Secondary battery and electric device

Abstract

The invention discloses a secondary battery and a power utilization device, and belongs to the technical field of batteries, the thickness and the ventilation value of a diaphragm, the single-side surface density of a negative electrode active material layer, the viscosity of an electrolyte and the mass percent of lithium fluorosulfonate in the electrolyte are controlled to meet the condition that Y is more than or equal to 0.037 and less than or equal to 3.1; the impedance of the secondary battery is effectively reduced, and the cycle performance of the secondary battery is improved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a secondary battery and an electrical device. Background Art

[0002] To achieve sustainable human development, researchers are focusing on finding green, economical, and renewable energy systems. As electric vehicles become ubiquitous in households, higher demands are being placed on power batteries. Cycling performance is a key factor influencing electric vehicle adoption.

[0003] In view of this, this application is filed. Summary of the Invention

[0004] The purpose of the present application is to overcome the deficiencies of the prior art and provide a secondary battery and an electrical device, which effectively reduce the impedance of the secondary battery and improve the cycle performance of the secondary battery.

[0005] To achieve the above-mentioned object, the first aspect of the present application provides a secondary battery, comprising a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer on at least one surface of the negative electrode current collector; the electrolyte comprises lithium fluorosulfonate;

[0006] The secondary battery satisfies the following conditions: 0.037≤Y≤3.1, Y=C / η+10×P×H / X;

[0007] Wherein, C% is the mass percentage of the lithium fluorosulfonate in the electrolyte;

[0008] ηmPa.s is the viscosity of the electrolyte at 25°C;

[0009] P g / 1540.25mm 2 is the single-surface density of the negative electrode active material layer;

[0010] H μm is the thickness of the diaphragm;

[0011] X s / 100cc is the air permeability value of the diaphragm.

[0012] As an embodiment of the present application, the secondary battery satisfies: 0.153≤Y≤1.787.

[0013] As an embodiment of the present application, at least one of the following (1) to (5) is satisfied:

[0014] (1)0.1≤C≤5;

[0015] (2)2≤η≤5;

[0016] (3) 0.05≤P≤0.2;

[0017] (4)10≤H<30;

[0018] (5)100≤X<300.

[0019] As an embodiment of the present application, 3≤H / η≤10 is satisfied.

[0020] As an implementation scheme of the present application, 15≤η / P≤60 is satisfied.

[0021] As an embodiment of the present application, the electrolyte further includes a first additive, which includes at least one of lithium difluorooxalatoborate, lithium tetrafluoroborate, and lithium bis(oxalatoborate); the mass percentage of the first additive in the electrolyte is 0.1 to 5%.

[0022] As an embodiment of the present application, the mass ratio of the first additive to lithium fluorosulfonate is 1:(0.05-20).

[0023] As an embodiment of the present application, the electrolyte further includes a second additive, which includes at least one of tris(trimethylsilyl)phosphate, vinyl sulfate, and lithium difluorophosphate; the mass percentage of the second additive in the electrolyte is 0.1 to 5%.

[0024] As an embodiment of the present application, the diaphragm includes a base layer, and a ceramic coating and a polymer coating sequentially disposed on at least one surface of the base layer.

[0025] A second aspect of the present application provides an electrical device, comprising the secondary battery described above, wherein the secondary battery serves as a power supply for the electrical device.

[0026] The beneficial effects of the present application are as follows: by controlling the thickness and air permeability of the diaphragm, the single-surface density of the negative electrode active material layer, the viscosity of the electrolyte, and the mass percentage of lithium fluorosulfonate in the electrolyte, the present application satisfies the following conditions: 0.037≤Y≤3.1; the lithium fluorosulfonate can form an inorganic interface layer rich in lithium fluoride, lithium nitride, lithium sulfur compounds, etc. on the negative electrode plate, thereby improving the ion conductivity of the negative electrode plate, effectively reducing impedance, improving the stability of the electrolyte, and reducing electrolyte decomposition and side reactions. By designing the thickness and air permeability of the diaphragm, the liquid absorption of the diaphragm is improved, more electrolyte is retained at the interface between the positive electrode plate, the negative electrode plate, and the diaphragm, reducing the diffusion path of lithium ions, improving the mechanical strength of the diaphragm, reducing the impact of external forces such as puncture or extrusion on the diaphragm, reducing gas production in the secondary battery, and reducing impedance. By designing the single-surface density of the negative electrode active material layer, the electrolyte's wetting effect is improved, promoting uniform distribution of the negative electrode active material on the negative electrode sheet and reducing the migration and diffusion pathways of lithium ions in the negative electrode active material. The electrolyte's viscosity is also designed to increase conductivity and enhance wetting of the separator and negative electrode sheet. The combined effects of the separator's thickness and permeability, the single-surface density of the negative electrode active material layer, the electrolyte's viscosity, and the mass percentage of lithium fluorosulfonate in the electrolyte significantly reduce the secondary battery's impedance and improve its cycling performance. DETAILED DESCRIPTION

[0027] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of this application, not all of them. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0028] In this application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0029] In this application, when referring to numerical ranges, unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges subsumed therein.

[0030] The embodiment of the present application provides a secondary battery, comprising a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer on at least one surface of the negative electrode current collector; the electrolyte comprises lithium fluorosulfonate;

[0031] The secondary battery satisfies: 0.037≤Y≤3.1, Y=C / η+10×P×H / X; for example, it can be 0.037, 0.04, 0.05, 0.06, 0.08, 0.1, 0.15, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.4, 1.5, 1.6, 1.8, 2, 2.2, 2.4, 2.5, 2.6, 2.8, 3, 3.1, or a range consisting of any two of these values.

[0032] Wherein, C% is the mass percentage of the lithium fluorosulfonate in the electrolyte;

[0033] ηmPa.s is the viscosity of the electrolyte at 25°C;

[0034] P g / 1540.25mm 2 is the single-surface density of the negative electrode active material layer;

[0035] H μm is the thickness of the diaphragm;

[0036] X s / 100cc is the air permeability value of the diaphragm.

