Secondary battery, battery device and electric device

Abstract

Provided in the present application are a secondary battery, a battery device and an electric device. A negative electrode sheet in the secondary battery comprises a negative electrode current collector and a negative electrode film layer, wherein the negative electrode film layer is arranged on at least one side of the negative electrode current collector and comprises a negative electrode active material. The negative electrode active material comprises graphite, and the powder compaction density of the negative electrode active material under 20,000 N is 1.5 g / cm3 to 1.85 g / cm3. An electrolyte comprises an organic solvent and an organic additive, wherein the organic solvent comprises a first solvent, the first solvent comprising a cyclic carbonate, and the mass content of the first solvent being 17-34% based on the total mass of the electrolyte; and the organic additive comprises a first additive and a second additive, the first additive comprising vinylene carbonate, the second additive comprising an ethylene carbonate derivative, and based on the total mass of the electrolyte, the mass content of the first additive being 1.5-8%, and the mass content of the second additive being 0.5-4%.

Description

Secondary battery, battery device and electric device TECHNICAL FIELD

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

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

[0003] In recent years, secondary batteries such as lithium ion batteries are widely used in energy storage power systems such as hydroelectric, thermal, wind and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. With the increasingly wide application of secondary batteries, the demand for energy density of the battery cells is gradually increasing, but the improvement of energy density will deteriorate the cycle performance and fast charging performance of the battery, so how to make the secondary battery have high energy density, cycle performance and fast charging performance has become a problem to be solved.

[0004] SUMMARY

[0005] Based on this, the present application provides a secondary battery, a battery device and an electric device, which can have high energy density, cycle performance and fast charging performance.

[0006] The first aspect of the present application provides a secondary battery, comprising:

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

[0008] A negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode film layer, the negative electrode film layer being arranged on at least one side of the negative electrode current collector, the negative electrode film layer comprising a negative electrode active material, the negative electrode active material comprising graphite, the powder compaction density of the negative electrode active material under 20000N being 1.5g / cm 3 ~1.85g / cm 3 ; and

[0009] An electrolyte, the electrolyte comprising an organic solvent and an organic additive, the organic solvent comprising a first solvent, the first solvent comprising a cyclic carbonate, the mass content of the first solvent being 17%~34% based on the total mass of the electrolyte; the organic additive comprising a first additive and a second additive, the first additive comprising vinylene carbonate, the second additive comprising a vinylene carbonate derivative, the mass content of the first additive being 1.5%~8% and the mass content of the second additive being 0.5%~4% based on the total mass of the electrolyte.

[0010] The negative active material of the above secondary battery includes graphite and has a high powder compaction density, and thus a high energy density can be provided. However, the negative electrode sheet with a high powder compaction density has poor kinetic performance, which is not conducive to improving the fast-charging performance. In addition, due to the limited internal space of the battery cell, the injection amount of the electrolyte needs to be reduced under the high energy density battery cell, and thus there is a risk of a sharp drop in the cycle performance of the battery cell due to insufficient electrolyte. Therefore, the above secondary battery is further improved by the electrolyte, which is matched with the negative electrode sheet with a high energy density. Specifically, the first solvent, the first additive and the second additive in the above electrolyte and the content are improved, so that the electrolyte has good thermal stability and suitable electrical conductivity, thereby reducing the electrolyte consumption rate and the direct current resistance DCR of the battery, and further improving the cycle performance, storage life and fast-charging performance of the high energy density system battery cell. Thus, the above secondary battery can balance the high energy density, cycle performance and fast-charging performance.

[0011] In some embodiments, the vinyl carbonate derivative has the following structure:

[0012] R1and R2each independently include any one of a hydrogen element, a halogen element, a C1-C5 alkyl group and a C1-C5 halogenated alkyl group, and R1and R2are not hydrogen elements at the same time. These second additives have good film-forming property, conductivity and stability, and can improve the fast-charging performance and cycle performance of the battery, especially the cycle performance at room temperature.

[0013] In some embodiments, the vinyl carbonate derivative includes at least one of fluoroethylene carbonate, difluoroethylene carbonate and trifluoromethyl ethylene carbonate.

[0014] In some embodiments, the cyclic carbonate includes at least one of vinyl carbonate and propylene carbonate.

[0015] In some embodiments, the mass content of the first solvent is 25.5%-34% based on the total mass of the electrolyte.

[0016] In some embodiments, the mass content of the first additive is 1.5%-6.5% based on the total mass of the electrolyte; and / or,

[0017] The mass content of the second additive is 0.5%-3% based on the total mass of the electrolyte.

[0018] In some embodiments, the total mass content of the first additive and the second additive is 2%-10% based on the total mass of the electrolyte.

[0019] In some embodiments, the total mass content of the first additive and the second additive is 3% to 8% based on the total mass of the electrolyte.

[0020] In some embodiments, the powder compaction density of the positive electrode active material is ≥2.43 g / cm3 under 30000 N. 3 , optionally 2.48 g / cm3 3 to 2.85 g / cm3 3 .

[0021] In some embodiments, the positive electrode active material comprises at least one of lithium-containing phosphate with olivine structure and derivatives thereof.

[0022] In some embodiments, the positive electrode active material comprises:

[0023] a core portion comprising at least one of lithium-containing phosphate with olivine structure and derivatives thereof; and

[0024] an ion-conducting layer, the ion-conducting layer being coated on the surface of the core portion, the ion-conducting layer comprising at least one element selected from Fe, C, Ti, Zr, Hf, Ge and Sn.

[0025] The core portion coated with the ion-conducting layer on the surface can improve the electrical conductivity of lithium-containing phosphate with olivine structure and derivatives thereof, reduce the powder resistivity of the material, and is conducive to the migration rate of lithium ions, thereby improving the rapid charging capability of the battery and reducing the heat generation of the battery cell.

[0026] In some embodiments, the lithium-containing phosphate with olivine structure and derivatives thereof comprises a general formula of Li x1 A1 y1 M1 a1 M2 b1 P 1-c1 X c1 Q1 z1, wherein 0.5≤x1≤1.3, 0≤y1≤1.3, and 0.9≤x1+y1≤1.3; 0.9≤a1≤1.5, 0≤b1≤0.5, and 0.9≤a1+b1≤1.5; 0≤c1≤0.5; 3≤z1≤5; A1 comprises at least one of Na, K, and Mg; M1 comprises at least one of Mn, Fe, Co, and Ni; M2 comprises at least one of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X comprises at least one of S, Si, Cl, B, C, and N, P; and Q1 comprises at least one of O and F. The lithium-containing phosphate of olivine structure has excellent cycle stability, which is beneficial to improving the cycle performance of the battery cell.

[0027] In some embodiments, the lithium-containing phosphate of olivine structure and derivatives thereof comprise at least one of lithium iron phosphate, lithium manganese phosphate, lithium nickel phosphate, and lithium cobalt phosphate.

[0028] In some embodiments, the ion-conducting layer comprises a chemical formula of Li 3-b Fe 2-b M3 b (PO m ) n , M3 comprises at least one of Ti, Zr, Hf, Ge, and Sn in +4 valence, 0≤b≤1, 3≤m≤5, and 2≤n≤4.

[0029] In some embodiments, the ion conductor comprises at least one of lithium titanium iron phosphate, lithium zirconium iron phosphate, and lithium tin iron phosphate. Coating the core surface with the ion conductor comprising the NASICON structure can significantly improve the transmission rate of lithium ions in the positive electrode end during multiple lithium extraction / insertion, improve the ion conductivity of the positive electrode active material, improve the rapid charging capacity of the battery cell, and further improve the specific capacity and the energy density of the corresponding battery cell.

[0030] In some embodiments, at least one of the following conditions is met:

[0031] (1) the compaction density of the positive electrode tab is 2.5 g / cm 3 ~ 2.8 g / cm 3 ;

[0032] (2) the mass content of carbon in the positive electrode active material is 1%~2%;

[0033] (3) the powder resistivity of the positive electrode active material is ≤20 Ω·cm;

[0034] (4) the volume average particle diameter of the positive electrode active material satisfies: 1 μm ≤ Dv50 ≤ 2 μm, 0.4 μm ≤ Dv10 ≤ 0.7 μm.

[0035] In some embodiments, the positive electrode film layer further includes a lithium supplement agent, and the lithium supplement agent includes at least one of a ternary lithium supplement material, lithium phosphate, lithium hydrogen phosphate, lithium sulfate, lithium sulfite, lithium molybdate, lithium nickelate, lithium ferrite, lithium oxalate, lithium titanate, lithium metaborate, lithium metavanadate, lithium tartrate, and trilithium citrate.

[0036] In some embodiments, the ternary lithium supplement material includes Li x2 A2 y2 Ni a2 Co b2 Mn c2 M4(1-a2-b2-c2)Q2 z2 wherein 0 < x2 ≤ 2.1, 0 ≤ y2 ≤ 2.1; 0 ≤ a2 ≤ 1, 0 ≤ b2 ≤ 1, 0 ≤ c2 ≤ 1, and 0.1 ≤ a2+b2+c2 ≤ 1; 1.8 ≤ z2 ≤ 3.5; A2 includes at least one of Na, K, and Mg; M4 includes at least one of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; and Q2 includes at least one of O and F.

[0037] In some embodiments, the positive electrode tab further includes a positive electrode conductive layer, the positive electrode conductive layer is arranged between the positive electrode current collector and the positive electrode film layer, and the positive electrode conductive layer includes a conductive agent, and the conductive agent includes at least one of super-conductive carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0038] In some embodiments, the thickness of the positive electrode conductive layer is 0.5 μm to 2 μm.

[0039] In some embodiments, the positive electrode conductive layer includes a binder, and the binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and a fluorine-containing acrylic ester resin.

[0040] In some embodiments, 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%.

[0041] In some embodiments, the secondary battery has a compaction density of the negative electrode tab of the secondary battery in a 100% SOC state of ≥ 1.15 g / cm 3 ~ 1.46 g / cm 3 , and optionally 1.25 g / cm 3 ~ 1.40 g / cm 3 .

[0042] In some embodiments, the secondary battery has a compaction density of the negative electrode tab of the secondary battery in a 100% SOC state of ≥ 1.25 g / cm 3 and < 1.35 g / cm 3 .

[0043] In some embodiments, the secondary battery satisfies at least one of the following conditions in a 100% SOC state:

[0044] (1) the second additive has a mass content of 0.5% to 3% in the electrolyte;

[0045] (2) the first solvent has a mass content of 25.5% to 34% in the electrolyte;

[0046] (3) the first additive has a mass content of 1.5% to 6% in the electrolyte.

[0047] In some embodiments, the secondary battery has a compaction density of the negative electrode tab of the secondary battery in a 100% SOC state of ≥ 1.35 g / cm 3 ~ 1.40 g / cm 3 .

[0048] In some embodiments, the secondary battery satisfies at least one of the following conditions in a 100% SOC state:

[0049] (1) the second additive has a mass content of 0.7% to 3.5% in the electrolyte;

[0050] (2) the first solvent has a mass content of 21.25% to 34% in the electrolyte;

[0051] (3) the first additive has a mass content of 2.5% to 7% in the electrolyte.

[0052] In some embodiments, the secondary battery has an electrolyte mass of 2.2 g to 3.0 g at a unit battery rated capacity of 1 Ah.

[0053] In some embodiments, the electrolyte further includes a second solvent, and the second solvent includes at least one of a linear carbonate, a carboxylic acid ester, an ether, a nitrile, and a sulfone.

[0054] In some embodiments, the second solvent comprises a carboxylic acid ester; more optionally, the carboxylic acid ester comprises at least one of methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, and 1,4-butyrolactone.

[0055] In some embodiments, the volumetric energy density of the secondary battery is in the range of 400 Wh / L to 450 Wh / L, the mass content of the carboxylic acid ester in the electrolyte is in the range of 25.5% to 59.5%, and the total mass content of the first additive and the second additive in the electrolyte is in the range of 2% to 7%.

[0056] In some embodiments, the volumetric energy density of the secondary battery is > 450 Wh / L and ≤ 480 Wh / L, the mass content of the carboxylic acid ester in the electrolyte is in the range of 25.5% to 63.75%, and the total mass content of the first additive and the second additive in the electrolyte is in the range of 3.5% to 8%.

[0057] In some embodiments, the charging time of the secondary battery from 10% SOC to 80% SOC at 30°C is in the range of 6 min to 15 min, the mass content of the carboxylic acid ester in the electrolyte is in the range of 17% to 63.7%, and the total mass content of the first additive and the second additive in the electrolyte is in the range of 2% to 8%.

[0058] In some embodiments, the mass content of the first additive in the electrolyte is in the range of 1.5% to 6.5%, and the mass content of the second additive in the electrolyte is in the range of 0.5% to 3.5%.

[0059] In some embodiments, the electrolyte comprises a lithium salt, and the lithium salt comprises at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, a fluorine-containing sulfimide salt, lithium triflate, lithium difluorophosphate, lithium difluoro oxalate borate, lithium bisoxalate borate, lithium difluoro bisoxalate phosphate, and lithium tetrafluoro oxalate phosphate.

[0060] In some embodiments, the mass content of the lithium salt in the electrolyte is in the range of 10% to 20%.

