Secondary battery and electric device

Abstract

A secondary battery and an electric device. A negative electrode sheet in the secondary battery comprises 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, and the negative electrode film layer comprises a negative electrode active material. The negative electrode active material comprises a first graphite with a Dv50 particle size of 2.2-7.7 μm. The electrolyte comprises an organic solvent and an organic additive. The organic solvent comprises a first solvent which comprises 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 comprises a first additive and a second additive, wherein the first additive comprises vinylene carbonate, and the second additive comprises an ethylene carbonate derivative, and the mass percentage of the first additive in the electrolyte is 2-10% and the mass percentage of the second additive in the electrolyte is 0.3-6% based on the total mass of the electrolyte.

Description

Secondary battery and electric device TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a secondary battery and an electric device. BACKGROUND

[0002] The statements herein merely provide background information related to the present application and do not necessarily constitute the prior art.

[0003] In recent years, with the rapid development of secondary batteries such as lithium ion batteries, secondary batteries are widely used in energy storage power systems such as hydroelectric, thermal, wind and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. With the increasingly wide range of applications of secondary batteries, the demand for fast charging performance of secondary batteries is gradually increasing, but it is currently difficult to balance fast charging performance and cycle performance, so how to make secondary batteries have good fast charging performance and cycle performance has become a pressing problem.

[0004] SUMMARY

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

[0006] In a first aspect, the present application provides a secondary battery, 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 arranged 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 sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode film layer, the negative electrode film layer being arranged 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, the Dv50 particle size of the first graphite being 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, the mass content of the first solvent being 25% to 40% based on the total mass of the organic solvent; the organic additive comprising a first additive and a second additive, the first additive comprising vinylene carbonate, the second additive comprising a vinylene carbonate derivative, the mass percentage of the first additive in the electrolyte being 2% to 10% and the mass percentage of the second additive in the electrolyte being 0.3% to 6% based on the total mass of the electrolyte.

[0010] Therefore, the negative active material of the above-mentioned secondary battery includes the first graphite with a small particle size, and the negative electrode sheet containing the first graphite can improve the fast charging performance of the battery. However, the small particle size graphite has more surface defects and stronger reaction activity, and the electrolyte is consumed faster. In addition, the temperature of the battery core is higher in the fast charging condition, and the stability of the electrolyte is affected, thereby making 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 the content, the electrolyte has good thermal stability, and a stable interface film is formed on the surface of the negative electrode sheet, thereby reducing the electrolyte consumption rate and the direct current resistance DCR of the battery, and further improving the cycle performance and the fast charging performance of the secondary battery. Therefore, the above-mentioned secondary battery can have 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 vinyl carbonate derivative is as follows:

[0012] R1 and R2 each independently include any one of a hydrogen element, a halogen element, a C1-C5 alkyl group and a C1-C5 halogenated alkyl group, and R1 and R2 are not hydrogen elements at the same time. These second additives have good film forming property, conductivity and stability, and can improve the fast charging performance and cycle performance of the battery, especially the normal temperature cycle performance.

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

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

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

[0016] In any embodiment of the present application, the mass content of the first additive is 3%-8% and / or the mass content of the second additive is 1.5%-5% based on the total mass of the electrolyte. Controlling the mass content of the first additive and / or the second additive in the electrolyte in the optional range can make the battery 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%, 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 small particle size of the graphite active material, and the faster consumption rate of the additives during the cycle process to cause the cycle performance to drop, thereby improving the cycle performance of the battery.

[0018] In any embodiment of the present application, the mass of the electrolyte under the rated capacity of 1 Ah per unit battery of the secondary battery is 2.2 g to 2.95 g.

[0019] In any embodiment of the present application, the mass of the electrolyte under the rated capacity of 1 Ah per unit battery of the secondary battery is 2.2 g to 2.65 g, and the total mass content of the first additive and the second additive in the electrolyte is 5% to 9%.

[0020] Alternatively, the mass of the electrolyte under the rated capacity of 1 Ah per unit battery of the secondary battery is > 2.65 g and ≤ 2.95 g, and the total mass content of the first additive and the second additive in the electrolyte is 3.5% to 6.5%.

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

[0022] In any embodiment of the present application, the positive electrode active material comprises at least one of lithium-containing olivine structure phosphate and derivatives thereof.

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

[0024] a core portion comprising at least one of lithium-containing olivine structure phosphate and derivatives thereof; and

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

[0026] The core portion coated with the ion-conducting layer can improve the conductivity of the lithium-containing olivine structure phosphate and derivatives thereof, reduce the powder resistivity of the material, and facilitate the migration rate of lithium ions, thereby improving the rapid charging capacity of the battery and reducing the heat generation of the battery monomer.

[0027] In any embodiment of the present application, the lithium-containing olivine structure phosphate and derivatives thereof comprise a general formula of Lix1 A1 y1 M1 a1 M2 b1 P 1-c1 X c1 Q1 z1 , wherein 0.5≤x1≤1.3, 0≤y1≤1.3, and 0.9≤x1+y1≤1.3; 0.9≤a1≤1.5, 0≤b1≤0.5, and 0.9≤a1+b1≤1.5; 0≤c1≤0.5; 3≤z1≤5; A1 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, and N, P; and Q1 comprises at least one of O and F. The lithium-containing phosphate of olivine structure has excellent cycle stability, which is beneficial to improve the cycle performance of the battery cell.

[0028] In any embodiment of the present application, the lithium-containing phosphate of olivine structure and derivatives thereof comprise 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 fast ion conductor of the chemical formula Li 3-b Fe 2-b M3 b (PO m ) n , M3 comprises at least one element of Ti, Zr, Hf, Ge, and Sn in +4 valence, 0≤b≤1, 3≤m≤5, and 2≤n≤4.

[0030] In any embodiment of the present application, the fast ion conductor comprises at least one of lithium titanium iron phosphate, lithium zirconium iron phosphate, and lithium tin iron phosphate. Coating the core surface with the fast ion conductor comprising the NASICON structure can significantly improve the transmission rate of lithium ions in the positive electrode end during multiple lithium extraction / insertion, improve the ion conductivity of the positive electrode active material, improve the rapid charging capacity of the battery cell, and further improve the specific capacity and the 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 2.5 g / cm 3 ~2.8 g / cm 3 ;

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

[0034] (3) the powder resistivity of the positive electrode active material ranges from 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 comprises a lithium supplementing agent, and the lithium supplementing agent comprises at least one of a ternary lithium supplementing material, lithium phosphate, lithium hydrogen phosphate, lithium sulfate, lithium sulfite, lithium molybdate, lithium nickelate, lithium ferrite, lithium oxalate, lithium titanate, lithium tetraborate, lithium metasilicate, lithium manganite, lithium tartrate and trilithium citrate. The lithium supplementing agent can supplement lithium ions for the positive electrode film layer, make up for the irreversible loss of lithium ions in the system, and improve the capacity, thereby improving the energy density of the battery cell.

[0037] In any embodiment of the present application, the ternary lithium supplementing material comprises Li x2 A2 y2 Ni a2 Co b2 Mn c2 M4(1-a2-b2-c2)Q2 z2 , wherein 0

[0038] In any embodiment of the present application, the positive electrode tab further comprises a positive electrode conductive layer, and the positive electrode conductive layer 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 comprises a conductive agent, and the conductive agent comprises 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 0.5μm to 2μm.

[0040] In any embodiment of the present application, the positive electrode conductive layer comprises a binder, and the binder comprises at least one of polyvinylidene fluoride, polytetrafluoroethylene, a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, a polyacrylic acid, and a fluorine-containing acrylic ester 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 charge rate of 0.33 C is 1.15 g / cm 3 to 1.46 g / cm 3 , and optionally 1.15 g / cm 3 to 1.36 g / cm 3 .

[0043] 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 charge rate of 0.33 C is 1.15 g / cm 3 , and the mass content of the first additive in the electrolyte is 3% to 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 after the secondary battery is charged to 100% SOC at a charge rate of 0.33 C is > 1.26 g / cm 3 and ≤ 1.36 g / cm 3 , and the mass content of the first additive in the electrolyte is 2.5% to 6.5%.

[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 comprises a second solvent, the second solvent comprising at least one of linear carbonate, carboxylate, ether, nitrile and sulfone.

[0052] In any embodiment of the present application, the second solvent comprises carboxylate; optionally, the carboxylate comprises 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 secondary battery has a charging time of 6 min to 15 min from 10% SOC to 80% SOC at 30℃, 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 2% to 9%.

[0054] In any embodiment of the present application, the mass content of the first additive in the electrolyte is 1.5% to 7%, and the mass content of the second additive in the electrolyte is 0.5% to 4%.

[0055] In any embodiment of the present application, the electrolyte comprises a lithium salt, the lithium salt comprising at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, fluorine-containing sulfonimide salt, lithium triflate, lithium difluorophosphate, lithium difluoro oxalate borate, lithium di-oxalate borate, lithium difluoro di-oxalate phosphate and lithium tetrafluoro oxalate phosphate.

[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 comprises at least one of LiFSI and LiPF6, and the lithium salt satisfies at least one of the following conditions:

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

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

[0060] (3) the lithium salt comprises 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 tab further comprises a negative electrode conductive layer, the negative electrode conductive layer 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 comprises a conductive agent, the conductive agent comprising at least one of super-conductive 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 comprises a binder, the binder comprising at least one of styrene butadiene rubber, water-soluble unsaturated resin, 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 comprises at least one negative electrode active layer, and the at least one negative electrode active layer comprises the first graphite.

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

[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; or 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 comprises a first negative electrode active layer and a second negative electrode active layer stacked in sequence on the same side of the negative electrode current collector, the first negative electrode active layer comprises at least one of artificial graphite and natural graphite, and the second negative electrode active layer comprises the first graphite and third graphite, the first graphite comprises artificial graphite, and the Dv50 particle size of the third graphite is 7.8 μm to 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; or 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 the respective negative electrode active materials in the second negative electrode active layer and the first negative electrode active material layer is 3:7 to 7:3; or 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%; or 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; or the Dv50 particle size of the graphite in the first negative electrode active layer is 5.8 μm to 12.8 μm, or 7.8 μm to 12.8 μm; or the Dv50 particle size of the graphite in the second negative electrode active layer is 2.2 μm to 7.7 μm, or 4.2 μm to 7.2 μm.

[0076] In any embodiment of the present application, the artificial graphite comprises graphite bulk particles and a coating layer, the graphite bulk particles comprise secondary particles formed by aggregation of a plurality of primary particles, the coating layer is coated on the surface of the bulk particles, and the coating layer comprises amorphous carbon.

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

[0078] (1) The mass content of the amorphous carbon is 2% to 5% based on the total mass of the artificial graphite.

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

[0080] In any embodiment of the present application, the first graphite has a charge specific capacity ≥350 mAh / g at a 0.1C rate in a button cell, which is optionally 350 mAh / g to 440 mAh / g.

[0081] In any embodiment of the present application, the negative electrode active material further comprises a silicon-based material, the silicon-based material comprising at least one of a silicon oxide compound and a silicon-carbon composite; the mass content of silicon in the silicon-based material in the negative electrode active material is 0.3% to 10%, which is optionally 1% to 6%.

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

[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 film is ≤12 μm, which is optionally ≤9 μm;

[0085] (2) the porosity of the porous base film is 20% to 70%, which is optionally 35% to 60%.

[0086] In any embodiment of the present application, the separator film comprises a first functional layer and a second functional layer arranged on both sides of the porous base film, the first functional layer comprises first inorganic particles, the second functional layer comprises composite particles, the composite particles comprise second inorganic particles and non-fluoropolymer particles, the second inorganic particles are attached to the surface of the non-fluoropolymer particles and / or dispersed in the interior of the non-fluoropolymer particles.

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

[0088] (1) the non-fluoropolymer particles comprise acrylate polymer particles;

[0089] (2) the first functional layer is located between the negative electrode tab and the porous base film, and the second functional layer is located between the positive electrode tab and the porous base film.

[0090] The 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 accompanying drawings and the description below. Other features, objects, and advantages of the present application will be apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF DRAWINGS

[0092] In order to make the technical solutions in the embodiments of the present application or the prior art clearer, the accompanying drawings needed in the embodiments or the prior art description will be briefly introduced. Obviously, the accompanying drawings in the following description only aim at the embodiments of the present application, and for those skilled in the art, other drawings can be obtained without creative effort based on the disclosed drawings.

[0093] FIG. 1 is a schematic diagram of a battery cell according to an embodiment of the present application.

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

[0095] FIG. 3 is a schematic diagram of a battery module according to an embodiment of the present application.

[0096] FIG. 4 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0097] FIG. 5 is an exploded view of the battery pack shown in FIG. 4 according to an embodiment of the present application.

