Secondary battery, battery device and power-consuming device

Abstract

Secondary battery, including a positive electrode sheet comprising a positive electrode current collector and a positive electrode film layer, wherein 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, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer, wherein the negative electrode film layer is arranged on at least one side of the negative electrode current collector and the negative electrode film layer comprises a negative electrode active material, wherein the negative electrode active material comprises graphite and the powder compaction density of the negative electrode active material at 20,000 N is 1.5 g / cm³ 3 up to 1.85 g / cm³ 3 is; and an electrolyte comprising an organic solvent and an organic additive, wherein the organic solvent comprises a first solvent, the first solvent comprising cyclic carbonate, and the mass fraction of the first solvent, based on the total mass of the electrolyte, is 17% to 34%; wherein the organic additive comprises a first and a second additive, the first additive comprising vinylene carbonate and the second additive comprising an ethylene carbonate derivative, and the mass fraction of the first additive is 1.5% to 8% and the mass fraction of the second additive is 0.5% to 4%, each based on the total mass of the electrolyte.

Description

Technical field

[0001] The present application relates to the field of battery technology and in particular to a secondary battery, a battery device and a power-consuming device. State of the art

[0002] The statements made here serve only to provide background information regarding the present application and do not necessarily represent the state of the art.

[0003] In recent years, secondary batteries such as lithium-ion batteries have been widely used in energy storage systems for hydroelectric, coal, wind, and solar power plants, as well as in many different applications including power tools, e-bikes, e-motorcycles, electric vehicles, military equipment, and aerospace. With the increasing use of secondary batteries, the demand for higher energy density in their cells is constantly growing. However, increasing energy density negatively impacts the cycle life and fast-charging performance of the batteries, making it a pressing issue how secondary batteries can combine high energy density with good cycle life and fast-charging capabilities. Disclosure of the invention

[0004] In light of this, the present application offers a secondary battery, a battery device and a power-consuming device that can combine high energy density as well as good cycle performance and fast charging performance.

[0005] A first aspect of the present application offers a secondary battery comprising the following: a positive electrode sheet comprising a positive electrode current collector and a positive electrode film layer, wherein 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, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer, wherein the negative electrode film layer is arranged on at least one side of the negative electrode current collector and the negative electrode film layer comprises a negative electrode active material, wherein the negative electrode active material comprises graphite and the powder compaction density of the negative electrode active material at 20,000 N is 1.5 g / cm³ 3 up to 1.85 g / cm³ 3 is; and an electrolyte comprising an organic solvent and an organic additive, wherein the organic solvent comprises a first solvent, the first solvent comprising cyclic carbonate, and the mass fraction of the first solvent, based on the total mass of the electrolyte, is 17% to 34%; wherein the organic additive comprises a first and a second additive, the first additive comprising vinylene carbonate and the second additive comprising an ethylene carbonate derivative, and the mass fraction of the first additive is 1.5% to 8% and the mass fraction of the second additive is 0.5% to 4%, each based on the total mass of the electrolyte.

[0006] The negative electrode active material of the secondary battery described above comprises graphite and has a high powder compaction density, enabling it to offer high energy density. However, the negative electrode sheet with its high powder compaction density has poor kinetic performance, which is detrimental to improving fast-charging performance. Furthermore, due to the limited space inside the cell, the electrolyte fill volume must be reduced in the high-energy-density cell. Therefore, there is a risk of a drop in the cell's cycle performance due to electrolyte deficiency.Therefore, in the secondary battery described above, the electrolyte is improved and a high-energy-density negative electrode sheet is used. This is achieved by enhancing the first solvent, the first and second additives, and their concentrations to give the electrolyte good thermal stability and suitable conductivity, reduce the electrolyte consumption rate and the direct current resistance (DCR) of the battery, and thus improve the cycle life, storage life, and fast-charging performance of the high-energy-density cell system. Thus, the secondary battery described above can combine high energy density with good cycle life and fast-charging performance.

[0007] In some embodiments, the structure of the ethylene carbonate derivative is as follows: where R1 and R2 each independently comprise any one of the elements hydrogen, halogen, C1 to C5 alkyl groups, or halogenated C1 to C5 alkyl groups, and R1 and R2 are not simultaneously the element hydrogen. These second additives exhibit good film formation, conductivity, and stability, which can improve the fast-charging performance and cycle performance, particularly the room-temperature cycle performance, of the battery.

[0008] In some of the embodiments, the ethylene carbonate derivative comprises at least one of fluoroethylene carbonate, difluoroethylene carbonate and trifluoromethylethylene carbonate.

[0009] In some of the embodiments, the cyclic carbonate comprises at least one of ethylene carbonate and propylene carbonate.

[0010] In some of the embodiments, the mass fraction of the first solvent, based on the total mass of the electrolyte, is 25.5% to 34%.

[0011] In some of the embodiments, the mass fraction of the first additive, based on the total mass of the electrolyte, is 1.5% to 6.5%; and / or The mass fraction of the second additive is 0.5% to 3%, based on the total mass of the electrolyte.

[0012] In some of the embodiments, the total mass fraction of the first additive and the second additive, based on the total mass of the electrolyte, is 2% to 10%.

[0013] In some of the embodiments, the total mass fraction of the first additive and the second additive, based on the total mass of the electrolyte, is 3% to 8%.

[0014] In some of the embodiments, the powder compaction density of the positive electrode active material at 30,000 N is ≥ 2.43 g / cm³. 3 , optional 2.48 g / cm² 3 up to 2.85 g / cm³ 3 .

[0015] In some of the embodiments, the positive electrode active material comprises at least one lithium-containing phosphate with an olivine structure and its derivatives.

[0016] In some of the embodiments, the positive electrode active material comprises: a core section comprising at least one lithium-containing phosphate with an olivine structure and its derivatives; and an ion-conducting layer, wherein the surface of the core section is coated with the ion-conducting layer and the ion-conducting layer comprises at least one element of Fe, C, Ti, Zr, Hf, Ge and Sn.

[0017] By coating the surface of the core section with the ion-conducting layer, the conductivity of the lithium-containing phosphate with olivine structure and its derivatives can be improved, the powder resistance of the material reduced, and the migration rate of the lithium ions increased, thereby improving the fast-charging capability of the battery and reducing the heat generation of the battery cell.

[0018] In some of the embodiments, the lithium-containing phosphate with olivine structure and its derivatives comprise a compound with the general formula Li x1 A1 y1 M1 a1 M2 b1 P 1-c1 X c1 Q1 z1, where 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 comprises at least one of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X comprises at least one of S, Si, Cl, B, C, N, and P; Q1 comprises at least one of O and F. The lithium-containing phosphate with an olivine structure exhibits excellent cycle stability, which contributes to improving the cycle performance of the battery cell.

[0019] In some of the embodiments, the lithium-containing phosphate with olivine structure and its derivatives comprise at least one of lithium iron phosphate, lithium manganese phosphate, lithium nickel phosphate and lithium cobalt phosphate.

[0020] In some of the embodiments, the ion-conducting layer comprises 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, 2 ≤ n ≤ 4.

[0021] In some embodiments, the ion conductor comprises at least one of lithium iron titanium phosphate, lithium iron zirconium phosphate, and lithium iron tin phosphate. Coating the surface of the core section with an ion conductor having a NASICON structure can significantly increase the lithium ion transfer rate during multiple deintercalations and intercalations of lithium ions at the positive electrode, improve the ionic conductivity of the positive electrode active material, and enhance the fast-charging capability of the battery cell. Furthermore, this can increase the capacity per gram and the energy density of the corresponding battery cell.

[0022] In some of the embodiments, at least one of the following conditions is met: (1) The compaction density of the positive electrode sheet is 2.5 g / cm³. 3 up to 2.8 g / cm³ 3 ; (2) the mass fraction of carbon in the positive electrode active material is 1% to 2%; (3) the powder resistance of the positive electrode active material is ≤ 20 Ω·cm; (4) the volume-averaged particle size of the positive electrode active material meets the following conditions: 1 µm ≤ Dv50 ≤ 2 µm, 0.4 µm ≤ Dv10 ≤ 0.7 µm.

[0023] In some of the embodiments, the positive electrode film layer also includes a lithium supplement comprising at least one of ternary lithium supplement material, lithium phosphate, lithium dihydrogen phosphate, lithium sulfate, lithium sulfite, lithium molybdate, lithium nickelate, lithium ferrate, lithium oxalate, lithium titanate, lithium tetraborate, lithium metasilicate, lithium metamanganate, lithium tartrate and trilithium citrate.

[0024] In some of the embodiments, the ternary lithium supplement material Li comprises x2 A2 y2 Ni a2 Co b2 Mn c2M4 (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.

[0025] In some embodiments, the positive electrode sheet also includes a conductive layer of the positive electrode, wherein the conductive layer of the positive electrode is arranged between the positive electrode current collector and the positive electrode film layer, and the conductive layer of the positive electrode comprises a conductive means, wherein the conductive means comprises at least one of superconducting carbon, conductive graphite, acetylene carbon black, carbon black, Ketjen carbon black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0026] In some of the embodiments, the thickness of the conductive layer of the positive electrode is 0.5 µm to 2 µm.

[0027] In some of the embodiments, the conductive layer of the positive electrode comprises a binder, wherein the binder comprises at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid and fluorine-containing acrylate resin.

[0028] In some of the embodiments, the mass fraction of the conductive medium in the conductive layer of the positive electrode is 30% to 50% and the mass fraction of the binder is 50% to 70%.

[0029] In some of the embodiments, the compaction density of the negative electrode sheet, when the secondary battery is at 100% SOC, is 1.15 g / cm³. 3 up to 1.46 g / cm³ 3 , optional 1.25 g / cm² 3 up to 1.40 g / cm³ 3 .

[0030] In some of the embodiments, the compaction density of the negative electrode sheet, when the secondary battery is at 100% SOC, is ≥ 1.25 g / cm³. 3 and < 1.35 g / cm³ 3 .

[0031] In some of the embodiments, the secondary battery at 100% SOC satisfies at least one of the following conditions: (1) The mass fraction of the second additive in the electrolyte is 0.5% to 3%; (2) the mass fraction of the first solvent in the electrolyte is 25.5% to 34%; (3) the mass fraction of the first additive in the electrolyte is 1.5% to 6%.

[0032] In some of the embodiments, the compaction density of the negative electrode sheet, when the secondary battery is at 100% SOC, is 1.35 g / cm³. 3 up to 1.40 g / cm³ 3 .

[0033] In some of the embodiments, the secondary battery at 100% SOC satisfies at least one of the following conditions: (1) The mass fraction of the second additive in the electrolyte is 0.7% to 3.5%; (2) the mass fraction of the first solvent in the electrolyte is 21.25% to 34%; (3) the mass fraction of the first additive in the electrolyte is 2.5% to 7%.

[0034] In some of the embodiments, the electrolyte mass per nominal capacity of 1 Ah of the secondary battery is 2.2 g to 3.0 g.

[0035] In some of the embodiments, the electrolyte also comprises a second solvent, which includes at least one of linear carbonate, carboxylic acid ester, ether, nitrile and sulfone.

[0036] In some of the embodiments, the second solvent comprises a carboxylic acid ester; furthermore, optionally, the carboxylic acid ester comprises at least one of methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate and 1,4-butyrolactone.

[0037] In some of the embodiments, the volume energy density of the secondary battery is 400 Wh / L to 450 Wh / L, the mass fraction of the carboxylic acid ester in the electrolyte is 25.5% to 59.5%, and the total mass fraction of the first additive and the second additive in the electrolyte is 2% to 7%.

[0038] In some of the embodiments, the volume energy density of the secondary battery is > 450 Wh / L and ≤ 480 Wh / L, the mass fraction of the carboxylic acid ester in the electrolyte is 25.5% to 63.75%, and the total mass fraction of the first additive and the second additive in the electrolyte is 3.5% to 8%.

[0039] In some of the embodiments, the charging time of the secondary battery charging process at 30 °C from 10% SOC to 80% SOC is 6 minutes to 15 minutes, the mass fraction of the carboxylic acid ester in the electrolyte is 17% to 63.7%, and the total mass fraction of the first additive and the second additive in the electrolyte is 2% to 8%.

[0040] In some of the embodiments, the mass fraction of the first additive in the electrolyte is 1.5% to 6.5% and of the second additive is 0.5% to 3.5%.

[0041] In some of the embodiments, the electrolyte comprises lithium salt comprising at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, fluorine-containing sulfonylimide salt, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluorobisoxalatophosphate and lithium tetrafluoro(oxalato)phosphate.

[0042] In some of the embodiments, the mass fraction of the lithium salt in the electrolyte is 10% to 20%.

[0043] In some of the embodiments, the lithium salt comprises LiFSI and LiPF6, wherein at least one of the following conditions is met: (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 stoichiometric ratio of LiFSI to LiPF6 is (2 to 5) : 10.

[0044] In some embodiments, the negative electrode sheet also includes a conductive layer of the negative electrode, which is arranged between the negative electrode current collector and the negative electrode film layer on at least one side, wherein the conductive layer of the negative electrode comprises a conductive means comprising at least one of superconducting carbon, conductive graphite, acetylene carbon black, carbon black, Ketjen carbon black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0045] In some of the embodiments, the thickness of the conductive layer of the negative electrode is 0.5 µm to 2 µm.

[0046] In some of the embodiments, the conductive layer of the negative electrode comprises a binder, wherein the binder comprises at least one of styrene-butadiene rubber, water-soluble unsaturated resin, water-based acrylic resin, polyvinyl alcohol, sodium alginate and carboxymethyl chitosan.

[0047] In some of the embodiments, the mass fraction of the conductive material in the conductive layer of the negative electrode is 20% to 40% and of the binder 60% to 80%.

[0048] In some of the embodiments, the negative electrode film layer comprises at least one negative electrode active layer, wherein the at least one negative electrode active layer comprises the graphite.

[0049] In some embodiments, the negative electrode film layer comprises a negative electrode active layer, wherein the negative electrode active layer contains the graphite, wherein the Dv50 particle size of the graphite is 8.2 µm to 13.5 µm.

