WO2021238052A1 - 一种锂离子二次电池的电解液及其应用 - Google Patents

一种锂离子二次电池的电解液及其应用 Download PDF

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WO2021238052A1
WO2021238052A1 PCT/CN2020/124715 CN2020124715W WO2021238052A1 WO 2021238052 A1 WO2021238052 A1 WO 2021238052A1 CN 2020124715 W CN2020124715 W CN 2020124715W WO 2021238052 A1 WO2021238052 A1 WO 2021238052A1
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electrolyte
ion secondary
secondary battery
carbonate
lithium ion
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PCT/CN2020/124715
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English (en)
French (fr)
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冯绍伟
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蜂巢能源科技有限公司
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Priority to EP20937349.7A priority Critical patent/EP4024552A1/en
Priority to JP2022572790A priority patent/JP7481503B2/ja
Priority to US17/782,599 priority patent/US20230038758A1/en
Publication of WO2021238052A1 publication Critical patent/WO2021238052A1/zh

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0567—Liquid materials characterised by the additives
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0568—Liquid materials characterised by the solutes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0569—Liquid materials characterised by the solvents
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0025—Organic electrolyte
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0025—Organic electrolyte
    • H01M2300/0028—Organic electrolyte characterised by the solvent
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0048—Molten electrolytes used at high temperature
    • H01M2300/0051—Carbonates
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present disclosure relates to the battery field, for example, to an electrolyte of a lithium ion secondary battery and its application.
  • Lithium ion secondary battery with higher energy density, better high temperature cycle, storage performance and low temperature rate performance.
  • the electrochemical stability of the electrolyte has a significant impact on the high-temperature cycle, storage, and low-temperature charge and discharge performance of lithium ion secondary batteries. Therefore, the composition of the electrolyte is improved, so that the positive and negative electrodes can be formed with high temperature stability and cycle stability.
  • the SEI film is of great significance to improve the overall performance of the battery cell at high and low temperatures.
  • the cathodes used in lithium-ion power batteries are mostly ternary cathode materials with high nickel content (LiNi x Co y Mn Z O 2 , LiNi X Co 1-X O 2 ).
  • cobalt-free cathode materials due to the global cobalt metal resources Scarcity, cobalt-free cathode materials (LiNi X Mn 1-X O 2 ) have become a research hotspot.
  • this positive electrode material is unstable in high temperature, and the surface is prone to irreversible phase transition, oxygen release, and non-conductive NiOx compounds; and during the cycle, Ni and Mn metal ions are prone to occur It dissolves and reduces on the surface of the negative electrode to increase the impedance; in addition, the high-valence Ni 4+ in the positive electrode is prone to catalytic oxidation reaction with the electrolyte, leading to gas production and reducing cycle life.
  • the present disclosure provides an electrolyte for a lithium-ion secondary battery and an application thereof, which can improve the high-temperature cycle and storage performance of the lithium-ion battery, suppress gas production during high-temperature storage, and improve the overall performance of the battery.
  • an electrolyte for a lithium ion secondary battery includes an organic solvent, a lithium salt, and an additive, and the additive includes a borate compound having the structural formula shown in Formula I ,
  • the value range of n is 0, 1, 2, 3, 4,
  • the added amount of the borate compound is 0.01-5wt% of the total mass of the electrolyte, for example: 0.01wt%, 0.1wt%, 0.5wt%, 1wt%, 2wt%, 3wt% , 4wt% or 5wt%, etc.
  • the carbon atom in the structural formula shown in Formula I contains a halogen substituent.
  • the borate compound includes Namely trimethylene borate.
  • the additive includes vinylene carbonate, and the added amount of vinylene carbonate can be 0.1-3wt% of the total mass of the electrolyte, for example: 0.1wt%, 0.5wt%, 1wt%, 1.4wt%, 1.8wt%, 2.2wt%, 2.6wt% or 3wt%, etc.
  • the organic solvent includes a sulfone compound having the structural formula shown in Formula II, and the value range of n is 0, 1, 2, 3, and 4.
  • the addition amount of the sulfone compound is 1-20 wt% of the total mass of the organic solvent, for example: 1 wt%, 3 wt%, 5 wt%, 10 wt%, 12 wt%, 14 wt%, 16 wt%, 18wt% or 20wt%, etc.
  • the sulfone compound includes: At least one of them.
  • the organic solvent includes cyclic carbonate and/or chain carbonate, and the cyclic carbonate is at least one selected from ethylene carbonate, propylene carbonate, and ⁇ -butyrolactone ;
  • the chain carbonate is selected from dimethyl carbonate, butylene carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethylene propyl carbonate, methyl formate , At least one of ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate.
  • the lithium salt is selected from LiPF 6 , LiBF 4 , LiBOB, LiDFOB, LiAsF 6 , Li(CF 3 SO 2 ) 2 N, Li(FSO 2 ) 2 N, LiPO 2 F 2 , LiCF 3 At least one of SO 3 and LiClO 4.
  • a lithium ion secondary battery having the above-mentioned lithium ion secondary battery electrolyte.
  • the positive electrode active material used in the lithium ion secondary battery is selected from LiCoO 2 , LiMn 2 O 4 , LiMnO 2 , Li 2 MnO 4 , LiFePO 4 , LiNi x Mn 1-x O 2 , LiNi x Co y Mn z O 2 , Li 1+a Mn 1-x M x O 2 , LiCo 1-x M x O 2 , LiFe 1-x M x PO 4 , LiMn 2-y M y O 4 and Li 2 At least one of Mn 1-x O 4 , where M is at least one selected from Ni, Co, Mn, Al, Cr, Mg, Zr, Mo, V, Ti, B, F, and Y, a The value range of is 0 ⁇ 0.2, the value range of x is 0 ⁇ 1, the value range of y is 0 ⁇ 1, and the value range of z is 0 ⁇ 1.
  • the positive electrode active material used in the lithium ion secondary battery is a low-cobalt or cobalt-free positive electrode material.
  • the cobalt-free cathode material described in the present disclosure can relieve the limitation of the existing scarce metal cobalt source on the cathode material on the basis of ensuring that the cathode material has comprehensive performance such as excellent rate performance and cycle stability.
  • the negative electrode active material used in the lithium ion secondary battery is at least one selected from natural graphite, artificial graphite, soft carbon, hard carbon, lithium titanate, silicon, silicon-carbon alloy, and silicon-oxygen alloy. kind.