[0037] The inventors of this application have discovered that the thickness and permeability of the secondary battery's separator, the single-surface density of the negative electrode active material layer, the viscosity of the electrolyte, and the mass percentage of lithium fluorosulfonate in the electrolyte can affect the battery's performance. This application controls the separator's thickness and permeability, the single-surface density of the negative electrode active material layer, the viscosity of the electrolyte, and the mass percentage of lithium fluorosulfonate in the electrolyte to satisfy the following conditions: 0.037≤Y≤3.1. The lithium fluorosulfonate can form an inorganic interface layer rich in lithium fluoride, lithium nitride, lithium-sulfur compounds, and other inorganic compounds on the negative electrode sheet, improving the negative electrode's ion conductivity, effectively reducing impedance, improving electrolyte stability, and reducing electrolyte decomposition and side reactions. By designing the separator's thickness and permeability, the separator's liquid absorption is improved, retaining more electrolyte at the interface between the positive and negative electrode sheets and the separator, reducing the diffusion path for lithium ions, improving the separator's mechanical strength, and reducing the effects of external forces such as puncture or extrusion on the separator, thereby reducing gas production and impedance in the secondary battery. By designing the single-surface density of the negative electrode active material layer, the electrolyte's wetting effect is improved, promoting uniform distribution of the negative electrode active material on the negative electrode sheet and reducing the migration and diffusion pathways of lithium ions in the negative electrode active material. The electrolyte's viscosity is also designed to increase conductivity and enhance wetting of the separator and negative electrode sheet. The combined effects of the separator's thickness and permeability, the single-surface density of the negative electrode active material layer, the electrolyte's viscosity, and the mass percentage of lithium fluorosulfonate in the electrolyte significantly reduce the secondary battery's impedance and improve its cycling performance.

[0038] In one embodiment, the secondary battery satisfies: 0.153≤Y≤1.787. In particular, when Y is within this range, the impedance of the secondary battery can be further reduced and the cycle performance of the secondary battery can be improved.

[0039] In one embodiment, 0.1≤C≤5, for example, it can be 0.1, 0.2, 0.5, 0.8, 1, 1.2, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 or a range consisting of any two of these values. By controlling C within this range, the conductivity of the electrolyte can be effectively improved, and a denser and more stable inorganic interface layer rich in lithium fluoride, lithium nitride, lithium sulfur compounds, etc. can be formed on the negative electrode sheet, thereby inhibiting the formation of lithium dendrites, effectively reducing the impedance of the secondary battery, and improving the cycle performance of the secondary battery.

[0040] In one embodiment, 2≤η≤5, for example, it can be 2, 2.5, 3, 3.5, 4, 4.5, 5 or a range consisting of any two values ​​therein. By controlling the η value, that is, controlling the viscosity of the electrolyte at 25°C within this range, the conductivity of the electrolyte can be effectively improved, promoting freer migration of lithium ions, increasing the migration rate of lithium ions, making it easier to penetrate into the pores of the diaphragm and the negative electrode sheet, increasing the contact area with the diaphragm and the negative electrode sheet, and increasing the infiltration rate of the diaphragm and the negative electrode sheet, the impedance of the secondary battery can be further reduced, and the cycle performance of the secondary battery can be improved.

[0041] In this application, the viscosity of the electrolyte is measured at 25° C. using an Ubbelohde viscometer.

[0042] In one embodiment, 0.05≤P≤0.2, for example, it can be 0.05, 0.06, 0.08, 0.1, 0.12, 0.15, 0.16, 0.18, 0.2 or a range consisting of any two of these values. By controlling P, that is, the single-surface density of the negative electrode active material layer, within this range, the expansion and contraction of the negative electrode active material can be improved, the wetting effect of the electrolyte can be improved, the uniform distribution of the negative electrode active material on the negative electrode sheet can be promoted, the migration and diffusion pathways of lithium ions in the negative electrode active material can be reduced, the impedance of the secondary battery can be further reduced, and the cycle performance of the secondary battery can be improved.

[0043] In this application, the single-side density test method of the negative electrode active material layer is: cut the negative electrode sheet into pieces with an area of ​​1540.25 mm 2 The mass of the small disc is weighed with a high-precision balance, and the mass of the small disc is deducted from the mass of the current collector, divided by the area of ​​the disc and then divided by 2 to calculate the single-side density of the negative electrode active material layer.

[0044] In one embodiment, 10≤H<30, for example, it can be 10, 12, 15, 16, 18, 20, 22, 24, 25, 26, 28, 30 or a range consisting of any two values ​​therein. By controlling the H value, that is, the thickness of the diaphragm, within this range, the diffusion path of lithium ions can be shortened, the wetting effect of the electrolyte can be improved, the mechanical strength of the diaphragm can be improved, the impact of external forces such as puncture or extrusion on the diaphragm can be reduced, the gas production of the secondary battery can be reduced, the impedance can be reduced, and the cycle performance of the secondary battery can be improved.

[0045] In one embodiment, 100≤X<300, for example, it can be 100, 120, 140, 150, 160, 180, 200, 220, 240, 250, 260, 280, 300 or a range consisting of any two values ​​therein. By controlling the X value, that is, the permeability of the diaphragm, within this range, the wettability of the electrolyte to the diaphragm is further improved, the washability of the diaphragm is improved, more electrolyte is retained at the interface of the positive electrode sheet, the negative electrode sheet and the diaphragm, further reducing the impedance and improving the cycle performance of the secondary battery.

[0046] In this application, the test method for the air permeability of the diaphragm is as follows: a pressure of 1.21 kPa is applied to the diaphragm, and 100 mL of air passes through an area of ​​6.45 cm 2 The time required for the diaphragm.

[0047] In one embodiment, 3≤H / η≤10 is satisfied, for example, it can be 3, 4, 5, 6, 7, 8, 9, 10 or a range consisting of any two values ​​therein. By controlling H / η within this range, the wettability of the electrolyte to the diaphragm can be more significantly improved, the adsorption amount of the electrolyte can be increased, the internal resistance of the secondary battery can be reduced, the formation of lithium dendrites can be avoided, the impedance of the battery can be further reduced, and the cycle performance of the secondary battery can be improved.

[0048] In one embodiment, 15≤η / P≤60 is satisfied, for example, it can be 15, 18, 20, 25, 30, 35, 40, 45, 50, 55, 60 or a range consisting of any two values ​​therein. By controlling η / P within this range, a fast-flow channel is provided for the electrolyte, which is beneficial to the rapid infiltration of the electrolyte on the negative electrode sheet, and can further improve the wettability of the electrolyte, reduce the transmission barrier of lithium ions, further reduce the impedance of the battery, and improve the cycle performance of the secondary battery.

[0049] In one embodiment, the electrolyte further includes a first additive, which includes at least one of lithium difluorooxalatoborate, lithium tetrafluoroborate, and lithium bis(oxalatoborate); the mass percentage of the first additive in the electrolyte is 0.1-5%, for example, it can be 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or a range consisting of any two values ​​therein. By adding the first additive to the electrolyte and controlling its content within the above range, the corrosion of the positive electrode current collector by the addition of lithium fluorosulfonate can be improved, the occurrence of side reactions can be reduced, the impedance of the battery can be further reduced, and the cycle performance of the secondary battery can be improved.

