Secondary battery and electric device

Abstract

In a secondary battery and an electric device, the negative electrode sheet in the secondary battery comprises a negative electrode current collector and a negative electrode film layer installed on at least one side of the negative electrode current collector, the negative electrode film layer comprises a negative electrode active material, the negative electrode active material comprises a first graphite, and the Dv50 particle size of the first graphite is 2.2 μm to 7.7 μm; the electrolyte comprises an organic solvent and an organic additive, wherein the organic solvent comprises a first solvent, the first solvent comprises a cyclic carbonate, and the mass content of the first solvent is 25% to 40% based on the total mass of the organic solvent; and 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 based on the total mass of the electrolyte, the mass percentage of the first additive in the electrolyte is 2% to 10%, and the mass percentage of the second additive in the electrolyte is 0.3% to 6%.

Description

Technology Field

[0001] This application relates to the field of battery technology, and in particular to secondary batteries and electric devices. Background Technology

[0002] The description herein provides only background information related to the present application and does not necessarily constitute prior art.

[0003] With the recent rapid advancement of rechargeable batteries, such as lithium-ion batteries, they are being widely utilized in various fields, including energy storage power systems for hydroelectric, thermal, wind, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. As the scope of rechargeable battery applications expands, the demand for rapid charging performance is steadily increasing. However, since it is currently difficult to consider both rapid charging and circulation performance simultaneously, determining how rechargeable batteries can achieve both improved rapid charging and circulation capabilities has become an urgent challenge that needs to be addressed. The problem to be solved

[0004] The present application provides a secondary battery and an electric device having good rapid charging performance, room temperature circulation performance, and high temperature circulation performance. means of solving the problem

[0005] The first aspect of the present application is,

[0006] A positive current collector and a positive film layer installed on at least one side of the positive current collector, wherein the positive film layer comprises a positive sheet including a positive active material;

[0007] A cathode sheet comprising a cathode current collector and a cathode film layer installed on at least one side of the cathode current collector, wherein the cathode film layer comprises a cathode active material, and the cathode active material comprises a first graphite having a Dv50 particle size of 2.2 μm to 7.7 μm; and

[0008] The present invention provides a secondary battery comprising an organic solvent and an organic additive, wherein the organic solvent comprises a first solvent, the first solvent comprises a cyclic carbonate, and the mass content of the first solvent is 25% to 40% based on the total mass of the organic solvent; and 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% to 10% based on the total mass of the electrolyte, and the mass percentage of the second additive in the electrolyte is 0.3% to 6%.

[0009] Thus, the negative electrode active material of the secondary battery comprises the first graphite with a small particle size. Although the negative electrode sheet containing the first graphite improves the rapid charging performance of the battery, the surface of the graphite with a small particle size has relatively many defects and relatively strong reaction activity, resulting in relatively rapid consumption of the electrolyte. Furthermore, when rapid charging is performed, the temperature rise of the cell is relatively high, which affects the stability of the electrolyte and makes it difficult to improve the circulation performance of the battery. Therefore, by improving the content of the first solvent, first additive, and second additive in the electrolyte to ensure that the electrolyte has good thermal stability, a stable interfacial film is formed on the surface of the negative electrode sheet, thereby reducing the electrolyte consumption rate and the DC internal resistance (DCR) of the battery, and further improving the circulation performance and rapid charging performance of the secondary battery. Thus, the secondary battery can consider good rapid charging performance, room temperature circulation performance, and high temperature circulation performance.

[0010] In any embodiment of the present application, the structure of the ethylene carbonate derivative is,

[0011] And,

[0012] R1 and R2 each independently contain one of a hydrogen element, a halogen element, a C1-C5 alkyl group, and a C1-C5 halogen alkyl group, and R1 and R2 are not simultaneously hydrogen elements. This second additive has good film-forming properties, conductivity, and stability, which can improve the rapid charging performance and cycling performance of the battery, especially the room temperature cycling performance.

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

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

[0015] In any embodiment of the present application, the mass content of the first solvent is 30% to 40% based on the total mass of the organic solvent. By controlling the mass content of the first solvent in the organic solvent to within this range, the battery can be made to have superior circulation performance.

[0016] In any embodiment of the present application, based on the total mass of the electrolyte, the mass content of the first additive is 3% to 8%, and / or the mass content of the second additive is 1.5% to 5%. By controlling the mass content of the first additive and / or the second additive in the electrolyte to within this optional range, the battery can be made to have better cycling 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%. By controlling the total mass of the first additive and the second additive within the above range, the activity of graphite with a small particle size can be further improved, and the circulation performance of the battery can be further improved in relation to the problem of reduced circulation performance due to a faster rate of additive consumption during the circulation process.

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

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

[0020] Alternatively, the mass of the electrolyte at a unit cell rated capacity of 1Ah of the secondary battery 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%.

[0021] In any embodiment of the present application, the anode active material has a powder compression density ≥ 2.43 g / cm³ at 30,000 N. 3 , optionally 2.48 g / cm³ 3 ~ 2.85 g / cm 3 am.

[0022] In any embodiment of the present application, the positive active material comprises at least one of a lithium-containing phosphate and a derivative having an olivine structure.

[0023] In any embodiment of the present application, the positive active material is,

[0024] A nucleus comprising at least one of a lithium-containing phosphate having an olivine structure and a derivative thereof; and

[0025] The above-mentioned core surface is coated, and the ion conductive layer comprises an ion conductive layer containing at least one element among Fe, C, Ti, Zr, Hf, Ge, and Sn.

[0026] The core can improve the conductivity of lithium-containing phosphates of olivine structure and their derivatives by coating an ion-conducting layer on the surface, lower the powder resistivity of the material, is advantageous for the mobility of lithium ions, improves the high-speed charging capability of the battery, and reduces the heat production of the battery cell.

[0027] In any embodiment of the present application, the lithium-containing phosphate of the olivine structure and its derivatives are of the general formula Li x1 A1 y1 M1 a1 M2 b1 P 1-c1 X c1 Q1 z1 It includes a compound, wherein 0.5≤x1≤1.3, 0≤y1≤1.3, 0.9≤x1+y1≤1.3; 0.9≤a1≤1.5, 0≤b1≤0.5, 0.9≤a1+b1≤1.5; 0≤c1≤0.5; 3≤z1≤5; 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, P; and Q1 includes at least one of O and F. The cyclization stability of lithium-containing phosphates with an olivine structure is relatively excellent, which is advantageous for improving the cyclization performance of battery cells.

[0028] In any embodiment of the present application, the lithium-containing phosphate of the olivine structure and its derivative comprises at least one of lithium iron phosphate, lithium manganese phosphate, lithium nickel phosphate, and tritium cobalt phosphate.

[0029] In any embodiment of the present application, the ion conductive layer has the chemical formula Li 3-b Fe 2-b M3 b (PO m ) n It includes a high-speed ion conductor, M3 includes at least one element among +4 valence Ti, Zr, Hf, Ge and Sn, and 0≤b≤1, 3≤m≤5, 2≤n≤4.

[0030] In any embodiment of the present application, the high-speed ion conductor comprises at least one of lithium titanium iron phosphate, lithium zirconium iron phosphate, and lithium tin iron phosphate. By coating the surface of the core with a high-speed ion conductor having a NASICON structure, the transfer rate of lithium ions withdrawing / inserting lithium multiple times at the positive terminal can be significantly improved, the ion conductivity of the positive active material can be improved, and the high-speed charging capability of the battery cell can be improved, as well as the capacity per gram and the energy density of the battery cell can be improved.

[0031] In any embodiment of the present application,

[0032] (1) The compression density of the anode sheet is 2.5 g / cm³ 3 ~ 2.8g / cm 3 thing;

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

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

[0035] (4) The volume average particle size of the above positive active material satisfies at least one of the conditions of 1μm≤Dv50≤2μm and 0.4μm≤Dv10≤0.7μm.

[0036] In any embodiment of the present application, the anode film layer further comprises a lithium supplement, and the lithium supplement comprises at least one of a ternary lithium supplement material, lithium phosphate, lithium dihydrogen phosphate, lithium sulfate, lithium sulfite, lithium molybdate, lithium nickelate, lithium ironate, lithium oxalate, lithium titanate, lithium tetraborate, lithium metasilicate, lithium metamanganate, lithium tartrate, and lithium citrate. The lithium supplement can replenish lithium ions in the anode film layer, compensate for irreversible lithium ion loss within the system, and improve the energy density of the battery cell by improving capacity.

[0037] In any embodiment of the present application, the ternary lithium supplement material is Li x2 A2 y2 Ni a2 Co b2 Mn c2 M4 (1-a2-b2-c2) Q2 z2 It includes, where 0<x2≤2.1, 0≤y2≤2.1; 0≤a2≤1, 0≤b2≤1, 0≤c2≤1, 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; and Q2 includes at least one of O and F.

[0038] In any embodiment of the present application, the anode sheet further comprises an anode conductive layer, wherein the anode conductive layer is installed between the anode current collector and at least one anode film layer, and the anode conductive layer comprises a conductive agent, wherein 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 anode conductive layer is 0.5 μm to 2 μm.

[0040] In any embodiment of the present application, the anode conductive layer comprises a binder, wherein the binder comprises at least one of polyvinylidene fluoride, polytetrafluoroethylene, difluoroethylene tetrafluoroethylene propylene terpolymer, vinylidene fluoride hexafluoropropyl tetrafluoroethylene terpolymer, tetrafluoroethylene hexafluoropropene copolymer, polyacrylic acid, and fluorine-containing acrylate resin;

[0041] Optionally, in the anode 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 compression density of the negative electrode sheet after charging the secondary battery to 100% SOC at a charging rate of 0.33C is 1.15 g / cm³ 3 ~ 1.46g / cm 3 , optionally 1.15 g / cm³ 3 ~ 1.36g / cm 3 am.

[0043] In any embodiment of the present application, the compression density of the negative electrode sheet after charging the secondary battery to 100% SOC at a charging rate of 0.33C is 1.15 to 1.26 g / cm³ 3 And, the mass content of the first additive in the electrolyte is 3% to 8%.

[0044] In any embodiment of the present application,

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

[0046] (2) At least one of the conditions is satisfied, wherein the mass content of the first solvent in the organic solvent is 30% to 40%.

[0047] In any embodiment of the present application, the compression density of the negative electrode sheet after charging the secondary battery to 100% SOC at a charging rate of 0.33C is >1.26 g / cm³ 3 and ≤1.36 g / cm³ 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,

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

[0050] (2) At least one of the conditions is satisfied, wherein 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, and the second solvent comprises at least one of a linear carbonate, a carboxylic acid ester, an ether, a nitrile, and a sulfone.

[0052] In any embodiment of the present application, the second solvent comprises a carboxylic acid ester; optionally, the carboxylic acid ester 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 charging time for charging the secondary battery from 10% SOC to 80% SOC at 30°C is 6 min to 15 min, the mass content of the carboxylic acid ester in the organic solvent is 20% to 75%, and the total mass content of the first additive and the second additive in the electrolyte is 2% to 9%.

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

[0055] In any embodiment of the present application, the electrolyte comprises a lithium salt, and the lithium salt comprises at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, fluorosulfonylimide salt, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluorobis(oxalato)phosphate, and lithium tetrafluoro(oxalato)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 is,

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

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

[0060] (3) The lithium salt satisfies at least one of the conditions that the above lithium salt contains LiFSI and LiPF6, and the concentration ratio of LiFSI to LiPF6 is (2 to 5):10.

[0061] In any embodiment of the present application, the cathode sheet further comprises a cathode conductive layer, wherein the cathode conductive layer is installed between the cathode current collector and at least one side of the cathode film layer, and the cathode conductive layer comprises a conductive agent, wherein 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.

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

[0063] In any embodiment of the present application, the cathode conductive layer comprises a binder, and the binder comprises at least one of styrene butadiene rubber, water-soluble unsaturated resin, water-soluble acrylic resin, polyvinyl alcohol, sodium alginate, and carboxymethyl chitosan.

[0064] In any embodiment of the present application, in the cathode 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 cathode film layer comprises at least one cathode active layer, and at least one cathode active layer comprises the first graphite.

[0066] In any embodiment of the present application, the cathode film layer comprises only one cathode active layer, and the cathode 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; optionally 3:7 to 5:5.

[0068] In any embodiment of the present application, the mass content of the first graphite in the cathode 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 cathode 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 cathode film layer comprises a first cathode active layer and a second cathode active layer installed to be sequentially stacked on the same side of the cathode current collector, the first cathode active layer comprises at least one of artificial graphite and natural graphite, the second cathode active layer comprises the first graphite and a 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 cathode active layer, the mass ratio of the first graphite to the third graphite is 2:8 to 8:2; optionally 3:7 to 7:3.

[0072] In any embodiment of the present application,

[0073] (1) The ratio of the total amount of each cathode active material in the second cathode active layer and the first cathode active layer is 3:7 to 7:3; optionally 4:6 to 6:4;

[0074] (2) The mass content of the first graphite in the second cathode active layer is 20% to 70%; optionally, the mass content of the first graphite in the second cathode 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 cathode 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) At least one of the following conditions is satisfied: the Dv50 particle size of graphite in the first cathode active layer is ≥ the Dv50 particle size of graphite in the second cathode active layer; optionally, the Dv50 particle size of graphite in the first cathode active layer is 5.8 μm to 12.8 μm, optionally 7.8 μm to 12.8 μm; optionally, the Dv50 particle size of graphite in the second cathode active layer is 2.2 μm to 7.7 μm, optionally 4.2 μm to 7.2 μm.

[0076] In any embodiment of the present application, the artificial graphite comprises graphite body particles and a coating layer, wherein the graphite body particles comprise secondary particles aggregated into a plurality of primary particles, and the coating layer is coated on the surface of the body particles, and the coating layer comprises amorphous carbon.

[0077] In any embodiment of the present application,

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

[0079] (2) At least one of the conditions of the above artificial graphite powder resistivity ≤ 0.04 Ω·cm is satisfied.

[0080] In any embodiment of the present application, the first graphite has a capacity per gram of charge at a 0.1C multiplier in a button-type battery ≥ 350 mAh / g, 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, and the silicon-based material comprises at least one of silicon oxide and a silicon-carbon composite; the mass content of silicon elements in the silicon-based material in the negative electrode active material is 0.3% to 10%, optionally 1% to 6%.