[0061] In some embodiments, the lithium salt comprises LiFSI and LiPF6, and the lithium salt satisfies at least one of the following conditions:

[0062] (1) the concentration of the LiFSI in the electrolyte is in the range of 0.2 mol / L to 0.5 mol / L;

[0063] (2) the concentration of the LiPF6 in the electrolyte is in the range of 0.5 mol / L to 1.3 mol / L;

[0064] (3) the substance amount ratio of the LiFSI and the LiPF6 is (2-5):10.

[0065] In some embodiments, the negative electrode tab further comprises a negative electrode conductive layer, the negative electrode conductive layer is arranged between the negative electrode current collector and the negative electrode film layer on at least one side, the negative electrode conductive layer comprises a conductive agent, the conductive agent comprises at least one of super conductive carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0066] In some embodiments, the thickness of the negative electrode conductive layer is 0.5-2 μm.

[0067] In some embodiments, the negative electrode conductive layer comprises a binder, the binder comprises at least one of styrene butadiene rubber, water-soluble unsaturated resin, water-based acrylic resin, polyvinyl alcohol, sodium alginate and carboxymethyl chitosan.

[0068] In some embodiments, in the negative electrode conductive layer, the mass content of the conductive agent is 20-40%, and the mass content of the binder is 60-80%.

[0069] In some embodiments, the negative electrode film layer comprises at least one negative electrode active layer, and the at least one negative electrode active layer comprises the graphite.

[0070] In some embodiments, the negative electrode film layer comprises one negative electrode active layer, the negative electrode active layer contains the graphite, and the Dv50 particle size of the graphite is 8.2-13.5 μm.

[0071] In some embodiments, the negative electrode film layer comprises a first negative electrode active layer and a second negative electrode active layer which are sequentially stacked on the same side of the negative electrode current collector, the graphite comprises at least one of artificial graphite and natural graphite, the graphite in the first negative electrode active layer comprises at least one of the artificial graphite and the natural graphite, and the graphite in the second negative electrode active layer comprises the artificial graphite.

[0072] In some embodiments, the Dv50 particle size of the graphite in the first negative electrode active layer is greater than the Dv50 particle size of the graphite in the second negative electrode active layer.

[0073] In some embodiments, the Dv50 particle size of the graphite in the first negative electrode active layer is 9.5-18.5 μm, which can be 9.5-14.8 μm.

[0074] The Dv50 particle size of the graphite in the second negative electrode active layer is 7.8-14.3 μm, which can be 7.8-12.8 μm.

[0075] In some embodiments, the mass ratio of graphite in the first negative electrode active layer and the second negative electrode active layer is 3:7 to 7:3, or 4:6 to 6:4.

[0076] In some embodiments, the artificial graphite includes graphite bulk particles and a coating layer, the graphite bulk particles include secondary particles aggregated by a plurality of primary particles, and the coating layer is coated on the surface of the bulk particles and includes amorphous carbon.

[0077] In some embodiments, at least one of the following conditions is met:

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

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

[0080] In some embodiments, the graphite has a charge specific capacity ≥350 mAh / g at a 0.1C rate in a button cell, or 350 mAh / g to 440 mAh / g.

[0081] In some embodiments, the negative electrode active material further includes a silicon-based material, the silicon-based material includes at least one of a silicon oxide compound and a silicon-carbon composite, and the mass content of silicon in the silicon-based material in the negative electrode active material is 0.3% to 10%, or 1% to 6%.

[0082] In some embodiments, the separator film includes a porous base film and a functional layer provided on at least one side of the porous base film.

[0083] In some embodiments, at least one of the following conditions is met:

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

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

[0086] In some embodiments, the separator film includes a first functional layer and a second functional layer provided on both sides of the porous base film, the first functional layer includes first inorganic particles, and the second functional layer includes composite particles, the composite particles include second inorganic particles and non-fluoropolymer particles, and the second inorganic particles are attached to the surface of the non-fluoropolymer particles and / or dispersed in the interior of the non-fluoropolymer particles.

[0087] In some embodiments, the non-fluoropolymer particles include acrylate polymer particles.

[0088] The second aspect of the present application provides a battery device including the secondary battery according to the first aspect of the present application.

[0089] The third aspect of the present application provides a power consuming device including at least one of the secondary battery according to the first aspect of the present application and the battery device according to the second aspect of the present application.

[0090] The power consuming device according to the present application includes the secondary battery according to the present application, and thus has at least the same advantages as the secondary battery.

[0091] The details of one or more embodiments of the application are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the application will be apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF DRAWINGS

[0092] For better understanding and illustrating the embodiments or examples provided by the present application, one or more drawings can be referred to. Additional details or examples used to describe the drawings should not be considered as limiting the scope of the disclosed application, the presently described embodiments or examples, and any one of the best modes of these applications presently understood. Moreover, the same reference numbers are used to denote the same components throughout the drawings. In the drawings:

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

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

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

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

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

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

[0099] REFERENCE NUMERALS:

[0100] 1: battery pack; 2: upper case; 3: lower case; 4: battery module; 5: battery cell; 51: case; 52: electrode assembly; 53: cover plate; 6: power consuming device. DETAILED DESCRIPTION

[0101] With reference to the drawings, the technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative effort are within the protection scope of the present application.

[0102] The "range" disclosed in the present application can be limited in the form of lower limit and upper limit, a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit limit the boundary of the particular range. The range limited in this way can be inclusive or exclusive of the end values, either end value can be independently included or excluded, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if the ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that the ranges of 60-110 and 80-120 are also contemplated. In addition, if the minimum range values of 1 and 2 are listed, and if the maximum range values of 3, 4 and 5 are also listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "a-b" represents a shorthand notation for any integer combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all the real numbers between "0-5" have been listed herein, and "0-5" is only a shorthand notation for these numerical combinations. In addition, when it is stated that a parameter is an integer ≥2, it is equivalent to disclose that the parameter is, for example, integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when it is stated that a parameter is an integer selected from "2-10", it is equivalent to list the integers 2, 3, 4, 5, 6, 7, 8, 9 and 10.

[0103] In the present application, "a plurality of", "a plurality of kinds" and the like are used without specific limitation, which means more than 2 or equal to 2 in quantity. For example, "at least one" means one or more than two.

[0104] If not specifically stated, all the embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0105] In the present application, the reference to "embodiments" means that the specific features, structures or properties described in connection with the embodiments can be included in at least one embodiment or implementation of the present application. The appearance of this phrase in various places in the specification does not necessarily mean that the same embodiments are referred to, nor are the independent or alternative embodiments that are not mutually exclusive. A person of ordinary skill in the art understands explicitly and implicitly that the embodiments described herein can be combined with other embodiments. In the present application, the reference to "implementation" has a similar understanding.

[0106] Those skilled in the art can understand that the sequence of writing each step in the method of each embodiment or example does not mean a strict execution sequence and constitutes any limitation on the implementation process. The detailed execution sequence of each step should be determined by its function and possible internal logic. If not specifically stated, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method comprises steps (a) and (b), which means that the method can comprise sequentially performed steps (a) and (b), or sequentially performed steps (b) and (a). For example, the method can also comprise step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0107] In the present application, the open technical features or technical solutions described by the words "containing", "including", "comprising" and the like do not exclude additional members other than the listed members, and can be regarded as providing both a closed feature or solution composed of the listed members and an open feature or solution including additional members in addition to the listed members. For example, A includes a1, a2 and a3, and unless otherwise specified, it can also include other members or can not include additional members, and can be regarded as providing both the feature or solution that "A is composed of a1, a2 and a3" and the feature or solution that "A not only includes a1, a2 and a3, but also includes other members".

[0108] In the present application, A (such as B) means that B is a non-limiting example of A, and A can be understood as not limited to B, unless otherwise specified.

[0109] In the present application, "optionally", "optional" and "optional" mean that it can or can not be present, i.e. it means to select from two parallel schemes of "have" or "not have". If there are multiple "options" in a technical solution, each "option" is independent of each other unless otherwise specified, and there is no contradictory relationship or mutual restriction.

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

[0111] The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer, the positive electrode film layer is arranged on at least one side of the positive electrode current collector, and the positive electrode film layer comprises a positive electrode active material.

[0112] The negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer. The negative electrode film layer is arranged on at least one side of the negative electrode current collector, and the negative electrode film layer comprises a negative electrode active material, the negative electrode active material comprises graphite, and the powder compaction density of the negative electrode active material under 20000N is 1.5g / cm 3 ~1.85g / cm 3 .

[0113] In the embodiments of the present application, the powder compaction density of the negative electrode active material is a meaning known to those skilled in the art, and can be tested by using a compaction density tester and referring to GB / T 24533-2009, and the test pressure is 20000N.

[0114] The electrolyte comprises an organic solvent and an organic additive, the organic solvent comprises a first solvent, the first solvent comprises a cyclic carbonate (EC), and the mass content of the first solvent is 17% to 34% based on the total mass of the electrolyte. The organic additive comprises a first additive and a second additive, the first additive comprises vinylene carbonate (VC), the second additive comprises a vinyl carbonate derivative, the mass content of the first additive is 1.5% to 8% based on the total mass of the electrolyte, and the mass content of the second additive is 0.5% to 4%.

[0115] The negative electrode active material of the above-mentioned secondary battery comprises graphite and has a high powder compaction density, so that a high energy density can be provided, but the negative electrode sheet with a high powder compaction density has poor kinetic performance, which is not conducive to the improvement of fast charging performance. In addition, due to the limited internal space of the battery cell, the injection amount of the electrolyte under the high energy density battery cell needs to be reduced, so there is a risk of a sharp drop in the cycle performance of the battery cell due to insufficient electrolyte. Therefore, the above-mentioned secondary battery is further improved by the electrolyte, which is matched with the negative electrode sheet with a high energy density, specifically by improving the first solvent, the first additive and the second additive in the above-mentioned electrolyte and the content, so that the electrolyte has good thermal stability and suitable electrical conductivity, so as to reduce the consumption rate of the electrolyte and the direct current resistance DCR of the battery, and further improve the cycle performance, storage life and fast charging performance of the high energy density system battery cell. Thus, the above-mentioned secondary battery can balance the high energy density and the fast charging performance.

[0116] The above-mentioned first solvent comprises a cyclic carbonate, and the cyclic carbonate has a high dielectric constant and good film forming performance. If the content of the first solvent in the electrolyte is too low, the stability of the electrolyte itself will be poor, which will reduce the electrical conductivity. However, if the content of the first solvent is too high, the viscosity and melting point of the electrolyte will increase, which will also deteriorate the electrical conductivity of the electrolyte and the kinetic performance of the battery, thereby causing the cycle performance to deteriorate. Therefore, by controlling the content of the first solvent in the above-mentioned range, the electrolyte can have good thermal stability and suitable electrical conductivity.

[0117] The first additive includes vinylene carbonate (VC), the second additive includes a vinyl carbonate derivative, the first additive and the second additive can participate in interface film formation, the content of the first additive and the second additive is too low, the first solvent will participate in film formation too much, which destroys the stability of the electrolyte, and then accelerates the consumption rate of the electrolyte, and deteriorates the cycle performance and storage life of the battery; with the increase of the content of the first additive, the high-temperature cycle life of the battery is improved, but the content of the first additive is too high, which will deteriorate the battery kinetic window and direct current resistance DCR, thereby leading to the deterioration of the cycle performance and being not conducive to the improvement of the fast charging performance; with the increase of the content of the second additive, the room temperature cycle life and the fast charging performance of the battery are improved, but the content of the second additive is too high, which deteriorates the high-temperature performance of the battery and reduces the high-temperature cycle life. Therefore, the first additive and the second additive are respectively within the above range, so that the electrolyte achieves a balance between film formation stability and battery kinetics.

[0118] Therefore, the electrolyte regulates the content of the first solvent within the above range, which can improve the thermal stability of the electrolyte and make the conductivity of the electrolyte within a suitable range, and the first additive and the second additive are respectively within the above range, so that the electrolyte achieves a balance between battery kinetics and film formation stability, thereby reducing the consumption rate of the electrolyte, improving the cycle performance and storage life of the battery under low liquid injection coefficient; in addition, the battery also has a lower direct current resistance DCR, and has good fast charging performance. The electrolyte can be applied to the above high-energy-density negative electrode sheet and battery system, so that the secondary battery has higher energy density, cycle performance and fast charging performance, especially room temperature cycle performance and high-temperature cycle performance. The electrolyte

[0119] In some embodiments of the present application, the cyclic carbonate in the first solvent includes at least one of ethylene carbonate (EC) and propylene carbonate (PC).

[0120] By way of example, the mass content of the first solvent in the electrolyte can be, but is not limited to, 17%, 18.7%, 21.25%, 23.8%, 25.5%, 27.2%, 29.75%, 32.3%, 34%. Further, the mass content of the first solvent in the electrolyte is 21.25% to 34% or 25.5% to 34%, or is within a range formed by any two of the above point values as end values, and the like hereinafter. Controlling the mass content of the first solvent in the electrolyte within the optional range can make the battery have better cycle performance.