  • the negative electrode active material described in the present disclosure can cause lithium ion insertion and extraction reactions, and can further ensure the electrochemical performance and cycle performance of the lithium ion secondary battery.
  • a lithium ion secondary battery in one embodiment, includes a positive electrode sheet, a negative electrode sheet, a separator, the above-mentioned lithium ion secondary battery electrolyte and packaging, wherein the positive electrode
  • the sheet includes a positive electrode current collector and a positive electrode film containing a positive electrode active material arranged on the positive electrode current collector.
  • the negative electrode sheet includes a negative electrode current collector and a negative electrode film containing the negative electrode active material arranged on the negative electrode current collector.
  • the packaging can be aluminum plastic film, stainless steel cylinder, square aluminum shell, etc.
  • An embodiment of the present disclosure provides an energy storage device.
  • the energy storage device includes the foregoing lithium ion secondary battery or the foregoing lithium ion secondary battery electrolyte.
  • an electrolyte for a lithium ion secondary battery includes an organic solvent, a lithium salt, and an additive, and the additive includes a borate compound having the structural formula shown in Formula I ,
  • the value range of n is 0, 1, 2, 3, 4,
  • the electrolyte described in the present disclosure can be better applied to low-cobalt or cobalt-free cathode materials, because the cobalt-free materials do not contain cobalt metal, the structure is unstable at high temperatures, and the surface is prone to irreversible phase change, oxygen release, and formation Non-conductive NiOx compound;
  • Ni and Mn metal ions are prone to dissolve and reduce on the surface of the negative electrode to increase impedance; in addition, the high-valence Ni 4+ in the positive electrode is prone to catalytic oxidation reaction with the electrolyte, resulting in Produce gas and reduce cycle life.
  • the electrolyte described in the present disclosure can form a stable SEI film during charging and discharging, can effectively inhibit the reaction of the electrolyte on the surface of the electrode material, inhibit the dissolution of the metal of the positive electrode material, and improve the high-temperature cycle and storage performance of lithium-ion batteries. Inhibit gas production during high-temperature storage, thereby improving the overall performance of the battery.
  • the added amount of the borate compound is 0.01-5wt% of the total mass of the electrolyte, for example: 0.01wt%, 0.1wt%, 0.5wt%, 1wt%, 2wt%, 3wt% , 4wt% or 5wt%, etc. If the addition amount of borate compound is too small, not only the effect of reducing the catalytic reaction activity of the positive electrode metal is not obvious, but also it is not conducive to the formation of a stable SEI film on the surface of the positive electrode material.
  • the amount of borate compound to be added it is possible to effectively inhibit the reaction of the electrolyte on the surface of the electrode material, inhibit the dissolution of the metal of the positive electrode material, and improve the high temperature cycle of the lithium ion battery without reducing the electrochemical performance. Storage performance, and suppress gas production during high-temperature storage, which can significantly improve the overall performance of the battery.
  • the carbon atom in the structural formula shown in Formula I contains a halogen substituent.
  • the borate compound includes Namely trimethylene borate.
  • the trimethylene borate described in the present disclosure has a relatively low molecular weight. Using it as an electrolyte additive can not only react with the electron-rich positive electrode metal elements Ni and Mn, but also reduce the catalytic reaction activity of the positive electrode metal.
  • the surface oxidation reaction of the material forms a stable SEI film, which can also reduce the negative influence of the borate compound on the electrolyte viscosity, thereby further improving the electrochemical performance and cycle performance of the lithium ion secondary battery, and reducing the battery's gas production at high temperatures Rate, so that the lithium battery has better overall performance at both high and low temperatures.
  • the additive includes vinylene carbonate, and the added amount of vinylene carbonate can be 0.1-3wt% of the total mass of the electrolyte, for example: 0.1wt%, 0.5wt%, 1wt%, 1.4wt%, 1.8wt%, 2.2wt%, 2.6wt% or 3wt%, etc.
  • the combination of vinylene carbonate and borate compound described in the present disclosure is used in the electrolyte, and the addition amount of ethylene carbonate is controlled to better improve the high and low temperature performance and gas generation problems of lithium ion secondary batteries. , The cycle performance of the battery and the storage performance under high temperature have been improved significantly.
  • the added amount of the vinylene carbonate may be 0.5 to 1 wt% of the total mass of the electrolyte, which can further improve the high and low temperature performance and gas generation problems of the lithium ion secondary battery, and increase its temperature at room temperature. And comprehensive performance at high temperature.
  • the organic solvent includes a sulfone compound having the structural formula shown in Formula II, and the value range of n is 0, 1, 2, 3, and 4.
  • the cyclic sulfone solvent shown in formula II of the present disclosure has higher oxidation resistance than carbonate solvents, and is not easily oxidized by the high-valence metal Ni 4+ on the surface of the positive electrode, thereby significantly improving the oxidation resistance of the electrolyte, and is effective Improve the high-temperature performance of the battery and reduce gas production, especially after the sulfone compound is used together with the borate compound and/or vinylene carbonate, it can also have a synergistic effect.
  • the addition amount of the sulfone compound is 1-20 wt% of the total mass of the organic solvent, for example: 1 wt%, 3 wt%, 5 wt%, 10 wt%, 12 wt%, 14 wt%, 16 wt%, 18wt% or 20wt%, etc.
  • the addition amount of the sulfone compound described in the present disclosure is too small to significantly improve the oxidation resistance of the electrolyte, and if the addition amount of the sulfone compound is too large, the sulfone compound cannot be completely dissolved in the electrolyte, which will cause the sulfone The compound and the electrolyte layer each other.
  • the amount of sulfone compound to be added not only can the oxidation resistance of the electrolyte be significantly improved, the high temperature performance of the battery and the gas production can be effectively improved, but also the dielectric constant of the electrolyte can be increased, and the ions of the electrolyte can be improved. Conductivity.
  • the sulfone compound includes: At least one of them.
  • the sulfolane and sulfolane described in the present disclosure have a smaller molecular weight and lower viscosity than other sulfones. Using them as a solvent in the electrolyte can further ensure that the electrolyte has a lower viscosity and a higher conductivity. Under the premise of improving the oxidation resistance of the electrolyte, it can further improve the electrochemical performance, high temperature performance of the battery and its gas production problem at high temperature.
  • the organic solvent includes cyclic carbonate and/or chain carbonate, and the cyclic carbonate is at least one selected from ethylene carbonate, propylene carbonate, and ⁇ -butyrolactone ;
  • the chain carbonate is selected from dimethyl carbonate, butylene carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethylene propyl carbonate, methyl formate , At least one of ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate.
