Secondary battery, battery device, and electric device

Abstract

The invention provides a secondary battery, a battery device and a power utilization device, a negative pole piece in the secondary battery comprises a negative pole current collector and a negative pole film layer, the negative pole film layer is arranged on at least one side of the negative pole current collector, the negative pole film layer comprises a negative pole active material, the negative pole active material comprises graphite, and the powder compaction density of the negative pole active material under 20000N is 1.5-1.85 g / cm < 3 >; the electrolyte comprises an organic solvent and an organic additive, the organic solvent comprises a first solvent, the first solvent comprises cyclic carbonate, and the mass content of the first solvent is 17-34% based on the total mass of the electrolyte; the organic additives comprise a first additive and a second additive, the first additive comprises vinylene carbonate, the second additive comprises an ethylene carbonate derivative, based on the total mass of the electrolyte, the mass content of the first additive is 1.5%-8%, and the mass content of the second additive is 0.5%-4%.

Description

[0001] This application claims the priority of PCT International Application PCT / CN2024 / 105814 entitled "Battery and Electrical Device" filed on July 16, 2024, the entire content of which is incorporated herein by reference. Technical Field

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

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

[0004] In recent years, secondary batteries such as lithium-ion batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power stations, as well as in multiple fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. With the increasingly wide application range of secondary batteries, the demand for the core energy density of secondary batteries has gradually increased. However, the improvement of energy density will deteriorate the cycle performance and fast charging performance of the battery. Therefore, how to enable secondary batteries to balance high energy density, cycle performance, and fast charging performance has become an urgent problem to be solved. Summary of the Invention

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

[0006] The first aspect of this application provides a secondary battery, including: a positive electrode tab, the positive electrode tab includes a positive electrode current collector and a positive electrode film layer, the positive electrode film layer is disposed on at least one side of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material; a negative electrode tab, the negative electrode tab includes a negative electrode current collector and a negative electrode film layer, the negative electrode film layer is disposed on at least one side of the negative electrode current collector, the negative electrode film layer includes a negative electrode active material, the negative electrode active material includes graphite, and the powder compaction density of the negative electrode active material under 20000N is 1.5g / cm 3 ~1.85g / cm 3 ; and An electrolyte, the electrolyte includes an organic solvent and an organic additive, the organic solvent includes a first solvent, the first solvent includes a cyclic carbonate, based on the total mass of the electrolyte, the mass content of the first solvent is 17% - 34%; the organic additive includes a first additive and a second additive, the first additive includes vinylene carbonate, the second additive includes a vinyl carbonate derivative, based on the total mass of the electrolyte, the mass content of the first additive is 1.5% - 8%, and the mass content of the second additive is 0.5% - 4%.

[0007] The negative electrode active material of the above secondary battery includes graphite and has a high powder compaction density, so it can provide a high energy density. However, for the negative electrode sheet with a high powder compaction density, its kinetic performance is poor, which is not conducive to improving the fast charging performance. In addition, due to the limited internal space of the battery cell, the amount of electrolyte injection in the high energy density battery cell needs to be reduced accordingly. Therefore, there is a risk of a significant drop in the cycle performance of the battery cell due to insufficient electrolyte. Therefore, the above secondary battery is further improved by the electrolyte and is paired with a negative electrode sheet with a high energy density. Specifically, by improving the first solvent, the first additive, the second additive and their contents in the above electrolyte, the electrolyte has good thermal stability and appropriate conductivity, so as to reduce the electrolyte consumption rate and the DC internal resistance DCR of the battery, and then improve the cycle performance, storage life and fast charging performance of the battery cell in the high energy density system. In this way, the above secondary battery can take into account high energy density, cycle performance and fast charging performance.

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

[0009] In some embodiments, the vinyl carbonate derivative includes at least one of fluoroethylene carbonate, difluoroethylene carbonate and trifluoromethyl ethylene carbonate.

[0010] In some embodiments, the cyclic carbonate includes at least one of ethylene carbonate and propylene carbonate.

[0011] In some embodiments, based on the total mass of the electrolyte, the mass content of the first solvent is 25.5% - 34%.

[0012] In some embodiments, based on the total mass of the electrolyte, the mass content of the first additive is 1.5% to 6.5%; and / or, based on the total mass of the electrolyte, the mass content of the second additive is 0.5% to 3%.

[0013] In some embodiments, based on the total mass of the electrolyte, the total mass content of the first additive and the second additive is 2% to 10%.

[0014] In some embodiments, based on the total mass of the electrolyte, the total mass content of the first additive and the second additive is 3% to 8%.

[0015] In some embodiments, the powder compaction density of the positive electrode active material under 30000N is ≥2.43 g / cm 3 , optionally 2.48 g / cm 3 ~2.85 g / cm 3 .

[0016] In some embodiments, the positive electrode active material includes at least one of lithium-containing phosphates with an olivine structure and their derivatives.

[0017] In some embodiments, the positive electrode active material includes: a core part, including at least one of lithium-containing phosphates with an olivine structure and their derivatives; and an ion-conducting layer, which coats the surface of the core part, and the ion-conducting layer includes at least one element among Fe, C, Ti, Zr, Hf, Ge, and Sn.

[0018] By coating the surface of the core part with the ion-conducting layer, the conductivity of the lithium-containing phosphates with an olivine structure and their derivatives can be improved, the powder resistivity of the material can be reduced, and it is beneficial to the migration rate of lithium ions, improving the fast charging ability of the battery and reducing the heat generation of the battery cell.

[0019] In some embodiments, the lithium-containing phosphates with an olivine structure and their derivatives include a general formula of Li x1 A1 y1 M1 a1 M2 b1 P 1-c1 X c1 Q1 z1a compound, wherein 0.5 ≤ x1 ≤ 1.3, 0 ≤ y1 ≤ 1.3, and 0.9 ≤ x1 + y1 ≤ 1.3; 0.9 ≤ a1 ≤ 1.5, 0 ≤ b1 ≤ 0.5, and 0.9 ≤ a1 + b1 ≤ 1.5; 0 ≤ c1 ≤ 0.5; 3 ≤ z1 ≤ 5; A1 includes at least one of Na, K, and Mg; M1 includes at least one of Mn, Fe, Co, and Ni; M2 includes at least one of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X includes at least one of S, Si, Cl, B, C, N, and P; Q1 includes at least one of O and F. The lithium-containing phosphate with an olivine structure has excellent cycling stability, which is beneficial to improving the cycling performance of a single battery cell.

[0020] In some embodiments, the lithium-containing phosphate with an olivine structure and its derivatives include at least one of lithium iron phosphate, lithium manganese phosphate, lithium nickel phosphate, and lithium cobalt phosphate.

[0021] In some embodiments, the ion-conducting layer includes an ion conductor with the chemical formula Li 3-b Fe 2-b M3 b (PO m ) n , where M3 includes at least one element of +4-valent Ti, Zr, Hf, Ge, and Sn, 0 ≤ b ≤ 1, 3 ≤ m ≤ 5, and 2 ≤ n ≤ 4.

[0022] In some embodiments, the ion conductor includes at least one of lithium iron titanium phosphate, lithium iron zirconium phosphate, and lithium iron tin phosphate. Coating the surface of the core with an ion conductor containing a NASICON structure can significantly improve the transport rate of lithium ions during multiple deintercalation / insertion of lithium at the positive electrode end, improve the ionic conductivity of the positive electrode active material, improve the fast charging ability of a single battery cell, and in addition, can also improve the specific capacity and the energy density of the corresponding single battery cell.

[0023] In some embodiments, at least one of the following conditions is satisfied: (1) The tap density of the positive electrode sheet is 2.5 g / cm 3 ~2.8 g / cm 3 ; (2) The mass content of carbon in the positive electrode active material is 1% - 2%; (3) The powder resistivity of the positive electrode active material is ≤ 20 Ω•cm; (4) The volume average particle size of the positive electrode active material satisfies: 1 µm ≤ Dv50 ≤ 2 µm, 0.4 µm ≤ Dv10 ≤ 0.7 µm.

[0024] In some of these 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 ferrate, lithium oxalate, lithium titanate, lithium tetraborate, lithium metasilicate, lithium manganate, lithium tartrate, and lithium citrate.

[0025] In some of these embodiments, the ternary lithium supplement material includes Li x2 A2 y2 Ni a2 Co b2 Mn c2 M4 (1-a2-b2-c2) Q2 z2 , where 0 < x2 ≤ 2.1, 0 ≤ y2 ≤ 2.1; 0 ≤ a2 ≤ 1, 0 ≤ b2 ≤ 1, 0 ≤ c2 ≤ 1, and 0.1 ≤ a2 + b2 + c2 ≤ 1; 1.8 ≤ z2 ≤ 3.5; A2 includes at least one of Na, K, and Mg; M4 includes at least one of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; Q2 includes at least one of O and F.

[0026] In some of these embodiments, the positive electrode tab further includes a positive electrode conductive layer, the positive electrode conductive layer is disposed between the positive electrode current collector and the positive electrode film layer, the positive electrode conductive layer includes a conductive agent, and the conductive agent includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0027] In some of these embodiments, the thickness of the positive electrode conductive layer is 0.5 μm to 2 μm.

[0028] In some of these embodiments, the positive electrode conductive layer includes a binder, and the binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride - tetrafluoroethylene - propylene terpolymer, vinylidene fluoride - hexafluoropropylene - tetrafluoroethylene terpolymer, tetrafluoroethylene - hexafluoropropylene copolymer, polyacrylic acid, and fluorinated acrylate resins.

[0029] In some of these 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%.

[0030] In some of these embodiments, the compaction density of the negative electrode tab of the secondary battery in the 100% SOC state is 1.15 g / cm 3 ~1.46 g / cm 3, optionally 1.25 g / cm 3 ~1.40 g / cm 3 .

[0031] In some of these 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 .

[0032] In some of these embodiments, the secondary battery in the 100% SOC state satisfies at least one of the following conditions: (1) The mass content of the second additive in the electrolyte is 0.5% - 3%; (2) The mass content of the first solvent in the electrolyte is 25.5% - 34%; (3) The mass content of the first additive in the electrolyte is 1.5% - 6%.

[0033] In some of these embodiments, the compaction density of the negative electrode sheet of the secondary battery in the 100% SOC state is 1.35 g / cm 3 ~1.40 g / cm 3 .

[0034] In some of these embodiments, the secondary battery in the 100% SOC state satisfies at least one of the following conditions: (1) The mass content of the second additive in the electrolyte is 0.7% - 3.5%; (2) The mass content of the first solvent in the electrolyte is 21.25% - 34%; (3) The mass content of the first additive in the electrolyte is 2.5% - 7%.

[0035] In some of these embodiments, the mass of the electrolyte per unit battery rated capacity of 1 Ah of the secondary battery is 2.2 g - 3.0 g.

[0036] In some of these embodiments, the electrolyte further includes a second solvent, and the second solvent includes at least one of linear carbonates, carboxylates, ethers, nitriles, and sulfones.

[0037] In some of these embodiments, the second solvent includes carboxylates; more optionally, the carboxylates include 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.

[0038] In some of these embodiments, the volumetric 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%.

[0039] In some of these 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 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%.

[0040] In some of these embodiments, the charging time of the secondary battery from 10% SOC to 80% SOC at 30 °C is 6 min to 15 min, the mass content of the carboxylic acid ester in the electrolyte is 17% to 63.7%, and the total mass content of the first additive and the second additive in the electrolyte is 2% to 8%.

[0041] In some of these embodiments, 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%.

[0042] In some of these embodiments, the electrolyte includes a lithium salt, and the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, fluorosulfonylimide salt, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(oxalato)borate, lithium difluorobis(oxalato)phosphate, and lithium tetrafluorooxalate phosphate.

[0043] In some of these embodiments, the mass content of the lithium salt in the electrolyte is 10% to 20%.

[0044] In some of these embodiments, the lithium salt includes LiFSI and LiPF 6 , and the lithium salt satisfies at least one of the following conditions: (1) The concentration of LiFSI in the electrolyte is 0.2 mol / L to 0.5 mol / L; (2) The concentration of LiPF 6 in the electrolyte is 0.5 mol / L to 1.3 mol / L; (3) The molar ratio of LiFSI to LiPF 6 is (2 to 5):10.

