WO2022117086A1 - 一种适用于硅碳体系锂离子电池的电解液 - Google Patents

一种适用于硅碳体系锂离子电池的电解液 Download PDF

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WO2022117086A1
WO2022117086A1 PCT/CN2021/135477 CN2021135477W WO2022117086A1 WO 2022117086 A1 WO2022117086 A1 WO 2022117086A1 CN 2021135477 W CN2021135477 W CN 2021135477W WO 2022117086 A1 WO2022117086 A1 WO 2022117086A1
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lithium
electrolyte
ion battery
lithium ion
carbonate
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PCT/CN2021/135477
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English (en)
French (fr)
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母英迪
王龙
王海
李素丽
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珠海冠宇电池股份有限公司
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Priority to EP21900110.4A priority Critical patent/EP4160771A1/en
Publication of WO2022117086A1 publication Critical patent/WO2022117086A1/zh
Priority to US18/146,032 priority patent/US20230131127A1/en

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    • H—ELECTRICITY
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    • 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
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
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    • 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
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    • 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
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    • 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
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    • 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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
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    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/134—Electrodes based on metals, Si or alloys
    • 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
    • H01M4/362—Composites
    • H01M4/364—Composites as mixtures
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    • 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
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    • 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
    • H01M4/483—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides for non-aqueous cells
    • 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
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    • 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
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
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    • 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
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    • 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
    • H01M2300/0025—Organic electrolyte
    • H01M2300/0028—Organic electrolyte characterised by the solvent
    • H01M2300/0034—Fluorinated solvents
    • 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 invention belongs to the technical field of lithium ion batteries, and particularly relates to an electrolyte suitable for a silicon carbon system lithium ion battery.
  • lithium-ion batteries Since its commercialization, lithium-ion batteries have been widely used in digital, energy storage, power, military aerospace and communication equipment due to its high specific energy and good cycle performance. With the wide application of lithium-ion batteries, consumers have continuously improved the use environment and demand for lithium-ion batteries, and at the same time have higher and higher requirements for the endurance of electronic equipment, which requires lithium-ion batteries to have both high and low temperature performance. Has a high energy density.
  • Silicon carbon battery is one of the effective means to improve the energy density of battery
  • the electrolyte is one of the main materials of silicon carbon lithium ion battery, which plays the role of transporting Li + in silicon carbon lithium ion battery. Therefore, the research and development of electrolyte is very important for silicon-carbon lithium-ion batteries. However, it is not easy to develop an electrolyte that can alleviate the large cyclic expansion of silicon anode and take into account high and low temperature performance. At this stage, the use of additives in the electrolyte is an efficient weapon to solve the above problems.
  • the invention provides an electrolyte suitable for a silicon-carbon system lithium-ion battery, and the silicon-carbon lithium-ion battery using the electrolyte can effectively alleviate the problems of large battery cycle expansion, low battery cycle life, and difficulty in taking into account the high and low temperature performance of the battery.
  • the high and low temperature performance and cycle life of the silicon-carbon system lithium-ion battery can be significantly improved, and the safety performance of the silicon-carbon system lithium-ion battery can be significantly improved, which is suitable for large-scale commercial production.
  • the present invention provides the following technical solutions:
  • An electrolyte suitable for silicon-carbon system lithium ion batteries wherein the electrolyte includes an organic solvent, an additive and a lithium salt, and the additive includes trifluoromethyltriethyl lithium borate, propenyl-1,3- Sultone and Fluoroethylene Carbonate.
  • the usage amount of the lithium trifluoromethyl triethylborate accounts for 0.1-2 wt % of the total mass of the electrolyte, preferably 0.2-1.0 wt %, more preferably 0.2-0.5 wt %, for example, 0.1 wt % , 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.8wt%, 0.9wt%, 1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.7wt% %, 1.8 wt %, 1.9 wt % or 2.0 wt %.
  • the lithium trifluoromethyltriethylborate can be prepared by methods known in the art, or can be purchased through commercial channels.
  • the amount of the propenyl-1,3-sultone used accounts for 0.2-3.5wt% of the total mass of the electrolyte, preferably 0.5-2wt%, such as 0.2wt%, 0.3wt%, 0.4wt% %, 0.5wt%, 0.8wt%, 0.9wt%, 1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.7wt%, 1.8wt%, 1.9wt%, 2.0 wt%, 3.0 wt% or 3.5 wt%.
  • the English name of the propenyl-1,3-sultone is prop-1-ene-1,3-sultone, and its CAS number is 21806-61-1, which can be obtained by It can be prepared by known methods, and can also be purchased through commercial channels.
  • the amount of the fluoroethylene carbonate used accounts for 8-20wt% of the total mass of the electrolyte, such as 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt% or 20wt%.
  • the English name of the fluoroethylene carbonate is fluoroethylene carbonate, and its CAS number is 114435-02-8, which can be prepared by methods known in the art or purchased through commercial channels.