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

[0099] BRIEF DESCRIPTION OF DRAWINGS 1: battery pack; 2: upper case; 3: lower case; 4: battery module; 5: battery cell; 51: case; 52: electrode assembly; 53: cover plate; 6: electric device. DETAILED DESCRIPTION

[0100] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative effort belong to the scope of protection of the present application.

[0101] "ranges" disclosed herein can be defined, for example, by the lower and upper values. Any lower limit can independently be combined with any upper limit to define a range of any value. For example, if a range of 60-120 and 80-110 is listed, it is understood that a range of 60-110 and 80-120 is also contemplated. Furthermore, if a minimum range value of 1 and 2 is listed, and if a maximum range value of 3, 4, and 5 is also listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, the use of "a" or "an" to describe a single item can be taken as a non-limiting term that means "one or more". Unless otherwise noted, the use of the singular includes the plural. The use of "or" means "and / or", unless otherwise noted. The use of the term "including" as well as other forms for, e.g., "include", "includes", "included", is not limiting. The terms "example" and "exemplary" are used herein to mean "serving as an example, instance, or illustration", and not to imply or warrant that also corresponds to preferred implementation.

[0102] As used herein, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. "A" or "an" can mean "one or more" unless otherwise indicated.

[0103] All embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, if not specifically stated otherwise.

[0104] Reference herein to "an embodiment" or "one embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment or implementation of the application. The appearances of the phrase that the phrase in the specification appear not necessarily all refer to the same embodiment, or that they are mutually exclusive or alternative embodiments to the other. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. Reference herein to "an implementation" has a similar understanding.

[0105] It is understood by those skilled in the art that the order of writing each step in the method of each embodiment or example does not mean a strict execution order and does not constitute any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. If not specifically stated, all steps of the present application can be performed in sequence or randomly, preferably in sequence. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method also comprises step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0106] In the present application, the open technical features or technical solutions described by the words "containing", "including", "comprising" and the like do not exclude additional members other than the listed members, and can be regarded as providing both a closed feature or solution composed of the listed members and an open feature or solution including additional members in addition to the listed members. For example, A includes a1, a2 and a3, and unless otherwise specified, it can also include other members or can not include additional members, and can be regarded as providing both the feature or solution that "A is composed of a1, a2 and a3" and the feature or solution that "A includes a1, a2 and a3, and also includes other members".

[0107] In the present application, A (such as B) means that B is a non-limiting example of A, and A can be understood as not limited to B unless otherwise specified.

[0108] In the present application, "optionally", "optional" and "optional" mean that it can or can not be present, i.e. it can be selected from either of the two parallel schemes "yes" or "no". If there are multiple "options" in a technical solution, each "option" is independent of each other unless otherwise specified and there is no contradictory relationship or mutual restriction.

[0109] An embodiment of the present application provides a secondary battery, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte.

[0110] The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer, the positive electrode film layer is arranged on at least one side of the positive electrode current collector, and the positive electrode film layer comprises a positive electrode active material.

[0111] The negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer arranged on at least one side of the negative electrode current collector, the negative electrode film layer comprising a negative electrode active material, the negative electrode active material comprising a first graphite, the Dv50 particle size of the first graphite being 2.2-7.7 μm.

[0112] The electrolyte comprises an organic solvent and an organic additive, the organic solvent comprising a first solvent. The first solvent comprises a cyclic carbonate (EC), the mass content of the first solvent being 25-40% based on the total mass of the organic solvent. The organic additive comprises a first additive and a second additive, the first additive comprising vinylene carbonate (VC) and the second additive comprising a vinyl carbonate derivative, the mass percentage of the first additive in the electrolyte being 2-10% and the mass percentage of the second additive in the electrolyte being 0.3-6% based on the total mass of the electrolyte.

[0113] Thus, the negative electrode active material of the above-mentioned secondary battery comprises the above-mentioned first graphite with a small particle size, so that the negative electrode sheet containing the first graphite can improve the fast charging performance of the battery. However, the surface of the small-particle-size graphite has many defects and is highly reactive, so that the electrolyte is consumed quickly. In addition, the temperature of the battery rises rapidly during fast charging, which affects the stability of the electrolyte and 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 adjusting the contents of the first solvent, the first additive and the second additive, the electrolyte has good thermal stability, a stable interface film is formed on the surface of the negative electrode sheet, the consumption rate of the electrolyte and the direct current resistance (DCR) of the battery are reduced, and the cycle performance and the fast charging performance of the secondary battery are improved. Thus, the above-mentioned secondary battery can have good fast charging performance, room-temperature cycle performance and high-temperature cycle performance.

[0114] The first solvent comprises a cyclic carbonate, which has a high dielectric constant and good film-forming performance. If the content of the first solvent in the electrolyte is too low, the stability of the electrolyte itself is poor, which reduces the electrical conductivity. However, if the content of the first solvent is too high, the viscosity and the melting point of the electrolyte increase, which will deteriorate the electrical conductivity of the electrolyte and the kinetic performance of the battery, thereby deteriorating the cycle performance. Thus, by adjusting the content of the first solvent within the above-mentioned range, the electrolyte has good thermal stability and appropriate electrical conductivity.

[0115] The first additive includes vinylene carbonate (VC), the second additive includes a vinyl carbonate derivative, the first additive and the second additive can participate in interface film formation, the content of the first additive and the second additive is too low, the first solvent will excessively participate in film formation, which destroys the stability of the electrolyte, and then accelerates the consumption rate of the electrolyte, and deteriorates the cycle performance and storage life of the battery; with the increase of the content of the first additive, the high-temperature cycle life of the battery is improved, but the content of the first additive is too high, which will deteriorate the battery kinetic window and direct current resistance DCR, thereby leading to the deterioration of the cycle performance and being not conducive to the improvement of the fast charging performance; with the increase of the content of the second additive, the room temperature cycle life and the fast charging performance of the battery are improved, but the content of the second additive is too high, which deteriorates the high-temperature performance of the battery and reduces the high-temperature cycle life. Therefore, the first additive and the second additive are respectively in the above range, so that the electrolyte realizes the balance between the film formation stability and the battery kinetics.

[0116] Therefore, the electrolyte regulates the content of the first solvent in the above range, which can improve the thermal stability of the electrolyte and make the conductivity of the electrolyte in a suitable range, and the first additive and the second additive are respectively in the above range, so that the electrolyte realizes the balance between the battery kinetics and the film formation stability, thereby reducing the consumption rate of the electrolyte and improving the room temperature and high temperature cycle performance and storage life of the battery cell; in addition, the battery also has a lower direct current resistance DCR, and has good fast charging performance. The electrolyte can be applied to the negative electrode sheet including the first graphite with the above smaller particle size and the battery system, so that the secondary battery has higher fast charging performance, room temperature cycle performance and high temperature cycle performance.

[0117] Electrolyte

[0118] In some embodiments of the present application, the cyclic carbonate in the first solvent includes at least one of vinyl carbonate (EC) and propylene carbonate (PC).

[0119] For 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%. Further, the mass content of the first solvent in the organic solvent is 25% to 38% or 30% to 40%, or is in a range formed by any of the above values as end values, and the like hereinafter. Controlling the mass content of the first solvent in the organic solvent in the range can make the battery have better cycle performance.

[0120] As an example, the mass content of the first additive in the electrolyte can be, but is not limited to, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%. Further, the mass content of the first additive in the electrolyte is 3% to 8%. Further, the first additive is vinylene carbonate (VC). Controlling the mass content of the first additive in the electrolyte within the optional range can make the battery have better cycle performance, especially high-temperature cycle performance.

[0121] In some embodiments of the present application, the structure of the vinyl carbonate derivative in the second additive is as follows:

[0122] R1and R2each independently include any one of a hydrogen element, a halogen element, a C1-C5 alkyl group, and a C1-C5 haloalkyl group, and R1and R2are not hydrogen elements at the same time. Further, the halogen element includes at least one of a fluorine element, a chlorine element, and a bromine element, and the C1-C5 alkyl group and the C1-C5 haloalkyl group 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 isomers thereof. These second additives have good film-forming property, conductivity, and stability, and can improve the fast-charging performance and cycle performance, especially room-temperature cycle performance, of the battery.

[0123] Further, the above-mentioned vinyl carbonate derivative includes at least one of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), and trifluoromethyl ethylene carbonate.

[0124] As an example, the mass content of the second additive in the electrolyte can be, but is not limited to, 0.3%, 0.4%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%. Further, the mass content of the second additive in the electrolyte is 1.5% to 5%. Controlling the mass content of the second additive in the electrolyte within the optional range can make the battery have better fast-charging performance and cycle performance, especially room-temperature cycle performance.

[0125] 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%, 12%. Further, 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 small particle size of the graphite active material and the faster consumption of the additives during the cycle process, thereby improving the cycle performance of the battery.

[0126] In some embodiments of the present application, the electrolyte further comprises a second solvent. Further, the second solvent comprises at least one of linear carbonate, carboxylic ester, ether, nitrile, and sulfone. The second solvent, together with the first solvent, functions as a solvent, which lowers the melting point and viscosity of the electrolyte system and improves the lithium ion transmission performance of the electrolyte.

[0127] Further, the linear carbonate comprises at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl ethyl carbonate (EMC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC).

[0128] Further, the carboxylic ester comprises 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 comprises the carboxylic ester. Further, the second solvent comprises both the carboxylic ester and the linear carbonate.

[0129] Further, the ether comprises, but is not limited to, at least one of diethyl ether and 1,2-dimethoxyethane (DME, also known as ethylene glycol dimethyl ether).

[0130] Further, the nitrile comprises, but is not limited to, acetonitrile (AN).

[0131] Further, the sulfone comprises, but is not limited to, at least one of sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0132] Further, the mass content of the second solvent in the organic solvent is 20% to 75%; as the mass content can be 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 73%, 75%. Further, the mass content of the carboxylic ester in the organic solvent is 30% to 60%, 30% to 75%. In a specific example, the second solvent is the carboxylic ester.

[0133] In some embodiments of the present application, the electrolyte further comprises an electrolyte salt, and the concentration of the electrolyte salt in the electrolyte is 0.1 mol / L to 2 mol / L. For 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, 2 mol / L; further, it can be 0.6 mol / L to 1.3 mol / L, or in the range formed by any two of the above values as end values.

[0134] In some embodiments of the present application, the electrolyte salt comprises a lithium salt, and the lithium salt comprises at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonylimide (LiFSI), lithium bis-trifluoromethanesulfonylimide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS, CF3SO2Li), lithium difluorophosphate (LiPO2F2), lithium difluoro-oxalato-borate (LiDFOB), lithium bis-oxalato-borate (LiBOB), lithium difluoro-bis-oxalato-phosphate (LiDFOP), and lithium tetrafluoro-oxalato-phosphate (LiTFOP).

[0135] Optionally, the concentration of the lithium salt in the electrolyte is 0.7 mol / L to 1.5 mol / L. Optionally, the lithium salt comprises at least one of a fluorine-containing sulfonylimide salt and LiPF6. More optionally, the fluorine-containing sulfonylimide salt comprises at least one of LiFSI and LiTFSI.

[0136] Further, the lithium salt comprises at least one of LiFSI and LiPF6. Still further, the concentration of LiFSI in the electrolyte is 0.2 mol / L to 0.5 mol / L; still further, the concentration of LiPF6 in the electrolyte is 0.5 mol / L to 1.3 mol / L. Further, the lithium salt comprises LiFSI and LiPF6, and the molar ratio of LiFSI to LiPF6 is (2-5):10. Lithium bisfluorosulfonylimide LiFSI has good conductivity and heat resistance, and is not easy to hydrolyze at high temperature, and is particularly suitable for the fast-charging system of the present application with large temperature rise; however, when the temperature is too high, for example, reaches 200°C or above, LiFSI will decompose and generate heat, which will worsen the safety margin of the battery, and therefore LiPF6 is added as a lithium salt, which also effectively improves the safety performance of the battery.

[0137] In some embodiments of the present application, the mass of the electrolyte under the rated capacity of 1 Ah per unit cell of the secondary battery is 2.2 g to 2.95 g, and as an example, can be 2.2 g, 2.3 g, 2.4 g, 2.5 g, 2.6 g, 2.65 g, 2.7 g, 2.8 g, 2.9 g, 2.95 g. Further, it can be 2.2 g to 2.65 g or 2.65 g to 2.95 g. The above-mentioned electrolyte of the present application is particularly suitable for a battery of a low electrolyte injection coefficient system, and the consumption rate of the electrolyte is low, the kinetics is good, and thus the cycle performance of the battery of the low electrolyte injection coefficient system can be improved.