[0050] In some embodiments, the negative electrode film layer comprises a first and a second negative electrode active layer stacked on top of each other on the same side of the negative electrode current collector, wherein the graphite comprises at least one of artificial graphite and natural graphite, wherein the graphite in the first negative electrode active layer comprises at least one of the artificial graphite and the natural graphite, while the graphite in the second negative electrode active layer comprises the artificial graphite.

[0051] In some of the embodiments, 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.

[0052] In some of the embodiments, the Dv50 particle size of the graphite in the first negative electrode active layer is 9.5 µm to 18.5 µm, optionally 9.5 µm to 14.8 µm;

[0053] The Dv50 particle size of the graphite in the second negative electrode active layer is 7.8 µm to 14.3 µm, optionally 7.8 µm to 12.8 µm.

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

[0055] In some embodiments, 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 surface of the graphite body particles is coated with the coating layer, and the coating layer comprises amorphous carbon.

[0056] In some of the embodiments, at least one of the following conditions is met: (1) The mass fraction of amorphous carbon is 2% to 5% in relation to the total mass of artificial graphite; (2) the powder resistance of the synthetic graphite is ≤ 0.04 Ω·cm.

[0057] In some of the embodiments, the charging capacity per gram of graphite in a button cell at a 0.1 C rate is ≥ 350 mAh / g, optionally 350 mAh / g to 440 mAh / g.

[0058] In some of the embodiments, the negative electrode active material also comprises a silicon-based material comprising at least one silicon oxide compound and a silicon-carbon composite; the mass fraction of the element silicon in the silicon-based material in the negative electrode active material is 0.3% to 10%, optionally 1% to 6%.

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

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

[0061] In some embodiments, the separator comprises a first functional layer and a second functional layer arranged on both sides of the porous base film, wherein the first functional layer comprises first inorganic particles and the second functional layer comprises composite particles, wherein the composite particles comprise second inorganic particles and non-fluoropolymer particles, wherein the second inorganic particles adhere to the surface of the non-fluoropolymer particles and / or are dispersed inside the non-fluoropolymer particles.

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

[0063] A second aspect of the present application provides a battery device comprising a secondary battery according to the first aspect of the present application.

[0064] A third aspect of the present application provides a power-consuming device comprising a secondary battery according to the first aspect and / or a battery device according to the second aspect of the present application.

[0065] The power-consuming device of the present application comprises the secondary battery provided in the present application and therefore has at least the same advantages as the secondary battery.

[0066] Details of one or more embodiments of the present application are illustrated in the following drawings and the description. Further features, objectives and advantages of the present application will become apparent from the description, the drawings and the claims. Brief description of the drawings

[0067] For better description and illustration of the embodiments or examples provided in this application, reference may be made to one or more drawings. Additional details or examples described in the drawings are not to be considered as limiting the scope of the disclosed application, the embodiments or examples described, or the best mode of this application currently understood. Furthermore, the same reference numerals are used in all drawings to represent identical parts. In the figures: Fig. Figure 1 is a schematic representation of a battery cell of an embodiment of the present application. Fig. 2 is an exploded view of the in Fig. 1 battery cell of the embodiment of the present application shown. Fig.Figure 3 is a schematic representation of a battery module of an embodiment of the present application. Fig. Figure 4 is a schematic representation of a battery pack of an embodiment of the present application. Fig. 5 is an exploded view of the in Fig. 4 battery packs shown in the embodiment of the present application. Fig. Figure 6 is a schematic representation of a power-consuming device that uses a secondary battery as a power source in an embodiment of the present application. Reference symbol list:

[0068] 1. Battery pack; 2. Upper housing body; 3. Lower housing body; 4. Battery module; 5. Battery cell; 51. Housing body; 52. Electrode assembly; 53. Cover plate; 6. Current-consuming device. Detailed descriptions

[0069] The following section, in conjunction with the drawings in the embodiments of the present application, clearly and completely describes the technical solutions in those embodiments. Obviously, the described embodiments represent only a subset of the embodiments of the present application, but not all of them. All other embodiments that a person skilled in the art could have derived without creative effort based on the embodiments of the present application fall within the scope of protection of the present application.

[0070] The “range” disclosed in the present application can be defined in the form of a lower bound and an upper bound. A given range is defined by selecting a lower bound and an upper bound. The selected lower bound and upper bound define the limits of the specific range. The ranges thus defined may or may not include the end values; each end value may be included or excluded independently; and they may be specified in any combination, i.e., any lower bound can be combined with any upper bound to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a particular parameter, then ranges of 60 to 110 and 80 to 120 are also conceivable. Furthermore, if minimum range values ​​of 1 and 2 and maximum range values ​​of 3, 4, and 5 are listed, then all of the following ranges are conceivable: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5.In the present application, unless otherwise specified, a range of numbers "a to b" represents an abbreviation for any combination of real numbers between a and b, where a and b are both real numbers. For example, the range "0 to 5" means that all real numbers between "0 to 5" have been listed therein, and "0 to 5" is simply an abbreviation for these combinations of numbers. Furthermore, if a particular parameter is specified as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, if a particular parameter is selected from the integers "2 to 10", this is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0071] In the present application, “several” and “a multitude of” refer to a number greater than or equal to 2, unless otherwise specified. For example, “at least one” means one, two, or more.

[0072] Unless otherwise stated, all embodiments and optional embodiments of the present application may be combined to form a new technical solution.

[0073] A reference to "exemplarity" in this document means that certain features, structures, or properties described in connection with an exemplary embodiment may be included in at least one exemplary embodiment or embodiment of the present application. The appearance of the preceding phrase at various points in the description does not necessarily mean that it refers to the same exemplary embodiment, nor does it represent an independent or alternative embodiment that is mutually exclusive with other embodiments. A person skilled in the art will expressly and implicitly understand that the exemplary embodiments described herein may be combined with other exemplary embodiments. A reference to "portion" in this document is to be understood similarly.

[0074] A person skilled in the art can understand that the order in which steps are described in the methods of the various embodiments or exemplary embodiments does not necessarily represent a mandatory order of execution, nor does it constitute a restriction of the execution process. The precise order of execution of the steps should be determined by their function and possible internal logic. Unless otherwise specified, all steps of the present application can be carried out both sequentially and in any order, but preferably sequentially. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out sequentially, or that it can include steps (b) and (a) carried out sequentially.For example, if it is mentioned that the procedure may further include step (c), this means that step (c) can be added in any order. For example, the procedure may include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0075] In the present application, open technical features or technical solutions described by terms such as "comprehensive," "containing," or "including" are, unless otherwise specified, not limited to the listed elements and do not exclude additional elements. They can be considered both as closed features or solutions consisting exclusively of the listed elements and as open features or solutions that include further elements beyond those listed. For example, "A includes a1, a2, and a3," unless otherwise specified, means that it may be the case that no further elements are included (thus giving the feature or embodiment "A consists of a1, a2, and a3") or that further elements are included (thus giving the feature or embodiment "A includes not only a1, a2, and a3, but also further elements").

[0076] In the present application, unless otherwise stated, A (like B) means that B is a non-restrictive example of A, and it is to be understood that A is not restricted to B.

[0077] In the present application, "optional," "possibly," or "alternatively" means that something may or may not be present, i.e., that one can choose between two alternative possibilities: "present" or "not present." If "optional" occurs multiple times in a technical solution and nothing else is specified, and there are no contradictions or mutual dependencies, each "optional" is independent.

[0078] One embodiment of the present application provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet and an electrolyte.

[0079] The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer, wherein 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.

[0080] The negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer. The negative electrode film layer is arranged on at least one side of the negative electrode current collector and comprises a negative electrode active material, wherein the negative electrode active material comprises graphite and has a powder compaction density of 1.5 g / cm³ at 20,000 N. 3 up to 1.85 g / cm³ 3 amounts.

[0081] In the embodiments of the present application, the powder compaction density of the negative electrode active material has a meaning known to the skilled person and can be tested using a compaction density tester according to GB / T 24533-2009 at a test pressure of 20,000 N.

[0082] The electrolyte comprises an organic solvent and an organic additive, the organic solvent comprising a first solvent. The first solvent comprises cyclic carbonate (EC), and its mass fraction in the electrolyte is 17% to 34%, based on the total mass of the electrolyte. The organic additive comprises a first and a second additive, the first additive comprising vinylene carbonate (VC) and the second additive comprising an ethylene carbonate derivative. The mass fraction of the first additive in the electrolyte is 1.5% to 8%, and the mass fraction of the second additive is 0.5% to 4%, based on the total mass of the electrolyte.

[0083] The negative electrode active material of the secondary battery described above comprises graphite and has a high powder compaction density, enabling it to offer high energy density. However, the negative electrode sheet with its high powder compaction density has poor kinetic performance, which is detrimental to improving fast-charging performance. Furthermore, due to the limited space inside the cell, the electrolyte fill volume must be reduced in the high-energy-density cell. Therefore, there is a risk of a drop in the cell's cycle performance due to electrolyte deficiency.Therefore, in the secondary battery described above, the electrolyte is improved and a high-energy-density negative electrode sheet is used. This is achieved by improving the first solvent, the first and second additives, and their concentrations to give the electrolyte good thermal stability and suitable conductivity, reduce the electrolyte consumption rate and the direct current resistance (DCR) of the battery, and thus improve the cycle life, storage life, and fast-charging performance of the high-energy-density cell system. Thus, the secondary battery described above combines both high energy density and good fast-charging performance.

[0084] The first solvent described above comprises cyclic carbonate; cyclic carbonate has a high dielectric constant and good film properties. If the concentration of the first solvent in the electrolyte is too low, the electrolyte's stability decreases, leading to lower conductivity; conversely, if the concentration of the first solvent is too high, the electrolyte's viscosity and melting point increase, which in turn worsens the electrolyte's conductivity and the battery's kinetic performance, thus impairing cycle life. Therefore, controlling the concentration of the first solvent within the aforementioned range ensures that the electrolyte exhibits good thermal stability and adequate conductivity.

[0085] The first additive described above comprises vinylene carbonate (VC), and the second additive comprises an ethylene carbonate derivative. Both additives contribute to interfacial film formation. If the concentration of the first and second additives is too low, the first solvent can contribute excessively to film formation, impairing electrolyte stability and thereby accelerating electrolyte consumption, which degrades the battery's cycle life and storage life. Increasing the concentration of the first additive improves the battery's high-temperature cycle life; however, excessively high concentrations of the first additive negatively affect the battery's kinetic window and direct current resistance (DCR), further reducing cycle life and failing to improve fast-charging performance.As the concentration of the second additive increases, the battery's room-temperature cycle life and fast-charging performance improve. However, excessively high concentrations of the second additive degrade high-temperature performance and reduce the high-temperature cycle life. By simultaneously controlling the concentrations of the first and second additives within the aforementioned range, a balance can be achieved between the electrolyte film formation stability and battery kinetics.

[0086] By adjusting the first solvent in the electrolyte to the aforementioned ranges, the electrolyte's thermal stability can be improved, and its conductivity remains within an appropriate range. Simultaneously, adjusting the first and second additives to these ranges achieves a balance between battery kinetics and electrolyte film formation stability. This reduces the electrolyte consumption rate, improving the cell's cycle life and storage life at low electrolyte fill coefficients. Furthermore, the battery's DC resistance is reduced, resulting in good fast-charging performance.This electrolyte is suitable for the aforementioned negative electrode sheet and high-energy-density battery system, enabling the secondary battery to combine high energy density with good cycle life and fast charging performance, particularly with regard to room temperature cycle life and high-temperature cycle life.

[0087] In some embodiments of the present application, the cyclic carbonate in the first solvent comprises at least one of ethylene carbonate (EC) and propylene carbonate (PC).

[0088] For example, the mass fraction 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%, or 34%. Furthermore, the mass fraction of the first solvent in the electrolyte can be between 21.25% and 34%, or between 25.5% and 34%, or lie within a range defined by any two of the aforementioned point values ​​as endpoints. The same applies below for similar specifications. Controlling the mass fraction of the first solvent in the electrolyte within the optional range can result in the battery exhibiting excellent cycle performance.

[0089] For example, the mass fraction 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%, or 8%, or within a range defined by any two of the aforementioned point values. Furthermore, the mass fraction of the first additive in the electrolyte is 1.5% to 6.5%. The first additive is vinylene carbonate (VC). Controlling the mass fraction of the first additive in the electrolyte within the specified range can result in improved battery cycle performance, particularly enhanced high-temperature cycle performance.

[0090] In some embodiments of the present application, the structure of the ethylene carbonate derivative in the second additive is as follows: wherein R1 and R2 each independently comprise any one of the elements hydrogen, halogen, C1 to C5 alkyl groups, or halogenated C1 to C5 alkyl groups, and R1 and R2 are not simultaneously hydrogen. Furthermore, the halogen comprises at least one element of fluorine, chlorine, and bromine. The C1 to C5 alkyl group and halogenated C1 to C5 alkyl group comprise, but are not limited to, at least one of the halogenated or non-halogenated methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, and n-pentyl groups and their isomers. These second additives have good film formation, conductivity and stability, which can improve the fast charging performance and cycle performance, especially the room temperature cycle performance, of the battery.

[0091] Furthermore, the above-mentioned ethylene carbonate derivative includes at least one of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC) and trifluoromethylethylene carbonate.

[0092] For example, the mass fraction of the second additive in the electrolyte can be, without limitation, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, or within a range defined by any two of the aforementioned point values. Furthermore, the mass fraction of the second additive in the electrolyte is 0.5% to 3%. Controlling the mass fraction of the second additive in the electrolyte within this optional range can result in improved fast-charging performance and cycle life of the battery, particularly improved room-temperature cycle life.

[0093] In some embodiments of the present application, the total mass fraction of the first and second additives is 2% to 10%. For example, this total mass fraction can be 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, or 10%. Furthermore, the total mass fraction of the first and second additives is 2% to 9%, and even further, 3% to 8%. Controlling the total mass fraction of the first and second additives within the aforementioned range can improve the battery's cycle performance.