  • the lithium salt is selected from LiPF 6 , LiBF 4 , LiBOB, LiDFOB, LiAsF 6 , Li(CF 3 SO 2 ) 2 N, Li(FSO 2 ) 2 N, LiPO 2 F 2 , LiCF 3 At least one of SO 3 and LiClO 4.
  • the lithium ion secondary battery electrolyte described in the present disclosure has at least the following advantages: the borate compound used contains boron atoms and is a Lewis acid with an electron-deficient structure. On the one hand, it can interact with the electron-rich positive metal elements Ni and Mn.
  • a complex reaction occurs, which reduces the catalytic activity of the positive electrode metal; on the other hand, it can form a stable SEI film on the surface of the positive electrode material during the charge and discharge process, which effectively inhibits the reaction of the electrolyte on the surface of the electrode material and inhibits the positive electrode material metal
  • the dissolution of lithium-ion batteries can improve the high-temperature cycle and storage performance of lithium-ion batteries, and inhibit gas production during high-temperature storage, thereby improving the overall performance of the battery.
  • the electrolyte can be suitable for low-cobalt or cobalt-free cathode materials.
  • the lithium-ion secondary battery with the above-mentioned electrolyte of the present disclosure has better cycle stability and a higher capacity retention rate after high-temperature storage. And the gas production rate is lower, and the overall performance under high temperature and low temperature is better.
  • a lithium ion secondary battery having the above-mentioned lithium ion secondary battery electrolyte.
  • the positive electrode active material used in the lithium ion secondary battery is selected from LiCoO 2 , LiMn 2 O 4 , LiMnO 2 , Li 2 MnO 4 , LiFePO 4 , LiNi x Mn 1-x O 2 , LiNi x Co y Mn z O 2 , Li 1+a Mn 1-x M x O 2 , LiCo 1-x M x O 2 , LiFe 1-x M x PO 4 , LiMn 2-y M y O 4 and Li 2 At least one of Mn 1-x O 4 , where M is at least one selected from Ni, Co, Mn, Al, Cr, Mg, Zr, Mo, V, Ti, B, F, and Y, a The value range of is 0 ⁇ 0.2, the value range of x is 0 ⁇ 1, the value range of y is 0 ⁇ 1, and the value range of z is 0 ⁇ 1.
  • the positive electrode active material used in the lithium ion secondary battery is a low-cobalt or cobalt-free positive electrode material.
  • the cobalt-free cathode material described in the present disclosure can relieve the limitation of the existing scarce metal cobalt source on the cathode material on the basis of ensuring that the cathode material has comprehensive performance such as excellent rate performance and cycle stability.
  • the negative electrode active material used in the lithium ion secondary battery is at least one selected from natural graphite, artificial graphite, soft carbon, hard carbon, lithium titanate, silicon, silicon-carbon alloy, and silicon-oxygen alloy. kind.
  • the negative electrode active material described in the present disclosure can cause lithium ion insertion and extraction reactions, and can further ensure the electrochemical performance and cycle performance of the lithium ion secondary battery.
  • a lithium ion secondary battery in one embodiment, includes a positive electrode sheet, a negative electrode sheet, a separator, the above-mentioned lithium ion secondary battery electrolyte and packaging, wherein the positive electrode
  • the sheet includes a positive electrode current collector and a positive electrode film containing a positive electrode active material arranged on the positive electrode current collector.
  • the negative electrode sheet includes a negative electrode current collector and a negative electrode film containing the negative electrode active material arranged on the negative electrode current collector.
  • the packaging can be aluminum plastic film, stainless steel cylinder, square aluminum shell, etc.
  • the lithium ion secondary battery described in the present disclosure has at least the following advantages: good cycle stability, high capacity retention rate after high-temperature storage, low gas production rate, low cell expansion rate, and excellent integration at both high and low temperatures performance.
  • An embodiment of the present disclosure provides an energy storage device.
  • the energy storage device includes the foregoing lithium ion secondary battery or the foregoing lithium ion secondary battery electrolyte.
  • the energy storage device described in the present disclosure has good cycle stability, low battery expansion rate after high-temperature storage, high safety and longer service life.
  • This embodiment provides a lithium ion secondary battery, and the specific preparation method includes:
  • the positive electrode active material lithium nickel manganate (LiNi 0.75 Mn 0.25 O 2 ), the conductive agent Super-P (superconducting carbon black), and the binder PVDF (polyvinylidene fluoride) are dissolved in the solvent at a mass ratio of 96:2.0:2.0 N-methylpyrrolidone was mixed uniformly to make a positive electrode slurry, and then the positive electrode slurry was uniformly coated on the current collector aluminum foil, the coating amount was 18mg/cm 2 , and then it was dried at 85 °C and then cold pressed and cut. The edges, pieces, and strips are then dried at 85°C for 4 hours under vacuum conditions, and the tabs are welded to form the positive electrode sheet of the lithium ion secondary battery that meets the requirements.
  • the negative active material artificial graphite, conductive agent Super-P (superconducting carbon black), thickener CMC (carboxymethyl cellulose), and binder SBR (styrene butadiene rubber) are in a mass ratio of 96.5:1.0:1.0:1.5 Dissolve in the solvent deionized water and mix uniformly to make the negative electrode slurry.
  • the negative electrode slurry is evenly coated on the copper foil of the current collector, the coating amount is 8.9mg/cm 2 , and then it is dried at 85 °C and then cold pressed , Trimming, cutting, and slitting, and then drying at 110°C for 4 hours under vacuum conditions, welding the tabs, and forming the negative electrode sheet of the lithium ion secondary battery that meets the requirements.
  • the electrolyte of the lithium ion secondary battery uses 1mol/L LiPF 6 as the lithium salt, and uses a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) as a non-aqueous organic solvent.
  • EC ethylene carbonate
  • EMC ethyl methyl carbonate
  • DEC diethyl carbonate
  • the volume ratio of EC:EMC:DEC is 30:50:20.
  • the electrolyte of the lithium ion secondary battery also contains an additive, and the additive is trimethylene borate, which accounts for 0.5% of the total mass of the electrolyte of the lithium ion secondary battery, that is, a compound in which n is 1 in the structural formula shown in Formula I.