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

[0083] In any embodiment of the present application,

[0084] (1) The thickness of the porous substrate film is ≤12μm, optionally ≤9μm;

[0085] (2) The porosity of the porous substrate film satisfies at least one of the following conditions: 20% to 70%, optionally 35% to 60%.

[0086] In any embodiment of the present application, the separator comprises a first functional layer and a second functional layer installed on both sides of the porous substrate film, wherein the first functional layer comprises a first inorganic particle, and the second functional layer comprises a composite particle, wherein the composite particle comprises a second inorganic particle and a non-fluorinated polymer particle, and the second inorganic particle is attached to the surface of the non-fluorinated polymer particle and / or dispersed within the non-fluorinated polymer particle.

[0087] In any embodiment of the present application,

[0088] (1) The above non-fluorine polymer particles include acrylate-based polymer particles;

[0089] (2) At least one of the conditions is satisfied that the first functional layer is located between the cathode sheet and the porous substrate film, and the second functional layer is located between the anode sheet and the porous substrate film.

[0090] A second aspect of the present application provides an electric device comprising a secondary battery according to a first aspect of the present application.

[0091] Details of one or more embodiments of the present application are set forth in the drawings and description below. Other features, purposes, and advantages of the present application will become apparent from the specification, drawings, and claims. Brief explanation of the drawing

[0092] In order to make the embodiments of the present application or the technical solutions in the traditional art more distinct, we would like to briefly introduce the drawings that should be used in the description of the embodiments or traditional art below. The drawings in the description below are merely embodiments of the present application, and it is obvious to those skilled in the art that other drawings can be obtained based on these drawings without the need to strive for inventive creation. FIG. 1 is a schematic diagram of a battery cell according to one embodiment of the present application. FIG. 2 is an exploded view of a battery cell according to one embodiment of the present application shown in FIG. 1. FIG. 3 is a schematic diagram of a battery module according to one embodiment of the present application. FIG. 4 is a schematic diagram of a battery pack according to one embodiment of the present application. FIG. 5 is an exploded view of a battery pack according to one embodiment of the present application shown in FIG. 4. FIG. 6 is a schematic diagram of an electric device using a secondary battery as a power source according to one embodiment of the present application. Specific details for implementing the invention

[0093] The technical solution of the embodiments of the present application is to be clearly and completely explained below in conjunction with the drawings of the embodiments of the present application; however, it is obvious that the described embodiments are merely some embodiments of the present application and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present application without needing to strive for inventive creation are all within the scope of protection of the present application.

[0094] The “ranges” disclosed in this application may be limited in the form of lower and upper limits, and a given range is limited by selecting a lower and upper limit, and the selected lower and upper limits define the boundaries of a particular range. A range defined in this way may include or exclude end values, and end values ​​may include or exclude independently, and any lower limit may form any combination of upper limits. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is understood that ranges of 60-110 and 80-120 are also expected. Furthermore, if the listed minimum range values ​​are 1 and 2 and the maximum range values ​​are 3, 4, and 5, ranges such as 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5 are all expected. In this application, unless otherwise stated, numeric ranges “a ~ b” represent a shortened expression of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range “0 to 5” indicates that all real numbers between “0 to 5” are listed in this specification, and “0 to 5” is merely an abbreviated expression for combinations of these numbers. Additionally, if a parameter is represented as an integer ≥ 2, this corresponds to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, if a parameter is an integer selected from “2 to 10”, it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0095] The present application relates to "plural," "multiple," etc., and unless otherwise specifically limited, the quantity refers to something greater than or equal to 2. For example, "one or plural" indicates something greater than or equal to one or two.

[0096] Unless otherwise specified, all embodiments and optional embodiments of the present application may be combined with one another to form a new technical solution.

[0097] The term "Example" as used herein means that the specific features, structures, and properties described in connection with the Example are included in at least one embodiment or embodiment of this application. Such phrases located at various positions within the specification do not necessarily refer to the same Example, nor do they refer to separate or alternative embodiments that are mutually exclusive from other embodiments. Those skilled in the art may understand, expressly and implicitly, that the Example described herein may be combined with other Examples. The term "Format" as used herein has a similar understanding.

[0098] Those skilled in the art will understand that in the method of the embodiment or example, the order of each step does not imply a strict order of execution and does not impose any limitations on the course of execution, and that the specific order of execution of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present application may proceed sequentially or randomly, and preferably sequentially. For example, “the method comprises steps (a) and (b)” indicates that the method may include steps (a) and (b) performed sequentially, and may also include steps (b) and (a) performed sequentially. For example, if it is stated that "the above method may further include step (c)," this indicates that step (c) may be added to the above method in any order. For example, the above method may include steps (a), (b), and (c), steps (a), (c), and (b), and steps (c), (a), and (b), etc.

[0099] In this application, unless otherwise stated, additional members other than those listed in the open technical features or technical solutions described by words such as "containing," "including," or "comprehensive" are not excluded and may be deemed to provide a closed feature or solution composed of the listed members. A includes a1, a2, and a3, and unless otherwise stated, may include other members or may not include additional members, which is deemed to provide not only the feature or solution that "A consists of a1, a2, and a3" but also the feature or solution that "A includes other members in addition to a1, a2, and a3".

[0100] In this application, unless otherwise stated, A (e.g., B) indicates that B is a non-limiting example of A and is understood not to be limited to B.

[0101] In this application, "optional," "optional," and "optional" indicate that they may or may not be present, that is, they may be selected from one of two parallel solutions: "present" or "absent." If "optional" appears in multiple places within a single technical solution, each "optional" is independent unless otherwise specified or there is a sequential or restrictive relationship.

[0102] One embodiment of the present application provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte.

[0103] The positive sheet comprises a positive current collector and a positive film layer installed on at least one side of the positive current collector, and the positive film layer comprises a positive active material.

[0104] The cathode sheet comprises a cathode current collector and a cathode film layer installed on at least one side of the cathode current collector, the cathode film layer comprises a cathode active material, the cathode active material comprises a first graphite, and the Dv50 particle size of the first graphite is 2.2 μm to 7.7 μm.

[0105] The electrolyte comprises an organic solvent and an organic additive, wherein the organic solvent comprises a first solvent. The first solvent comprises a cyclic carbonate (EC), and the mass content of the first solvent is 25% to 40% based on the total mass of the organic solvent. The organic additive comprises a first additive and a second additive, wherein the first additive comprises vinylene carbonate (VC) and the second additive comprises an ethylene carbonate derivative, and the mass percentage of the first additive in the electrolyte is 2% to 10% based on the total mass of the electrolyte, and the mass percentage of the second additive in the electrolyte is 0.3% to 6%.

[0106] Thus, since the negative electrode active material of the secondary battery includes the first graphite with a small particle size, the negative electrode sheet of this first graphite improves the rapid charging performance of the battery. However, the surface of the graphite with a small particle size has relatively many defects and relatively strong reaction activity, so the consumption of the electrolyte is relatively fast. Furthermore, when rapid charging is performed, the temperature rise of the cell is relatively high, which affects the stability of the electrolyte and makes it difficult to improve the circulation performance of the battery. Therefore, by improving the content of the first solvent, first additive, and second additive in the electrolyte so that the electrolyte has good thermal stability, a stable interfacial film is formed on the surface of the negative electrode sheet, thereby reducing the electrolyte consumption rate and the DC internal resistance (DCR) of the battery, and further improving the circulation performance and rapid charging performance of this secondary battery. Thus, the secondary battery can consider good rapid charging performance, room temperature circulation performance, and high temperature circulation performance.

[0107] The first solvent above contains a cyclic carbonate, which has a high dielectric constant and good film formation performance. If the content of the first solvent in the electrolyte is too low, the self-stability of the electrolyte deteriorates, thereby lowering the conductivity; however, if the content of the first solvent is too high, the viscosity and melting point of the electrolyte improve, thereby deteriorating the conductivity of the electrolyte and the kinetic performance of the battery, leading to a deterioration in circulation performance. Thus, by controlling the first solvent within the above content range, the electrolyte can have good thermal stability and suitable conductivity.

[0108] The first additive comprises vinylene carbonate (VC), and the second additive comprises an ethylene carbonate derivative. The first additive and the second additive may participate in the interfacial film formation. If the content of the first additive and the second additive is too low, the first solvent participates too much in the film formation, thereby destroying the stability of the electrolyte and accelerating the rate of electrolyte consumption, which degrades the circulation performance and storage life of the battery; as the content of the first additive increases, the high-temperature circulation life of the battery improves, but if the content of the first additive is too high, it degrades the dynamic window and DC internal resistance (DCR) of the battery, causing a deterioration in circulation performance and becoming disadvantageous for improving rapid charging performance; as the content of the second additive increases, the room-temperature circulation life and rapid charging performance of the battery improve, but if the content of the second additive is too high, the high-temperature performance of the battery deteriorates and the high-temperature circulation life decreases. Thus, by controlling the first additive and the second additive to be within the above ranges, the electrolyte achieves equilibrium between film formation stability and battery kinetics.

[0109] Thus, the electrolyte can reduce the rate of electrolyte consumption and improve the room temperature and high temperature cycling performance and storage life of the cell by regulating the first solvent within the above-mentioned content range to improve the thermal stability of the electrolyte and the conductivity of the electrolyte to a suitable range, and by regulating the first additive and the second additive to the above-mentioned ranges to ensure that the electrolyte achieves equilibrium between battery kinetics and film formation stability; furthermore, the battery can be equipped with a low DC internal resistance (DCR) to ensure good rapid charging performance. This electrolyte is applied to a negative electrode sheet and battery system containing the first graphite of the small particle size, thereby enabling the secondary battery to consider high rapid charging performance, room temperature cycling performance, and high temperature cycling performance.

[0110] electrolyte

[0111] In some embodiments of the present application, the cyclic carbonate in the first solvent comprises at least one of ethylene carbonate (EC) and propylene carbonate (PC).

[0112] As an example, the mass content of the first solvent in an organic solvent may include, but is not limited to, 25%, 28%, 30%, 32%, 35%, 38%, and 40%. Furthermore, the mass content of the first solvent in an organic solvent may be 25% to 38% or 30% to 40%, or within a range configured with any of the above point values ​​as end values, the following sentence is similar. By controlling the mass content of the first solvent in the organic solvent to within this range, the battery can be made to have superior circulation performance.

[0113] As an example, the mass content of the first additive in the electrolyte may include, 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%, and 10%. Furthermore, the mass content of the first additive in the electrolyte is 3% to 8%. Furthermore, the first additive is vinylene carbonate (VC). By controlling the mass content of the first additive in the electrolyte within this optional range, the battery can be made to have superior circulation performance, particularly high-temperature circulation performance.

[0114] In some embodiments of the present application, the structure of the ethylene carbonate derivative in the second additive is:

[0115] And,

[0116] R1 and R2 each independently comprise any one of a hydrogen element, a halogen element, a C1-C5 alkyl group, and a C1-C5 halogen alkyl group, and R1 and R2 are not simultaneously hydrogen elements. Furthermore, the halogen element comprises at least one of a fluorine element, a chlorine element, and a bromine element, and the C1-C5 alkyl group and the C1-C5 halogen alkyl group comprise, 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 isomeric isomers thereof. Such a second additive has good film-forming properties, conductivity, and stability, and can improve the rapid charging performance and cycling performance of the battery, particularly the room temperature cycling performance.

[0117] Furthermore, the ethylene carbonate derivative comprises at least one of fluoroethylene carbonate (FEC), ethylene difluorocarbonate (DFEC), and trifluoromethyl vinyl carbonate.

[0118] As an example, the mass content of the second additive in the electrolyte may include, 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%, and 6%. Furthermore, the mass content of the second additive in the electrolyte is 1.5% to 5%. By controlling the mass content of the second additive in the electrolyte within this optional range, the battery can be made to have excellent rapid charging performance and circulation performance, particularly room temperature circulation performance.

[0119] 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, this total mass content may be 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 11%, and 12%. Furthermore, the total mass content of the first additive and the second additive is 3.5% to 9%. By controlling the total mass of the first additive and the second additive within the above range, the activity of graphite with a small particle size can be further improved, and the circulation performance of the battery can be further improved in relation to the problem of reduced circulation performance caused by a faster rate of additive consumption during the circulation process.

[0120] In some embodiments of the present application, the electrolyte further comprises a second solvent. Furthermore, the second solvent comprises at least one of a linear carbonate, a carboxylic acid ester, an ether, a nitrile, and a sulfone. The second solvent is used as a solvent together with the first solvent, and its function is to lower the melting point and viscosity of the electrolyte system and improve the lithium ion transport performance of the electrolyte.

[0121] Furthermore, linear carbonates include at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropylene carbonate (DPC), methyl ethyl carbonate (EMC), methylpropyl carbonate (MPC), and ethyl propyl carbonate (EPC).

[0122] Furthermore, the carboxylic acid 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 acid ester. Furthermore, the second solvent simultaneously comprises the carboxylic acid ester and the linear carbonate.

[0123] Furthermore, the ether includes at least one of ether and 1,2-dimethoxyethane (DME, also known as ethylene glycol dimethyl ether), but is not limited thereto.

[0124] Furthermore, nitriles include, but are not limited to, acetonitrile (AN).

[0125] Furthermore, sulfone includes at least one of cyclobutylsulfone, dimethylsulfone, methylethylsulfone, and diethylsulfone, but is not limited thereto.

[0126] Furthermore, the mass content of the second solvent in the organic solvent is 20% to 75%; this mass content may be 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 73%, and 75%. Furthermore, the mass content of the carboxylic acid ester in the organic solvent is 30% to 60%, 30% to 75%. In one specific example, the second solvent is a carboxylic acid ester.

[0127] 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. As an example, the concentration of the electrolyte salt in the electrolyte may 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; furthermore, it may be 0.6 mol / L to 1.3 mol / L, and may be within a range formed by setting any two point values ​​as end values.

[0128] 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 difluorosulfonylimide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS, CF3SO2Li), lithium difluorophosphate (LiPO2F2), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium difluorobis(oxalato)phosphate (LiDFOP), and lithium tetrafluoro(oxalato)phosphate (LiTFOP).