[0094] In some embodiments of the present application, the electrolyte also comprises a second solvent. Furthermore, the second solvent comprises at least one linear carbonate, carboxylic acid ester, ether, nitrile, and sulfone. The second solvent, together with the first solvent, acts as a solvent to lower the melting point and viscosity of the electrolyte system and to improve the lithium ion transfer properties of the electrolyte.

[0095] Furthermore, the linear carbonate comprises 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).

[0096] Furthermore, the carboxylic acid ester comprises at least one of methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate, methyl propionate, ethyl propionate (EP), propyl propionate, methyl butyrate, ethyl butyrate, and 1,4-butyrolactone. In some embodiments of the present application, the second solvent comprises a carboxylic acid ester.

[0097] Furthermore, the ether comprises, but is not limited to, at least one of diethyl ether and 1,2-dimethoxyethane (DME, also known as ethylene glycol dimethyl ether).

[0098] Furthermore, the nitrile includes, but is not limited to, acetonitrile (AN).

[0099] Furthermore, the sulfone includes, but is not limited to, at least one of sulfolane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0100] Furthermore, the mass fraction of the second solvent in the electrolyte is 17% to 63.75%; and this mass fraction can be 17%, 21.25%, 25.5%, 29.75%, 34%, 38.25%, 42.5%, 46.75%, 51%, 55.25%, 59.5%, 62.05% and

[0101] The mass fraction of the carboxylic acid ester in the electrolyte ranges from 25.5% to 51%, and from 25.5% to 63.75%, respectively. In a specific example, the second solvent is the carboxylic acid ester.

[0102] In some embodiments of the present application, the electrolyte salt comprises a lithium salt, wherein the lithium salt comprises at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS, CF3SO2Li), lithium difluorophosphate (LiPO2F2), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium difluorobisoxalatophosphate (LiDFOP) and lithium tetrafluoro(oxalato)phosphate (LiTFOP).

[0103] In some embodiments of the present application, the mass fraction of the lithium salt in the electrolyte is 10% to 20%. For example, it can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or lie in a range formed by any two of the above-mentioned point values ​​as end values.

[0104] In some embodiments of the present application, the concentration of the lithium salt in the electrolyte is 0.8 mol / L to 1.5 mol / L. For example, the concentration of the electrolyte salt in the electrolyte can be 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.3 mol / L and 1.5 mol / L; furthermore, it can lie in a range formed by any two of the above-mentioned point values ​​as end values.

[0105] Optionally, the lithium salt comprises at least one fluorinated sulfonylimide salt and LiPF6. Furthermore, optionally, the fluorinated sulfonylimide salt comprises at least one LiFSI and one LiTFSI.

[0106] Furthermore, the lithium salt comprises LiFSI and LiPF6. The concentration of LiFSI in the electrolyte is 0.2 mol / L to 0.5 mol / L, and the concentration of LiPF6 in the electrolyte is 0.5 mol / L to 1.3 mol / L. The molar ratio of LiFSI and LiPF6 is (2 to 5) : 10. Lithium bis(fluorosulfonyl)imide (LiFSI) has good conductivity and heat resistance and does not decompose readily at high temperatures, making it particularly suitable for the high-energy-density system of the present application, which generates a relatively large amount of heat. However, LiFSI can generate heat at excessively high temperatures, for example, above 200 °C, which compromises the cell's safety. Therefore, LiPF6 is added to act together as a lithium salt and effectively improve the battery's safety.

[0107] In some embodiments of the present application, the electrolyte mass per nominal capacity of 1 Ah of the secondary battery is 2.2 g to 3.0 g; for 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, or 3.0 g. Furthermore, it can be 2.2 g to 2.8 g or 2.5 g to 3.0 g. The electrolyte described above in the present application is particularly suitable for battery systems with a low electrolyte fill factor, since the electrolyte consumption rate is lower and the kinetics are better, which improves the battery with a low electrolyte fill factor and increases its cycle performance.

[0108] The test method for the electrolyte mass per nominal capacity of 1 Ah of the secondary battery is as follows: (1) A battery cell is removed and its mass M0 is measured; (2) the battery cell is disassembled, the free electrolyte is drained, and the electrode sheets, separator, mechanical components, and adhesive films are removed; (3) the electrode sheets, separator, mechanical components, and adhesive films are each cleaned with dimethyl carbonate (DMC), soaked for 24 hours, and rinsed at least three times; (4) after cleaning, the electrode sheets, separator, mechanical components, and adhesive films are dried in a drying oven until they are completely free of solvents; (5) the electrode sheets, separator, mechanical components, and adhesive films are weighed, and their mass is recorded as M1; (6) the electrolyte mass per nominal capacity of 1 Ah of the secondary battery = (M0 - M1) / a.a = Nominal capacity of the secondary battery, unit Ah. Positive electrode sheet

[0109] As a non-restrictive example, the positive electrode current collector has two opposing surfaces in its own thickness direction, with the positive electrode film layer being arranged on one or both of these opposing surfaces of the positive electrode current collector.

[0110] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, aluminum foil can be used as the metal foil. The composite current collector can comprise 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 electrode current collector, the metal material can, as a non-limiting example, comprise at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. In the positive electrode current collector, the polymer material substrate can, as a non-limiting example, comprise at least one polymer material substrate made of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE).

[0111] In some embodiments, the thickness of the positive electrode current collector is 10 µm to 15 µm, optionally 12 µm to 15 µm. For example, the thickness of the positive electrode current collector is 10 µm, 10.5 µm, 11 µm, 11.5 µm, 12 µm, 12.5 µm, 13 µm, 13.5 µm, 14 µm, 14.5 µm, 15 µm, or lies in a range consisting of any two of the above values.

[0112] If the thickness of the positive electrode current collector is within the range mentioned above, the positive electrode current collector exhibits relatively excellent current conductivity and allows for a higher energy density of the battery cell.

[0113] In the embodiments of the present application, the thickness of the positive electrode current collector has a meaning known in the art and can be determined using devices and methods known in the art. For example, the thickness of the positive electrode sheet is measured using a high-precision micrometer, the film layer is removed from the surface of the positive electrode current collector, and the thickness of the positive electrode current collector is measured with a high-precision micrometer.

[0114] The positive electrode film layer is typically formed by applying a positive electrode paste to the positive electrode current collector, followed by drying and cold pressing. The positive electrode paste is generally formed by dispersing and uniformly stirring the positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent. The solvent may be, but is not limited to, N-methyl-2-pyrrolidone (NMP).

[0115] The positive electrode sheet does not exclude further additional functional layers besides the positive electrode film layer. For example, in some embodiments, the positive electrode sheet according to the embodiments of the present application also comprises a conductive layer of the positive electrode, which is arranged between the positive electrode current collector and the positive electrode film layer. In other embodiments, the positive electrode sheet according to the embodiments of the present application also comprises a protective layer that covers the surface of the positive electrode film layer.

[0116] The positive electrode active material can be a known positive electrode active material for batteries. In some of the embodiments, the powder compaction density of the positive electrode active material at 30,000 N is ≥ 2.43 g / cm³. 3 , optional 2.48 g / cm² 3 up to 2.85 g / cm³3 Furthermore, the powder compaction density of the positive electrode active material at 30,000 N is 2.5 g / cm³. 3 up to 2.8 g / cm³ 3 .

[0117] By using a positive electrode active material with this higher powder compaction density, the compaction density of the positive electrode sheet can be increased, which can further increase the energy density of the battery.

[0118] As an example, the powder compaction density of the positive electrode active material in the positive electrode sheet at 30,000 N is 2.43 g / cm³. 3 , 2.45 g / cm³ 3 , 2.5 g / cm³ 3 , 2.55 g / cm³ 3 , 2.6 g / cm³ 3 , 2.65 g / cm³ 3 , 2.7 g / cm³ 3 , 2.75 g / cm³ 3 , 2.8 g / cm³ 3 , 2.85 g / cm³ 3 be.

[0119] In the embodiments of the present application, the powder compaction density of the positive electrode active material has a meaning known to the skilled person and can be tested using a compaction density tester according to GB / T 24533-2009 at a test pressure of 30,000 N.

[0120] As a non-restrictive example, the positive electrode active material can comprise at least one of phosphate-like positive electrode material, lithium transition metal oxide, and their modified compounds. The phosphate-like positive electrode material includes at least one of lithium-containing phosphate with an olivine structure and its derivatives.

[0121] Furthermore, the positive electrode active material comprises at least one lithium phosphate compound with an olivine structure and its derivatives. The particle size of the positive electrode active material made from lithium phosphate and its derivatives is smaller, and the specific surface area is larger, which promotes water absorption. Therefore, electrolyte hydrolysis is more severe in this battery system, resulting in a greater amount of RF generated during hydrolysis. Consequently, electrolyte consumption is a significant issue. The electrolyte described above can leverage its advantages of a slower consumption rate, which in turn improves the cycle life of such batteries. Simultaneously, the benefits of high energy density, long cycle life, and good safety performance of lithium phosphate and its derivatives can be better utilized.

[0122] In some embodiments of the present application, the lithium-containing phosphate with olivine structure and its derivatives comprise a compound with the general formula Li x1 A1 y1 M1 a1 M2 b1 P 1-c1 X c1 Q1 z1 , where 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 comprises at least one of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X comprises at least one of S, Si, Cl, B, C, N, and P; Q1 comprises at least one of O and F. The lithium-containing phosphate with an olivine structure exhibits excellent cycle stability, which contributes to improving the cycle performance of the battery cell.

[0123] Furthermore, the connection Li includes x1 A1y1 M1 a1 M2 b1 P 1-c1 X c1 Q1 z1 at least one of lithium iron phosphate (LiFePO4), lithium manganese phosphate (LiMnPO4), lithium nickel phosphate (LiNiPO4) and lithium cobalt phosphate (LiCoPO4), as well as doped compounds of these compounds.

[0124] The lithium-containing phosphate with an olivine structure and its derivatives may or may not have a coating layer. In some embodiments of the present application, the positive electrode active material comprises a core section and an ion-conducting layer. The core section comprises at least one of the lithium-containing phosphate with an olivine structure and its derivatives, and the surface of the core section is coated with the ion-conducting layer. The ion-conducting layer comprises at least one of the elements Fe, C, Ti, Zr, Hf, Ge, and Sn.

[0125] By coating the surface of the core section with the ion-conducting layer, the conductivity of the lithium-containing phosphate with olivine structure and its derivatives can be improved, the powder resistance of the material reduced, and the migration rate of the lithium ions increased, thereby improving the fast-charging capability of the battery and reducing the heat generation of the battery cell.

[0126] Furthermore, 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, 2 ≤ n ≤ 4.

[0127] For example, the ion conductor is a material with a NASICON structure and comprises, for example, one or more of lithium iron titanium phosphate Li2FeTi(PO4)3, lithium iron zirconium phosphate Li,FeZr(PO4)3, lithium iron tin phosphate Li2FeSn(PO4)3.

[0128] The ion conductor with NASICON structure is a material with superior ionic conductivity and features numerous three-dimensional diffusion and transport channels for lithium ions. It is characterized by high ionic conduction efficiency and structural stability during multiple deintercalations and intercalations of lithium ions. Coating the surface of the core section with an ion conductor with NASICON structure significantly increases the lithium ion transfer rate during multiple deintercalations and intercalations at the positive electrode, improves the ionic conductivity of the positive electrode active material, and enhances the fast-charging capability of the battery cell. Furthermore, this can increase the capacity per gram and the energy density of the corresponding battery cell.

[0129] In some embodiments, the ion-conducting layer also includes elemental carbon to further improve the material.

[0130] The elemental carbon and the ionic conductor can be arranged in layers. For example, the elemental carbon can be formed as a separate carbon coating layer, and the ionic conductor as a separate ionic conductor layer. The surface of the core section can be coated with the carbon coating layer, and the ionic conductor layer is located on the surface of the carbon coating layer; that is, the ionic conductor layer is located on the side of the carbon coating layer facing away from the core section. Alternatively, the surface of the core section can be coated with the ionic conductor layer, and the carbon coating layer is located on the surface of the ionic conductor layer; that is, the carbon coating layer is located on the side of the ionic conductor layer facing away from the core section.Of course, the elemental carbon and the ion conductor can also be arranged in the same layer.

[0131] Optionally, the surface of the ion conductor layer can be coated with a carbon coating layer formed by carbonizing an organic carbon source (e.g., glucose, polyethylene glycol, etc.). This carbon coating layer can partially or completely cover the surface of the fast ion conductor layer. By providing this carbon coating layer, the electronic conductivity of the core section can be significantly improved, compensating for any lack of electronic conductivity in the core section and enhancing the energy density of the battery cell.

[0132] In particular, the arrangement of the carbon coating layer enables the positive electrode active material of the present application to have the following advantages:

[0133] The carbon coating layer in the positive electrode active material of the present application provides a suitable channel for electron transfer, thereby significantly increasing the electron conductivity during multiple deintercalations and intercalations of lithium, improving the electronic conductivity of the lithium-containing phosphate, improving the charging capability of the corresponding battery cell, and also increasing the energy density.

[0134] The carbon coating layer of the positive electrode active material of the present application is loose and porous, allowing the electrolyte to come into complete and effective contact with the lithium-containing phosphate, thus increasing the transfer rate of lithium ions at the phase interface and improving the charging capability of the battery cell.

[0135] Coating the surface of the lithium-containing phosphate with a carbon coating layer can not only improve the conductivity of the lithium-containing phosphate, but also improve the structural stability of the positive electrode active material, thereby effectively preventing iron dissolution of the positive electrode active material during long-term storage and cyclic use of the battery cell, thus ensuring the cycle life of the battery cell.

[0136] The positive electrode active material of the present application uses lithium phosphate as a substrate and can fully exploit the advantages of lithium phosphate, such as low cost, high operational reliability, and good cycle stability. Simultaneously, an ion-conducting layer (ion conductor layer and carbon coating layer) is used to overcome the disadvantages of poor electronic and ionic conductivity. The battery cell manufactured with the positive electrode active material of the present application offers a significantly improved energy density with excellent cycle performance.

