CN117855608A

CN117855608A - Electrolyte, secondary battery, and electronic device

Info

Publication number: CN117855608A
Application number: CN202410260553.4A
Authority: CN
Inventors: 陈敏晶
Original assignee: Ningde Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd
Priority date: 2024-03-07
Filing date: 2024-03-07
Publication date: 2024-04-09

Abstract

The application discloses electrolyte, secondary battery and electronic device, the electrolyte includes ethylene sulfate and vinylene carbonate, based on the mass of the electrolyte, the mass percentage content of ethylene sulfate is A%, the mass percentage content of vinylene carbonate is B%,0.1 is less than or equal to A/B is less than or equal to 4, the electrolyte at least includes ethyl propionate, propylene carbonate, the electrolyte still includes first material, the first material is selected from at least two of lithium difluorophosphate, lithium difluorooxalato borate, lithium bistrifluoromethane sulfonyl imide or lithium hexafluorophosphate, and contains at least lithium difluorophosphate, based on the total mass of the electrolyte, the mass percentage content of the first material is 0.3wt% -1.2 wt%. The secondary battery can improve the low-temperature cycle performance of the secondary battery and the electrochemical device and the overcharge preventing capability of the secondary battery and the electrochemical device under the condition of large current in the charge and discharge process.

Description

Electrolyte, secondary battery, and electronic device

Technical Field

The present disclosure relates to the field of electrochemical energy storage, and more particularly, to an electrolyte, a secondary battery, and an electronic device.

Background

The lithium ion battery has the advantages of high energy storage density, high nominal voltage, small size, portability and the like, and is widely applied to the fields of portable electronic equipment, electric bicycles, electric automobiles, energy storage equipment and the like. Along with the development of science and technology and the improvement of life quality, the lithium ion battery has more various application scenes in daily life, and the demands of people on the performance of the lithium ion battery are also increasing.

Disclosure of Invention

In view of this, the present application provides an electrolyte, a secondary battery, and an electronic device, which can further improve various performances of a lithium ion battery.

In a first aspect, the present application provides an electrolyte, the electrolyte comprising vinyl sulfate (DTD) and Vinylene Carbonate (VC), the mass percentage of the vinyl sulfate being a%, the mass percentage of the vinylene carbonate being B%,0.1 ∈a/b+.4, based on the mass of the electrolyte, the electrolyte comprising at least ethyl propionate, propylene carbonate, the electrolyte further comprising a first substance, the first substance being selected from at least two of lithium difluorophosphate, lithium difluorooxalato borate, lithium bistrifluoromethanesulfonimide or lithium hexafluorophosphate, and containing at least lithium difluorophosphate, the mass percentage of the first substance being 0.3wt% to 1.2wt% based on the mass of the electrolyte. The electrolyte meeting the conditions can form a stable and uniform mixed solid electrolyte interface film (SEI film) at the interface of the negative electrode in the charge and discharge process, reduce the generation of other side reactions at the interface, reduce the gas production at the interface, improve the low-temperature cycle performance of the assembled secondary battery and the electrochemical device, and improve the overcharge prevention capability of the assembled secondary battery and the electrochemical device under the condition of high current. Preferably, the electrolyte satisfies: A/B is more than or equal to 0.2 and less than or equal to 3.

In some embodiments, the electrolyte satisfies at least one of the following conditions: (1) A is more than or equal to 0.2 and less than or equal to 0.5; (2) B is more than or equal to 0.5 and less than or equal to 1. On the premise that A/B is more than or equal to 0.1 and less than or equal to 4, the range of A or B is further enabled to meet the range, a more stable mixed solid electrolyte interface film (SEI film) can be further formed, the generation of side reaction is reduced, the interface gas production is further reduced, the low-temperature cycle performance of the assembled secondary battery and the electrochemical device is improved, and the overcharge preventing capability of the secondary battery and the electrochemical device under the condition of high current is improved.

In some embodiments, the mass percent of the Ethyl Propionate (EP) is C% and the sum of the mass percent of the ethyl propionate and the vinyl sulfate is W%, based on the mass of the electrolyte, with 8.6.ltoreq.W.ltoreq.15.5. At this time, it is advantageous to further enhance the overcharge prevention capability of the assembled secondary battery and electrochemical device under high current conditions.

In some embodiments, the Propylene Carbonate (PC) is present in an amount of D% by mass, based on the mass of the electrolyte, and the sum of the mass percentages of propylene carbonate and vinylene carbonate is W '< 3.7 < W' < 12.5. The electrolyte solution meeting the range can further improve the low-temperature cycle performance of the assembled secondary battery and the electrochemical device and improve the overcharge preventing capability of the secondary battery and the electrochemical device under the condition of high current.

In some embodiments, the first substance is 0.4wt% to 2wt% based on the mass of the electrolyte, and the electrolyte further comprises diethyl carbonate and propyl propionate, wherein the mass ratio of ethyl propionate, propylene carbonate, diethyl carbonate and propyl propionate is (4-8): (10-14): (40-44): (38-42). Thus, the low-temperature cycle performance of the assembled secondary battery and electrochemical device can be improved, and the thermal box of the secondary battery can be further improved to pass the test, so that the thermal safety performance of the secondary battery and the electrochemical device can be further improved.