[0050] In one embodiment, the mass ratio of the first additive to lithium fluorosulfonate is 1:(0.05-20), for example, it can be 1:0.05, 1:0.1, 1:0.5, 1:1, 1:2, 1:3, 1:5, 1:10, 1:15, 1:20 or a range consisting of any two values ​​therein. By controlling the mass ratio of the first additive to lithium fluorosulfonate within this range, a more stable and dense SEI film can be formed on the negative electrode sheet, further reducing the impedance of the battery and improving the cycle performance of the secondary battery.

[0051] In one embodiment, the electrolyte further includes a second additive, the second additive including at least one of tris(trimethylsilyl)phosphate, vinyl sulfate, and lithium difluorophosphate; the second additive accounts for 0.1-5% by mass of the electrolyte, for example, 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or a range consisting of any two of these values. The mass percentage of the second additive is limited within the above range, which can better cooperate with lithium fluorosulfonate to effectively reduce battery impedance, improve kinetics, and improve cycle performance.

[0052] In one embodiment, the electrolyte further includes a lithium salt, and the lithium salt is at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium perchlorate, and lithium tetrafluorophosphate.

[0053] In one embodiment, the concentration of the lithium salt in the electrolyte is 0.5-2 M, for example, 0.5 M, 0.6 M, 0.8 M, 1 M, 1.2 M, 1.5 M, 1.8 M, 2 M or a range consisting of any two values ​​therein.

[0054] In one embodiment, the lithium salt includes lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide.

[0055] In one embodiment, the concentration of lithium hexafluorophosphate in the electrolyte is 0.4-1.8 M, for example, 0.4 M, 0.5 M, 0.6 M, 0.8 M, 1 M, 1.2 M, 1.5 M, 1.8 M or a range consisting of any two values ​​therein.

[0056] In one embodiment, the concentration of the lithium bis(fluorosulfonyl)imide in the electrolyte is 0.1-1.6 M, for example, 0.1 M, 0.2 M, 0.4 M, 0.5 M, 0.6 M, 0.8 M, 1 M, 1.2 M, 1.5 M, 1.6 M or a range consisting of any two values ​​therein.

[0057] The present application adopts a combination of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide as the lithium salt, which can improve the lithium ion migration number and antioxidant performance, and has good aluminum foil passivation ability. It has good compatibility with the additive system and diaphragm of the electrolyte of the present application, improves stability, repairs the electrode / electrolyte interface, improves ionic conductivity, and promotes the conduction of lithium ions in the bulk phase.

[0058] In one embodiment, the electrolyte further includes an organic solvent, and the organic solvent includes at least one of ethylene carbonate, propylene carbonate, butylene carbonate, trifluoroethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methylpropyl carbonate, diphenyl carbonate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, ethyl 2,2-difluoroacetate, methyl 2,2-difluoroacetate, methyl 2,3,3,3-tetrafluoropropionate, γ-butyrolactone, acetonitrile, and sulfolane.

[0059] In one embodiment, the organic solvent includes cyclic carbonate and chain carbonate. By adding cyclic carbonate and chain carbonate to the electrolyte at the same time, the stability of the electrolyte can be improved, and the wetting effect of the electrolyte on the separator and the negative electrode can be improved.

[0060] In one embodiment, the cyclic carbonate includes at least one of propylene carbonate and ethylene carbonate.

[0061] In one embodiment, the linear carbonate includes at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and dipropyl carbonate.

[0062] In one embodiment, the mass percentage of the cyclic carbonate in the organic solvent is 20-40%, for example, 20%, 25%, 30%, 35%, 40% or a range consisting of any two values ​​therein.

[0063] In particular, when the mass percentage of the chain carbonate and the cyclic carbonate is controlled within the above range, the solvent system of the electrolyte is in a better state, which can make the performance of the secondary battery better.

[0064] In one embodiment, the mass percentage of the linear carbonate in the organic solvent is 20-60%, for example, it can be 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60% or a range consisting of any two values ​​therein.

[0065] In one embodiment, the organic solvent further includes a chain carboxylate, and the mass percentage of the chain carboxylate in the organic solvent is 10 to 60%, for example, it can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60% or a range consisting of any two values ​​therein. When the electrolyte of the secondary battery further contains a chain carboxylate, it can effectively improve the wettability of the electrode, provide better electron conduction and ion diffusion channels, reduce internal resistance, and improve cycle performance.

[0066] In one embodiment, the chain carboxylic acid ester includes at least one of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate.

[0067] In one embodiment, the diaphragm includes a base layer, and a ceramic coating and a polymer coating on at least one surface of the base layer, wherein the ceramic coating is disposed between the base layer and the polymer coating.

[0068] In one embodiment, a ceramic coating and a polymer coating are sequentially provided on the surface of at least one substrate layer.

[0069] The diaphragm of the present application has excellent air permeability and stability, can effectively improve the mechanical strength of the diaphragm, reduce the impact of external forces such as puncture or extrusion on the diaphragm, reduce gas production of secondary batteries, reduce impedance, and improve the cycle performance of secondary batteries.

[0070] In one embodiment, the ceramic coating includes ceramic particles, and the ceramic particles include at least one of SiO2, TiO2, ZrO2, Al2O3, MgO, SiC, and boehmite.

[0071] In one embodiment, the ceramic coating further includes a binder.

[0072] In one embodiment, the binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorine-containing acrylate resin, cellulose, nitrocellulose, styrene-butadiene rubber, acrylonitrile-butadiene rubber, fluororubber, isoprene rubber, polybutadiene rubber, and ethylene-propylene rubber.

[0073] In one embodiment, the mass percentage of the ceramic particles in the ceramic coating is 50-99%, for example, it can be 50%, 60%, 70%, 80%, 90%, 95%, 99% or a range consisting of any two values ​​therein.

[0074] In one embodiment, the mass percentage of the binder in the ceramic coating is 1-50%, for example, it can be 1%, 5%, 10%, 20%, 30%, 40%, 50% or a range consisting of any two values ​​therein.

[0075] In one embodiment, the polymer layer includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyurethane, acrylic polymer, and styrene acrylic latex.

[0076] In one embodiment, the base layer includes at least one of polyethylene, polypropylene, polyimide, oxidized polyethylene, oxidized polyethylene, polyvinyl alcohol copolymer, and ethylene-vinylidene fluoride copolymer.

[0077] In one embodiment, the thickness of the base layer is 5 to 15 μm, for example, it can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm or a range consisting of any two values ​​therein.