[0129] 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 fluorosulfonylimide salt and LiPF6. More optionally, the fluorosulfonylimide salt comprises at least one of LiFSI and LiTFSI.

[0130] Furthermore, the lithium salt comprises at least one of LiFSI and LiPF6. Furthermore, the concentration of LiFSI in the electrolyte is 0.2 mol / L to 0.5 mol / L; furthermore, the concentration of LiPF6 in the electrolyte is 0.5 mol / L to 1.3 mol / L. Furthermore, the lithium salt comprises LiFSI and LiPF6, and the ratio of the amounts of LiFSI and LiPF6 is (2 to 5):10. The conductivity and heat resistance of difluorosulfonylimide lithium LiFSI are relatively good, and it does not easily hydrolyze at high temperatures, and is particularly applicable to rapid charging systems where the temperature rise is relatively large in this application; however, if the temperature becomes too high, for example, above 200°C, LiFSI decomposes and generates heat, thereby worsening the safety boundary of the cell, so LiPF6 is used as a lithium salt together with the first solvent to effectively improve the safety performance of the battery.

[0131] In some embodiments of the present application, the mass of the electrolyte at a unit cell rated capacity of 1Ah of a secondary battery is 2.2g to 2.95g, and as an example, may be 2.2g, 2.3g, 2.4g, 2.5g, 2.6g, 2.65g, 2.7g, 2.8g, 2.9g, or 2.95g. Furthermore, it may be 2.2g to 2.65g or 2.65g to 2.95g. The electrolyte of the present application is applied to a battery with a low liquid injection rate system, and since the consumption rate of the electrolyte is relatively low and the kinetics are relatively excellent, the circulation performance of the battery with a low liquid injection rate system can be improved.

[0132] Furthermore, the mass of the electrolyte in a unit cell of the secondary battery with 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%. Since the mass of the electrolyte in a unit cell of the secondary battery with a rated capacity of 1Ah is relatively small, the total mass content of the first additive and the second additive can be appropriately increased to improve the circulation performance of the battery with a low liquid injection coefficient system. Here, as an example, the mass of the electrolyte at a unit cell rated capacity of 1Ah of a secondary battery may be 2.2g, 2.3g, 2.4g, 2.5g, 2.6g, 2.65g, or any two of the above values, and the total mass content of the first additive and the second additive in the electrolyte may be 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, or any two of the above values.

[0133] Alternatively, the mass of the electrolyte at a unit cell rated capacity of 1Ah of the secondary battery 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%. Since the mass of the electrolyte at a unit cell rated capacity of 1Ah of the secondary battery is relatively large, the total mass content of the first additive and the second additive can be appropriately reduced to consider both cost and the circulation performance of the battery. Here, as an example, the mass of the electrolyte at a unit cell rated capacity of 1Ah of the secondary battery may be 2.68g, 2.7g, 2.8g, 2.9g, 2.95g, 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 may be 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, or a range composed of any two of the above values.

[0134] The test method for the mass of the electrolyte at a unit cell rated capacity of 1Ah of a secondary battery is as follows: ① Take the battery and weigh the battery mass M0; ② Disassemble the battery and pour out the glass electrolyte to remove the sheet, separator, mechanical component, and adhesive paper; ③ Immerse the sheet, separator, mechanical component, and adhesive paper in dimethyl carbonate (DMC) for 24 hours, and then wash them repeatedly at least three times; ④ After washing is complete, place the sheet, separator, mechanical component, and adhesive paper in an oven and dry them until completely dry; ⑤ Weigh the sheet, separator, mechanical component, and adhesive paper and record the mass as M1; ⑥ The mass of the electrolyte at a unit cell rated capacity of 1Ah of a secondary battery = (M0-M1) / a, where a = the rated capacity of the secondary battery and the unit is Ah.

[0135] As a non-limiting example, the anode current collector has two opposing surfaces in its own thickness direction, and the anode film layer is installed on either or both of the two opposing surfaces of the anode current collector.

[0136] In some embodiments, the positive current collector may use a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be obtained by forming a metal material on the polymer material substrate. Non-limiting examples of the metal material in the positive current collector may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. Non-limiting examples of the polymer material substrate in the positive current collector may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0137] In some embodiments, the thickness of the positive current collector is 10 μm to 15 μm, and optionally 12 μm to 15 μm. For example, the thickness of the positive current collector is a range of 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 any two of the above values.

[0138] When the thickness of the positive current collector is within the above range, the current-carrying capacity of the positive current collector is relatively excellent, allowing the battery cell to have a relatively high energy density.

[0139] In the embodiments of the present application, the thickness of the positive film layer and the positive current collector can be detected using instruments and methods known in the art, in the sense known in the art. For example, the thickness of the positive sheet can be measured with a millimeter to remove the film layer on the surface of the positive current collector, and the thickness of the positive current collector can be measured with a millimeter. When the positive film layer is coated on one side, the thickness of the positive film layer is the value obtained by subtracting the thickness of the positive current collector from the thickness of the positive sheet; and when the positive film layer is coated on both sides, the thickness of the positive film layer is (thickness of the positive sheet - thickness of the positive current collector) / 2.

[0140] The anode film layer is typically formed by coating an anode slurry onto an anode current collector and then drying and cold-pressing. The anode slurry is typically formed by dispersing an anode active material, an optional conductive agent, an optional binder, and any other compositional components in a solvent and stirring them uniformly. The solvent may be N-methylpyrrolidone (NMP), but is not limited thereto.

[0141] The anode sheet does not exclude additional functional layers other than the anode film layer. For example, in some embodiments, the anode sheet according to the embodiment of the present application further comprises an anode conductive layer sandwiched between the anode current collector and the anode film layer and installed on the surface of the anode current collector. In other embodiments, the anode sheet according to the embodiment of the present application further comprises a protective layer covering the surface of the anode film layer.

[0142] The positive electrode active material may be any positive electrode active material for a battery known in the art. In some of these embodiments, the positive electrode active material has a powder compression density ≥ 2.43 g / cm³ at 30,000 N. 3 , optionally 2.48 g / cm³ 3 ~ 2.85 g / cm 3 Furthermore, the powder compression density of the cathode active material at 30,000 N is 2.5 g / cm³ 3 ~ 2.8g / cm 3 am.

[0143] By using this high powder compression density cathode active material, the compression density of the cathode sheet can be improved, and thereby the energy density of the battery can be improved.

[0144] As an example, the powder compression density of the positive active material in the positive sheet at 30,000 N is 2.43 g / cm³ 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 / cm 3 , 2.85g / cm 3 It could be.

[0145] As a non-limiting example, the positive electrode active material may comprise at least one of materials such as a phosphate-based positive electrode material, a lithium transition metal oxide, and a modified compound thereof. Here, the phosphate-based positive electrode material may comprise at least one of a lithium-containing phosphate having an olivine structure and a derivative thereof.

[0146] Furthermore, the positive electrode active material comprises at least one of a lithium-containing phosphate with an olivine structure and a derivative thereof. If the particle size of the lithium-containing phosphate and its derivative-based positive electrode active material is smaller and the specific surface area is larger, it can easily absorb water, so hydrolysis of the electrolyte in this system battery is more severe, and furthermore, since there is more HF due to hydrolysis, the problem of electrolyte consumption becomes more pronounced. However, the above electrolyte is advantageous for exhibiting a slow rate of electrolyte consumption, thereby improving the cycling performance of such a battery. At the same time, the lithium-containing phosphate and its derivative are advantageous for exhibiting high energy density, long cycling life, and good safety.

[0147] In some embodiments of the present application, lithium-containing phosphates of an olivine structure and derivatives thereof are of the general formula Lix1 A1 y1 M1 a1 M2 b1 P 1-c1 X c1 Q1 z1 It includes a compound, wherein 0.5≤x1≤1.3, 0≤y1≤1.3, 0.9≤x1+y1≤1.3; 0.9≤a1≤1.5, 0≤b1≤0.5, 0.9≤a1+b1≤1.5; 0≤c1≤0.5; 3≤z1≤5; 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, P; and Q1 includes at least one of O and F. The cyclization stability of lithium-containing phosphates with an olivine structure is relatively excellent, which is advantageous for improving the cyclization performance of battery cells.

[0148] Furthermore, Li x1 A1 y1 M1 a1 M2 b1 P 1-c1 X c1 Q1 z1 The compound comprises at least one of lithium iron phosphate (LiFePO4), lithium manganese phosphate (LiMnPO4), lithium nickel phosphate (LiNiPO4), and tritium cobalt phosphate (LiCoPO4), and may be a doping compound of such a compound.

[0149] Lithium-containing phosphates of an olivine structure and derivatives thereof may or may not contain a coating layer. In some embodiments of the present application, the positive electrode active material comprises a core and an ion-conducting layer. The core comprises at least one of lithium-containing phosphates of an olivine structure and derivatives thereof, and the ion-conducting layer is coated on the surface of the core, and the ion-conducting layer comprises at least one element selected from Fe, C, Ti, Zr, Hf, Ge, and Sn.

[0150] The core can improve the conductivity of lithium-containing phosphates of olivine structure and their derivatives by coating an ion-conducting layer on the surface, lower the powder resistivity of the material, is advantageous for the mobility of lithium ions, improves the high-speed charging capability of the battery, and reduces the heat production of the battery cell.

[0151] Furthermore, the ion conductive layer has the chemical formula Li 3-b Fe 2-b M3 b (PO m ) n It includes a high-speed ion conductor, M3 includes at least one element among +4 valence Ti, Zr, Hf, Ge and Sn, and 0≤b≤1, 3≤m≤5, 2≤n≤4.

[0152] For example, a high-speed ion conductor comprises a material of a NASICON structure, such that it includes, for instance, 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.

[0153] A high-speed ion conductor having a NASICON structure is a material with ultra-high-speed ion conductivity, possessing abundant three-dimensional lithium ion diffusion and transmission channels, and has advantages such as high ion conductivity and strong structural stability during multiple lithium release and insertion processes. By coating the surface of the core with a high-speed ion conductor containing a NASICON structure, the transmission speed of lithium ions releasing and inserting lithium multiple times at the positive terminal can be significantly improved, the ion conductivity of the positive active material can be improved, and the high-speed charging capability of the battery cell can be enhanced, as well as the capacity per gram and the energy density of the battery cell can be improved.

[0154] In some embodiments, the ion conductive layer further comprises a carbon single atom, and the carbon single atom and the high-speed ion conductor may be installed in separate layers, for example, the carbon single atom may be used as an independent carbon coating layer and the high-speed ion conductor may be used as an independent high-speed ion conductor layer, and the carbon coating layer may be coated on the surface of the core, and the high-speed ion conductor layer may be located on the surface of the carbon coating layer, that is, the high-speed ion conductor layer may be located on one side of the carbon coating layer away from the core; or, the high-speed ion conductor layer may be coated on the surface of the core, and the carbon coating layer may be located on the surface of the high-speed ion conductor layer, that is, the carbon coating layer may be located on one side of the high-speed ion conductor layer away from the core. Of course, the carbon single atom and the high-speed ion conductor may be installed in the same layer.

[0155] Optionally, the carbon coating layer can be coated on the surface of the high-speed ion conductor layer through a carbonization process using an organic carbon source such as glucose or polyethylene glycol. The carbon coating layer may partially cover the high-speed ion conductor layer or completely cover the high-speed ion conductor layer. The installation of the carbon coating layer can significantly improve the electron conductivity of the core, thereby compensating for defects where the electron conductivity of the core is weak and improving the energy density of the battery cell.

[0156] Specifically, the installation of the carbon coating layer enables the positive electrode active material of the present application to have the following advantages.

[0157] The carbon coating layer in the positive electrode active material of the present application provides a channel suitable for electron transmission, thereby significantly improving the conduction speed during the process of multiple lithium withdrawals and lithium insertions, enhancing the electronic conductivity of the lithium-containing phosphate, improving the charging capacity of the corresponding battery cell, and also improving high energy density.

[0158] The carbon coating layer of the positive electrode active material of the present application has loose porosity, thereby allowing the electrolyte to contact the lithium-containing phosphate sufficiently and effectively, which can improve the transmission rate of lithium ions at the phase interface and improve the charging capacity of the battery cell.

[0159] By coating a carbon coating layer on the surface of a lithium-containing phosphate, the conductivity of the lithium-containing phosphate can be improved, and the structural stability of the positive electrode active material can also be improved, thereby effectively preventing iron leaching from the positive electrode active material during the long-term storage and circulation of the battery cell, which can ensure the circulation life of the battery cell.

[0160] The cathode active material of the present application is based on a lithium-containing phosphate, fully utilizing the advantages of the lithium-containing phosphate, such as low cost, high reliability of use, and good cycling stability, while the ion conductive layer (high-speed ion conductor layer and carbon coating layer) resolves the defect of weak electronic and ion conductivity. A battery cell manufactured with the cathode active material of the present application possesses a significantly improved energy density under the premise of excellent cycling performance.

[0161] In some of these embodiments, the mass content of carbon in the cathode active material may be 1% to 2%, for example, 1%, 1.5%, or 2%. By controlling the mass content of carbon in the cathode active material to this range, the conductivity of the cathode active material can be further improved, thereby improving the rapid charging performance of the battery. It is understood that this carbon element is derived from, but is not limited to, a coated carbon layer. For example, a carbon coating layer is coated on the surface of an olivine-structured lithium-containing phosphate and its derivatives.

[0162] In some of these embodiments, the powder resistivity of the positive active material is ≤20Ω·cm, thereby improving the conductivity of the positive active material and improving the rapid charging performance of the battery. As an example, the powder resistivity of the positive active material may be 20Ω·cm, 15Ω·cm, 10Ω·cm, 8Ω·cm, 5Ω·cm, etc., and optionally ≤11Ω·cm.

[0163] In some of these embodiments, the rapid charging and output performance of the battery can be further improved by satisfying the volume average particle size of the positive electrode active material as 1 μm ≤ Dv50 ≤ 2 μm and 0.4 μm ≤ Dv10 ≤ 0.7 μm. As an example, the Dv50 particle size of the positive electrode active material may be 1 μm, 1.5 μm, or 2 μm. As an example, the volume average particle size Dv10 of the positive electrode active material may be 0.4 μm, 0.5 μm, 0.6 μm, or 0.7 μm.