[0138] Further, the mass of the electrolyte under the rated capacity of 1 Ah per unit cell of the secondary battery is 2.2 g to 2.65 g, and the total mass content of the first additive and the second additive in the electrolyte is 5% to 9%. The mass of the electrolyte under the rated capacity of 1 Ah per unit cell of the secondary battery is small, and the total mass content of the first additive and the second additive can be appropriately increased, and thus the cycle performance of the battery of the low electrolyte injection coefficient system can be improved. As an example, the mass of the electrolyte under the rated capacity of 1 Ah per unit cell of the secondary battery can be 2.2 g, 2.3 g, 2.4 g, 2.5 g, 2.6 g, 2.65 g, or a range composed of any two of the above values, and the total mass content of the first additive and the second additive in the electrolyte can be 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, or a range composed of any two of the above values.

[0139] Alternatively, the mass of the electrolyte under the rated capacity of 1 Ah per unit cell of the secondary battery is > 2.65 g and ≤ 2.95 g, and the total mass content of the first additive and the second additive in the electrolyte is 3.5% to 6.5%. The mass of the electrolyte under the rated capacity of 1 Ah per unit cell of the secondary battery is large, and the total mass content of the first additive and the second additive can be appropriately reduced, and thus the cost and the cycle performance of the battery can be considered. As an example, the mass of the electrolyte under the rated capacity of 1 Ah per unit cell of the secondary battery can be 2.68 g, 2.7 g, 2.8 g, 2.9 g, 2.95 g, or a range composed of any two of the above values, and the total mass content of the first additive and the second additive in the electrolyte can be 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, or a range composed of any two of the above values.

[0140] The test method of the electrolyte mass under the rated capacity of 1 Ah of the unit battery of the secondary battery is as follows: ① Take the battery, and weigh the battery mass M0; ② Disassemble the battery, and pour out the free electrolyte, and take out the electrode sheet, the separator, the mechanical part and the adhesive paper; ③ Soak and clean the electrode sheet, the separator, the mechanical part and the adhesive paper using dimethyl carbonate (DMC), the soaking time is 24 h, and the cleaning is repeated more than 3 times; ④ After the cleaning, place the electrode sheet, the separator, the mechanical part and the adhesive paper in an oven until completely dried; ⑤ Weigh the electrode sheet, the separator, the mechanical part and the adhesive paper, and the mass is recorded as M1; ⑥ The electrolyte mass under the rated capacity of 1 Ah of the unit battery of the secondary battery = (M0-M1) / a. a = the rated capacity of the battery of the secondary battery, unit Ah.

[0141] As a non-limiting example, the positive electrode current collector has two surfaces opposite in the thickness direction thereof, and the positive electrode film layer is provided on either one or both of the two opposite surfaces of the positive electrode current collector.

[0142] In some embodiments, the positive electrode current collector can employ a metal foil or a composite current collector. For example, as the metal foil, an aluminum foil can be employed. The composite current collector can 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 can be obtained by forming a metal material on a polymer material base material. Non-limiting examples of the metal material in the positive electrode current collector can include at least one of aluminum, an aluminum alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, a silver alloy, and the like. Non-limiting examples of the polymer material base material in the positive electrode current collector can include at least one of a polypropylene (PP) base material, a polyethylene terephthalate (PET) base material, a polybutylene terephthalate (PBT) base material, a polystyrene (PS) base material, a polyethylene (PE) base material, and the like.

[0143] In some embodiments, the thickness of the positive electrode current collector is 10 μm to 15 μm, which can be optionally 12 μm to 15 μm. Exemplarily, 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.

[0144] When the thickness of the positive electrode current collector is in the above range, the positive electrode current collector has excellent flow capacity, and the battery monomer can have a high energy density.

[0145] In the embodiments of the present application, the thickness of the positive electrode film layer and the positive electrode current collector is in the meaning known in the art, which can be detected by using the devices and methods known in the art, for example, the thickness of the positive electrode tab is measured by using a micrometer, the thickness of the positive electrode current collector is measured by removing the film layer on the surface of the positive electrode current collector, and the thickness of the positive electrode film layer is the thickness of the positive electrode tab minus the thickness of the positive electrode current collector when the positive electrode film layer is coated on one side, and the thickness of the positive electrode film layer is (the thickness of the positive electrode tab minus the thickness of the positive electrode current collector) / 2 when the positive electrode film layer is coated on both sides.

[0146] The positive electrode film layer is usually formed by coating the positive electrode slurry on the positive electrode current collector, drying and cold pressing. The positive electrode slurry is usually formed by dispersing the positive electrode active material, the optional conductive agent, the optional binder and any other components in a solvent and stirring uniformly. The solvent can be N-methyl pyrrolidone (NMP), but is not limited thereto.

[0147] The positive electrode tab does not exclude other additional functional layers in addition to the positive electrode film layer. For example, in some embodiments, the positive electrode tab of the embodiments of the present application further comprises a positive electrode conductive layer arranged between the positive electrode current collector and the positive electrode film layer and arranged on the surface of the positive electrode current collector. In some other embodiments, the positive electrode tab of the embodiments of the present application further comprises a protective layer arranged on the surface of the positive electrode film layer.

[0148] The positive electrode active material can be the positive electrode active material known in the art for use in batteries. In some embodiments, the powder compaction density of the positive electrode active material under 30000N is ≥2.43g / cm 3 , and optionally 2.48g / cm 3 ~2.85g / cm 3 . Further, the powder compaction density of the positive electrode active material under 30000N is 2.5g / cm 3 ~2.8g / cm 3 .

[0149] The use of the positive electrode active material with the higher powder compaction density can increase the compaction density of the positive electrode tab, thereby improving the energy density of the battery.

[0150] For example, the powder compaction density of the positive electrode active material in the positive electrode tab under 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 2.85 g / cm3 3 .

[0151] As a non-limiting example, the positive active material can include at least one of the following materials: phosphate-based positive active material, lithium transition metal oxide, and modified compounds thereof. Among them, the phosphate-based positive active material includes at least one of lithium-containing phosphate with olivine structure and its derivatives.

[0152] Further, the positive active material includes at least one of lithium-containing phosphate with olivine structure and its derivatives. The particle size of the lithium-containing phosphate and its derivative-based positive active material is smaller, the specific surface area is larger, and it is easy to absorb water, so the hydrolysis of the electrolyte in this system battery is more serious, and the HF generated by the hydrolysis is more, so the problem of electrolyte consumption is more prominent. The use of the above electrolyte can help to take advantage of its slow electrolyte consumption rate, thereby improving the cycle performance of such batteries. At the same time, it is beneficial to take advantage of the advantages of large energy density, long cycle life and good safety performance of lithium-containing phosphate and its derivatives.

[0153] In some embodiments of the present application, the lithium-containing phosphate with olivine structure and its derivatives include compounds with the general formula Li x1 A1 y1 M1 a1 M2 b1 P 1-c1 X c1 Q1 z1 , wherein 0.5≤x1≤1.3, 0≤y1≤1.3, and 0.9≤x1+y1≤1.3; 0.9≤a1≤1.5, 0≤b1≤0.5, and 0.9≤a1+b1≤1.5; 0≤c1≤0.5; 3≤z1≤5; A1 includes at least one of Na, K and Mg; M1 includes at least one of Mn, Fe, Co and Ni; M2 includes at least one of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La and Ce; X includes at least one of S, Si, Cl, B, C and N, P; Q1 includes at least one of O and F. The lithium-containing phosphate with olivine structure has excellent cycle stability, which is beneficial to improve the cycle performance of the battery monomer.

[0154] Further, Li x1 A1 y1 M1 a1 M2 b1 P 1-c1 X c1 Q1 z1The lithium-containing phosphate of olivine structure and its derivatives can or can not contain a coating layer. In some embodiments of the present application, the positive active material comprises a core and an ion-conducting layer. The core comprises at least one of the lithium-containing phosphate of olivine structure and its derivatives, and the ion-conducting layer is coated on the surface of the core, and the ion-conducting layer comprises at least one of Fe, C, Ti, Zr, Hf, Ge, and Sn.

[0155] The lithium-containing phosphate of olivine structure and its derivatives can or can not contain a coating layer. In some embodiments of the present application, the positive active material comprises a core and an ion-conducting layer. The core comprises at least one of the lithium-containing phosphate of olivine structure and its derivatives, and the ion-conducting layer is coated on the surface of the core, and the ion-conducting layer comprises at least one of Fe, C, Ti, Zr, Hf, Ge, and Sn.

[0156] The core is coated with the ion-conducting layer, which can improve the electrical conductivity of the lithium-containing phosphate of olivine structure and its derivatives, reduce the powder resistivity of the material, and facilitate the migration rate of lithium ions, thereby improving the rapid charging capability of the battery and reducing the heat generation of the battery cell.

[0157] Further, the ion-conducting layer comprises a fast ion conductor of the formula Li 3-b Fe 2-b M3 b (PO m ) n , M3 comprises at least one of Ti, Zr, Hf, Ge, and Sn in the +4 valence, 0≤b≤1, 3≤m≤5, and 2≤n≤4.

[0158] For example, the fast ion conductor is a material having a NASICON structure, such as one or more of lithium titanium iron phosphate Li2FeTi(PO4)3, lithium zirconium iron phosphate Li2FeZr(PO4)3, and lithium tin iron phosphate Li2FeSn(PO4)3.

[0159] The fast ion conductor having a NASICON structure is a material having super-fast ion conduction capability, with abundant three-dimensional lithium ion diffusion and transport channels, and has the advantages of high ion conduction efficiency and strong structural stability during multiple lithium extraction and intercalation processes. Coating the core surface with the fast ion conductor having a NASICON structure can significantly improve the transport rate of lithium ions in the positive electrode during multiple lithium extraction and intercalation, improve the ion conductivity of the positive active material, improve the rapid charging capability of the battery cell, and further improve the specific capacity and the energy density of the corresponding battery cell.

[0160] In some embodiments, the ion-conducting layer further comprises elemental carbon, which further improves the material.

[0161] The carbon element and the fast ion conductor can be arranged in layers, for example, the carbon element as an independent carbon coating layer and the fast ion conductor as an independent fast ion conductor layer. The carbon coating layer can be coated on the surface of the core, and the fast ion conductor layer is on the surface of the carbon coating layer, that is, the fast ion conductor layer is on the side of the carbon coating layer away from the core. Alternatively, the fast ion conductor layer can be coated on the surface of the core, and the carbon coating layer is on the surface of the fast ion conductor layer, that is, the carbon coating layer is on the side of the fast ion conductor layer away from the core. Of course, the carbon element and the fast ion conductor can also be arranged in the same layer.

[0162] Optionally, the carbon coating layer can be coated on the surface of the fast ion conductor layer by carbonization of an organic carbon source, for example, glucose, polyethylene glycol, etc. The carbon coating layer can partially coat the fast ion conductor layer or completely coat the fast ion conductor layer. The arrangement of the carbon coating layer can significantly improve the electronic conductivity of the core, compensate for the poor electronic transmission performance of the core, and improve the energy density of the battery cell.

[0163] Specifically, the arrangement of the carbon coating layer provides the following advantages for the positive electrode active material of the application:

[0164] The carbon coating layer in the positive electrode active material of the application provides a suitable channel for the transmission of electrons, which can significantly improve the conduction rate of electrons during multiple delithiation and lithiation processes, improve the electronic conductivity of the lithium-containing phosphate, and improve the charging capacity and energy density of the corresponding battery cell.

[0165] The carbon coating layer of the positive electrode active material of the application has a loose and porous structure, which enables the electrolyte to fully and effectively contact the lithium-containing phosphate, thereby improving the transmission rate of lithium ions at the phase interface and the charging capacity of the battery cell.

[0166] The carbon coating layer coated on the surface of the lithium-containing phosphate not only improves the electronic conductivity of the lithium-containing phosphate, but also improves the structural stability of the positive electrode active material, effectively prevents iron dissolution of the positive electrode active material during long-term storage and cyclic use of the battery cell, and thus ensures the cycle life of the battery cell.

[0167] The positive electrode active material of the application uses lithium-containing phosphate as the base material, fully utilizes the advantages of low cost, high reliability, and good cycle stability of lithium-containing phosphate, and solves the disadvantages of poor electronic conductivity and ion conductivity by using the ion-conducting layer (fast ion conductor layer and carbon coating layer). The battery cell prepared from the positive electrode active material of the application has significantly improved energy density under the premise of excellent cycle performance.

[0168] In some embodiments, the mass content of carbon in the positive electrode active material is 1% to 2%, for example, 1%, 1.5%, or 2%. Controlling the mass content of carbon in the positive electrode active material in this range can further improve the conductivity of the positive electrode active material, and thus improve the fast-charging performance of the battery. Understandably, the carbon element can come from, but is not limited to, a carbon coating layer. For example, the surface of the olivine-structured lithium-containing phosphate and its derivatives is coated with a carbon coating layer.