  • the positive electrode sheet, the negative electrode sheet and the separator (PE film) of the lithium ion secondary battery prepared according to the foregoing process are made into a battery core with a thickness of 8mm, a width of 60mm, and a length of 130mm through a winding process, and the battery is at 75°C Vacuum bake for 10 hours, inject electrolyte, and stand for 24 hours, then charge to 4.2V with a constant current of 0.1C (160mA), then charge with a constant voltage of 4.2V until the current drops to 0.05C (80mA), and then charge at 0.1C ( 160mA) constant current discharge to 2.8V, repeat the charge and discharge twice, and finally charge to 3.8V with a constant current of 0.1C (160mA) to complete the preparation of the lithium ion secondary battery.
  • step (3) the additive in the electrolyte is trimethylene borate, which accounts for 1% of the total mass of the electrolyte of the lithium ion secondary battery.
  • step (3) the additives in the electrolyte are trimethylene borate, which accounts for 0.5% of the total mass of the electrolyte of the lithium ion secondary battery, and the total mass of the electrolyte of the lithium ion secondary battery. 0.5% vinylene carbonate (VC).
  • SL sulfolane
  • SL sulfolane
  • SL sulfolane
  • step (3) no additives and sulfone solvents are added to the electrolyte.
  • the test method is: at 60°C, first charge the lithium ion secondary battery with a constant current of 1C to 4.2V, then charge with a constant voltage of 4.2V to a current of 0.05C, and then charge the lithium ion secondary battery with a constant current of 1C.
  • the battery is discharged to 2.8V, which is a charge-discharge cycle.
  • the discharge capacity this time is the discharge capacity of the first cycle.
  • the lithium ion secondary battery was subjected to a cyclic charge and discharge test in the above manner, and the discharge capacity of the 500th cycle was taken.
  • the capacity retention rate (%) of the lithium ion secondary battery after 500 cycles [discharge capacity at the 500th cycle/discharge capacity at the first cycle] ⁇ 100%.
  • the test results are shown in Table 1.
  • the test method is: first charge the lithium-ion secondary battery with a constant current of 1C to 4.2V at 25°C, then charge the lithium-ion secondary battery with a constant voltage of 4.2V to a current of 0.05C, and then charge the lithium-ion secondary battery with a constant current of 1C.
  • the battery is discharged to 2.8V, the discharge capacity this time is the discharge capacity of the lithium ion secondary battery before high temperature storage; then the lithium ion secondary battery is charged to 4.2V with a constant current of 1C, and the lithium ion secondary battery is placed at 60 Store at °C for 30 days.
  • the lithium-ion secondary battery After the storage is over, place the lithium-ion secondary battery in an environment of 25°C, then discharge the lithium-ion secondary battery to 2.8V with a constant current of 0.5C, and then discharge the lithium-ion battery with a constant current of 1C. Charge the ion secondary battery to 4.2V, and further charge it at a constant voltage of 4.2V to a current of 1C, and then discharge the lithium ion secondary battery to 2.8V at a constant current of 1C. The last discharge capacity is the high temperature of the lithium ion secondary battery. Discharge capacity after storage.
  • Capacity retention rate (%) of lithium ion secondary battery after high temperature storage [discharge capacity of lithium ion secondary battery after high temperature storage/discharge capacity of lithium ion secondary battery before high temperature storage] ⁇ 100%.
  • the test results are shown in Table 1.
  • the test method is: first charge the lithium-ion secondary battery with a constant current of 1C to 4.2V at 25°C, then charge the lithium-ion secondary battery with a constant voltage of 4.2V to a current of 0.05C, and then charge the lithium-ion secondary battery with a constant current of 1C.
  • the battery is discharged to 2.8V, and the discharge capacity this time is the discharge capacity of the lithium ion secondary battery before high temperature storage; then the lithium ion secondary battery is charged to 4.2V with a constant current of 1C, and charged to a current of 4.2V with a constant voltage 0.05C, fully charge the lithium-ion battery.
  • Use the drainage method to test the volume of the cell, and use a micrometer to measure the thickness of the cell.
  • the lithium ion battery was stored at 60°C for 30 days. After the storage was completed, the lithium ion secondary battery was placed in an environment of 25°C, the volume of the battery cell was measured by the drainage method, and the thickness of the battery cell was measured with a micrometer. Then discharge the lithium-ion secondary battery with a constant current of 0.5C to 2.8V, then charge the lithium-ion secondary battery with a constant current of 1C to 4.2V, and further charge with a constant voltage of 4.2V until the current is 1C, and then with 1C Discharge the lithium-ion secondary battery to 2.8V with a constant current of, and the last discharge capacity is the discharge capacity of the lithium-ion secondary battery after high-temperature storage.
  • the lithium ion secondary battery having the electrolyte composition of the above-mentioned embodiments of the present disclosure has good cycle stability and high-temperature storage stability at room temperature and high temperature.