[0164] In this text, Dv50 and Dv10 have the meaning known in the art and can be tested by methods already known in the art. For example, they are measured using a laser particle size analyzer (e.g., Malvern Master Size 3000). Here, Dv50 represents the particle size corresponding when the percentage of particle volume distribution from the smallest particle size accumulates to 50% according to the particle size volume distribution. Dv10 represents the particle size corresponding when the percentage of particle volume distribution from the smallest particle size accumulates to 10% according to the particle size volume distribution.

[0165] The particle size volume distribution can be obtained by testing using the following method. Take a clean beaker, place an appropriate amount of the test sample inside, and perform sufficient sonication to ensure the sample is completely dispersed. The test instrument is a Malvin 2000 from the USA. Pour the sample into the sample injection tower, circulate it along with the solution through the test optical path system, and irradiate it with a laser beam. By receiving and measuring the energy distribution of the emitted light, the particle size distribution characteristics (light opacity: 8% to 12%) can be obtained. Based on the test data, a particle size volume distribution map is constructed.

[0166] In some of these embodiments, the anode film layer further comprises a lithium supplement. Furthermore, the lithium supplement comprises at least one of a ternary lithium supplement material, lithium phosphate, lithium dihydrogen phosphate, lithium sulfate, lithium sulfite, lithium molybdate, lithium nickelate, lithium ironate, lithium oxalate, lithium titanate, lithium tetraborate, lithium metasilicate, lithium metamanganate, lithium tartrate, and lithium citrate. The lithium supplement can replenish lithium ions in the anode film layer, compensate for irreversible lithium ion loss within the system, and improve the energy density of the battery cell by enhancing capacity.

[0167] Furthermore, the ternary lithium supplement material is Li x2 A2 y2 Ni a2 Co b2 Mn c2 M4 (1-a2-b2-c2) Q2 z2It includes, where 0<x2≤2.1, 0≤y2≤2.1; 0≤a2≤1, 0≤b2≤1, 0≤c2≤1, 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; and Q2 includes at least one of O and F.

[0168] Furthermore, 0.9≤x2+y2≤2.1.

[0169] For example, the ternary material is 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 It includes at least one of O2.

[0170] The lithium supplement may be located in the same layer as the positive electrode active material or in a different layer. If the lithium supplement is located in a different layer from the positive electrode active material, the lithium supplement may be located in the lithium supplement layer and the positive electrode active material may be located in the positive electrode active material layer; in other words, the positive electrode film layer may include the lithium supplement layer and the positive electrode active material layer. The positive electrode active material layer may be installed on at least one side of the positive electrode current collector, and the lithium supplement layer may be located between the positive electrode active material layer and the positive electrode current collector. Alternatively, the lithium supplement layer may be installed on at least one side of the positive electrode current collector, and the positive electrode active material layer may be located between the lithium supplement layer and the positive electrode current collector. Optionally, the lithium supplement layer may be located between the positive electrode active material layer and the positive electrode current collector.

[0171] In some of these embodiments, the mass content of the positive active material in the positive film layer is 80% to 98%, and as an example, this mass content may be 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 96%, 98%. Furthermore, the mass content of the positive active material in the positive film layer may be 90% to 98%.

[0172] In some of these embodiments, the anode film layer may optionally further comprise a binder. As a non-limiting example, the binder may comprise at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyfluoroethylene-tetrafluoroethylene-propylene terpolymer, polyfluoroethylene-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene hexafluoropropene copolymer, and fluorine-containing acrylate resin. In some embodiments, the mass content of the binder is ≤5% based on the total mass of the anode film layer.

[0173] In some of these embodiments, the anode film layer may optionally further include a conductive agent. As a non-limiting example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass content of the conductive agent is ≤5% based on the total mass of the anode film layer.

[0174] In some of these embodiments, an anode sheet can be manufactured in the following manner. A compositional component for manufacturing an anode sheet, such as an anode active material, a conductive agent, a binder, and any other compositional component, is dispersed in a solvent to form an anode slurry; and the anode slurry is applied to at least one surface of an anode current collector, and an anode sheet can be obtained after undergoing processes such as drying and cold pressing. The type of solvent may be selected from any one of the aforementioned embodiments, such as N-methylpyrrolidone (NMP), but is not limited thereto. The surface of the anode current collector coated with the anode slurry may be a single surface of the anode current collector or two surfaces of the anode current collector.

[0175] In some of the embodiments thereof, the anode sheet further comprises an anode conductive layer, and the anode conductive layer is installed between an anode current collector and at least one anode film layer. The anode conductive layer comprises a conductive agent. The anode conductive layer can be formed by first coating the surface of the anode current collector with a corresponding slurry, and then coating and drying the anode slurry described above. The anode conductive layer can be advantageous for improving the electron transfer rate by improving the bonding strength between the anode film layer and the anode current collector and the overall conductivity of the anode sheet.

[0176] Furthermore, 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. The superconducting agent in the anode conductive layer can improve the conductivity of the anode conductive layer, thereby improving the conductivity of the anode sheet and reducing the heat production of the battery.

[0177] Furthermore, the thickness of the anode conductive layer is 0.5 μm to 2 μm, and as an example, it may be 0.5 μm, 1 μm, 1.5 μm, or 2 μm. When the thickness of the anode conductive layer is within the above range, the conductivity performance of the anode sheet can be further improved, and the improvement of the energy density of the battery cell can also be taken into account.

[0178] Furthermore, the anode conductive layer further comprises a binder. Furthermore, the binder comprises at least one of polyvinylidene fluoride, polytetrafluoroethylene, difluoroethylene tetrafluoroethylene propylene terpolymer, vinylidene fluoride hexafluoropropyl tetrafluoroethylene terpolymer, tetrafluoroethylene hexafluoropropene copolymer, polyacrylic acid, and fluorine-containing acrylate resin. The binder in the anode conductive layer can improve the adhesion performance between the anode current collector and the anode film layer, and can improve the structural stability of the anode sheet.

[0179] Optionally, in the anode conductive layer, the mass content of the conductive agent is 30% to 50%, and may be, for example, 30%, 35%, 40%, 45%, and 50%; optionally, in the anode conductive layer, the mass content of the binder is 50% to 70%, and may be 50%, 55%, 60%, 65%, and 70%. In some examples, the anode conductive layer is composed of a conductive agent and a binder.

[0180] cathode sheet

[0181] As a non-limiting example, the cathode current collector has two opposing surfaces in its own thickness direction, and the cathode film layer is installed on either or both of the two opposing surfaces of the cathode current collector.

[0182] In some of the embodiments thereof, the negative current collector may use a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer installed on at least one surface of the polymer material substrate. The composite current collector may be obtained by forming a metal material on the polymer material substrate. In the negative current collector, non-limiting examples of the metal material may include at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. In the negative current collector, non-limiting examples of the polymer material substrate may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0183] In some of these embodiments, the compression density of the negative electrode sheet after charging the secondary battery to 100% SOC at a charging rate of 0.33C is 1.15 g / cm³ 3 ~ 1.46g / cm 3 , optionally 1.15 g / cm³ 3 ~ 1.36g / cm 3 As such, the cathode sheet still has a high compression density after being fully charged. For example, the compression density of the cathode sheet after charging the secondary battery to 100% SOC at a charging rate of 0.33C is 1.15 g / cm³. 3 , 1.18g / cm 3 , 1.20g / cm 3 , 1.22g / cm 3 , 1.25g / cm 3 , 1.28g / cm 3 , 1.3g / cm 3 , 1.32g / cm3 , 1.35g / cm 3 , 1.36g / cm 3 , 1.38g / cm 3 , 1.4g / cm 3 , 1.42g / cm 3 , 1.45g / cm 3 , 1.46g / cm 3 Or it is a range composed of any two values ​​above. When the compression density of the cathode film layer is within the above range, it is advantageous to improve the energy density of the battery cell; and since the stack of cathode active material in the cathode film layer is relatively dense, the contact resistance between particles is small, which can further reduce the resistance of the sheet and reduce heat generation.

[0184] In an embodiment of the present application, the compression density of the negative electrode sheet after charging the secondary battery to 100% SOC at a charging rate of 0.33C is in the sense known in the art, that is, the compression density of the positive electrode film layer is measured by decomposing the positive electrode sheet of the battery cell charged to 100% SOC at a charging rate of 0.33C.

[0185] In an embodiment of the present application, 100% SOC is defined according to the following method.

[0186] The battery cell is charged to the upper limit voltage of the battery at a constant current charging rate of 0.33C, and then charged at a constant voltage of 0.05C, which corresponds to the 100% SOC state of the battery cell. Correspondingly, the battery cell is discharged until it reaches the cutoff voltage at a constant current discharge rate of 0.33C, which corresponds to the 0% SOC state of the battery cell.

[0187] Since the type of positive active material of the battery varies, the fully charged cutoff voltage may also vary. As an example, the battery charge upper limit voltage may be 3.65V or 3.8V; and the battery discharge stop voltage may be 2.5V or 2.0V. Taking the positive active material in the positive sheet as lithium iron phosphate as an example, if the secondary battery is charged to 3.65V at a charging rate of 0.33C and then charged to 0.05C at a constant voltage (charged to 100% SOC at a charging rate of 0.33C), the compression density of the negative sheet is 1.15g / cm³. 3 ~ 1.46g / cm 3 am.

[0188] In some of these embodiments, the compression density of the cathode sheet after cold pressing is 1.5 g / cm³ 3 ~ 1.7g / cm 3 , optionally 1.55 g / cm³ 3 ~ 1.65g / cm 3 The compression density after cold pressing the cathode sheet refers to the compression density of the cathode sheet after cold pressing and before assembly into a battery.

[0189] In some of these embodiments, the compression density of the negative electrode sheet after charging the secondary battery to 100% SOC at a charging rate of 0.33C is 1.15 to 1.26 g / cm³ 3 And; at the same time, the mass content of the first additive in the electrolyte is 3% to 8%.

[0190] A low full-charge consolidation of the cathode sheet indicates that the graphite activity is stronger when the rebound thickness is greater or the initial consolidation is lower, thus requiring the consumption of more electrolyte and the addition of more additives to the electrolyte; this strengthens the interfacial film stability of the cathode sheet and improves the circulation performance of the battery. Therefore, there is a matching relationship between the compressive density of the cathode sheet and the mass content of the first additive in the electrolyte, and thus, when the compressive density of the cathode sheet is within the above range after the secondary battery is charged to 100% SOC at a charging rate of 0.33C, the mass content of the first additive in the electrolyte is 3% to 8%, which allows the battery to better account for both high rapid charging performance and circulation performance.

[0191] Although the low film-forming impedance of the second additive in the electrolyte improves the kinetic performance of the battery and can enhance the rapid charging performance of the battery ID, its content should not be excessive to improve the battery's cycling performance. Therefore, a matching relationship exists between the compression density of the negative electrode sheet and the mass content of the second additive in the electrolyte, so that after the secondary battery is charged to 100% SOC at a charging rate of 0.33C, the compression density of the negative electrode sheet is 1.15 to 1.26 g / cm³ 3 And, the mass content of the second additive in the electrolyte is 0.5% to 3%.

[0192] Furthermore, the compression density of the negative electrode sheet after charging the above secondary battery to 100% SOC at a charging rate of 0.33C is 1.15 to 1.26 g / cm³ 3 And, the mass content of the first solvent in the organic solvent of the electrolyte is 30% to 40%.

[0193] Furthermore, the compression density of the negative electrode sheet after the above secondary battery is charged to 100% SOC at a charging rate of 0.33C is 1.15 to 1.26 g / cm³ 3 And, the mass of the electrolyte at a unit cell rated capacity of 1Ah of a secondary battery is 2.5g to 3.0g.

[0194] In some of these embodiments, the compression density of the negative electrode sheet after charging the secondary battery to 100% SOC at a charging rate of 0.33C is >1.26 g / cm³ 3 and ≤1.36 g / cm³ 3 And, the mass content of the first additive in the electrolyte is 2.5% to 6.5%. Thus, when the compression density of the negative electrode sheet after the secondary battery is charged to 100% SOC at a charging rate of 0.33C is within the above range, the mass content of the first additive in the electrolyte is 2.5% to 6.5%, which allows the battery to better consider both high rapid charging performance and circulation performance.

[0195] Furthermore, the compression density of the negative electrode sheet after charging the above secondary battery to 100% SOC at a charging rate of 0.33C is >1.26 g / cm³ 3 and ≤1.36 g / cm³ 3 And, the mass content of the second additive in the electrolyte is 1% to 4%. Furthermore, the mass content of the first solvent in the organic solvent of the electrolyte is 25% to 38%.

[0196] Furthermore, the compression density of the negative electrode sheet after charging the above secondary battery to 100% SOC at a charging rate of 0.33C is >1.26 g / cm³ 3 and ≤1.36 g / cm³ 3 And, the mass of the electrolyte at a unit cell rated capacity of 1Ah of a secondary battery is 2.2g to 2.8g.

[0197] In some of these embodiments, the charging time for the secondary battery to charge 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%. Thus, based on providing high energy density using graphite of high consolidation density, this battery is simultaneously a rapid-charge type battery, and by adding the carboxylic acid ester in the above amount to the electrolyte and improving the capacity of the first additive and the second additive, the secondary battery is made to have high energy density, rapid-charge performance, and cycling performance. Furthermore, in the electrolyte, the mass content of the first additive is 1.5% to 7%, and the mass content of the second additive is 0.5% to 4%.

[0198] In some embodiments, the process of charging a secondary battery from a 10% charged state to an 80% charged state includes a plurality of charging stages, wherein the difference between the maximum charged state of any charging stage in the plurality of charging stages and the maximum charged state in an adjacent charging stage is less than or equal to 5%, such as a 1% charged state, a 1.5% charged state, a 2% charged state, a 2.5% charged state, a 3% charged state, a 3.5% charged state, a 4% charged state, a 4.5% charged state, a 5% charged state, or a range composed of any two of the above values.

[0199] The secondary battery includes a plurality of charging stages from a 10% charged state to a 40% charged state, and for any one charging stage, it can be charged at any one multiplier between 5C and 10C, and the charging multiplier corresponding to each charging stage may be any numeric value of 5C, 5.5C, 6C, 6.5C, 7C, 7.5C, 8C, 8.5C, 9C, 9.5C, 10C, or a value within a range composed of any two of the above numeric values.