[0169] In some embodiments, the powder resistivity of the positive electrode active material is ≤20 Ω·cm, which further improves the conductivity of the positive electrode active material, and thus improves the fast-charging performance of the battery. For example, the powder resistivity of the positive electrode active material can be 20 Ω·cm, 15 Ω·cm, 10 Ω·cm, 8 Ω·cm, 5 Ω·cm, or the like, and optionally ≤11 Ω·cm.

[0170] In some embodiments, the volume average particle size of the positive electrode active material satisfies 1 μm≤Dv50≤2 μm and 0.4 μm≤Dv10≤0.7 μm, which further improves the fast-charging and power performance of the battery. For example, the Dv50 particle size of the positive electrode active material can be 1 μm, 1.5 μm, or 2 μm. For example, the volume average particle size Dv10 of the positive electrode active material can be 0.4 μm, 0.5 μm, 0.6 μm, or 0.7 μm.

[0171] Herein, Dv50 and Dv10 are meanings known in the art, and can be tested using methods known in the art. For example, a laser particle size analyzer (such as a Malvern Master Size 3000) is used for testing. Herein, Dv50 represents the particle size corresponding to the cumulative percentage of 50% of the volume distribution of particles according to the volume distribution of particle sizes, starting from a small particle size. Dv10 represents the particle size corresponding to the cumulative percentage of 10% of the volume distribution of particles according to the volume distribution of particle sizes, starting from a small particle size.

[0172] The particle size volume distribution can be obtained by the following method: a clean beaker is taken, and an appropriate amount of the sample to be tested is added, and ultrasonic is applied to ensure complete dispersion of the sample. The testing instrument is a Malvern 2000. After the sample is poured into the sample tower and circulated to the testing light path system with the solution, the particle size distribution characteristics of the particles can be obtained by receiving and measuring the energy distribution of the scattered light under the irradiation of the laser beam (light blocking degree: 8% to 12%). The particle size volume distribution graph is plotted according to the test data.

[0173] In some embodiments, the positive electrode film layer further comprises a lithium supplement agent. Further, the lithium supplement agent comprises at least one of a ternary lithium supplement material, lithium phosphate, lithium hydrogen phosphate, lithium sulfate, lithium sulfite, lithium molybdate, lithium nickelate, lithium ferrite, lithium oxalate, lithium titanate, lithium metaborate, lithium metavanadate, lithium tartrate, and trilithium citrate. The lithium supplement agent can supplement lithium ions for the positive electrode film layer, make up for irreversible loss of lithium ions in the system, and improve the capacity, thereby improving the energy density of the battery cell.

[0174] Further, the ternary lithium supplement material comprises 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 comprises at least one of Na, K, and Mg; M4 comprises 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; and Q2 comprises at least one of O and F.

[0175] Further, 0.9≤ x2+y2≤ 2.1.

[0176] Exemplarily, the ternary material comprises 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 O2.

[0177] The lithium supplement agent can be located in the same layer as the positive active material, or in different layers. When the lithium supplement agent and the positive active material are located in different layers, the lithium supplement agent can be located in a lithium supplement layer, and the positive active material can be located in a positive active material layer, in other words, the positive electrode film layer includes the lithium supplement layer and the positive active material layer. The positive active material layer can be arranged on at least one side of the positive current collector, and the lithium supplement layer can be located between the positive active material layer and the positive current collector. Alternatively, the lithium supplement layer can be arranged on at least one side of the positive current collector, and the positive active material layer can be located between the lithium supplement layer and the positive current collector. Alternatively, the lithium supplement layer can be located between the positive active material layer and the positive current collector.

[0178] In some embodiments, the mass content of the positive active material in the positive electrode film layer is 80% to 98%, for example, the mass content can be 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 96%, or 98%. Further, the mass content of the positive active material in the positive electrode film layer can be 90% to 98%.

[0179] In some embodiments, the positive electrode film layer can further optionally include a binder. As a non-limiting example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic ester resin. In some embodiments, the mass content of the binder is ≤5% based on the total mass of the positive electrode film layer.

[0180] In some embodiments, the positive electrode film layer can further optionally include a conductive agent. As a non-limiting example, the conductive agent can include at least one of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass content of the conductive agent is ≤5% based on the total mass of the positive electrode film layer.

[0181] In some embodiments, the positive electrode tab can be prepared by dispersing the above-mentioned components for preparing the positive electrode tab, such as the positive active material, the conductive agent, the binder, and any other components, in a solvent to form a positive electrode slurry; coating the positive electrode slurry on at least one side surface of the positive current collector, and after processes such as drying, cold pressing, etc., the positive electrode tab can be obtained. The type of the solvent can be selected from, but is not limited to, any of the foregoing embodiments, for example, N-methyl pyrrolidone (NMP). The positive electrode slurry can be coated on a single surface of the positive current collector, or on both surfaces of the positive current collector.

[0182] In some embodiments, the positive electrode tab further comprises a positive electrode conductive layer disposed between the positive electrode current collector and the at least one positive electrode film layer. The positive electrode conductive layer comprises a conductive agent. The positive electrode conductive layer can be formed by first coating a corresponding slurry on the surface of the positive electrode current collector, then coating the above-mentioned positive electrode slurry, and drying.

[0183] Further, the conductive agent comprises at least one of super-conductive 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 tab and reducing the heat generation of the battery.

[0184] Further, 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 tab can be further improved, and the energy density of the battery cell can be improved.

[0185] Further, the positive electrode conductive layer further comprises a binder. Further, the binder comprises 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 fluorine-containing acrylic ester resin. The binder in the positive electrode conductive layer can improve the adhesion between the positive electrode current collector and the positive electrode film layer, and improve the structural stability of the positive electrode tab.

[0186] Optionally, in the positive electrode conductive layer, the mass content of the conductive agent is 30% to 50%, and as examples, can be 30%, 35%, 40%, 45%, or 50%; and optionally, in the positive electrode conductive layer, the mass content of the binder is 50% to 70%, and 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.

[0187] Negative electrode tab

[0188] As a non-limiting example, the negative electrode current collector has two surfaces opposite in the thickness direction thereof, and the negative electrode film layer is disposed on either one or both of the two opposite surfaces of the negative electrode current collector.

[0189] In some embodiments, the negative current collector can employ a metal foil or a composite current collector. For example, as a metal foil, a copper foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base material. The composite current collector can be obtained by forming a metal material on a polymer material base material. Non-limiting examples of the metal material in the negative current collector can include at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, and the like. Non-limiting examples of the polymer material base material in the negative current collector can include at least one of a polypropylene (PP) base material, a polyethylene terephthalate (PET) base material, a polybutylene terephthalate (PBT) base material, a polystyrene (PS) base material, a polyethylene (PE) base material, and the like.

[0190] In some embodiments, the compaction density of the negative electrode tab after the secondary battery is charged to 100% SOC at a charge rate of 0.33 C is 1.15 g / cm 3 ~ 1.46 g / cm 3 , optionally 1.15 g / cm 3 ~ 1.36 g / cm 3 . Thus, the above negative electrode tab still has a high compaction density after full charging. For example, the compaction density of the negative electrode tab after the secondary battery is charged to 100% SOC at a charge rate of 0.33 C is 1.15 g / cm 3 , 1.18 g / cm 3 , 1.20 g / cm 3 , 1.22 g / cm 3 , 1.25 g / cm 3 , 1.28 g / cm 3 , 1.3 g / cm 3 , 1.32 g / cm 3 , 1.35 g / cm 3 , 1.36 g / cm 3 , 1.38 g / cm 3 , 1.4 g / cm 3 , 1.42 g / cm 3 , 1.45 g / cm 3 , 1.46 g / cm 3 , or a range composed of any two of the above values. When the compaction density of the negative electrode film layer is in the above range, it is beneficial to improve the energy density of the battery cell; and since the negative electrode active material in the negative electrode film layer is accumulated more closely, the contact resistance between particles is smaller, which can further reduce the resistance of the tab, thereby reducing heat generation.

[0191] In the embodiments of the present application, the compaction density of the negative electrode sheet after the secondary battery is charged to 100% SOC at a charge rate of 0.33C is the meaning known in the art, that is, the positive electrode sheet is disassembled from the battery monomer charged to 100% state of charge (SOC) at a charge rate of 0.33C, and the compaction density of the positive electrode film layer is measured.

[0192] In the embodiments of the present application, 100% SOC is defined as follows:

[0193] The battery monomer is charged to the upper limit voltage of the battery at a constant current charge rate of 0.33C, and then charged to 0.05C at a constant voltage, corresponding to the state of 100% SOC of the battery monomer. Correspondingly, the battery monomer is discharged to the cut-off voltage at a constant current discharge rate of 0.33C, corresponding to the state of 0% SOC of the battery monomer.

[0194] Due to the different types of positive active materials of the battery, the cut-off voltage of full charge may also be different. For example, the upper limit voltage of battery charge can be 3.65V, 3.8V; the cut-off voltage of battery discharge can be 2.5V, 2.0V. Taking lithium iron phosphate as the positive active material in the positive electrode sheet as an example, the compaction density of the negative electrode sheet after the above-mentioned secondary battery is charged to 3.65V at a charge rate of 0.33C and then charged to 0.05C (i.e. after being charged to 100% SOC at a charge rate of 0.33C) is 1.15g / cm 3 ~1.46g / cm 3 .

[0195] In some embodiments, the compaction density of the negative electrode sheet after cold pressing is 1.5g / cm 3 ~1.7g / cm 3 , and optionally 1.55g / cm 3 ~1.65g / cm 3 . The compaction density of the negative electrode sheet after cold pressing refers to the compaction density of the negative electrode sheet after cold forming before being assembled into a battery.

[0196] In some embodiments, the compaction density of the negative electrode sheet after the secondary battery is charged to 100% SOC at a charge rate of 0.33C is 1.15~1.26g / cm 3 ; at the same time, the mass content of the first additive in the electrolyte is 3%~8%.

[0197] The lower the full charge pressure of the negative electrode sheet, the greater the rebound thickness or the lower the initial compaction, the stronger the graphite activity, and thus more electrolyte needs to be consumed, and more additives need to be added in the electrolyte to strengthen the interface film stability of the negative electrode sheet and improve the cycle performance of the battery. Therefore, the compaction density of the negative electrode sheet and the mass content of the first additive in the electrolyte have a matching relationship, so that when the compaction density of the negative electrode sheet is within the above range after the secondary battery is charged to 100% SOC at a charge rate of 0.33C, and the mass content of the first additive in the electrolyte is 3% to 8%, the battery can better balance the high fast-charging performance and cycle performance.

[0198] The second additive in the electrolyte has a low film-forming resistance, which can improve the kinetic performance of the battery and thus improve the ID fast-charging performance of the battery, but the content thereof should not be too high to further improve the cycle performance of the battery. Therefore, the compaction density of the negative electrode sheet and the mass content of the second additive in the electrolyte have a matching relationship, and further, when the compaction density of the negative electrode sheet is 1.15 to 1.26 g / cm 3 after the secondary battery is charged to 100% SOC at a charge rate of 0.33C, and the mass content of the second additive in the electrolyte is 0.5% to 3%.

[0199] Further, when the compaction density of the negative electrode sheet is 1.15 to 1.26 g / cm 3 after the secondary battery is charged to 100% SOC at a charge rate of 0.33C, and the mass content of the first solvent in the organic solvent of the electrolyte is 30% to 40%.

[0200] Further, when the compaction density of the negative electrode sheet is 1.15 to 1.26 g / cm 3 after the secondary battery is charged to 100% SOC at a charge rate of 0.33C, and the mass of the electrolyte per unit battery capacity of 1 Ah of the secondary battery is 2.5 g to 3.0 g.

[0201] In some embodiments, the compaction density of the negative electrode sheet is > 1.26 g / cm 3 and ≤ 1.36 g / cm 3 after the secondary battery is charged to 100% SOC at a charge rate of 0.33C, and the mass content of the first additive in the electrolyte is 2.5% to 6.5%. So that when the compaction density of the negative electrode sheet is within the above range after the secondary battery is charged to 100% SOC at a charge rate of 0.33C, and the mass content of the first additive in the electrolyte is 2.5% to 6.5%, the battery can better balance the high fast-charging performance and cycle performance.

[0202] Further, the compaction density of the negative electrode tab is > 1.26 g / cm3 and ≤ 1.36 g / cm3 after the secondary battery is charged to 100% SOC at a charge rate of 0.33 C. 3 and ≤ 1.36 g / cm3 3 Further, the mass content of the first solvent in the organic solvent of the electrolyte is 25% to 38%.

[0203] Further, the compaction density of the negative electrode tab is > 1.26 g / cm3 and ≤ 1.36 g / cm3 after the secondary battery is charged to 100% SOC at a charge rate of 0.33 C. 3 and ≤ 1.36 g / cm3 3 Further, the mass of the electrolyte per unit battery rated capacity of 1 Ah of the secondary battery is 2.2 g to 2.8 g.