[0121] As an example, the mass content of the first additive in the electrolyte can be, but is not limited to, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, or a range formed by any two of the above point values as end values. Further, the mass content of the first additive in the electrolyte is 1.5% to 6.5%. Further, the first additive is vinylene carbonate (VC). Controlling the mass content of the first additive in the electrolyte within the optional range can make the battery have better cycle performance, especially high-temperature cycle performance.

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

[0123] R1and R2each independently include any one of a hydrogen element, a halogen element, a C1-C5 alkyl group, and a C1-C5 haloalkyl group, and R1and R2are not hydrogen elements at the same time. Further, the halogen element includes at least one of a fluorine element, a chlorine element, and a bromine element, and the C1-C5 alkyl group and the C1-C5 haloalkyl group include, but are not limited to, at least one of halogenated or non-halogenated methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, and isomers thereof. These second additives have good film-forming property, conductivity, and stability, and can improve the fast-charging performance and cycle performance, especially room-temperature cycle performance, of the battery.

[0124] Further, the above-mentioned vinyl carbonate derivative includes at least one of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), and trifluoromethyl ethylene carbonate.

[0125] As an example, the mass content of the second additive in the electrolyte can be, but is not limited to, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, or a range formed by any two of the above point values as end values. Further, the mass content of the second additive in the electrolyte is 0.5% to 3%. Controlling the mass content of the second additive in the electrolyte within the optional range can make the battery have better fast-charging performance and cycle performance, especially room-temperature cycle performance.

[0126] In some embodiments of the present application, the total mass content of the first additive and the second additive is 2% to 10%. As an example, the total mass content can be 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%. Further, the total mass content of the first additive and the second additive is 2% to 9%; further, 3% to 8%. Controlling the total mass of the first additive and the second additive within the above range can improve the cycle performance of the battery.

[0127] In some embodiments of the present application, the electrolyte further comprises a second solvent. Further, the second solvent comprises at least one of linear carbonate, carboxylic ester, ether, nitrile, and sulfone. The second solvent, together with the first solvent, functions as a solvent, which lowers the melting point and viscosity of the electrolyte system, and improves the lithium ion transport performance of the electrolyte.

[0128] Further, the linear carbonate comprises at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl ethyl carbonate (EMC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC).

[0129] Further, the carboxylic ester comprises at least one of methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate, methyl propionate, ethyl propionate (EP), propyl propionate, methyl butyrate, ethyl butyrate, and 1,4-butyrolactone. In some embodiments of the present application, the second solvent comprises carboxylic ester.

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

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

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

[0133] Further, the mass content of the second solvent in the electrolyte is 17% to 63.75%; as the mass content can be 17%, 21.25%, 25.5%, 29.75%, 34%, 38.25%, 42.5%, 46.75%, 51%, 55.25%, 59.5%, 62.05%, 63.75%. Further, the mass content of the carboxylic ester in the electrolyte is 25.5% to 51%, 25.5% to 63.75%. In a specific example, the second solvent is carboxylic ester.

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

[0135] In some embodiments of the present application, the mass content of the lithium salt in the electrolyte is 10% to 20%, for example, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or a range formed by any two of the above values as end values.

[0136] In some embodiments of the present application, the concentration of the lithium salt in the electrolyte is 0.8 mol / L to 1.5 mol / L. For example, the concentration of the electrolyte salt in the electrolyte can be 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.5 mol / L; further, it can also be a range formed by any two of the above values as end values.

[0137] Optionally, the lithium salt comprises at least one of a fluorine-containing sulfonylimide salt and LiPF6. More optionally, the fluorine-containing sulfonylimide salt comprises at least one of LiFSI and LiTFSI.

[0138] Further, the lithium salt comprises LiFSI and LiPF6. More further, the concentration of LiFSI in the electrolyte is 0.2 mol / L to 0.5 mol / L; more further, the concentration of LiPF6 in the electrolyte is 0.5 mol / L to 1.3 mol / L. Further, the molar ratio of LiFSI to LiPF6 is (2-5):10. Lithium bisfluorosulfonylimide LiFSI has good conductivity and heat resistance, and is not easy to hydrolyze at high temperature, and is particularly suitable for high-energy-density systems with large heat production in the present application; however, when the temperature is too high, for example, reaches 200°C or above, LiFSI will decompose and generate heat, which will worsen the safety margin of the battery, so LiPF6 is added as a lithium salt, which also effectively improves the safety performance of the battery.

[0139] In some embodiments of the present application, the mass of the electrolyte under the rated capacity of 1 Ah per unit cell of the secondary battery is 2.2 g to 3.0 g, and as an example, can be 2.2 g, 2.3 g, 2.4 g, 2.5 g, 2.6 g, 2.7 g, 2.8 g, 2.9 g, or 3.0 g. Further, it can be 2.2 g to 2.8 g or 2.5 g to 3.0 g. The above-mentioned electrolyte of the present application is particularly suitable for a battery of a low electrolyte injection coefficient system. The electrolyte has a low consumption rate and good kinetics, and thus can improve the battery of the low electrolyte injection coefficient system and improve the cycle performance of the battery.

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

[0141] Positive electrode sheet

[0142] As a non-limiting example, the positive current collector has two opposite surfaces in the thickness direction of the positive current collector, and the positive film layer is arranged on any one or both of the two opposite surfaces of the positive current collector.

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

[0144] In some embodiments, the thickness of the positive current collector is 10-15 μm, optionally 12-15 μm. For example, the thickness of the positive current collector is 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, or a range defined by any two of the above values.

[0145] When the thickness of the positive current collector is within the above range, the positive current collector has excellent flow capacity, and the battery cell has high energy density.

[0146] In some embodiments of the present application, the thickness of the positive current collector is measured by a method known in the art. For example, the thickness of the positive electrode sheet is measured by using a micrometer, and the thickness of the positive current collector is measured by removing the film layer on the surface of the positive current collector.

[0147] The positive film layer is usually formed by coating a positive slurry on the positive current collector, drying, and cold pressing. The positive slurry is usually formed by dispersing and stirring uniformly the positive active material, optionally the conductive agent, optionally the binder, and any other components in a solvent. The solvent can be N-methyl pyrrolidone (NMP), but is not limited thereto.

[0148] The positive electrode sheet does not exclude other additional functional layers other than the positive film layer. For example, in some embodiments, the positive electrode sheet of the embodiments of the present application further comprises a positive conductive layer disposed between the positive current collector and the positive film layer. In some other embodiments, the positive electrode sheet of the embodiments of the present application further comprises a protective layer covering the surface of the positive film layer.

[0149] The positive active material can be any positive active material known in the art. In some embodiments, the powder compaction density of the positive active material under 30000 N is ≥ 2.43 g / cm 3 , optionally 2.48 g / cm 3 ~2.85 g / cm 3 . Further, the powder compaction density of the positive active material under 30000 N is 2.5 g / cm 3 ~2.8 g / cm 3 .

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

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

[0152] In the embodiments of the present application, the compaction of the positive active material powder is the meaning known to those skilled in the art, and a compaction density tester can be used to test it according to GB / T 24533-2009, and the test pressure is 30000N.

[0153] As a non-limiting example, the positive active material can include at least one of the following materials: phosphate-based positive materials, lithium transition metal oxides, and their respective modified compounds. Among them, the phosphate-based positive material includes at least one of lithium phosphate containing olivine structure and its derivatives.

[0154] Further, the positive active material includes at least one of lithium phosphate containing olivine structure and its derivatives. The particle size of the lithium phosphate containing olivine structure and its derivatives is smaller, the specific surface area is larger, and it is easy to absorb water, so the hydrolysis of the electrolyte in this system battery is more serious, and the HF generated by the hydrolysis is more, so the problem of electrolyte consumption is more prominent. The use of the above electrolyte can help to take advantage of its slow electrolyte consumption rate, thereby improving the cycle performance of such batteries. At the same time, it is beneficial to take advantage of the advantages of lithium phosphate containing olivine structure and its derivatives, such as high energy density, long cycle life, and good safety performance.

[0155] In some embodiments of the present application, the lithium phosphate containing olivine structure and its derivatives include a general formula of Li x1 A1 y1 M1 a1 M2 b1 P 1-c1 X c1 Q1 z1A compound of formula (I) wherein 0.5≤x1≤1.3, 0≤y1≤1.3, and 0.9≤x1+y1≤1.3; 0.9≤a1≤1.5, 0≤b1≤0.5, and 0.9≤a1+b1≤1.5; 0≤c1≤0.5; 3≤z1≤5; A1 comprises at least one of Na, K and Mg; M1 comprises at least one of Mn, Fe, Co and Ni; M2 comprises at least one of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La and Ce; X comprises at least one of S, Si, Cl, B, C and N, P; Q1 comprises at least one of O and F. The lithium-containing phosphate with olivine structure has excellent cycle stability, which is beneficial to improve the cycle performance of the battery cell.

[0156] Further, Li x1 A1 y1 M1 a1 M2 b1 P 1-c1 X c1 Q1 z1 The compound of formula (I) comprises at least one of lithium iron phosphate (LiFePO4), lithium manganese phosphate (LiMnPO4), lithium nickel phosphate (LiNiPO4) and lithium cobalt phosphate (LiCoPO4), and can also be a doped compound of these compounds.

[0157] The lithium-containing phosphate with olivine structure and its derivatives can contain a coating layer or not. In some embodiments of the present application, the positive active material comprises a core part and an ion-conducting layer. The core part comprises at least one of the lithium-containing phosphate with olivine structure and its derivatives, and the ion-conducting layer is coated on the surface of the core part, and the ion-conducting layer comprises at least one element of Fe, C, Ti, Zr, Hf, Ge and Sn.

[0158] The core part is coated with the ion-conducting layer on the surface, which can improve the electrical conductivity of the lithium-containing phosphate with olivine structure and its derivatives, reduce the powder resistivity of the material, and is beneficial to the migration rate of lithium ions, improve the rapid charging capacity of the battery, and reduce the heat generation of the battery cell.

[0159] Further, the ion-conducting layer comprises an ion conductor of formula (II) Li 3-b Fe 2-b M3 b (PO m ) n M3 comprises at least one element of Ti, Zr, Hf, Ge and Sn in +4 valence, 0≤b≤1, 3≤m≤5, and 2≤n≤4.

[0160] Exemplarily, the ion conductor is a material having a NASICON structure, such as one or more of lithium titanium iron phosphate Li2FeTi(PO4)3, lithium zirconium iron phosphate Li2FeZr(PO4)3, lithium tin iron phosphate Li2FeSn(PO4)3.

[0161] The ion conductor having a NASICON structure is a material having superfast ion conduction capability, having abundant three-dimensional lithium ion diffusion and transmission channels, and having high ion conduction efficiency and strong structural stability in the process of multiple lithium extraction and intercalation. Coating the ion conductor having a NASICON structure on the surface of the core can significantly improve the transmission rate of lithium ions in the positive electrode end in the process of multiple lithium extraction and intercalation, improve the ion conductivity of the positive electrode active material, and improve the rapid charging capability of the battery cell. In addition, it can also improve the specific capacity and the energy density of the corresponding battery cell.

[0162] In some embodiments, the ion-conducting layer further comprises carbon elements, further improving the material.

[0163] The carbon elements and the ion conductor can be arranged in layers, for example, the carbon elements as an independent carbon coating layer and the ion conductor as an independent ion conductor layer. The carbon coating layer can be coated on the surface of the core, and the ion conductor layer is located on the surface of the carbon coating layer, i.e., the ion conductor layer is located on the side of the carbon coating layer away from the core. Alternatively, the ion conductor layer can be coated on the surface of the core, and the carbon coating layer is located on the surface of the ion conductor layer, i.e., the carbon coating layer is located on the side of the ion conductor layer away from the core. Of course, the carbon elements and the ion conductor can also be arranged in the same layer.

[0164] Optionally, the carbon coating layer can be coated on the surface of the ion conductor layer by carbonization of an organic carbon source, such as glucose, polyethylene glycol, etc. The carbon coating layer can partially coat the ion conductor layer or completely coat the ion conductor layer. The arrangement of the carbon coating layer can significantly improve the electronic conductivity of the core, compensate for the poor electronic conduction performance of the core, and improve the energy density of the battery cell.

[0165] Specifically, the arrangement of the carbon coating layer provides the following advantages for the positive electrode active material of the application:

[0166] The carbon coating layer in the positive electrode active material of the application provides a suitable channel for the transmission of electrons, which can significantly improve the conduction rate of electrons in the process of multiple lithium extraction and intercalation, improve the electronic conductivity of the lithium-containing phosphate, and improve the charging capability and energy density of the corresponding battery cell.

[0167] The carbon coating layer of the positive electrode active material of the application has a loose and porous structure, which enables the electrolyte to fully and effectively contact the lithium-containing phosphate, thereby improving the transmission rate of lithium ions at the interface and improving the charging capability of the battery cell.

[0168] Coating the lithium-containing phosphate with a carbon coating layer can not only improve the conductivity of the lithium-containing phosphate, but also improve the structural stability of the positive electrode active material, effectively prevent the iron dissolution phenomenon of the positive electrode active material in the process of long-term storage and cycle use of the battery monomer, and thus ensure the cycle life of the battery monomer.