[0200] The secondary battery includes multiple charging stages from a 40% charged state to an 80% charged state, and the charging ratio of any charging stage is smaller than the charging ratio of any charging stage from a 10% charged state to a 40% charged state, and the charging ratio of the stage for charging to an 80% charged state can be any value from 2.5C to 5C, for example, 2.7C.

[0201] For example, the charging stage of a secondary battery from 10% to 80% can be carried out in the following manner.

[0202] A method of charging from 10% SOC to 15% SOC with a constant current of 5.0C;

[0203] A method of charging from 15% SOC to 20% SOC with a constant current of 5.0C;

[0204] A method of charging from 20% SOC to 25% SOC with a constant current of 5.0C;

[0205] A method of charging from 25% SOC to 30% SOC with a constant current of 5.0C;

[0206] A method of charging from 30% SOC to 35% SOC with a constant current of 5.0C;

[0207] A method of charging from 35% SOC to 40% SOC with a constant current of 5.0C;

[0208] A method of charging from 40% SOC to 45% SOC with a constant current of 4.6C;

[0209] A method of charging from 45% SOC to 50% SOC with a constant current of 4.3C;

[0210] A method of charging from 50% SOC to 55% SOC with a constant current of 4.0C;

[0211] A method of charging from 55% SOC to 60% SOC with a constant current of 3.7C;

[0212] A method of charging from 60% SOC to 65% SOC with a constant current of 3.4C;

[0213] 3.1C constant current charging method from 65% SOC to 70% SOC;

[0214] A method of charging from 70% SOC to 75% SOC with a constant current of 2.9C;

[0215] A method of charging from 75% SOC to 80% SOC with a constant current of 2.7C.

[0216] In some embodiments, the time for charging the secondary battery from a 10% charged state to an 80% charged state is 6 min to 15 min. For example, the time for charging the secondary battery from a 10% charged state to an 80% charged state 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 composed of any two of the above values.

[0217] In some of the embodiments thereof, the cathode sheet further comprises a cathode conductive layer, and the cathode conductive layer is installed between a cathode current collector and at least one cathode film layer. The cathode conductive layer can improve the conductivity of the entire cathode sheet, which is advantageous for improving the electron transfer rate.

[0218] The cathode conductive layer comprises a conductive agent. The cathode conductive layer can be formed by first coating the surface of a cathode current collector with a corresponding slurry, then coating the cathode slurry described above again, and drying it to form the cathode sheet. Furthermore, the conductive agent in the cathode 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.

[0219] Optionally, the thickness of the cathode conductive layer is 0.5 μm to 2 μm, and as an example, may be a range composed of 0.5 μm, 1 μm, 1.5 μm, 2 μm, or any two of the above values. When the thickness of the cathode conductive layer is within the above range, the conductivity performance of the cathode sheet can be further improved and the heat generation of the battery cell can be reduced by reducing the heat generation of the cathode sheet; and the energy density of the battery cell can be taken into account.

[0220] In some of these embodiments, the cathode conductive layer comprises a binder, and the binder comprises at least one of styrene butadiene rubber (SBR), water-soluble unsaturated resin, water-soluble acrylic resin, polyvinyl alcohol, sodium alginate, and carboxymethyl chitosan. The cathode conductive layer can improve the adhesion between the cathode film layer and the cathode current collector and the conductivity of the entire cathode sheet, which is advantageous for improving the electron transfer rate.

[0221] Optionally, in the cathode conductive layer, the mass content of the conductive agent is 20% to 40%, and, for example, may be a range of 20%, 25%, 30%, 35%, 40%, or any two of the above values. Optionally, in the cathode conductive layer, the mass content of the binder is 60% to 80%. For example, it is a range of 60%, 65%, 70%, 75%, 80%, or any two of the above values.

[0222] In some of these embodiments, the cathode film layer may optionally further include a binder. The binder may include at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0223] In some of these embodiments, the cathode film layer may optionally further include a conductive agent. The conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0224] In some of these embodiments, the cathode film layer may optionally further include other auxiliary agents such as a thickener (e.g., sodium carboxymethylcellulose (CMC-Na)).

[0225] In some of the embodiments thereof, a cathode sheet can be manufactured by the following method. The compositional components for manufacturing the cathode sheet, such as a cathode active material, a conductive agent, a binder, and any other compositional components, are dispersed in a solvent (a non-limiting example of the solvent is deionized water) to form a cathode slurry; and the cathode slurry is applied to at least one surface of a cathode current collector, and a cathode sheet can be obtained after undergoing processes such as drying and cold pressing. The surface of the cathode current collector coated with the cathode slurry may be a single surface of the cathode current collector or two surfaces of the cathode current collector.

[0226] Furthermore, the first graphite comprises at least one of artificial graphite and natural graphite. Furthermore, by using artificial graphite, the artificial graphite surface active sites are smaller, and the consumption rate of the first solvent and the first additive in the electrolyte is lower, which can satisfy the demand for a long lifespan of the battery. Furthermore, the capacity per gram of discharge of the graphite is ≤358 mAh / g. If the capacity per gram of graphite is within this range, the activity of the graphite is appropriate, which is advantageous for reducing the consumption rate of the electrolyte and can improve the circulation performance of the battery.

[0227] The Dv50 particle size of the first graphite is 2.2 μm to 7.7 μm, and as an example, it may be a range composed of 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 any two of the above values. Furthermore, the Dv50 particle size of the first graphite may be 2.2 μm to 7 μm.

[0228] In some of these embodiments, the cathode film layer comprises at least one cathode active layer, and at least one cathode active layer comprises the first graphite.

[0229] In one embodiment thereof, the cathode film layer comprises only one cathode active layer, and the cathode active layer comprises the first graphite and the second graphite, wherein 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. Since the particle size range of the first graphite is small, the compression density is low, and the reaction activity between it and the electrolyte is strong, it affects the energy density, circulation performance, and storage performance of the battery. To further improve the energy density, circulation performance, and storage performance of the battery, a second graphite with a large particle size is incorporated into the cathode active layer.

[0230] As an example, the Dv50 particle size of the second graphite may be 7.8μm, 8μm, 8.2μm, 8.5μm, 9μm, 9.2μm, 9.5μm, 9.6μm, 10μm, 10.2μm, 10.5μm, 10.6μm, 11μm, 11.8μm, 12μm, 12.5μm, 12.8μm, 13μm, 13.5μm, 13.7μm, 14μm, 14.2μm, 14.5μm, 14.8μm, or a range composed of any two of the above values.

[0231] Furthermore, the mass ratio of the first graphite to the second graphite is 2:8 to 6:4; optionally 3:7 to 5:5; and as an example, this mass ratio may be a range composed of 2:8, 3:7, 4:6, 5:5, 6:4 or any two of the above values.

[0232] Furthermore, the mass content of the first graphite in the cathode active layer is 20% to 70%, and as an example, the mass content of the first graphite in the cathode active layer is a range composed of 20%, 25%, 30%, 35%, 40%, 45%, 48%, 50%, 55%, 60%, 65%, 70%, or any two of the above values.

[0233] Furthermore, the total mass content of both the first graphite and the second graphite in the cathode active layer is 30% to 98%, and as an example, this total mass content may be a range composed of 30%, 35%, 40%, 45%, 48%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 98% or any two of the above values.

[0234] Optionally, the mass content of the first graphite in the negative electrode active layer may be ≥20% and <50%, and may be, for example, 20%, 25%, 30%, 35%, 40%, 45%, 48%, and at the same time, the total mass content of the first additive and the second additive in the electrolyte may be 3% to 8%, and for example, the total mass content of the first additive and the second additive may 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 additive in the electrolyte have a matching relationship. Through the above installation, the content of the first graphite and the total mass content of the first additive and the second additive are further matched, so that the rapid charging performance and circulation performance of the battery can be effectively improved.

[0235] Optionally, the mass content of the first graphite in the cathode active layer is 50% to 70%, and may be in a range composed of, for example, 50%, 55%, 60%, 65%, 70% or any two of the above values, and the total mass content of the first additive and the second additive in the electrolyte is 4% to 10%, and may be in a range composed of, for example, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10% or any two of the above values. The higher the content of the first graphite, the more additive must be added to the electrolyte accordingly. Thus, the content of the first graphite and the total mass content of the first additive and the second additive are better matched, so that the rapid charging performance and circulation performance of the battery can be effectively improved.

[0236] In another embodiment, the cathode film layer comprises a first cathode active layer and a second cathode active layer installed to be sequentially stacked on the same side of the cathode current collector, wherein the graphite comprises at least one of artificial graphite and natural graphite, the graphite in the first cathode active layer comprises at least one of the artificial graphite and the natural graphite, and the second cathode active layer comprises a first graphite and a third graphite, wherein the first graphite comprises the artificial graphite, and the Dv50 particle size of the third graphite is 7.8 μm to 14.8 μm. The smaller the surface active area of ​​the artificial graphite, the lower the consumption rate of the first solvent and the first additive in the electrolyte. The first graphite is installed in the upper second cathode active layer, and the third graphite with a large particle size is added to the second cathode active layer to further improve the energy density, circulation performance, and storage performance of the battery.

[0237] Optionally, in the second cathode active layer, the mass ratio of the first graphite to the third graphite is 2:8 to 8:2; optionally, 3:7 to 7:3. As an example, this mass ratio may be a range composed of 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, or any two of the above values.

[0238] Furthermore, the mass content of the first graphite in the second cathode active layer is 20% to 70%, for example, the mass content of the first graphite in the cathode active layer is 20%, 25%, 30%, 35%, 40%, 45%, 48%, 50%, 55%, 60%, 65%, 70%, or any two of the above values.

[0239] Optionally, the mass content of the first graphite in the second cathode active layer may be ≥20% and <50%, and may be, 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 may be 3% to 7%, and for example, the total mass content of the first additive and the second additive may 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 have a matching relationship. Through the above installation, the content of the first graphite and the total mass content of the first additive and the second additive are further matched, so that the rapid charging performance and circulation performance of the battery can be effectively improved.

[0240] Optionally, the mass content of the first graphite in the second negative electrode active layer may be 50% to 70%, and may be composed of a range of, for example, 50%, 55%, 60%, 65%, 70%, or any two of the above values; and the total mass content of the first additive and the second additive in the electrolyte may be 3.5% to 8%, and for example, the total mass content of the first additive and the second additive may 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 additive must be added to the electrolyte accordingly. This allows the content of the first graphite to be better matched with the total mass content of the first additive and the second additive, thereby effectively improving the rapid charging performance and circulation performance of the battery.

[0241] Furthermore, the Dv50 particle size of the graphite in the first cathode active layer ≥ the Dv50 particle size of the first graphite in the second cathode active layer. Furthermore, the Dv50 particle size of the graphite in the first cathode active layer > the Dv50 particle size of the graphite in the second cathode active layer. The first graphite is installed in the upper second cathode active layer, and the distance between the cathode active material particles in the upper second cathode active layer is reduced and the contact area between the cathode active material particles is increased, thereby increasing the conductive channels and bridges and increasing the active area participating in the reaction, which significantly improves the battery's capacity and rapid charging performance; and since graphite with a large particle size is added to the lower first cathode active layer and the first cathode active layer has large pores and good electrolyte infiltration performance, it may be advantageous to further improve the rapid performance and circulation performance of the battery.

[0242] Furthermore, the Dv50 particle size of the graphite in the first cathode active layer is 5.8 μm to 12.8 μm, and optionally 7.8 μm to 12.8 μm. As an example, the Dv50 particle size of the graphite in the first cathode active layer may be 5.8 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 12 μm, 13 μm, 14 μm, 14.5 μm, 14.8 μm, 15 μm, 16 μm, 17 μm, 18 μm, 18.5 μm, or a range composed of any two of the above values.

[0243] Furthermore, the Dv50 particle size of the first graphite in the second cathode active layer is 2.2 μm to 7.7 μm, optionally 4.2 μm to 7.2 μm.

[0244] Furthermore, the ratio of the thickness of the second cathode active layer to the total thickness of the first cathode active layer and the second cathode active layer may be 30% to 70%, for example, 30%, 40%, 50%, 60%, 70%, or any two of the above values.

[0245] It can be understood that the first cathode active layer and the second cathode active layer can be obtained by sequentially stacking and applying two slurries, respectively, followed by processes such as drying and cold pressing.

[0246] In some of the embodiments thereof, the artificial graphite comprises graphite body particles and a coating layer, wherein the graphite body particles comprise secondary particles aggregated into a plurality of primary particles, and the coating layer is coated on the surface of the body particles, and the coating layer comprises amorphous carbon. Amorphous carbon refers to a transient carbon material similar to amorphous (or lacking a fixed shape and periodic structural regularity) with a very low degree of graphite crystallization. In this application, amorphous carbon refers to a product carbonized from an organic carbon source.

[0247] Since the graphite body particles contain secondary particles, there are relatively many migration paths for lithium ions in the artificial graphite, and the migration paths in the primary particles are relatively short, which can improve the migration speed of lithium ions; and since the amorphous carbon layer has many cross-sections and defects, the greater the number of sites from which lithium ions can escape, the better the conductivity of the amorphous carbon layer becomes, which can reduce the internal resistance of the negative electrode sheet and reduce the heat production of the battery cell.

[0248] Furthermore, based on the total mass of the artificial graphite, the mass content of the amorphous carbon is 2% to 5%. For example, the mass content of the amorphous carbon layer is a range of 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any two of the above values.

[0249] If the mass content of the amorphous carbon layer is within the above range, it can further reduce the internal resistance of the cathode sheet and reduce the heat production of the battery cell.

[0250] In an embodiment of the present application, artificial graphite may be manufactured by a method known in the art, for example, a manufacturing method comprises providing graphite body particles and an organic carbon source, mixing the two, and then undergoing a carbonization treatment to form an amorphous carbon layer on at least a portion of the surface of the graphite body particles.

[0251] Optionally, the organic carbon source comprises one or more of coal asphalt, petroleum asphalt, phenolic resin, and coconut shells. More optionally, the organic carbon source comprises petroleum asphalt. Optionally, the softening point of the coal asphalt and petroleum asphalt is 250°C or lower.