In some embodiments, the first substance further comprises at least lithium bis (trifluoromethanesulfonyl) imide, the sum of the mass percentages of the lithium difluorophosphate and the lithium bis (trifluoromethanesulfonyl) imide ranges from 0.4wt% to 0.5wt%, the mass ratio of the lithium difluorophosphate to the lithium difluorooxalato borate ranges from 2:5 to 1, and the mass ratio of the lithium difluorophosphate to the lithium bis (trifluoromethanesulfonyl) imide ranges from 1:5 to 1. Preferably, the mass ratio of the lithium difluorophosphate to the lithium bistrifluoromethane sulfonyl imide is 0.6-1.

In a second aspect, the present application provides a secondary battery comprising the above electrolyte.

In some embodiments, the secondary battery further includes a positive electrode tab including a positive electrode current collector and a positive electrode material layer disposed on at least one side surface of the positive electrode current collector, the positive electrode material layer including at least one of first material particles, second material particles, or inorganic ceramic particles, and containing at least the first material particles. The first material particles are lithium transition metal phosphate compound particles having an olivine-type crystal structure, and the second material particles are lithium manganese composite oxide particles having a layered crystal structure.

In some embodiments, the positive electrode material layer further includes a conductive agent and a binder, the first material particles include lithium iron phosphate, the lithium iron phosphate is 75wt% to 88wt% based on the mass of the positive electrode material layer, the binder is 6wt% to 15wt%, and the conductive agent is 2wt% to 10wt%. Thus, the stability of the positive electrode material can be further improved, and the rate performance of the secondary battery at high temperature can be improved. In addition, the positive electrode material meeting the range is selected to be combined with the electrolyte solution mentioned in the application, so that the floating thickness expansion rate of the electrochemical device assembled by the secondary battery can be reduced, and the floating capacity retention rate of the electrochemical device can be improved. Preferably, the lithium iron phosphate is 80 to 84wt%, the binder is 6 to 12wt%, and the conductive agent is 8 to 10wt%.

In some embodiments, the positive electrode material layer has a compacted density Pg/cm ³ P is more than or equal to 2.8 and less than or equal to 4.0. At this time, the stability of the cathode material can be further improved, thereby improving the rate capability of the secondary battery at high temperature, and further reducing the floating thickness expansion rate of the electrochemical device assembled by the secondary battery, and improving the floating capacity retention rate thereof.

In some embodiments, the secondary battery further includes a separator including a base film and a functional coating layer disposed on at least one side surface of the base film, the functional coating layer containing polymer particles therein, the polymer particles having a swelling degree of less than 45% when placed in the electrolyte at 90 ℃ for 20 hours. The secondary battery meeting the range has better adaptation effect between the isolating film and the electrolyte, has good permeability of the holes of the isolating film at high temperature (80-100 ℃) and can reduce the impedance of the secondary battery, thereby improving the high-temperature rate performance of the battery and reducing the floating charge thickness expansion rate of an electrochemical device assembled by the secondary battery and further improving the floating charge capacity retention rate of the electrochemical device.

In a third aspect, the present application provides an electronic device comprising the secondary battery described above.

The secondary battery can improve the low-temperature cycle performance of the assembled secondary battery and the electrochemical device and the overcharge prevention capability of the assembled secondary battery and the electrochemical device under the condition of high current in the charge and discharge process. The electrolyte is combined with the positive electrode material meeting the requirement of the application, so that the rate performance of the secondary battery at high temperature can be improved, the expansion rate of the floating charge thickness of the secondary battery is reduced, and the retention rate of the floating charge capacity of the secondary battery is improved.

Detailed Description

Embodiments of the present application will be described in detail below. The examples of the present application should not be construed as limiting the present application. As used herein, the terms "comprising," "including," and "containing" are used in their open, non-limiting sense.

Additionally, amounts, ratios, and other numerical values are sometimes presented herein in a range format. It is to be understood that such range format is used for convenience and brevity and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited.

In the detailed description and claims, a list of items connected by the terms "one or more of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items a and B are listed, the phrase "at least one of a or B" means only a; only B; or A and B. In another example, if items A, B and C are listed, the phrase "at least one of A, B or C" means only a; or only B; only C; a and B (excluding C); a and C (excluding B); b and C (excluding A); or A, B and C. Item a may comprise a single element or multiple elements. Item B may comprise a single element or multiple elements. Item C may comprise a single element or multiple elements.

Electrolyte solution

The electrolyte comprises vinyl sulfate and vinylene carbonate, wherein the mass percentage of the vinyl sulfate is A%, the mass percentage of the vinylene carbonate is B%, the mass percentage of the vinylene carbonate is 0.1-4, the electrolyte at least comprises ethyl propionate and propylene carbonate, the electrolyte further comprises a first substance, the first substance is at least two of lithium difluorophosphate, lithium difluorooxalato borate, lithium bistrifluoromethane sulfonyl imide or lithium hexafluorophosphate, and at least comprises lithium difluorophosphate, and the mass percentage of the first substance is 0.3-1.2 wt% based on the total mass of the electrolyte. Illustratively, the ratio of A/B is 0.1, 0.2, 0.4, 0.6, 0.8, 1, 1.3, 1.5, 1.8, 2, 2.4, 2.6, 2.8, 3, 3.5, 4 or a range of any two of the foregoing values. Illustratively, the first material comprises 0.3wt%, 0.4wt%, 0.5wt%, 0.8wt%, 1.0wt%, 1.2wt% or a range of any two of the foregoing values.