[0169] The positive electrode active material of the present application takes the lithium-containing phosphate as the base material, fully utilizes the advantages of low cost, high reliability and good cycle stability of the lithium-containing phosphate, and solves the disadvantages of poor electronic conductivity and ionic conductivity by using the ion conducting layer (ion conductor layer and carbon coating layer). The battery monomer prepared from the positive electrode active material of the present application has significantly improved energy density under the premise of excellent cycle performance.

[0170] In some embodiments, the mass content of carbon in the positive electrode active material is 1% to 2%, which may, for example, be 1%, 1.5%, or 2%. Controlling the mass content of carbon in the positive electrode active material in this range can further improve the conductivity of the positive electrode active material, and thus improve the fast charging performance of the battery. Understandably, the carbon element can come from, but is not limited to, the carbon coating layer. For example, the surface of the olivine structure lithium-containing phosphate and its derivatives is coated with a carbon coating layer.

[0171] In some embodiments, the powder resistivity of the positive electrode active material is ≤20 Ω·cm, which further improves the conductivity of the positive electrode active material, and thus improves the fast charging performance of the battery. For example, the powder resistivity of the positive electrode active material can be 20 Ω·cm, 15 Ω·cm, 10 Ω·cm, 8 Ω·cm, 5 Ω·cm, or the like, and optionally ≤11 Ω·cm.

[0172] In some embodiments, the volume average particle size of the positive electrode active material satisfies 1 μm≤Dv50≤2 μm and 0.4 μm≤Dv10≤0.7 μm, which further improves the fast charging and power performance of the battery. For example, the Dv50 particle size of the positive electrode active material can be 1 μm, 1.5 μm, or 2 μm. For example, the volume average particle size Dv10 of the positive electrode active material can be 0.4 μm, 0.5 μm, 0.6 μm, or 0.7 μm.

[0173] In this document, Dv50 and Dv10 have the meanings known in the art and can be tested by methods known in the art. For example, a laser particle size analyzer (such as Malvern Master Size 3000) is used for determination. Among them, Dv50 represents the particle size corresponding to the cumulative volume percentage of 50% of the particles according to the particle size volume distribution, from small particle size. Dv10 represents the particle size corresponding to the cumulative volume percentage of 10% of the particles according to the particle size volume distribution, from small particle size.

[0174] Particle size distribution can be obtained by the following method: Take a clean beaker, add an appropriate amount of the sample to be tested, and sonicate thoroughly to ensure complete dispersion. The testing instrument is a Malvern 2000 (USA). After the sample is poured into the injection tower, it circulates with the solution to the test optical path system. Under the illumination of the laser beam, the particle size distribution characteristics can be obtained by receiving and measuring the energy distribution of the scattered light (opause: 8%–12%). Particle size distribution diagrams are plotted based on the test data.

[0175] In some embodiments, the positive electrode film layer further includes a lithium replenishing agent. Further, the lithium replenishing agent includes at least one of ternary lithium replenishing materials, lithium phosphate, lithium hydrogen phosphate, lithium sulfate, lithium sulfite, lithium molybdate, lithium nickel oxide, lithium ferrite, lithium oxalate, lithium titanate, lithium tetraborate, lithium metasilicate, lithium metamanganese oxide, lithium tartrate, and lithium trilithium citrate.

[0176] Furthermore, ternary lithium supplementary materials include Li x2 A2 y2 Ni a2 Co b2 Mn c2 M4(1-a2-b2-c2)Q2 z2 Wherein, 0 < x2 ≤ 2.1, 0 ≤ y2 ≤ 2.1; 0 ≤ a2 ≤ 1, 0 ≤ b2 ≤ 1, 0 ≤ c2 ≤ 1, and 0.1 ≤ a2 + b2 + c2 ≤ 1; 1.8 ≤ z2 ≤ 3.5; A2 includes at least one of Na, K and Mg; M4 includes at least one of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La and Ce; Q2 includes at least one of O and F.

[0177] Furthermore, 0.9 ≤ x² + y² ≤ 2.1.

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

[0179] In some embodiments, the mass content of the positive electrode active material in the positive electrode film layer is 80-98%, for example, the mass content can be 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 96%, 98%. Further, the mass content of the positive electrode active material in the positive electrode film layer can be 90-98%.

[0180] In some embodiments, the positive electrode film layer further optionally comprises a binder. As a non-limiting example, the binder can comprise at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin. In some embodiments, the mass content of the binder is ≤5% based on the total mass of the positive electrode film layer.

[0181] In some embodiments, the positive electrode film layer further optionally comprises a conductive agent. As a non-limiting example, the conductive agent can comprise at least one of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass content of the conductive agent is ≤5% based on the total mass of the positive electrode film layer.

[0182] In some embodiments, the positive electrode tab can be prepared by dispersing the above-mentioned components for preparing the positive electrode tab, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent to form a positive electrode slurry; coating the positive electrode slurry on at least one side surface of the positive electrode current collector, and after processes such as drying, cold pressing, etc., the positive electrode tab can be obtained. The type of the solvent can be selected from, but not limited to, any of the foregoing embodiments, for example, N-methyl pyrrolidone (NMP). The surface of the positive electrode current collector coated with the positive electrode slurry can be on a single surface of the positive electrode current collector, or on both surfaces of the positive electrode current collector.

[0183] In some embodiments, the positive electrode tab further comprises a positive electrode conductive layer, which is arranged between the positive electrode current collector and the positive electrode film layer on at least one side. The positive electrode conductive layer comprises a conductive agent. The positive electrode conductive layer can also be coated on the surface of the positive electrode current collector by a corresponding slurry, and then the above-mentioned positive electrode slurry is coated, and dried to form the positive electrode tab. The positive electrode conductive layer can improve the adhesion between the positive electrode film layer and the positive electrode current collector and the overall conductivity of the positive electrode tab, which is conducive to improving the electron transmission rate.

[0184] Further, the conductive agent comprises at least one of super P, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0185] Further, the thickness of the positive electrode conductive layer is 0.5 μm to 2 μm, and as an example, can be 0.5 μm, 1 μm, 1.5 μm, 2 μm, or a range formed by any two of the above values as end values. When the thickness of the positive electrode conductive layer is in the above range, the conductive performance of the positive electrode tab can be further improved, and the energy density of the battery cell can be improved.

[0186] Further, the positive electrode conductive layer further includes a binder. Further, the binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, a polyacrylic acid, and a fluorine-containing acrylic ester-based resin. The binder in the positive electrode conductive layer can improve the adhesion between the positive electrode current collector and the positive electrode film layer, and improve the structural stability of the positive electrode tab.

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

[0188] Negative electrode tab

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

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

[0191] Understandably, the negative electrode film layer described above can contain one or more graphites having a powder compaction density of 1.5 g / cm 3 ~ 1.85 g / cm 3 ​

[0192] As mentioned above, the negative active material includes graphite, and the powder compaction density of the negative active material under 20000 N is 1.5 g / cm 3 ~ 1.85 g / cm 3 , for example, but not limited to 1.5 g / cm 3 , 1.55 g / cm 3 , 1.6 g / cm 3 , 1.65 g / cm 3 , 1.7 g / cm 3 , 1.72 g / cm 3 , 1.75 g / cm 3 , 1.8 g / cm 3 , 1.82 g / cm 3 , 1.85 g / cm 3 , or a range formed by any two of the above values as end values. The graphite with such a high powder compaction density allows the secondary battery to have a high energy density. Alternatively, the powder compaction density of the graphite under 20000 N is 1.6 g / cm 3 ~ 1.85 g / cm 3 . Alternatively, the powder compaction density of the graphite under 20000 N is 1.55 g / cm 3 ~ 1.75 g / cm 3 .

[0193] In some embodiments, the compaction density of the negative electrode sheet of the above-mentioned secondary battery under 100% SOC is 1.15 g / cm 3 ~ 1.46 g / cm 3 , optionally 1.25 g / cm 3 ~ 1.40 g / cm 3 . Thus, the above-mentioned negative electrode sheet still has a high compaction density after full charging. For example, the compaction density of the negative electrode sheet of the secondary battery under 100% SOC is 1.15 g / cm 3 , 1.18 g / cm 3 , 1.20 g / cm 3 , 1.22 g / cm 3 , 1.25 g / cm 3 , 1.28 g / cm 3 , 1.3 g / cm 3 , 1.32 g / cm 3 , 1.35 g / cm 3 , 1.36 g / cm 3 , 1.38 g / cm 3 , 1.4 g / cm 3 , 1.42 g / cm 3 , 1.45 g / cm3 1.46 g / cm3 3 or a range consisting of any two of the aforementioned values. The higher the tap density of the negative electrode tab, the lower the rebound, indicating that the battery has less swelling force. When the tap density of the negative electrode film layer is in the above range, not only does it have a high energy density, but it also helps to improve the cycle performance of the battery.

[0194] In some embodiments of the present application, the tap density of the negative electrode tab of the secondary battery at 100% SOC is the meaning known in the art, that is, the negative electrode tab is disassembled from the battery monomer charged to 100% state of charge (SOC), and the tap density of the negative electrode film layer is measured.

[0195] In some embodiments of the present application, the 100% SOC state of the secondary battery is defined as follows:

[0196] The battery monomer is charged to the upper limit voltage of the battery at a constant current charge rate of 0.33C, and then charged at a constant voltage of 0.05C, corresponding to the 100% SOC state of the battery monomer. Correspondingly, the battery monomer is discharged to the cut-off voltage at a constant current discharge rate of 0.33C, corresponding to the 0% SOC state of the battery monomer.

[0197] Because the types of positive active materials of the battery are different, the cut-off voltage of the full charge may also be different. For example, the upper limit voltage of the battery charge can be 3.65V, 3.8V; the cut-off voltage of the battery discharge can be 2.5V, 2.0V. Taking lithium iron phosphate as the positive active material in the positive electrode tab as an example, the above-mentioned secondary battery is charged at a charge rate of 0.33C to 3.65V, and then charged at a constant voltage of 0.05C, corresponding to the 100% SOC state of the battery monomer. At this time, the tap density of the negative electrode tab is 1.15 g / cm3 3 ~ 1.46 g / cm3 3 .

[0198] In some embodiments, the tap density of the above-mentioned negative electrode tab after cold pressing is 1.5 g / cm3 3 ~ 1.8 g / cm3 3 , optionally 1.6 g / cm3 3 ~ 1.75 g / cm3 3 . The tap density of the negative electrode tab after cold pressing refers to the tap density of the negative electrode tab after cold pressing and forming before being assembled into a battery.

[0199] The lower the full charge pressure density of the negative electrode sheet, the greater the rebound thickness or the lower the initial pressure density, the stronger the graphite activity, and thus more electrolyte needs to be consumed, and more additives need to be added in the electrolyte to strengthen the interface film stability of the negative electrode sheet and improve the cycle performance of the battery. Moreover, the higher the full charge pressure density of the negative electrode sheet, the higher the energy density of the battery, the smaller the space reserved for the electrolyte, and the lower the electrolyte injection amount, and thus the higher the concentration of the first additive in the electrolyte needs to be in order to improve the fast charging performance of the battery. Therefore, there is a matching relationship between the compaction density of the negative electrode sheet and the mass content of the first additive in the electrolyte.

[0200] In some embodiments, the compaction density of the negative electrode sheet of the secondary battery in the 100% SOC state is ≥ 1.25 g / cm 3 and < 1.35 g / cm 3 .

[0201] Further, when the compaction density of the negative electrode sheet of the secondary battery in the 100% SOC state is ≥ 1.25 g / cm 3 and < 1.35 g / cm 3 , the mass content of the first additive in the electrolyte is 1.5% to 6%.

[0202] The second additive in the electrolyte has a low film-forming resistance, which can improve the kinetic performance of the battery and thus improve the fast charging performance of the battery, but the content thereof should not be too high in order to further improve the cycle performance of the battery. The higher the energy density of the battery, the smaller the space reserved for the electrolyte, and the lower the electrolyte injection amount, and thus the higher the concentration of the second additive in the electrolyte needs to be in order to improve the fast charging performance of the battery. Therefore, there is a matching relationship between the compaction density of the negative electrode sheet and the mass content of the second additive in the electrolyte.

[0203] Further, when the compaction density of the negative electrode sheet of the secondary battery in the 100% SOC state is ≥ 1.25 g / cm 3 and < 1.35 g / cm 3 , the mass content of the second additive in the electrolyte is 0.5% to 3%.

[0204] Further, when the compaction density of the negative electrode sheet of the secondary battery in the 100% SOC state is ≥ 1.25 g / cm 3 and < 1.35 g / cm 3 , the mass content of the first solvent in the electrolyte is 22.5% to 34%, and optionally 25.5% to 34%.

[0205] Further, when the compaction density of the negative electrode sheet of the secondary battery in the 100% SOC state is ≥ 1.25 g / cm 3 and < 1.35 g / cm 3 , the mass of the electrolyte under the rated capacity of 1 Ah of the unit battery is 2.5 g to 3.0 g.

[0206] In some embodiments, the compaction density of the negative electrode sheet of the secondary battery in the 100% SOC state is 1.35 g / cm 3 to 1.40 g / cm 3 .