[0252] Optionally, the carbonization treatment temperature is 700°C to 1800°C. Optionally, the carbonization treatment temperature is 1000°C to 1300°C. The carbonization treatment temperature is placed within a suitable range to carbonize the organic carbon source and form a coating layer containing amorphous carbon on at least a portion of the surface of the artificial graphite.

[0253] Optionally, the carbonization treatment time is 1h to 6h.

[0254] Furthermore, the powder resistivity of artificial graphite is ≤ 0.04 Ω·cm.

[0255] In some of these embodiments, the graphite has a capacity per gram of charge at a 0.1C ratio in a button cell ≥ 350 mAh / g, optionally 350 mAh / g to 440 mAh / g.

[0256] In some of these embodiments, the negative electrode active material may further include silicon-based materials, except for the graphite described above. The inclusion of silicon-based materials can improve the capacity of the negative electrode active material and improve the energy density of the battery cell.

[0257] Furthermore, the silicon-based material may include at least one of silicon oxide and a silicon-carbon composite.

[0258] Furthermore, in silicon-based materials, the mass content of silicon elements in the negative electrode active material is 0.3% to 10%, optionally 1% to 6%. For example, the mass content of silicon element in silicon-based materials is a range composed of 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 any two of the above values.

[0259] Qualitative and quantitative detection of each substance or each element of the present application can be performed using appropriate instruments and methods already known to those skilled in the art. Related detection methods may refer to domestic and international test standards, domestic and international corporate standards, etc. Those skilled in the art may obtain more accurate detection results by adaptively changing specific detection steps / instrument parameters, etc., in terms of detection accuracy. Qualitative or quantitative detection may be performed using a single detection method, or qualitative or quantitative testing may be performed by using a combination of several methods.

[0260] separator

[0261] In some of these embodiments, the secondary battery further includes a separator. The separator is installed between the positive sheet and the negative sheet and primarily functions to prevent a positive-negative short circuit while allowing ions to pass through.

[0262] In some of these embodiments, the anode sheet, cathode sheet, and separator can be manufactured to form an electrode assembly through a winding method or a laminating method.

[0263] In this application, the type of separator is not particularly limited, and any known porous structure separator with excellent chemical and mechanical stability may be selected. The separator may be a single-layer film or a multilayer composite film, and is not particularly limited. If the separator is a multilayer composite film, the material of each layer may be the same or different, and is not particularly limited. In some embodiments, the thickness of the separator is 6 μm to 40 μm, optionally 12 μm to 20 μm.

[0264] In some of these embodiments, the separator comprises a porous substrate film and a functional layer installed on at least one side of the porous substrate film.

[0265] Furthermore, the material of the porous substrate film may include at least one of glass fiber, nonwoven fabric, and polyolefin. Optionally, the polyolefin includes at least one of polyethylene, polypropylene, and polyvinylidene fluoride.

[0266] Furthermore, the thickness of the porous substrate film is ≤12μm, optionally ≤9μm, and optionally 6μm to 9μm. For example, the thickness of the substrate film is a range composed of 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, 10μm, 10.5μm, 11μm, 11.5μm, 12μm, or any two of the above values.

[0267] In an embodiment of the present application, if the porosity of the separator is within the above range, the ability of lithium ions to move within the separator can be improved, and the internal resistance of the battery cell can be further reduced, thereby reducing heat generation.

[0268] In the embodiments of the present application, porosity refers to the percentage of the total volume of the separator occupied by the volume of pores within the separator. Porosity can be tested according to the standard GB / T36363-2018 "Polyolefin Separator for Battery Cells." It should be noted that the actual testing process may adopt a testing procedure that differs slightly from the standard in order to eliminate as much as possible the influence of differences in testing equipment, testing errors, and porosity testing, thereby obtaining more accurate test values.

[0269] Furthermore, the porosity of the porous substrate film is 20% to 70%, optionally 35% to 60%. For example, the porosity of the substrate film is a range composed of 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or any two of the above values.

[0270] When the thickness of the porous substrate film is within the above range, the movement path of lithium ions in the substrate film is short, which can further reduce the internal resistance of the battery cell and reduce heat generation.

[0271] In an embodiment of the present application, the separator may be a base film; optionally, the separator further comprises a functional layer installed on at least one side of the base film, and the functional layer may include inorganic particles to improve the heat resistance of the separator. Optionally, the functional layer is installed on both sides of the base film.

[0272] In some embodiments, the functional layer comprises a first functional layer and a second functional layer, wherein the first functional layer is installed on one side of a substrate film and comprises a first inorganic particle, and the second functional layer is installed on the other side of the substrate film and comprises a composite particle, wherein the composite particle comprises a second inorganic particle and a plurality of non-fluorinated polymer particles, and the second inorganic particle is attached to the surface of the non-fluorinated polymer particle and / or dispersed inside the non-fluorinated polymer particle.

[0273] The heat resistance performance of the first functional layer and the second functional layer is good, so the heat resistance performance of the separator can be improved.

[0274] Optionally, the first functional layer may include a binder, and optionally, at least one of a fluorine-containing binder or a polyacrylic acid binder, for example, polyvinylidene fluoride may be optionally included.

[0275] Optionally, the first 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. The first inorganic particles can improve the heat resistance performance of the first functional layer.

[0276] In an embodiment of the present application, the meaning of the thickness of the base film is a meaning known in the art, and can be detected using a device and a meaning known in the art. For example, a newly manufactured separator is used as a sample, or a battery cell that has been discharged (discharged to a lower cutoff voltage so that the charge state of the battery becomes about 0% SOC) is disassembled in reverse to obtain a separator from the battery cell, and after drying the separator, the separator is cut with an ion beam cutter to form a cross-section; then, the cross-sectional thickness of the separator and each layer is measured using a scanning electron microscope.

[0277] The second functional layer non-fluorinated polymer particles refer to polymers that are non-fluoropolymers. For example, the non-fluorinated polymer particles include acrylate copolymers, and optionally, the acrylate copolymer includes acrylate-acrylonitrile-acrylamide-acrylate copolymers. Acrylate copolymers have excellent adhesive performance and high adhesion stability with the substrate film. The molar ratio of each monomer in the copolymer can be any ratio such as 35%:30%:15%:20% or 40%, 20%, 10%, 30% or 45%, 15%, 20%, 20%, etc.

[0278] Among the composite particles, the second inorganic particle does not adhere well to the non-fluorine polymer particles due to the high-temperature treatment during the assembly process, resulting in the composite particle having voids, which is advantageous for lithium ion transport and improves the ion conductivity of the separator; the second inorganic particle can increase the compression modulus of the composite particle, and since the composite particle does not easily deform during the charge-discharge process, the structure of the separator becomes more stable, thereby improving the kinetic performance of the battery cell and enhancing high-speed charging performance. Optionally, compared to when the first and second functional layers are installed close to the negative electrode sheet, the composite particle does not easily deform, so the separator basically does not cause adverse effects such as extrusion to the negative electrode sheet, thereby stabilizing the kinetic performance of the negative electrode sheet. Correspondingly, the first functional layer is installed close to the anode sheet.

[0279] 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; optionally, the second inorganic particles comprise silicon oxide. The second inorganic particles can improve the heat resistance performance of the second functional layer, form composite particles by combining with a non-fluorine polymer, further improve the circulation stability and kinetic performance of the separator, and improve the circulation performance and high-speed charging performance of the battery cell.

[0280] The average particle size of the second inorganic particle is 5 nm to 100 nm, optionally 10 nm to 100 nm, and optionally 5 nm to 20 nm. For example, the average particle size of the second inorganic particle is a range composed of 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 any two of the above values. When the average particle size of the second inorganic particle is within the above range, it is advantageous for improving the heat resistance performance and compression modulus of the composite particle.

[0281] In an embodiment of the present application, the average particle size of the second inorganic particle is in the sense known in the art and can be detected using the sense known in the art and instruments known in the art, for example, after obtaining a separator, the separator is dried and used as a sample, and the separator is cut with an ion beam cutter to form a cross-section; then, the particle size of the second inorganic particle in the separator is measured using a scanning electron microscope, and the particle sizes of a plurality of second inorganic particles, such as 50, are measured, and the average value is calculated and used as the average particle size of the second inorganic particle.

[0282] In some embodiments, the ionic conductivity of the separator is 0.3 mS / cm to 0.6 mS / cm. For example, the ionic conductivity of the separator is a range of 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 any two of the above values.

[0283] When the ion conductivity of the separator is within the above range, the lithium ion mobility of the separator can be further improved and the high-speed charging performance of the battery cell can be enhanced.

[0284] In an embodiment of the present application, the ion conductivity of the separator can be detected using a device and in the sense known in the art, for example, manufacturing a test type 2025 button battery: in a vacuum glove box, a lithium sheet is placed in the negative electrode case of the battery, and 150 μL of electrolyte is added thereto, wherein the electrolyte uses a 1M LiPF6 solution with EC / EMC / DEC = 3 / 5 / 2 (mass ratio), and also a separator (area 3.14 cm² 2 (12 μm thick) is inserted and adhered to the lithium sheet, then 25 μL of electrolyte is added, and finally, an anode sheet (the anode sheet of Example 1 can be used) is placed on top and sealed. The assembled button battery is removed from the vacuum glove box and left for 24 hours for the next test.

[0285] Test: 10 on an electrochemical workstation -1 ~10 6 The separator resistance Rb is obtained by conducting a test in the frequency range of Hz, and the ionic conductivity σ (unit: mS / cm) is calculated using the formula below,

[0286] σ = L / (R b ХS)

[0287] Here, R b is the equivalent resistance, and L and S are the thickness and area of ​​the test standby separator, respectively.

[0288] The secondary battery includes at least one battery cell. The secondary battery may include one or more battery cells.

[0289] In this application, unless otherwise stated, "battery cell" refers to a basic unit capable of achieving the interconversion of chemical energy and electrical energy, and furthermore generally comprises at least a positive electrode sheet, a negative electrode sheet, and an electrolyte. During the charging and discharging process of the battery, active ions move between the positive electrode sheet and the negative electrode sheet, being inserted and removed. The electrolyte serves to conduct active ions between the positive electrode sheet and the negative electrode sheet.

[0290] The present application has no particular restrictions on the shape of the battery cell and may be cylindrical, square, or any other shape. For example, the secondary battery shown in FIG. 1 is a battery cell and is an example of a battery cell (5) with a square structure.

[0291] In some of the embodiments thereof, the battery cell (5) may include an outer casing. This outer casing may package the electrode assembly and the electrolyte. In some of the embodiments thereof, the outer casing of the battery cell (5) may be a hard case, such as a hard plastic case, an aluminum case, or a steel case. The outer casing of the battery cell (5) may be a soft pack, such as a pocket-type soft bag. The material of the soft bag may be plastic, and furthermore, non-limiting examples of plastic may include at least one of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0292] In some of these embodiments, referring to FIG. 2, the outer body may include a case (51) and a cover plate (53). Here, the case (51) includes a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate form a receiving cavity. The case (51) has an opening communicating with the receiving cavity, and the cover plate (53) is installed to cover the opening and seal the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator may manufacture an electrode assembly (52) through a winding method or a laminating method. The electrode assembly (52) is packaged within the receiving cavity. The electrolyte is infiltrated into the electrode assembly (52). The number of electrode assemblies (52) included in the battery cell (5) may be one or multiple, and a person skilled in the art may select according to actual demand.

[0293] In some embodiments, the secondary battery may be a battery module or a battery pack, and the battery module includes at least one battery cell. The number of battery cells included in the battery module may be one or a plurality, and those skilled in the art may select a suitable number depending on the application and capacity of the battery module.

[0294] The secondary battery illustrated in FIG. 3 is a battery module, which is an exemplary battery module (4). Referring to FIG. 3, a plurality of battery cells (5) may be installed in the battery module (4) in a sequential arrangement along the length direction of the battery module (4). Of course, they may also be arranged in any other arbitrary manner. Additionally, these plurality of battery cells (5) may be secured through a fastening member.

[0295] Optionally, the battery module (4) may further include a housing having a receiving space, and a plurality of battery cells (5) are received in this receiving space.

[0296] In some of these embodiments, the battery module may be assembled into a battery pack, and the number of battery modules included in the battery pack may be one or a number, and those skilled in the art may select a suitable number depending on the application and capacity of the battery pack.

[0297] The secondary battery illustrated in FIGS. 4 and 5 is a battery pack, which is an exemplary battery pack (1). Referring to FIGS. 4 and 5, the battery pack (1) may include a battery box and a plurality of battery modules (4) installed within the battery box. The battery box includes an upper box (2) and a lower box (3), and the upper box (2) may be covered by the lower box (3) to form a sealed space for accommodating the battery modules (4). The plurality of battery modules (4) may be arranged in the battery box in any manner.

[0298] In addition, one embodiment of the present application further provides an electric device comprising the secondary battery provided in the present application. The secondary battery may be used as a power source for the electric device or as an energy storage unit for the electric device. The electric device may include, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Here, the mobile device may be, for example, a mobile phone, a laptop, etc.; and the electric vehicle may be, for example, a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc., but is not limited thereto.

[0299] As an electrical device, a secondary battery can be selected according to its usage demand.

[0300] FIG. 6 is an exemplary electric device (6). The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the electric device's requirements for high power and high energy density of a secondary battery, a battery pack or a battery module may be adopted.

[0301] Other examples of devices may include mobile phones, tablets, laptops, etc. These devices typically require lightweight design and can use battery cells (5) as a power source.

[0302] To further clarify the technical problem, technical solution, and advantages to be solved by this application, the application will be described in more detail below in combination with the embodiments and the accompanying drawings. It will be apparent that the described embodiments are merely some of the embodiments of this application and do not represent all of them. The description of at least one exemplary embodiment below is actually merely illustrative and does not limit the application and its applications. All other embodiments obtained by a person skilled in the art without creative effort based on the embodiments of this application fall within the scope of protection of the present invention.

[0303] In the examples, where specific techniques or conditions are not specified, the work is performed in accordance with the techniques or conditions described in literature in the art or product descriptions. If the manufacturer is not specified for the reagents or equipment used, they are all general products available on the market.