[0137] In some embodiments, the mass fraction of carbon in the positive electrode active material is 1% to 2%; for example, it can be 1%, 1.5%, or 2%. Controlling the mass fraction of carbon in the positive electrode active material within this range can further improve the conductivity of the positive electrode active material, thereby increasing the fast-charging performance of the battery. Understandably, this carbon can, but is not limited to, originate from a carbon coating layer. For example, the surface of lithium-containing phosphate with an olivine structure and its derivatives is coated with a carbon coating layer.

[0138] In some embodiments, the powder resistance of the positive electrode active material is ≤ 20 Ω·cm, which further improves the conductivity of the positive electrode active material and increases the fast-charging performance of the battery. For example, the powder resistance of the positive electrode active material can be 20 Ω·cm, 15 Ω·cm, 10 Ω·cm, 8 Ω·cm, 5 Ω·cm, etc., optionally ≤ 11 Ω·cm.

[0139] In some of the embodiments, the volume-averaged particle size of the positive electrode active material meets the following conditions: 1 µm ≤ Dv50 ≤ 2 µm, 0.4 µm ≤ Dv10 ≤ 0.7 µm, further improving the fast-charging and performance capabilities of the battery. For example, the Dv50 particle size of the positive electrode active material can be 1 µm, 1.5 µm, or 2 µm. For example, the volume-averaged particle size Dv10 of the positive electrode active material can be 0.4 µm, 0.5 µm, 0.6 µm, or 0.7 µm.

[0140] In this text, Dv50 and Dv10 have their established meanings in engineering and can be determined using established methods. For example, a laser particle size analyzer (such as the Malvern Master Size 3000) is used for this purpose. Dv50 represents the particle size at which the cumulative volume distribution of the particles, based on the particle size distribution, reaches 50% of the smallest particle size. Dv10 represents the particle size at which the cumulative volume distribution of the particles, based on the particle size distribution, reaches 10% of the smallest particle size.

[0141] The particle size distribution can be tested using the following method: A clean beaker is filled with an appropriate amount of the sample to be tested and thoroughly sonicated to ensure complete dispersion. The Malvern 2000 model is used as the test instrument. After the sample is placed in the sample inlet, it circulates with the solution to the optical measurement system. Under laser beam irradiation, the energy distribution of the scattered light is recorded and measured, from which the particle size distribution is derived (coverage: 8% to 12%). Based on the measurement data, a diagram of the volumetric particle size distribution is generated.

[0142] In some of the embodiments, the positive electrode film layer also comprises a lithium supplement. Furthermore, the lithium supplement comprises at least one of the following: ternary lithium supplement material, lithium phosphate, lithium dihydrogen phosphate, lithium sulfate, lithium sulfite, lithium molybdate, lithium nickelate, lithium ferrate, lithium oxalate, lithium titanate, lithium tetraborate, lithium metasilicate, lithium metamanganate, lithium tartrate, and trilithium citrate.

[0143] Furthermore, the ternary lithium supplement material 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.

[0144] The following still holds true: 0.9 ≤ x2 + y2 ≤ 2.1.

[0145] The lithium supplement can be located in the same layer as the positive electrode active material or in a different layer. If the lithium supplement is located in a different layer than the positive electrode active material, the lithium supplement can be located in a lithium supplement layer, and the positive electrode active material can be located in the positive electrode active material layer. In other words, the positive electrode film layer comprises the lithium supplement layer and the positive electrode active material layer. The positive electrode active material layer can be located on at least one side of the positive electrode current collector, and the lithium supplement layer can be located between the positive electrode active material layer and the positive electrode current collector.Alternatively, the lithium supplement layer can be arranged on at least one side of the positive electrode current collector, and the positive electrode active material layer can be located between the lithium supplement layer and the positive electrode current collector. Optionally, the lithium supplement layer can be arranged between the positive electrode active material layer and the positive electrode current collector.

[0146] In some of the embodiments, the mass fraction of the positive electrode active material in the positive electrode film layer is 80% to 98%. For example, this mass fraction can be 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 96%, or 98%. Furthermore, the mass fraction of the positive electrode active material in the positive electrode film layer can be 90% to 98%.

[0147] In some embodiments, the positive electrode film layer may optionally include a binder. As a non-limiting example, the binder may comprise at least one of the following: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin. In some embodiments, the mass fraction of the binder, based on the total mass of the positive electrode film layer, is ≤ 5%.

[0148] In some embodiments, the positive electrode film layer may optionally comprise a conductive material. As a non-limiting example, the conductive material may comprise at least one of superconducting carbon, carbon black, carbon black, Ketjen carbon black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass fraction of the conductive material is ≤ 5%, based on the total mass of the positive electrode film layer.

[0149] In some embodiments, the positive electrode sheet can be produced as follows: The components mentioned above for producing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder, and any other components, are dispersed in a solvent to form a positive electrode paste; at least one side of the positive electrode current collector is coated with the positive electrode paste. After drying, cold pressing, and other processes, the positive electrode sheet can be obtained. The type of solvent can be selected from any of the previously mentioned embodiments, for example, N-methyl-2-pyrrolidone (NMP).The coating of the surface of the positive electrode current collector with the positive electrode paste can be carried out on a single surface of the positive electrode current collector or on both surfaces of the positive electrode current collector.

[0150] In some embodiments, the positive electrode sheet also includes a conductive positive electrode layer located between the positive electrode current collector and the positive electrode film layer on at least one side. The conductive positive electrode layer comprises a conductive medium. Alternatively, the conductive positive electrode layer can be formed by coating the surface of the positive electrode current collector with the appropriate paste, and then coating and drying the positive electrode paste to form the positive electrode sheet. The conductive positive electrode layer can increase the adhesion between the positive electrode film layer and the positive electrode current collector, as well as improve the overall conductivity of the positive electrode sheet, thus promoting an increase in the electron transfer rate.

[0151] Furthermore, the conductive medium comprises at least one of superconducting carbon, conductive graphite, acetylene carbon black, carbon black, Ketjen carbon black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0152] Furthermore, the thickness of the conductive layer of the positive electrode is between 0.5 µm and 2 µm. For example, it could be 0.5 µm, 1 µm, 1.5 µm, 2 µm, or within a range defined by any two of the aforementioned point values. If the thickness of the conductive layer of the positive electrode is within this range, the conductivity of the positive electrode sheet can be further improved, and the energy density of the battery cell can be increased.

[0153] Furthermore, the conductive layer of the positive electrode also includes a binder. This binder comprises at least one of the following: polyvinylidene fluoride, polytetrafluoroethylene, a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and a fluorine-containing acrylate resin. The binder in the conductive layer of the positive electrode can improve the bonding performance between the positive electrode current collector and the positive electrode film layer, and enhance the structural stability of the positive electrode sheet.

[0154] Optionally, the mass fraction of the conductive material in the conductive layer of the positive electrode is 30% to 50%. For example, it could be 30%, 35%, 40%, 45%, or 50%. Optionally, the mass fraction of the binder in the conductive layer of the positive electrode is 50% to 70% and could be 50%, 55%, 60%, 65%, or 70%. In some examples, the conductive layer of the positive electrode consists of a conductive material and a binder. Negative electrode sheet

[0155] As a non-restrictive example, the negative electrode current collector has two opposing surfaces in its own thickness direction, with the negative electrode film layer being arranged on one or both of these opposing surfaces of the negative electrode current collector.

[0156] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, copper foil can be used as the metal foil. The composite current collector can comprise a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be obtained by forming a metal material on a polymer material substrate. In the negative electrode current collector, the metal material can, as a non-limiting example, comprise at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. In the negative electrode current collector, the polymer material substrate can, as a non-limiting example, comprise at least one polymer material substrate made of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE).

[0157] Understandably, the aforementioned negative electrode film layer can contain one or more graphites with a powder compaction density of 1.5 g / cm². 3 up to 1.85 g / cm³ 3 Included at 20,000 N.

[0158] As described above, the negative electrode active material comprises graphite and the powder compaction density of the negative electrode active material at 20,000 N is 1.5 g / cm³. 3 up to 1.85 g / cm³ 3 For example, it can, but is not limited to, 1.5 g / cm². 3 1.55 g / cm³ 3 , 1.6 g / cm³ 3 , 1.65 g / cm³ 3 , 1.7 g / cm³ 3 , 1.72 g / cm³ 3 , 1.75 g / cm³ 3 , 1.8 g / cm³ 3 , 1.82 g / cm³ 3 , 1.85 g / cm³ 3The values ​​should be or fall within a range defined by any two of the aforementioned point values ​​as endpoints. By using graphite with this high powder compaction density, the secondary battery achieves a high energy density. Optionally, the powder compaction density of the graphite at 20,000 N is 1.6 g / cm³. 3 up to 1.85 g / cm³ 3 Optionally, the powder compaction density of the graphite at 20,000 N is 1.55 g / cm³. 3 up to 1.75 g / cm³ 3 .

[0159] In some of the embodiments, the compaction density of the negative electrode sheet, when the secondary battery is at 100% SOC, is 1.15 g / cm³. 3 up to 1.46 g / cm³ 3 , optional 1.25 g / cm² 3 up to 1.40 g / cm³ 3Thus, the negative electrode sheet still has a high density even after a full charge. For example, the density of the negative electrode sheet when the secondary battery is at 100% state of charge (SOC) is 1.15 g / cm³. 3 , 1.18 g / cm³ 3 , 1.20 g / cm³ 3 , 1.22 g / cm³ 3 , 1.25 g / cm³ 3 , 1.28 g / cm³ 3 , 1.3 g / cm³ 3 , 1.32 g / cm³ 3 , 1.35 g / cm³ 3 , 1.36 g / cm³ 3 , 1.38 g / cm³ 3 , 1.4 g / cm³ 3 , 1.42 g / cm³ 3 , 1.45 g / cm³ 3 , 1.46 g / cm³ 3or lies within a range consisting of any two of the values ​​mentioned above. The higher the compression density of the negative electrode sheet after a full charge, the lower the rebound force, indicating a lower expansion force in the battery. If the compression density of the negative electrode film layer is within the specified range, it not only has a high energy density but also contributes to improved cycle performance of the battery.

[0160] In some embodiments of the present application, the density of the negative electrode sheet when the secondary battery is in a state of 100% SOC has a meaning known in the art, which means that the negative electrode sheet is removed from a battery cell charged to a state of charge (SOC) of 100% in order to measure the density of the negative electrode film layer.

[0161] In some embodiments of the present application, the state of 100% SOC of the secondary battery is defined as follows:

[0162] The battery cell is charged to its upper limit voltage with a constant current of 0.33C and then discharged to 0.05C with a constant voltage, corresponding to a 100% state of charge (SOC). Similarly, the battery cell is discharged to its final voltage with a constant current of 0.33C, corresponding to a 0% state of charge (SOC).

[0163] Since the type of positive electrode active material in batteries can vary, the final voltage of a full charge can also differ. For example, the upper charging limit voltage of the battery can be 3.65 V or 3.8 V; the discharge cut-off voltage of the battery can be 2.5 V or 2.0 V. Using lithium iron phosphate as the positive electrode active material in the positive electrode sheet as an example, the aforementioned secondary battery is charged to 3.65 V at a charging rate of 0.33 C and then further charged to 0.05 C at a constant voltage, which corresponds to a state of charge (SOC) of 100%, with a density of 1.15 g / cm³ for the negative electrode sheet. 3 up to 1.46 g / cm³ 3 amounts.

[0164] In some of the embodiments, the compaction density of the negative electrode sheet after cold pressing is 1.5 g / cm³. 3 up to 1.8 g / cm³ 3 , optional 1.6 g / cm² 3 up to 1.75 g / cm³3 The compression density of the negative electrode sheet after cold pressing refers to the compression density of the negative electrode sheet before it is assembled into the battery.

[0165] The lower the density of the negative electrode after a full charge, the greater the rebound height or the lower the initial compression, leading to higher graphite activity and thus increased electrolyte consumption. More additives must be added to the electrolyte to increase the stability of the negative electrode's interfacial film and improve the battery's cycle performance. Conversely, the higher the density of the negative electrode after a full charge, the higher the battery's energy density, and the less space is available for the electrolyte, resulting in a lower electrolyte fill volume. Therefore, to improve the battery's fast-charging performance, the concentration of the first additive in the electrolyte must be increased. Thus, there is a relationship between the density of the negative electrode and the mass fraction of the first additive in the electrolyte.

[0166] In some of the embodiments, the compaction density of the negative electrode sheet, when the secondary battery is at 100% SOC, is ≥ 1.25 g / cm³. 3 and < 1.35 g / cm³ 3 .

[0167] Furthermore, the mass fraction of the first additive in the electrolyte is 1.5% to 6% if the compaction density of the negative electrode sheet, when the secondary battery is in a state of 100% SOC, is ≥ 1.25 g / cm³. 3 and < 1.35 g / cm³ 3 If the compression density of the negative electrode sheet, when the secondary battery is in a state of 100% SOC, is within the range mentioned above, and the mass fraction of the first additive in the electrolyte is 1.5% to 6%, the battery can combine both high energy density and good fast-charging performance.

[0168] The second additive in the electrolyte exhibits a lower film-forming impedance, which can improve the battery's kinetic performance and thus increase fast-charging capability. However, its concentration should not be too high to further enhance the battery's cycle life. The higher the battery's energy density, the less space is available for the electrolyte, resulting in a smaller electrolyte fill volume. Therefore, to improve the battery's fast-charging capability, the concentration of the second additive in the electrolyte must also be increased. Thus, there is a relationship between the density of the negative electrode and the mass fraction of the second additive in the electrolyte.

[0169] Furthermore, the mass fraction of the second additive in the electrolyte is 0.5% to 3% if the compaction density of the negative electrode sheet, when the secondary battery is in a state of 100% SOC, is ≥ 1.25 g / cm³. 3 and < 1.35 g / cm³3 amounts.

