battery is charged to 100% SOC at a charge 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%.

29. The secondary battery according to claim 28, wherein 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%.

30. The secondary battery according to claim 26, wherein After the secondary battery is charged to 100% SOC at a charge rate of 0.33C, the compaction density of the negative electrode sheet is greater than 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%.

31. The secondary battery according to claim 30, wherein 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%.

32. The secondary battery according to claim 1, wherein The electrolyte further includes a second solvent, and the second solvent includes at least one of linear carbonate, carboxylate, ether, nitrile, and sulfone.

33. The secondary battery according to claim 32, wherein The second solvent includes a carboxylic acid ester.

34. The secondary battery according to claim 32, wherein 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.

35. The secondary battery according to claim 33, wherein 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 carboxylate 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%.

36. The secondary battery according to claim 35, wherein 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%.

37. The secondary battery according to claim 1, wherein 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 salt, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate and lithium tetrafluorooxalatophosphate.

38. The secondary battery according to claim 37, wherein The concentration of the lithium salt in the electrolyte is 0.7 mol / L to 1.5 mol / L.

39. The secondary battery according to claim 37 or 38, wherein 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.

40. The secondary battery according to claim 1, wherein 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. 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.

41. The secondary battery according to claim 40, wherein The thickness of the negative electrode conductive layer is 0.5 μm to 2 μm.

42. The secondary battery according to claim 40 or 41, wherein 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.

43. The secondary battery according to claim 42, wherein 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%.

44. The secondary battery according to claim 1, wherein 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.

45. The secondary battery according to claim 44, wherein 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 4.2μm~7.2μm, and the Dv50 particle size of the second graphite is 7.8μm~14.8μm.

46. The secondary battery according to claim 45, wherein The mass ratio of the first graphite to the second graphite is 2:8 to 6:

4.

47. The secondary battery according to claim 46, wherein The mass ratio of the first graphite to the second graphite is 3:7 to 5:

5.

48. The secondary battery according to claim 45 or 46, wherein 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%.

49. The secondary battery according to claim 44, wherein The negative electrode film layer includes a first negative electrode active layer and a second negative electrode active layer stacked sequentially 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.

50. The secondary battery according to claim 49, wherein In the second negative active layer, a mass ratio of the first graphite to the third graphite is 2:8 to 8:

2.

51. The secondary battery according to claim 50, wherein In the second negative active layer, a mass ratio of the first graphite to the third graphite is 3:7 to 7:

3.

52. The secondary battery according to claim 49 or 50, wherein: 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 the total amount of negative electrode active material 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 greater than or equal to the Dv50 particle size of the first graphite in the second negative electrode active layer.

53. The secondary battery according to claim 52, wherein 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 the total amount of negative electrode active material 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.

54. The secondary battery according to claim 53, wherein 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.

55. The secondary battery according to claim 49, wherein The artificial graphite includes graphite body particles and a coating layer, wherein the graphite body particles include secondary particles formed by aggregation of multiple primary particles, and the coating layer is coated on the surface of the body particles and includes amorphous carbon.

56. The secondary battery according to claim 55, wherein 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.

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

58. The secondary battery according to claim 57, wherein 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.

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

60. The secondary battery according to claim 59, wherein The mass content of silicon element in the silicon-based material in the negative electrode active material is 1% to 6%.

61. The secondary battery according to claim 1, wherein The separator includes a porous base membrane and a functional layer disposed on at least one side of the porous base membrane.

62. The secondary battery according to claim 61, wherein At least one of the following conditions is met: (1) The thickness of the porous base membrane is ≤12 μm; (2) The porosity of the porous base membrane is 20% to 70%.

63. The secondary battery according to claim 62, wherein At least one of the following conditions is met: (1) The thickness of the porous base membrane is ≤9 μm; (2) The porosity of the porous base membrane is 35% to 60%.

64. The secondary battery according to claim 61 or 62, wherein 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, and the second inorganic particles are attached to the surface of the non-fluoropolymer particles and / or dispersed inside the non-fluoropolymer particles.

65. The secondary battery according to claim 64, wherein 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.

66. An electrical device, characterized in that: A secondary battery comprising the secondary battery according to any one of claims 1 to 65.

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