  • the additive further includes at least one of succinonitrile, adiponitrile, glycerol trinitrile, 1,3,6-hexanetrinitrile and 1,2-bis(cyanoethoxy)ethane, Its usage amount accounts for 0-10 wt % of the total mass of the electrolyte; an exemplary amount may be 1-5 wt %.
  • the organic solvent is selected from at least one of carbonate, carboxylate and fluoroether, wherein the carbonate is selected from ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate One or more combinations in ester, diethyl carbonate, methyl propyl carbonate; Described carboxylate is selected from one or more combinations in ethyl propionate, propyl propionate; Described fluorine
  • the substituted ether is selected from 1,1,2,3-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.
  • the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium bisfluorosulfonimide or lithium bis(trifluoromethylsulfonyl)imide.
  • the usage amount of the lithium salt accounts for 10-20wt% of the total mass of the electrolyte, such as 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt% or 20wt%.
  • the present invention also provides a method for preparing an electrolyte, the method comprising the steps of:
  • An organic solvent, an additive, and a lithium salt are mixed, wherein the additive includes lithium trifluoromethyltriethylborate, propenyl-1,3-sultone, and fluoroethylene carbonate.
  • the method includes the following steps:
  • the present invention also provides a lithium ion battery, the lithium ion battery comprising the above-mentioned electrolyte.
  • the lithium ion battery is a silicon carbon system lithium ion battery.
  • the lithium ion battery further includes a positive electrode sheet, a negative electrode sheet and a separator.
  • the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated on one side or both sides of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material is selected from the group consisting of: A silicon carbon anode material composed of nano-silicon and/or SiO x (0.8 ⁇ x ⁇ 1.3) and graphite.
  • the nano-silicon and/or SiO x accounts for 1-55wt% of the total mass of the silicon carbon anode material, such as 1wt%, 2wt%, 5wt%, 8wt%, 10wt%, 12wt%, 15wt%, 18wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt%.
  • the negative electrode active material layer further includes a binder, a conductive agent and a dispersant.
  • the mass percentage content of each component in the negative electrode active material layer is: negative electrode active material 70-99.7 wt %, binder 0.1-10 wt %, dispersant 0.1-10 wt %, conductive agent 0.1-10 wt % .
  • the mass percentage of each component in the negative electrode active material layer is: negative electrode active material 76-98.5 wt %, binder 0.5-8 wt %, dispersant 0.5-8 wt %, conductive agent 0.5-8 wt % .
  • the mass percentage of each component in the negative electrode active material layer is: negative electrode active material 85-98.5 wt %, binder 0.5-5 wt %, dispersant 0.5-5 wt %, conductive agent 0.5-5 wt % %.
  • the binder is selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyethyleneimine (PEI), polyaniline (PAN), polyacrylic acid (PAA), sodium alginate, At least one of high molecular polymers such as styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), phenolic resin or epoxy resin.
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • PEI polyethyleneimine
  • PAN polyaniline
  • PAA polyacrylic acid
  • SBR styrene-butadiene rubber
  • CMC carboxymethyl cellulose
  • epoxy resin epoxy resin
  • the dispersing agent is selected from polypropylene (PVA), cetyl ammonium bromide, sodium dodecyl benzene sulfonate, silane coupling agent, ethanol, N-methylpyrrolidone (NMP), N, At least one of N-dimethylformamide (DMF) and the like, more preferably at least one of cetylammonium bromide, sodium dodecylbenzenesulfonate, silane coupling agent, and ethanol.
  • PVA polypropylene
  • NMP N-methylpyrrolidone
  • DMF N-dimethylformamide
  • the conductive agent is selected from carbon nanotubes (CNTs), carbon fibers (VGCF), conductive graphite (KS-6, SFG-6), mesocarbon microspheres (MCMB), graphene, Ketjen black, Super At least one of P, acetylene black, conductive carbon black or hard carbon.
  • the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer coated on one side or both sides of the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material is selected One or more of LiCoO 2 , LiNiO 2 , LiMn 2 O 4 , LiFePO 4 , Li x Ni y M 1-y O 2 , wherein 0.9 ⁇ x ⁇ 1.2, 0.5 ⁇ y ⁇ 1, and M is selected from One or more of Co, Mn, Al, Mg, Ti, Zr, Fe, Cr, Mo, Cu, and Ca.
  • the positive electrode active material layer further includes a binder and a conductive agent.
  • the mass percentage content of each component in the positive electrode active material layer is: positive electrode active material 80-99.8 wt %, binder 0.1-10 wt %, and conductive agent 0.1-10 wt %.
  • the mass percentage content of each component in the positive electrode active material layer is: positive electrode active material 84-99 wt %, binder 0.5-8 wt %, and conductive agent 0.5-8 wt %.
  • the mass percentage of each component in the positive electrode active material layer is: positive electrode active material 90-99 wt %, binder 0.5-5 wt %, and conductive agent 0.5-5 wt %.
  • the binder is selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyethyleneimine (PEI), polyaniline (PAN), polyacrylic acid (PAA), sodium alginate, At least one of high molecular polymers such as styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), phenolic resin or epoxy resin.