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Abstract

本公开提供一种了锂离子二次电池的电解液及其应用。所述锂离子二次电池的电解液包括有机溶剂、锂盐和添加剂，所述添加剂包括硼酸酯化合物。所述电解液可以更好地适用于低钴或无钴正极材料，提高锂离子电池的高温循环和存储性能，抑制高温存储时的产气，从而提高电池的综合性能。

Description

一种锂离子二次电池的电解液及其应用 技术领域
本公开涉及电池领域，例如涉及一种锂离子二次电池的电解液及其应用。
背景技术
近年来，应用于汽车上的锂离子电池产业蓬勃发展，为了满足电动汽车长时间工作、高续航里程、可在高温及低温环境正常使用、可快速充电以及具有较长使用寿命的要求，需要开发具有更高能量密度、更优异的高温循环、存储性能及低温倍率性能的锂离子二次电池。而电解液的电化学稳定性对锂离子二次电池的高温循环、储存、低温充放电性能有着显著的影响，因此，改善电解液的组成，使正负极上能够形成高温稳定和循环稳定的SEI膜，对提高电芯在高温和低温下的综合性能具有十分重要的意义。
发明内容
现有技术中，锂离子动力电池所用正极多为高镍含量的三元正极材料(LiNi xCo yMn ZO 2，LiNi XCo 1-XO 2)，而近年来由于全球钴金属资源的稀缺性，无钴正极材料(LiNi XMn 1-XO 2)成为研究的热点。然而，由于不含有钴金属，这种正极材料在高温下结构不稳定，表面容易发生不可逆相变、释氧，生成不导电的NiOx化合物；并且，在循环过程中，Ni、Mn金属离子容易发生溶出，在负极表面还原，提高阻抗；此外，正极中高价态的Ni 4+容易与电解液发生催化氧化反应，导致产气，降低循环寿命。
本公开提供了一种锂离子二次电池的电解液及其应用，可以提高锂离子电池的高温循环和存储性能，抑制高温存储时的产气，提高电池的综合性能。
本公开在一实施例中提供一种锂离子二次电池的电解液，所述的电解液包括：有机溶剂、锂盐和添加剂，所述添加剂中包括如式I所示结构式的硼酸酯化合物，n的取值范围为0、1、2、3、4，
Figure PCTCN2020124715-appb-000001
在一实施例中，所述硼酸酯化合物的添加量为所述电解液总质量的0.01～5wt％，例如：0.01wt％、0.1wt％、0.5wt％、1wt％、2wt％、3wt％、4wt％ 或5wt％等。
在一实施例中，式I所示结构式中的碳原子上含有卤素取代基。
在一实施例中，所述硼酸酯化合物包括
Figure PCTCN2020124715-appb-000002
即硼酸三亚甲酯。
在一实施例中，所述添加剂包括碳酸亚乙烯酯，所述的碳酸亚乙烯酯的添加量可以为电解液总质量的0.1～3wt％，例如：0.1wt％、0.5wt％、1wt％、1.4wt％、1.8wt％、2.2wt％、2.6wt％或3wt％等。
在一实施例中，所述有机溶剂包括如式II所示结构式的砜类化合物，n的取值范围为0、1、2、3、4，
Figure PCTCN2020124715-appb-000003
在一实施例中，所述砜类化合物的添加量为所述有机溶剂总质量的1～20wt％，例如：1wt％、3wt％、5wt％、10wt％、12wt％、14wt％、16wt％、18wt％或20wt％等。
在一实施例中，所述砜类化合物包括：
Figure PCTCN2020124715-appb-000004
中的至少之一。
在一实施例中，所述有机溶剂包括环状碳酸酯和/或链状碳酸酯，所述环状碳酸酯为选自碳酸乙烯酯、碳酸丙烯酯和γ-丁内酯中的至少一种；所述链状碳酸酯为选自碳酸二甲酯、碳酸丁烯酯、二乙基碳酸酯、二丙基碳酸酯、碳酸甲乙酯、碳酸甲丙酯、碳酸乙丙酯、甲酸甲酯、甲酸乙酯、甲酸丙酯、乙酸甲酯、乙酸乙酯、乙酸丙酯、丙酸甲酯、丙酸乙酯和丙酸丙酯中的至少一种。
在一实施例中，所述锂盐为选自LiPF 6、LiBF 4、LiBOB、LiDFOB、LiAsF 6、Li(CF 3SO 2) 2N、Li(FSO 2) 2N、LiPO 2F 2、LiCF 3SO 3和LiClO 4中至少一种。
本公开在一实施例中提供一种具有上述锂离子二次电池电解液的锂离子二次电池。
在一实施例中，所述锂离子二次电池采用的正极活性材料为选自LiCoO 2、LiMn 2O 4、LiMnO 2、Li 2MnO 4、LiFePO 4、LiNi xMn 1-xO 2、LiNi xCo yMn zO 2、Li 1+aMn 1-xM xO 2、LiCo 1-xM xO 2、LiFe 1-xM xPO 4、LiMn 2-yM yO 4和Li 2Mn 1-xO 4中的至少一种，其中，M为选自Ni、Co、Mn、Al、Cr、Mg、Zr、Mo、V、Ti、B、F和Y中的至少一种，a的取值范围为0～0.2，x的取值范围为0～1，y的取值范围为0～1，z的取值范围为0～1。
在一实施例中，所述锂离子二次电池采用的正极活性材料为低钴或无钴正极材料。
本公开所述的无钴正极材料可以在确保正极材料具有优异的倍率性能、循环稳定性等综合性能的基础上解除现有稀缺金属钴来源对正极材料的限制。
在一实施例中，所述锂离子二次电池采用的负极活性材料为选自天然石墨、人造石墨、软碳、硬碳、钛酸锂、硅、硅碳合金和硅氧合金中的至少一种。
本公开所述的负极活性材料能够发生锂离子嵌入脱出反应，可以进一步确保锂离子二次电池的电化学性能及循环性能等。
本公开在一实施例中提供了一种锂离子二次电池，所述的锂离子二次电池包括正极片、负极片、隔膜、上述锂离子二次电池电解液以及包装，其中所述的正极片包括正极集流体以及设置于正极集流体上的含有正极活性材料的正极膜片，所述的负极片包括负极集流体以及设置于负极集流体上的含有负极活性材料的负极膜片，隔膜设在正极片和负极片之间，包装可以是铝塑膜、不锈钢圆柱、方形铝壳等。
本公开在一实施例中提供一种储能设备，所述的储能设备包括上述锂离子二次电池或上述锂离子二次电池电解液。
具体实施方式
本公开在一实施例中提供一种锂离子二次电池的电解液，所述的电解液包括：有机溶剂、锂盐和添加剂，所述添加剂中包括如式I所示结构式的硼酸酯化合物，n的取值范围为0、1、2、3、4，
Figure PCTCN2020124715-appb-000005