In some embodiments, 0.2.ltoreq.A.ltoreq.0.5. Illustratively, the vinyl sulfate comprises 0.2wt%, 0.25wt%, 0.3wt%, 0.35wt%, 0.4wt%, 0.45wt%, 0.5wt% or a range of any two of the foregoing values.

In some embodiments, 0.5.ltoreq.B.ltoreq.1. The mass percent of the vinylene carbonate B is 0.5-wt%, 0.6-7%, 0.8-9%, 1-1% or the range of any two values.

In some embodiments, the mass percent of ethyl propionate is C, and the sum of the mass percent of ethyl propionate and the mass percent of vinyl sulfate is W.ltoreq.W.ltoreq.15.5 based on the mass of the electrolyte. Illustratively, the sum W of the mass percentages of the ethyl propionate and the vinyl sulfate is 8.6 wt%, 8.8wt%, 9wt%, 9.5wt%, 10wt%, 10.5wt%, 11wt%, 11.5wt%, 12wt%, 12.5wt%, 13wt%, 13.5wt%, 14wt%, 14.5wt%, 15wt%, 15.5wt%, or a range of any two of the above values.

In some embodiments, the propylene carbonate is present in a mass percent of D based on the mass of the electrolyte, and the sum of the mass percent of propylene carbonate and the mass percent of vinylene carbonate is W '+.3.7.ltoreq.w'.ltoreq.12.5. Illustratively, the sum W' of the mass percentages of the propylene carbonate and the vinylene carbonate is 3.7, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5 or a range of any two of the foregoing values.

In some embodiments, the first substance further comprises at least lithium bis (trifluoromethanesulfonyl) imide, the sum of the mass percentages of the lithium difluorophosphate and the lithium bis (trifluoromethanesulfonyl) imide ranges from 0.4wt% to 0.5wt% wt%, the mass ratio of the lithium difluorophosphate to the lithium difluorooxalato borate ranges from 2:5 to 1, and the mass ratio of the lithium difluorophosphate to the lithium bis (trifluoromethanesulfonyl) imide ranges from 1:5 to 1. Illustratively, the mass ratio of the lithium difluorophosphate to the lithium difluorooxalato borate is 2:5, 2.5:5, 3:5, 3.5:5, 4:5, 4.5:5, 5:5, or a range of any two of the foregoing values. Illustratively, the mass ratio of the lithium difluorophosphate to the lithium bistrifluoromethane sulfonimide is 1:5, 1.5:5, 2:5, 2.5:5, 3:5, 3.5:5, 4:5, 4.5:5, 5:5, or a range of any two of the foregoing values.

In particular, the concentration of the first substance in the electrolyte is not particularly limited, but is preferably 0.5 mol/liter or more, more preferably 0.8 mol/liter or more, and still more preferably 1.0 mol/liter or more. Further, it is preferably 3 mol/liter or less, more preferably 2 mol/liter or less, and still more preferably 1.7 mol/liter or less. If the concentration of the first substance is too low, it may cause an insufficient amount of mobile lithium ions in the electrolyte, and on the other hand, if the concentration of the first substance is too high, it may cause an increase in viscosity of the electrolyte, with an increase in impedance of the electrolyte, which may cause a decrease in performance of the electrochemical device.

In some embodiments, the electrolyte further includes other additives including at least one of diethyl carbonate (DEC), propyl Propionate (PP), 4-methyl ethylene sulfate (MDTD), 1, 3-Propane Sultone (PS), 1, 4-Butane Sultone (BS) or 1, 3-Propene Sultone (PST), succinonitrile (SN), glutaronitrile (GN), adiponitrile (ADN), 2-methyleneglutaronitrile, dipropylpropiodinitrile, 1,3, 6-hexane tri-nitrile (HTCN), 1,2, 6-hexane tri-nitrile, 1,3, 5-pentane tri-nitrile or 1, 2-bis (cyanoethoxy) Ethane (EDPN). Based on the mass of the electrolyte, the ratio of the other additives to the sum of the mass percentages of the vinyl sulfate and the vinylene carbonate is 8-16.

In some embodiments, the electrolyte further comprises at least one of fluoroether, fluoroethylene carbonate, or ether nitrile.