[0304] Example 1

[0305] (1) Manufacturing of anode sheets

[0306] The cathode active material comprises lithium iron phosphate and an ion conductive layer, wherein the ion conductive layer is coated on the surface of the lithium iron phosphate and comprises titanium iron lithium Li2FeTi(PO4)3 phosphate and amorphous carbon. The Dv50 of the cathode active material is 1.6 μm, and the Dv10 is 0.64 μm. The powder compression density at 30,000 N is 2.53 g / cm³. 3 am.

[0307] The positive current collector is an aluminum foil with a thickness of 10 μm, and a positive conductive layer is installed on the positive current collector. The positive conductive layer is formed by uniformly mixing conductive carbon SP, binder polyvinylidene fluoride (PVDF), and solvent N-methylpyrrolidone (NMP) and then applying it to the surface of the current collector, and has a thickness of 1 μm.

[0308] A positive active material lithium iron phosphate LiFePO4, a binder polyvinylidene fluoride, and a conductive agent acetylene black are mixed in a mass ratio of 97:2:1, then a solvent N-methylpyrrolidone (NMP) is added and uniformly stirred to form a positive slurry; the positive slurry is uniformly coated onto the positive conductive layer of an aluminum foil positive current collector, and a positive sheet is obtained through drying and cold pressing. The positive sheet includes a positive current collector and a positive conductive layer and a positive film layer sequentially installed on the positive current collector.

[0309] Here, based on the mass of the anode film layer, the cross-sectional coating weight of the anode sheet is 300 mg / 1540.25 mm 2 And; the battery has a compressed density of the positive sheet of 2.63 g / cm³ at 100% SOC with a charging scale of 0.33 C. 3 Charge until it becomes.

[0310] Here, charging the battery to 100% SOC at a charging rate of 0.33C proceeds in the following manner. The battery cell is charged to the upper limit voltage (3.65V) of the battery at a constant current charging rate of 0.33C, and then charged to 0.05C at a constant voltage to correspond to the state of the battery cell at 100% SOC.

[0311] (2) Manufacturing of the cathode sheet

[0312] The method for manufacturing a two-layer cathode sheet is as follows.

[0313] The Dv50 particle sizes of the first graphite, second graphite, and third graphite are 5.8 μm, 9.6 μm, and 9.6 μm, respectively.

[0314] The cathode current collector is a copper foil with a thickness of 5 μm, and a cathode conductive layer is installed on the cathode current collector. The cathode conductive layer is formed by uniformly mixing conductive carbon SP, binder SBR, dispersant CMC, and solvent water, and then applying it to the surface of the current collector, and has a thickness of 1 μm.

[0315] A cathode active material, graphite, a conductive agent, acetylene black, a binder, styrene butadiene rubber, and a thickener, sodium carboxymethylcellulose, are mixed in a mass ratio of 96:0.5:2.5:1, then deionized water is added as a solvent and stirred uniformly to form a first cathode slurry.

[0316] The first graphite, the second graphite, the conductive agent acetylene black, the binder styrene butadiene rubber, and the thickener sodium carboxymethylcellulose are mixed in a mass ratio of 54.9:41.1:0.5:2.5:1, then deionized water is added as a solvent and uniformly stirred to form a second cathode slurry.

[0317] A first cathode slurry is uniformly coated onto the cathode conductive layer of a copper foil cathode current collector and dried; a second cathode slurry is coated onto the surface of the dried first cathode slurry, and a cathode sheet is obtained by drying and cold pressing. The cathode sheet includes a cathode current collector and a cathode conductive layer and a cathode film layer sequentially installed on the cathode current collector. The cathode film layer includes a first cathode active layer and a second cathode active layer sequentially installed on the cathode conductive layer.

[0318] Here, based on the total mass of the cathode film layer, the cross-sectional coating weight of the cathode sheet is 138 mg / mm 2And; the battery has a compression density of the negative sheet of 1.2 g / cm³ at 100% SOC with a charging scale of 0.33 C. 3 It is charged until it becomes; based on the total mass of the first graphite, second graphite, and third graphite in the cathode film layer, the mass ratios of the first graphite, second graphite, and third graphite are 40%, 30%, and 30%, respectively.

[0319] (3) Preparation of electrolyte

[0320] An organic solvent is obtained by uniformly mixing a first solvent carbonate (EC), a second solvent ethyl acetate (EA), and a dimethyl carbonate (DMC) in a fixed mass ratio in an argon atmosphere glove box with a water content < 10 ppm, and the mass contents of carbonate (EC), ethyl acetate (EA), and dimethyl carbonate (DMC) in the organic solvent are 25%, 50%, and 25%, respectively, as indicated in Table 1; a fixed amount of lithium hexafluorophosphate (LiPF6) is slowly added as a lithium salt and stirred sufficiently until completely dissolved, with the concentration of LiPF6 in the electrolyte being 1 mol / L. After returning to room temperature, a first additive vinylene carbonate (VC), which accounts for 6% of the total mass of the electrolyte, and a second additive fluoroethylene carbonate (FEC), which accounts for 4% of the total mass of the electrolyte, are added and the mixture is uniformly and sufficiently stirred to obtain the electrolyte. The mass b of the electrolyte in a unit cell of a secondary battery with a rated capacity of 1Ah is 2.65g, as shown in Table 1.

[0321] (4) Separator

[0322] The separator includes a substrate film, the substrate film is a 7 μm polyethylene film layer, and the porosity is 42%.

[0323] (5) Manufacturing of secondary batteries

[0324] A positive electrode sheet, a separator, and a negative electrode sheet are stacked and wound in sequence to obtain a wound electrode assembly; the electrode assembly is placed in a rectangular aluminum case as an outer layer, dried, and then an electrolyte is injected, and a secondary battery is obtained through processes such as packaging, storage, formation, aging, secondary packaging, and capacitance.

[0325] The manufacturing methods of Examples 2 to 4 are similar to those of Example 1, but the difference is that the mass content of the first solvent, ethylene carbonate (EC), in the organic solvent is adjusted (the mass content of dimethyl carbonate (DMC) is adjusted accordingly), and the specific details are as shown in Table 1.

[0326] The manufacturing methods of Examples 5 to 8 are similar to those of Example 2, but the difference is that the mass content of the first additive VC in the electrolyte is adjusted, and the specific details are as shown in Table 1.

[0327] The manufacturing methods of Examples 9 to 13 are similar to those of Example 2, but the difference is that the mass content of the second additive FEC in the electrolyte is adjusted, and the specific details are as shown in Table 1.

[0328] The manufacturing method of Example 14 is similar to that of Example 2, but the difference is that the type and content of the second solvent are adjusted, and at the same time, the cross-sectional coating weight of the active layer of the anode sheet and the cathode sheet is adjusted. Specific details are as shown in Table 1.

[0329] The manufacturing methods of Examples 15 to 17 are similar to those of Example 2, but the difference is that the type of the first graphite of the negative electrode active material is adjusted, and the Dv50 parameter is different, as shown in Table 1.

[0330] The manufacturing method of Examples 18 to 19 is similar to that of Example 10, but the difference is that the mass b of the electrolyte at the rated capacity of the secondary battery unit cell of 1Ah is adjusted, and at the same time the mass content of the first additive in the electrolyte is adjusted, and the specific details are as shown in Table 1.

[0331] Example 19

[0332] The manufacturing method is similar to Example 3, but the difference is that the cathode sheet has a single-layer structure, and the manufacturing method is as follows.

[0333] A cathode active material, first graphite, second graphite, a conductive agent, acetylene black, a binder, styrene butadiene rubber, and a thickener, sodium carboxymethylcellulose, are mixed in a mass ratio of 38.4:5:7.6:0.5:2.5:1, and then deionized water as a solvent is added and uniformly stirred to form a cathode slurry; the cathode slurry is uniformly coated onto the cathode conductive layer of a copper foil cathode current collector, and a cathode sheet is obtained by drying and cold pressing.

[0334] The cathode sheet includes a cathode current collector and a cathode conductive layer and a cathode active layer sequentially installed on the cathode current collector.

[0335] Here, based on the total mass of the cathode active layer, the cross-sectional coating weight of the cathode sheet is 138 mg / mm² 2 And; the battery has a compressed density of the positive sheet of 1.2 g / cm³ at 100% SOC with a charging scale of 0.33 C. 3 It is charged until it becomes; based on the total mass of the first graphite and the second graphite in the cathode active layer, the mass ratio of the first graphite and the second graphite is 40% and 60%, respectively.

[0336] The manufacturing methods of Comparative Examples 1 to 5 are similar to those of Example 3, but the difference is that at least one of the mass content of ethylene carbonate (EC) in the organic solvent and the mass content of the first additive and the second additive in the electrolyte is adjusted, and the specific details are as shown in Table 1.

[0337] Below is a performance test.

[0338] (1) The test steps for the capacity retention rate after 1000 cycles of the battery at 60℃ are as follows.

[0339] One charge-discharge cycle is defined as charging the battery at 60°C with a constant current of 1C to a cutoff voltage of 3.65V, leaving it for 30 minutes, and then discharging it with a constant current of 1C to 2.0V; the capacity C0 after the first cycle is recorded; the above charge-discharge cycle steps are repeated up to 1,000 times, and the capacity Cn corresponding to the 1,000th cycle is recorded to obtain the capacity retention rate = Cn / C0 × 100% for the battery after 1,000 cycles at 60°C. The higher the capacity retention rate, the better the battery's cycling performance.

[0340] (2) The test steps for charging time T, in which the secondary battery is charged from 10% SOC to 80% SOC at 30℃, are as follows.

[0341] Charge at an ambient temperature of 30℃ with the battery at 10% SOC,

[0342] Step of charging from 10% SOC to 15% SOC with a constant current of 5.0C;

[0343] Step of charging from 15% SOC to 20% SOC with a constant current of 5.0C;

[0344] Step of charging from 20% SOC to 25% SOC with a constant current of 5.0C;

[0345] Step of charging from 25% SOC to 30% SOC with a constant current of 5.0C;

[0346] Step of charging from 30% SOC to 35% SOC with a constant current of 5.0C;

[0347] Step of charging from 35% SOC to 40% SOC with a constant current of 5.0C;

[0348] Step of charging from 40% SOC to 45% SOC with a constant current of 4.6C;

[0349] Step of charging from 45% SOC to 50% SOC with a constant current of 4.3C;

[0350] Step of charging from 50% SOC to 55% SOC with a constant current of 4.0C;

[0351] Step of charging from 55% SOC to 60% SOC with a constant current of 3.7C;

[0352] Step of charging from 60% SOC to 65% SOC with a constant current of 3.4C;

[0353] Step of charging from 65% SOC to 70% SOC with a constant current of 3.1C;

[0354] Step of charging from 70% SOC to 75% SOC with a constant current of 2.9C;

[0355] Step of charging from 75% SOC to 80% SOC with a constant current of 2.7C;

[0356] Record the total charging time.

[0357] (3) The test steps for the capacity retention rate after 1000 cycles of the battery at 30℃ are as follows.

[0358] At 30°C, each battery is charged starting from 10% SOC, and then charged to 80% SOC according to the multiplier corresponding to the different SOCs. Afterward, the battery is charged to 3.65V using a constant current with a charging multiplier of 0.33C, left for 30 minutes, and then discharged to 2.0V using a constant current of 1C. This constitutes one charge-discharge cycle, and the capacity C0 after the first cycle is recorded; the above charge-discharge cycle steps are repeated up to 1000 times, and the capacity Cn corresponding to the 1000th cycle is recorded to obtain the capacity retention rate = Cn / C0 × 100% for the battery having undergone 1000 cycles at 30°C. The higher the capacity retention rate, the better the battery's cycling performance.

[0359] Some parameters of each example and comparative example are as shown in Table 1, where all contents are mass contents and the unit of cross-sectional coating weight of the anode and cathode is all mg / 1540.25 mm 2 am.

[0360] The performance test results of each example and comparative example are as shown in Table 2.

[0362]

[0363]

[0364]

[0365] As can be seen from Tables 1 and 2, if the content of the first additive in Comparative Example 1 is too high, the room temperature cycling performance of the battery deteriorates; if the content of the first additive in Comparative Example 2 is too low, the high temperature cycling performance of the battery deteriorates and the rapid charging time becomes longer, which explains that the rapid charging performance is weak; if the content of the second additive in Comparative Example 3 is too high, the high temperature cycling performance of the battery deteriorates; if the content of the second additive in Comparative Example 4 is too low, the room temperature cycling performance of the battery deteriorates; and if the content of the first solvent in Comparative Example 5 is too low, the self-stability of the electrolyte deteriorates, causing a decrease in conductivity, resulting in deterioration of both room temperature and high temperature cycling performances.

[0366] Each example allows the secondary battery manufactured by adjusting the composition and ratio of the electrolyte and combining it with a negative electrode sheet having a first graphite with a small particle size to achieve good rapid charging performance, room temperature cycling performance, and high temperature cycling performance. Here, in the electrolyte of Example 14, the second solvent is entirely a carbonate solvent, and since the conductivity of the electrolyte is reduced, the cross-sectional coating weight of the positive and negative electrode sheets is reduced, thereby improving the rapid charging performance of the battery.

[0367] Each technical feature of the above embodiments may be combined arbitrarily; however, for the sake of brevity, not all possible combinations of each technical feature in the above embodiments have been described. Therefore, as long as such combinations of technical features are not contradictory to one another, they should all be considered to be within the scope described in this specification.