本公开所述的电解液可以更好地适用于低钴或无钴正极材料，因为，无钴材料中不含有钴金属，在高温下结构不稳定，表面容易发生不可逆相变、释氧，生成不导电的NiOx化合物；并且，在循环过程中，Ni、Mn金属离子容易发生溶出，在负极表面还原，提高阻抗；此外，正极中高价态的Ni 4+容易与电解液发生催化氧化反应，导致产气，降低循环寿命。
本公开所述的电解液在充放电过程中能够形成稳定的SEI膜，可以有效地抑制电解液在电极材料表面的反应，抑制正极材料金属的溶出，提高锂离子电池的高温循环和存储性能，抑制高温存储时的产气，从而提高电池的综合性能。
在一实施例中，所述硼酸酯化合物的添加量为所述电解液总质量的0.01～5wt％，例如：0.01wt％、0.1wt％、0.5wt％、1wt％、2wt％、3wt％、4wt％或5wt％等。硼酸酯化合物的添加量过少，不仅对降低正极金属催化反应活性的效果不明显，而且不利于在正极材料表面形成稳定的SEI膜，不能有效解决正极材料在高温下结构不稳定，易出现金属溶出和产气的问题；而若硼酸酯化合物的添加量过多，不仅会导致电解液粘度过大，影响电池的电化学性能，同时还会降低电解液在低温下的电导率，导致电池低温性能下降。本公开中通过控制硼酸酯化合物为上述添加量，可以在不降低电化学性能的前提下有效抑制电解液在电极材料表面的反应，抑制正极材料金属的溶出，提高锂离子电池的高温循环、存储性能，并抑制高温存储时的产气，从而能够显著提高电池的综合性能。
在一实施例中，式I所示结构式中的碳原子上含有卤素取代基。
在一实施例中，所述硼酸酯化合物包括
Figure PCTCN2020124715-appb-000006
即硼酸三亚甲酯。
本公开所述的硼酸三亚甲酯的分子量较低，将其用作电解液的添加剂不仅能够与富电子的正极金属元素Ni、Mn发生络合反应，降低正极金属的催化反应活性，并在正极材料表面氧化反应形成稳定的SEI膜，还可以降低硼酸酯化合物对电解液粘度的负面影响，从而能够进一步提高锂离子二次电池的电化学性能和循环性能，降低电池在高温下的产气率，使锂电池在高温和低温下均具有较好的综合性能。
在一实施例中，所述添加剂包括碳酸亚乙烯酯，所述的碳酸亚乙烯酯的添 加量可以为电解液总质量的0.1～3wt％，例如：0.1wt％、0.5wt％、1wt％、1.4wt％、1.8wt％、2.2wt％、2.6wt％或3wt％等。
本公开所述的将碳酸亚乙烯酯与硼酸酯化合物组合用于电解液中，并控制碳酸乙烯酯为上述添加量，可以更好地改善锂离子二次电池的高低温性能及产气问题，电池的循环性能及高温下存储性能得到更明显地提高。
在一实施例中，所述碳酸亚乙烯酯的添加量可以为电解液总质量的0.5～1wt％，由此可以进一步改善锂离子二次电池的高低温性能及产气问题，提高其在常温及高温下的综合性能。
在一实施例中，所述有机溶剂包括如式II所示结构式的砜类化合物，n的取值范围为0、1、2、3、4，
Figure PCTCN2020124715-appb-000007
本公开式II所示的环状砜类溶剂相比碳酸酯溶剂具有更高的耐氧化性，不容易被正极表面高价态金属Ni 4+氧化，从而能够显著提高电解液的耐氧化性，有效改善电池的高温性能并降低产气，特别是将该砜类化合物和硼酸酯化合物和/或碳酸亚乙烯酯共同使用后还可以具有协同增效的作用。
在一实施例中，所述砜类化合物的添加量为所述有机溶剂总质量的1～20wt％，例如：1wt％、3wt％、5wt％、10wt％、12wt％、14wt％、16wt％、18wt％或20wt％等。
本公开所述的砜类化合物的添加量过少，不能显著改善电解液的耐氧化性，而若砜类化合物的添加量过多，砜类化合物在电解液中无法完全溶解，会导致砜类化合物与电解液相互分层。本公开中通过控制砜类化合物为上述添加量，不仅可以显著改善电解液的耐氧化性，有效改善电池的高温性能并降低产气，还能提高电解液的介电常数，改善电解液的离子电导率。
在一实施例中，所述砜类化合物包括：
Figure PCTCN2020124715-appb-000008
中的至少之一。
本公开所述的环丁砜和环戊砜比其它环砜类具有较小的分子量和较低的粘 度，将其作为溶剂用于电解液中可以进一步确保电解液具有较低的粘度和较高的电导率，又可以在提高电解液的耐氧化性的前提下进一步改善电池的电化学性能、高温性能以及其在高温下的产气问题。
在一实施例中，所述有机溶剂包括环状碳酸酯和/或链状碳酸酯，所述环状碳酸酯为选自碳酸乙烯酯、碳酸丙烯酯和γ-丁内酯中的至少一种；所述链状碳酸酯为选自碳酸二甲酯、碳酸丁烯酯、二乙基碳酸酯、二丙基碳酸酯、碳酸甲乙酯、碳酸甲丙酯、碳酸乙丙酯、甲酸甲酯、甲酸乙酯、甲酸丙酯、乙酸甲酯、乙酸乙酯、乙酸丙酯、丙酸甲酯、丙酸乙酯和丙酸丙酯中的至少一种。
在一实施例中，所述锂盐为选自LiPF 6、LiBF 4、LiBOB、LiDFOB、LiAsF 6、Li(CF 3SO 2) 2N、Li(FSO 2) 2N、LiPO 2F 2、LiCF 3SO 3和LiClO 4中至少一种。
本公开所述的锂离子二次电池电解液至少具有以下优势：采用的硼酸酯化合物含有硼原子，是一种缺电子结构的路易斯酸，一方面能够与富电子的正极金属元素Ni、Mn发生络合反应，降低正极金属的催化反应活性；另一方面在充放电过程中能够在正极材料表面氧化反应形成稳定的SEI膜，有效地抑制电解液在电极材料表面的反应，抑制正极材料金属的溶出，提高锂离子电池的高温循环和存储性能，抑制高温存储时的产气，从而提高电池的综合性能。与现有电解液相比，该电解液可以适用于低钴或无钴正极材料，具有本公开上述电解液的锂离子二次电池的循环稳定性更好，高温存储后的容量保持率更高且产气率更低，在高温和低温下的综合性能更佳。
本公开在一实施例中提供一种具有上述锂离子二次电池电解液的锂离子二次电池。
在一实施例中，所述锂离子二次电池采用的正极活性材料为选自LiCoO 2、LiMn 2O 4、LiMnO 2、Li 2MnO 4、LiFePO 4、LiNi xMn 1-xO 2、LiNi xCo yMn zO 2、Li 1+aMn 1-xM xO 2、LiCo 1-xM xO 2、LiFe 1-xM xPO 4、LiMn 2-yM yO 4和Li 2Mn 1-xO 4中的至少一种，其中，M为选自Ni、Co、Mn、Al、Cr、Mg、Zr、Mo、V、Ti、B、F和Y中的至少一种，a的取值范围为0～0.2，x的取值范围为0～1，y的取值范围为0～1，z的取值范围为0～1。