In some embodiments, the electrolyte may further include a non-aqueous solvent selected from the group consisting of carbonate compounds, carboxylate compounds, ether compounds, other organic solvents, or combinations thereof. Wherein the carbonate compound may be a chain carbonate compound, a cyclic carbonate compound, a fluorocarbonate compound, or a combination thereof. The chain carbonate compound is selected from Ethyl Propionate (EP), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), ethylmethyl carbonate (MEC), or a combination thereof. The cyclic carbonate compound is selected from Ethylene Carbonate (EC), propylene Carbonate (PC), butylene Carbonate (BC), vinyl Ethylene Carbonate (VEC), or a combination thereof. The fluorocarbonate compound is selected from fluoroethylene carbonate (FEC), 1, 2-difluoroethylene carbonate, 1, 2-trifluoroethylene carbonate, 1, 2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1, 2-difluoro-1-methylethylene carbonate, 1, 2-trifluoro-2-methylethylene carbonate, trifluoromethyl ethylene carbonate, or a combination thereof. The carboxylate compound is selected from methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, gamma-butyrolactone, decalactone, valerolactone, mevalonic acid lactone, caprolactone, methyl formate, or a combination thereof. The ether compound is selected from dibutyl ether, tetraglyme, diglyme, 1, 2-dimethoxyethane, 1, 2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, or a combination thereof. The other organic solvent is selected from dimethyl sulfoxide, 1, 2-dioxolane, sulfolane, methyl sulfolane, 1, 3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, phosphate esters, or combinations thereof.

Secondary battery

The secondary battery comprises the electrolyte, the positive electrode plate, the isolating film and the negative electrode plate, wherein the positive electrode plate and the negative electrode plate are separated by the isolating film arranged between the positive electrode plate and the negative electrode plate.

Positive electrode plate

In some embodiments, the positive electrode tab includes a positive electrode current collector and a positive electrode material layer disposed on at least one side surface of the positive electrode current collector, the positive electrode material layer including at least one of first material particles, second material particles, or inorganic ceramic particles, and containing at least the first material particles. Wherein the first material particles are lithium transition metal phosphate compound particles having an olivine-type crystal structure, and the second material particles are lithium manganese composite oxide particles having a layered crystal structure.

In some embodiments, the positive electrode material layer further includes a conductive agent and a binder, the first material particles include lithium iron phosphate, the lithium iron phosphate is 75wt% to 88wt% based on the mass of the positive electrode material layer, the binder is 6wt% to 15wt%, and the conductive agent is 2wt% to 10wt%. Illustratively, the lithium iron phosphate is 75wt%, 77wt%, 79wt%, 80wt%, 82wt%, 84wt%, 86wt%, 88wt%, or a range of any two of the above values. Illustratively, the binder comprises 6wt%, 8wt%, 10wt%, 11wt%, 12wt%, 13wt%, 15wt% or a range of any two of the foregoing values by mass. Illustratively, the conductive agent is present in an amount by mass ranging from 2wt%, 4wt%, 5wt%, 6wt%, 8wt%, 10wt%, or any two of the foregoing.

In some embodiments, the positive electrode material layer has a compacted density of P g/cm ³ P is more than or equal to 2.8 and less than or equal to 4.0. Illustratively, the positive electrode material layer has a compacted density P of 2.8g/cm ³ 、3.0g/cm ³ 、3.2g/cm ³ 、3.4g/cm ³ 、3.6g/cm ³ 、3.8g/cm ³ 、4.0g/cm ³ Or a range of any two values recited above.

In some embodiments, the positive current collector may be aluminum foil, although other positive current collectors commonly used in the art may be used. The thickness of the positive electrode current collector may be 1 μm to 200 μm. The positive electrode active material layer may be coated only on a partial region of the positive electrode current collector. The thickness of the positive electrode active material layer may be 10 μm to 500 μm. It should be understood that these are merely exemplary and that other suitable thicknesses may be employed.

In some embodiments, the binder comprises at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, styrene-acrylate copolymer, styrene-butadiene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinyl acetate, polyvinylpyrrolidone, polyvinyl ether, polytetrafluoroethylene, or polyhexafluoropropylene.

In some embodiments, the conductive agent includes at least one of conductive carbon black, acetylene black, ketjen black, graphene, carbon nanotubes, or carbon fibers.

The positive electrode sheet of the present application may be prepared according to a conventional method in the art. For example, a positive electrode slurry containing first material particles, second material particles, inorganic ceramic particles, a conductive agent and a binder is coated on at least one surface of a positive electrode current collector to obtain a positive electrode active material coating, and then the positive electrode sheet is obtained through procedures such as drying, cold pressing and the like.

Isolation film

In some embodiments, the separator comprises a base film and a functional coating disposed on at least one side surface of the base film, the functional coating comprising polymer particles having a swelling of less than 45% when placed in the electrolyte at 90 ℃ for 20 hours. The polymer particles include polymer particles based on propylene, such as polypropylene (PP).

The base film of the isolating film is at least one selected from polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide or aramid. For example, the polyethylene includes at least one selected from high density polyethylene, low density polyethylene, or ultra high molecular weight polyethylene. In particular, polyethylene and polypropylene, which have good effects in preventing short circuits and can improve the safety of the battery through a shutdown effect. The thickness of the separator is in the range of about 3 μm to 500 μm.