[0078] In one embodiment, the thickness of the ceramic coating is 1 to 6 μm, for example, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, or a range consisting of any two values ​​therein.

[0079] In one embodiment, the thickness of the polymer layer is 1 to 10 μm, for example, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm or a range consisting of any two values ​​therein.

[0080] In one embodiment, the negative electrode active material can be graphite, mesophase microcarbon beads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel structure lithium titanate Li4Ti5O 12 , at least one of Li-Al alloy and metallic lithium.

[0081] The present invention provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer on at least one surface of the negative electrode current collector; the negative electrode active material layer comprises graphite; the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer on at least one surface of the positive electrode current collector; the positive electrode active material layer comprises a positive electrode active material; and the electrolyte comprises lithium fluorosulfonate.

[0082] The secondary battery satisfies the following conditions: 0.037≤Y≤3.1, Y=C / η+10×P×H / X;

[0083] Wherein, C% is the mass percentage of the lithium fluorosulfonate in the electrolyte;

[0084] ηmPa.s is the viscosity of the electrolyte;

[0085] P g / 1540.25mm 2 is the single-surface density of the negative electrode active material layer;

[0086] H μm is the thickness of the diaphragm;

[0087] X s / 100cc is the air permeability value of the diaphragm.

[0088] When the negative electrode active material contains graphite, the electrolyte, negative electrode plate and separator meet the above conditions, which can make the secondary battery system better matched, the overall performance of the secondary battery better, further improve the cycle performance of the secondary battery and reduce impedance.

[0089] In the present application, there is no particular limitation on the negative electrode current collector, as long as it can achieve the purpose of the present application. For example, it can be copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper or a composite current collector.

[0090] In one embodiment, the negative electrode active material layer further includes a conductive agent and a binder.

[0091] In one embodiment, the secondary battery further includes a positive electrode plate.

[0092] In one embodiment, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material.

[0093] In one embodiment, the positive electrode active material may be a positive electrode active material for a secondary battery that is well known in the art. As non-limiting examples, the positive electrode active material may include lithium-containing phosphates, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials or substances, and other traditional materials or substances that can be used as positive electrode active materials for secondary batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, non-limiting examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds.

[0094] In one embodiment, the positive electrode active material includes a lithium-containing phosphate, wherein the lithium-containing phosphate includes a chemical formula of Li a Fe 1-b M b PO4 compound, wherein 0.8≤a≤1.2, 0≤b≤0.9, and M is selected from at least one of Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, and Ti.

[0095] The present invention provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer on at least one surface of the negative electrode current collector. The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer on at least one surface of the positive electrode current collector. The positive electrode active material layer comprises a positive electrode active material, wherein the positive electrode active material comprises a lithium-containing phosphate. The electrolyte comprises lithium fluorosulfonate.

[0096] The secondary battery satisfies the following conditions: 0.037≤Y≤3.1, Y=C / η+10×P×H / X;

[0097] Wherein, C% is the mass percentage of the lithium fluorosulfonate in the electrolyte;

[0098] ηmPa.s is the viscosity of the electrolyte;

[0099] P g / 1540.25mm 2 is the single-surface density of the negative electrode active material layer;

[0100] H μm is the thickness of the diaphragm;

[0101] X s / 100cc is the air permeability value of the diaphragm.

[0102] When the positive electrode active material includes lithium phosphate, the electrolyte, negative electrode plate and separator meet the above conditions, which can make the secondary battery system better matched, the overall performance of the secondary battery better, and further improve the cycle performance of the secondary battery and reduce impedance.

[0103] In one embodiment, the type of positive electrode current collector is not particularly limited and can be any known material suitable for use as a positive electrode current collector. In one embodiment, the positive electrode current collector includes metal materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum, and carbon materials such as carbon cloth and carbon paper.

[0104] The form of the positive electrode current collector is not particularly limited. When the positive electrode current collector is a metal material, the positive electrode current collector may be in the form of metal foil, metal cylinder, metal strip coil, metal plate, metal foil, metal mesh, stamped metal, foamed metal, etc. When the positive electrode current collector is a carbon material, the positive electrode current collector may be in the form of, but not limited to, carbon plate, carbon film, carbon cylinder, etc.

[0105] In one embodiment, the positive electrode active material layer further includes a conductive agent and a binder.

[0106] In one embodiment, the type of the conductive agent mentioned in the present application is not limited, and any known conductive agent can be used.

[0107] In one embodiment, the conductive agent includes at least one carbon material selected from the group consisting of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0108] In one embodiment, the types of the binder in the negative electrode active material layer and the binder in the positive electrode active material layer mentioned in the present application are not limited, and known binders can be used.

[0109] In one embodiment, the binder in the negative electrode active material layer and the binder in the positive electrode active material layer independently include at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin, polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, nitrocellulose, styrene-butadiene rubber, nitrile rubber, fluororubber, isoprene rubber, polybutadiene rubber, and ethylene-propylene rubber.

[0110] In one embodiment, the secondary battery may include an outer packaging, which may be used to encapsulate the electrode assembly and the electrolyte.

[0111] In one embodiment, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0112] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square, or any other shape.

[0113] One embodiment of the present application provides an electrical device including the secondary battery described above.

[0114] Exemplarily, the above-mentioned electrical devices may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited to these.

[0115] The present application is further described below with specific examples:

[0116] Example 1

[0117] A method for preparing a secondary battery comprises the following steps:

[0118] (1) Preparation of electrolyte

[0119] At room temperature, in an argon-filled glove box (H2O<1ppm, O2<1ppm), EC (ethylene carbonate), EMC (ethyl methyl carbonate), DMC (dimethyl carbonate), and EA (ethyl acetate) were mixed in a mass ratio of 30:20:30:20 and heated to 400°C. Molecular sieves are used to remove water to obtain a mixed solvent, and mixed lithium salts (0.7M LiPF6 and 0.3M LiFSI) are successively added to the obtained mixed solvent, and the mixture is stirred continuously and cooled with dry ice to ensure that the temperature of the electrolyte does not rise by more than 2°C, so as to finally obtain a colorless transparent liquid, and then lithium difluorooxalatoborate, lithium fluorosulfonate, and tris(trimethylsilyl)phosphate are added to obtain an electrolyte, wherein the mass percentage of lithium difluorooxalatoborate (LiDFOB) is 0.5%, the mass percentage of lithium fluorosulfonate is 1%, and the mass percentage of tris(trimethylsilyl)phosphate is 0.5%;

[0120] (2) Preparation of positive electrode sheets.