[0368] The above embodiments merely represent a few embodiments of the present application. Although the description is relatively specific and detailed, it should not be understood as limiting the scope of the patent of the application. It should be noted that those skilled in the art to which the present application pertains may make slight modifications and improvements without departing from the concept of the present application, and that all such modifications and improvements fall within the scope of protection of the present application. Explanation of the symbols

[0369] 1: Battery pack 2: Upper box 3: Bottom box 4: Battery Module 5: Battery cell 51: Case 52: Electrode assembly 53: Cover plate 6: Electrical device

Claims

Claim 1 A secondary battery comprises: a positive electrode current collector and a positive electrode film layer installed on at least one side of the positive electrode current collector, wherein the positive electrode film layer comprises a positive electrode active material; a negative electrode sheet comprising a negative electrode current collector and a negative electrode film layer installed on at least one side of the negative electrode current collector, wherein the negative electrode film layer comprises a negative electrode active material, and the negative electrode active material comprises a first graphite having a Dv50 particle size of 2.2 μm to 7.7 μm; and an organic solvent and an organic additive, wherein the organic solvent comprises a first solvent, and the first solvent comprises a cyclic carbonate, and the mass content of the first solvent is 25% to 40% based on the total mass of the organic solvent; A secondary battery comprising: an electrolyte in which 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, based on the total mass of the electrolyte, the mass percentage of the first additive in the electrolyte is 2% to 10% and the mass percentage of the second additive in the electrolyte is 0.3% to 6%. Claim 2 In claim 1, the structure of the ethylene carbonate derivative is, A secondary battery in which R1 and R2 each independently contain any one of a hydrogen element, a halogen element, a C1-C5 alkyl group, and a C1-C5 halogen alkyl group, and R1 and R2 are not simultaneously hydrogen elements. Claim 3 A secondary battery according to any one of claims 1 to 2, wherein the ethylene carbonate derivative comprises at least one of fluoroethylene carbonate, ethylene difluorocarbonate, and trifluoromethyl vinyl carbonate. Claim 4 A secondary battery according to any one of claims 1 to 3, wherein the cyclic carbonate comprises at least one of ethylene carbonate and propylene carbonate. Claim 5 A secondary battery according to any one of claims 1 to 4, wherein the mass content of the first solvent is 30% to 40% based on the total mass of the organic solvent. Claim 6 A 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%. Claim 7 A 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%, optionally 3.5% to 9%. Claim 8 A secondary battery according to any one of claims 1 to 7, wherein the mass of the electrolyte at a unit cell rated capacity of 1Ah of the secondary battery is 2.2g to 2.95g. Claim 9 In claim 8, the mass of the electrolyte in the unit cell rated capacity of 1Ah of the secondary battery 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%; or, the mass of the electrolyte in the unit cell rated capacity of 1Ah of the secondary battery 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%. Claim 10 In any one of claims 1 to 9, the positive active material has a powder compression density ≥ 2.43 g / cm³ at 30,000 N. 3 , optionally 2.48 g / cm³ 3 ~ 2.85 g / cm 3 Phosphorus, secondary battery. Claim 11 In claim 10, the positive active material comprises at least one of a lithium-containing phosphate and a derivative having an olivine structure, in a secondary battery. Claim 12 A secondary battery according to claim 11, wherein the positive active material comprises: a core portion comprising at least one of a lithium-containing phosphate having an olivine structure and a derivative thereof; and an ion-conducting layer coated on the surface of the core portion, wherein the ion-conducting layer comprises at least one element among Fe, C, Ti, Zr, Hf, Ge, and Sn. Claim 13 In claim 11 or 12, the lithium-containing phosphate of the olivine structure and its derivatives are of the general formula Li x1 A1 y1 M1 a1 M2 b1 P 1-c1 X c1 Q1 z1 A secondary battery comprising a compound, wherein 0.5≤x1≤1.3, 0≤y1≤1.3, 0.9≤x1+y1≤1.3; 0.9≤a1≤1.5, 0≤b1≤0.5, 0.9≤a1+b1≤1.5; 0≤c1≤0.5; 3≤z1≤5; A1 comprises at least one of Na, K, and Mg; M1 comprises at least one of Mn, Fe, Co, and Ni; M2 comprises at least one of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X comprises at least one of S, Si, Cl, B, C, N, and P; and Q1 comprises at least one of O and F. Claim 14 In claim 13, the lithium-containing phosphate of the olivine structure and its derivative comprises at least one of lithium iron phosphate, lithium manganese phosphate, lithium nickel phosphate, and tritium cobalt phosphate, in a secondary battery. Claim 15 In Clause 12, the above ion conductive layer has the chemical formula Li 3-b Fe 2-b M3 b (PO m ) n A secondary battery comprising a high-speed ion conductor, wherein M3 comprises at least one element among +4 valence Ti, Zr, Hf, Ge and Sn, and 0≤b≤1, 3≤m≤5, and 2≤n≤4. Claim 16 In claim 15, the high-speed ion conductor comprises at least one of titanium iron lithium phosphate, zirconium iron lithium phosphate, and tin iron lithium phosphate, in a secondary battery. Claim 17 In any one of claims 1 to 16, (1) the compression density of the anode sheet is 2.5 g / cm³ 3 ~ 2.8g / cm 3 A secondary battery satisfying at least one of the following conditions: (2) a mass percentage content of carbon in the positive active material is 1% to 2%; (3) a powder resistivity range R≤20Ω·cm, optionally R≤11Ω·cm of the positive active material; and (4) a volume average particle size of the positive active material is 1μm≤Dv50≤2μm, 0.4μm≤Dv10≤0.7μm. Claim 18 A secondary battery according to any one of claims 1 to 17, wherein the positive electrode film layer further comprises a lithium supplement, and the lithium supplement comprises at least one of a ternary lithium supplement material, lithium phosphate, lithium dihydrogen phosphate, lithium sulfate, lithium sulfite, lithium molybdate, lithium nickelate, lithium ironate, lithium oxalate, lithium titanate, lithium tetraborate, lithium metasilicate, lithium metamanganate, lithium tartrate, and lithium citrate. Claim 19 In paragraph 18, the above-mentioned ternary lithium supplement material is Li x2 A2 y2 Ni a2 Co b2 Mn c2 M4 (1-a2-b2-c2) Q2 z2 A secondary battery comprising, wherein 0<x2≤2.1, 0≤y2≤2.1; 0≤a2≤1, 0≤b2≤1, 0≤c2≤1, 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. Claim 20 A secondary battery according to any one of claims 1 to 19, wherein the positive sheet further comprises a positive conductive layer, the positive conductive layer is installed between the positive current collector and at least one positive film layer, the positive 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. Claim 21 A secondary battery according to claim 20, wherein the thickness of the positive electrode conductive layer is 0.5 μm to 2 μm. Claim 22 A secondary battery according to claim 20 or 21, wherein the positive electrode conductive layer comprises a binder, and the binder comprises at least one of polyvinylidene fluoride, polytetrafluoroethylene, difluoroethylene tetrafluoroethylene propylene terpolymer, vinylidene fluoride hexafluoropropyl tetrafluoroethylene terpolymer, tetrafluoroethylene hexafluoropropene copolymer, polyacrylic acid, and fluorine-containing acrylate resin. Claim 23 A secondary battery according to 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%. Claim 24 In any one of claims 1 to 23, the compression density of the negative electrode sheet after charging the secondary battery to 100% SOC at a charging rate of 0.33C is 1.15 g / cm³ 3 ~ 1.46g / cm 3 , optionally 1.15 g / cm³ 3 ~ 1.36g / cm 3 Phosphorus, secondary battery. Claim 25 In claim 24, the compression density of the negative electrode sheet after charging the secondary battery to 100% SOC at a charging rate of 0.33C is 1.15 to 1.26 g / cm³ 3 A secondary battery, wherein the mass content of the first additive in the electrolyte is 3% to 8%. Claim 26 A secondary battery satisfying at least one of the following conditions in claim 25: (1) the mass content of the second additive in the electrolyte is 0.5% to 3%; and (2) the mass content of the first solvent in the organic solvent is 30% to 40%. Claim 27 In claim 24, the compression density of the negative electrode sheet after charging the secondary battery to 100% SOC at a charging rate of 0.33C is >1.26 g / cm³ 3 and ≤1.36 g / cm³ 3 A secondary battery having a mass content of the first additive in the electrolyte of 2.5% to 6.5%. Claim 28 A secondary battery according to claim 27, satisfying at least one of the following conditions: (1) the mass content of the second additive in the electrolyte is 1% to 4%; and (2) the mass content of the first solvent in the organic solvent is 25% to 38%. Claim 29 A secondary battery according to any one of claims 1 to 28, wherein the electrolyte further comprises a second solvent, and the second solvent comprises at least one of a linear carbonate, a carboxylic acid ester, an ether, a nitrile, and a sulfone. Claim 30 A secondary battery according to claim 29, wherein the second solvent comprises a carboxylic acid ester; optionally, the carboxylic acid ester comprises at least one of methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and methyl butyrate. Claim 31 A secondary battery according to claim 32, wherein the charging time for charging the secondary battery from 10% SOC to 80% SOC at 30℃ 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%. Claim 32 A secondary battery according to 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%. Claim 33 A secondary battery according to any one of claims 1 to 32, wherein the electrolyte comprises a lithium salt, and the lithium salt comprises at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, fluorosulfonylimide salt, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluorobis(oxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate. Claim 34 A secondary battery according to claim 33, wherein the concentration of the lithium salt in the electrolyte is 0.7 mol / L to 1.5 mol / L. Claim 35 A secondary battery according to claim 33 or 34, wherein the lithium salt comprises at least one of LiFSI and LiPF6, and the lithium salt satisfies at least one of the following conditions: (1) the concentration of LiFSI is 0.2 mol / L to 0.5 mol / L; (2) the concentration of LiPF6 is 0.5 mol / L to 1.3 mol / L; (3) the lithium salt comprises LiFSI and LiPF6, and the concentration ratio of LiFSI to LiPF6 is (2 to 5):

10. Claim 36 A secondary battery according to any one of claims 1 to 35, wherein the cathode sheet further comprises a cathode conductive layer, the cathode conductive layer is installed between the cathode current collector and at least one side of the cathode film layer, the cathode 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. Claim 37 A secondary battery according to claim 36, wherein the thickness of the negative electrode conductive layer is 0.5 μm to 2 μm. Claim 38 A secondary battery according to claim 36 or 37, wherein the negative electrode conductive layer comprises a binder, and the binder comprises at least one of styrene butadiene rubber, water-soluble unsaturated resin, water-soluble acrylic resin, polyvinyl alcohol, sodium alginate, and carboxymethyl chitosan. Claim 39 A secondary battery according to claim 38, wherein in the cathode conductive layer, the mass content of the conductive agent is 20% to 40% and the mass content of the binder is 60% to 80%. Claim 40 A secondary battery according to any one of claims 1 to 39, wherein the cathode film layer comprises at least one cathode active layer, and the at least one cathode active layer comprises the first graphite. Claim 41 A secondary battery according to claim 40, wherein the cathode film layer comprises only one cathode active layer, the cathode active layer comprises 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. Claim 42 A secondary battery according to claim 41, wherein the mass ratio of the first graphite to the second graphite is 2:8 to 6:4; optionally 3:7 to 5:

5. Claim 43 A secondary battery according to claim 41 or 42, wherein the mass content of the first graphite in the negative electrode active layer is ≥20% and <50%, and the total mass content of the first additive and the second additive in the electrolyte is 3% to 8%; or, wherein 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%. Claim 44 A secondary battery according to claim 40, wherein the cathode film layer comprises a first cathode active layer and a second cathode active layer installed to be sequentially stacked on the same side of the cathode current collector, wherein the first cathode active layer comprises at least one of artificial graphite and natural graphite, and the second cathode active layer comprises the first graphite and a third graphite, wherein the first graphite comprises artificial graphite, and the Dv50 particle size of the third graphite is 7.8 μm to 14.8 μm. Claim 45 A secondary battery according to 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 3:7 to 7:

3. Claim 46 In claim 44 or 45, (1) the ratio of the total amount of each cathode active material in the second cathode active layer and the first cathode active layer is 3:7 to 7:3; optionally 4:6 to 6:4; (2) the mass content of the first graphite in the second cathode active layer is 30% to 70%; optionally, the mass content of the first graphite in the second cathode 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 8%; (3) the Dv50 particle size of the graphite in the first negative electrode active layer ≥ the Dv50 particle size of the first graphite in the second negative electrode active layer; optionally, the Dv50 particle size of the graphite in the first negative electrode active layer is 5.8μm to 12.8μm, optionally 7.8μm to 12.8μm; optionally, the Dv50 particle size of the graphite in the second negative electrode active layer is 2.2μm to 7.7μm, optionally 4.2μm to 7.2μm, satisfying at least one of the conditions. Claim 47 A secondary battery according to any one of claims 44 to 46, wherein the artificial graphite comprises graphite body particles and a coating layer, the graphite body particles comprise secondary particles aggregated into a plurality of primary particles, the coating layer is coated on the surface of the body particles, and the coating layer comprises amorphous carbon. Claim 48 A secondary battery satisfying at least one of the following conditions in claim 47: (1) the mass content of the amorphous carbon is 2% to 5% based on the total mass of the artificial graphite; and (2) the powder resistivity of the artificial graphite is ≤ 0.04 Ω·cm. Claim 49 A secondary battery according to any one of claims 1 to 48, wherein the first graphite has a capacity per gram of charge at a 0.1C multiplier in a button-type battery ≥ 350 mAh / g, optionally 350 mAh / g to 440 mAh / g. Claim 50 A secondary battery according to any one of claims 1 to 49, wherein the negative electrode active material further comprises a silicon-based material, and the silicon-based material comprises at least one of silicon oxide and a silicon-carbon composite; wherein the mass content of silicon elements in the silicon-based material in the negative electrode active material is 0.3% to 10%, optionally 1% to 6%. Claim 51 A secondary battery according to any one of claims 1 to 50, wherein the separator comprises a porous substrate film and a functional layer installed on at least one side of the porous substrate film. Claim 52 A secondary battery according to claim 51, satisfying at least one of the following conditions: (1) the thickness of the porous substrate film is ≤12 μm and optionally ≤9 μm; (2) the porosity of the porous substrate film is 20% to 70% and optionally 35% to 60%. Claim 53 A secondary battery according to claim 51 or 52, wherein the separator comprises a first functional layer and a second functional layer installed on both sides of the porous substrate film, the first functional layer comprises a first inorganic particle, the second functional layer comprises a composite particle, the composite particle comprises a second inorganic particle and a non-fluorinated polymer particle, and the second inorganic particle is attached to the surface of the non-fluorinated polymer particle and / or dispersed inside the non-fluorinated polymer particle. Claim 54 A secondary battery according to claim 53, satisfying at least one of the following conditions: (1) the non-fluorine polymer particles include acrylate-based polymer particles; (2) the first functional layer is located between the cathode sheet and the porous substrate film, and the second functional layer is located between the anode sheet and the porous substrate film. Claim 55 An electric device comprising a secondary battery according to any one of claims 1 to 54.

Images