In some embodiments, a porous layer is also disposed between the base film and the functional coating, the porous layer comprising inorganic particles and binder particles. The inorganic particles are selected from the group consisting of alumina (Al) ₂ O ₃ ) Silicon oxide (SiO) ₂ ) Magnesium oxide (MgO), titanium oxide (TiO) ₂ ) Hafnium oxide (HfO) ₂ ) Tin oxide (SnO) ₂ ) Cerium oxide (CeO) ₂ ) Nickel oxide (NiO), zinc oxide (ZnO), calcium oxide (CaO), zirconium oxide (ZrO) ₂ ) Yttria (Y) ₂ O ₃ ) At least one of silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The binder particles are at least one selected from polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polytetrafluoroethylene or polyhexafluoropropylene. The pores of the separator have a diameter in the range of about 0.01 μm to 1 μm. The porous layer on the surface of the isolating membrane can improve the heat resistance, oxidation resistance and electrolyte infiltration performance of the isolating membrane, and enhance the adhesion between the isolating membrane and the pole piece.

Negative pole piece

The negative electrode tab includes a negative electrode current collector and a negative electrode material layer disposed on at least one side surface of the negative electrode current collector, the negative electrode material layer including a negative electrode active material. In some embodiments, the negative electrode current collector may employ at least one of a copper foil, a nickel foil, or a carbon-based current collector. In some embodiments, the thickness of the negative electrode current collector may be 1 μm to 200 μm. In some embodiments, the anode material layer may be coated on only a partial region of the anode current collector. In some embodiments, the thickness of the negative electrode material layer may be 10 μm to 500 μm. It should be understood that these are merely exemplary and that other suitable thicknesses may be employed.

In some embodiments, the negative active material includes at least one of natural graphite, artificial graphite, or a silicon-based material. In some embodiments, the silicon-based material includes at least one of silicon, a silicon oxygen compound, a silicon carbon compound, or a silicon alloy.

In some embodiments, a negative electrode conductive agent and/or a negative electrode binder may also be included in the negative electrode material layer. The negative electrode conductive agent may include at least one of carbon black, acetylene black, ketjen black, graphene, carbon nanotubes, or carbon fibers. In some embodiments, the anode binder may include at least one of sodium carboxymethyl cellulose, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyimide, polysiloxane, or styrene butadiene rubber. It should be understood that the above disclosed materials are merely exemplary, and that any other suitable materials may be used for the anode active material layer.

In some embodiments, the mass ratio of the anode active material, the anode conductive agent, and the anode binder in the anode active material layer may be (80-99): (0.5-10), it being understood that this is merely exemplary and not intended to limit the present application.

The negative electrode sheet may be prepared according to conventional methods in the art. Illustratively, the negative electrode active material, and optionally, the conductive agent and the binder are dispersed in a solvent, which may be N-methyl pyrrolidone (NMP) or deionized water, to form a uniform negative electrode slurry, the negative electrode slurry is coated on a negative electrode current collector, and the negative electrode sheet is obtained through processes such as drying, cold pressing, and the like.

Electronic device

The electronic device of the embodiment of the present application is not particularly limited, and may be any electronic device known in the art. In some embodiments, the electronic device may include, but is not limited to, a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copier, a portable printer, a headset, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini-compact disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable audio recorder, a radio, a backup power source, a motor, an automobile, a motorcycle, a power assisted bicycle, a lighting fixture, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a household large-sized battery, a lithium ion capacitor, and the like.

Hereinafter, embodiments of the present application will be described in more detail with reference to examples and comparative examples. Unless otherwise indicated, the parts, percentages and ratios listed below are based on weight, and the starting materials used are either commercially available or synthetically obtained according to conventional methods.

Example 1-1

Preparation of lithium ion battery

< preparation of Positive electrode sheet >

Mixing the first material particles of lithium iron phosphate, the positive electrode conductive agent of acetylene black and the positive electrode binder of polyvinylidene fluoride (PVDF) according to a mass ratio of 85:7:8, adding N-methyl pyrrolidone (NMP) as a solvent, uniformly stirring, and preparing into positive electrode slurry with a solid content of 75wt%. Uniformly coating the positive electrode slurry on one surface of a positive electrode current collector aluminum foil with the thickness of 13 mu m, drying at the temperature of 85 ℃ to obtain a positive electrode plate with a single-sided coating positive electrode mixture layer, repeating the steps on the other surface of the positive electrode current collector aluminum foil to obtain a positive electrode plate with a double-sided coating positive electrode active material layer, and then carrying out cold pressing, cutting and slitting, and drying for 4 hours under the vacuum condition at the temperature of 85 ℃ to obtain the positive electrode plate with the specification of 74mm multiplied by 867 mm.

< preparation of negative electrode sheet >

Mixing negative active material artificial graphite, conductive carbon black, binder styrene-butadiene rubber (SBR) and thickener sodium carboxymethyl cellulose according to the weight ratio of 96.5:1.5:1:1, adding deionized water, and uniformly stirring under the action of a vacuum stirrer to obtain negative slurry, wherein the solid content of the negative slurry is 75wt%. Uniformly coating the negative electrode slurry on one side surface of a 13 mu m negative electrode current collector copper foil, drying at 120 ℃ to obtain a negative electrode plate with a single side coated with a negative electrode active material layer with the thickness of 90 mu m, repeating the steps on the other side surface of the negative electrode current collector copper foil to obtain a negative electrode plate with double sides coated with the negative electrode active material layer, and then carrying out cold pressing, cutting and slitting to obtain the negative electrode plate with the specification of 76mm multiplied by 851 mm.