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • PEI polyethyleneimine
  • PAN polyaniline
  • PAA polyacrylic acid
  • SBR styrene-butadiene rubber
  • CMC carboxymethyl cellulose
  • epoxy resin epoxy resin
  • the conductive agent is selected from carbon nanotubes (CNTs), carbon fibers (VGCF), conductive graphite (KS-6, SFG-6), mesocarbon microspheres (MCMB), graphene, Ketjen black, Super At least one of P, acetylene black, conductive carbon black or hard carbon.
  • the separator is a separator known in the art, such as a polyethylene separator, a polypropylene separator, and the like.
  • the present invention also provides a method for preparing the above-mentioned lithium ion battery, the method comprising the following steps:
  • the positive electrode sheet contains a positive electrode active material
  • the negative electrode sheet contains a negative electrode active material
  • the method specifically includes the following steps:
  • the positive active material LiCoO 2 , the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black are mixed according to the weight ratio of 96.5:2:1.5, and N-methylpyrrolidone (NMP) is added.
  • NMP N-methylpyrrolidone
  • the silicon carbon anode material with a mass ratio of 95.9% (compounded by SiO and graphite, SiO mass ratio of 3%), a single-wall carbon nanotube (SWCNT) conductive agent with a mass ratio of 0.1%, and a mass ratio of 1% of conductive carbon black (SP) conductive agent, 1% by mass of sodium carboxymethyl cellulose (CMC) dispersant and 2% by mass of styrene-butadiene rubber (SBR) binder to wet
  • SWCNT single-wall carbon nanotube
  • SP conductive carbon black
  • SP conductive carbon black
  • CMC sodium carboxymethyl cellulose
  • SBR styrene-butadiene rubber
  • the positive electrode sheet, separator and negative electrode sheet prepared above are wound to obtain a bare cell without liquid injection; the bare cell is placed in the outer packaging foil, and the prepared electrolyte is injected into the dried bare cell. , After vacuum packaging, standing, forming, shaping, sorting and other processes, the required lithium-ion battery is obtained.
  • the combination of fluoroethylene carbonate and lithium trifluoromethyl triethylborate in the electrolyte provided by the invention can form a tough low-impedance SEI composite film on the surface of the silicon carbon negative electrode, and can obviously inhibit the cyclic expansion of the silicon carbon negative electrode material. It can prolong the cycle life of the battery, and at the same time, it also makes the lithium ions more easily reversibly extracted/inserted, thereby improving the low temperature performance of the battery.
  • the combination of propenyl-1,3-sultone and lithium trifluoromethyltriethylborate can form a stronger composite protective film on the surface of the positive and negative electrodes, which can effectively improve the high temperature performance and safety of the battery.
  • three additives are used in combination, and the cycle life of the silicon carbon battery can be significantly improved through the synergistic effect of the three additives, and both high and low temperature performance and safety performance can be taken into consideration.
  • the lithium ion batteries of Comparative Examples 1-6 and Examples 1-8 were prepared according to the following preparation methods, the difference only lies in the selection and addition amount of each component in the electrolyte. The specific differences are shown in Table 1.
  • the positive active material LiCoO 2 , the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black are mixed according to the weight ratio of 96.5:2:1.5, and N-methylpyrrolidone (NMP) is added.
  • NMP N-methylpyrrolidone
  • the silicon carbon anode material with a mass ratio of 95.9% (compounded by SiO and graphite, SiO mass ratio of 3%), a single-wall carbon nanotube (SWCNT) conductive agent with a mass ratio of 0.1%, and a mass ratio of 1% of conductive carbon black (SP) conductive agent, 1% by mass of sodium carboxymethyl cellulose (CMC) dispersant and 2% by mass of styrene-butadiene rubber (SBR) binder to wet
  • the negative electrode slurry is made by the same method; the negative electrode slurry is uniformly coated on the copper foil with a thickness of 9-12 ⁇ m; after the above-mentioned coated copper foil is baked in an oven with 5 different temperature gradients, it is placed in the Dry in an oven at 85°C for 5 hours, and then roll and cut to obtain the desired silicon carbon negative electrode sheet.
  • the positive electrode sheet, separator and negative electrode sheet prepared above are wound to obtain a bare cell without liquid injection; the bare cell is placed in the outer packaging foil, and the prepared electrolyte is injected into the dried bare cell. , After vacuum packaging, standing, forming, shaping, sorting and other processes, the required lithium-ion battery is obtained.
  • the batteries obtained from the above examples and comparative examples were placed in a (45 ⁇ 2) °C environment, and allowed to stand for 2-3 hours.
  • the battery body reached (45 ⁇ 2) °C
  • the battery was charged with a 1C constant current and the cut-off current was 0.05 C.
  • the cut-off current was 0.05 C.
  • the battery After the battery is fully charged, put it on hold for 5 minutes, and then discharge it at a constant current of 0.7C to a cut-off voltage of 3.0V.
  • the cycle reaches the required number of times , record the battery's last discharge capacity Q 1 and battery thickness T 1 , and record the results as shown in Table 2.