[0204] In some embodiments, the secondary battery has a charge time of 6 min to 15 min from 10% SOC to 80% SOC at 30°C, 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 2% to 9%. Thus, on the basis of providing high energy density with high-pressure dense graphite, the battery is also a fast-charging type battery, and the carboxylate is added to the electrolyte in the above amount, and the amount of the first additive and the second additive is increased, so that the secondary battery has high energy density, fast-charging performance, and cycle performance. Further, 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%.

[0205] In some embodiments, the secondary battery includes a plurality of charging steps in a charging process from 10% state of charge to 80% state of charge, and the difference between the maximum state of charge of any charging step and the maximum state of charge of its adjacent charging step is less than or equal to 5% state of charge, such as 1% state of charge, 1.5% state of charge, 2% state of charge, 2.5% state of charge, 3% state of charge, 3.5% state of charge, 4% state of charge, 4.5% state of charge, 5% state of charge, or a range formed by any two of the above values.

[0206] The secondary battery includes a plurality of charging steps from 10% state of charge to 40% state of charge, and for any charging step, it can be charged at any rate between 5C and 10C, and the charging rate corresponding to each charging step can be any value in the range of 5C, 5.5C, 6C, 6.5C, 7C, 7.5C, 8C, 8.5C, 9C, 9.5C, 10C, or a range formed by any two of the above values.

[0207] The charging steps from 40% state of charge to 80% state of charge also include multiple charging steps, the charging rate of any charging step is less than the charging rate of any charging step from 10% state of charge to 40% state of charge, and the charging rate of the step of charging to 80% state of charge is any value from 2.5C to 5C, for example, it can be 2.7C.

[0208] Exemplarily, the charging steps of the secondary battery from 10% to 80% can be carried out in the following manner:

[0209] Charging from 10% SOC to 15% SOC at 5.0C constant current;

[0210] Charging from 15% SOC to 20% SOC at 5.0C constant current;

[0211] Charging from 20% SOC to 25% SOC at 5.0C constant current;

[0212] Charging from 25% SOC to 30% SOC at 5.0C constant current;

[0213] Charging from 30% SOC to 35% SOC at 5.0C constant current;

[0214] Charging from 35% SOC to 40% SOC at 5.0C constant current;

[0215] Charging from 40% SOC to 45% SOC at 4.6C constant current;

[0216] Charging from 45% SOC to 50% SOC at 4.3C constant current;

[0217] Charging from 50% SOC to 55% SOC at 4.0C constant current;

[0218] Charging from 55% SOC to 60% SOC at 3.7C constant current;

[0219] Charging from 60% SOC to 65% SOC at 3.4C constant current;

[0220] Charging from 65% SOC to 70% SOC at 3.1C constant current;

[0221] Charging from 70% SOC to 75% SOC at 2.9C constant current;

[0222] Charging from 75% SOC to 80% SOC at 2.7C constant current.

[0223] 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. Illustratively, 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 defined by any two of the aforementioned values.

[0224] In some embodiments, the negative electrode tab further comprises a negative electrode conductive layer, the negative electrode conductive layer is disposed between the negative electrode current collector and the negative electrode film layer on at least one side. The negative electrode conductive layer can improve the overall conductivity of the negative electrode tab, which is conducive to improving the electron transmission rate.

[0225] The negative electrode conductive layer comprises a conductive agent. The negative electrode conductive layer can also be formed by first coating a corresponding slurry on the surface of the negative electrode current collector, then coating the above-mentioned negative electrode slurry, and drying to form the negative electrode tab. Further, the conductive agent in the negative electrode conductive layer comprises at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0226] 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 defined by any two of the aforementioned values. When the thickness of the negative electrode conductive layer is within the above range, the conductivity of the negative electrode tab can be further improved, the heat generation of the negative electrode tab can be reduced, thereby reducing the heat generation of the battery monomer; and the energy density of the battery monomer can be improved.

[0227] In some embodiments, the negative electrode conductive layer comprises a binder, and the binder comprises at least one of styrene butadiene rubber (SBR), water-soluble unsaturated resin, water-based acrylic resin, polyvinyl alcohol, sodium alginate, and carboxymethyl chitosan. The negative electrode conductive layer can improve the adhesion between the negative electrode film layer and the negative electrode current collector, and the overall conductivity of the negative electrode tab, which is conducive to improving the electron transmission rate.

[0228] Optionally, in the negative electrode conductive layer, the mass content of the conductive agent is 20% to 40%, for example, 20%, 25%, 30%, 35%, 40%, or a range defined by any two of the aforementioned values. Optionally, in the negative electrode conductive layer, the mass content of the binder is 60% to 80%. For example, 60%, 65%, 70%, 75%, 80%, or a range defined by any two of the aforementioned values.

[0229] In some embodiments, the negative electrode film layer further optionally includes a binder. The binder can include at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0230] In some embodiments, the negative electrode film layer further optionally includes a conductive agent. The conductive agent can include at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0231] In some embodiments, the negative electrode film layer further optionally includes other auxiliary agents, such as thickening agents (e.g., sodium carboxymethyl cellulose (CMC-Na)), and the like.

[0232] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the 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 surface of the negative electrode current collector, and after processes such as drying, cold pressing, and the like, the negative electrode sheet can be obtained. The surface of the negative electrode current collector coated with the negative electrode slurry can be on a single surface of the negative electrode current collector, or on both surfaces of the negative electrode current collector.

[0233] Further, the first graphite includes at least one of artificial graphite and natural graphite. Further, the graphite adopts artificial graphite, which has fewer active sites on the surface and a lower consumption rate of the first solvent and the first additive in the electrolyte, and can meet the demand for long battery life. Further, the graphite has a discharge capacity of ≤ 358 mAh / g. Within this range, the activity of the graphite is appropriate, which is conducive to reducing the consumption rate of the electrolyte and further improving the cycle performance of the battery.

[0234] The Dv50 particle size of the above-mentioned first graphite is 2.2 μm to 7.7 μm, and as an example, can be 2.2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.2 μm, 4.5 μm, 5 μm, 5.5 μm, 5.8 μm, 6 μm, 6.5 μm, 7 μm, 7.2 μm, 7.5 μm, 7.7 μm, or a range composed of any two of the above-mentioned values. Further, the Dv50 particle size of the first graphite can be 2.2 μm to 7 μm.

[0235] 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.

[0236] In one embodiment, the negative electrode film layer includes only one negative electrode active layer containing the first graphite and the second graphite, the first graphite having a Dv50 particle size of 4.2 μm to 7.2 μm, and the second graphite having a Dv50 particle size of 7.8 μm to 14.8 μm. The first graphite has a smaller particle size range and a lower compaction density, and in addition, it has a stronger activity in reaction with electrolyte, thus affecting the energy density, cycle performance and storage performance of the battery. In order to further improve the energy density, cycle performance and storage performance of the battery, the second graphite with a larger particle size is matched in the negative electrode active layer.

[0237] For example, the Dv50 particle size of the second graphite can be 7.8 μm, 8 μm, 8.2 μm, 8.5 μm, 9 μm, 9.2 μm, 9.5 μm, 9.6 μm, 10 μm, 10.2 μm, 10.5 μm, 10.6 μm, 11 μm, 11.8 μm, 12 μm, 12.5 μm, 12.8 μm, 13 μm, 13.5 μm, 13.7 μm, 14 μm, 14.2 μm, 14.5 μm, 14.8 μm, or a range defined by any two of the above values.

[0238] Further, the mass ratio of the first graphite to the second graphite is 2:8 to 6:4; optionally 3:7 to 5:5; for example, the mass ratio can be 2:8, 3:7, 4:6, 5:5, 6:4, or a range defined by any two of the above values.

[0239] Further, the mass content of the first graphite in the negative electrode active layer where it is located is 20% to 70%; for example, the mass content of the first graphite in the negative electrode active layer where it is located can be 20%, 25%, 30%, 35%, 40%, 45%, 48%, 50%, 55%, 60%, 65%, 70%, or a range defined by any two of the above values.

[0240] Further, the total mass content of the first graphite and the second graphite in the negative electrode active layer where they are located is 30% to 98%; for 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 defined by any two of the above values.

[0241] Optionally, the mass content of the first graphite in the negative electrode active layer is ≥20% and <50%, for example, 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%-8%, for example, the total mass content of the first additive and the second additive can be 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, or a range composed of any two of the above values. The content of the first graphite and the content of the additives in the electrolyte are matched. Through the above setting, the content of the first graphite and the total mass content of the first additive and the second additive are more matched, which can effectively improve the fast charging performance and cycle performance of the battery.

[0242] Optionally, the mass content of the first graphite in the negative electrode active layer is 50%-70%, for example, 50%, 55%, 60%, 65%, 70%, or a range composed of any two of the above values, and the total mass content of the first additive and the second additive in the electrolyte is 4%-10%, for example, the total mass content of the first additive and the second additive can be 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5, 9%, 9.5%, 10%, or a range composed of any two of the above values. The higher the content of the first graphite, the more additives need to be added in the electrolyte. In this way, the content of the first graphite and the total mass content of the first additive and the second additive are more matched, which can effectively improve the fast charging performance and cycle performance of the battery.

[0243] In another embodiment, the negative electrode film layer includes a first negative electrode active layer and a second negative electrode active layer stacked in sequence on the same side of the negative electrode current collector, the 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, the second negative electrode active layer includes first graphite and third graphite, the first graphite includes the artificial graphite, and the Dv50 particle size of the third graphite is 7.8 μm-14.8 μm. The artificial graphite has fewer active sites on the surface and a lower consumption rate of the first solvent and the first additive in the electrolyte. The first graphite is arranged in the upper second negative electrode active layer, and the third graphite with a larger particle size is added in the second negative electrode active layer, which further improves the energy density, cycle performance, and storage performance of the battery.

[0244] 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, and optionally 3:7 to 7:3. For example, the mass ratio can be 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, or a range composed of any two of the above values.

[0245] Further, the mass content of the first graphite in the second negative electrode active layer is 20% to 70%, for example, the mass content of the first graphite in the negative electrode active layer where it is located is 20%, 25%, 30%, 35%, 40%, 45%, 48%, 50%, 55%, 60%, 65%, 70%, or a range composed of any two of the above values.

[0246] Optionally, the mass content of the first graphite in the second negative electrode active layer is ≥20% and <50%, for 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%, for 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 composed of any two of the above values. The content of the first graphite and the content of the additive in the electrolyte are in a matching relationship. Through the above setting, the content of the first graphite and the total mass content of the first additive and the second additive are more matched, which can effectively improve the fast charging performance and cycle performance of the battery.

[0247] Optionally, the mass content of the first graphite in the second negative electrode active layer is 50% to 70%, for example, it can be 50%, 55%, 60%, 65%, 70%, or a range composed of any two of the above values, and the total mass content of the first additive and the second additive in the electrolyte is 3.5% to 8%, for 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%, 8%. The higher the content of the first graphite, the more additives need to be added in the electrolyte. In this way, the content of the first graphite and the total mass content of the first additive and the second additive are more matched, which can effectively improve the fast charging performance and cycle performance of the battery.

[0248] Further, 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. 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. Due to the reduced distance between the negative electrode active material particles in the upper second negative electrode active layer, the contact area between the negative electrode active material particles is increased, the conductive channels and bridges are increased, and the active area capable of participating in the reaction is increased, thereby significantly improving the specific capacity and fast charging performance of the battery. The first negative electrode active layer has a larger pore size and better electrolyte infiltration performance due to the addition of graphite with a larger particle size in the lower first negative electrode active layer, and thus the fast charging performance and cycle performance of the battery can be further improved.

[0249] Further, the Dv50 particle size of the graphite in the first negative electrode active layer is 5.8 μm to 12.8 μm, and can be 7.8 μm to 12.8 μm. For example, the Dv50 particle size of the graphite in the first negative electrode active layer can 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 defined by any two of the above values.

[0250] Further, the Dv50 particle size of the first graphite in the second negative electrode active layer is 2.2 μm to 7.7 μm, and can be 4.2 μm to 7.2 μm.

[0251] Further, the proportion of the thickness of the second negative electrode active layer in the total thickness of the first negative electrode active layer and the second negative electrode active layer is 30% to 70%, for example, can be 30%, 40%, 50%, 60%, 70%, or a range defined by any two of the above values.

[0252] It can be understood that the first negative electrode active layer and the second negative electrode active layer can be obtained by sequentially stacking and coating two slurries, and then performing processes such as drying and cold pressing.

[0253] In some embodiments, the artificial graphite includes graphite bulk particles and a coating layer, the graphite bulk particles include secondary particles aggregated by a plurality of primary particles, and the coating layer is coated on the surface of the bulk particles and includes amorphous carbon. Amorphous carbon refers to a transition state carbon material with a very low degree of graphitization and an approximate amorphous state (or a structure with no fixed shape and periodicity). In this application, amorphous carbon refers to the product after carbonization treatment of an organic carbon source.