在一实施例中，所述锂离子二次电池采用的正极活性材料为低钴或无钴正极材料。
本公开所述的无钴正极材料可以在确保正极材料具有优异的倍率性能、循 环稳定性等综合性能的基础上解除现有稀缺金属钴来源对正极材料的限制。
在一实施例中，所述锂离子二次电池采用的负极活性材料为选自天然石墨、人造石墨、软碳、硬碳、钛酸锂、硅、硅碳合金和硅氧合金中的至少一种。
本公开所述的负极活性材料能够发生锂离子嵌入脱出反应，可以进一步确保锂离子二次电池的电化学性能及循环性能等。
本公开在一实施例中提供了一种锂离子二次电池，所述的锂离子二次电池包括正极片、负极片、隔膜、上述锂离子二次电池电解液以及包装，其中所述的正极片包括正极集流体以及设置于正极集流体上的含有正极活性材料的正极膜片，所述的负极片包括负极集流体以及设置于负极集流体上的含有负极活性材料的负极膜片，隔膜设在正极片和负极片之间，包装可以是铝塑膜、不锈钢圆柱、方形铝壳等。
本公开所述的锂离子二次电池至少具有以下优势：循环稳定性好，高温存储后的容量保持率高且产气率低，电芯膨胀率低，在高温和低温下均具有优异的综合性能。
本公开在一实施例中提供一种储能设备，所述的储能设备包括上述锂离子二次电池或上述锂离子二次电池电解液。
与相关技术相比，本公开所述的储能设备循环稳定性好、高温存储后电池膨胀率低，安全性高且使用寿命更长。
实施例1
本实施例提供一种锂离子二次电池，具体制备方法包括：
(1)锂离子二次电池的正极片的制备
将正极活性材料镍锰酸锂(LiNi 0.75Mn 0.25O 2)、导电剂Super-P(超导炭黑)、粘结剂PVDF(聚偏氟乙烯)按质量比96:2.0:2.0溶于溶剂N-甲基吡咯烷酮中混合均匀制成正极浆料，之后将正极浆料均匀涂布在集流体铝箔上，涂布量为18mg/cm 2，随后在85℃下烘干后进行冷压、切边、裁片、分条，之后在85℃真空条件下干燥4h，焊接极耳，制成满足要求的锂离子二次电池的正极片。
(2)锂离子二次电池的负极片的制备
将负极活性材料人造石墨、导电剂Super-P(超导炭黑)、增稠剂CMC(羧甲基纤维素)、粘结剂SBR(丁苯橡胶)按质量比96.5:1.0:1.0:1.5溶于溶剂去 离子水中混合均匀制成负极浆料，之后将负极浆料均匀涂布在集流体铜箔上，涂布量为8.9mg/cm 2，随后在85℃下烘干后进行冷压、切边、裁片、分条，之后在110℃真空条件下干燥4h，焊接极耳，制成满足要求的锂离子二次电池的负极片。
(3)锂离子二次电池的电解液的制备
锂离子二次电池的电解液以1mol/L的LiPF 6为锂盐，以碳酸乙烯酯(EC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)的混合物为非水有机溶剂，其中EC:EMC:DEC的体积比为30:50:20。此外，锂离子二次电池的电解液中还含有添加剂，添加剂为占锂离子二次电池电解液总质量0.5％的硼酸三亚甲酯，即式I所示结构式中n为1的化合物。
(4)锂离子二次电池的制备
将根据前述工艺制备的锂离子二次电池的正极片、负极片以及隔离膜(PE膜)经过卷绕工艺制作成厚度为8mm、宽度为60mm、长度为130mm的电芯，并在75℃下真空烘烤10h、注入电解液、静置24h，之后用0.1C(160mA)的恒定电流充电至4.2V，然后以4.2V恒压充电至电流下降到0.05C(80mA)，然后以0.1C(160mA)的恒定电流放电至2.8V，重复2次充放电，最后以0.1C(160mA)的恒定电流充电至3.8V，完成锂离子二次电池的制备。
实施例2
与实施例1的区别在于：步骤(3)中，电解液中添加剂为占锂离子二次电池电解液总质量1％的硼酸三亚甲酯。
实施例3
本实施例与实施例1的区别在于：步骤(3)中，电解液中添加剂为占锂离子二次电池电解液总质量0.5％的硼酸三亚甲酯和占锂离子二次电池电解液总质量0.5％的碳酸亚乙烯酯(VC)。
实施例4
本实施例与实施例1的区别在于：步骤(3)中，电解液中有机溶剂还包括环丁砜(SL)，环丁砜占有机溶剂总质量的5％，有机溶剂的组成及体积比为EC:EMC:DEC:SL＝30:50:15:5。
实施例5
与实施例1的区别在于：步骤(3)中，电解液中有机溶剂还包括环丁砜(SL)，环丁砜占有机溶剂总质量的10％，有机溶剂的组成及体积比为EC:EMC:DEC:SL＝30:50:10:10。
实施例6
本实施例与实施例1的区别在于：步骤(3)中，电解液中有机溶剂还包括环丁砜(SL)，环丁砜占有机溶剂总质量的10％，有机溶剂的组成及体积比为EC:EMC:DEC:SL＝30:50:10:10；电解液中添加剂为占锂离子二次电池电解液总质量0.5％的硼酸三亚甲酯和占锂离子二次电池电解液总质量0.5％的碳酸亚乙烯酯(VC)。
对比例1
本实施例与实施例1的区别在于：步骤(3)中，电解液中不添加任何添加剂与砜类溶剂。
对实施例1～6及对比例1制备得到的锂离子二次电池及配制的电解液进行评价：
1、测试锂离子二次电池的高温循环性能
测试方法为：在60℃下，先以1C的恒定电流对锂离子二次电池充电至4.2V，再以4.2V恒定电压充电至电流为0.05C，然后以1C的恒定电流对锂离子二次电池放电至2.8V，此为一个充放电循环过程，此次的放电容量为第一次循环的放电容量。将锂离子二次电池按上述方式进行循环充放电测试，取第500次循环的放电容量。
锂离子二次电池500次循环后的容量保持率(％)＝[第500次循环的放电容量/第一次循环的放电容量]×100％。测试结果如表1所示。
2、测试锂离子二次电池的高温存储性能
测试方法为：在25℃下，先以1C的恒定电流对锂离子二次电池充电至4.2V，进一步以4.2V恒定电压充电至电流为0.05C，然后以1C的恒定电流对锂离子二次电池放电至2.8V，此次的放电容量为锂离子二次电池高温存储前的放电容量；然后以1C的恒定电流对锂离子二次电池充电至4.2V，将锂离子二次电池置于60℃下存储30天，待存储结束后，将锂离子二次电池置于25℃环境下，然后以0.5C的恒定电流对锂离子二次电池放电至2.8V，之后以1C的恒定电流对锂离子二次电池充电至4.2V，进一步以4.2V恒定电压充电至电流为1C，然后以1C 的恒定电流对锂离子二次电池放电至2.8V，最后一次的放电容量为锂离子二次电池高温存储后的放电容量。