  • Capacity retention rate (%) Q 1 /Q ⁇ 100%
  • Thickness change rate (%) (T 1 ⁇ T)/T ⁇ 100%.
  • the batteries obtained from the above examples and comparative examples were placed at room temperature to carry out 3 charge-discharge cycle tests with a charge-discharge rate of 0.5C, and then the 0.5C rate was charged to a fully charged state, and the highest discharge capacity of the first 3 0.5C cycles was recorded respectively.
  • Q 2 and cell thickness T 2 Store the fully charged battery at 85°C for 10 hours, record the battery thickness T 3 and 0.5C discharge capacity Q 3 after 10 hours, calculate the experimental data such as the thickness change rate and capacity retention rate of the battery stored at high temperature, and record the results as table 2.
  • Capacity retention rate (%) Q 3 /Q 2 ⁇ 100%
  • Thickness change rate (%) (T 3 -T 2 )/T 2 ⁇ 100%.
  • the batteries obtained in the above examples and comparative examples were heated with a convection method or a circulating hot air box at an initial temperature of 25 ⁇ 3°C, a temperature change rate of 5 ⁇ 2°C/min, and the temperature was increased to 130 ⁇ 2°C and kept for 60min. Test, record the battery state results as shown in Table 2.
  • the batteries obtained in the above examples and comparative examples were first discharged to 3.0V at 0.2C at an ambient temperature of 25 ⁇ 3°C, and then put on hold for 5 minutes; charged at 0.7C, and when the cell terminal voltage reached the charging limit voltage, it was changed to constant voltage charging. , until the charging current ⁇ cut-off current, stop charging, after 5 minutes, discharge at 0.2C to 3.0V, and record the discharge capacity as the normal temperature capacity Q 4 . Then the cell is charged at 0.7C.
  • the electrolyte suitable for the silicon-carbon system lithium ion battery provided by the present invention contains the additives of lithium trifluoromethyltriethylborate, propenyl-1,3-sultone and fluoroethylene carbonate Combined, through the synergistic effect between the additives, the silicon-carbon system lithium-ion battery can have excellent high-temperature cycling, high-temperature storage and low-temperature discharge performance while taking into account high safety.