[0045] In some of these embodiments, the negative electrode tab further includes a negative electrode conductive layer disposed between the negative electrode current collector and at least one side of the negative electrode film layer. The negative electrode conductive layer includes a conductive agent, and the conductive agent includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0046] In some of these embodiments, the thickness of the negative electrode conductive layer is 0.5 μm to 2 μm.

[0047] In some of these embodiments, the negative electrode conductive layer includes a binder, and the binder includes at least one of styrene-butadiene rubber, water-soluble unsaturated resin, water-based acrylic resin, polyvinyl alcohol, sodium alginate, and carboxymethyl chitosan.

[0048] In some of these embodiments, 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%.

[0049] In some of these embodiments, the negative electrode film layer includes at least one negative electrode active layer, and at least one negative electrode active layer includes the graphite.

[0050] In some of these embodiments, the negative electrode film layer includes one negative electrode active layer, and the negative electrode active layer contains the graphite. The Dv50 particle size of the graphite is 8.2 μm to 13.5 μm.

[0051] In some of these embodiments, the negative electrode film layer includes a first negative electrode active layer and a second negative electrode active layer that are sequentially stacked on the same side of the negative electrode current collector. The graphite includes at least one of artificial graphite and natural graphite. The graphite in the first negative electrode active layer includes at least one of artificial graphite and natural graphite, and the graphite in the second negative electrode active layer includes artificial graphite.

[0052] In some of these embodiments, the Dv50 particle size of the graphite in the first negative electrode active layer ≥ the Dv50 particle size of the graphite in the second negative electrode active layer.

[0053] In some of these embodiments, 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 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 optionally 7.8 μm to 12.8 μm.

[0054] In some of these embodiments, the mass ratio of the graphite in the first negative electrode active layer to the graphite in the second negative electrode active layer is 3:7 to 7:3; and can be optionally 4:6 to 6:4.

[0055] In some of these embodiments, the artificial graphite includes graphite body particles and a coating layer. The graphite body particles include secondary particles aggregated from a plurality of primary particles. The coating layer coats the surface of the body particles, and the coating layer includes amorphous carbon.

[0056] In some of these embodiments, at least one of the following conditions is satisfied: (1) Based on the total mass of the artificial graphite, the mass content of the amorphous carbon is 2% - 5%; (2) The powder resistivity of the artificial graphite is ≤0.04 Ω•cm.

[0057] In some of these embodiments, the charging specific capacity of the graphite in a coin cell at a rate of 0.1C is ≥350 mAh / g, and optionally it is in the range of 350 mAh / g - 440 mAh / g.

[0058] In some of these embodiments, the negative electrode active material further includes a silicon-based material, and the silicon-based material includes at least one of silicon oxides and silicon-carbon composites; the mass content of silicon element in the silicon-based material in the negative electrode active material is 0.3% - 10%, and optionally it is 1% - 6%.

[0059] In some of these embodiments, the separator includes a porous base film and a functional layer provided on at least one side of the porous base film.

[0060] In some of these embodiments, at least one of the following conditions is satisfied: (1) The thickness of the porous base film is ≤12 μm, and optionally it is ≤9 μm; (2) The porosity of the porous base film is 20% - 70%, and optionally it is 35% - 60%.

[0061] In some of these embodiments, the separator 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, and the composite particles include second inorganic particles and non-fluoropolymer particles. The second inorganic particles adhere to the surface of and / or are dispersed inside the non-fluoropolymer particles.

[0062] In some of these embodiments, the non-fluoropolymer particles include acrylate polymer particles.

[0063] The second aspect of the present application provides a battery device, including the secondary battery provided in the first aspect of the present application.

[0064] The third aspect of the present application provides an electrical device, including at least one of the secondary battery provided in the first aspect of the present application and the battery device provided in the second aspect.

[0065] The electrical device of the present application includes the secondary battery provided by the present application, and thus has at least the same advantages as the secondary battery.

[0066] Details of one or more embodiments of the present application are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the present application will become apparent from the specification, the drawings, and the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] To better describe and illustrate the embodiments or examples provided by the present application, reference may be made to one or more of the accompanying drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed application, the currently described embodiments or examples, and the currently understood best mode of these applications. Also, in all the drawings, the same reference numerals are used to denote the same components. In the drawings: Figure 1 is a schematic diagram of a battery cell according to an embodiment of the present application.

[0068] Figure 2 is Figure 1 an exploded view of the battery cell according to an embodiment of the present application shown.

[0069] Figure 3 is a schematic diagram of a battery module according to an embodiment of the present application.

[0070] Figure 4 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0071] Figure 5 is Figure 4 an exploded view of the battery pack according to an embodiment of the present application shown.

[0072] Figure 6 is a schematic diagram of an electrical device using the secondary battery as a power source according to an embodiment of the present application.

[0073] Description of Reference Numerals: 1, battery pack; 2, upper box body; 3, lower box body; 4, battery module; 5, battery cell; 51, housing; 52, electrode assembly; 53, cover plate; 6, electrical device. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0074] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts shall fall within the protection scope of the present application.

[0075] The "range" disclosed in this application can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a specific range. The range defined in this way can include or exclude the end values. Any end value can be independently included or not included, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 - 120 and 80 - 110 are listed for a specific parameter, ranges of 60 - 110 and 80 - 120 are understood to be anticipated. 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 anticipated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5. In this application, unless otherwise specified, the numerical range "a - b" represents an abbreviated representation of any real number combination between a and b, where both a and b are real numbers. For example, the numerical range "0 - 5" means that all real numbers between "0 - 5" are fully listed in this article, and "0 - 5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, the integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when stating that a certain parameter is an integer selected from "2 - 10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0076] In this application, when it comes to "multiple", "a variety of", etc., unless otherwise specifically defined, it means greater than 2 or equal to 2 in quantity. For example, "at least one kind" means one kind or greater than or equal to two kinds.

[0077] If there is no special instruction, all the embodiments and optional embodiments of this application can be combined with each other to form a new technical solution.

[0078] Referring to "embodiment" in this article means that the specific features, structures, or characteristics described in combination with the embodiment can be included in at least one embodiment or implementation manner of this application. The appearance of this phrase in various positions in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments. The same understanding applies to the "implementation manner" mentioned in this article.

[0079] Those skilled in the art can understand that in the methods of various embodiments or examples, the written order of each step does not mean a strict execution order that constitutes any limitation to the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. If there is no special explanation, all steps of this application can be carried out sequentially or randomly, and preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) carried out sequentially, or may also include steps (b) and (a) carried out sequentially. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may also include steps (a), (c) and (b), or may also include steps (c), (a) and (b), etc.

[0080] In this application, in the open technical features or technical solutions described by words such as "containing", "comprising", "including", etc., without other explanations, additional members other than the listed members are not excluded, and it can be regarded as providing both a closed feature or solution composed of the listed members and an open feature or solution that further includes additional members outside the listed members. For example, A includes a1, a2 and a3. Without other explanations, it may also include other members or may not include additional members, and it can be regarded as providing both a feature or solution that "A is composed of a1, a2 and a3" and a feature or solution that "A not only includes a1, a2 and a3, but also includes other members".

[0081] In this application, without other explanations, A (such as B) means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0082] In this application, "optionally", "optional", "option" mean that it can be there or not, that is, it refers to any one of the two parallel options of "yes" or "no". If "optional" appears multiple times in a technical solution, without special explanations and without contradictions or mutual restrictions, each "optional" is independent.

[0083] An embodiment of this application provides a secondary battery, including a positive electrode plate, a negative electrode plate and an electrolyte.

[0084] The positive electrode plate includes a positive electrode current collector and a positive electrode film layer. The positive electrode film layer is disposed on at least one side of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

[0085] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer. The negative electrode film layer is disposed on at least one side of the negative electrode current collector. The negative electrode film layer includes a negative electrode active material. The negative electrode active material includes graphite. The powder compaction density of the negative electrode active material under 20000N is 1.5g / cm 3 ~1.85g / cm 3 .

[0086] In the embodiments of the present application, the powder compaction density of the negative electrode active material is a well-known meaning to those skilled in the art. A compaction density tester can be used for testing with reference to GB / T 24533-2009, and the test pressure is 20000N.

[0087] The electrolyte includes an organic solvent and an organic additive. The organic solvent includes a first solvent. The first solvent includes cyclic carbonate (EC). Based on the total mass of the electrolyte, the mass content of the first solvent is 17% - 34%. The organic additive includes a first additive and a second additive. The first additive includes vinylene carbonate (VC). The second additive includes ethylene carbonate derivatives. Based on the total mass of the electrolyte, the mass content of the first additive is 1.5% - 8%, and the mass content of the second additive is 0.5% - 4%.

[0088] The negative electrode active material of the above secondary battery includes graphite and has a relatively high powder compaction density, so it can provide a relatively high energy density. However, for the negative electrode plate with a relatively high powder compaction density, its kinetic performance is not good, which is not conducive to improving the fast charging performance. In addition, due to the limited internal space of the battery cell, the injection volume of the battery cell with a high energy density needs to be reduced accordingly. Therefore, there is a risk that the cycle performance of the battery cell will drop due to insufficient electrolyte. Therefore, the above secondary battery is further improved through the electrolyte and is matched with the negative electrode plate with a relatively high energy density. Specifically, by improving the first solvent, the first additive, the second additive and their contents in the above electrolyte, the electrolyte has good thermal stability and appropriate conductivity, so as to reduce the electrolyte consumption rate and the DC internal resistance DCR of the battery, and further improve the cycle performance, storage life and fast charging performance of the battery cell in the high energy density system. In this way, the above secondary battery can take into account relatively high energy density and fast charging performance.

[0089] The above first solvent includes cyclic carbonate. The cyclic carbonate has a relatively high dielectric constant and good film-forming performance. If the content of the first solvent in the electrolyte is too low, the self-stability of the electrolyte becomes poor, resulting in a decrease in conductivity. However, if the content of the first solvent is too high, the viscosity and melting point of the electrolyte increase, which will also deteriorate the conductivity of the electrolyte and the kinetic performance of the battery, resulting in the deterioration of the cycle performance. Therefore, controlling the first solvent within the above content range can make the electrolyte have good thermal stability and appropriate conductivity.

[0090] The above first additive includes vinylene carbonate (VC), the second additive includes ethylene carbonate derivatives. The first additive and the second additive can participate in the formation of the interface film. If the contents of the first additive and the second additive are too low, the first solvent will participate in the film formation excessively, destroying the stability of the electrolyte, thereby accelerating the electrolyte consumption rate and deteriorating the cycle performance and storage life of the battery. As the content of the first additive increases, the high-temperature cycle life of the battery is improved. However, if the content of the first additive is too high, it will deteriorate the battery kinetic window and the direct current internal resistance DCR, resulting in the deterioration of the cycle performance and being unfavorable for the improvement of the fast charging performance. As the content of the second additive increases, the normal-temperature cycle life and the fast charging performance of the battery are improved. However, if the content of the second additive is too high, the high-temperature performance of the battery deteriorates and the high-temperature cycle life decreases. Thus, when the first additive and the second additive are respectively within the above ranges, the electrolyte achieves the balance between the film formation stability and the battery kinetics.

[0091] Therefore, by regulating the first solvent within the above content range, the thermal stability of the electrolyte can be improved and the conductivity of the electrolyte can be within a suitable range. At the same time, by regulating the first additive and the second additive respectively within the above ranges, the electrolyte achieves the balance between the battery kinetics and the film formation stability, thereby reducing the electrolyte consumption rate and improving the cycle performance and storage life of the battery cell under a low liquid injection coefficient. In addition, the battery also has a lower direct current internal resistance DCR and good fast charging performance. This electrolyte can be applied to the above-mentioned anode electrode sheet and battery system with high energy density, enabling the secondary battery to have high energy density, cycle performance and fast charging performance, especially the normal-temperature cycle performance and the high-temperature cycle performance. Electrolyte In some embodiments of the present application, the cyclic carbonate in the first solvent includes at least one of ethylene carbonate (EC) and propylene carbonate (PC).