[0254] The graphite bulk particles include secondary particles, so the migration path of lithium ions in the artificial graphite is more, and the migration path in the primary particles is shorter, which can improve the migration rate of lithium ions; the amorphous carbon layer has more end faces and defects, so the number of sites capable of deintercalating lithium ions is more, so the conductivity of the amorphous carbon layer is more excellent, which can reduce the internal resistance of the negative electrode sheet and the heat generation of the battery cell.

[0255] Further, the mass content of the amorphous carbon is 2% to 5% based on the total mass of the artificial graphite. Illustratively, the mass content of the amorphous carbon layer is 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or a range composed of any two of the above values.

[0256] When the mass content of the amorphous carbon layer is in the above range, the internal resistance of the negative electrode sheet and the heat generation of the battery cell can be further reduced.

[0257] In the embodiments of the present application, the artificial graphite can be prepared by methods known in the art, for example, the preparation method includes: providing graphite bulk particles and an organic carbon source, mixing the two, and then forming an amorphous carbon layer on at least part of the surface of the graphite bulk particles after carbonization treatment.

[0258] Optionally, the organic carbon source includes one or more of coal tar pitch, petroleum pitch, phenolic resin, and coconut shell. Further optionally, the organic carbon source includes petroleum pitch. Optionally, the softening point of the coal tar pitch and petroleum pitch is 250°C or less.

[0259] Optionally, the carbonization treatment temperature is 700°C to 1800°C. Optionally, the carbonization treatment temperature is 1000°C to 1300°C. When the carbonization treatment temperature is in a suitable range, the organic carbon source can be carbonized, and a coating layer containing amorphous carbon can be formed on at least part of the surface of the artificial graphite.

[0260] Optionally, the carbonization treatment time is 1h to 6h.

[0261] Further, the powder resistivity of the artificial graphite is ≤0.04Ω·cm.

[0262] In some embodiments, the charge specific capacity of the graphite in the button cell at 0.1C rate is ≥350mAh / g, which can be optionally 350mAh / g to 440mAh / g.

[0263] In some embodiments, the negative electrode active material can include a silicon-based material in addition to the above-mentioned graphite. The introduction of the silicon-based material can improve the capacity of the negative electrode active material and increase the energy density of the battery cell.

[0264] Further, the silicon-based material can include at least one of a silicon oxide compound and a silicon-carbon composite.

[0265] Further, the mass content of silicon element in the silicon-based material in the negative electrode active material is 0.3% to 10%, and can be 1% to 6%. For example, the mass content of silicon element in the silicon-based material is 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.8%, 5%, 5.2%, 5.5%, 5.8%, 6%, 6.2%, 6.5%, 6.8%, 7%, 7.2%, 7.5%, 7.8%, 8%, 8.2%, 8.5%, 8.8%, 9%, 9.2%, 9.5%, 9.8%, 10%, or a range between any two of the above values.

[0266] The qualitative and quantitative detection of each substance or element in the present application can be performed by using suitable devices and methods known to those skilled in the art. The relevant detection methods can refer to domestic and foreign detection standards, domestic and foreign enterprise standards, etc. Those skilled in the art can also adaptively change certain detection steps / instrument parameters from the perspective of detection accuracy to obtain more accurate detection results. One detection method can be used for qualitative or quantitative determination, or several detection methods can be used in combination for qualitative or quantitative determination.

[0267] Separating film

[0268] In some embodiments, a secondary battery further comprises a separating film. The separating film is arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent short circuit between the positive electrode and the negative electrode, and at the same time to allow ions to pass through.

[0269] In some embodiments, the positive electrode sheet, the negative electrode sheet and the separating film can be made into an electrode assembly by a rolling process or a stacking process.

[0270] The present application does not have special restrictions on the type of separating film, and any known porous structure separating film with good chemical stability and mechanical stability can be selected. The separating film can be a single-layer film or a multi-layer composite film, and there is no special restriction. When the separating film is a multi-layer composite film, the materials of each layer can be the same or different, and there is no special restriction. In some embodiments, the thickness of the separating film is 6 μm to 40 μm, and can be 12 μm to 20 μm.

[0271] In some embodiments, the separating film comprises a porous base film and a functional layer arranged on at least one side of the porous base film.

[0272] Further, the material of the porous base film can include at least one of glass fiber, non-woven fabric, and polyolefin. Optionally, the polyolefin includes at least one of polyethylene, polypropylene, and polyvinylidene fluoride.

[0273] Further, 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 between any two of the above values.

[0274] When the porosity of the separator film is in the above range in the embodiments of the present application, the migration ability of lithium ions in the separator film can be improved, and the internal resistance of the battery cell can be further reduced, thereby reducing heat generation.

[0275] In the embodiments of the present application, the porosity refers to the percentage of the volume of the pores in the separator film to the total volume of the separator film. The porosity can be tested according to the standard GB / T 36363-2018 "Polyolefin Separator for Battery Cell". It should be noted that the actual testing process can be slightly different from the standard in order to eliminate the influence on the testing of the porosity as much as possible, and to obtain more accurate test values according to the difference of testing instruments, testing errors, and the like.

[0276] Further, the porosity of the porous base film is 20% to 70%, and optionally 35% to 60%. Exemplarily, the porosity of the base film is 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or a range between any two of the above values.

[0277] When the thickness of the porous base film is in the above range, the migration path of lithium ions in the base film is shorter, and the internal resistance of the battery cell can be further reduced, thereby reducing heat generation.

[0278] In the embodiments of the present application, the separator film can be a base film; optionally, the separator film further comprises a functional layer arranged on at least one side of the base film, and the functional layer can comprise inorganic particles to improve the heat resistance of the separator film. Optionally, the functional layer is arranged on both sides of the base film.

[0279] In some embodiments, the functional layer comprises 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 comprises first inorganic particles, the second functional layer is located on the other side of the base film, and the second functional layer comprises composite particles, the composite particles comprise second inorganic particles and a plurality of 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.

[0280] The first functional layer and the second functional layer have good heat resistance, and can improve the heat resistance of the separator film.

[0281] Optionally, the first functional layer can include a binder, optionally including at least one of a fluorine-containing binder or a polyacrylic binder, for example, polyvinylidene fluoride.

[0282] Optionally, the first inorganic particles include one or more of silicon oxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide. The above first inorganic particles can improve the heat resistance of the first functional layer.

[0283] In the embodiments of the present application, the thickness of the base film has the meaning known in the art, which can be detected by using the meaning and equipment known in the art, for example, a newly prepared separator film can be taken as a sample, or a battery cell that has been discharged (discharged to the lower limit cutoff voltage so that the charged state of the battery cell is about 0% SOC) is disassembled in reverse, the separator film is obtained from the battery cell, and the separator film is dried and taken as a sample, the separator film is cut by an ion beam cutting instrument to form a cross section; then, the thickness of the cross section of the separator film and each layer thereof is measured by using a scanning electron microscope.

[0284] The non-fluoropolymer particles in the second functional layer refer to polymers that are non-fluorinated polymers, for example, the non-fluoropolymer particles include acrylate copolymers, which optionally include acrylate-acrylonitrile-acrylamide-acryl copolymers. The acrylate copolymers have excellent bonding properties, and have high bonding stability with the base film. The molar ratio of each monomer in the copolymer can be any ratio, for example, the molar ratio is 35%:30%:15%:20%, or 40%:20%:10%:30%, or 45%:15%:20%:20%, etc.

[0285] The second inorganic particles in the composite particles make it difficult for the non-fluoropolymer particles to be bonded due to high-temperature treatment in the granulation process, so that the composite particles have pores, which is beneficial to the transmission of lithium ions and improves the ion conductivity of the separator film; and the second inorganic particles can also improve the compression modulus of the composite particles, so that the composite particles are less likely to deform during charging and discharging, making the structure of the separator film more stable, which can improve the kinetic performance of the battery cell and improve the rapid charging performance. Optionally, compared with the first functional layer, the second functional layer is arranged close to the negative electrode tab, and since the composite particles are less likely to deform, the separator film is less likely to cause side effects such as extrusion to the negative electrode tab, making the kinetic performance of the negative electrode tab stable. Correspondingly, the first functional layer is arranged close to the positive electrode tab.

[0286] Optionally, the second inorganic particles comprise one or more of silicon oxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide; and optionally, the second inorganic particles comprise silicon oxide. The second inorganic particles described above can improve the heat resistance of the second functional layer, and can form composite particles with the non-fluoropolymer, further improving the cycle stability and kinetic performance of the separator film, and improving the cycle performance and fast charging performance of the battery cell.

[0287] The average particle size of the second inorganic particles is 5 nm to 100 nm, optionally 10 nm to 100 nm, and optionally 5 nm to 20 nm. Illustratively, 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 defined by any two of the above values. When the average particle size of the second inorganic particles is within the above range, the heat resistance and compression modulus of the composite particles can be improved.

[0288] In the embodiments of the present application, the average particle size of the second inorganic particles has the meaning known in the art and can be detected using devices and methods known in the art. For example, after obtaining the separator film, the separator film is dried as a sample, and the separator film is cut using an ion beam cutter to form a cross section. Then, the particle size of the second inorganic particles in the separator film is measured using a scanning electron microscope, and the particle size of a plurality of, for example, 50, second inorganic particles is measured to calculate the average value as the average particle size of the second inorganic particles.

[0289] In some embodiments, the ion conductivity of the separator film is 0.3 mS / cm to 0.6 mS / cm. Illustratively, the ion conductivity of the separator film 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 defined by any two of the above values.

[0290] When the ion conductivity of the separator film is within the above range, the migration ability of lithium ions of the separator film can be further improved, and the fast charging performance of the battery cell can be improved.

[0291] In the embodiments of the present application, the ion conductivity of the separator film has the meaning known in the art and can be detected using devices and methods known in the art. For example,

[0292] Preparation of test 2025 button cell: In a vacuum glove box, lithium sheet was put into the negative electrode shell, 150 μL of electrolyte was added, the electrolyte was 1 M LiPF6 solution in EC / EMC / DEC = 3 / 5 / 2 (mass ratio), then the separator film (area of 3.14 cm 2 , thickness of 12 μm) was put to make it close to the lithium sheet, 25 μL of electrolyte was added, and finally the positive electrode sheet (the positive electrode sheet can be the positive electrode sheet in Example 1) was put on it, and then it was packaged. The assembled button cell was taken out of the vacuum glove box and placed for 24 h for the next test.

[0293] Test: In an electrochemical workstation, the test was carried out in the frequency range of 10 -1 ~ 10 6 Hz, the resistance Rb of the separator film was obtained, and the ionic conductivity σ (unit: mS / cm) was calculated by the following formula, σ = L / (R b × S)

[0294] wherein R b is the equivalent resistance, L and S are the thickness and area of the separator film to be tested, respectively.

[0295] The secondary battery includes at least one battery cell. The secondary battery can include one or more battery cells.

[0296] In the present application, unless otherwise specified, the "battery cell" refers to a basic unit capable of realizing the mutual conversion between chemical energy and electrical energy, and further, generally includes at least a positive electrode sheet, a negative electrode sheet and an electrolyte. In the process of charging and discharging the battery, active ions are embedded and extracted between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting active ions between the positive electrode sheet and the negative electrode sheet.

[0297] The shape of the battery cell is not particularly limited in the present application, and it can be cylindrical, square or any other shape. For example, the secondary battery shown in FIG. 1 is a battery cell, which is an example of a square structure battery cell 5.

[0298] In some embodiments, the battery cell 5 can include an outer package. The outer package can be used to package the electrode assembly and the electrolyte described above. In some embodiments, the outer package of the battery cell 5 can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the battery cell 5 can also be a soft package, such as a pouch soft package. The material of the soft package can be plastic, and further, non-limiting examples of the plastic can include at least one of polypropylene, polybutylene terephthalate, and polybutylene succinate, etc.

[0299] In some embodiments, referring to FIG. 2, the outer package can include a housing 51 and a cover plate 53. The housing 51 can include a bottom plate and side plates connected to the bottom plate, which enclose a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be arranged on the opening to close the receiving cavity. The positive electrode tab, the negative electrode tab, and the separator film can form an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is packaged 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, which can be selected by those skilled in the art according to actual needs.

[0300] In some embodiments, the secondary battery can be a battery module or a battery pack. The battery module includes at least one battery cell. The number of battery cells contained in the battery module can be one or more, which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0301] The secondary battery shown in FIG. 3 is a battery module, which is a battery module 4 as an example. Referring to FIG. 3, in the battery module 4, a plurality of battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, other arbitrary arrangements can also be used. Further, the plurality of battery cells 5 can be fixed by fasteners.

[0302] Optionally, the battery module 4 can also include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.