[0207] Further, when the compaction density of the negative electrode sheet of the secondary battery in the 100% SOC state is 1.35 g / cm 3 to 1.40 g / cm 3 , the mass content of the first additive in the electrolyte is 2.5% to 7%. In this way, when the compaction density of the negative electrode sheet of the secondary battery in the 100% SOC state is in the above range, the mass content of the first additive in the electrolyte is 2.5% to 7%, the battery can simultaneously give better consideration to higher energy density and fast charging performance.

[0208] Further, when the compaction density of the negative electrode sheet of the secondary battery in the 100% SOC state is 1.35 g / cm 3 to 1.40 g / cm 3 , the mass content of the second additive in the electrolyte is 0.7% to 3.5%, optionally 1.5% to 3.5%. Further, when the compaction density of the negative electrode sheet of the secondary battery in the 100% SOC state is 1.35 g / cm 3 to 1.40 g / cm 3 , the mass content of the first solvent in the electrolyte is 21.25% to 34%.

[0209] Further, when the compaction density of the negative electrode sheet of the secondary battery in the 100% SOC state is 1.35 g / cm 3 to 1.40 g / cm 3 , the mass of the electrolyte under the rated capacity of 1 Ah of the unit battery is 2.2 g to 2.8 g.

[0210] In some embodiments, the volume energy density of the secondary battery is 400-450 Wh / L, the mass content of the carboxylic acid ester in the electrolyte is 25.5-59.5%, and the total mass content of the first additive and the second additive in the electrolyte is 2-7%. When the volume energy density of the secondary battery is in this higher energy density range, adding the carboxylic acid ester to the organic solvent of the electrolyte can improve the fast-charging performance of the secondary battery, but the content of the carboxylic acid ester should not be too high, otherwise the problem of gas generation in the graphite-based negative electrode sheet will lead to deterioration of the cycle performance. Therefore, the amount of the first additive and the second additive is further increased to improve the cycle life of the battery. Further, the compaction density of the negative electrode sheet after cold pressing is 1.55-1.65 g / cm 3 . 3

[0211] In some embodiments, the volume energy density of the secondary battery is >450 Wh / L and ≤480 Wh / L, the mass content of the carboxylic acid ester in the electrolyte is 25.5-63.75%, and the total mass content of the first additive and the second additive in the electrolyte is 3.5-8%. As the volume energy density of the secondary battery increases, the content of the carboxylic acid ester and the content of the first additive and the second additive in the electrolyte need to be increased accordingly to ensure good cycle life at this higher energy density.

[0212] Further, the compaction density of the negative electrode sheet after cold pressing is 1.6-1.7 g / cm 3 . 3

[0213] In some embodiments, the charging time of the secondary battery from 10% SOC to 80% SOC at 30°C is 6-15 min, the mass content of the carboxylic acid ester in the electrolyte is 17-63.75%, and the total mass content of the first additive and the second additive in the electrolyte is 2-8%, optionally 5-7%. In this way, based on the use of high-pressure dense graphite to provide higher energy density, this battery is also a fast-charging type battery, and the above content of the carboxylic acid ester is added to the electrolyte, and the amount of the first additive and the second additive is increased, so that the secondary battery has higher energy density, fast-charging performance, and cycle performance. Further, in the electrolyte, the mass content of the first additive is 1.5-6.5%, optionally 3.5-5.5%, and the mass content of the second additive is 0.5-6.5%, optionally 1.5-3.5%.

[0214] ​​In some embodiments, the charging of the secondary battery from 10% SOC to 80% SOC includes a plurality of charging steps, and the maximum state of charge of any charging step in the plurality of charging steps is less than or equal to 5% SOC, e.g., 1% SOC, 1.5% SOC, 2% SOC, 2.5% SOC, 3% SOC, 3.5% SOC, 4% SOC, 4.5% SOC, 5% SOC, or a range defined by any two of the foregoing values.

[0215] The charging of the secondary battery from 10% SOC to 40% SOC includes a plurality of charging steps, and for any charging step, the charging can be at any rate between 5C and 10C. The charging rate for each charging step can be any value in the range of 5C, 5.5C, 6C, 6.5C, 7C, 7.5C, 8C, 8.5C, 9C, 9.5C, 10C, or a range defined by any two of the foregoing values.

[0216] The charging of the secondary battery from 40% SOC to 80% SOC also includes a plurality of charging steps, and the charging rate for any charging step is less than the charging rate for any charging step from 10% SOC to 40% SOC. The charging rate for the step charging to 80% SOC can be any value in the range of 2.5C to 5C, e.g., 2.7C.

[0217] By way of example, the charging steps of the secondary battery from 10% SOC to 80% SOC can be performed as follows:

[0218] Charge from 10% SOC to 15% SOC at 5.0C constant current;

[0219] Charge from 15% SOC to 20% SOC at 5.0C constant current;

[0220] Charge from 20% SOC to 25% SOC at 5.0C constant current;

[0221] Charge from 25% SOC to 30% SOC at 5.0C constant current;

[0222] Charge from 30% SOC to 35% SOC at 5.0C constant current;

[0223] Charge from 35% SOC to 40% SOC at 5.0C constant current;

[0224] Charge from 40% SOC to 45% SOC at 4.6C constant current;

[0225] Charge from 45% SOC to 50% SOC at 4.3C constant current;

[0226] charging from 50% SOC to 55% SOC at 4.0 C;

[0227] charging from 55% SOC to 60% SOC at 3.7 C;

[0228] charging from 60% SOC to 65% SOC at 3.4 C;

[0229] charging from 65% SOC to 70% SOC at 3.1 C;

[0230] charging from 70% SOC to 75% SOC at 2.9 C;

[0231] charging from 75% SOC to 80% SOC at 2.7 C.

[0232] Exemplarily, the charging time of the secondary battery from 10% SOC to 80% SOC is 6 min, 6.5 min, 7 min, 7.5 min, 8 min, 8.5 min, 9 min, 9.5 min, 10 min, 10.5 min, 11 min, 11.5 min, 12 min, 12.5 min, 13 min, 14 min, 14.5 min, 15 min, or a range formed by any two of the above values.

[0233] In some embodiments, the negative electrode tab further comprises a negative electrode conductive layer, which is disposed between the negative electrode current collector and the negative electrode film layer on at least one side. The negative electrode conductive layer comprises a conductive agent. The negative electrode conductive layer can be formed by first coating a corresponding slurry on the surface of the negative electrode current collector, then coating the above-mentioned negative electrode slurry, and drying. Further, the conductive agent in the negative electrode conductive layer comprises at least one of super-conductive carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The negative electrode conductive layer can improve the adhesion between the negative electrode film layer and the negative electrode current collector and the overall conductivity of the negative electrode tab, which is conducive to improving the electron transmission rate.

[0234] Optionally, the thickness of the negative electrode conductive layer is 0.5 μm to 2 μm, for example, 0.5 μm, 1 μm, 1.5 μm, or 2 μm.

[0235] In some embodiments, the negative electrode conductive layer comprises a binder, which comprises at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin, water-based acrylic resin, polyvinyl alcohol, sodium alginate, and carboxymethyl chitosan.

[0236] Optionally, in the negative electrode conductive layer, the mass content of the conductive agent is 20% to 40%, and the mass content of the binder is 60% to 80%.

[0237] Further, the graphite includes at least one of artificial graphite and natural graphite. Further, the graphite adopts artificial graphite, and the artificial graphite has fewer surface active sites and a lower consumption rate of the first solvent and the first additive in the electrolyte, thereby meeting the demand for long battery life. Further, the graphite has a discharge specific capacity of ≤ 358 mAh / g. The graphite has a specific capacity within the range, and the activity of the graphite is suitable, which is conducive to reducing the consumption rate of the electrolyte and thereby improving the cycle performance of the battery.

[0238] In some embodiments, the mass content of the negative electrode active material in the negative electrode film layer is 94% to 98%, and for example, the mass content can be 94%, 96%, or 98%.

[0239] In some embodiments, the negative electrode film layer optionally further includes a binder. The binder can include at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0240] In some embodiments, the negative electrode film layer optionally further includes a conductive agent. The conductive agent can include at least one of super-conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0241] In some embodiments, the negative electrode film layer optionally further includes other auxiliary agents, such as a thickening agent (e.g., sodium carboxymethyl cellulose (CMC-Na)) and the like.

[0242] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder, and any other components, in a solvent (a non-limiting example of the solvent is deionized water) to form a negative electrode slurry; coating the negative electrode slurry on at least one side surface of the negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode sheet can be obtained. The surface of the negative electrode current collector coated with the negative electrode slurry can be a single surface of the negative electrode current collector, or both surfaces of the negative electrode current collector.

[0243] In some embodiments, the negative electrode film layer includes at least one negative electrode active layer, and the at least one negative electrode active layer includes the graphite.

[0244] In a specific example, the negative electrode film layer includes one negative electrode active layer, and the negative electrode active layer contains the graphite, and the Dv50 particle size of the graphite is 8.2 μm to 13.5 μm.

[0245] In another specific example, the negative electrode film layer includes a first negative electrode active layer and a second negative electrode active layer stacked in sequence on the same side of the negative electrode current collector, the graphite includes at least one of artificial graphite and natural graphite, the graphite in the first negative electrode active layer includes at least one of the artificial graphite and the natural graphite, and the graphite in the second negative electrode active layer includes the artificial graphite. Artificial graphite has fewer surface active sites and a lower consumption rate of the first solvent and the first additive in the electrolyte.

[0246] Further, the Dv50 particle size of the graphite in the first negative electrode active layer is greater than the Dv50 particle size of the graphite in the second negative electrode active layer. In this way, the distance between the negative electrode active material particles in the upper second negative electrode active layer is reduced, the contact area between the negative electrode active material particles is increased, the conductive channels and bridges are increased, the active area capable of participating in the reaction is increased, thereby significantly improving the specific capacity of the battery, and the larger pores in the lower first negative electrode active layer have better kinetic performance, which is beneficial to improve the fast charging performance.

[0247] Further, the Dv50 particle size of the graphite in the first negative electrode active layer is greater than the Dv50 particle size of the graphite in the second negative electrode active layer.

[0248] It can be understood that the first negative electrode active layer and the second negative electrode active layer can be obtained by coating two slurries in sequence, and then performing processes such as drying and cold pressing.

[0249] Further, the Dv50 particle size of the graphite in the first negative electrode active layer is 9.5 μm to 18.5 μm, and can be 9.5 μm to 14.8 μm. As an example, the Dv50 particle size of the graphite in the first negative electrode active layer can be 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.

[0250] Further, the Dv50 particle size of the graphite in the second negative electrode active layer is 7.8 μm to 14.3 μm, and can be 7.8 μm to 12.8 μm. As an example, the Dv50 particle size of the graphite in the second negative electrode active layer can be 7.8 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 12.8 μm, 13 μm, 14 μm, 14.3 μm.

[0251] Optionally, the mass ratio of the graphite in the first negative electrode active layer and the second negative electrode active layer is 3:7 to 7:3, and can be 4:6 to 6:4. As an example, the mass ratio can be 3:7, 4:6, 5:5, 6:4, 7:3, or a range composed of any two of the above values.

[0252] Further, the mass content of graphite in the first negative active layer is 30% to 70% in the total amount of graphite in the first negative active layer and the second negative active layer, for example, 30%, 35%, 40%, 45%, 48%, 50%, 55%, 60%, 65%, 70%, or a range formed by any two of the above values.

[0253] Further, the thickness of the second negative active layer accounts for 30% to 70% in the total thickness of the first negative active layer and the second negative active layer, for example, 30%, 40%, 50%, 60%, 70%, or a range formed by any two of the above values as the end value, and optionally 40% to 60%.

[0254] In some embodiments, the artificial graphite includes graphite bulk particles and a coating layer, the graphite bulk particles include secondary particles aggregated by a plurality of primary particles, and the coating layer is coated on the surface of the bulk particles and includes amorphous carbon.

[0255] Further, the mass content of amorphous carbon is 2% to 5% based on the total mass of the artificial graphite, for example, 2%, 3%, 4%, 5%, or a range formed by any two of the above values as the end value.

[0256] Further, the powder resistivity of the artificial graphite is ≤0.04 Ω·cm.

[0257] In some embodiments, the charge specific capacity of graphite at a rate of 0.1C in a button cell is ≥350 mAh / g, and optionally 350 mAh / g to 440 mAh / g.

[0258] In some embodiments, the negative active material includes not only the above-mentioned graphite but also a silicon-based material. Further, the silicon-based material can include at least one of a silicon oxide compound, a silicon-carbon composite, elemental silicon, a silicon-nitrogen composite, and a silicon alloy. Further, the mass content of silicon in the silicon-based material in the negative active material is 0.3% to 10%, and optionally 1% to 6%.

[0259] Separator film

[0260] In some embodiments, the secondary battery further includes a separator film. The separator film is arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent short circuit of the positive and negative electrodes, and at the same time to allow ions to pass through.

[0261] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator film can be made into an electrode assembly through a rolling process or a stacking process.