锂离子二次电池高温存储后的容量保持率(％)＝[锂离子二次电池高温存储后的放电容量/锂离子二次电池高温存储前的放电容量]×100％。测试结果如表1所示。
3、测试锂离子二次电池的高温存储产气性能
测试方法为：在25℃下，先以1C的恒定电流对锂离子二次电池充电至4.2V，进一步以4.2V恒定电压充电至电流为0.05C，然后以1C的恒定电流对锂离子二次电池放电至2.8V，此次的放电容量为锂离子二次电池高温存储前的放电容量；然后以1C的恒定电流对锂离子二次电池充电至4.2V，以4.2V恒定电压充电至电流为0.05C，将锂离子电池充满电。采用排水法测试电芯的体积，用千分尺测量电芯的厚度。
之后将锂离子电池置于60℃下存储30天，待存储结束后，将锂离子二次电池置于25℃环境下，采用排水法测试电芯的体积，用千分尺测量电芯的厚度。然后以0.5C的恒定电流对锂离子二次电池放电至2.8V，之后以1C的恒定电流对锂离子二次电池充电至4.2V，进一步以4.2V恒定电压充电至电流为1C，然后以1C的恒定电流对锂离子二次电池放电至2.8V，最后一次的放电容量为锂离子二次电池高温存储后的放电容量。
电芯体积膨胀率＝(存储后的体积/存储前的体积-1)×100％。测试结果如表1所示。
表1
Figure PCTCN2020124715-appb-000009
Figure PCTCN2020124715-appb-000010
由表1可知，由实施例1～2和对比例1的比较中可以看出，与不添加任何添加剂的电池相比，随着硼酸三亚甲酯的加入，锂离子二次电池在60℃存储30天后的容量保持率增加，60℃循环后的容量保持率也有提高，且高温存储产气后降低，说明该硼酸酯化合物可在高温下抑制电解液与正极材料的副反应，提高电池在高温循环存储后的容量保持率。
由实施例3中可以看出，当添加剂硼酸三亚甲酯与添加剂VC(碳酸亚乙烯酯)组合后，电池的循环性能和存储性能的改善更为明显。
由实施例4～6中可以看出，当溶剂中添加砜类溶剂环丁砜后(SL)，电池的循环寿命改善，产气降低，说明环丁砜提高了电解液的耐氧化性，降低了正极界面的副反应。
由实施例1～6中可以看出，当电解液中同时添加硼酸三亚甲酯、碳酸亚乙烯酯和环丁砜后，对电池的循环寿命、高温存储容量保持率及产气的改善具有协同作用。
综上所述，说明具有本公开上述实施例电解液组成的锂离子二次电池在常温高温下均具有较好的循环稳定性和高温存储稳定性。

Claims (15)

  1. 一种锂离子二次电池的电解液，所述锂离子二次电池的电解液包括有机溶剂、锂盐和添加剂，所述添加剂中包括如式I所示结构式的硼酸酯化合物，n的取值范围为0、1、2、3、4，
    Figure PCTCN2020124715-appb-100001
  2. 根据权利要求1所述的电解液，其中，所述硼酸酯化合物的添加量为所述电解液总质量的0.01～5wt％。
  3. 根据权利要求1或2所述的电解液，其中，式I所示结构式中的碳原子上含有卤素取代基。
  4. 根据权利要求1-3任一项所述的电解液，其中，硼酸酯化合物包括
    Figure PCTCN2020124715-appb-100002
  5. 根据权利要求1-4所述的电解液，其中，所述添加剂包括碳酸亚乙烯酯。
  6. 根据权利要求1-5任一项所述的电解液，其中，所述有机溶剂包括如式II所示结构式的砜类化合物，n的取值范围为0、1、2、3、4，
    Figure PCTCN2020124715-appb-100003
  7. 根据权利要求1-6任一项所述的电解液，其中，所述砜类化合物的添加量为所述有机溶剂总质量的1～20wt％。
  8. 根据权利要求1-7所述的电解液，其中，所述砜类化合物包括：
    Figure PCTCN2020124715-appb-100004
    和/或
    Figure PCTCN2020124715-appb-100005
  9. 根据权利要求1-8任一项所述的电解液，其中，所述有机溶剂包括环状碳酸酯和/或链状碳酸酯，所述环状碳酸酯为选自碳酸乙烯酯、碳酸丙烯酯和γ-丁内酯中的至少一种；所述链状碳酸酯为选自碳酸二甲酯、碳酸丁烯酯、二乙基碳酸酯、二丙基碳酸酯、碳酸甲乙酯、碳酸甲丙酯、碳酸乙丙酯、甲酸甲酯、甲酸乙酯、甲酸丙酯、乙酸甲酯、乙酸乙酯、乙酸丙酯、丙酸甲酯、丙酸乙酯和丙酸丙酯中的至少一种。
  10. 根据权利要求1-9任一项所述的电解液，其中，所述锂盐为选自LiPF 6、LiBF 4、LiBOB、LiDFOB、LiAsF 6、Li(CF 3SO 2) 2N、Li(FSO 2) 2N、LiPO 2F 2、LiCF 3SO 3和LiClO 4中的至少一种。
  11. 一种锂离子二次电池，所述锂离子二次电池包含如权利要求1-10任意一项所述的电解液。
  12. 根据权利要求11所述的锂离子二次电池，其中，采用的正极活性材料为选自LiCoO 2、LiMn 2O 4、LiMnO 2、Li 2MnO 4、LiFePO 4、LiNi xMn 1-xO 2、LiNi xCo yMn zO 2、Li 1+aMn 1-xM xO 2、LiCo 1-xM xO 2、LiFe 1-xM xPO 4、LiMn 2-yM yO 4和Li 2Mn 1-xO 4中的至少一种，其中，M为选自Ni、Co、Mn、Al、Cr、Mg、Zr、Mo、V、Ti、B、F和Y中的至少一种，a是取值范围为0～0.2，x的取值范围为0～1，y的取值范围为0～1，z的取值范围为0～1。
  13. 根据权利要求11或12所述的锂离子二次电池，其中，采用的正极活 性材料为低钴或无钴正极材料。
  14. 如权利要求11-13任一项所述的锂离子二次电池，其中，采用的负极活性材料为选自天然石墨、人造石墨、软碳、硬碳、钛酸锂、硅、硅碳合金和硅氧合金中的至少一种。
  15. 一种储能设备，所述储能设备包含如权利要求11-14任意一项所述的锂离子二次电池。
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