[0092] As an 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% - 34% or 25.5% - 34%, or within the range formed by any two of the above point values as the end values. The same applies hereinafter. Controlling the mass content of the first solvent in the electrolyte within this optional range can enable the battery to have better cycle performance.

[0093] 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 within the range formed by any two of the above point values as the 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 this optional range can make the battery have better cycling performance, especially high-temperature cycling performance.

[0094] In some embodiments of the present application, the structure of the ethylene carbonate derivative in the second additive is as follows: , R 1 and R 2 each independently includes any one of a hydrogen element, a halogen element, an alkyl group having 1 to 5 carbon atoms, and a halogenated alkyl group having 1 to 5 carbon atoms, and R 1 and R 2 are not simultaneously hydrogen elements. Further, the halogen element includes at least one of a fluorine element, a chlorine element, and a bromine element, and the alkyl group having 1 to 5 carbon atoms and the halogenated alkyl group having 1 to 5 carbon atoms include, but are not limited to, at least one of halogenated or unhalogenated methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, and their isomers. These second additives have good film-forming properties, electrical conductivity, and stability, and can improve the fast charging performance and cycling performance of the battery, especially room-temperature cycling performance.

[0095] Further, the above ethylene carbonate derivative includes at least one of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), and trifluoromethyl carbonate.

[0096] 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 within the range formed by any two of the above point values as the 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 this optional range can make the battery have better fast charging performance and cycling performance, especially room-temperature cycling performance.

[0097] 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 may 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%; more preferably 3% to 8%. Controlling the total mass of the first additive and the second additive within the above range can improve the cycling performance of the battery.

[0098] In some embodiments of the present application, the electrolyte further includes a second solvent. Further, the second solvent includes at least one of linear carbonates, carboxylates, ethers, nitriles, and sulfones. The second solvent and the first solvent together serve as solvents, and their function is to lower the melting point and viscosity of the electrolyte system and improve the lithium ion transport performance of the electrolyte.

[0099] Further, the linear carbonate includes at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC).

[0100] Further, the carboxylate includes at least one of methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate, methyl propionate, ethyl propionate (EP), propyl propionate, methyl butyrate, ethyl butyrate, and 1,4-butyrolactone. In some embodiments of the present application, the second solvent includes a carboxylate.

[0101] Further, the ether includes but is not limited to at least one of diethyl ether and 1,2-dimethoxyethane (DME, also known as ethylene glycol dimethyl ether).

[0102] Further, the nitrile includes but is not limited to acetonitrile (AN).

[0103] Further, the sulfone includes but is not limited to at least one of sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0104] Further, the mass content of the second solvent in the electrolyte is 17% to 63.75%; as this 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 carboxylate in the electrolyte is 25.5% to 51%, 25.5% to 63.75%. In a specific example, the second solvent is a carboxylate.

[0105] In some embodiments of the present application, the electrolyte salt includes a lithium salt, and the lithium salt includes lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ), lithium hexafluoroarsenate (LiAsF 6 ), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS, CF 3 SO 2 Li), lithium difluorophosphate (LiPO 2 F 2 ), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium difluoro(dioxalato)phosphate (LiDFOP), and lithium tetrafluoro(oxalato)phosphate (LiTFOP), or at least one of them.

[0106] In some embodiments of the present application, the mass content of the lithium salt in the electrolyte is 10% - 20%. As an example, it can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or within the range formed by any two of the above point values as the end values.

[0107] In some embodiments of the present application, the concentration of the lithium salt in the electrolyte is 0.8 mol / L - 1.5 mol / L. As an 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 within the range formed by any two of the above point values as the end values.

[0108] Optionally, the lithium salt includes at least one of a fluorosulfonylimide salt and LiPF 6 . More optionally, the fluorosulfonylimide salt includes at least one of LiFSI and LiTFSI.

[0109] Further, the lithium salt includes LiFSI and LiPF 6 . Even further, the concentration of LiFSI in the electrolyte is 0.2 mol / L - 0.5 mol / L; even further, the concentration of LiPF 6 in the electrolyte is 0.5 mol / L - 1.3 mol / L. Further, the molar ratio of LiFSI and LiPF 6 is (2 - 5):10. Lithium bis(fluorosulfonyl)imide LiFSI has good conductivity and heat resistance, and is not easily hydrolyzed at high temperatures, and is particularly suitable for the high energy density system with large heat generation in the present application; however, when the temperature is too high, for example, above 200 °C, LiFSI will decompose and generate heat, deteriorating the safety margin of the battery cell. Therefore, LiPF6 As lithium salts together, they can also effectively improve the safety performance of the battery.

[0110] In some embodiments of the present application, the mass of the electrolyte per unit battery rated capacity of 1 Ah of the secondary battery is 2.2 g to 3.0 g. As an example, it 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, 3.0 g. Further, it can be 2.2 g to 2.8 g or 2.5 g to 3.0 g. The above electrolyte of the present application is particularly suitable for batteries with a low electrolyte injection coefficient system. The consumption rate of this electrolyte is relatively low and the kinetics is better. Therefore, it can improve the batteries with a low electrolyte injection coefficient system and enhance their battery cycling performance.

[0111] The test method for the mass of the electrolyte per unit battery rated capacity of 1 Ah of the secondary battery is as follows: ① Take the battery and weigh the mass of the battery as M 0 ; ② Disassemble the battery, pour out the free electrolyte, and take out the electrode sheet, separator, mechanical parts and adhesive tape; ③ Immerse and clean the electrode sheet, separator, mechanical parts and adhesive tape with dimethyl carbonate (DMC) respectively for 24 h, and wash repeatedly for more than 3 times; ④ After cleaning, place the electrode sheet, separator, mechanical parts and adhesive tape in an oven until completely dried; ⑤ Weigh the electrode sheet, separator, mechanical parts and adhesive tape, and record the mass as M 1 ; ⑥ The mass of the electrolyte per unit battery rated capacity of 1 Ah of the secondary battery = (M 0 - M 1 ) / a. a = the battery rated capacity of the secondary battery, unit Ah.

[0112] Positive electrode sheet As a non-limiting example, the positive current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive current collector.

[0113] In some embodiments, the positive current collector can be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector can include a polymer material 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 substrate. In the positive current collector, non-limiting examples of the metal material can include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc. In the positive current collector, non-limiting examples of the polymer material substrate can include at least one of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0114] In some embodiments, the thickness of the positive current collector is from 10 μm to 15 μm, and optionally from 12 μm to 15 μm. Exemplarily, the thickness of the positive current collector is 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm or a range composed of any two of the above values.

[0115] When the thickness of the positive current collector is within the above range, the current-carrying capacity of the positive current collector is relatively excellent, and the battery cell can have a relatively high energy density.

[0116] In some embodiments of the present application, the thickness of the positive current collector has the meaning well-known in the art and can be detected by devices and methods well-known in the art. For example, the thickness of the positive electrode sheet is measured with a micrometer, the film layer on the surface of the positive current collector is removed, and the thickness of the positive current collector is measured with a micrometer.

[0117] The positive electrode film layer is usually formed by coating a positive electrode slurry on the positive current collector and drying and cold pressing. The positive electrode slurry is usually formed by dispersing a positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring evenly. The solvent can be N-methylpyrrolidone (NMP), but is not limited thereto.

[0118] The positive electrode sheet does not exclude other additional functional layers other than the positive electrode film layer. For example, in some embodiments, the positive electrode sheet of the present application embodiment further includes a positive electrode conductive layer disposed between the positive current collector and the positive electrode film layer. In some other embodiments, the positive electrode sheet of the present application embodiment further includes a protective layer covering the surface of the positive electrode film layer.

[0119] The positive electrode active material can be a positive electrode active material well-known in the art for batteries. In some of these embodiments, the powder compaction density of the positive electrode active material under 30,000 N ≥ 2.43 g / cm 3 , and optionally 2.48 g / cm 3 ~2.85 g / cm 3 . Further, the powder compaction density of the positive electrode active material under 30,000 N is 2.5 g / cm 3 ~2.8 g / cm 3 .

[0120] Using the positive electrode active material with a relatively high powder compaction density can increase the compaction density of the positive electrode sheet, thereby further improving the energy density of the battery.

[0121] As an example, the powder compaction density of the positive electrode active material in the positive electrode sheet under 30,000 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 .

[0122] In the embodiments of the present application, the compaction and densification of the positive electrode active material powder are well-known to those skilled in the art. A compaction density tester can be used for testing with reference to GB / T 24533-2009, and the test pressure is 30,000 N.

[0123] As a non-limiting example, the positive electrode active material may include at least one of the following materials: phosphate-based positive electrode materials, lithium transition metal oxides, and their respective modified compounds. Among them, the phosphate-based positive electrode materials include at least one of olivine-structured lithium-containing phosphates and their derivatives.

[0124] Furthermore, the positive electrode active material includes at least one of olivine-structured lithium-containing phosphates and their derivatives. The particle size of the lithium-containing phosphate and its derivative-based positive electrode active material is smaller, the specific surface area is larger, and it is easy to absorb water. Therefore, the hydrolysis of the electrolyte in this system of the battery is more serious, and thus more HF is generated by hydrolysis. Therefore, the problem of electrolyte consumption is more prominent. Using the above electrolyte can help to exert its advantage of slower electrolyte consumption rate, thereby improving the cycle performance of such batteries. At the same time, it is beneficial to exert the advantages of large energy density, long cycle life, and good safety performance of the lithium-containing phosphate and its derivatives.

[0125] In some embodiments of the present application, the olivine-structured lithium-containing phosphate and its derivatives include the general formula Li x1 A1 y1 M1 a1 M2 b1 P 1-c1 X c1 Q1 z1A compound, wherein 0.5 ≤ x1 ≤ 1.3, 0 ≤ y1 ≤ 1.3, and 0.9 ≤ x1 + y1 ≤ 1.3; 0.9 ≤ a1 ≤ 1.5, 0 ≤ b1 ≤ 0.5, and 0.9 ≤ a1 + b1 ≤ 1.5; 0 ≤ c1 ≤ 0.5; 3 ≤ z1 ≤ 5; A1 includes at least one of Na, K, and Mg; M1 includes at least one of Mn, Fe, Co, and Ni; M2 includes at least one of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X includes at least one of S, Si, Cl, B, C, N, and P; Q1 includes at least one of O and F. The lithium-containing phosphate with olivine structure has excellent cycle stability, which is beneficial to improving the cycle performance of the battery cell.

[0126] Furthermore, Li x1 A1 y1 M1 a1 M2 b1 P 1-c1 X c1 Q1 z1 The compound of includes lithium iron phosphate (LiFePO 4 ), lithium manganese phosphate (LiMnPO 4 ), lithium nickel phosphate (LiNiPO 4 ), and lithium cobalt phosphate (LiCoPO 4 ), and may also be a doped compound of these compounds.

[0127] The lithium-containing phosphate with olivine structure and its derivatives may or may not contain a coating layer. In some embodiments of the present application, the positive electrode active material includes a core and an ion-conducting layer. The core includes at least one of the lithium-containing phosphate with olivine structure and its derivatives, and the ion-conducting layer is coated on the surface of the core. The ion-conducting layer includes at least one element of Fe, C, Ti, Zr, Hf, Ge, and Sn.

[0128] By coating the surface of the core with the ion-conducting layer, the conductivity of the lithium-containing phosphate with olivine structure and its derivatives can be improved, the powder resistivity of the material can be reduced, the migration rate of lithium ions is facilitated, the fast charging ability of the battery can be improved, and the heat generation of the battery cell can be reduced.

[0129] Furthermore, the ion-conducting layer includes a chemical formula of Li 3-b Fe 2-b M3 b (PO m ) nThe ion conductor M3 includes at least one element of Ti, Zr, Hf, Ge and Sn with a valence of +4, 0≤b≤1, 3≤m≤5, 2≤n≤4.

[0130] Exemplarily, the ion conductor is a material having a NASICON structure, for example, lithium iron titanium phosphate Li 2 FeTi(PO 4 ) 3 、Lithium Zirconium Iron Phosphate Li 2 FeZr(PO 4 ) 3 、Lithium iron tin phosphate Li 2 FeSn(PO 4 ) 3 One or more of .