< preparation of electrolyte >

In a glove box filled with argon, liPO accounting for 0.2 percent of the total mass of the electrolyte is firstly added ₂ F ₂ Lithium difluorophosphate and 0.5% LiDFOB (lithium difluorooxalato borate), and the electrolyte solvent of which the ratio of EP (ethyl propionate) to PC (propylene carbonate) to DEC (diethyl carbonate) to PP (propyl propionate) is 6:12:42:40 is weighed according to the mass ratio. Further, the additive of DTD: vc=1:10 mass ratio was further weighed so that the mass ratio of DTD (vinyl sulfate) was 0.2% and the mass ratio of VC (vinylene carbonate) was 0.5% in the final electrolyte.

< separation Membrane >

A 10 μm thick Polyethylene (PE) microporous membrane was selected as the separator.

Inorganic particle boehmite with Dv50 of 1.5 mu m and polyacrylate are mixed according to the mass ratio of 90:10 and dissolved into deionized water to form inorganic coating slurry with the solid content of 50%, then the obtained inorganic coating slurry is uniformly coated on two sides of a PE base film by adopting a micro-concave coating method to obtain a heat-resistant layer, drying is completed in an oven, and the thickness of the inorganic coating is 1.5 mu m.

Preparation of functional coatings

Sequentially adding polymer particles PP (weight average molecular weight 10000-14000), sodium carboxymethylcellulose and dimethyl siloxane serving as a wetting agent into a stirrer, uniformly stirring, adding deionized water, stirring, and adjusting the viscosity of the slurry to 40mPa.s and the solid content to 5% to obtain the organic coating slurry. And uniformly coating the inorganic coating on the two sides of the base film with the organic coating slurry, and drying in an oven to obtain a first coating. The thickness of the first coating layer was 3 μm. The mass ratio of the polymer particles, the sodium carboxymethyl cellulose and the dimethyl siloxane is 95:0.5:4.5. Wherein the polymer particles are spherical or spheroid in the isolating film, and the sphericity R of the polymer is more than or equal to 0.7 and less than or equal to 1.0.

< preparation of lithium ion Battery >

Sequentially stacking the positive electrode plate, the isolating film and the negative electrode plate, enabling the isolating film to be positioned between the positive electrode plate and the negative electrode plate to play a role of isolation, winding to obtain an electrode assembly, placing the electrode assembly in an outer packaging aluminum plastic film after welding the electrode lugs, dehydrating at 80 ℃, injecting the electrolyte, and carrying out vacuum packaging, standing, formation, shaping, capacity testing and other procedures to obtain the lithium ion battery.

(II) test method

(1) Low temperature performance test:

the prepared battery is charged to 4.0V at 0.5C after being circularly charged and discharged twice at 0.2C, the battery is placed in an environment of-15 ℃ to be discharged to 2.5V at a rate of 0.5C, the battery is circularly circulated for 500 circles, and the ratio of the discharge capacity of 500 th circle to 15 ℃ to the discharge capacity of 0.5C at room temperature is the low-temperature capacity retention rate of the material at-15 ℃.

(2) 3c 5.5v overcharge test:

the cells were discharged to 2.5V at 25C at 0.5C, charged to 5V at 3C constant current, charged at constant voltage for 3h again, and the cell surface temperature change was monitored (by standard that the cells were not fired, burned, exploded), 10 cells were selected for each example for testing, and the number of passes was calculated.

(3) And (3) hot box test:

the lithium ion batteries in each example and each comparative example were charged to a full charge voltage of 3.8V at normal temperature with a constant current of 0.5C and continuously charged to a cut-off current of 0.05C at a constant voltage of 3.80V, so that they were in a full charge state, and the appearance was checked to ensure that the lithium ion batteries were in a normal usable state. The fully charged battery was placed in an oven and warmed up at a rate of 5 c/min until the temperature reached 140 c, the temperature was maintained for one hour, at which time the state of the battery was observed.

Judgment standard: the battery does not get on fire and explode.

Hot box test pass = hot box test pass/total.

(4) Testing the multiplying power performance at 45 ℃):

and placing the lithium ion battery in a 45 ℃ incubator, and standing for 30 minutes to keep the lithium ion battery at a constant temperature.

The battery charge and discharge performance test is carried out according to the following steps:

a) When the battery is charged to 3.8V at a constant current of 0.1C (1 C=0.38mA), the constant voltage charging is switched to stop charging when the charging current is reduced to 0.05C multiplying power;

b) The battery stops discharging when the constant current of the current of 0.1C multiplying power is discharged to 2.0V;

c) And counting the charge and discharge capacity of the battery.

The battery rate performance test is carried out by respectively testing the first discharge specific capacity of 1C/2C/3C/5C rate and taking 3C rate as an example, and comprises the following steps:

a) When the battery is charged to 3.8V with 3C multiplying power current constant current, the constant voltage charging is switched to stop charging when the charging current is reduced to 0.05C multiplying power current;

b) The battery stops discharging when the current constant current of the 3C multiplying power is discharged to 2.0V;

c) The percentage of the battery's first discharge capacity to the charge capacity was calculated.