[0121] The positive electrode material LiFePO4, conductive agent SP, and binder PVDF were mixed in a mass ratio of 96:2:2, and NMP was added and stirred under vacuum until the system became uniform to obtain the positive electrode slurry. The positive electrode slurry was then evenly coated on a 16μm positive electrode current collector aluminum foil, dried in an oven, and then cold pressed to obtain the positive electrode sheet. The compacted density of the positive electrode sheet is 2.45g / cm 3 .

[0122] (3) Preparation of negative electrode sheet

[0123] The negative electrode active material graphite, conductive agent acetylene black (SuperP) and binder SBR were mixed uniformly in a mass ratio of graphite:SuperP:SBR=94:3:3, and evenly dispersed in deionized water to prepare a uniform negative electrode slurry. The mixed negative electrode slurry was poured into a 0.12g / 1540.25mm 2The coating amount was coated on both sides of the 6μm copper foil, and then baked, rolled and cut into pieces to obtain the negative electrode sheet, wherein the compaction density of the negative electrode sheet was 1.6g / cm 3 .

[0124] (4) Diaphragm

[0125] A 6μm-thick polyethylene (PE) film was used as the substrate. Ceramic boehmite particles and a polyacrylate binder were mixed in a suitable amount of deionized water at a weight ratio of 7:1 to form a ceramic slurry with a solid content of 60%. This slurry was applied to both surfaces of the substrate using a coater and dried to form a 2μm-thick ceramic coating on each side. The coating speed was 10 m / min, the drying temperature was 40°C, and the drying time was 2 hours. Polyvinylidene fluoride (PVDF) slurry was then sprayed onto the ceramic layer and dried to form a 5μm-thick PVDF layer, thus forming a separator.

[0126] (5) Production of secondary batteries

[0127] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order with the separator placed between the positive and negative electrode sheets. After winding, hot pressing and shaping, and tab welding, a bare battery cell is obtained. The bare battery cell is placed in an outer packaging aluminum-plastic film and baked in an oven at 85±10℃ for 24 hours. The above-prepared electrolyte is injected into the dried battery, allowed to stand, formed, and capacity divided to obtain a secondary battery.

[0128] The parameters of Example 1 are shown in Table 1 and Table 2.

[0129] Examples 2 to 8

[0130] The difference between Examples 2 to 8 and Example 1 is that the mass percentage of the lithium fluorosulfonate and / or LiDFOB in the electrolyte is changed.

[0131] Example 9

[0132] The difference between Example 9 and Example 1 is that Example 9 uses EA, EC and EMC as solvents, and changes the ratio of EA, EC and EMC in the electrolyte to thereby change the viscosity η of the electrolyte, wherein EC:EMC:EA=30:50:20.

[0133] Example 10

[0134] The difference between Example 10 and Example 1 is that Example 10 uses EC, EMC, DMC and EA as solvents, and changes the ratio of EC, EMC, DMC and EA in the electrolyte to thereby change the viscosity η of the electrolyte, wherein EC:EMC:DMC:EA=30:50:10:10.

[0135] Example 11

[0136] The difference between Example 11 and Example 1 is that Example 11 uses EA, EC and EMC as solvents, and changes the ratio of EA, EC and EMC in the electrolyte to thereby change the viscosity η of the electrolyte, wherein EC:EMC:EA=30:20:50.

[0137] Examples 12 to 14

[0138] The difference between Examples 12 to 14 and Example 1 is that the coating amount of the negative electrode slurry on the copper foil is adjusted to thereby change the single-side areal density P of the negative electrode active material layer.

[0139] The coating amount of the negative electrode slurry of Example 12 is 0.05g / 1540.25mm 2 .

[0140] The coating amount of the negative electrode slurry of Example 13 is 0.15g / 1540.25mm 2 .

[0141] The coating amount of the negative electrode slurry of Example 14 is 0.2 g / 1540.25 mm 2 .

[0142] Example 15

[0143] The difference between Example 15 and Example 1 is that the coating amount of the negative electrode slurry on the copper foil, the preparation method of the separator, and the solvent of the electrolyte are adjusted to thereby change the single-sided surface density P of the negative electrode active material layer, the separator thickness H, and the viscosity η of the electrolyte.

[0144] The coating amount of the negative electrode slurry in this embodiment is 0.2g / 1540.25mm 2 .

[0145] This embodiment uses EA, EC and EMC as solvents, and changes the ratio of EA, EC and EMC in the electrolyte to thereby change the viscosity η of the electrolyte, wherein EC:EMC:EA=30:20:50.

[0146] The preparation method of the diaphragm of this embodiment is as follows: a polyethylene (PE) film with a thickness of 6 μm is used as the substrate; ceramic particles boehmite and adhesive polyacrylate are mixed uniformly in an appropriate amount of deionized water solvent at a weight ratio of 7:1 to obtain a ceramic slurry with a solid content of 70%. The ceramic slurry is applied to both surfaces of the substrate using a coater and dried to form a ceramic coating with a single-side thickness of 2 μm. The coating speed of the coater is 10 m / min, the drying temperature is 40°C, and the drying time is 2 hours. The polymer PVDF slurry is then sprayed onto the ceramic layer and dried to form a polymer PVDF layer with a thickness of 1.67 μm to obtain the diaphragm.

[0147] Example 16

[0148] The difference between Example 16 and Example 1 is that the coating amount of the negative electrode slurry on the copper foil, the preparation method of the separator, and the solvent in the electrolyte are adjusted to thereby change the single-sided surface density P of the negative electrode active material layer, the separator thickness H, and the viscosity η of the electrolyte.

[0149] The coating amount of the negative electrode slurry in this embodiment is 0.05g / 1540.25mm 2 .

[0150] This example uses EC:EMC:DMC:EA as the solvent. By varying the ratio of EC:EMC:DMC to EA in the electrolyte, the viscosity η of the electrolyte is adjusted to 30:50:10:10. The separator of this example is prepared by: using a 6μm thick polyethylene (PE) film as the substrate; mixing ceramic boehmite particles and a polyacrylate binder in a suitable amount of deionized water at a weight ratio of 7:1 to form a ceramic slurry with a solid content of 40%. The ceramic slurry is applied to both surfaces of the substrate using a coater and dried to form a ceramic coating with a single-side thickness of 5.67μm. The coating speed of the coater is 10m / min, the drying temperature is 40°C, and the drying time is 2 hours. A polymer PVDF slurry is then sprayed onto the ceramic layer and dried to form an 8μm thick polymer PVDF layer, thereby obtaining the separator.

[0151] Examples 17 to 19

[0152] The difference between Examples 17 to 19 and Example 1 is that the preparation method of the diaphragm is changed, thereby adjusting the thickness of the diaphragm.