[0131] Ion conductors with NASICON structures are materials with ultrafast ion conduction capabilities, rich three-dimensional lithium ion diffusion and transmission channels, and have the advantages of high ion conduction efficiency and strong structural stability during multiple lithium stripping and insertion processes. Coating the surface of the core with an ion conductor containing a NASICON structure can significantly increase the transmission rate of lithium ions in multiple lithium stripping / insertion at the positive terminal, improve the ionic conductivity of the positive electrode active material, and improve the rapid charging capability of the battery cell. In addition, it can also increase the gram capacity and the energy density of the corresponding battery cell.

[0132] In some embodiments, the ion-conducting layer further includes carbon to further improve the material.

[0133] The carbon element and the ion conductor can be arranged in layers, for example, the carbon element is used as an independent carbon coating layer, and the ion conductor is used as an independent ion conductor layer. The carbon coating layer can be coated on the surface of the core portion, and the ion conductor layer is located on the surface of the carbon coating layer, that is, the ion conductor layer is located on the side of the carbon coating layer away from the core portion; or the ion conductor layer can be coated on the surface of the core portion, and the carbon coating layer is located on the surface of the ion conductor layer, that is, the carbon coating layer is located on the side of the ion conductor layer away from the core portion. Of course, the carbon element and the ion conductor can also be arranged in the same layer.

[0134] Optionally, the carbon coating layer can be made of an organic carbon source, such as glucose, polyethylene glycol, etc., and coated on the surface of the ion conductor layer through a carbonization process. The carbon coating layer can partially cover the ion conductor layer, or it can completely cover the ion conductor layer. The provision of the carbon coating layer can significantly improve the electronic conductivity of the core, make up for the defect of poor electronic conductivity of the core, and improve the energy density of the battery cell.

[0135] Specifically, the provision of the carbon coating layer enables the positive electrode active material of the present application to have the following advantages: The carbon coating layer in the positive electrode active material of the present application provides a suitable channel for the transmission of electrons, which can significantly improve the conduction rate of electrons during multiple de-lithiation and intercalation processes, improve the electronic conductivity of lithium-containing phosphate, improve the charging ability of the corresponding battery monomer, and also improve the energy density.

[0136] The carbon coating layer of the positive electrode active material of the present application has a loose and porous structure, which enables the electrolyte to come into full and effective contact with the lithium-containing phosphate, thereby improving the transmission rate of lithium ions at the phase interface and improving the charging ability of the battery monomer.

[0137] Coating a layer of carbon coating on the surface of lithium-containing phosphate can not only improve the conductivity of lithium-containing phosphate, but also improve the structural stability of the positive electrode active material, effectively preventing the iron dissolution phenomenon of the positive electrode active material during the long-term storage and cyclic use of the battery monomer, thereby ensuring the cycle life of the battery monomer.

[0138] The positive electrode active material of the present application uses lithium-containing phosphate as the base material, giving full play to the advantages of low cost, high use reliability, and good cycle stability of lithium-containing phosphate. At the same time, the ion-conducting layer (ion conductor layer and carbon coating layer) is used to solve the disadvantages of poor electronic conductivity and ion conductivity. The battery monomer prepared from the positive electrode active material of the present application has a significantly improved energy density on the premise of excellent cycle performance.

[0139] In some embodiments, the mass content of carbon in the positive electrode active material is 1% - 2%. As an example, it can be 1%, 1.5%, or 2%. Controlling the mass content of carbon in the positive electrode active material within this range can further improve the conductivity of the positive electrode active material and thus improve the fast charging performance of the battery. It is understandable that the carbon element can come from, but is not limited to, the coated carbon layer. As an example, the surface of olivine-structured lithium-containing phosphate and its derivatives is coated with a carbon coating layer.

[0140] 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. As an example, the powder resistivity of the positive electrode active material can be 20 Ω•cm, 15 Ω•cm, 10 Ω•cm, 8 Ω•cm, 5 Ω•cm, etc., and optionally ≤11 Ω•cm.

[0141] In some embodiments, the volume average particle size of the positive electrode active material satisfies: 1 µm ≤ Dv50 ≤ 2 µm, 0.4 µm ≤ Dv10 ≤ 0.7 µm, which further improves the fast charging and power performance of the battery. As an example, the Dv50 particle size of the positive electrode active material can be 1 µm, 1.5 µm, or 2 µm. As an example, the volume average particle size Dv10 of the positive electrode active material can be 0.4 µm, 0.5 µm, 0.6 µm, or 0.7 µm.

[0142] In this text, Dv50 and Dv10 have meanings well-known in the art and can be tested using methods known in the art. For example, they can be measured using a laser particle size analyzer (such as Malvern Master Size 3000). Among them, Dv50 represents the particle size corresponding to when the cumulative volume percentage of particles reaches 50% starting from the smaller particle size according to the particle size volume distribution. Dv10 represents the particle size corresponding to when the cumulative volume percentage of particles reaches 10% starting from the smaller particle size according to the particle size volume distribution.

[0143] The particle size volume distribution can be obtained through the following method: Take a clean beaker, add an appropriate amount of the sample to be tested, and ultrasonically treat it sufficiently to ensure complete dispersion of the sample. The testing instrument is Malvern 2000 from the United States. After the sample is poured into the injection tower, it circulates with the solution to the test optical path system. When the particles are irradiated by the laser beam, the particle size distribution characteristics of the particles can be obtained by receiving and measuring the energy distribution of the scattered light (light obscuration: 8% - 12%). Draw a particle size volume distribution diagram based on the test data.

[0144] In some of these embodiments, the positive electrode film layer further includes a lithium supplementing agent. Further, the lithium supplementing agent includes at least one of ternary lithium supplementing materials, lithium phosphate, lithium hydrogen phosphate, lithium sulfate, lithium sulfite, lithium molybdate, lithium nickelate, lithium ferrate, lithium oxalate, lithium titanate, lithium tetraborate, lithium metasilicate, lithium manganite, lithium tartrate, and trilithium citrate.

[0145] Further, the ternary lithium supplementing material includes Li x2 A2 y2 Ni a2 Co b2 Mn c2 M4 (1-a2-b2-c2) Q2 z2 , where 0 < x2 ≤ 2.1, 0 ≤ y2 ≤ 2.1; 0 ≤ a2 ≤ 1, 0 ≤ b2 ≤ 1, 0 ≤ c2 ≤ 1, and 0.1 ≤ a2 + b2 + c2 ≤ 1; 1.8 ≤ z2 ≤ 3.5; A2 includes at least one of Na, K, and Mg; M4 includes at least one of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; Q2 includes at least one of O and F.

[0146] Even further, 0.9 ≤ x2 + y2 ≤ 2.1.

[0147] The lithium supplement agent can be in the same layer as the cathode active material or in different layers. When the lithium supplement agent and the cathode active material are in different layers, the lithium supplement agent can be in the lithium supplement layer and the cathode active material can be in the cathode active material layer. In other words, the cathode film layer includes a lithium supplement layer and a cathode active material layer. The cathode active material layer can be disposed on at least one side of the cathode current collector, and the lithium supplement layer can be located between the cathode active material layer and the cathode current collector. Alternatively, the lithium supplement layer can be disposed on at least one side of the cathode current collector, and the cathode active material layer can be located between the lithium supplement layer and the cathode current collector. Optionally, the lithium supplement layer can be located between the cathode active material layer and the cathode current collector.

[0148] In some of these embodiments, in the cathode film layer, the mass content of the cathode active material is 80% - 98%. As an example, this mass content can be 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 96%, 98%. Further, in the cathode film layer, the mass content of the cathode active material can be 90% - 98%.

[0149] In some of these embodiments, the cathode film layer may also optionally include a binder. As a non-limiting example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin. In some embodiments, based on the total mass of the cathode film layer, the mass content of the binder is ≤5%.

[0150] In some of these embodiments, the cathode film layer may also optionally include a conductive agent. As a non-limiting example, the conductive agent can include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, based on the total mass of the cathode film layer, the mass content of the conductive agent is ≤5%.

[0151] In some of these embodiments, the cathode electrode sheet can be prepared by the following method: dispersing the components for preparing the cathode electrode sheet described above, such as the cathode active material, the conductive agent, the binder, and any other components, in a solvent to form a cathode slurry; coating the cathode slurry on at least one surface of the cathode current collector, and after processes such as drying and cold pressing, the cathode electrode sheet can be obtained. The type of the solvent can be selected from, but not limited to, any one of the foregoing embodiments, such as N-methylpyrrolidone (NMP). The surface of the cathode current collector on which the cathode slurry is coated can be a single surface of the cathode current collector or two surfaces of the cathode current collector.

[0152] In some of these embodiments, the positive electrode tab further includes a positive electrode conductive layer disposed between the positive electrode current collector and at least one side of the positive electrode film layer. The positive electrode conductive layer includes a conductive agent. The positive electrode conductive layer can also be formed by first coating the surface of the positive electrode current collector with a corresponding slurry and then coating the above-mentioned positive electrode slurry and drying it. 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 beneficial to improving the electron transfer rate.

[0153] Further, the conductive agent includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0154] Further, the thickness of the positive electrode conductive layer is 0.5 μm to 2 μm. As an example, it can be 0.5 μm, 1 μm, 1.5 μm, 2 μm, or within the range formed by any two of the above point values as the end values. When the thickness of the positive electrode conductive layer is within the above range, it can further improve the conductive performance of the positive electrode tab and can also take into account the improvement of the energy density of the battery cell.

[0155] Further, the positive electrode conductive layer further includes a binder. Further, the binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and fluorinated acrylate resins. The binder in the positive electrode conductive layer can improve the adhesion between the positive electrode current collector and the positive electrode film layer and enhance the structural stability of the positive electrode tab.

[0156] Optionally, in the positive electrode conductive layer, the mass content of the conductive agent is 30% to 50%. As an example, it can be 30%, 35%, 40%, 45%, 50%. Optionally, in the positive electrode conductive layer, the mass content of the binder is 50% to 70%, and it can be 50%, 55%, 60%, 65%, 70%. In some examples, the positive electrode conductive layer is composed of a conductive agent and a binder.

[0157] Negative electrode tab As a non-limiting example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0158] In some of these embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, a copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be obtained by forming a metal material on the polymer material substrate. In the negative electrode current collector, non-limiting examples of the metal material may include at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc. In the negative electrode current collector, non-limiting examples of the polymer material substrate may include at least one of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE), etc.

[0159] Understandably, the above-mentioned negative electrode film layer may contain one or more graphites with a powder compaction density of 1.5 g / cm 3 ~1.85 g / cm 3 under 20000 N.

[0160] As described above, the negative electrode active material includes graphite, and the powder compaction density of the negative electrode active material is 1.5 g / cm 3 ~1.85 g / cm 3 under 20000 N. As an example, it may be but is 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 within the range formed by any two of the above point values as the end values. Using the graphite with such a high powder compaction density makes the secondary battery have a higher energy density. Optionally, the powder compaction density of the graphite is 1.6 g / cm 3 ~1.85 g / cm 3 under 20000 N. Optionally, the powder compaction density of the graphite is 1.55 g / cm 3 ~1.75 g / cm 3 under 20000 N.

[0161] In some of these embodiments, the compaction density of the negative electrode sheet of the above-mentioned secondary battery in the 100% SOC state 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 charge. Exemplarily, the compaction density of the negative electrode sheet of the secondary battery at 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 / cm 3 , 1.46 g / cm 3 or a range composed of any two of the above values. The higher the full charge compaction density of the negative electrode sheet, the lower the rebound, indicating that the expansion force of the battery is smaller. When the compaction density of the negative electrode film layer is within the above range, it not only has a high energy density but also is beneficial to improving the cycle performance of the battery.

[0162] In some embodiments of the present application, the compaction density of the negative electrode sheet of the secondary battery in the 100% SOC state has the meaning well known in the art, that is, the negative electrode sheet is disassembled from the battery cell charged to 100% state of charge (SOC), and the compaction density of the negative electrode film layer is measured.