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Abstract

本发明提供一种适用于硅碳体系锂离子电池的电解液及包括该电解液的硅碳体系锂离子电池。本发明中提供的电解液包括有机溶剂、添加剂和锂盐，所述添加剂包括三氟甲基三乙基硼酸锂、丙烯基-1,3-磺酸内酯和氟代碳酸乙烯酯，该添加剂组合使用可以显著提升硅碳电池的循环寿命，同时兼顾高低温性能和安全性能，从而使硅碳电池更适合大规模商业化生产。

Description

一种适用于硅碳体系锂离子电池的电解液
本申请要求于2020年12月03日提交中国专利局、申请号202011396207.7、申请名称为“一种适用于硅碳体系锂离子电池的电解液”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本发明属于锂离子电池技术领域，具体涉及一种适用于硅碳体系锂离子电池的电解液。
背景技术
锂离子电池自从商业化以来，由于它的比能量高、循环性能好，被广泛用于数码、储能、动力、军用航天和通讯设备等领域。随着锂离子电池的广泛应用，消费者对锂离子电池的使用环境、需求不断提升，同时对电子设备的续航能力要求越来越高，这就要求锂离子电池具有高低温性能兼顾的同时能够具有较高的能量密度。
硅碳电池是提高电池能量密度的有效手段之一，而其中电解液是硅碳锂离子电池的主材之一，它在硅碳锂离子电池中起到传输Li +的作用。因此，电解液的研究与开发对硅碳锂离子电池来说至关重要，然而缓解硅负极循环膨胀大和兼顾高低温性能的电解液并不容易开发。现阶段，电解液中添加剂的使用是解决以上问题的高效武器。但是，当前的电解液添加剂往往难以形成坚固有韧性的SEI膜来抵挡循环过程中硅负极膨胀带来的破坏，且高温添加剂带来的阻抗较大，且严重影响了电池的低温性能。因此，迫切需要开发一种能够延长硅碳电池循环寿命以及高低温兼顾的适用于硅碳体系锂离子电池的电解液。
发明内容
本发明提供了一种适用于硅碳体系锂离子电池的电解液，使用该电解液的硅碳锂离子电池可以有效缓解电池循环膨胀大、电池循环寿命低和电池高低温性能难兼顾等问题，从而显著提升硅碳体系锂离子电池的高低温性能和循环寿命，此外还能显著提升硅碳体系锂离子电池的安全性能，适合大规模商业化生产。
具体的，本发明提供了如下技术方案：
一种适用于硅碳体系锂离子电池的电解液，其中，所述电解液包括有机溶剂、添加剂和锂盐，所述添加剂包括三氟甲基三乙基硼酸锂、丙烯基-1,3-磺酸内酯和氟代碳酸乙烯酯。
进一步地，所述三氟甲基三乙基硼酸锂的使用量占电解液总质量的0.1-2wt％，优选为0.2-1.0wt％，再优选为0.2-0.5wt％，例如为0.1wt％、0.2wt％、0.3wt％、0.4wt％、0.5wt％、0.8wt％、0.9wt％、1wt％、1.2wt％、1.3wt％、1.4wt％、1.5wt％、1.6wt％、1.7wt％、1.8wt％、1.9wt％或2.0wt％。
本发明中，所述的三氟甲基三乙基硼酸锂可以通过本领域已知的方法制备得到，也可以通过商业途径购买获得。
本发明中，所述的三氟甲基三乙基硼酸锂的结构如式1所示：
Figure PCTCN2021135477-appb-000001
进一步地，所述丙烯基-1,3-磺酸内酯的使用量占电解液总质量的0.2-3.5wt％，优选为0.5-2wt％，例如为0.2wt％、0.3wt％、0.4wt％、0.5wt％、0.8wt％、0.9wt％、1wt％、1.2wt％、1.3wt％、1.4wt％、1.5wt％、1.6wt％、1.7wt％、 1.8wt％、1.9wt％、2.0wt％、3.0wt％或3.5wt％。
本发明中，所述的丙烯基-1,3-磺酸内酯的英文名称为prop-1-ene-1,3-sultone，其CAS号：21806-61-1，其可以通过本领域已知的方法制备得到，也可以通过商业途径购买获得。
进一步地，所述氟代碳酸乙烯酯的使用量占电解液总质量的8-20wt％，例如为8wt％、9wt％、10wt％、11wt％、12wt％、13wt％、14wt％、15wt％、16wt％、17wt％、18wt％、19wt％或20wt％。
本发明中，所述的氟代碳酸乙烯酯的英文名称为fluoroethylene carbonate，其CAS号：114435-02-8，其可以通过本领域已知的方法制备得到，也可以通过商业途径购买获得。
进一步地，所述添加剂还包括丁二腈、己二腈、甘油三腈、1,3,6-己烷三腈和1,2-双(氰乙氧基)乙烷中的至少一种，其使用量占电解液总质量的0-10wt％；示例性的可以为1-5wt％。