[0153] The preparation method of the diaphragm of Example 17 is as follows: a polyethylene (PE) film with a thickness of 6 μm is used as the substrate; ceramic boehmite particles and a binder polyacrylate are mixed uniformly in an appropriate amount of deionized water as a solvent in a weight ratio of 7:1 to obtain a ceramic slurry with a solid content of 75%. The ceramic slurry is applied to both surfaces of the substrate using a coater and dried to form a ceramic coating with a thickness of 1 μm on one side. The coating speed of the coater is 10 m / min, the drying temperature is 40°C, and the drying time is 2 hours. A polymer PVDF slurry is then sprayed onto the ceramic layer and dried to form a polymer PVDF layer with a thickness of 1 μm to obtain the diaphragm.

[0154] The preparation method of the diaphragm of Example 18 is as follows: a polyethylene (PE) film with a thickness of 6 μm is used as the substrate; ceramic boehmite particles and a binder polyacrylate are mixed uniformly in an appropriate amount of deionized water solvent at a weight ratio of 7:1 to obtain a ceramic slurry with a solid content of 55%. The ceramic slurry is applied to both surfaces of the substrate using a coater and dried to form a ceramic coating with a single-side thickness of 3.5 μm. The coating speed of the coater is 10 m / min, the drying temperature is 40°C, and the drying time is 2 hours. A polymer PVDF slurry is then sprayed onto the ceramic layer and dried to form a polymer PVDF layer with a thickness of 6 μm to obtain a diaphragm.

[0155] The preparation method of the diaphragm of Example 19 is as follows: a polyethylene (PE) film with a thickness of 6 μm is used as the substrate; ceramic particles boehmite and adhesive polyacrylate are mixed uniformly in an appropriate amount of deionized water solvent at a weight ratio of 7:1 to obtain a ceramic slurry with a solid content of 45%. The ceramic slurry is applied to both surfaces of the substrate using a coater and dried to form a ceramic coating with a single-side thickness of 4.5 μm. The coating speed of the coater is 10 m / min, the drying temperature is 40°C, and the drying time is 2 hours. The polymer PVDF slurry is then sprayed onto the ceramic layer and dried to form a polymer PVDF layer with a thickness of 7.5 μm to obtain the diaphragm.

[0156] Example 20

[0157] The difference between Example 20 and Example 1 is that the viscosity η of the electrolyte, the single-sided surface density P of the negative electrode active material layer, the thickness H of the diaphragm, and the air permeability X of the diaphragm are changed by adjusting the solvent of the electrolyte, the coating amount of the negative electrode slurry on the copper foil, the thickness of the diaphragm, and the preparation method of the diaphragm.

[0158] This embodiment uses EA, EC and EMC as solvents, and changes the ratio of EA, EC and EMC in the electrolyte to thereby change the viscosity η of the electrolyte, wherein EC:EMC:EA=30:20:50.

[0159] The coating amount of the negative electrode slurry on the copper foil of this embodiment is 0.08g / 1540.25mm 2 .

[0160] The preparation method of the diaphragm of this embodiment is as follows: a polyethylene (PE) film with a thickness of 6 μm is used as the substrate; ceramic particles boehmite and adhesive polyacrylate are mixed uniformly in an appropriate amount of solvent deionized water at a weight ratio of 6:1 to obtain a ceramic slurry with a solid content of 60%, and the ceramic slurry is applied to both surfaces of the substrate using a coater and dried to form a ceramic coating with a single-side thickness of 4.5 μm. The coating speed of the coater is 10 m / min, the drying temperature is 40°C, and the drying time is 2 hours. Then, a polymer PVDF slurry is sprayed onto the ceramic layer and dried to form a polymer PVDF layer with a thickness of 7.5 μm to obtain a diaphragm.

[0161] Example 21

[0162] The difference between Example 21 and Example 1 is that the viscosity η of the electrolyte, the single-sided surface density P of the negative electrode active material layer, the thickness H of the diaphragm, and the air permeability X of the diaphragm are changed by adjusting the solvent of the electrolyte, the coating amount of the negative electrode slurry on the copper foil, the thickness of the diaphragm, and the preparation method of the diaphragm.

[0163] In this embodiment, EC:EMC:DMC:EA is used as the solvent. By changing the ratio of EC:EMC:DMCEA in the electrolyte, the viscosity η of the electrolyte is changed, EC:EMC:DMC:EA=30:50:10:10.

[0164] The coating amount of the negative electrode slurry on the copper foil of this embodiment is 0.2g / 1540.25mm 2 .

[0165] The preparation method of the diaphragm of this embodiment is as follows: a polyethylene (PE) film with a thickness of 6 μm is used as the substrate; ceramic particles boehmite and adhesive polyacrylate are mixed uniformly in an appropriate amount of deionized water solvent at a weight ratio of 7:1 to obtain a ceramic slurry with a solid content of 75%. The ceramic slurry is applied to both surfaces of the substrate using a coater and dried to form a ceramic coating with a thickness of 1 μm on one side. The coating speed of the coater is 10 m / min, the drying temperature is 40°C, and the drying time is 2 hours. The polymer PVDF slurry is then sprayed onto the ceramic layer and dried to form a polymer PVDF layer with a thickness of 1 μm to obtain the diaphragm.

[0166] Examples 22 to 24

[0167] The difference between Examples 22 to 24 and Example 1 is that the air permeability value X of the diaphragm is changed by adjusting the preparation method of the diaphragm.

[0168] The diaphragm of Example 22 was prepared as follows: a 6-μm-thick polyethylene (PE) film was used as the substrate; ceramic boehmite particles and a polyacrylate binder were mixed uniformly in a suitable amount of deionized water at a weight ratio of 7:1 to form a ceramic slurry with a solid content of 51%. The slurry was applied to both surfaces of the substrate using a coater and dried to form a ceramic coating with a thickness of 2 μm on each side. The coating speed was 10 m / min, the drying temperature was 40°C, and the drying time was 2 hours. A polymer PVDF slurry was then sprayed onto the ceramic layer and dried to form a 5-μm-thick polymer PVDF layer, thereby producing the diaphragm.

[0169] The diaphragm of Example 23 was prepared as follows: a 6-μm-thick polyethylene (PE) film was used as the substrate; boehmite ceramic particles and polyacrylate binder were mixed uniformly in a suitable amount of deionized water at a weight ratio of 7:1 to form a ceramic slurry with a solid content of 55%. The slurry was applied to both surfaces of the substrate using a coater and dried to form a ceramic coating with a thickness of 2 μm on each side. The coating speed was 10 m / min, the drying temperature was 40°C, and the drying time was 2 hours. A PVDF polymer slurry was then sprayed onto the ceramic layer and dried to form a 5-μm-thick PVDF polymer layer, thereby producing the diaphragm.