[0170] Furthermore, the mass fraction of the first solvent in the electrolyte is 22.5% to 34%, optionally 25.5% to 34%, if the compaction density of the negative electrode sheet, when the secondary battery is in a state of 100% SOC, is ≥ 1.25 g / cm³. 3 and < 1.35 g / cm³ 3 amounts.

[0171] Furthermore, the electrolyte mass per nominal capacity of 1 Ah of the secondary battery is 2.5 g to 3.0 g if the compression density of the negative electrode sheet, when the secondary battery is in a state of 100% SOC, is ≥ 1.25 g / cm³. 3 and < 1.35 g / cm³ 3 amounts.

[0172] In some of the embodiments, the compaction density of the negative electrode sheet, when the secondary battery is at 100% SOC, is 1.35 g / cm³. 3 up to 1.40 g / cm³ 3 .

[0173] Furthermore, the mass fraction of the first additive in the electrolyte is 2.5% to 7%, when the compaction density of the negative electrode sheet, when the secondary battery is in a state of 100% SOC, is 1.35 g / cm³. 3 up to 1.40 g / cm³ 3 If the compression density of the negative electrode sheet of the secondary battery at 100% SOC is within the range mentioned above, and the mass fraction of the first additive in the electrolyte is between 2.5% and 7%, the battery can better combine both high energy density and good fast-charging performance.

[0174] Furthermore, the mass fraction of the second additive in the electrolyte is 0.7% to 3.5%, optionally 1.5% to 3.5%, if the compaction density of the negative electrode sheet, when the secondary battery is in a state of 100% SOC, is 1.35 g / cm³. 3 up to 1.40 g / cm³ 3Furthermore, the mass fraction of the first solvent in the electrolyte is 21.25% to 34% when the compaction density of the negative electrode sheet, when the secondary battery is at 100% state of charge (SOC), is 1.35 g / cm³. 3 up to 1.40 g / cm³ 3 amounts.

[0175] Furthermore, the electrolyte mass per nominal capacity of 1 Ah of the secondary battery is 2.2 g to 2.8 g if the compression density of the negative electrode sheet, when the secondary battery is in a state of 100% SOC, is 1.35 g / cm³. 3 up to 1.40 g / cm³ 3 amounts.

[0176] In some of the embodiments, the volume energy density of the secondary battery is 400 Wh / L to 450 Wh / L, the mass fraction of the carboxylate ester in the electrolyte is 25.5% to 59.5%, and the combined mass fraction of the first and second additives in the electrolyte is 2% to 7%. If the volume energy density of the secondary battery is within this high energy density range and the carboxylate is added to the organic solvent of the electrolyte, the fast-charging performance of the secondary battery can be improved. However, the proportion of the carboxylate ester should not be too high, as this can lead to gas production in the negative electrode sheet in a graphite system and thus to a deterioration of the cycle performance. Therefore, the use of the first and second additives is further increased to improve the cycle life of the battery. Furthermore, the compaction density of the negative electrode sheet after cold pressing is 1.55 g / cm³. 3up to 1.65 g / cm³ 3 .

[0177] In some of the embodiments, the volume energy density of the secondary battery is > 450 Wh / L and ≤ 480 Wh / L, the mass fraction of the carboxylic acid ester in the electrolyte is 25.5% to 63.75%, and the total mass fraction of the first and second additives in the electrolyte is 3.5% to 8%. With the increase in the volume energy density of the secondary battery, it is necessary to increase the concentration of the carboxylic acid ester in the electrolyte as well as the concentrations of the first and second additives in order to simultaneously ensure a good cycle life at this high energy density.

[0178] Furthermore, the compaction density of the negative electrode sheet after cold pressing is 1.6 g / cm³. 3 up to 1.7 g / cm³ 3 .

[0179] In some of the embodiments, the charging time of the secondary battery at 30 °C from 10% SOC to 80% SOC is 6 to 15 minutes, the mass fraction of the carboxylic acid ester in the electrolyte is 17% to 63.75%, and the total mass fraction of the first and second additives in the electrolyte is 2% to 8%, optionally 5% to 7%. Because the high-density graphite ensures high energy density, and the battery is also fast-charging capable, the aforementioned concentration of carboxylic acid ester in the electrolyte is added, and the amounts of the first and second additives are increased, the secondary battery combines high energy density, fast-charging capability, and cycle life. Furthermore, the mass fraction of the first additive in the electrolyte is 1.5% to 6.5%, optionally 3.5% to 5.5%, and the mass fraction of the second additive is 0.5% to 6.5%, optionally 1.5% to 3.5%.

[0180] In some embodiments, the charging process of the secondary battery from a state of charge of 10% to 80% comprises several charging steps. The difference between the maximum state of charge of any one charging step within these multiple charging steps and the maximum state of charge in the adjacent charging step is less than or equal to the state of charge of 5%, for example, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%, or lies within a range consisting of any two of the aforementioned values.

[0181] The charging process of the secondary battery from a state of charge of 10% to 40% comprises several charging steps. Each charging step can be performed at any charging rate between 5C and 10C. The charging rate for each step can be any value from 5C, 5.5C, 6C, 6.5C, 7C, 7.5C, 8C, 8.5C, 9C, 9.5C, or 10C, or any combination of these two values.

[0182] The charging process of the secondary battery from a state of charge of 40% to 80% comprises several charging steps. The charging rate of each of these steps is lower than the charging rate of each of the steps used to charge the battery from a state of charge of 10% to 40%. The charging rate of the step at the state of charge of 80% is any value between 2.5C and 5C; for example, it could be 2.7C.

[0183] For example, the charging steps of the secondary battery charging process from 10% SOC to 80% SOC can be carried out as follows: With a constant current of 5.0 C, charging from 10% SOC to 15% SOC is achieved; With a constant current of 5.0 C, charging from 15% SOC to 20% SOC is achieved; With a constant current of 5.0 C, charging from 20% SOC to 25% SOC is achieved; With a constant current of 5.0 C, charging from 25% SOC to 30% SOC is achieved; With a constant current of 5.0 C, charging from 30% SOC to 35% SOC is achieved; With a constant current of 5.0 C, charging from 35% SOC to 40% SOC is achieved; With a constant current of 4.6 C, it charges from 40% SOC to 45% SOC; With a constant current of 4.3 C, it charges from 45% SOC to 50% SOC; Charging with a constant current of 4.0 C from 50% SOC to 55% SOC; With a constant current of 3.7 C, it charges from 55% SOC to 60% SOC; With a constant current of 3.4 C, it charges from 60% SOC to 65% SOC; With a constant current of 3.1 C, it charges from 65% SOC to 70% SOC; With a constant current of 2.9 C, it charges from 70% SOC to 75% SOC; With a constant current of 2.7 C, the battery is charged from 75% SOC to 80% SOC.

[0184] For example, the charging time of the secondary battery charging process from 10% SOC to 80% SOC is 6 minutes, 6.5 minutes, 7 minutes, 7.5 minutes, 8 minutes, 8.5 minutes, 9 minutes, 9.5 minutes, 10 minutes, 10.5 minutes, 11 minutes, 11.5 minutes, 12 minutes, 12.5 minutes, 13 minutes, 14 minutes, 14.5 minutes, 15 minutes, or lies in a range consisting of any two of the above values.

[0185] In some embodiments, the negative electrode sheet also includes a conductive layer of the negative electrode, which is arranged between the negative electrode current collector and the negative electrode film layer on at least one side. The conductive layer of the negative electrode comprises a conductive agent. The conductive layer of the negative electrode can also be formed by coating the surface of the negative electrode current collector with the appropriate paste, and then coating and drying the negative electrode paste to form the negative electrode sheet. Furthermore, the conductive agent in the conductive layer of the negative electrode comprises at least one of superconducting carbon, conductive graphite, carbon black, carbon black, Ketjen carbon black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.The conductive layer of the negative electrode can increase the adhesion between the negative electrode film layer and the negative electrode current collector, as well as improve the overall conductivity of the negative electrode sheet, which promotes an increase in the electron transfer rate.

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

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

[0188] Optionally, in the conductive layer of the negative electrode, the mass fraction of the conductive medium is 20% to 40% and that of the binder is 60% to 80%.

[0189] Furthermore, the graphite comprises at least one type of synthetic and one type of natural graphite. Synthetic graphite is used, which has fewer active sites on its surface. This results in a lower consumption rate of the first solvent and the first additive in the electrolyte, thus extending the battery's lifespan. Additionally, the discharge capacity per gram of graphite is ≤ 358 mAh / g. Within this capacity-per-gram range, the graphite exhibits suitable activity, contributing to a reduced electrolyte consumption rate and improved cycle life of the battery.

[0190] In some of the embodiments, the mass fraction of the negative electrode active material in the negative electrode film layer is 94% to 98%; for example, this mass fraction can be 94%, 96% or 98%.

[0191] In some of the embodiments, the negative electrode film layer may optionally also include a binder. The binder may comprise at least one of the following: 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 the embodiments, the negative electrode film layer can optionally also include a conductive material. The conductive material can comprise at least one of superconducting carbon, carbon black, carbon black, Ketjen carbon black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0193] In some of the embodiments, the negative electrode film layer may optionally also include other excipients, such as a thickening agent (such as sodium carboxymethylcellulose (CMC-Na)).

[0194] In some embodiments, the negative electrode sheet can be produced as follows: The components mentioned above for producing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder, and any other components, are dispersed in a solvent (a non-limiting example of the solvent is deionized water) to form a negative electrode paste; at least one side surface of the negative electrode current collector is coated with the negative electrode paste. After drying, cold pressing, and other processes, the negative electrode sheet can be obtained. The coating of the surface of the negative electrode current collector with the negative electrode paste can be carried out on a single surface of the negative electrode current collector or on both surfaces of the negative electrode current collector.

[0195] In some of the embodiments, the negative electrode film layer comprises at least one negative electrode active layer, wherein the at least one negative electrode active layer comprises the graphite.

[0196] In a specific example, the negative electrode film layer comprises a negative electrode active layer, wherein the negative electrode active layer contains the graphite, where 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 comprises a first and a second negative electrode active layer stacked on top of each other on the same side of the negative electrode current collector. The graphite in the first negative electrode active layer comprises at least one of the artificial graphite and one of the natural graphite, while the graphite in the second negative electrode active layer comprises the artificial graphite. The artificial graphite has fewer active sites on its surface, resulting in 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 is ≥ the Dv50 particle size of the graphite in the second negative electrode active layer. This reduces the distance between the particles of the negative electrode active material in the upper second negative electrode active layer, increases the contact area between the particles of the negative electrode active material, increases conductive channels and bridges, and thus increases the active area that can participate in reactions, thereby significantly increasing the specific capacity of the battery. Meanwhile, the porosity of the lower first negative electrode active layer is greater, resulting in better kinetic conductivity, which can improve fast-charging performance.

[0199] Furthermore, 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.

[0200] It is understood that the first and second negative electrode active layers are obtained by applying two different pastes on top of each other, followed by drying, cold pressing and other steps.

[0201] Furthermore, the Dv50 particle size of the graphite in the first negative electrode active layer is 9.5 µm to 18.5 µm, optionally 9.5 µm to 14.8 µm. For 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, or 18.5 µm.

[0202] Furthermore, the Dv50 particle size of the graphite in the second negative electrode active layer is 7.8 µm to 14.3 µm, optionally 7.8 µm to 12.8 µm. For 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, or 14.3 µm.

[0203] Optionally, the mass ratio of graphite in the first negative electrode active layer to that in the second negative electrode active layer is 3:7 to 7:3; optionally 4:6 to 6:4. For example, this mass ratio can be 3:7, 4:6, 5:5, 6:4, 7:3, or lie within a range consisting of any two of the above values.

[0204] Furthermore, the mass fraction of graphite in the first and second negative electrode active layers is 30% to 70% of the total graphite content. For example, it can be 30%, 35%, 40%, 45%, 48%, 50%, 55%, 60%, 65% or 70%, or it can be in a range consisting of any two of the values ​​mentioned above.

[0205] Furthermore, the thickness of the second negative electrode active layer relative to the total thickness of the first and second negative electrode active layers is 30% to 70%. For example, it can be 30%, 40%, 50%, 60%, 70%, or lie within a range defined by any two of the aforementioned point values. Optionally, it can be 40% to 60%.

[0206] In some embodiments, 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 surface of the graphite body particles is coated with the coating layer, and the coating layer comprises amorphous carbon.

[0207] Furthermore, with respect to the total mass of the artificial graphite, the mass fraction of amorphous carbon is 2% to 5%; for example, it can be 2%, 3%, 4%, 5%, or lie in a range formed by any two of the above-mentioned point values ​​as end values.

[0208] Furthermore, the powder resistance of the synthetic graphite is ≤ 0.04 f2-cm.

[0209] In some of the embodiments, the charging capacity per gram of graphite in a button cell at a 0.1 C rate is > 350 mAh / g, optionally 350 mAh / g to 440 mAh / g.

[0210] In some of the embodiments, the negative electrode active material can comprise a silicon-based material in addition to the aforementioned graphite. Furthermore, the silicon-based material can comprise at least one of the following: silicon oxide compound, silicon-carbon composite, elemental silicon, silicon-nitrogen composite, and silicon alloy. In the silicon-based material, the mass fraction of elemental silicon in the negative electrode active material is 0.3% to 10%, optionally 1% to 6%. separator

[0211] In some embodiments, the secondary battery also includes a separator. The separator is arranged between the positive and negative electrode sheets and serves primarily to prevent a short circuit between the electrodes while simultaneously allowing ion permeability.

[0212] In some of the embodiments, the positive electrode sheet, the negative electrode sheet and the separator can be formed into an electrode arrangement by a winding or a stacking process.

[0213] The present application does not impose any specific restrictions on the type of separator, and any known separator with good chemical and mechanical stability and a porous structure may be used. The separator may, without specific restriction, be a single-layer film or a multi-layer composite film. If the separator is a multi-layer composite film, the materials of each layer may be the same or different without specific restriction. In some embodiments, the thickness of the separator is 6 µm to 40 µm, optionally 12 µm to 20 µm.

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

[0215] Furthermore, the material of the porous base film can comprise at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene and polyvinylidene fluoride.