[0163] In some embodiments of the present application, the 100% SOC state of the secondary battery is defined as follows: The battery cell is charged at a constant current charging rate of 0.33C to the upper limit voltage of the battery, and then charged at a constant voltage to 0.05C, corresponding to the 100% SOC state of the battery cell. Correspondingly, the battery cell is discharged at a constant current discharge rate of 0.33C to the cut-off voltage, corresponding to the 0% SOC state of the battery cell.

[0164] Due to the different types of cathode active materials in the battery, the cut-off voltage for full charge may also be different. Exemplarily, the upper limit voltage for battery charging can be 3.65V, 3.8V; the cut-off voltage for battery discharging can be 2.5V, 2.0V. Taking the cathode active material in the cathode electrode sheet as lithium iron phosphate as an example, the secondary battery is charged at a charging rate of 0.33C to 3.65V, and then charged at a constant voltage until 0.05C, corresponding to the state of 100% SOC of the battery cell. At this time, the compaction density of the anode electrode sheet is 1.15g / cm 3 ~1.46g / cm 3 .

[0165] In some of these embodiments, the compaction density of the above-mentioned anode electrode sheet after cold pressing is 1.5g / cm 3 ~1.8g / cm 3 , and can be optionally 1.6g / cm 3 ~1.75g / cm 3 . The compaction density of the anode electrode sheet after cold pressing refers to the compaction density of the anode electrode sheet before it is assembled into a battery after cold pressing and forming.

[0166] The lower the full charge compaction density of the anode electrode sheet, the greater the rebound thickness or the lower the initial compaction density, and the stronger the graphite activity. Therefore, more electrolyte needs to be consumed, and more additives need to be added to the electrolyte; to enhance the interfacial film stability of the anode electrode sheet and improve the cycle performance of the battery. Moreover, the higher the full charge compaction density of the anode electrode sheet, the higher the energy density of the battery, the smaller the space reserved for the electrolyte, and the lower the electrolyte filling amount. Therefore, in order to improve the fast charging performance of the battery, the concentration of the first additive in the electrolyte needs to be higher. Therefore, there is a matching relationship between the compaction density of the anode electrode sheet and the mass content of the first additive in the electrolyte.

[0167] In some of these embodiments, the compaction density of the anode electrode sheet of the secondary battery in the 100% SOC state is ≥1.25g / cm 3 and <1.35g / cm 3 .

[0168] Furthermore, when the compaction density of the anode electrode sheet of the secondary battery in the 100% SOC state is ≥1.25g / cm 3 and <1.35g / cm 3 , the mass content of the first additive in the electrolyte is 1.5% - 6%. Thus, when the compaction density of the anode electrode sheet of the secondary battery in the 100% SOC state is within the above range and the mass content of the first additive in the electrolyte is 1.5% - 6%, the battery can better balance the higher energy density and fast charging performance at the same time.

[0169] The film-forming impedance of the second additive in the electrolyte is relatively low, which can improve the kinetic performance of the battery and thus enhance the fast charging performance of the battery. However, its content should not be too high 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 filling amount of the electrolyte. Therefore, in order to improve the fast charging performance of the battery, the concentration of the second additive in the electrolyte needs to be higher. 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.

[0170] Further, when the compaction density of the negative electrode sheet of the secondary battery is ≥ 1.25 g / cm 3 and < 1.35 g / cm 3 at the 100% SOC state, the mass content of the second additive in the electrolyte is 0.5% - 3%.

[0171] Further, when the compaction density of the negative electrode sheet of the secondary battery is ≥ 1.25 g / cm 3 and < 1.35 g / cm 3 at the 100% SOC state, the mass content of the first solvent in the electrolyte is 22.5% - 34%, and can be optionally 25.5% - 34%.

[0172] Further, when the compaction density of the negative electrode sheet of the secondary battery is ≥ 1.25 g / cm 3 and < 1.35 g / cm 3 at the 100% SOC state, the mass of the electrolyte per unit battery rated capacity of 1 Ah of the secondary battery is 2.5 g - 3.0 g.

[0173] In some embodiments, the compaction density of the negative electrode sheet of the secondary battery is 1.35 g / cm 3 - 1.40 g / cm 3 .

[0174] Further, when the compaction density of the negative electrode sheet of the secondary battery is 1.35 g / cm 3 - 1.40 g / cm 3 at the 100% SOC state, the mass content of the first additive in the electrolyte is 2.5% - 7%. Thus, when the compaction density of the negative electrode sheet of the secondary battery is within the above range at the 100% SOC state, the mass content of the first additive in the electrolyte is 2.5% - 7%, which can enable the battery to better balance the higher energy density and the fast charging performance.

[0175] Further, when the compaction density of the negative electrode sheet of the secondary battery is 1.35 g / cm 3 - 1.40 g / cm 3, the mass content of the second additive in the electrolyte is 0.7% to 3.5%, and can be optionally 1.5% to 3.5%. Further, when the negative electrode sheet of the secondary battery has a tap density of 1.35 g / cm 3 ~1.40 g / cm 3 , the mass content of the first solvent in the electrolyte is 21.25% to 34%.

[0176] Further, when the negative electrode sheet of the secondary battery has a tap density of 1.35 g / cm 3 ~1.40 g / cm 3 , the mass of the electrolyte per unit battery rated capacity of 1 Ah of the secondary battery is 2.2 g to 2.8 g.

[0177] In some embodiments, the volumetric energy density of the secondary battery is 400 Wh / L to 450 Wh / L. The mass content of the carboxylic 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%. When the volumetric energy density of the secondary battery is in this higher energy density range, adding carboxylic ester to the organic solvent of the electrolyte can improve the fast charging performance of the secondary battery. However, the content of carboxylic ester should not be too high, as too high a content will cause gas generation in the negative electrode sheet of the graphite system, leading to deterioration of the cycle performance. Therefore, the dosages of the first additive and the second additive are further increased to improve the cycle life of the battery. Further, the tap density of the cold-pressed negative electrode sheet is 1.55 g / cm 3 ~1.65 g / cm 3 .

[0178] 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 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%. As the volumetric energy density of the secondary battery increases, correspondingly, it is necessary to increase the content of carboxylic ester and the content of the first additive and the second additive in the electrolyte to achieve good cycle life at this higher energy density.

[0179] Further, the tap density of the cold-pressed negative electrode sheet is 1.6 g / cm 3 ~1.7 g / cm 3 , In some of these embodiments, the charging time of the secondary battery from 10% SOC to 80% SOC at 30 °C is 6 min to 15 min. The mass content of the carboxylic ester in the 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%, optionally 5% to 7%. Thus, on the basis of using high-voltage dense graphite to provide a relatively high energy density, this battery is also a fast-charging type battery. By adding the carboxylic ester with the above content to the electrolyte and increasing the dosage of the first additive and the second additive, the secondary battery has both a relatively high energy density, fast-charging performance, and cycling performance. Further, in the electrolyte, the mass content of the first additive is 1.5% to 6.5%, optionally 3.5% to 5.5%, and the mass content of the second additive is 0.5% to 6.5%, optionally 1.5% to 3.5%.

[0180] In some embodiments, during the charging process of the secondary battery from 10% state of charge to 80% state of charge, it includes multiple charging steps. The difference between the maximum state of charge of any charging step and the maximum state of charge of its adjacent charging step in the multiple charging steps is less than or equal to 5% state of charge, such as 1% state of charge, 1.5% state of charge, 2% state of charge, 2.5% state of charge, 3% state of charge, 3.5% state of charge, 4% state of charge, 4.5% state of charge, 5% state of charge, or a range composed of any two of the above values.

[0181] The secondary battery from 10% state of charge to 40% state of charge includes multiple charging steps. For any charging step, it can be charged at any rate between 5C and 10C. The charging rate corresponding to each charging step can be any value among 5C, 5.5C, 6C, 6.5C, 7C, 7.5C, 8C, 8.5C, 9C, 9.5C, 10C, or a value within a range composed of any two of the above values.

[0182] The secondary battery from 40% state of charge to 80% state of charge also includes multiple charging steps. The charging rate of any charging step is less than the charging rate of any charging step from 10% state of charge to 40% state of charge, and the charging rate of the step of charging to 80% state of charge is any value between 2.5C and 5C. For example, it can be 2.7C.

[0183] Exemplarily, the charging steps of the secondary battery from 10% SOC to 80% SOC can be carried out in the following manner: Charge from 10% SOC to 15% SOC at a constant current of 5.0C; Charge from 15% SOC to 20% SOC at a constant current of 5.0C; Charge from 20% SOC to 25% SOC at a constant current of 5.0C; Charge from 25% SOC to 30% SOC at a constant current of 5.0C; Charge from 30% SOC to 35% SOC at a constant current of 5.0C; Charge from 35% SOC to 40% SOC at a constant current of 5.0C; Charge from 40% SOC to 45% SOC at a constant current of 4.6C; Charge from 45% SOC to 50% SOC at a constant current of 4.3C; Charge from 50% SOC to 55% SOC at a constant current of 4.0C; Charge from 55% SOC to 60% SOC at a constant current of 3.7C; Charge from 60% SOC to 65% SOC at a constant current of 3.4C; Charge from 65% SOC to 70% SOC at a constant current of 3.1C; Charge from 70% SOC to 75% SOC at a constant current of 2.9C; Charge from 75% SOC to 80% SOC at a constant current of 2.7C.

[0184] 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 composed of any two of the above values.

[0185] Optionally, the negative electrode tab further includes a negative electrode conductive layer, and the negative electrode conductive layer is disposed between the negative electrode current collector and at least one side of the negative electrode film layer. The negative electrode conductive layer includes a conductive agent. The negative electrode conductive layer can also be formed by first coating the surface of the negative electrode current collector with a corresponding slurry, and then coating the above-mentioned negative electrode slurry and drying. Further, the conductive agent in the negative electrode conductive layer includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. 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 beneficial to improving the electron transfer rate.

[0186] Optionally, the thickness of the negative electrode conductive layer is 0.5 μm to 2 μm, and as an example, it can be 0.5 μm, 1 μm, 1.5 μm, 2 μm.

[0187] In some of these embodiments, the negative electrode conductive layer includes a binder, and the binder includes at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin, water-based acrylic resin, polyvinyl alcohol, sodium alginate, and carboxymethyl chitosan.

[0188] Optionally, 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%.

[0189] Furthermore, the graphite includes at least one of artificial graphite and natural graphite. Further, artificial graphite is used. Artificial graphite has fewer surface active sites and a lower consumption rate of the first solvent and the first additive in the electrolyte, which can meet the requirements of the long life of the battery. Further, the discharge specific capacity of the graphite is ≤ 358 mAh / g. When the specific capacity of the graphite is within this range, the activity of the graphite is appropriate, which is beneficial to reducing the consumption rate of the electrolyte and thus improving the cycle performance of the battery.

[0190] In some of these embodiments, in the negative electrode film layer, the mass content of the negative electrode active material is 94% - 98%. As an example, this mass content can be 94%, 96%, or 98%.

[0191] In some of these embodiments, the negative electrode film layer may further optionally include a binder. The binder may include at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0192] In some of these embodiments, the negative electrode film layer may further optionally include a conductive agent. The conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0193] In some of these embodiments, the negative electrode film layer may further optionally include other additives, such as a thickening agent (such as sodium carboxymethyl cellulose (CMC-Na)), etc.

[0194] In some of these embodiments, the negative electrode plate can be prepared in the following manner: dispersing the above components for preparing the negative electrode plate, 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 surface of the negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode plate can be obtained. The surface of the negative electrode current collector on which the negative electrode slurry is coated can be a single surface of the negative electrode current collector or two surfaces of the negative electrode current collector.

[0195] In some of these embodiments, the negative electrode film layer includes at least one negative electrode active layer, and at least one negative electrode active layer includes the graphite.

[0196] In a specific example, the negative electrode film layer includes 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.