[0170] The diaphragm of Example 24 was prepared as follows: a 6-μm-thick polyethylene (PE) film was used as the substrate; ceramic boehmite particles and a polyacrylate binder were mixed uniformly in a suitable amount of deionized water at a weight ratio of 7:1 to form a ceramic slurry with a solid content of 76%. The slurry was applied to both surfaces of the substrate using a coater and dried to form a ceramic coating with a thickness of 2 μm on each side. The coating speed was 10 m / min, the drying temperature was 40°C, and the drying time was 2 hours. A polymer PVDF slurry was then sprayed onto the ceramic layer and dried to form a 5-μm-thick polymer PVDF layer, thereby producing the diaphragm.

[0171] Example 25

[0172] Example 25 differs from Example 1 in that the mass percentage C of lithium fluorosulfonate in the electrolyte, the viscosity η of the electrolyte, the single-sided surface density P of the negative electrode active material layer, the thickness H of the diaphragm, and the air permeability X of the diaphragm are changed by adjusting the mass percentage of lithium fluorosulfonate in the electrolyte, the solvent of the electrolyte, the coating amount of the negative electrode slurry on the copper foil, the thickness of the diaphragm, and the preparation method of the diaphragm.

[0173] The coating amount of the negative electrode slurry in this embodiment is 0.2g / 1540.25mm 2 .

[0174] This embodiment uses EA, EC and EMC as solvents, and changes the ratio of EA, EC and EMC in the electrolyte to thereby change the viscosity η of the electrolyte, wherein EC:EMC:EA=30:20:50.

[0175] The preparation method of the diaphragm of this embodiment is as follows: a polyethylene (PE) film with a thickness of 6 μm is used as the substrate; ceramic particles boehmite and adhesive polyacrylate are mixed uniformly in an appropriate amount of deionized water solvent at a weight ratio of 7:1 to obtain a ceramic slurry with a solid content of 40%, and the ceramic slurry is applied to both surfaces of the substrate using a coater and dried to form a ceramic coating with a single-side thickness of 4.5 μm. The coating speed of the coater is 10 m / min, the drying temperature is 40°C, and the drying time is 2 hours. The polymer PVDF slurry is then sprayed onto the ceramic layer and dried to form a polymer PVDF layer with a thickness of 7.5 μm to obtain the diaphragm.

[0176] Example 26

[0177] Example 26 differs from Example 1 in that the mass percentage C of lithium fluorosulfonate in the electrolyte, the viscosity η of the electrolyte, the single-sided surface density P of the negative electrode active material layer, the thickness H of the diaphragm, and the air permeability X of the diaphragm are changed by adjusting the mass percentage of lithium fluorosulfonate in the electrolyte, the solvent of the electrolyte, the coating amount of the negative electrode slurry on the copper foil, the thickness of the diaphragm, and the preparation method of the diaphragm.

[0178] The coating amount of the negative electrode slurry in this embodiment is 0.05g / 1540.25mm 2 .

[0179] In this embodiment, EC:EMC:DMC:EA is used as the solvent. By changing the ratio of EC:EMC:DMCEA in the electrolyte, the viscosity η of the electrolyte is changed, EC:EMC:DMC:EA=30:50:10:10.

[0180] The preparation method of the diaphragm of this embodiment is as follows: a polyethylene (PE) film with a thickness of 6 μm is used as the substrate; ceramic particles boehmite and adhesive polyacrylate are mixed uniformly in an appropriate amount of deionized water solvent at a weight ratio of 8:1 to obtain a ceramic slurry with a solid content of 79%. The ceramic slurry is applied to both surfaces of the substrate using a coater and dried to form a ceramic coating with a thickness of 1 μm on one side. The coating speed of the coater is 10 m / min, the drying temperature is 40°C, and the drying time is 2 hours. The polymer PVDF slurry is then sprayed onto the ceramic layer and dried to form a polymer PVDF layer with a thickness of 1 μm to obtain the diaphragm.

[0181] Comparative Example 1

[0182] The difference between Comparative Example 1 and Example 1 is that the mass percentage C of lithium fluorosulfonate in the electrolyte, the solvent of the electrolyte, the coating amount of the negative electrode slurry on the copper foil, the thickness of the diaphragm, and the preparation method of the diaphragm are adjusted, thereby changing the mass percentage C of lithium fluorosulfonate in the electrolyte, the viscosity η of the electrolyte, the single-sided surface density P of the negative electrode active material layer, the thickness H of the diaphragm, and the permeability value X of the diaphragm.

[0183] The coating amount of the negative electrode slurry in this comparative example is 0.2g / 1540.25mm 2 .

[0184] In this comparative example, EA, EC and EMC were used as solvents, and the viscosity η of the electrolyte was changed by changing the ratio of EA, EC and EMC in the electrolyte, wherein EC:EMC:EA=30:25:45.

[0185] The diaphragm of this comparative example was prepared as follows: a 6μm-thick polyethylene (PE) film was used as the substrate; ceramic boehmite particles and a polyacrylate binder were mixed uniformly in a suitable amount of deionized water at a weight ratio of 7:1 to obtain a ceramic slurry with a solid content of 40%. The ceramic slurry was applied to both surfaces of the substrate using a coater and dried to form a ceramic coating with a thickness of 4.5μm on one side. The coating speed of the coater was 10m / min, the drying temperature was 40°C, and the drying time was 2 hours. A polymer PVDF slurry was then sprayed onto the ceramic layer and dried to form a polymer PVDF layer with a thickness of 7.5μm, thereby obtaining the diaphragm.

[0186] Comparative Example 2

[0187] The difference between Comparative Example 2 and Example 1 is that the mass percentage C of lithium fluorosulfonate in the electrolyte, the solvent of the electrolyte, the coating amount of the negative electrode slurry on the copper foil, the thickness of the diaphragm, and the preparation method of the diaphragm are adjusted, thereby changing the mass percentage C of lithium fluorosulfonate in the electrolyte, the viscosity η of the electrolyte, the single-sided surface density P of the negative electrode active material layer, the thickness H of the diaphragm, and the permeability value X of the diaphragm.

[0188] The coating amount of the negative electrode slurry in this comparative example is 0.01 g / 1540.25 mm 2 .

[0189] In this comparative example, EC and DEC were used as solvents, and the viscosity η of the electrolyte was changed by changing the ratio of EC to DEC in the electrolyte, wherein EC:DEC=20:80.