[0216] Furthermore, the thickness of the porous base film is ≤ 12 µm, optionally ≤ 9 µm, optionally 6 µm to 9 µm. For example, the thickness of the base film is 6 µm, 6.5 µm, 7 µm, 7.5 µm, 8 µm, 8.5 µm, 9 µm, 9.5 µm, 10 µm, 10.5 µm, 11 µm, 11.5 µm, 12 µm, or lies within a range consisting of any two of the values ​​mentioned above.

[0217] If the porosity of the separator in the embodiments of the present application is within the aforementioned range, the migration capability of the lithium ions in the separator can be improved and the internal resistance of the battery cell can be further reduced, thereby reducing heat generation.

[0218] In some embodiments of the present application, porosity refers to the percentage of the pore volume relative to the total volume of the separator. The porosity can be tested in accordance with standard GB / T 36363-2018 "Polyolefin separators for battery cells". It should be noted that the actual test process may employ test procedures that deviate from the standard to obtain more accurate measurements, depending on test equipment variations, measurement errors, and the need to minimize the influence of porosity measurements.

[0219] Furthermore, the porosity of the porous base film is 20% to 70%, optionally 35% to 60%. For example, the porosity of the base film is 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or lies within a range consisting of any two of the values ​​mentioned above.

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

[0221] In some embodiments of the present application, the separator can be a base film. Optionally, the separator further comprises a functional layer arranged on at least one side of the base film. The functional layer can comprise inorganic particles to increase the heat resistance of the separator. Optionally, a functional layer is arranged on each side of the base film.

[0222] In some embodiments, the functional layer comprises a first functional layer and a second functional layer, wherein the first functional layer is located on one side of the base film, the first functional layer comprises first inorganic particles, the second functional layer is located on the other side of the base film, and the second functional layer comprises composite particles, wherein the composite particles comprise second inorganic particles and non-fluoropolymer particles, wherein the second inorganic particles adhere to the surface of the non-fluoropolymer particles and / or are dispersed inside the non-fluoropolymer particles.

[0223] The first functional layer and the second functional layer exhibit good heat resistance and can increase the heat resistance of the separator.

[0224] Optionally, the first functional layer may include a binder, which may optionally include at least one fluorinated binder or a polyacrylic binder, such as polyvinylidene fluoride.

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

[0226] In some embodiments of the present application, the thickness of the base film has a meaning known in the art and can be determined using means and devices known in the art. For example, a freshly manufactured separator can be taken as a sample, or a fully discharged battery cell (discharged to the lower limit voltage so that the battery's state of charge is approximately 0% SOC) can be reverse disassembled and the separator removed. The separator is dried and used as a sample. Subsequently, the separator is cut with an ion beam cutter to produce a cross-section. The thickness of the separator cross-section and its various layers is then measured using a scanning electron microscope.

[0227] The non-fluorinated polymer particles in the second functional layer are non-fluorinated polymers. For example, the non-fluorinated polymer particles include acrylate copolymer particles. Optionally, the acrylate copolymer particles include an acrylate-acrylonitrile-acrylamide-propylene copolymer. The acrylate copolymer is characterized by excellent bonding performance and high bond stability with the base film. The molar ratio of the individual monomers in the copolymer can be any desired ratio, for example, 35% : 30% : 15% : 20% or 40% : 20% : 10% : 30% or 45% : 15% : 20% : 20%, etc.

[0228] Within the composite particles, the secondary inorganic particles prevent the non-fluoropolymer particles from bonding during the high-temperature granulation process. This creates pores in the composite particles that promote lithium ion transport and improve the separator's ion conductivity. Additionally, these secondary inorganic particles increase the bulk modulus of the composite particles, making them less prone to deformation during charging and discharging. This stabilizes the separator's structure, improves the battery cell's kinetic performance, and enhances fast-charging capabilities.

[0229] Optionally, the second functional layer is positioned closer to the negative electrode sheet than the first. Since the composite particles do not deform easily, the separator generally does not cause any side effects such as pressure on the negative electrode sheet, thus ensuring that the kinetic performance of the negative electrode sheet remains stable. Accordingly, the first functional layer is positioned closer to the positive electrode sheet.

[0230] Optionally, the second inorganic particles comprise one or more of silicon dioxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium dioxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide. Silicon dioxide is also optionally included. These second inorganic particles can enhance the heat resistance of the second functional layer and, together with non-fluorinated polymers, form composite particles to further improve the separator's cycle stability and dynamic performance, thereby enhancing the battery cell's cycle life and fast-charging performance.

[0231] The average particle size of the second inorganic particle is 5 nm to 100 nm, optionally 10 nm to 100 nm, and optionally 5 nm to 20 nm. For example, the average particle size of the second inorganic particle could be 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, or a range consisting of any two of the above values. Having the average particle size of the second inorganic particle within the above range is advantageous for increasing the heat resistance and bulk modulus of the composite particles.

[0232] In some embodiments of the present application, the average particle size of the second inorganic particles has a meaning known in the art and can be determined using devices and methods known in the art. For example, after receiving the separator, it is dried and used as a sample. Subsequently, the separator is cut with an ion beam cutter to produce a cross-section. The particle size of the second inorganic particles in the separator is then measured with a scanning electron microscope. The particle sizes of several, for example 50, second inorganic particles are measured, and the average value is calculated as the average particle size of the second inorganic particles.

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

[0234] If the ionic conductivity of the separator is within the range mentioned above, the migration capability of the lithium ions in the separator can be further improved, thereby improving the fast charging performance of the battery cell.

[0235] In some embodiments of the present application, the ionic conductivity of the separator has a meaning known in the art and can be determined using devices and methods known in the art, for example:

[0236] Production of a 2025 button cell for testing purposes: A lithium sheet is placed in a negative electrode casing of the battery within a vacuum glovebox. 150 µL of electrolyte are added. The electrolyte used is a 1M LiPF6 solution in an EC / EMC / DEC ratio of 3 / 5 / 2 (mass ratio). A separator (3.14 cm²) is then used. 2 A surface area (12 µm thick) is placed on the lithium sheet. An additional 25 µL of electrolyte is added. Finally, a positive electrode sheet (the positive electrode sheet can be the one from embodiment 1) is placed on top before the cell is encapsulated. The assembled button cell is removed from the vacuum glove box and stored for 24 hours to prepare for subsequent testing.

[0237] Test: At an electrochemical workstation, measurements are taken in the frequency range of 10 -1 up to 10 6The frequency was measured in Hz to determine the separator resistance Rb. The ionic conductivity σ (unit: mS / cm) is calculated using the following formula: σ=L / (Rb×S) where R b corresponds to the equivalent resistance, while L and S correspond to the thickness and area of ​​the separator to be tested, respectively.

[0238] The secondary battery comprises at least one battery cell. The secondary battery can comprise one or more battery cells.

[0239] In this application, unless otherwise specified, "battery cell" refers to the basic unit that enables the conversion of chemical energy into electrical energy and vice versa, and generally comprises at least the positive electrode sheet, the negative electrode sheet, and the electrolyte. During the charging and discharging process, the active ions intercalate and deintercalate between the positive and negative electrode sheets. The electrolyte serves to conduct the active ions between the positive and negative electrode sheets.

[0240] The present application does not impose any specific restrictions regarding the shape of the battery cell; it can be cylindrical, rectangular, or any other shape. For example, the one in Fig. 1 Secondary battery shown is a battery cell which serves as an example of a battery cell 5 in a rectangular structure.

[0241] In some of the embodiments, the battery cell 5 may include an outer packaging. This outer packaging may be used to encapsulate the electrode arrangement and electrolyte mentioned above. In some of the embodiments, the outer packaging of the battery cell 5 may be a rigid casing, for example, a rigid plastic casing, an aluminum casing, a steel casing, etc. The outer packaging of the battery cell 5 may also be a flexible casing, for example, a pouch-like flexible casing. The material of the flexible casing may be plastic, and non-limiting examples of the plastic may include at least one of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0242] In some of the embodiments, the outer packaging, referring to Fig.2, comprising a housing body 51 and a cover plate 53. The housing body 51 may include a base plate and a side plate connected to the base plate, the base plate and the side plate forming a receiving chamber. The housing body 51 has an opening that communicates with the receiving chamber, and the cover plate 53 may cover the opening to close the receiving chamber. The positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly 52 by a winding or stacking process. The electrode assembly 52 is enclosed in the receiving chamber. The electrolyte is impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 may be one or more; the person skilled in the art may choose according to actual requirements.

[0243] In the present application, the secondary battery refers to a battery cell.

[0244] In some embodiments, the battery device includes a secondary battery; the battery device may be a battery module, a battery pack, or an energy storage battery.

[0245] The battery module comprises at least one battery cell. The number of battery cells contained in the battery module can be one or more; the person skilled in the art can select the appropriate number depending on the application and capacity of the battery module.

[0246] The in Fig. The battery module shown in section 3 is an example battery module 4. Referring to Fig. 3. Several battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, other arrangements are also possible. Furthermore, the multiple battery cells 5 can be secured by fastening elements.

[0247] Optionally, the battery module 4 can also include a housing with a receiving space, in which the multiple battery cells 5 are received.

[0248] In some of the embodiments, the above-mentioned battery module can also be assembled into a battery pack, wherein the number of battery modules contained in the battery pack can be one or more; the person skilled in the art can choose the appropriate number depending on the application and capacity of the battery pack.

[0249] The Fig. 4 and Fig. Figure 5 shows a battery pack that serves as an example of battery pack 1. Referring to the Fig. 4 and Fig.5. The battery pack 1 can comprise a battery box and several battery modules 4 arranged therein. The battery box comprises an upper box body 2 and a lower box body 3; the upper box body 2 can cover the lower box body 3 and form an enclosed space for receiving the battery modules 4. The multiple battery modules 4 can be arranged in any way within the battery box.

[0250] Furthermore, one embodiment of the present application also provides a power-consuming device comprising a secondary battery according to the present application and / or a battery device according to the present application. The power-consuming device may include, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Mobile devices may include, for example, mobile phones, laptops, etc.; electric vehicles may include, for example, fully electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc., but are not limited to.

[0251] The secondary battery in the power-consuming device can be selected as needed.

[0252] Fig.Figure 6 shows an example of a power-consuming device. The power-consuming device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the power-consuming device's requirements for high power and high energy density of the secondary battery, a battery pack or battery module can be used.

[0253] As another example, the device could be a mobile phone, a tablet, a laptop, etc. This power-consuming device usually needs to be light and thin, and battery cell 5 can be used as its power source.

[0254] To more clearly illustrate the technical problem solved by the present application, its embodiments, and its advantageous effects, the present application is described in further detail below with reference to exemplary embodiments and accompanying drawings. Obviously, the described exemplary embodiments are only a subset of the embodiments of the present application, but not all of them. The following description of at least one exemplary embodiment serves only for clarification and does not constitute a limitation of the present application and its applications. All other embodiments that a person skilled in the art could have derived without creative effort based on the embodiments of the present application fall within the scope of protection of the present application.

[0255] If no specific techniques or conditions are indicated in the examples, the techniques or conditions described in the technical literature or product instructions must be followed. All reagents and instruments used without manufacturer information are commercially available products. Exemplary embodiment 1(1) Production of the positive electrode sheet:

[0256] The positive electrode active material lithium iron phosphate LiFePO4 exhibited the following performance parameters: The powder compaction density at 30,000 N was 2.53 g / cm³. 3 .

[0257] The positive electrode active material lithium iron phosphate LiFePO4, the binder polyvinylidene fluoride and the conductive agent acetylene carbon black were mixed in a mass ratio of 97 : 2 : 1, then the solvent N-methyl-2-pyrrolidone (NMP) was added and stirred uniformly to form the positive electrode paste; the aluminum foil of the positive electrode current collector was uniformly coated with the positive electrode paste, and after drying and cold pressing, the positive electrode sheet was obtained.

[0258] The coating weight of the positive electrode sheet was 300 mg / 1540.25 mm². 2 The compaction density of the positive electrode sheet was 2.63 g / cm³. 3 , when the battery was charged to 100% SOC at a charging rate of 0.33 C. (2) Production of the negative electrode sheet:

[0259] The manufacturing process for the negative electrode sheet with a two-layer negative electrode structure was as follows: The negative electrode active material, first graphite, exhibited the following performance parameters: The powder compaction density at 20,000 N was 1.67 g / cm³. 3 The Dv50 particle size of the graphite was 12.8 µm, and the mass fraction of amorphous carbon was 2.5%.

[0260] The negative electrode active material second graphite exhibited the following performance parameters: The powder compaction density at 20,000 N was 1.6 g / cm³. 3 , the Dv50 particle size of the graphite was 9.6 µm, and the mass fraction of amorphous carbon was 3.4%.

[0261] The negative electrode active material first, graphite, the conductive agent acetylene carbon black, the binder styrene-butadiene rubber, and the thickening agent sodium carboxymethylcellulose were mixed in a mass ratio of 96 : 0.5 : 2.5 : 1 and then added to the solvent deionized water to form the negative electrode paste 1 by uniform stirring; the negative electrode active material second, graphite, the conductive agent acetylene carbon black, the binder styrene-butadiene rubber, and the thickening agent sodium carboxymethylcellulose were mixed in a mass ratio of 96 : 0.5 : 2.5 : 1 and then added to the solvent deionized water to form the negative electrode paste 2 by uniform stirring.

[0262] The copper foil of the negative electrode current collector was uniformly coated with negative electrode paste 1. After drying, the dried surface of negative electrode paste 1 was coated with negative electrode paste 2. After drying and cold pressing, the negative electrode sheet was obtained. The negative electrode sheet comprised a current collector and a first negative electrode active layer and a second negative electrode active layer, which were stacked successively on the negative electrode current collector. The mass ratio of graphite in the first negative electrode active layer to that in the second negative electrode active layer was 50%:50%.