[0197] In another specific example, the negative electrode film layer includes a first negative electrode active layer and a second negative electrode active layer that are sequentially stacked on the same side of the negative electrode current collector. The graphite includes at least one of artificial graphite and natural graphite. The graphite in the first negative electrode active layer includes at least one of artificial graphite and natural graphite, and the graphite in the second negative electrode active layer includes artificial graphite. The surface of artificial graphite has fewer active sites and a lower consumption rate of the first solvent and the first additive in the electrolyte.

[0198] Furthermore, the Dv50 particle size of the graphite in the first negative electrode active layer ≥ the Dv50 particle size of the graphite in the second negative electrode active layer. 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. The pores in the lower first negative electrode active layer are larger, so it has better kinetic performance, which is beneficial to improving the fast charging performance.

[0199] Even further, the Dv50 particle size of the graphite in the first negative electrode active layer > the Dv50 particle size of the graphite in the second negative electrode active layer.

[0200] It can be understood that the first negative electrode active layer and the second negative electrode active layer can be obtained by sequentially stacking and coating two slurries, and then through processes such as drying and cold pressing.

[0201] Furthermore, 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 selected as 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.

[0202] 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 optionally 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.

[0203] Optionally, the mass ratio of the graphite in the first negative electrode active layer to the graphite in the second negative electrode active layer is 3:7 to 7:3; it can be optionally 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.

[0204] Further, in the total amount of graphite in the first negative electrode active layer and the second negative electrode active layer, the mass content of the graphite in the first negative electrode active layer is 30% to 70%. As an example, it can be 30%, 35%, 40%, 45%, 48%, 50%, 55%, 60%, 65%, 70% or a range composed of any two of the above values.

[0205] Further, the proportion of the thickness of the second negative electrode active layer in the total thickness of the first negative electrode active layer and the second negative electrode active layer is 30% to 70%. For example, it can be 30%, 40%, 50%, 60%, 70% or within a range with any two of the above point values as the end values, and can be optionally 40% to 60%.

[0206] In some embodiments, the artificial graphite includes graphite body particles and a coating layer. The graphite body particles include secondary particles aggregated by a plurality of primary particles. The coating layer is coated on the surface of the body particles, and the coating layer includes amorphous carbon.

[0207] Further, based on the total mass of the artificial graphite, the mass content of the amorphous carbon is 2% to 5%. As an example, it can be 2%, 3%, 4%, 5% or within a range with any two of the above point values as the end values.

[0208] Further, the powder resistivity of the artificial graphite is ≤0.04 Ω•cm.

[0209] In some embodiments, the charging gram capacity of the graphite in the coin cell at a 0.1C rate is ≥350 mAh / g, and can be optionally 350 mAh / g to 440 mAh / g.

[0210] In some of these embodiments, the negative electrode active material may include, in addition to the above-mentioned graphite, a silicon-based material. Further, the silicon-based material may include at least one of silicon oxides, silicon-carbon composites, elemental silicon, silicon-nitrogen composites, and silicon alloys. Further, the mass content of silicon element in the silicon-based material in the negative electrode active material is 0.3% to 10%, and may be optionally 1% to 6%.

[0211] Separator In some of these embodiments, the secondary battery further includes a separator. The separator is disposed between the positive electrode plate and the negative electrode plate, mainly serving to prevent short circuit between the positive and negative electrodes, and at the same time allowing ions to pass through.

[0212] In some of these embodiments, the positive electrode plate, the negative electrode plate, and the separator can be made into an electrode assembly by a winding process or a stacking process.

[0213] This application does not particularly limit the type of the separator, and any well-known porous structure separator with good chemical stability and mechanical stability can be selected. The separator can be a single-layer thin film or a multi-layer composite thin film, without particular limitation. When the separator is a multi-layer composite thin film, the materials of each layer can be the same or different, without particular limitation. In some embodiments, the thickness of the separator is 6 μm to 40 μm, and may be optionally 12 μm to 20 μm.

[0214] In some of these embodiments, the separator includes a porous base film and a functional layer disposed on at least one side of the porous base film.

[0215] Further, the material of the porous base film may include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride.

[0216] Further, the thickness of the porous base film ≤ 12 μm, and may be optionally ≤ 9 μm, and may be optionally 6 μm to 9 μm. Exemplarily, the thickness of the base film is 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm or a range composed of any two of the above values.

[0217] When the porosity of the separator in the embodiments of this application is within the above range, the migration ability of lithium ions in the separator can be improved, the internal resistance of the battery cell can be further reduced, and thus the heat generation can be reduced.

[0218] In some embodiments of the present application, porosity refers to the percentage of the pore volume in the separator to the total volume of the separator. The porosity can be tested in accordance with the standard GB / T 36363-2018 "Polyolefin separator for battery monomers". It should be noted that the actual test process can be slightly different from the standard test process to obtain a more accurate test value based on the differences in test instruments, test errors, and in order to eliminate the test effects on porosity as much as possible.

[0219] Further, the porosity of the porous base film is 20% to 70%, and can be 35% to 60%. Exemplarily, the porosity of the base film is 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or a range consisting of any two of the above values.

[0220] When the thickness of the porous base film is within the above range, the migration path of lithium ions in the base film is shorter, which can further reduce the internal resistance of the battery cell and thus reduce heat generation.

[0221] In some embodiments of the present application, the isolation film may be a base film; optionally, the isolation film further comprises a functional layer disposed on at least one side of the base film, and the functional layer may comprise inorganic particles to enhance the heat resistance of the isolation film. Optionally, the functional layer is disposed on both sides of the base film.

[0222] In some embodiments, the functional layer includes a first functional layer and a second functional layer, the first functional layer is located on one side of the base film, the first functional layer includes first inorganic particles, the second functional layer is located on the other side of the base film, the second functional layer includes composite particles, the composite particles include second inorganic particles and non-fluoropolymer particles, the second inorganic particles are attached to the surface of the non-fluoropolymer particles and / or dispersed in the interior of the non-fluoropolymer particles.

[0223] The first functional layer and the second functional layer have good heat resistance and can improve the heat resistance of the isolation film.

[0224] Optionally, the first functional layer may include a binder, optionally including at least one of a fluorine-containing binder or a polyacrylic binder, such as polyvinylidene fluoride.

[0225] Optionally, the first inorganic particles include one or more of silicon oxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide and tin oxide. The first inorganic particles can improve the heat resistance of the first functional layer.

[0226] In some embodiments of the present application, the meaning of the thickness of the base film is the meaning well-known in the art, and it can be detected by using the meaning and equipment well-known in the art. For example, a newly prepared separator film can be taken as a sample, or a battery cell that has been discharged (discharged to the lower cut-off voltage so that the charged state of the battery is about 0% SOC) can be disassembled in reverse, the separator film is obtained from the battery cell, and after drying the separator film, it is used as a sample. The separator film is cut by an ion beam cutter to form a cross-section; subsequently, a scanning electron microscope is used to measure the thickness of the cross-section of the separator film and its respective layers.

[0227] The non-fluoropolymer particles in the second functional layer refer to polymers that are non-fluorinated polymers. For example, the non-fluoropolymer particles include acrylate copolymer particles. Optionally, the acrylate copolymer includes acrylate-acrylonitrile-acrylamide-propylene copolymer, and the acrylate copolymer has excellent adhesion performance and relatively high adhesion stability with the base film. The molar ratio of each monomer in the copolymer can be any ratio, such as a molar ratio of 35%:30%:15%:20%, or 40%, 20%, 10%, 30%, or 45%, 15%, 20%, 20%, etc.

[0228] The second inorganic particles in the composite particles make it difficult for the non-fluoropolymer particles to adhere to each other due to the high-temperature treatment during the granulation process, resulting in pores in the composite particles, which is beneficial to the transport of lithium ions and improves the ion-conducting ability of the separator film; and the second inorganic particles can also increase the compression modulus of the composite particles. During the charge and discharge process, the composite particles are not easily deformed, making the structure of the separator film more stable, which can improve the kinetic performance of the battery cell and the fast-charging performance.

[0229] Optionally, compared with the first functional layer, the second functional layer is disposed closer to the negative electrode tab. Since the composite particles are not easily deformed, the separator film basically does not cause side effects such as extrusion to the negative electrode tab, making the kinetic performance of the negative electrode tab stable. Correspondingly, the first functional layer is disposed closer to the positive electrode tab.

[0230] Optionally, the second inorganic particles include one or more of silicon oxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide; optionally, the second inorganic particles include silicon oxide. The above-mentioned second inorganic particles can improve the heat resistance of the second functional layer and can form composite particles in cooperation with the non-fluoropolymer, further improving the cycle stability and kinetic performance of the separator film, and improving the cycle performance and fast-charging performance of the battery cell.

[0231] The average particle size of the second inorganic particles is from 5 nm to 100 nm, optionally from 10 nm to 100 nm, and optionally from 5 nm to 20 nm. Exemplarily, the average particle size of the second inorganic particles is 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm or a range composed of any two of the above values. When the average particle size of the second inorganic particles is within the above range, it is beneficial to improve the heat resistance and compression modulus of the composite particles.

[0232] In some embodiments of the present application, the average particle size of the second inorganic particles has the meaning well-known in the art and can be detected by using the equipment and methods well-known in the art. For example, after obtaining the separator and drying the separator as a sample, the separator is cut by an ion beam cutter to form a cross-section; subsequently, a scanning electron microscope is used to measure the particle size of the second inorganic particles in the separator, and the particle sizes of multiple, such as 50, second inorganic particles are measured, and the average value thereof is calculated as the average particle size of the second inorganic particles.

[0233] In some embodiments, the ionic conductivity of the separator is from 0.3 mS / cm to 0.6 mS / cm. Exemplarily, the ionic conductivity of the separator is 0.3 mS / cm, 0.35 mS / cm, 0.4 mS / cm, 0.45 mS / cm, 0.5 mS / cm, 0.55 mS / cm, 0.6 mS / cm or a range composed of any two of the above values.

[0234] When the ionic conductivity of the separator is within the above range, the migration ability of lithium ions in the separator can be further improved, and the fast charging performance of the battery cell can be improved.

[0235] In some embodiments of the present application, the ionic conductivity of the separator has the meaning well-known in the art and can be detected by using the equipment and methods well-known in the art. For example, Prepare a 2025-type button battery for testing: In a vacuum glove box, place a lithium sheet in the battery negative electrode case, add 150 μL of electrolyte thereto, and the electrolyte is a solution of 1 M LiPF 6 in EC / EMC / DEC = 3 / 5 / 2 (mass ratio), then place the separator (with an area of 3.14 cm 2 , a thickness of 12 μm) to make it close to the lithium sheet, then add 25 μL of electrolyte, and finally place the positive electrode sheet (the positive electrode sheet can be the positive electrode sheet in Example 1) thereon and encapsulate. Take out the assembled button battery from the vacuum glove box and place it for 24 h for the next test.

[0236] Test: On an electrochemical workstation, at 10-1 ~10 6 Test within the frequency range of Hz to obtain the separator resistance Rb, and calculate the ionic conductivity σ (unit: mS / cm) through the following formula: σ = L / (R b ×S) where: R b is the equivalent resistance, and L and S are the thickness and area of the separator to be measured, respectively.

[0237] The secondary battery includes at least one battery cell. The secondary battery may include one or more battery cells.

[0238] In this application, unless otherwise specified, a "battery cell" refers to a basic unit capable of converting chemical energy and electrical energy into each other. Further, generally, it includes at least a positive electrode plate, a negative electrode plate, and an electrolyte. During the charge and discharge process of the battery, active ions are embedded and extracted back and forth between the positive electrode plate and the negative electrode plate. The electrolyte plays a role in conducting active ions between the positive electrode plate and the negative electrode plate.

[0239] This application does not particularly limit the shape of the battery cell, which can be cylindrical, square, or any other shape. For example, Figure 1 the shown secondary battery is a battery cell, which is an example of the battery cell 5 with a square structure.

[0240] In some embodiments, the battery cell 5 may include an outer package. The outer package can be used to encapsulate the above-mentioned electrode assembly and electrolyte. In some embodiments, the outer package of the battery cell 5 can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the battery cell 5 can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic. Further, non-limiting examples of the plastic can include at least one of polypropylene, polybutylene terephthalate, and polybutylene succinate, etc.