[0303] In some embodiments, the above-mentioned battery module can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0304] FIGS. 4 and 5 show that the secondary battery is a battery pack, which is a battery pack 1 as an example. Referring to FIGS. 4 and 5, the battery pack 1 can include a battery box and a plurality of battery modules 4 arranged in the battery box. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be arranged on the lower box body 3 to form a closed space for receiving the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0305] In addition, the embodiment of the present application also provides a power utilization device, which comprises the above-mentioned secondary battery provided by the present application. The secondary battery can be used as a power supply of the power utilization device, or can be used as an energy storage unit of the power utilization device. The power utilization device can include a mobile device, an electric vehicle, an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto. Among them, the mobile device can be a mobile phone, a notebook computer, etc.; the electric vehicle can be a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc., but is not limited thereto.

[0306] As the power utilization device, the secondary battery can be selected according to the use requirement thereof.

[0307] FIG. 6 is a power utilization device 6 as an example. The power utilization device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirement of high power and high energy density of the secondary battery for the power utilization device, a battery pack or a battery module can be used.

[0308] The device as another example can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thinness, and a battery monomer 5 can be used as a power supply.

[0309] In order to make the technical problems, technical solutions and beneficial effects solved by the present application clearer, the present application will be further described in detail below in combination with embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The description of the at least one exemplary embodiment below is actually only illustrative, but not as any limitation on the present application and its application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0310] Unless specific techniques or conditions are specified in the embodiments, the techniques or conditions described in the literature in the art or according to the product instructions are used. Unless the manufacturer of the reagent or instrument is specified, it is a conventional product that can be obtained by purchase in the market.

[0311] Embodiment 1

[0312] (1) Preparation of the positive electrode sheet:

[0313] The positive electrode active material comprises lithium iron phosphate and an ion-conducting layer, the ion-conducting layer is coated on the surface of the lithium iron phosphate, and the ion-conducting layer comprises lithium titanium iron phosphate Li2FeTi(PO4)3 and amorphous carbon. The Dv50 of the positive electrode active material is 1.6 μm, and the Dv10 is 0.64 μm. The powder compaction density under 30000 N is 2.53 g / cm 3 .

[0314] The positive electrode current collector is an aluminum foil with a thickness of 10 pm, and a positive electrode conductive layer is arranged on the positive electrode current collector. The positive electrode conductive layer is formed by uniformly mixing conductive carbon SP and a binder polyvinylidene fluoride (PVDF) and a solvent N-methyl pyrrolidone NMP, and then coating on the surface of the current collector to form a thickness of 1 pm.

[0315] The positive electrode active material lithium iron phosphate LiFePO4, the binder polyvinylidene fluoride, and the conductive agent acetylene black are mixed in a mass ratio of 97:2:1, and then a solvent N-methyl pyrrolidone (NMP) is added and stirred uniformly to form a positive electrode slurry; the positive electrode slurry is uniformly coated on the positive electrode conductive layer of the positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode sheet is obtained. The positive electrode sheet includes a positive electrode current collector and a positive electrode conductive layer and a positive electrode film layer arranged on the positive electrode current collector in sequence.

[0316] The single-sided coating weight of the positive electrode sheet is 300 mg / 1540.25 mm 2 ; the compaction density of the positive electrode sheet at 100% SOC of the battery charged at a charge rate of 0.33 C is 2.63 g / cm 3 .

[0317] The battery is charged to 100% SOC at a charge rate of 0.33 C in the following manner: the battery monomer is charged to the upper limit voltage of the battery (3.65 V) at a constant current charge rate of 0.33 C, and then charged at a constant voltage of 0.05 C corresponding to the state of 100% SOC of the battery monomer.

[0318] (2) Preparation of the negative electrode sheet:

[0319] The preparation method of the double-layer structure negative electrode sheet is as follows:

[0320] The Dv50 particle sizes of the first graphite, the second graphite, and the third graphite are 5.8 pm, 9.6 pm, and 9.6 pm, respectively.

[0321] The negative electrode current collector is a copper foil with a thickness of 5 pm, and a negative electrode conductive layer is arranged on the negative electrode current collector. The negative electrode conductive agent is formed by uniformly mixing conductive carbon SP, a binder SBR, a dispersing agent CMC, and a solvent water, and then coating on the surface of the current collector to form a thickness of 1 pm.

[0322] The negative electrode active material third graphite, the conductive agent acetylene black, the binder styrene butadiene rubber, and the thickening agent sodium carboxymethyl cellulose are mixed in a mass ratio of 96:0.5:2.5:1, and then a solvent deionized water is added and stirred uniformly to form a first negative electrode slurry.

[0323] The negative active material first graphite, the second graphite, the conductive agent acetylene black, the binder styrene-butadiene rubber, and the thickening agent sodium carboxymethyl cellulose are mixed according to a mass ratio of 54.9:41.1:0.5:2.5:1, and then the solvent deionized water is added to form the second negative electrode slurry after being stirred uniformly.

[0324] The first negative electrode slurry is uniformly coated on the negative electrode conductive layer of the negative electrode current collector copper foil and dried; the second negative electrode slurry is coated on the surface of the dried first negative electrode slurry, and after drying and cold pressing, the negative electrode sheet is obtained. The negative electrode sheet includes a negative electrode current collector and a negative electrode conductive layer and a negative electrode film layer arranged on the negative electrode current collector in sequence. The negative electrode film layer includes a first negative electrode active layer and a second negative electrode active layer arranged on the negative electrode conductive layer in sequence.

[0325] Among them, the single-side coating weight of the negative electrode sheet is 138 mg / mm 2 ; the compaction density of the positive electrode sheet under the 100% SOC of the battery is 1.2 g / cm 3 ; and the mass ratio of the first graphite, the second graphite, and the third graphite in the total mass of the first graphite, the second graphite, and the third graphite in the negative electrode film layer is 40%, 30%, and 30%, respectively.

[0326] (3) Preparation of electrolyte:

[0327] In an argon atmosphere glove box with a water content of less than 10 ppm, the first solvent ethylene carbonate (EC), the second solvent ethyl acetate (EA), and dimethyl carbonate (DMC) are mixed uniformly at a certain mass ratio to obtain an organic solvent. The mass content of ethylene carbonate (EC), ethyl acetate (EA), and dimethyl carbonate (DMC) in the organic solvent is 25%, 50%, and 25%, respectively, as shown in Table 1. A certain mass of lithium hexafluorophosphate (LiPF6) is slowly added as a lithium salt, and fully stirred until it is completely dissolved. The concentration of LiPF6 in the electrolyte is 1 mol / L. After returning to room temperature, 6% of the first additive vinylene carbonate (VC) and 4% of the second additive fluoroethylene carbonate (FEC) are added to the total mass of the electrolyte, and fully mixed to obtain the electrolyte. The mass b of the electrolyte under the rated capacity of 1 Ah per unit battery of the secondary battery is 2.65 g, as shown in Table 1.

[0328] (4) Separation film:

[0329] The separation film includes a base film, which is a 7 μm polyethylene film layer with a porosity of 42%.

[0330] (5) Preparation of secondary battery:

[0331] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in sequence and wound to obtain a wound electrode assembly; the electrode assembly is added into an outer packaging square aluminum shell, and after drying, an electrolyte is injected, and after packaging, standing, formation, aging, secondary packaging, and capacity processes, a secondary battery is obtained.

[0332] The preparation method of examples 2-4 is similar to that of example 1, except that the mass content of the first solvent ethylene carbonate (EC) in the organic solvent is adjusted (and the mass content of dimethyl carbonate (DMC) is adjusted accordingly), as shown in Table 1.

[0333] The preparation method of examples 5-8 is similar to that of example 2, except that the mass content of the first additive VC in the electrolyte is adjusted, as shown in Table 1.

[0334] The preparation method of examples 9-13 is similar to that of example 2, except that the mass content of the second additive FEC in the electrolyte is adjusted, as shown in Table 1.

[0335] 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.

[0336] As shown in Table 1.

[0337] The preparation method of examples 15-17 is similar to that of example 2, except that the type of the first graphite of the negative active material is adjusted, and the Dv50 parameter is different, as shown in Table 1.

[0338] The preparation method of examples 18-19 is similar to that of example 10, except that the injection coefficient of the electrolyte is adjusted, so the mass b of the electrolyte under the rated capacity of 1 Ah per secondary battery is different, and the mass content of the first additive in the electrolyte is adjusted, as shown in Table 1.

[0339] Example 19

[0340] The preparation method is similar to that of example 3, except that the negative electrode sheet is a single-layer structure, and the preparation method is as follows:

[0341] The first graphite of the negative active material, the second graphite, the conductive agent acetylene black, the binder styrene-butadiene rubber, and the thickening agent sodium carboxymethyl cellulose are mixed in a mass ratio of 38.4:57.6:0.5:2.5:1, and then the solvent deionized water is added, stirred uniformly to form a negative electrode slurry; the negative electrode slurry is uniformly coated on the negative electrode conductive layer of the negative electrode current collector copper foil, dried, and cold-pressed to obtain a negative electrode sheet.

[0342] The negative electrode sheet comprises a negative electrode current collector and a negative electrode conductive layer and a negative electrode active layer arranged on the negative electrode current collector in sequence.

[0343] The single-side coating weight of the negative electrode sheet is 138 mg / mm 2 ; the compaction density of the positive electrode sheet at 100% SOC is 1.2 g / cm 3 ; the mass ratio of the first graphite and the second graphite is 40% and 60% respectively based on the total mass of the first graphite and the second graphite in the negative electrode active layer.

[0344] Comparative Examples 1-5 were prepared in a manner similar to 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 was adjusted, as shown in Table 1.

[0345] The following is a performance test.

[0346] (I) The test procedure for the capacity retention rate of the battery at 60°C after 1000 cycles is as follows:

[0347] At 60°C, the battery was charged at 1C constant current to a charge cut-off voltage of 3.65V, and then discharged at 1C constant current to 2.0V, which was one charge-discharge cycle. The capacity C0 after the first cycle was recorded. The above charge-discharge cycle steps were repeated until 1000 cycles were completed. The capacity Cn after the 1000th cycle was recorded. The capacity retention rate of the battery at 60°C after 1000 cycles was calculated as Cn / C0 x 100%. The higher the capacity retention rate, the better the cycle performance of the battery.

[0348] (II) The test procedure for the charging time T of the secondary battery at 30°C from 10% SOC to 80% SOC is as follows:

[0349] At an ambient temperature of 30°C, the battery was charged from 10% SOC,

[0350] charged at 5.0C constant current from 10% SOC to 15% SOC;

[0351] charged at 5.0C constant current from 15% SOC to 20% SOC;

[0352] charged at 5.0C constant current from 20% SOC to 25% SOC;

[0353] charged at 5.0C constant current from 25% SOC to 30% SOC;

[0354] charged at 5.0C constant current from 30% SOC to 35% SOC;

[0355] Charge from 35% SOC to 40% SOC at 5.0 C constant current;

[0356] Charge from 40% SOC to 45% SOC at 4.6 C constant current;

[0357] Charge from 45% SOC to 50% SOC at 4.3 C constant current;

[0358] Charge from 50% SOC to 55% SOC at 4.0 C constant current;

[0359] Charge from 55% SOC to 60% SOC at 3.7 C constant current;

[0360] Charge from 60% SOC to 65% SOC at 3.4 C constant current;

[0361] Charge from 65% SOC to 70% SOC at 3.1 C constant current;

[0362] Charge from 70% SOC to 75% SOC at 2.9 C constant current;

[0363] Charge from 75% SOC to 80% SOC at 2.7 C constant current;

[0364] Record the total charging time.

[0365] (III) The test procedure for the capacity retention rate of the battery cycled for 1000 cycles at 30°C is as follows:

[0366] At 30°C, charge the battery from 10% SOC, respectively, according to the above different SOC corresponding to the rate to 80% SOC, and then continue to use 0.33 C charging rate constant current charging to 3.65 V, stand for 30 min, then discharge to 2.0 V at 1 C constant current, which is a charge-discharge cycle, record the capacity C0 after the first cycle; repeat the above charge-discharge cycle steps until 1000 cycles, record the capacity Cn after the 1000th cycle, get the capacity retention rate of the battery cycled for 1000 cycles at 30°C = Cn / C0 x 100%. The higher the capacity retention rate, the better the cycle performance of the battery.

[0367] Some parameters of each example and comparative example are shown in Table 1, wherein the content is the mass content, the unit of single-sided coating weight of the positive electrode and the negative electrode is mg / 1540.25 mm 2 .

[0368] The above performance test results of each example and comparative example are shown in Table 2.

[0369] Table 1

[0370] Table 2

[0371] From the above Tables 1-2, it can be seen 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, and the high-temperature cycle performance of the battery deteriorates, and the fast charging time is longer, indicating that the 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, and the self-stability of the electrolyte deteriorates, resulting in a decrease in the electrical conductivity, and thus the room temperature and high-temperature cycle performances are poor.