[0262] The type of the separation film is not particularly limited in the present application, and any known porous structure separation film with good chemical stability and mechanical stability can be selected. The separation film can be a single-layer film or a multi-layer composite film, and is not particularly limited. When the separation film is a multi-layer composite film, the materials of the layers can be the same or different, and are not particularly limited. In some embodiments, the thickness of the separation film is 6-40 μm, and can be selected to be 12-20 μm.

[0263] In some embodiments, the separation film comprises a porous base film and a functional layer arranged on at least one side of the porous base film.

[0264] Further, the material of the porous base film can comprise at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.

[0265] Further, the thickness of the porous base film is ≤12 μm, and can be selected to be ≤9 μm, and can be selected to be 6-9 μm. For example, the thickness of the base film is 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm or a range composed of any two of the above values.

[0266] When the porosity of the separation film in the embodiments of the present application is in the above range, the migration ability of lithium ions in the separation film can be improved, and the internal resistance of the battery cell can be further reduced, thereby reducing the heat generation.

[0267] In some embodiments of the present application, the porosity refers to the percentage of the volume of the pores in the separation film to the total volume of the separation film. The porosity can be tested according to the standard GB / T 36363-2018 “Polyolefin Separation Film for Battery Cell”. It should be noted that the actual testing process can be slightly different from the standard in order to obtain more accurate test values, according to the differences in testing instruments, testing errors, and in order to eliminate the influence on the test of the porosity as much as possible.

[0268] Further, the porosity of the porous base film is 20-70%, and can be selected to be 35-60%. For example, the porosity of the base film is 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70% or a range composed of any two of the above values.

[0269] When the thickness of the porous base film is in the above range, the migration path of lithium ions in the base film is shorter, and the internal resistance of the battery cell can be further reduced, thereby reducing the heat generation.

[0270] In some embodiments of the present application, the separation film can be a base film; optionally, the separation film further comprises a functional layer disposed on at least one side of the base film, and the functional layer can comprise inorganic particles to improve the heat resistance of the separation film. Optionally, the functional layer is disposed on both sides of the base film.

[0271] In some embodiments, the functional layer comprises a first functional layer and a second functional layer, the first functional layer is disposed on one side of the base film, and the first functional layer comprises first inorganic particles; the second functional layer is disposed on the other side of the base film, and the second functional layer comprises composite particles, the composite particles comprise second inorganic particles and non-fluoropolymer particles, and the second inorganic particles are attached to the surface of the non-fluoropolymer particles and / or dispersed in the interior of the non-fluoropolymer particles.

[0272] The first functional layer and the second functional layer have good heat resistance, which can improve the heat resistance of the separation film.

[0273] Optionally, the first functional layer can comprise a binder, and the binder can comprise at least one of a fluorine-containing binder or a polyacrylic acid binder, such as polyvinylidene fluoride.

[0274] 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 above-mentioned first inorganic particles can improve the heat resistance of the first functional layer.

[0275] In some embodiments of the present application, the thickness of the base film has the meaning known in the art, and can be detected by using the meaning and equipment known in the art. For example, a newly prepared separation film can be taken as a sample, or a battery cell that has been discharged (discharged to the lower limit cutoff voltage so that the charged state of the battery cell is about 0% SOC) can be disassembled in reverse, and the separation film can be obtained from the battery cell and dried as a sample. The separation film is cut by an ion beam cutter to form a cross section; then, the thickness of the cross section of the separation film and each layer thereof is measured by using a scanning electron microscope.

[0276] The non-fluoropolymer particles in the second functional layer refer to polymers that are non-fluorinated polymers, for example, the non-fluoropolymer particles comprise acrylate copolymer particles, and the acrylate copolymer can comprise acrylate-acrylonitrile-acrylamide-acrylate copolymer. The acrylate copolymer has excellent bonding performance, and has high bonding stability with the base film. The molar ratio of each monomer in the copolymer can be any ratio, for example, the molar ratio is 35%:30%:15%:20%, or 40%:20%:10%:30%, or 45%:15%:20%:20%, etc.

[0277] The second inorganic particles in the composite particles make it difficult for the non-fluoropolymer particles to adhere to each other due to high-temperature treatment in the granulation process, so that the composite particles have pores, which is beneficial to the transmission of lithium ions and improves the ion conductivity of the separator film; and the second inorganic particles can also improve the compression modulus of the composite particles, so that the composite particles are less likely to deform during charging and discharging, making the structure of the separator film more stable, which can improve the kinetic performance of the battery monomer and improve the rapid charging performance.

[0278] Optionally, compared with the first functional layer, the second functional layer is arranged close to the negative electrode tab, and since the composite particles are less likely to deform, the separator film is less likely to cause side effects such as extrusion to the negative electrode tab, so that the kinetic performance of the negative electrode tab is stable. Correspondingly, the first functional layer is arranged close to the positive electrode tab.

[0279] Optionally, the second inorganic particles include one or more of silicon oxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide; and optionally, the second inorganic particles include silicon oxide. The above-mentioned second inorganic particles can improve the heat resistance of the second functional layer, and can cooperate with the non-fluoropolymer to form composite particles, further improving the cycle stability and kinetic performance of the separator film, and improving the cycle performance and rapid charging performance of the battery monomer.

[0280] The average particle size of the second inorganic particles is 5 nm to 100 nm, optionally 10 nm to 100 nm, and optionally 5 nm to 20 nm. Illustratively, the average particle size of the second inorganic particles is 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, or a range formed by any two of the above values. When the average particle size of the second inorganic particles is in the above range, it is beneficial to improve the heat resistance and compression modulus of the composite particles.

[0281] In some embodiments of the present application, the average particle size of the second inorganic particles has the meaning known in the art and can be detected by using devices and methods known in the art. For example, after obtaining the separator film, the separator film is dried as a sample, and an ion beam cutter is used to cut the separator film to form a cross section; then, a scanning electron microscope is used to measure the particle size of the second inorganic particles in the separator film, and the particle sizes of a plurality of, for example, 50, second inorganic particles are measured to calculate the average value as the average particle size of the second inorganic particles.

[0282] In some embodiments, the ion conductivity of the separator film is 0.3 mS / cm to 0.6 mS / cm. Exemplarily, the ion conductivity of the separator film is 0.3 mS / cm, 0.35 mS / cm, 0.4 mS / cm, 0.45 mS / cm, 0.5 mS / cm, 0.55 mS / cm, 0.6 mS / cm, or a range between any two of the above values.

[0283] When the ion conductivity of the separator film is within the above range, the migration ability of lithium ions of the separator film can be further improved, and the rapid charging performance of the battery cell can be improved.

[0284] In some embodiments of the present application, the ion conductivity of the separator film is within the meaning known in the art, and can be detected by using the devices and methods known in the art, for example,

[0285] Preparation of 2025 type button cell for testing: in a vacuum glove box, lithium sheet was put into the negative electrode shell, 150 μL of electrolyte was added, the electrolyte was 1M LiPF6 solution in EC / EMC / DEC = 3 / 5 / 2 (mass ratio), and then the separator film (area of 3.14 cm 2 , thickness of 12 μm) was put into the lithium sheet to make it close to the lithium sheet, 25 μL of electrolyte was added, and finally the positive electrode sheet (the positive electrode sheet can be the positive electrode sheet in Example 1) was placed on it, and then it was packaged. The assembled button cell was taken out of the vacuum glove box and placed for 24 h for the next step of testing.

[0286] Test: in an electrochemical workstation, the test was carried out in the frequency range of 10 -1 ~ 10 6 Hz, the resistance Rb of the separator film was obtained, and the ion conductivity σ (unit: mS / cm) was calculated by the following formula, σ = L / (R b × S)

[0287] Wherein: R b is the equivalent resistance, L and S are the thickness and area of the separator film to be tested, respectively.

[0288] The secondary battery comprises at least one battery cell. The secondary battery can comprise one or more battery cells.

[0289] In the present application, unless otherwise specified, the "battery cell" refers to a basic unit capable of realizing the mutual conversion between chemical energy and electrical energy. Further, generally, at least comprises a positive electrode sheet, a negative electrode sheet and an electrolyte. In the process of charging and discharging of the battery, active ions are embedded and extracted between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting active ions between the positive electrode sheet and the negative electrode sheet.

[0290] The shape of the battery cell is not particularly limited in the present application, and can be cylindrical, square, or any other shape. For example, the secondary battery shown in FIG. 1 is one battery cell, which is an example of a square-structured battery cell 5.

[0291] In some embodiments, the battery cell 5 can include an outer package. The outer package can be used to enclose the electrode assembly and the electrolyte described above. In some embodiments, the outer package of the battery cell 5 can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, or the like. The outer package of the battery cell 5 can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, and further, non-limiting examples of the plastic can include at least one of polypropylene, polybutylene terephthalate, and polybutylene succinate, or the like.

[0292] In some embodiments, referring to FIG. 2, the outer package can include a housing 51 and a cover plate 53. The housing 51 can include a bottom plate and a side plate connected to the bottom plate, which enclose a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be provided on the opening to close the receiving cavity. The positive electrode tab, the negative electrode tab, and the separator can form an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is enclosed in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, which can be selected by a person skilled in the art according to actual needs.

[0293] The secondary battery of the present application refers to a battery cell.

[0294] In some embodiments, the battery device includes a secondary battery, and the battery device can be a battery module, a battery pack, or an energy storage battery.

[0295] The battery module includes at least one battery cell. The number of battery cells contained in the battery module can be one or more, which can be selected by a person skilled in the art according to the application and capacity of the battery module.

[0296] The battery module shown in FIG. 3 is an example of a battery module 4. Referring to FIG. 3, in the battery module 4, a plurality of battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other manner. Further, the plurality of battery cells 5 can be fixed by fasteners.

[0297] Optionally, the battery module 4 can also include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.

[0298] In some embodiments, the battery module described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and a person skilled in the art can select a suitable number according to the application and capacity of the battery pack.

[0299] FIGS. 4 and 5 are battery packs shown as an example of a battery pack 1. Referring to FIGS. 4 and 5, a battery case and a plurality of battery modules 4 disposed in the battery case can be included in the battery pack 1. The battery case includes an upper case 2 and a lower case 3, and the upper case 2 can be disposed on the lower case 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery case in any manner.

[0300] In addition, an embodiment of the present application also provides a power consumption device, which includes at least one of the secondary battery provided by the present application and the battery device provided by the present application. The power consumption device can include a mobile device, an electric vehicle, an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto. Among them, the mobile device can be a mobile phone, a notebook computer, etc.; the electric vehicle can be a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc., but is not limited thereto.

[0301] As the power consumption device, the secondary battery can be selected according to the use requirement thereof.

[0302] FIG. 6 is a power consumption device 6 as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirement of high power and high energy density of the secondary battery for the power consumption device, a battery pack or a battery module can be used.

[0303] As another example of the device, it can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thin and light, and a battery monomer 5 can be used as a power supply.

[0304] In order to make the technical problems, technical solutions and beneficial effects solved by the present application clearer, the present application will be further described in detail in combination with embodiments and drawings. Obviously, the described embodiments are only some of the embodiments of the present application, not all the embodiments. The description of the at least one exemplary embodiment is actually only illustrative, but not as any limitation on the present application and its application. Based on the embodiments in the present application, all other embodiments obtained by a person skilled in the art without creative labor fall within the scope of protection of the present application.

[0305] Unless otherwise specified in the examples, the techniques or conditions described in the literature or according to the product specification were used. Unless otherwise specified, the reagents or instruments used were conventional products that can be obtained commercially.

[0306] Example 1

[0307] (1) Preparation of the positive electrode sheet:

[0308] The performance parameters of the positive electrode active material lithium iron phosphate LiFePO4: the powder compaction density under 30000N was 2.53 g / cm 3 .

[0309] The positive electrode active material lithium iron phosphate LiFePO4, the binder polyvinylidene fluoride, and the conductive agent acetylene black were mixed in a mass ratio of 97:2:1, and then the solvent N-methyl pyrrolidone (NMP) was added and stirred uniformly to form a positive electrode slurry; the positive electrode slurry was uniformly coated on the positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode sheet was obtained.

[0310] Among them, the coating weight of the positive electrode sheet was 300 mg / 1540.25 mm 2 ; the compaction density of the positive electrode sheet under 0.33C charging rate charging to 100% SOC was 2.63 g / cm 3 .

[0311] (2) Preparation of the negative electrode sheet:

[0312] The preparation method of the negative electrode sheet with a double-layer negative electrode structure is as follows:

[0313] The performance parameters of the first negative electrode active material graphite: the powder compaction density under 20000N was 1.67 g / cm 3 , the Dv50 particle size of the graphite was 12.8 μm, and the mass content of the amorphous carbon was 2.5%.

[0314] The performance parameters of the second negative electrode active material graphite: the powder compaction density under 20000N was 1.6 g / cm 3 , the Dv50 particle size of the graphite was 9.6 μm, and the mass content of the amorphous carbon was 3.4%.

[0315] The first negative electrode active material graphite, the conductive agent acetylene black, the binder styrene-butadiene rubber, and the thickening agent sodium carboxymethyl cellulose were mixed in a mass ratio of 96:0.5:2.5:1, and then the solvent deionized water was added and stirred uniformly to form a negative electrode slurry 1; the second negative electrode active material graphite, the conductive agent acetylene black, the binder styrene-butadiene rubber, and the thickening agent sodium carboxymethyl cellulose were mixed in a mass ratio of 96:0.5:2.5:1, and then the solvent deionized water was added and stirred uniformly to form a negative electrode slurry 2.