[0241] In some embodiments, referring to Figure 2 , the outer package may include a housing 51 and a cover plate 53. Among them, the housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode plate, the negative electrode plate, and the separator can form an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. The number of the electrode assemblies 52 included in the battery cell 5 can be one or more, and those skilled in the art can select according to actual needs.

[0242] The secondary battery of this application refers to a battery cell.

[0243] In some embodiments, the battery device includes a secondary battery, and the battery device may be a battery module, a battery pack, or an energy storage battery.

[0244] The battery module includes at least one battery cell. The number of battery cells included in the battery module may be one or more, and those skilled in the art can select a suitable number according to the application and capacity of the battery module.

[0245] Figure 3 The shown battery module is the battery module 4 as an example. Refer to Figure 3 , in the battery module 4, a plurality of battery cells 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other way. Further, the plurality of battery cells 5 can be fixed by fasteners.

[0246] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0247] In some of these embodiments, the above battery module can also be assembled into a battery pack. The number of battery modules included in the battery pack may be one or more, and those skilled in the art can select a suitable number according to the application and capacity of the battery pack.

[0248] Figure 4 and Figure 5 are the shown battery pack, which is the battery pack 1 as an example. Refer to Figure 4 and Figure 5 , in the battery pack 1, it may include a battery box and a plurality of battery modules 4 arranged in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any way.

[0249] In addition, an embodiment of the present application further provides an electrical device, which includes at least one of the above secondary battery provided by the present application and the battery device provided by the present application. The electrical device may include mobile devices, electric vehicles, electric trains, ships, satellites, energy storage systems, etc., but is not limited thereto. Among them, the mobile device may be, for example, a mobile phone, a laptop computer, etc.; the electric vehicle may be, for example, a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc., but is not limited thereto.

[0250] As the electrical device, the secondary battery can be selected according to its usage requirements.

[0251] Figure 6The electrical device 6 is taken as an example. The electrical device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc. In order to meet the requirements of the electrical device for the high power and high energy density of the secondary battery, a battery pack or a battery module can be adopted.

[0252] Another example of the device can be a mobile phone, a tablet computer, a laptop computer, etc. The device usually requires being thin and light, and the battery cell 5 can be adopted as the power source.

[0253] In order to make the technical problems, technical solutions and beneficial effects solved by the present application clearer, the present application will be further described in detail below in conjunction with embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and in no way constitutes a limitation to the present application and its application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope protected by the present application.

[0254] For those technical or conditions not specified in the embodiments, they shall be carried out according to the technologies or conditions described in the documents in the art or according to the product specifications. For the reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0255] Embodiment 1 (1)Preparation of the positive electrode plate: The performance parameters of the positive electrode active material lithium iron phosphate LiFePO 4 : The powder compaction density under 30000N is 2.53 g / cm 3 .

[0256] Mix the positive electrode active material lithium iron phosphate LiFePO 4 , the binder polyvinylidene fluoride, and the conductive agent acetylene black in a mass ratio of 97:2:1, and then add the solvent N-methylpyrrolidone (NMP) and stir evenly to form a positive electrode slurry; coat the positive electrode slurry evenly on the positive electrode current collector aluminum foil, and after drying and cold pressing, obtain the positive electrode plate.

[0257] Among them, the coating weight of the positive electrode plate is 300 mg / 1540.25 mm 2 ; When the battery is charged at a charging rate of 0.33C to 100% SOC, the compaction density of the positive electrode plate is 2.63 g / cm 3 .

[0258] (2)Preparation of the negative electrode plate: The preparation method of the negative electrode plate with a double-layer negative electrode structure is as follows: Performance parameters of the first graphite as the negative electrode active material: The powder compaction density under 20,000 N is 1.67 g / cm 3 , the Dv50 particle size of the graphite is 12.8 μm, and the mass content of amorphous carbon is 2.5%.

[0259] Performance parameters of the second graphite as the negative electrode active material: The powder compaction density under 20,000 N is 1.6 g / cm 3 , the Dv50 particle size of the graphite is 9.6 μm, and the mass content of amorphous carbon is 3.4%.

[0260] Mix the first graphite as the negative electrode active material, conductive agent acetylene black, binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose in a mass ratio of 96:0.5:2.5:1, and then add the solvent deionized water and stir evenly to form negative electrode slurry 1; mix the second graphite as the negative electrode active material, conductive agent acetylene black, binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose in a mass ratio of 96:0.5:2.5:1, and then add the solvent deionized water and stir evenly to form negative electrode slurry 2.

[0261] Coat negative electrode slurry 1 evenly on the negative electrode current collector copper foil and dry it; coat negative electrode slurry 2 on the surface of the dried negative electrode slurry 1, and after drying and cold pressing, a negative electrode plate is obtained. The negative electrode plate includes 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%.

[0262] Among them, the coating weight of the negative electrode plate is 138 mg / 1540.25 mm 2 ; when the battery is charged at a charging rate of 0.33C to 100% SOC, the compaction density of the negative electrode plate is 1.26 g / cm 3 .

[0263] (3) Preparation of electrolyte: In an argon atmosphere glove box with a water content < 10 ppm, mix the first solvent ethylene carbonate (EC), the second solvent ethyl acetate (EA), and dimethyl carbonate (DMC) in a certain mass ratio to obtain an organic solvent. The mass contents of ethylene carbonate (EC), ethyl acetate (EA), and dimethyl carbonate (DMC) in the electrolyte are shown in Table 1; slowly add a certain mass of lithium hexafluorophosphate (LiPF 6 ) as the lithium salt, and stir well until it is completely dissolved. LiPF in the electrolyte 6The mass content of is 15%. After returning to room temperature, add the first additive vinylene carbonate (VC) accounting for 5% of the total mass of the electrolyte and the second additive fluoroethylene carbonate (FEC) accounting for 2% of the total mass of the electrolyte, and mix them thoroughly to obtain the electrolyte. The mass b of the electrolyte at the rated capacity of the unit cell of the secondary battery of 1Ah is shown in Table 1.

[0264] (4) Preparation of isolation film: The isolation film comprises a base film, which is a 7 μm polyethylene film layer with a porosity of 42%.

[0265] Secondary battery preparation: 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 square aluminum shell, and after drying, the electrolyte is injected, and after packaging, standing, formation, aging, secondary packaging, capacity and other processes, a secondary battery is obtained.

[0266] The preparation methods of Examples 2 to 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 remains unchanged, and the mass content of DMC is changed accordingly), as shown in Table 1.

[0267] The preparation methods of Examples 5 to 7 are similar to those 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.

[0268] The preparation methods of Examples 8 to 10 are similar to those 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.

[0269] 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 at the same time, and at least one of the contents of the first solvent and the second solvent is adjusted accordingly, as shown in Table 1.

[0270] The preparation method of Example 12 is similar to that of Example 3, except that the type of the second solvent and its mass content in the electrolyte are adjusted (the mass content of EC remains unchanged, and the mass content of DMC is changed accordingly), as shown in Table 1.

[0271] The preparation method of Example 13 is similar to that of Example 3, except that the type of the negative electrode active material second graphite is adjusted, and its Dv50 particle size is different, as shown in Table 1; the powder compaction density of the second graphite at 20000N is 1.55g / cm 3 .

[0272] The preparation method of Example 14 is similar to that of Example 3, except that: the type of the first graphite as the anode active material is adjusted, and its Dv50 particle size is different, as shown in Table 1 specifically; the powder compaction density of the first graphite under 20,000 N is 1.72 g / cm 3 .

[0273] The preparation methods of Examples 15 to 16 are similar to that of Example 3, except that: the injection coefficient of the electrolyte is adjusted, so the electrolyte mass b per unit cell rated capacity of 1 Ah of the secondary battery is different, as shown in Table 1 specifically; In addition, for the lithium iron phosphate LiFePO as the cathode active material in Example 15 4 the performance parameters: the powder compaction density under 30,000 N is 2.55 g / cm 3 , and when the battery is charged at a charging rate of 0.33C to 100% SOC, the compaction density of the cathode electrode sheet is 2.72 g / cm 3 ; in the anode electrode sheet, 1% by mass of silicon carbide is used in both anode slurry 1 and anode slurry 2 to replace 1% of graphite in Example 3; For the lithium iron phosphate LiFePO as the cathode active material in Example 16 4 the performance parameters: the powder compaction density under 30,000 N is 2.56 g / cm 3 , and when the battery is charged at a charging rate of 0.33C to 100% SOC, the compaction density of the cathode electrode sheet is 2.75 g / cm 3 ; in the anode electrode sheet, 3% by mass of silicon carbide is used in both anode slurry 1 and anode slurry 2 to replace 3% of graphite in Example 3.

[0274] Example 17 The preparation method is similar to that of Example 3, except that: the anode electrode sheet is a single-layer structure, and its preparation method is as follows: The performance parameters of the third graphite as the anode active material: the powder compaction density under 20,000 N is 1.63 g / cm 3 , the Dv50 particle size of the graphite is 10.8 μm, and the mass content of amorphous carbon is 3.1%.

[0275] Mix the third graphite as the anode active material, conductive agent acetylene black, binder styrene-butadiene rubber and thickener sodium carboxymethyl cellulose in a mass ratio of 96:0.5:2.5:1, and then add the solvent deionized water and stir evenly to form the anode slurry; coat the anode slurry evenly on the anode current collector copper foil, and obtain the anode electrode sheet after drying and cold pressing.

[0276] Among them, the coating weight of the anode electrode sheet is 138 mg / 1540.25 mm 2(Single-sided); The battery is charged at a charging rate of 0.33C until the compaction density of the negative electrode sheet at 100% SOC is 1.26 g / cm 3 .

[0277] The preparation methods of Comparative Examples 1-5 are similar to those of 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, as specifically shown in Table 1.

[0278] The following are performance tests.

[0279] (I) Test of the volume energy density of the secondary battery Place the battery cell at 25°C and charge it at a constant current of 0.33C to 3.65V, then let it stand for 1 min, and then charge it at a constant current of 0.1C to 3.65V and let it stand for 30 min; discharge it at a constant current of 0.33C to 2.0V, and record the discharge capacity A0 at this time, unit: Ah; use a caliper to measure the length, width, and height of the battery cell (generally calculated based on the outer shell size of the battery, excluding the height of the pole column), and calculate the volume V0 of the single battery cell, unit L; the volume energy density VED of the battery cell = (A0 × discharge platform voltage) / V0, unit Wh / L.

[0280] (II) The test steps for the capacity retention rate of the battery after 1000 cycles at 60°C are as follows: At 60°C, charge the battery at a constant current of 1C to the charging cut-off voltage of 3.65V respectively, let it stand for 30 min, and then discharge it at a constant current of 1C to 2.0V. This is one charge-discharge cycle, and record the capacity C0 after the first cycle; repeat the above charge-discharge cycle steps until 1000 cycles, and record the corresponding capacity Cn after the 1000th cycle. The capacity retention rate of the battery after 1000 cycles at 60°C = Cn / C0 × 100%. The higher the capacity retention rate, the better the cycle performance of the battery.

[0281] (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: Under the ambient temperature of 30°C, charge the battery from the state of 10% SOC, Charge at a constant current of 5.0C from 10% SOC to 15% SOC; Charge at a constant current of 5.0C from 15% SOC to 20% SOC; Charge at a constant current of 5.0C from 20% SOC to 25% SOC; Charge at a constant current of 5.0C from 25% SOC to 30% SOC; Charge at a constant current of 5.0C from 30% SOC to 35% SOC; Charge from 35% SOC to 40% SOC at a constant current of 5.0C; Charge from 40% SOC to 45% SOC at a constant current of 4.6C; Charge from 45% SOC to 50% SOC at a constant current of 4.3C; Charge from 50% SOC to 55% SOC at a constant current of 4.0C; Charge from 55% SOC to 60% SOC at a constant current of 3.7C; Charge from 60% SOC to 65% SOC at a constant current of 3.4C; Charge from 65% SOC to 70% SOC at a constant current of 3.1C; Charge from 70% SOC to 75% SOC at a constant current of 2.9C; Charge from 75% SOC to 80% SOC at a constant current of 2.7C; Record the total charging time.