[0372] Each of the embodiments adjusts the composition and ratio of the electrolyte, and cooperates with the negative electrode plate containing the first graphite with a small particle size, so that the prepared secondary battery can have good fast charging performance, room temperature cycle performance and high-temperature cycle performance. In Example 14, the second solvent in the electrolyte is a carbonate solvent, and the electrical conductivity of the electrolyte decreases, so the single-sided coating weight of the positive electrode plate and the negative electrode plate is reduced to improve the fast charging performance of the battery.

[0373] Each of the technical features of the above-described embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described, however, as long as the combinations of the technical features do not exist contradictory, they should be considered as the scope of the present disclosure.

[0374] The above-described embodiments only express several embodiments of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent application. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of the present application. Therefore, the scope of the patent of the present application should be subject to the appended claims.

Claims

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

2. The secondary battery as described in 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 haloalkyl, and R1 and R2 are not both hydrogen.

3. The secondary battery according to any one of claims 1 to 2, wherein, The ethylene carbonate derivatives include at least one of fluoroethylene carbonate, difluoroethylene carbonate, and trifluoromethylethylene carbonate.

4. The secondary battery according to any one of claims 1 to 3, wherein, The cyclic carbonates include at least one of ethylene carbonate and propylene carbonate.

5. The secondary battery according to any one of claims 1 to 4, 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 any one of claims 1 to 5, 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 any one of claims 1 to 6, wherein, The total mass content of the first additive and the second additive in the electrolyte is 3% to 12%, and can be selected as 3.5% to 9%.

8. The secondary battery according to any one of claims 1 to 7, wherein, The electrolyte mass of the secondary battery at a rated capacity of 1 Ah is 2.2 g to 2.95 g.

9. The secondary battery as described in claim 8, wherein, The electrolyte mass of the secondary battery at a rated capacity of 1Ah is 2.2g to 2.65g, and the total mass content of the first additive and the second additive in the electrolyte is 5% to 9%. Alternatively, the electrolyte mass of the secondary battery at a rated capacity of 1 Ah is >2.65g and ≤2.95g, 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 any one of claims 1 to 9, wherein, The positive electrode active material has a powder compaction density ≥ 2.43 g / cm³ at 30000 N. 3 The option is 2.48g / cm³. 3 ~2.85g / cm 3 .

11. The secondary battery as claimed in claim 10, wherein, The positive electrode active material includes at least one of lithium phosphate with an olivine structure and its derivatives.

12. The secondary battery as claimed in claim 11, wherein, The positive electrode active material includes: The core includes at least one of lithium phosphates and their derivatives with an olivine structure; and An ion-conducting layer is provided, which covers the surface of the core. The lithium-ion-conducting layer includes at least one element selected from Fe, C, Ti, Zr, Hf, Ge, and Sn.

13. The secondary battery as described in claim 11 or 12, wherein, The lithium phosphates and their derivatives with the olivine structure include those of the general formula Li x1 A1 y1 M1 a1 M2 b1 P 1-c1 X c1 Q1 z1 The 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; Q1 includes at least one of O and F.

14. The secondary battery as claimed in claim 13, wherein, The lithium phosphates and their derivatives with the olivine structure include at least one of lithium iron phosphate, lithium manganese phosphate, lithium nickel phosphate, and lithium cobalt phosphate.

15. The secondary battery as described in claim 12, wherein, The ion-conducting layer comprises Li 3-b Fe 2-b M3 b (PO m ) n The fast ion conductor M3 includes at least one element selected from Ti, Zr, Hf, Ge and Sn in the +4 valence, 0≤b≤1, 3≤m≤5, 2≤n≤4.

16. The secondary battery as claimed in claim 15, wherein, The fast ion conductor includes at least one of lithium iron phosphate, lithium zirconium iron phosphate, and lithium tin iron phosphate.

17. The secondary battery according to any one of claims 1 to 16, wherein, At least one of the following conditions must be met: (1) The compaction density of the positive electrode sheet is 2.5 g / cm³. 3 ~2.8g / cm 3 ; (2) The carbon content in the positive electrode active material is 1% to 2% by mass; (3) The resistivity range of the positive electrode active material is R≤20Ω·cm, and R≤11Ω·cm is optional; (4) The volume average particle size of the positive electrode active material satisfies: 1μm≤Dv50≤2μm, 0.4μm≤Dv10≤0.7μm.

18. The secondary battery according to any one of claims 1 to 17, wherein, The positive electrode film layer also includes a lithium replenishing agent, which includes at least one of ternary lithium replenishing materials, lithium phosphate, lithium hydrogen phosphate, lithium sulfate, lithium sulfite, lithium molybdate, lithium nickel oxide, lithium ferrite, lithium oxalate, lithium titanate, lithium tetraborate, lithium metasilicate, lithium metamanganate, lithium tartrate, and lithium trilithium citrate.

19. The secondary battery as claimed in claim 18, wherein, The ternary lithium supplementary 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.

20. The secondary battery according to any one of claims 1 to 19, wherein, 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, which includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

21. The secondary battery as claimed in claim 20, wherein, The thickness of the positive electrode conductive layer is 0.5μm to 2μm.

22. The secondary battery as claimed in claim 20 or 21, wherein, The positive conductive layer includes an adhesive, which includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, a terpolymer of polyvinylidene fluoride-tetrafluoroethylene-propylene, a terpolymer of polyvinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, a terpolymer of tetrafluoroethylene-hexafluoropropylene, polyacrylic acid, and fluorinated acrylate resins.

23. The secondary battery as described in claim 20, 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%.

24. The secondary battery according to any one of claims 1 to 23, wherein, The secondary battery, after being charged to 100% SOC at a charging rate of 0.33C, has a negative electrode sheet with a compaction density of 1.15 g / cm³. 3 ~1.46g / cm 3 The option is 1.15g / cm³. 3 ~1.36g / cm 3 .

25. The secondary battery as claimed in claim 24, wherein, The secondary battery, after being charged to 100% SOC at a charging rate of 0.33C, has a negative electrode sheet with a compaction density of 1.15–1.26 g / cm³. 3 The mass content of the first additive in the electrolyte is 3% to 8%.

26. The secondary battery as claimed in claim 25, wherein, At least one of the following conditions must be 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%.

27. The secondary battery as claimed in claim 24, 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 >1.26 g / cm³. 3 And ≤1.36g / cm 3 The mass content of the first additive in the electrolyte is 2.5% to 6.5%.

28. The secondary battery as claimed in claim 27, wherein, At least one of the following conditions must be 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%.

29. The secondary battery according to any one of claims 1 to 28, wherein, The electrolyte further includes a second solvent, which includes at least one of linear carbonates, carboxylic esters, ethers, nitriles, and sulfones.

30. The secondary battery as claimed in claim 29, wherein, The second solvent includes a carboxylic acid ester; optionally, the carboxylic acid ester includes at least one of methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and methyl butyrate.

31. The secondary battery as described in claim 32, wherein, The charging time for 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%.

32. The secondary battery as described in claim 31, wherein, 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%.

33. The secondary battery according to any one of claims 1 to 32, wherein, The electrolyte includes a lithium salt, which includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, fluorosulfonyl imide salt, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

34. The secondary battery as described in claim 33, wherein, The concentration of the lithium salt in the electrolyte is 0.7 mol / L to 1.5 mol / L.

35. The secondary battery as described in claim 33 or 34, 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 the LiFSI is 0.2 mol / L to 0.5 mol / L; (2) The concentration of LiPF6 is 0.5 mol / L to 1.3 mol / L; (3) The lithium salt includes LiFSI and LiPF6, and the concentration ratio of LiFSI to LiPF6 is (2-5):

10.

36. The secondary battery according to any one of claims 1 to 35, wherein, The negative electrode sheet further includes a negative electrode conductive layer, which is disposed between the negative electrode current collector and at least one side of the negative electrode film layer. The negative electrode conductive layer includes a conductive agent, which includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

37. The secondary battery as claimed in claim 36, wherein, The thickness of the negative electrode conductive layer is 0.5μm to 2μm.

38. The secondary battery as described in claim 36 or 37, wherein, The negative electrode conductive layer includes an adhesive, which includes at least one of styrene-butadiene rubber, water-soluble unsaturated resin, water-based acrylic resin, polyvinyl alcohol, sodium alginate, and carboxymethyl chitosan.

39. The secondary battery as described in claim 38, 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%.

40. The secondary battery according to any one of claims 1 to 39, 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.

41. The secondary battery as claimed in claim 40, wherein, The negative electrode film layer includes only one negative electrode active layer, which contains the first graphite and the second graphite. The Dv50 particle size of the first graphite is 4.2 μm to 7.2 μm, and the Dv50 particle size of the second graphite is 7.8 μm to 14.8 μm.

42. The secondary battery as claimed in claim 41, wherein, 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.

43. The secondary battery as described in claim 41 or 42, wherein, The first graphite has a mass content of ≥20% and <50% in the negative electrode active layer, and the total mass content of the first additive and the second additive in the electrolyte is 3% to 8%. Alternatively, the first graphite has a mass content of 50% to 70% in the negative electrode active layer, and the total mass content of the first additive and the second additive in the electrolyte is 4% to 10%.

44. The secondary battery as claimed in claim 40, wherein, The negative electrode film layer includes a first negative electrode active layer and a second negative electrode active layer sequentially stacked on the same side of the negative electrode current collector. The first negative electrode active layer includes at least one of artificial graphite and natural graphite. The second negative electrode active layer includes the first graphite and a third graphite. The first graphite includes artificial graphite. The third graphite has a Dv50 particle size of 7.8 μm to 14.8 μm.

45. The secondary battery as claimed in claim 44, wherein, 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.

46. ​​The secondary battery as claimed in claim 44 or 45, wherein, At least one of the following conditions must be met: (1) The ratio of the total amount of negative electrode active material in the second negative electrode active layer and the first negative electrode active material layer is 3:7 to 7:3; or optionally 4:6 to 6:

4. (2) The mass content of the first graphite in the second negative electrode active layer is 30% to 70%; optionally, the mass content of the first graphite in the second negative electrode active layer is ≥20% and <50%, and the total mass content of the first additive and the second additive in the electrolyte is 3% to 7%; or, the first graphite in the second negative electrode... The active layer contains 50% to 70% by mass, and the total mass content of the first additive and the second additive in the electrolyte is 3.5% to 8% by mass. (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; optionally, the Dv50 particle size of the graphite in the first negative electrode active layer is 5.8 μm to 12.8 μm, and 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, and optionally 4.2 μm to 7.2 μm.

47. The secondary battery according to any one of claims 44 to 46, wherein, The artificial graphite includes graphite bulk particles and a coating layer. The graphite bulk particles include secondary particles formed by the aggregation of multiple primary particles. The coating layer covers the surface of the bulk particles and includes amorphous carbon.

48. The secondary battery as claimed in claim 47, wherein, At least one of the following conditions must be met: (1) Based on the total mass of the artificial graphite, the mass content of the amorphous carbon is 2% to 5%; (2) The resistivity of the artificial graphite powder is ≤0.04Ω·cm.

49. The secondary battery according to any one of claims 1 to 48, wherein, The first graphite has a charging capacity of ≥350mAh / g at a 0.1C rate in a coin cell, and can be selected from 350mAh / g to 440mAh / g.

50. The secondary battery according to any one of claims 1 to 49, wherein, The negative electrode active material further includes a silicon-based material, which includes at least one of silicon oxide and silicon-carbon composite; the silicon element in the silicon-based material has a mass content of 0.3% to 10%, optionally 1% to 6%.

51. The secondary battery according to any one of claims 1 to 50, wherein, The isolation membrane includes a porous base membrane and a functional layer disposed on at least one side of the porous base membrane.

52. The secondary battery as described in claim 51, wherein, At least one of the following conditions must be met: (1) The thickness of the porous base film is ≤12μm, and can be ≤9μm; (2) The porosity of the porous base membrane is 20% to 70%, and can be selected as 35% to 60%.

53. The secondary battery as described in claim 51 or 52, wherein, The isolation membrane includes a first functional layer and a second functional layer disposed on both sides of the porous base membrane. The first functional layer includes a first inorganic particle, and the second functional layer includes composite particles. The composite particles include a second inorganic particle and a non-fluoropolymer particle. The second inorganic particle is attached to the surface of the non-fluoropolymer particle and / or dispersed inside the non-fluoropolymer particle.

54. The secondary battery as described in claim 53, wherein, At least one of the following conditions must be met: (1) The non-fluoropolymer particles include acrylate polymer particles; (2) The first functional layer is located between the negative electrode sheet and the porous base film, and the second functional layer is located between the positive electrode sheet and the porous base film.

55. An electrical device comprising a secondary battery as described in any one of claims 1 to 54.

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