[0316] The negative electrode slurry 1 is uniformly coated on the negative electrode current collector copper foil and dried; the negative electrode slurry 2 is coated on the surface of the dried negative electrode slurry 1, and after drying and cold pressing, a negative electrode sheet is obtained. The negative electrode sheet comprises a current collector and a first negative electrode active layer and a second negative electrode active layer stacked in sequence on the negative electrode current collector, and the mass ratio of graphite in the first negative electrode active layer and the second negative electrode active layer is 50%:50%.

[0317] The coating weight of the negative electrode sheet is 138 mg / 1540.25 mm 2 ; the compaction density of the negative electrode sheet at 100% SOC under the charging rate of 0.33C is 1.26 g / cm 3 .

[0318] (3) Preparation of electrolyte:

[0319] In an argon atmosphere glove box with water content <10 ppm, the first solvent ethylene carbonate (EC), the second solvent ethyl acetate (EA) and dimethyl carbonate (DMC) are uniformly mixed in a certain mass ratio to obtain an organic solvent. The mass content of ethylene carbonate (EC), ethyl acetate (EA) and dimethyl carbonate (DMC) in the electrolyte is shown in Table 1. A certain mass of lithium hexafluorophosphate (LiPF6) is slowly added as a lithium salt, and stirred until it is completely dissolved. The mass content of LiPF6 in the electrolyte is 15%. After returning to room temperature, 5% of the first additive vinylene carbonate (VC) and 2% of the second additive fluoroethylene carbonate (FEC) based on the total mass of the electrolyte are added, and the mixture is uniformly mixed to obtain the electrolyte. The mass b of the electrolyte under the rated capacity of 1 Ah per unit battery of the secondary battery is shown in Table 1.

[0320] (4) Preparation of separator:

[0321] The separator comprises a base film, which is a 7 μm polyethylene film layer with a porosity of 42%.

[0322] Preparation of secondary battery:

[0323] The positive electrode sheet, the separator, and the negative electrode sheet are stacked and wound in order to obtain a wound electrode assembly; the electrode assembly is added to an outer packaging square aluminum shell, dried, and then injected with electrolyte, and after packaging, standing, formation, aging, secondary packaging, and capacity processes, a secondary battery is obtained.

[0324] The preparation methods of Examples 2-4 are similar to those of Example 1, except that the mass content of ethylene carbonate (EC) in the electrolyte is adjusted (the mass content of EA is unchanged, and the mass content of DMC is changed accordingly), as shown in Table 1.

[0325] The preparation method of Examples 5-7 is similar to that of Example 3, except that the mass content of the first additive VC in the electrolyte is adjusted, and at least one of the mass contents of the first solvent and the second solvent is adjusted accordingly, as shown in Table 1.

[0326] The preparation method of Examples 8-10 is similar to that of Example 3, except that the mass content of the second additive FEC in the electrolyte is adjusted, and at least one of the contents of the first solvent and the second solvent is adjusted accordingly, as shown in Table 1.

[0327] The preparation method of Example 11 is similar to that of Example 3, except that the mass contents of the first additive VC and the second additive FEC in the electrolyte are adjusted, and at least one of the contents of the first solvent and the second solvent is adjusted accordingly, as shown in Table 1.

[0328] The preparation method of Example 12 is similar to that of Example 3, except that the type of the second solvent is adjusted, and the mass content in the electrolyte is adjusted (the mass content of EC is unchanged, and the mass content of DMC is changed accordingly), as shown in Table 1.

[0329] The preparation method of Example 13 is similar to that of Example 3, except that the type of the second graphite of the negative electrode active material is adjusted, and the Dv50 particle size is different, as shown in Table 1; the powder compaction density of the second graphite under 20000N is 1.55g / cm 3 .

[0330] The preparation method of Example 14 is similar to that of Example 3, except that the type of the first graphite of the negative electrode active material is adjusted, and the Dv50 particle size is different, as shown in Table 1; the powder compaction density of the first graphite under 20000N is 1.72g / cm 3 .

[0331] The preparation method of Examples 15-16 is similar to that of Example 3, except that the injection coefficient of the electrolyte is adjusted, so the mass of the electrolyte b under the rated capacity of 1 Ah per cell of the secondary battery is different, as shown in Table 1.

[0332] In addition, the performance parameters of the positive electrode active material lithium iron phosphate LiFePO4 in Example 15 are: the powder compaction density under 30000N is 2.55g / cm 3 , the compaction density of the positive electrode sheet under charging to 100% SOC at a charging rate of 0.33C is 2.72g / cm 3 ; in the negative electrode sheet, 1% of silicon carbide is used to replace 1% of graphite in the negative electrode slurry 1 and the negative electrode slurry 2 in Example 3;

[0333] The performance parameters of the positive active material lithium iron phosphate LiFePO4 in Example 16 are as follows: the powder compaction density under 30000N is 2.56 g / cm 3 The compaction density of the positive electrode sheet under 100% SOC when the battery is charged at a charge rate of 0.33C is 2.75 g / cm 3 The silicon carbide is used to replace the 3% graphite in Example 3 in the negative electrode paste 1 and the negative electrode paste 2 in the negative electrode sheet.

[0334] Example 17

[0335] The preparation method is similar to that in Example 3, except that the negative electrode sheet is a single-layer structure, and the preparation method is as follows:

[0336] The performance parameters of the third graphite negative active material are as follows: the powder compaction density under 20000N is 1.63 g / cm 3 The Dv50 particle size of the graphite is 10.8 μm, and the mass content of the amorphous carbon is 3.1%.

[0337] The third graphite negative active material, the conductive agent acetylene black, the binder styrene-butadiene rubber, and the thickening agent sodium carboxymethyl cellulose are mixed in a mass ratio of 96:0.5:2.5:1, and then the solvent deionized water is added, and stirred uniformly to form a negative electrode paste; the negative electrode paste is uniformly coated on the negative electrode current collector copper foil, and dried and cold-pressed to obtain a negative electrode sheet.

[0338] The coating weight of the negative electrode sheet is 138 mg / 1540.25 mm 2 (single-sided); the compaction density of the negative electrode sheet under 100% SOC when the battery is charged at a charge rate of 0.33C is 1.26 g / cm 3 .

[0339] The preparation methods of Comparative Examples 1-5 are similar to those in Example 3, except that at least one of the mass content of ethylene carbonate (EC) in the electrolyte, the mass content of the first additive VC, and the mass content of the first additive FEC in the electrolyte is adjusted, and the specific adjustments are shown in Table 1.

[0340] The following is a performance test.

[0341] (I) Volume energy density test of secondary battery

[0342] The battery monomer is placed at 25°C, charged to 3.65V at a constant current of 0.33C, and rested for 1 min, then charged to 3.65V at a constant current of 0.1C, and rested for 30 min; discharged to 2.0V at a constant current of 0.33C, and the discharge capacity A0 at this time was recorded, unit: Ah; the length, width, and height of the battery monomer were measured using a caliper (generally calculated based on the size of the battery shell, excluding the height of the pole), and the volume V0 of the battery monomer was calculated, unit: L; the volume energy density VED of the battery monomer was (A0 x discharge platform voltage) / V0, unit: Wh / L.

[0343] (II) The test steps for the capacity retention rate of the battery after 1000 cycles at 60°C are as follows:

[0344] At 60°C, the battery was charged to a charge cut-off voltage of 3.65V at a constant current of 1C, and rested for 30 min, and then discharged to 2.0V at a constant current of 1C, which was one charge-discharge cycle, and the capacity C0 after the first cycle was recorded; the above charge-discharge cycle steps were repeated until 1000 cycles, and the capacity Cn after the 1000th cycle was recorded, and the capacity retention rate of the battery after 1000 cycles at 60°C was Cn / C0 x 100%. The higher the capacity retention rate, the better the cycle performance of the battery.

[0345] (III) The test steps for the charging time T of the secondary battery from 10% SOC to 80% SOC at 30°C are as follows:

[0346] At an ambient temperature of 30°C, the battery was charged from 10% SOC state,

[0347] charged from 10% SOC to 15% SOC at a constant current of 5.0C;

[0348] charged from 15% SOC to 20% SOC at a constant current of 5.0C;

[0349] charged from 20% SOC to 25% SOC at a constant current of 5.0C;

[0350] charged from 25% SOC to 30% SOC at a constant current of 5.0C;

[0351] charged from 30% SOC to 35% SOC at a constant current of 5.0C;

[0352] charged from 35% SOC to 40% SOC at a constant current of 5.0C;

[0353] charged from 40% SOC to 45% SOC at a constant current of 4.6C;

[0354] charged from 45% SOC to 50% SOC at a constant current of 4.3C;

[0355] Charge from 50% SOC to 55% SOC at 4.0 C constant current;

[0356] Charge from 55% SOC to 60% SOC at 3.7 C constant current;

[0357] Charge from 60% SOC to 65% SOC at 3.4 C constant current;

[0358] Charge from 65% SOC to 70% SOC at 3.1 C constant current;

[0359] Charge from 70% SOC to 75% SOC at 2.9 C constant current;

[0360] Charge from 75% SOC to 80% SOC at 2.7 C constant current;

[0361] Record the total charging time.

[0362] (IV) The test procedure for the capacity retention rate of the battery cycled at 30°C for 1000 cycles is as follows:

[0363] At 30°C, charge the battery from 10% SOC, respectively, according to the above different SOC corresponding to the rate to 80% SOC, and then continue to charge to 3.65 V using a 0.33 C charging rate, stand for 30 min, and then discharge to 2.0 V at 1 C constant current, which is one charge-discharge cycle. Record the capacity C0 after the first cycle. Repeat the above charge-discharge cycle until 1000 cycles, record the capacity Cn after the 1000th cycle, and get the capacity retention rate of the battery cycled at 30°C for 1000 cycles = Cn / C0 x 100%. The higher the capacity retention rate, the better the cycle performance of the battery.

[0364] Some parameters of each example and comparative example are shown in Table 1, wherein the content is the mass content, and the unit of the single-sided coating weight of the positive electrode and the negative electrode is mg / 1540.25 mm 2 .

[0365] The above performance test results of each example and comparative example are shown in Table 2.

[0366] Table 1

[0367] Table 2

[0368] From the above Table 1-2, it can be seen that the mass content of the first additive in the electrolyte of Comparative Example 1 is too high, the room temperature cycle performance and the fast charging performance of the battery are deteriorated; the mass content of the first additive in the electrolyte of Comparative Example 2 is too low, the high temperature cycle performance of the battery is deteriorated; the mass content of the second additive in the electrolyte of Comparative Example 3 is too high, the high temperature cycle performance of the battery is deteriorated, and the room temperature cycle performance is also not good; the mass content of the second additive in the electrolyte of Comparative Example 4 is too low, the room temperature cycle performance of the battery is decreased; the mass content of the first solvent in the electrolyte of Comparative Example 5 is too low, the self-stability of the electrolyte is deteriorated, which leads to the decrease of the conductivity, so that the room temperature and high temperature cycle performances are both poor.

[0369] Each embodiment adjusts the composition and proportion of the electrolyte, and cooperates with the negative electrode plate containing high-density graphite, so that the prepared secondary battery can have good energy density, fast charging performance, room temperature cycle performance and high temperature cycle performance. The second solvent in the electrolyte of Example 17 is a carbonate solvent, the conductivity of the electrolyte is decreased, so the single-sided coating weight of the positive electrode plate and the negative electrode plate is reduced to improve the fast charging performance of the battery.

[0370] Each technical feature of the above-described embodiments can be combined arbitrarily. In order to make the description simple, all possible combinations of each technical feature in the above-described embodiments are not described, however, as long as the combination of the technical features does not exist contradictory, it should be considered as the scope of the present application. The above-described embodiments only express several embodiments of the present application, the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the present application, several modifications and improvements can be made, which are within the scope of the present application. Therefore, the scope of the patent of the present application should be subject to the appended claims.

Claims

1. A secondary battery comprising: a positive electrode tab including a positive electrode current collector and a positive electrode film layer provided on at least one side of the positive electrode current collector, the positive electrode film layer including a positive electrode active material; The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one side of the negative electrode current collector, the negative electrode film layer including a negative electrode active material including graphite, the negative electrode active material having a powder compaction density under 20,000 N of 1.5 g / cm 3 ~ 1.85 g / cm 3 ; and an electrolyte including an organic solvent and an organic additive, the organic solvent including a first solvent including a cyclic carbonate, the first solvent having a mass content of 17% to 34% based on the total mass of the electrolyte, the organic additive including a first additive and a second additive, the first additive including vinylene carbonate, the second additive including a vinylene carbonate derivative, the first additive having a mass content of 1.5% to 8% and the second additive having a mass content of 0.5% to 4% based on the total mass of the electrolyte.

2. The secondary battery according to claim 1, wherein the vinylene carbonate derivative has the following structure: R1 and R2 each independently include any one of a hydrogen element, a halogen element, a C1 to C5 alkyl group, and a C1 to C5 haloalkyl group, and R1 and R2 are not simultaneously the hydrogen element.