[0282] (4) The test steps for the capacity retention rate of the battery cycled 1000 times at 30℃ are as follows: At 30℃, charge the battery starting from 10% SOC respectively, charge to 80% SOC at the corresponding rates according to different SOCs as described above, then continue to charge at a constant current of 0.33C until 3.65V, let it stand for 30 minutes, and then discharge at a constant current of 1C until 2.0V. This is one charge-discharge cycle. Record the capacity C0 after the first cycle; repeat the above charge-discharge cycle steps until 1000 cycles, record the corresponding capacity Cn after the 1000th cycle, and obtain the capacity retention rate of the battery cycled 1000 times at 30℃ = Cn / C0×100%. The higher the capacity retention rate, the better the cycle performance of the battery.

[0283] Partial parameters of each example and comparative example are shown in Table 1, where the contents are all mass contents, and the unit of the single-sided coating weight of the positive and negative electrodes is mg / 1540.25mm 2 .

[0284] The above performance test results of each example and comparative example are shown in Table 2.

[0285] Table 1

[0286] Table 2

[0287] As can be seen from Table 1-2 above, in Comparative Example 1, the mass content of the first additive in the electrolyte is too high, and the normal temperature cycle performance and fast charging performance of the battery deteriorate; in Comparative Example 2, the mass content of the first additive in the electrolyte is too low, and the high temperature cycle performance of the battery deteriorates; in Comparative Example 3, the mass content of the second additive in the electrolyte is too high, the high temperature cycle performance of the battery deteriorates, and the normal temperature cycle performance is also poor; in Comparative Example 4, the mass content of the second additive in the electrolyte is too low, and the normal temperature cycle performance of the battery decreases; in Comparative Example 5, the mass content of the first solvent in the electrolyte is too low, the self-stability of the electrolyte becomes poor, resulting in a decrease in conductivity, and the normal temperature and high temperature cycle performances are both poor.

[0288] In each of the examples, by adjusting the composition and ratio of the electrolyte and making it cooperate synergistically with the negative electrode sheet containing graphite with a relatively high tap density, the secondary battery prepared can take into account the fast charging performance, normal temperature cycle performance, and high temperature cycle performance on the basis of good energy density. In Example 17, the second solvent in the electrolyte is a carbonate solvent, and the conductivity of the electrolyte decreases. Therefore, the single-sided coating weight of the positive electrode sheet and the negative electrode sheet is reduced to improve the fast charging performance of the battery.

[0289] The technical features of the above-described examples can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above examples are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered to be within the scope described in this specification. The above-described examples only represent several implementation manners of the present application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the appended claims.

Claims

1. A secondary battery, characterized in that: include: A positive electrode sheet, the positive electrode sheet comprising a positive electrode current collector and a positive electrode film layer, the positive electrode film layer is arranged on at least one side of the positive electrode current collector, and the positive electrode film layer comprises a positive electrode active material; A negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode film layer, the negative electrode film layer being 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, and the powder compaction density of the negative electrode active material at 20000N is 1.5g / cm 3 ~1.85g / cm 3 ;and An electrolyte, the electrolyte comprising an organic solvent and an organic additive, the organic solvent comprising a first solvent, the first solvent comprising a cyclic carbonate, and the mass content of the first solvent 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 comprising vinylene carbonate, the second additive comprising a vinyl carbonate derivative, and 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%.

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

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

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

5. The secondary battery according to claim 1, wherein: Based on the total mass of the electrolyte, the mass content of the first solvent is 25.5% to 34%.

6. The secondary battery according to claim 1, wherein: Based on the total mass of the electrolyte, the mass content of the first additive is 1.5% to 6.5%; and / or, Based on the total mass of the electrolyte, the mass content of the second additive is 0.5% to 3%.

7. The secondary battery according to claim 1, wherein: Based on the total mass of the electrolyte, the total mass content of the first additive and the second additive is 2% to 10%.

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

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

10. The secondary battery according to claim 9, characterized in that The powder compaction density of the positive electrode active material under 30000N is 2.48g / cm 3 ~2.85 g / cm 3 .

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

12. The secondary battery according to claim 11, wherein: The positive electrode active material comprises: a core portion comprising at least one of an olivine-structured lithium-containing phosphate and a derivative thereof; and An ion-conducting layer is coated on the surface of the core portion, and the ion-conducting layer includes at least one element selected from the group consisting of Fe, C, Ti, Zr, Hf, Ge and Sn.

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

14. The secondary battery according to claim 13, characterized in that: The olivine-structured lithium-containing phosphate and its derivatives include at least one of lithium iron phosphate, lithium manganese phosphate, lithium nickel phosphate and lithium cobalt phosphate.

15. The secondary battery according to claim 12, wherein: The ion-conducting layer includes a chemical formula of Li 3-b Fe 2- b M3 b (PO m ) n The ion conductor M3 includes at least one element of Ti, Zr, Hf, Ge and Sn with a valence of +4, 0≤b≤1, 3≤m≤5, 2≤n≤4.

16. The secondary battery according to claim 15, characterized in that: The ion conductor includes at least one of lithium iron titanium phosphate, lithium iron zirconium phosphate and lithium iron tin phosphate.

17. The secondary battery according to claim 1, wherein: At least one of the following conditions is met: (1) The compaction density of the positive electrode sheet is 2.5 g / cm 3 ~2.8g / cm 3 ; (2) The mass content of carbon in the positive electrode active material is 1% to 2%; (3) The powder resistivity of the positive electrode active material is ≤20Ω•cm; (4) The volume average particle size of the positive electrode active material satisfies: 1µm≤Dv50≤2µm, 0.4µm≤Dv10≤0.7µm.

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

19. The secondary battery according to claim 18, wherein: The ternary lithium supplement material includes Li x2 A2 y2 Ni a2 Co b2 Mn c2 M4 (1-a2-b2-c2) Q2 z2 , wherein 0<x2≤2.1, 0≤y2≤2.1; 0≤a2≤1, 0≤b2≤1, 0≤c2≤1, and 0.1≤a2+b2+c2≤1; 1.8≤z2≤3.5; A2 includes at least one of Na, K and Mg; M4 includes at least one of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La and Ce; Q2 includes at least one of O and F.

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

21. The secondary battery according to claim 20, characterized in that: The thickness of the positive electrode conductive layer is 0.5 μm to 2 μm.

22. The secondary battery according to claim 20, characterized in that: The positive electrode conductive layer includes a binder, and the binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid and fluorine-containing acrylic resin.

23. The secondary battery according to claim 22, characterized in that: In the positive electrode conductive layer, the mass content of the conductive agent is 30% to 50%, and the mass content of the binder is 50% to 70%.

24. The secondary battery according to claim 1, characterized in that: The compaction density of the negative electrode sheet of the secondary battery at 100% SOC is 1.15 g / cm 3 ~1.46g / cm 3 .

25. The secondary battery according to claim 24, characterized in that: The compaction density of the negative electrode sheet of the secondary battery at 100% SOC is 1.25 g / cm 3 ~1.40g / cm 3 .

26. The secondary battery according to claim 1, characterized in that: The compaction density of the negative electrode sheet of the secondary battery at 100% SOC is ≥1.25g / cm 3 And <1.35g / cm 3 .

27. The secondary battery according to claim 26, characterized in that: The secondary battery satisfies at least one of the following conditions at 100% SOC: (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%.

28. The secondary battery according to claim 1, characterized in that: The compaction density of the negative electrode sheet of the secondary battery at 100% SOC is 1.35 g / cm 3 ~1.40g / cm 3 .

29. The secondary battery according to claim 28, characterized in that The secondary battery satisfies at least one of the following conditions at 100% SOC: (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%.

30. The secondary battery according to claim 1, characterized in that: The mass of the electrolyte of the secondary battery at a unit cell rated capacity of 1 Ah is 2.2 g to 3.0 g.

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

32. The secondary battery according to claim 31, characterized in that The second solvent includes a carboxylic acid ester.

33. The secondary battery according to claim 32, characterized in that: The carboxylic acid ester includes at least one of methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate and 1,4-butyrolactone.

34. The secondary battery according to claim 31, characterized in that The volume energy density of the secondary battery is 400Wh / L-450Wh / 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%.

35. The secondary battery according to claim 31, characterized in that The volume energy density of the secondary battery is greater than 450Wh / L and less than or equal to 480Wh / L, the mass content of the carboxylate 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%.

36. The secondary battery according to claim 31, characterized in that The charging time of the secondary battery from 10% SOC to 80% SOC at 30° C. is 6 min to 15 min, the mass content of the carboxylate 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%.

37. The secondary battery according to claim 36, characterized in that 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%.

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

39. The secondary battery according to claim 38, characterized in that The mass content of the lithium salt in the electrolyte is 10% to 20%.

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

10.

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

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

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

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

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

46. ​​The secondary battery according to claim 45, characterized in that The negative electrode film layer includes a negative electrode active layer, the negative electrode active layer contains the graphite, and the Dv50 particle size of the graphite is 8.2μm~13.5μm.

47. The secondary battery according to claim 45, characterized in that The negative electrode film layer includes a first negative electrode active layer and a second negative electrode active layer stacked in sequence on the same side of the negative electrode current collector, the 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.

48. The secondary battery according to claim 47, characterized in that The Dv50 particle size of the graphite in the first negative electrode active layer is ≥ the Dv50 particle size of the graphite in the second negative electrode active layer.

49. The secondary battery according to claim 47, characterized in that The Dv50 particle size of the graphite in the first negative electrode active layer is 9.5 μm to 18.5 μm; The Dv50 particle size of the graphite in the second negative electrode active layer is 7.8 μm to 14.3 μm.

50. The secondary battery according to claim 49, characterized in that The Dv50 particle size of the graphite in the first negative electrode active layer is 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 12.8 μm.

51. The secondary battery according to claim 47, characterized in that 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.

52. The secondary battery according to claim 47, characterized in that The mass ratio of graphite in the first negative electrode active layer and the second negative electrode active layer is 4:6 to 6:

4.

53. The secondary battery according to claim 47, characterized in that The artificial graphite comprises graphite body particles and a coating layer, wherein the graphite body particles comprise secondary particles formed by aggregation of a plurality of primary particles, the coating layer is coated on the surface of the body particles, and the coating layer comprises amorphous carbon.

54. The secondary battery according to claim 53, characterized in that At least one of the following conditions is met: (1) Based on the total mass of the artificial graphite, the mass content of the amorphous carbon is 2% to 5%; (2) The powder resistivity of the artificial graphite is ≤0.04Ω•cm.

55. The secondary battery according to claim 1, characterized in that The graphite has a charge capacity of ≥350 mAh / g at a rate of 0.1C in a button cell.

56. The secondary battery according to claim 55, characterized in that The graphite has a charge capacity of 350 mAh / g to 440 mAh / g at a charge rate of 0.1C in a button cell.

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

58. The secondary battery according to claim 57, characterized in that The mass content of silicon element in the silicon-based material in the negative electrode active material is 1% to 6%.

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

60. The secondary battery according to claim 59, characterized in that At least one of the following conditions is met: (1) The thickness of the porous base film is ≤12 μm; (2) The porosity of the porous base membrane is 20% to 70%.

61. The secondary battery according to claim 59, characterized in that At least one of the following conditions is met: (1) The thickness of the porous base film is ≤9 μm; (2) The porosity of the porous base membrane is 35% to 60%.

62. The secondary battery according to claim 60, characterized in that The isolation membrane includes a first functional layer and a second functional layer arranged on both sides of the porous base membrane, the first functional layer includes first inorganic particles, the second functional layer includes composite particles, the composite particles include second inorganic particles and non-fluoropolymer particles, the second inorganic particles are attached to the surface of the non-fluoropolymer particles and / or dispersed inside the non-fluoropolymer particles.

63. The secondary battery according to claim 62, characterized in that The non-fluorine polymer particles include acrylic polymer particles.

64. A battery device, characterized in that: A secondary battery comprising the secondary battery according to any one of claims 1 to 63.

65. An electrical device, characterized in that: Includes at least one of the secondary battery according to any one of claims 1 to 63 and the battery device according to claim 64.

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