进一步地，所述有机溶剂选自碳酸酯、羧酸酯和氟代醚中的至少一种，其中，所述的碳酸酯选自碳酸乙烯酯、碳酸丙烯酯、碳酸二甲酯、碳酸甲乙酯、碳酸二乙酯、碳酸甲丙酯中的一种或多种组合；所述的羧酸酯选自丙酸乙酯、丙酸丙酯中的一种或多种组合；所述的氟代醚选自1,1,2,3-四氟乙基-2,2,3,3-四氟丙基醚。
进一步地，所述锂盐选自六氟磷酸锂、双氟磺酰亚胺锂或双(三氟甲基磺酰)亚胺锂中的一种或多种。
进一步地，所述锂盐的使用量占电解液总质量的10-20wt％，例如为10wt％、11wt％、12wt％、13wt％、14wt％、15wt％、16wt％、17wt％、18wt％、19wt％或20wt％。
本发明还提供一种电解液的制备方法，所述方法包括如下步骤：
将有机溶剂、添加剂和锂盐混合，其中，所述添加剂包括三氟甲基三乙基硼酸锂、丙烯基-1,3-磺酸内酯和氟代碳酸乙烯酯。
示例性地，所述方法包括如下步骤：
在充满氩气水氧含量合格的手套箱中，准备有机溶剂，然后往其中快速加入充分干燥的锂盐、三氟甲基三乙基硼酸锂、丙烯基-1,3-磺酸内酯和氟代碳酸乙烯酯，制备得到所述电解液。
本发明还提供一种锂离子电池，所述锂离子电池包括上述的电解液。
进一步地，所述锂离子电池为硅碳体系锂离子电池。
进一步地，所述锂离子电池还包括正极片、负极片和隔膜。
进一步地，所述负极片包括负极集流体和涂覆在负极集流体一侧或两侧表面的负极活性物质层，其中，所述负极活性物质层中包括负极活性物质，所述负极活性物质选自纳米硅和/或SiO x(0.8≤x≤1.3)与石墨复合而成的硅碳负极材料。
进一步地，所述纳米硅和/或SiO x占硅碳负极材料总质量的1-55wt％，如1wt％、2wt％、5wt％、8wt％、10wt％、12wt％、15wt％、18wt％、20wt％、25wt％、30wt％、35wt％、40wt％、45wt％、50wt％、55wt％。
进一步地，所述负极活性物质层还包括粘结剂、导电剂和分散剂。
进一步地，所述负极活性物质层中各组分的质量百分含量为：负极活性物质70-99.7wt％，粘结剂0.1-10wt％、分散剂0.1-10wt％、导电剂0.1-10wt％。
优选地，所述负极活性物质层中各组分的质量百分含量为：负极活性物质76-98.5wt％，粘结剂0.5-8wt％、分散剂0.5-8wt％、导电剂0.5-8wt％。
还优选地，所述负极活性物质层中各组分的质量百分含量为：负极活性物质85-98.5wt％，粘结剂0.5-5wt％、分散剂0.5-5wt％、导电剂0.5-5wt％。
进一步地，所述粘结剂选自聚偏氟乙烯(PVDF)、聚四氟乙烯(PTFE)、聚乙烯亚胺(PEI)、聚苯胺(PAN)、聚丙烯酸(PAA)、海藻酸钠、丁苯橡胶(SBR)、羧甲基纤维素钠(CMC)、酚醛树脂或环氧树脂等高分子聚合物中的至少一种。
进一步地，所述分散剂选自聚丙烯(PVA)、十六烷基溴化铵、十二烷 基苯磺酸钠、硅烷偶联剂、乙醇、N-甲基吡咯烷酮(NMP)、N,N-二甲基甲酰胺(DMF)等的至少一种，更优选地为十六烷基溴化铵、十二烷基苯磺酸钠、硅烷偶联剂、乙醇中的至少一种。
进一步地，所述导电剂选自碳纳米管(CNTs)、碳纤维(VGCF)、导电石墨(KS-6、SFG-6)、中间相碳微球(MCMB)、石墨烯、科琴黑、Super P、乙炔黑、导电炭黑或硬碳中的至少一种。
进一步地，所述正极片包括正极集流体和涂覆在正极集流体一侧或两侧表面的正极活性物质层，其中，所述正极活性物质层中包括正极活性物质，所述正极活性物质选自LiCoO 2、LiNiO 2、LiMn 2O 4、LiFePO 4、Li xNi yM 1-yO 2中的一种或几种，其中，0.9≤x≤1.2，0.5≤y<1，M选自Co、Mn、Al、Mg、Ti、Zr、Fe、Cr、Mo、Cu、Ca中的一种或几种。
进一步地，所述正极活性物质层还包括粘结剂和导电剂。
进一步地，所述正极活性物质层中各组分的质量百分含量为：正极活性物质80-99.8wt％，粘结剂0.1-10wt％、导电剂0.1-10wt％。
优选地，所述正极活性物质层中各组分的质量百分含量为：正极活性物质84-99wt％，粘结剂0.5-8wt％、导电剂0.5-8wt％。
还优选地，所述正极活性物质层中各组分的质量百分含量为：正极活性物质90-99wt％，粘结剂0.5-5wt％、导电剂0.5-5wt％。
进一步地，所述粘结剂选自聚偏氟乙烯(PVDF)、聚四氟乙烯(PTFE)、聚乙烯亚胺(PEI)、聚苯胺(PAN)、聚丙烯酸(PAA)、海藻酸钠、丁苯橡胶(SBR)、羧甲基纤维素钠(CMC)、酚醛树脂或环氧树脂等高分子聚合物中的至少一种。
进一步地，所述导电剂选自碳纳米管(CNTs)、碳纤维(VGCF)、导电石墨(KS-6、SFG-6)、中间相碳微球(MCMB)、石墨烯、科琴黑、Super P、乙炔黑、导电炭黑或硬碳中的至少一种。
进一步地，所述隔膜为本领域已知的隔膜，例如为聚乙烯隔膜、聚丙烯 隔膜等。
本发明还提供上述锂离子电池的制备方法，所述方法包括如下步骤：
(1)准备正极片和负极片，所述正极片中含有正极活性物质，所述负极片中含有负极活性物质；
(2)将有机溶剂、添加剂和锂盐混合，制备得到电解液；