3. The secondary battery according to any one of claims 1 to 2, wherein the vinylene carbonate derivative includes at least one of fluoroethylene carbonate, difluoroethylene carbonate, and trifluoromethyl ethylene carbonate.

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

5. The secondary battery according to any one of claims 1 to 4, wherein the first solvent has a mass content of 25.5% to 34% based on the total mass of the electrolyte.

6. The secondary battery according to any one of claims 1 to 5, wherein the first additive has a mass content of 1.5% to 6.5% based on the total mass of the electrolyte; and / or, the second additive has a mass content of 0.5% to 3% based on the total mass of the electrolyte.

7. The secondary battery according to any one of claims 1 to 6, wherein the total mass content of the first additive and the second additive is 2% to 10% based on the total mass of the electrolyte.

8. The secondary battery according to any one of claims 1 to 7, wherein the total mass content of the first additive and the second additive is 3% to 8% based on the total mass of the electrolyte.

9. The secondary battery according to any one of claims 1 to 8, wherein The positive electrode active material has a powder compaction density ≥ 2.43 g / cm at 30000 N 3 , optionally 2.48 g / cm 3 ~ 2.85 g / cm 3 .

10. The secondary battery according to any one of claims 1 to 9, wherein the positive electrode active material includes at least one of an olivine-structured lithium-containing phosphate and a derivative thereof.

11. The secondary battery according to claim 10, wherein the positive electrode active material includes: a core portion including at least one of an olivine-structured lithium-containing phosphate and a derivative thereof; and an ion-conductive layer including at least one element of Fe, C, Ti, Zr, Hf, Ge, and Sn coated on a surface of the core portion.

12. The secondary battery according to claim 10 or 11, wherein The lithium-containing phosphate of olivine structure and its derivatives include compounds of the general formula Li x1 A1 y1 M1 a1 M2 b1 P 1-c1 X c1 Q1 z1 wherein 0.5≤x1≤1.3, 0≤y1≤1.3, and 0.9≤x1+y1≤1.3; 0.9≤a1≤1.5, 0≤b1≤0.5, and 0.9≤a1+b1≤1.5; 0≤c1≤0.5; 3≤z1≤5; A1 includes at least one of Na, K, and Mg; M1 includes at least one of Mn, Fe, Co, and Ni; M2 includes at least one of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X includes at least one of S, Si, Cl, B, C, and N, P; and Q1 includes at least one of O and F.

13. The secondary battery of claim 12, wherein, the olivine-structured lithium-containing phosphate and the derivative thereof include at least one of lithium iron phosphate, lithium manganese phosphate, lithium nickel phosphate, and lithium cobalt phosphate.

14. The secondary battery according to any one of claims 11 to 13, wherein The ion-conducting layer includes an ion conductor of the formula Li 3-b Fe 2-b M3 b (PO m ) n , M3 includes at least one of Ti, Zr, Hf, Ge, and Sn in the +4 valence, 0≤b≤1, 3≤m≤5, and 2≤n≤4.

15. The secondary battery of claim 15, wherein, the ion conductor includes at least one of lithium titanium iron phosphate, lithium zirconium iron phosphate, and lithium tin iron phosphate.

16. The secondary battery according to any one of claims 1 to 15, wherein at least one of the following conditions is satisfied: (1) the compacted density of the positive electrode plate is 2.5 g / cm 3 ~ 2.8 g / cm 3 ; (2) the mass content of carbon in the positive electrode active material is 1% to 2%; (3) the powder resistivity of the positive electrode active material is ≤ 20 Ω·cm; (4) the volume average particle diameter of the positive electrode active material satisfies 1 μm ≤ Dv50 ≤ 2 μm and 0.4 μm ≤ Dv10 ≤ 0.7 μm.

17. The secondary battery according to any one of claims 1 to 16, wherein The positive electrode film layer further comprises a lithium supplement agent, and the lithium supplement agent comprises at least one of ternary lithium supplement material, lithium phosphate, lithium hydrogen phosphate, lithium sulfate, lithium sulfite, lithium molybdate, lithium nickelate, lithium ferrite, lithium oxalate, lithium titanate, lithium tetraborate, lithium metasilicate, lithium metamanganate, lithium tartrate and trilithium citrate.

18. The secondary battery of claim 17, wherein, The ternary lithium supplementing material includes Li x2 A2 y2 Ni a2 Co b2 Mn c2 M4(1-a2-b2-c2)Q2 z2 wherein, 0 0 0 0 1.8 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.

19. The secondary battery of any one of claims 1 to 18, wherein, The positive electrode film layer further comprises a positive electrode conductive layer, and the positive electrode conductive layer is arranged between the positive electrode current collector and the positive electrode film layer, and the positive electrode conductive layer comprises a conductive agent, and the conductive agent comprises at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

20. The secondary battery of claim 19, wherein, The thickness of the positive electrode conductive layer is 0.5 μm to 2 μm.

21. The secondary battery of claim 19, wherein, The positive electrode conductive layer comprises a binder, and the binder comprises at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid and fluorine-containing acrylic ester resin.

22. The secondary battery of claim 21, 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%.

23. The secondary battery of any one of claims 1 to 22, wherein, The secondary battery has a compaction density of the negative electrode tab of 1.15 g / cm 3 ~ 1.46 g / cm 3 , and optionally 1.25 g / cm 3 ~ 1.40 g / cm 3 .

24. The secondary battery of any one of claims 1 to 23, wherein, The secondary battery has a compaction density of the negative electrode tab at 100% SOC state ≥ 1.25 g / cm 3 and < 1.35 g / cm 3 .

25. The secondary battery of claim 24, wherein, The secondary battery satisfies at least one of the following conditions in the 100% SOC state: (1) the mass content of the second additive in the electrolyte is 0.5% to 3%; (2) the mass content of the first solvent in the electrolyte is 22.5% to 34%; (3) the mass content of the first additive in the electrolyte is 1.5% to 6%.

26. The secondary battery of any one of claims 1 to 23, wherein, The secondary battery has a compaction density of the negative electrode tab of 1.35 g / cm 3 ~ 1.40 g / cm 3 .

27. The secondary battery of claim 26, wherein, The secondary battery satisfies at least one of the following conditions in the 100% SOC state: (1) the mass content of the second additive in the electrolyte is 0.7% to 3.5%; (2) the mass content of the first solvent in the electrolyte is 21.25% to 34%; (3) the mass content of the first additive in the electrolyte is 2.5% to 7%.

28. The secondary battery of any one of claims 1 to 27, wherein, The mass of the electrolyte of the secondary battery under the rated capacity of 1 Ah per battery is 2.2 g to 3.0 g.

29. The secondary battery of any one of claims 1 to 28, wherein, The electrolyte further comprises a second solvent, and the second solvent comprises at least one of linear carbonate, carboxylic acid ester, ether, nitrile and sulfone.

30. The secondary battery of claim 29, wherein, The second solvent comprises 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, methyl butyrate, ethyl butyrate and 1,4-butyrolactone.

31. The secondary battery of claim 29, wherein, The volume energy density of the secondary battery is 400 Wh / L to 450 Wh / L, the mass content of the carboxylic acid ester in the electrolyte is 25.5% to 59.5%, and the total mass content of the first additive and the second additive in the electrolyte is 2% to 7%.

32. The secondary battery of claim 29, wherein, The volume energy density of the secondary battery is > 450 Wh / L and ≤ 480 Wh / L, the mass content of the carboxylic acid ester in the electrolyte is 25.5% to 63.75%, and the total mass content of the first additive and the second additive in the electrolyte is 3.5% to 8%.

33. The secondary battery of claim 29, wherein, The charging time of the secondary battery from 10% SOC to 80% SOC at 30 DEG C is 6 min to 15 min, the mass content of the carboxylic acid ester in the electrolyte is 17% to 63.75%, and the total mass content of the first additive and the second additive in the electrolyte is 2% to 8%.

34. The secondary battery of claim 33, wherein, In the electrolyte, the mass content of the first additive is 1.5% to 6.5%, and the mass content of the second additive is 0.5% to 3.5%.

35. The secondary battery of any one of claims 1 to 34, wherein, The electrolyte comprises a lithium salt, and the lithium salt comprises at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, a fluorine-containing sulfonimide salt, lithium triflate, lithium difluorophosphate, lithium difluoro oxalate borate, lithium di oxalate borate, lithium difluoro di-oxalate phosphate, and lithium tetrafluoro oxalate phosphate.

36. The secondary battery of claim 34, wherein, The mass content of the lithium salt in the electrolyte is 10% to 20%.

37. The secondary battery of claim 35 or 36, wherein, The lithium salt comprises LiFSI and LiPF6, and the lithium salt satisfies at least one of the following conditions: (1) the concentration of the LiFSI in the electrolyte is 0.2 mol / L to 0.5 mol / L; (2) the concentration of the LiPF6 in the electrolyte is 0.5 mol / L to 1.3 mol / L; (3) the amount-of-substance ratio of the LiFSI to the LiPF6 is (2 to 5):

10.

38. The secondary battery of any one of claims 1 to 37, wherein, The negative electrode sheet further comprises a negative electrode conductive layer, the negative electrode conductive layer is arranged between the negative electrode current collector and the negative electrode film layer on at least one side, and the negative electrode conductive layer comprises a conductive agent, and the conductive agent comprises at least one of super-conductive carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

39. The secondary battery of claim 38, wherein, The thickness of the negative electrode conductive layer is 0.5 μm to 2 μm.

40. The secondary battery of claim 38, 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-based acrylic resin, polyvinyl alcohol, sodium alginate, and carboxymethyl chitosan.

41. The secondary battery of claim 38, wherein, In the negative electrode conductive layer, the mass content of the conductive agent is 20% to 40%, and the mass content of the binder is 60% to 80%.

42. The secondary battery of any one of claims 1 to 41, wherein, The negative electrode film layer comprises at least one negative electrode active layer, and the at least one negative electrode active layer comprises the graphite.

43. The secondary battery of claim 42, wherein, The negative electrode film layer comprises one negative electrode active layer, the negative electrode active layer contains the graphite, and the Dv50 particle size of the graphite is 8.2 μm to 13.5 μm.

44. The secondary battery of claim 42, wherein, The negative electrode film layer comprises a first negative electrode active layer and a second negative electrode active layer which are arranged in sequence on the same side of the negative electrode current collector, the graphite comprises at least one of artificial graphite and natural graphite, the graphite in the first negative electrode active layer comprises at least one of the artificial graphite and the natural graphite, and the graphite in the second negative electrode active layer comprises the artificial graphite.

45. The secondary battery of claim 44, wherein, The Dv50 particle size of the graphite in the first negative electrode active layer is greater than the Dv50 particle size of the graphite in the second negative electrode active layer.

46. The secondary battery of claim 44, wherein, The Dv50 particle size of the graphite in the first negative electrode active layer is 9.5 μm to 18.5 μm, and is optionally 9.5 μm to 14.8 μm; The Dv50 particle size of the graphite in the second negative electrode active layer is 7.8 μm to 14.3 μm, and can be 7.8 μm to 12.8 μm.

47. The secondary battery of claim 44, wherein, The mass ratio of the graphite in the first negative electrode active layer and the second negative electrode active layer is 3:7 to 7:3, and can be 4:6 to 6:

4.

48. The secondary battery of any one of claims 44 to 47, wherein, The artificial graphite includes graphite bulk particles and a coating layer, the graphite bulk particles include secondary particles formed by aggregation of a plurality of primary particles, and the coating layer is coated on the surface of the bulk particles, and the coating layer includes amorphous carbon.

49. The secondary battery of claim 48, wherein, At least one of the following conditions is satisfied: (1) The mass content of the amorphous carbon is 2% to 5% based on the total mass of the artificial graphite; (2) The powder resistivity of the artificial graphite is ≤0.04 Ω·cm.

50. The secondary battery of any one of claims 1 to 49, wherein, The charge capacity per gram of the graphite is ≥350 mAh / g at a rate of 0.1C in a button cell, and can be 350 mAh / g to 440 mAh / g.

51. The secondary battery of any one of claims 1 to 50, wherein, The negative electrode active material further includes a silicon-based material, the silicon-based material includes at least one of a silicon oxide compound and a silicon-carbon composite, and the mass content of silicon in the silicon-based material in the negative electrode active material is 0.3% to 10%, and can be 1% to 6%.

52. The secondary battery of any one of claims 1 to 52, wherein, The separator film includes a porous base film and a functional layer provided on at least one side of the porous base film.

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

54. The secondary battery of claim 53, wherein, The separator film includes a first functional layer and a second functional layer provided on both sides of the porous base film, the first functional layer includes first inorganic particles, the second functional layer includes composite particles, the composite particles include second inorganic particles and non-fluoropolymer particles, and the second inorganic particles are attached to the surface of the non-fluoropolymer particles and / or dispersed in the interior of the non-fluoropolymer particles.

55. The secondary battery of claim 54, wherein, The non-fluoropolymer particles include acrylate polymer particles.

56. A battery device comprising the secondary battery of any one of claims 1 to 55.

57. An electric device comprising at least one of the secondary battery of any one of claims 1 to 55 and the battery device of claim 56.

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