[0263] The coating weight of the negative electrode sheet was 138 mg / 1540.25 mm². 2 ; the compaction density of the negative electrode sheet was 1.26 g / cm³ 3 , when the battery was charged to 100% SOC at a charging rate of 0.33 C. (3) Preparation of the electrolyte:

[0264] In an argon atmosphere glovebox with a water content of < 10 ppm, the first solvent, ethylene carbonate (EC), the second solvent, ethyl acetate (EA), and dimethyl carbonate (DMC) were homogeneously mixed in a specific mass ratio to obtain an organic solvent. The mass fractions of ethylene carbonate (EC), ethyl acetate (EA), and dimethyl carbonate (DMC) in the electrolyte are listed in Table 1. Lithium hexafluorophosphate (LiPF6) was slowly added in a specific mass as the lithium salt and stirred thoroughly until completely dissolved. The mass fraction of LiPF6 in the electrolyte was 15%. After returning to ambient temperature, 5% vinylene carbonate (VC) as the first additive and 2% fluoroethylene carbonate (FEC) as the second additive, based on the total mass of the electrolyte, were added and thoroughly mixed to obtain the electrolyte.The electrolyte mass b per nominal capacity of 1 Ah of the secondary battery is listed in Table 1. (4) Production of the separator:

[0265] The separator comprised a base film, the base film being a 7 µm thick polyethylene film layer with a porosity of 42%. Production of the secondary battery:

[0266] The positive electrode sheet, separator, and negative electrode sheet were stacked and wound sequentially to form a wound electrode assembly. This assembly was then placed in a rectangular aluminum case as outer packaging, dried, and subsequently filled with electrolyte. After sealing, settling, formation, aging, resealing, and capacity determination, etc., the secondary battery was obtained.

[0267] The manufacturing processes of embodiments 2 to 4 were similar to that of embodiment 1, the difference being that the mass fraction of ethylene carbonate (EC) in the electrolyte was adjusted (the mass fraction of EA remains unchanged, the mass fraction of DMC was changed accordingly), as shown in Table 1.

[0268] The manufacturing processes of embodiments 5 to 7 were similar to that of embodiment 3, the difference being that the mass fraction of the first additive VC in the electrolyte was adjusted, with at least one of the mass fractions of the first and second solvents being adjusted accordingly, as shown in Table 1.

[0269] The manufacturing processes of embodiments 8 to 10 were similar to that of embodiment 3, the difference being that the mass fraction of the second additive FEC in the electrolyte was adjusted, with at least one of the proportions of the first and second solvents being adjusted accordingly, as shown in Table 1.

[0270] The manufacturing process of embodiment 11 was similar to that of embodiment 3, the difference being that both the mass fraction of the first additive VC and the second additive FEC in the electrolyte were adjusted, with at least one of the proportions of the first and second solvent being adjusted accordingly, as shown in Table 1.

[0271] The manufacturing process of embodiment 12 was similar to that of embodiment 3, the difference being that the type of the second solvent and its mass fraction in the electrolyte were changed (the mass fraction of EC remains unchanged, the mass fraction of DMC was changed accordingly), as shown in Table 1.

[0272] The manufacturing process of embodiment 13 was similar to that of embodiment 3, the difference being that the type of the second graphite of the negative electrode active material was changed and its Dv50 particle size was different, as shown in Table 1; and the powder compaction density of the second graphite at 20,000 N was 1.55 g / cm³. 3 fraud.

[0273] The manufacturing process of embodiment 14 was similar to that of embodiment 3, the difference being that the type of the first graphite of the negative electrode active material was changed and its Dv50 particle size was different, as shown in Table 1; and the powder compaction density of the first graphite at 20,000 N was 1.72 g / cm³. 3 fraud.

[0274] The manufacturing processes of embodiments 15 to 16 were similar to that of embodiment 3, the difference being that the electrolyte filling coefficient was adjusted, which is why the electrolyte mass b per nominal capacity of 1 Ah of the secondary battery was different, as shown in Table 1.

[0275] Furthermore, in embodiment 15, the positive electrode active material lithium iron phosphate LiFePO4 exhibited the following performance parameters: The powder compaction density at 30,000 N was 2.55 g / cm³. 3The compaction density of the positive electrode sheet was 2.72 g / cm³. 3 , when the battery was charged to 100% SOC at a charging rate of 0.33 C; in the negative electrode paste 1 and the negative electrode paste 2 of the negative electrode sheet, the graphite used in embodiment 3 with a mass fraction of 1% was replaced by silicon carbide with a mass fraction of 1%.

[0276] In embodiment 16, the positive electrode active material lithium iron phosphate LiFePO4 exhibited the following performance parameters: The powder compaction density at 30,000 N was 2.56 g / cm³. 3 The compaction density of the positive electrode sheet was 2.75 g / cm³. 3, when the battery was charged to 100% SOC at a charging rate of 0.33 C; in the negative electrode paste 1 and the negative electrode paste 2 of the negative electrode sheet, the graphite used in embodiment 3 with a mass fraction of 3% was replaced by silicon carbide with a mass fraction of 3%. Example 17

[0277] The manufacturing process was similar to that of embodiment 3, the difference being that the negative electrode sheet had a single-layer structure, the manufacturing process of which was as follows: The negative electrode active material third graphite exhibited the following performance parameters: The powder compaction density at 20,000 N was 1.63 g / cm³. 3 The Dv50 particle size of the graphite was 10.8 µm, and the mass fraction of amorphous carbon was 3.1%.

[0278] The negative electrode active material (third graphite), the conductive agent (acetylene carbon black), the binder (styrene-butadiene rubber), and the thickening agent (sodium carboxymethylcellulose) were mixed in a mass ratio of 96:0.5:2.5:1. Then, the solvent (deionized water) was added and stirred uniformly to form a negative electrode paste. The copper foil of the negative electrode current collector was uniformly coated with the negative electrode paste, and after drying and cold pressing, the negative electrode sheet was obtained.

[0279] The coating weight of the negative electrode sheet was 138 mg / 1540.25 mm². 2 (one-sided); the compaction density of the negative electrode sheet was 1.26 g / cm³ 3 , when the battery was charged to 100% SOC at a charging rate of 0.33 C.

[0280] The manufacturing processes of comparative examples 1 to 5 were similar to that of embodiment 3, the difference being that the mass fraction of ethylene carbonate (EC) in the electrolyte and at least one of the mass fractions of the first additive VC and the first additive FEC in the electrolyte were adjusted, as shown in Table 1. The following section explains the performance tests. (I) Test of the volumetric energy density of the secondary battery

[0281] The battery cell is charged at 25 °C with a constant current of 0.33 C to 3.65 V, allowed to rest for 1 minute, then charged again with a constant current of 0.1 C to 3.65 V and allowed to rest for 30 minutes; and then discharged with a constant current of 0.33 C to 2.0 V. The discharge capacity A0 is recorded at this time in Ah. The length, width, and height of the battery cell are measured with calipers (usually based on the battery case size, without considering the height of the electrode columns). The volume V0 of each battery is calculated in L. The volumetric energy density of the battery cell VED = (A0 × discharge platform voltage) / V0 in Wh / L. (II) The test steps for determining the capacity retention rate after 1000 cycles at 60 °C are as follows:

[0282] At 60 °C, the batteries are charged with a constant current of 1C to the final charging voltage of 3.65 V, left to rest for 30 minutes, and then discharged with a constant current of 1C to 2.0 V – this constitutes one charge-discharge cycle. The capacity C0 after the first cycle is recorded. This charge-discharge cycle is repeated 1,000 times. After repeating these cycles up to the 1,000th cycle, the corresponding capacity (Cn) is recorded. The capacity retention rate after 1,000 cycles at 60 °C is calculated as follows: Cn / C0 × 100%. The higher the capacity retention rate, the better the battery's cycle life. (III) The test steps for determining the charging time T of the secondary battery charging process at 30 °C from 10% SOC to 80% SOC are as follows:

[0283] At an ambient temperature of 30 °C, the battery is charged from a state of 10% SOC. With a constant current of 5.0 C, charging from 10% SOC to 15% SOC is achieved; With a constant current of 5.0 C, charging from 15% SOC to 20% SOC is achieved; With a constant current of 5.0 C, charging from 20% SOC to 25% SOC is achieved; With a constant current of 5.0 C, charging from 25% SOC to 30% SOC is achieved; With a constant current of 5.0 C, charging from 30% SOC to 35% SOC is achieved; With a constant current of 5.0 C, charging from 35% SOC to 40% SOC is achieved; With a constant current of 4.6 C, it charges from 40% SOC to 45% SOC; With a constant current of 4.3 C, it charges from 45% SOC to 50% SOC; Charging with a constant current of 4.0 C from 50% SOC to 55% SOC; With a constant current of 3.7 C, it charges from 55% SOC to 60% SOC; With a constant current of 3.4 C, it charges from 60% SOC to 65% SOC; With a constant current of 3.1 C, it charges from 65% SOC to 70% SOC; With a constant current of 2.9 C, it charges from 70% SOC to 75% SOC; With a constant current of 2.7 C, it charges from 75% SOC to 80% SOC; The entire charging time is recorded. (IV) The test steps for determining the capacity retention rate after 1,000 cycles at 30 °C are as follows:

[0284] At 30°C, the batteries are each charged from 10% SOC to 80% SOC using the charging rates assigned to the different SOC levels mentioned above. They are then charged to 3.65 V at a constant current of 0.33 C, left to rest for 30 minutes, and finally discharged to 2.0 V at a constant current of 1 C – this constitutes one charge-discharge cycle. The capacity C0 after the first cycle is recorded. This charge-discharge cycle is repeated 1,000 times. After each cycle up to the 1,000th cycle, the corresponding capacity (Cn) is recorded. The capacity retention rate after 1,000 cycles at 30°C is calculated as follows: Cn / C0 × 100%. The higher the capacity retention rate, the better the battery's cycle life.

[0285] The parameters of the exemplary embodiments and comparative examples are partially listed in Table 1, where all contents are mass fractions, the unit of the one-sided coating weight of the positive and negative electrode is mg / 1540.25 mm². 2 is.

[0286] The test results of the aforementioned performance tests for the exemplary implementations and comparison examples are listed in Table 2. Table 1 Table 2 Serial number Volume energy density (in Wh / L) Battery capacity retention rate after 1,000 cycles at 60 °C Battery capacity retention rate after 1,000 cycles at 30 °C Charging time from 10% to 80% SOC (in T / min) Example 1 410 80,20 % 92,40 % 10,6 Example 2 410 82 % 93,90 % 10,2 Example 3 410 82,80 % 94,30 % 9,7 Example 4 410 82,00 % 94,60 % 9,5 Example 5 410 78,90 % 94,90 % 9,1 Example 6 410 83,80 % 93,30 % 10,4 Example 7 410 84,50 % 92,60 % 10,9 Example 8 410 83,30 % 93,30 % 10,2 Example 9 410 81,10 % 94,50 % 9,5 Example 10 410 80,30 % 94,20 % 9,3 Example 11 410 77,50 % 92,60 % 8,90 Example 12 410 82,70 % 93,80 % 11,20 Example 13 410 81,50 % 93,70 % 9,20 Example 14 410 82,20 % 92,10 % 11,20 Example 15 450 81,40 % 93,10 % 9,7 Example 16 480 80,50 % 92,60 % 9,7 Example 17 410 80,3 % 92,20 % 10,8 Comparative example 1 410 84,80 % 88,50 % 11,6 Comparative example 2 410 54,80 % 89,50 % 9 Comparative example 3 410 73,90 % 91,90 % 9,3 Comparative example 4 410 72,40 % 92,60 % 8,90 Comparative example 5 410 67,20 % 90,10 % 11,2

[0287] Tables 1 and 2 above show that in comparison example 1, the mass fraction of the first additive in the electrolyte is too high, which impairs the cycle performance and fast-charging performance of the battery at room temperature; in comparison example 2, the mass fraction of the first additive in the electrolyte is too low, which impairs the high-temperature cycle performance of the battery; in comparison example 3, the mass fraction of the second additive in the electrolyte is too high, which impairs both the high-temperature cycle performance and the room-temperature cycle performance of the battery; in comparison example 4, the mass fraction of the second additive in the electrolyte is too low, which impairs the room-temperature cycle performance of the battery.In comparative example 5, the mass fraction of the first solvent in the electrolyte is too low, which impairs the stability of the electrolyte and reduces the conductivity, resulting in poor both room temperature and high-temperature cycle performance.

[0288] In the various embodiments, adjusting the composition and ratio of the electrolyte, in combination with the negative electrode sheet made of high-density graphite, enables the manufactured secondary batteries to combine good energy density with fast-charging performance, room-temperature cycle performance, and high-temperature cycle performance. In embodiment 17, only a carbonate solvent is used as the second solvent in the electrolyte, which reduces the conductivity of the electrolyte, thus reducing the single-sided coating weight of the positive and negative electrode sheets to improve the battery's fast-charging performance.