(3)将正极片、隔膜、负极片通过卷绕得到未注液的裸电芯；将裸电芯置于外包装箔中，将步骤(2)的电解液注入到干燥后的裸电芯中，制备得到所述锂离子电池。
示例性地，所述方法具体包括如下步骤：
(1)正极片制备
将正极活性物质LiCoO 2、粘结剂聚偏氟乙烯(PVDF)、导电剂乙炔黑按照重量比96.5:2:1.5进行混合，加入N-甲基吡咯烷酮(NMP)，在真空搅拌机作用下搅拌，直至混合体系成均一流动性的正极浆料；将正极浆料均匀涂覆于厚度为9～12μm的铝箔上；将上述涂覆好的铝箔在5段不同温度梯度的烘箱烘烤后，再将其在120℃的烘箱干燥8h，然后经过辊压、分切得到所需的正极片。
(2)硅碳负极片制备
将质量占比为95.9％的硅碳负极材料(采用SiO与石墨复合而成，SiO质量占比3％)，质量占比为0.1％的单壁碳纳米管(SWCNT)导电剂、质量占比为1％的导电炭黑(SP)导电剂、质量占比为1％的羧甲基纤维素钠(CMC)分散剂及质量占比为2％的丁苯橡胶(SBR)粘结剂以湿法工艺制成负极浆料；将负极浆料均匀涂覆于厚度为9～12μm的铜箔上；将上述涂覆好的铜箔在5段不同温度梯度的烘箱烘烤后，再将其在85℃的烘箱干燥5h，然后经过辊压、
分切得到所需的硅碳负极片。
(3)电解液制备
在充满氩气水氧含量合格的手套箱中，将碳酸乙烯酯、碳酸丙烯酯、丙酸丙酯和丙酸乙酯按照质量比1:2:5:2的比例混合均匀(溶剂需要归一化)，然 后往其中快速加入1mol/L(12.5wt％)的充分干燥的六氟磷酸锂(LiPF 6)、添加剂(包括三氟甲基三乙基硼酸锂、丙烯基-1,3-磺酸内酯和氟代碳酸乙烯酯等)，得到电解液。
(4)隔膜的制备
选用7～9μm厚的聚乙烯隔膜。
(5)锂离子电池的制备
将上述准备的正极片、隔膜、负极片通过卷绕得到未注液的裸电芯；将裸电芯置于外包装箔中，将上述制备好的电解液注入到干燥后的裸电芯中，经过真空封装、静置、化成、整形、分选等工序，获得所需的锂离子电池。
本发明的有益效果：
本发明提供的电解液中氟代碳酸乙烯酯和三氟甲基三乙基硼酸锂联用可以在硅碳负极表面形成坚韧的低阻抗SEI复合膜，对硅碳负极材料的循环膨胀有明显抑制作用，可以延长电池的循环寿命，同时还使得锂离子能够更易可逆脱出/嵌入，从而提高了电池的低温性能。丙烯基-1,3-磺酸内酯与三氟甲基三乙基硼酸锂联用能够在正负极表面生成更坚固的复合保护膜，有效提升电池的高温性能和安全性。本发明将三种添加剂组合使用，通过三者的协同作用可以显著提升硅碳电池的循环寿命，同时兼顾高低温性能和安全性能。
具体实施方式
下文将结合具体实施例对本发明做更进一步的详细说明。应当理解，下列实施例仅为示例性地说明和解释本发明，而不应被解释为对本发明保护范围的限制。凡基于本发明上述内容所实现的技术均涵盖在本发明旨在保护的范围内。
下述实施例中所使用的实验方法如无特殊说明，均为常规方法；下述实施例中所用的试剂、材料等，如无特殊说明，均可从商业途径得到。
对比例1-6和实施例1-8
对比例1-6和实施例1-8的锂离子电池均按照下述制备方法进行制备，区别仅在于电解液中的各组分的选择和加入量不同，具体区别如表1所示。
(1)正极片制备
将正极活性物质LiCoO 2、粘结剂聚偏氟乙烯(PVDF)、导电剂乙炔黑按照重量比96.5:2:1.5进行混合，加入N-甲基吡咯烷酮(NMP)，在真空搅拌机作用下搅拌，直至混合体系成均一流动性的正极浆料；将正极浆料均匀涂覆于厚度为9～12μm的铝箔上；将上述涂覆好的铝箔在5段不同温度梯度的烘箱烘烤后，再将其在120℃的烘箱干燥8h，然后经过辊压、分切得到所需的正极片。
(2)硅碳负极片制备
将质量占比为95.9％的硅碳负极材料(采用SiO与石墨复合而成，SiO质量占比3％)，质量占比为0.1％的单壁碳纳米管(SWCNT)导电剂、质量占比为1％的导电炭黑(SP)导电剂、质量占比为1％的羧甲基纤维素钠(CMC)分散剂及质量占比为2％的丁苯橡胶(SBR)粘结剂以湿法工艺制成负极浆料；将负极浆料均匀涂覆于厚度为9～12μm的铜箔上；将上述涂覆好的铜箔在5段不同温度梯度的烘箱烘烤后，再将其在85℃的烘箱干燥5h，然后经过辊压、分切得到所需的硅碳负极片。
(3)电解液制备
在充满氩气水氧含量合格的手套箱中，将碳酸乙烯酯、碳酸丙烯酯、丙酸丙酯和丙酸乙酯按照质量比1:2:5:2的比例混合均匀(溶剂需要归一化)，然后往其中快速加入1mol/L(12.5wt％)的充分干燥的六氟磷酸锂(LiPF 6)、质量占比为3wt％的1,3,6-己烷三腈和其他添加剂(包括三氟甲基三乙基硼酸锂、丙烯基-1,3-磺酸内酯和氟代碳酸乙烯酯，具体用量和选择如表1所示)，得到电解液。
(4)隔膜的制备
选用7～9μm厚的聚乙烯隔膜。
(5)锂离子电池的制备
将上述准备的正极片、隔膜、负极片通过卷绕得到未注液的裸电芯；将裸电芯置于外包装箔中，将上述制备好的电解液注入到干燥后的裸电芯中，经过真空封装、静置、化成、整形、分选等工序，获得所需的锂离子电池。
表1对比例1-6和实施例1-8的步骤(3)的电解液中的其他添加剂的组成和加入量