[0190] The diaphragm of this comparative example was prepared as follows: a 6μm-thick polyethylene (PE) film was used as the substrate; ceramic boehmite particles and a polyacrylate binder were mixed uniformly in a suitable amount of deionized water at a weight ratio of 7:1 to form a ceramic slurry with a solid content of 79%. The ceramic slurry was applied to both surfaces of the substrate using a coater and dried to form a ceramic coating with a thickness of 1μm on each side. The coating speed of the coater was 10m / min, the drying temperature was 40°C, and the drying time was 2 hours. A polymer PVDF slurry was then sprayed onto the ceramic layer and dried to form a polymer PVDF layer with a thickness of 1μm, thus forming the diaphragm.

[0191] Comparative Example 3

[0192] The difference between Comparative Example 3 and Example 1 is that the mass percentage C of lithium fluorosulfonate in the electrolyte, the viscosity η of the electrolyte, the thickness H of the diaphragm, and the preparation method of the diaphragm are adjusted, thereby changing the mass percentage C of lithium fluorosulfonate in the electrolyte, the viscosity η of the electrolyte, the thickness H of the diaphragm, and the permeability value X of the diaphragm.

[0193] This embodiment uses EA, EC and EMC as solvents, and changes the ratio of EA, EC and EMC in the electrolyte to thereby change the viscosity η of the electrolyte, wherein EC:EMC:EA=30:10:60.

[0194] The diaphragm of this comparative example was prepared as follows: a 6μm-thick polyethylene (PE) film was used as the substrate; ceramic boehmite particles and a polyacrylate binder were mixed uniformly in a suitable amount of deionized water at a weight ratio of 7:1 to form a ceramic slurry with a solid content of 75%. The ceramic slurry was applied to both surfaces of the substrate using a coater and dried to form a ceramic coating with a thickness of 1μm on each side. The coating speed of the coater was 10m / min, the drying temperature was 40°C, and the drying time was 2 hours. A polymer PVDF slurry was then sprayed onto the ceramic layer and dried to form a polymer PVDF layer with a thickness of 1μm, thereby obtaining the diaphragm.

[0195] Table 1 Parameters Table 1

[0196]

[0197] Table 2 Parameters Table 2

[0198]

[0199]

[0200] Performance Testing

[0201] 1. Room Temperature DCR Test: At 25±2°C, the secondary batteries of the Examples and Comparative Examples were charged at 1C to 3.65V, then discharged at 1C for 30 minutes. After adjusting to 50% SOC, they were pulse-discharged at 10C for 10 seconds. The SOC was then adjusted to 50% using the SOC adjustment method described above, and the battery was charged for another 10 seconds. DCR was calculated as (voltage before pulse discharge - voltage after pulse discharge) / discharge current. After 500 cycles, the DCR was retested. DCR change rate = (DCR after 500 cycles - initial DCR) / initial DCR * 100%. The recorded results are shown in Table 3.

[0202] 2. Cycling Performance Test: The secondary batteries of the examples and comparative examples were subjected to charge-discharge cycling tests at a charge-discharge rate of 1C / 1C within the voltage range of 2.5-3.65V at 25±2°C. The battery's first-cycle discharge capacity and the discharge capacity after 500 cycles were recorded. The 500-cycle capacity retention ratio = 500-cycle discharge capacity / first-cycle discharge capacity * 100%. The recorded data are shown in Table 3.

[0203] Table 3 Performance test table

[0204]

[0205]

[0206] As can be seen from Table 3, the present application controls the thickness and permeability of the diaphragm, the single-surface density of the negative electrode active material layer, the viscosity of the electrolyte, and the mass percentage of lithium fluorosulfonate in the electrolyte to meet the following conditions: 0.037≤Y≤3.1; thereby effectively reducing the impedance of the secondary battery and improving the cycle performance of the secondary battery.

[0207] Comparing Examples 1 to 6 with Examples 7 to 8, it can be seen that by controlling the mass ratio of the first additive to lithium fluorosulfonate to 1:(0.05-20), the impedance is further reduced and the cycle performance of the secondary battery is improved.

[0208] Comparing Examples 1 and 12 to 14 with Examples 15 to 16, it can be seen that by controlling 15≤η / P≤60, the impedance is further reduced and the cycle performance of the secondary battery is improved.

[0209] Comparing Examples 1 and 17 to 20 with Examples 21 to 22, it can be seen that by controlling 3≤H / η≤10, the impedance is further reduced and the cycle performance of the secondary battery is improved.

[0210] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application and are not intended to limit the scope of protection of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A secondary battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer on at least one surface of the negative electrode current collector; the electrolyte comprises lithium fluorosulfonate; The secondary battery satisfies the following conditions: 0.037≤Y≤3.1, Y=C / η+10×P×H / X; Wherein, C% is the mass percentage of the lithium fluorosulfonate in the electrolyte; ηmPa.s is the viscosity of the electrolyte at 25°C; P g / 1540.25mm 2 is the single-surface density of the negative electrode active material layer; H μm is the thickness of the diaphragm; X s / 100cc is the air permeability value of the diaphragm.

2. The secondary battery according to claim 1, wherein The secondary battery satisfies: 0.153≤Y≤1.

787.

3. The secondary battery according to claim 1, wherein Satisfy at least one of the following (1) to (5): (1)0.1≤C≤5； (2)2≤η≤5; (3)0.05≤P≤0.2； (4)10≤H<30； (5)100≤X<300。 4. The secondary battery according to claim 1, wherein Satisfies 3≤H / η≤10.

5. The secondary battery according to claim 1, wherein Satisfies 15≤η / P≤60.

6. The secondary battery according to claim 1, wherein The electrolyte further includes a first additive, which includes at least one of lithium difluorooxalatoborate, lithium tetrafluoroborate, and lithium bisoxalatoborate; the mass percentage of the first additive in the electrolyte is 0.1-5%.

7. The secondary battery according to claim 6, characterized in that The mass ratio of the first additive to lithium fluorosulfonate is 1:(0.05-20).

8. The secondary battery according to claim 1, wherein The electrolyte further includes a second additive, which includes at least one of tris(trimethylsilyl)phosphate, vinyl sulfate, and lithium difluorophosphate; the mass percentage of the second additive in the electrolyte is 0.1-5%.

9. The secondary battery according to claim 1, wherein The diaphragm includes a base layer, and a ceramic coating and a polymer coating sequentially arranged on at least one surface of the base layer.

10. An electrical device, characterized in that: The secondary battery comprises the secondary battery according to any one of claims 1 to 9, wherein the secondary battery serves as a power supply for the electrical device.

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