[0289] The technical features of the embodiments described above can be combined in any way. To keep the description concise, not all possible combinations of the technical features in the aforementioned embodiments have been described. However, as long as there are no contradictions in the combination of these technical features, all such combinations should be considered to be described within the scope of this specification. The embodiments described above represent only some of the embodiments of the present application and are described specifically and in detail, but they should not be considered a limitation of the scope of protection of the patent. It should be noted that a person skilled in the art can make numerous modifications and improvements based on the concept of the present application, which remain within the scope of protection of the present application.Therefore, the scope of protection of the present application should be based on the attached claims. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited non-patent literature

[0000] GB / T 24533-2009

[0081] 24533-2009

[0119] Standard GB / T 36363-2018 “Polyolefin separators for battery cells

[0218]

Claims

[1] Secondary battery, comprising a positive electrode sheet comprising a positive electrode current collector and a positive electrode film layer, wherein 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, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer, wherein the negative electrode film layer is arranged on at least one side of the negative electrode current collector and the negative electrode film layer comprises a negative electrode active material, wherein the negative electrode active material comprises graphite and the powder compaction density of the negative electrode active material at 20,000 N is 1.5 g / cm³ 3 up to 1.85 g / cm³ 3 amounts to; and an electrolyte comprising an organic solvent and an organic additive, wherein the organic solvent comprises a first solvent, the first solvent comprising cyclic carbonate, and the mass fraction of the first solvent, based on the total mass of the electrolyte, is 17% to 34%; wherein the organic additive comprises a first and a second additive, the first additive comprising vinylene carbonate and the second additive comprising an ethylene carbonate derivative, and the mass fraction of the first additive is 1.5% to 8% and the mass fraction of the second additive is 0.5% to 4%, each based on the total mass of the electrolyte. [2] Secondary battery according to claim 1, wherein the structure of the ethylene carbonate derivative is as follows:, wherein R1 and R2 each independently comprise any element hydrogen, a halogen element, a C1 to C5 alkyl group or a halogenated C1 to C5 alkyl group, and R1 and R2 are not simultaneously the element hydrogen. [3] Secondary battery according to claim 1 or 2, wherein the ethylene carbonate derivative comprises at least one of fluoroethylene carbonate, difluoroethylene carbonate and trifluoromethylethylene carbonate. [4] Secondary battery according to any one of claims 1 to 3, wherein the cyclic carbonate comprises at least one of ethylene carbonate and propylene carbonate. [5] Secondary battery according to any one of claims 1 to 4, wherein the mass fraction of the first solvent, based on the total mass of the electrolyte, is 25.5% to 34%. [6] Secondary battery according to any one of claims 1 to 5, wherein the mass fraction of the first additive, based on the total mass of the electrolyte, is 1.5% to 6.5%; and / or the mass fraction of the second additive, based on the total mass of the electrolyte, is 0.5% to 3%. [7] Secondary battery according to any one of claims 1 to 6, wherein the total mass fraction of the first additive and the second additive, based on the total mass of the electrolyte, is 2% to 10%. [8] Secondary battery according to any one of claims 1 to 7, wherein the total mass fraction of the first additive and the second additive, based on the total mass of the electrolyte, is 3% to 8%. [9] Secondary battery according to any one of claims 1 to 8, wherein the powder compaction density of the positive electrode active material at 30,000 N ≥ 2.43 g / cm³ 3 , optional 2.48 g / cm² 3 up to 2.85 g / cm³ 3 amounts. [10] Secondary battery according to any one of claims 1 to 9, wherein the positive electrode active material comprises at least one of lithium-containing phosphate with olivine structure and its derivatives. [11] Secondary battery according to claim 10, wherein the positive electrode active material comprises: a core section comprising at least one lithium-containing phosphate with an olivine structure and its derivatives; and an ion-conducting layer, wherein the surface of the core section is coated with the ion-conducting layer and the ion-conducting layer comprises at least one element of Fe, C, Ti, Zr, Hf, Ge and Sn. [12] Secondary battery according to claim 10 or 11, wherein the lithium-containing phosphate with olivine structure and its derivatives is a compound of the general formula Li x1 Al y1 M1 a1 M2 b1 P 1c1 X c1 Q1 z1include, where 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. [13] Secondary battery according to claim 12, wherein the lithium-containing phosphate with olivine structure and its derivatives comprise at least one of lithium iron phosphate, lithium manganese phosphate, lithium nickel phosphate and lithium cobalt phosphate. [14] Secondary battery according to one of claims 11 to 13, wherein the ion-conducting layer is an ion conductor having the chemical formula Li 3-b Fe 2-b M3 b (PO m ) nincludes, where M3 includes at least one element of +4-valent Ti, Zr, Hf, Ge and Sn, 0 ≤ b ≤ 1, 3 ≤ m ≤ 5, 2 ≤ n ≤ 4. [15] Secondary battery according to claim 14, wherein the ion conductor comprises at least one of lithium iron titanium phosphate, lithium iron zirconium phosphate and lithium iron tin phosphate. [16] Secondary battery according to any one of claims 1 to 15, wherein at least one of the following conditions is met: (1) The compaction density of the positive electrode sheet is 2.5 g / cm³. 3 up to 2.8 g / cm³ 3 ; (2) the mass fraction of carbon in the positive electrode active material is 1% to 2%; (3) the powder resistance of the positive electrode active material is ≤ 20 Ω·cm; (4) the volume-averaged particle size of the positive electrode active material meets the following conditions: 1 µm ≤ Dv50 ≤ 2 µm, 0.4 µm ≤ Dv10 ≤ 0.7 µm. [17] Secondary battery according to any one of claims 1 to 16, wherein the positive electrode film layer further comprises a lithium supplement, the lithium supplement comprising at least one of ternary lithium supplement material, lithium phosphate, lithium dihydrogen phosphate, lithium sulfate, lithium sulfite, lithium molybdate, lithium nickelate, lithium ferrate, lithium oxalate, lithium titanate, lithium tetraborate, lithium metasilicate, lithium metamanganate, lithium tartrate and trilithium citrate. [18] Secondary battery according to claim 17, wherein the ternary lithium supplement material Li x2 A2 y2 Ni a2 Co b2 Mn c2 M4 (1-a2-b2-c2) Q2 z2includes, 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. [19] Secondary battery according to any one of claims 1 to 18, wherein the positive electrode sheet further comprises a conductive layer of the positive electrode, wherein the conductive layer of the positive electrode is arranged between the positive electrode current collector and the positive electrode film layer, and the conductive layer of the positive electrode comprises a conductive means, wherein the conductive means comprises at least one of superconducting carbon, conductive graphite, acetylene carbon black, carbon black, Ketjen carbon black, carbon dots, carbon nanotubes, graphene and carbon nanofibers. [20] Secondary battery according to claim 19, wherein the thickness of the conductive layer of the positive electrode is 0.5 µm to 2 µm. [21] Secondary battery according to claim 19, wherein the conductive layer of the positive electrode comprises a binder, the binder comprising 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 acrylate resin. [22] Secondary battery according to claim 21, wherein in the conductive layer of the positive electrode the mass fraction of the conductive medium is 30% to 50% and the mass fraction of the binder is 50% to 70%. [23] Secondary battery according to any one of claims 1 to 22, wherein the compression density of the negative electrode sheet when the secondary battery is in a state of 100% SOC is 1.15 g / cm³ 3 up to 1.46 g / cm³ 3 , optional 1.25 g / cm² 3 up to 1.40 g / cm³ 3 amounts. [24] Secondary battery according to any one of claims 1 to 23, wherein the compression density of the negative electrode sheet when the secondary battery is in a state of 100% SOC is ≥ 1.25 g / cm³ 3 and < 1.35 g / cm³ 3 amounts. [25] Secondary battery according to claim 24, wherein the secondary battery in the state of 100% SOC satisfies at least one of the following conditions: (1) The mass fraction of the second additive in the electrolyte is 0.5% to 3%; (2) the mass fraction of the first solvent in the electrolyte is 22.5% to 34%; (3) the mass fraction of the first additive in the electrolyte is 1.5% to 6%. [26] Secondary battery according to any one of claims 1 to 23, wherein the compression density of the negative electrode sheet when the secondary battery is in a state of 100% SOC is 1.35 g / cm³ 3 up to 1.40 g / cm³ 3 amounts. [27] Secondary battery according to claim 26, wherein the secondary battery in the state of 100% SOC satisfies at least one of the following conditions: (1) The mass fraction of the second additive in the electrolyte is 0.7% to 3.5%; (2) the mass fraction of the first solvent in the electrolyte is 21.25% to 34%; (3) the mass fraction of the first additive in the electrolyte is 2.5% to 7%. [28] Secondary battery according to any one of claims 1 to 27, wherein the electrolyte mass per nominal capacity of 1 Ah of the secondary battery is between 2.2 g and 3.0 g. [29] Secondary battery according to any one of claims 1 to 28, wherein the electrolyte further comprises a second solvent, the second solvent comprising at least one of linear carbonate, carboxylic acid ester, ether, nitrile and sulfone. [30] Secondary battery according to claim 29, wherein the second solvent comprises a carboxylic acid ester, the carboxylic acid ester optionally comprising at least one of methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate and 1,4-butyrolactone. [31] Secondary battery according to claim 29, wherein the volume energy density of the secondary battery is 400 Wh / L to 450 Wh / L, the mass fraction of the carboxylic acid ester in the electrolyte is 25.5% to 59.5% and the total mass fraction of the first additive and the second additive in the electrolyte is 2% to 7%. [32] Secondary battery according to claim 29, wherein the volume energy density of the secondary battery is > 450 Wh / L and ≤ 480 Wh / L, the mass fraction of the carboxylic acid ester in the electrolyte is 25.5% to 63.75% and the total mass fraction of the first additive and the second additive in the electrolyte is 3.5% to 8%. [33] Secondary battery according to claim 29, wherein the charging time of the charging process of the secondary battery at 30 °C from 10 % SOC to 80 % SOC is 6 minutes to 15 minutes, the mass fraction of the carboxylic acid ester in the electrolyte is 17 % to 63.75 % and the total mass fraction of the first additive and the second additive in the electrolyte is 2 % to 8 %. [34] Secondary battery according to claim 33, wherein the mass fraction of the first additive in the electrolyte is 1.5% to 6.5% and the mass fraction of the second additive is 0.5% to 3.5%. [35] Secondary battery according to any one of claims 1 to 34, wherein the electrolyte comprises a lithium salt, the lithium salt comprising at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, fluorine-containing sulfonylimide salt, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluorobisoxalatophosphate and lithium tetrafluoro(oxalato)phosphate. [36] Secondary battery according to claim 34, wherein the mass fraction of the lithium salt in the electrolyte is 10% to 20%. [37] Secondary battery according to claim 35 or 36, wherein the lithium salt comprises LiFSI and LiPF6 and the lithium salt meets 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 stoichiometric ratio of LiFSI to LiPF6 is (2 to 5) :

10. [38] Secondary battery according to any one of claims 1 to 37, wherein the negative electrode sheet further comprises a conductive layer of the negative electrode, wherein the conductive layer of the negative electrode is arranged between the negative electrode current collector and the negative electrode film layer, and the conductive layer of the negative electrode comprises a conductive means, wherein the conductive means comprises at least one of superconducting carbon, conductive graphite, acetylene carbon black, carbon black, Ketjen carbon black, carbon dots, carbon nanotubes, graphene and carbon nanofibers. [39] Secondary battery according to claim 38, wherein the thickness of the conductive layer of the negative electrode is 0.5 µm to 2 µm. [40] Secondary battery according to claim 38, wherein the conductive layer of the negative electrode comprises a binder, the binder comprising at least one of styrene-butadiene rubber, water-soluble unsaturated resin, water-based acrylic resin, polyvinyl alcohol, sodium alginate and carboxymethyl chitosan. [41] Secondary battery according to claim 38, wherein in the conductive layer of the negative electrode the mass fraction of the conductive medium is 20% to 40% and the mass fraction of the binder is 60% to 80%. [42] Secondary battery according to any one of claims 1 to 41, wherein the negative electrode film layer comprises at least one negative electrode active layer, wherein the at least one negative electrode active layer comprises graphite. [43] Secondary battery according to claim 42, wherein the negative electrode film layer comprises a negative electrode active layer, wherein the negative electrode active layer contains the graphite, wherein the Dv50 particle size of the graphite is 8.2 µm to 13.5 µm. [44] Secondary battery according to claim 42, wherein the negative electrode film layer comprises a first and a second negative electrode active layer stacked on top of each other on the same side of the negative electrode current collector, wherein the graphite comprises at least one of artificial graphite and natural graphite, wherein the graphite in the first negative electrode active layer comprises at least one of the artificial graphite and the natural graphite, while the graphite in the second negative electrode active layer comprises the artificial graphite. [45] Secondary battery according to claim 44, wherein 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. [46] Secondary battery according to claim 44, wherein the Dv50 particle size of the graphite in the first negative electrode active layer is 9.5 µm to 18.5 µm, 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, optionally 7.8 µm to 12.8 µm. [47] Secondary battery according to claim 44, wherein the mass ratio of the graphite in the first negative electrode active layer to that in the second negative electrode active layer is 3 : 7 to 7 : 3, optionally 4 : 6 to 6 :

4. [48] ​​Secondary battery according to any one of claims 44 to 47, wherein 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 surface of the graphite body particles is coated with the coating layer, and the coating layer comprises amorphous carbon. [49] Secondary battery according to claim 48, wherein at least one of the following conditions is met: (1) The mass fraction of amorphous carbon is 2% to 5% in relation to the total mass of artificial graphite; (2) the powder resistance of the synthetic graphite is ≤ 0.04 Q·cm. [50] Secondary battery according to any one of claims 1 to 49, wherein the charging capacity per gram of graphite in a button cell at 0.1 C rate is ≥ 350 mAh / g, optionally 350 mAh / g to 440 mAh / g. [51] Secondary battery according to any one of claims 1 to 50, wherein the negative electrode active material further comprises a silicon-based material, wherein the silicon-based material comprises at least one of silicon oxide compound and silicon-carbon composite; the mass fraction of the element silicon in the silicon-based material in the negative electrode active material is 0.3% to 10%, optionally 1% to 6%. [52] Secondary battery according to any one of claims 1 to 51, wherein the separator comprises a porous base film and a functional layer arranged on at least one side of the porous base film. [53] Secondary battery according to claim 52, wherein at least one of the following conditions is met: (1) The thickness of the porous base film is ≤ 12 µm, optionally ≤ 9 µm; (2) the porosity of the porous base film is 20% to 70%, optionally 35% to 60%. [54] Secondary battery according to claim 53, wherein the separator comprises a first functional layer and a second functional layer arranged on both sides of the porous base film, wherein the first functional layer comprises first inorganic particles and the second functional layer comprises composite particles, wherein the composite particles comprise second inorganic particles and non-fluoropolymer particles, wherein the second inorganic particles adhere to the surface of the non-fluoropolymer particles and / or are dispersed inside the non-fluoropolymer particles. [55] Secondary battery according to claim 54, wherein the non-fluoropolymer particles comprise acrylate polymer particles. [56] Battery device comprising a secondary battery according to any one of claims 1 to 55. [57] Power consumption device comprising a secondary battery according to any one of claims 1 to 55 and / or a battery device according to claim 56.

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