(5) And (3) floating charge performance test:

and placing the lithium ion battery in a constant temperature box at 25 ℃, and standing for 30 minutes to enable the lithium ion battery to reach constant temperature. The lithium ion battery is charged with a constant current of 1C to a voltage of 3.8V, charged with a constant voltage to a current of 0.05C, and discharged with a constant current of 1C to a voltage of 2.0V, and the discharge capacity is recorded as the initial capacity of the lithium ion battery. Then charging to 3.8V with 0.5C constant current, charging to 0.05C constant voltage, testing with micrometer, and recording the thickness of the battery as initial thickness. And transferring the test lithium ion battery into a 45 ℃ incubator, charging for 60 days at a constant voltage of 3.8V, transferring the battery into the 25 ℃ incubator after 60 days, standing for 60 minutes, discharging at a constant current of 1C until the voltage is 2.0V, and recording the discharge capacity as the discharge capacity of the lithium ion battery after storage. Then charging to 3.8V with 1C constant current, charging to 0.05C constant voltage, discharging to 2.0V with 1C constant current, recording discharge capacity, measuring thickness of lithium ion battery, and floating charging thickness.

Expansion ratio of float thickness = (thickness after float-initial thickness)/initial thickness×100%

Float capacity retention= (initial discharge capacity-recoverable capacity)/initial discharge capacity x 100%.

(6) Swelling degree test of polymer:

and adding the polymer into water to obtain emulsion with the solid content of 30wt%, coating the emulsion on a glass substrate, and drying at 85 ℃ to obtain the polymer adhesive film. Will have a mass of m ₁ The polymer film is placed in a test electrolyte and soaked for 20 hours at 90 ℃, and the mass of the polymer film at the moment is recorded as m ₂ Swelling degree of polymer= (m ₂ -m ₁ ) M 1X 100%. Each example or comparative example was tested 3 times and averaged to give the final polymer swell. Wherein the test electrolyte is the same as the electrolyte from which the cell was prepared.

(7) And (3) testing the compaction density of the positive electrode material layer:

disassembling the battery discharged to the voltage of 2.0V, taking out the positive electrode plate, placing the positive electrode plate in a dimethyl carbonate solvent for soaking for 30min to remove electrolyte and byproducts on the surface of the positive electrode plate, drying in a fume hood for 4 hours, taking out the dried positive electrode plate, selecting 5 positive electrode plates with the size of 5cm multiplied by 5cm, measuring the thickness of the positive electrode plates respectively by a ten-thousandth ruler, and marking as d ₀ The method comprises the steps of carrying out a first treatment on the surface of the Scraping the positive electrode active material layer in the positive electrode plate by using a scraper, weighing the positive electrode active material layer by using a balance, and marking the weight as m ₁ The thickness of the current collector from which the active material was removed by measurement with a ten-thousandth ruler was denoted as d ₁ The compacted density of the positive electrode active material layer was calculated according to the following formula:

compaction density p=m ₁ /[5cm×5cm×(d ₀ -d ₁ )]Units g/cm ³ 。

The compacted density of the positive electrode active material layer was an average value of 5 positive electrode sheets.

Examples 1-2 to 1-19

The procedure of example 1-1 was repeated except that the relevant production parameters were adjusted as shown in Table 1.

Comparative examples 1-1 to 1-6

Comparative examples 1 to 7

The procedure of example 1-1 was repeated except that vinyl sulfate and vinylene carbonate were not added.

Examples 2-1 to 2-12

The procedure of example 1-1 was repeated except that the relevant production parameters were adjusted as shown in Table 2.

Examples 3-1 to 3-15

The procedure of example 1-1 was repeated except that the relevant production parameters were adjusted as shown in Table 3.

TABLE 1

In combination with table 1, the comparative examples 1-1 to 1-7 and example 1-1 have unsuitable ratios a/B of the vinyl sulfate and the vinylene carbonate in the electrolyte, resulting in failure of the vinyl sulfate and the vinylene carbonate to exert a synergistic effect with other components, failure of forming a mixed solid electrolyte interfacial film at the negative electrode interface, which is effective and capable of reducing the generation of other side reactions at the interface and the generation of gas at the interface, and thus, is disadvantageous in improving the low temperature cycle performance of the lithium ion battery and its overcharge preventing ability under a large current condition.

Particularly, when a proper amount of ethylene sulfate and a proper amount of ethylene carbonate are added into the electrolyte (namely the electrolyte at least containing ethyl propionate, propylene carbonate and a first substance) disclosed by the application, the ethylene sulfate, the ethylene carbonate and other components can better play a synergistic effect, and a mixed solid electrolyte interface film which is effective and can reduce the generation of other side reactions of the interface and the generation of gas of the interface is formed at the interface of the negative electrode, so that the low-temperature cycle performance of the lithium ion battery and the overcharge prevention capability of the lithium ion battery under the condition of high current are further improved.

Particularly, when a proper amount of ethyl propionate is added into the electrolyte, the overcharge prevention capability of the lithium ion battery under the condition of high current is further improved.

In particular, when a proper amount of propylene carbonate is added into the electrolyte, the low-temperature cycle performance of the lithium ion battery and the overcharge prevention capability of the lithium ion battery under the condition of high current can be further improved.

Particularly, when the contents of the ethylene sulfate, the ethylene carbonate, the ethyl propionate and the propylene carbonate in the electrolyte are all within the preferred ranges, the effect of improving the low-temperature cycle performance of the lithium ion battery and the overcharge preventing capability thereof under the condition of large current is better.