Figure PCTCN2021135477-appb-000002
对上述对比例和实施例所得电池进行电化学性能测试，相关说明如下：
(1)45℃循环实验：
将上述实施例和对比例所得电池置于(45±2)℃环境中，静置2-3个小时，待电池本体达到(45±2)℃时，电池按照1C恒流充电截止电流为0.05C，电池充满电后搁置5min，再以0.7C恒流放电至截止电压3.0V，记录前3次循环的最高 放电容量为初始容量Q，记录电芯初始厚度T，当循环达到所需的次数时，记录电池的最后一次的放电容量Q 1和电池厚度T 1，记录结果如表2。
其中用到的计算公式如下：
容量保持率(％)＝Q 1/Q×100％；
厚度变化率(％)＝(T 1-T)/T×100％。
(2)85℃高温存储10小时实验：
将上述实施例和对比例所得电池置于室温下以0.5C的充放电倍率进行3次充放电循环测试，然后0.5C倍率充到满电状态，分别记录前3次0.5C循环的最高放电容量Q 2和电池厚度T 2。将满电状态的电池在85℃下存储10小时，记录10小时后的电池厚度T 3和0.5C放电容量Q 3，计算得到电池高温存储的厚度变化率和容量保持率等实验数据，记录结果如表2。
其中用到的计算公式如下：
容量保持率(％)＝Q 3/Q 2×100％；
厚度变化率(％)＝(T 3-T 2)/T 2×100％。
(3)130℃热冲击实验：
将上述实施例和对比例所得电池用对流方式或循环热空气箱以起始温度25±3℃进行加热，温变率5±2℃/min，升温至130±2℃℃，保持60min后结束试验，记录电池状态结果如表2。
(4)低温放电实验：
将上述实施例和对比例所得电池在环境温度25±3℃，先以0.2C放电至3.0V，搁置5min；以0.7C充电，当电芯端电压达到充电限制电压时，改为恒压充电，直到充电电流≤截止电流，停止充电，搁置5分钟后，以0.2C放电至3.0V，记录此次放电容量为常温容量Q 4。然后电芯以0.7C充电，当电芯端电 压达到充电限制电压时，改为恒压充电，直到充电电流小于或等于截止电流，停止充电；将充满电的电池在-10±2℃条件下搁置4h后，以0.4C电流放电至截止电压3.0V，记录放电容量Q 5，计算可得低温放电容量保持率，记录结果如表2。
其中用到的计算公式如下：
低温放电容量保持率(％)＝Q 5/Q 4×100％。
表2对比例1-6和实施例1-8的性能测试结果
Figure PCTCN2021135477-appb-000003
Figure PCTCN2021135477-appb-000004
由表2结果可以看出：
综上所述，本发明提供的适用于硅碳体系锂离子电池的电解液含有三氟甲基三乙基硼酸锂、丙烯基-1,3-磺酸内酯和氟代碳酸乙烯酯的添加剂组合，通过添加剂之间的协同作用能够使硅碳体系锂离子电池具有优异的高温循环、高温储存和低温放电性能的同时还兼顾高安全性。
以上，对本发明的实施方式进行了说明。但是，本发明不限定于上述实施方式。凡在本发明的精神和原则之内，所做的任何修改、等同替换、改进等，均应包含在本发明的保护范围之内。

Claims (9)

  1. 一种适用于硅碳体系锂离子电池的电解液，其中，所述电解液包括有机溶剂、添加剂和锂盐，所述添加剂包括三氟甲基三乙基硼酸锂、丙烯基-1,3-磺酸内酯和氟代碳酸乙烯酯。
  2. 根据权利要求1所述的电解液，其中，所述三氟甲基三乙基硼酸锂的使用量占电解液总质量的0.1-2wt％，优选为0.2-1.0wt％，再优选为0.2-0.5wt％。
  3. 根据权利要求1或2所述的电解液，其中，所述丙烯基-1,3-磺酸内酯的使用量占电解液总质量的0.2-3.5wt％，优选为0.5-2wt％。
  4. 根据权利要求1-3任一项所述的电解液，其中，所述氟代碳酸乙烯酯的使用量占电解液总质量的8-20wt％。
  5. 根据权利要求1-4任一项所述的锂离子电池，其中，所述添加剂还包括丁二腈、己二腈、甘油三腈、1,3,6-己烷三腈和1,2-双(氰乙氧基)乙烷中的至少一种，其使用量占电解液总质量的0-10wt％。
  6. 根据权利要求1-5任一项所述的锂离子电池，其中，所述有机溶剂选自碳酸酯、羧酸酯和氟代醚中的至少一种，其中，所述的碳酸酯选自碳酸乙烯酯、碳酸丙烯酯、碳酸二甲酯、碳酸甲乙酯、碳酸二乙酯、碳酸甲丙酯中的一种或多种组合；所述的羧酸酯选自丙酸乙酯、丙酸丙酯中的一种或多种组合；所述的氟代醚选自1,1,2,3-四氟乙基-2,2,3,3-四氟丙基醚。
  7. 根据权利要求1-6任一项所述的锂离子电池，其中，所述锂盐选自六氟磷酸锂、双氟磺酰亚胺锂或双(三氟甲基磺酰)亚胺锂中的一种或多种；和/或，
    所述锂盐的使用量占电解液总质量的10-20wt％。
  8. 一种锂离子电池，其中，所述锂离子电池包括权利要求1-7任一项所述的电解液。
  9. 根据权利要求8所述的锂离子电池，其中，所述锂离子电池为硅碳体系锂离子电池。
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