TABLE 2

As can be seen from the combination of table 2, when an appropriate amount of the first substance is added to the electrolyte, and the kind and content of the first substance are all within the above ranges, it is possible to achieve further improvement of the thermal safety performance while improving the low-temperature cycle performance of the lithium ion battery. In particular, when the kind and content of the first substance are within the preferable ranges, the effect of improving the low-temperature cycle performance and the thermal safety performance of the lithium ion battery is better.

TABLE 3 Table 3

As can be seen from table 3, when the positive electrode active material layer contains the olivine-type crystal structure lithium iron phosphate and the contents of the lithium iron phosphate, the conductive agent and the binder are all in the proper ranges, the rate capability of the lithium ion battery at high temperature can be further improved, the floating thickness expansion rate of the lithium ion battery can be reduced, and the floating performance of the lithium ion battery can be improved. In particular, when the contents of lithium iron phosphate, conductive agent and binder are all within the preferred ranges, the effect of improving the performance of the lithium ion battery is better.

The foregoing description of the preferred embodiments of the present application is not intended to be limiting, but is intended to cover any and all modifications, equivalents, and alternatives falling within the spirit and principles of the present application.

Claims

1. The electrolyte is characterized by comprising vinyl sulfate and vinylene carbonate, wherein the mass percentage of the vinyl sulfate is A, and the mass percentage of the vinylene carbonate is B, and the mass percentage of the vinylene carbonate is more than or equal to 0.1 and less than or equal to 4;

the electrolyte at least comprises ethyl propionate and propylene carbonate;

the electrolyte further comprises a first substance selected from at least two of lithium difluorophosphate, lithium difluorooxalato borate, lithium bistrifluoromethane sulfonyl imide or lithium hexafluorophosphate, and at least comprises lithium difluorophosphate;

based on the mass of the electrolyte, the mass percentage of the first substance is 0.3-1.2-wt%.

2. The electrolyte of claim 1, wherein the electrolyte meets: A/B is more than or equal to 0.2 and less than or equal to 3.

3. The electrolyte according to claim 1 or 2, wherein the electrolyte satisfies at least one of the following conditions:

（1）0.2≤A≤0.5；

（2）0.5≤B≤1。

4. the electrolyte according to claim 1 or 2, wherein,

based on the mass of the electrolyte, the mass percentage of the ethyl propionate is C percent, and the sum of the mass percentages of the ethyl propionate and the vinyl sulfate is W percent, wherein W is more than or equal to 8.6 and less than or equal to 15.5.

5. The electrolyte according to claim 1 or 2, wherein,

based on the mass of the electrolyte, the mass percentage of the propylene carbonate is D, and the sum of the mass percentages of the propylene carbonate and the vinylene carbonate is W'% which is more than or equal to 3.7 and less than or equal to 12.5.

6. The electrolyte according to claim 1 or 2, wherein,

based on the mass of the electrolyte, the mass percentage of the first substance is 0.4-2wt%;

the electrolyte also comprises diethyl carbonate and propyl propionate, wherein the mass ratio of the ethyl propionate to the propylene carbonate to the diethyl carbonate to the propyl propionate is (4-8)/(10-14)/(40-44)/(38-42).

7. The electrolyte of claim 1, wherein the first substance further comprises at least lithium bis (trifluoromethanesulfonyl) imide, the sum of the mass percentages of the lithium difluorophosphate and the lithium bis (trifluoromethanesulfonyl) imide being in the range of 0.4wt% to 0.5wt%; and/or the number of the groups of groups,

the mass ratio of the lithium difluorophosphate to the lithium bistrifluoromethane sulfonyl imide is 1:5-1.

8. A secondary battery comprising the electrolyte according to any one of claims 1 to 7.

9. The secondary battery according to claim 8, further comprising a positive electrode tab including a positive electrode current collector and a positive electrode material layer disposed on at least one side surface of the positive electrode current collector;

the positive electrode material layer includes at least one of first material particles, second material particles, or inorganic ceramic particles, and contains at least the first material particles;

wherein the first material particles are lithium transition metal phosphate compound particles having an olivine-type crystal structure, and the second material particles are lithium manganese composite oxide particles having a layered crystal structure.

10. The secondary battery according to claim 9, wherein the positive electrode material layer further comprises a conductive agent and a binder;

the first material particles comprise lithium iron phosphate;

the lithium iron phosphate is 75 to 88wt%, the binder is 6 to 15wt%, and the conductive agent is 2 to 10wt%, based on the mass of the positive electrode material layer.

11. The secondary battery according to claim 9, wherein the positive electrode material layer has a compacted density of P g/cm ³ ，2.8≤P≤4.0。

12. The secondary battery according to claim 8, wherein the secondary battery further comprises a separator;

the barrier film comprises a base film and a functional coating layer arranged on at least one side surface of the base film;

the functional coating contains polymer particles, and the swelling degree of the polymer particles in the electrolyte is less than 45% when the polymer particles are placed at 90 ℃ for 20 hours.

13. An electronic device comprising the secondary battery according to any one of claims 8 to 12.