WO2022193226A1 - 电解液、电化学装置和电子装置 - Google Patents

电解液、电化学装置和电子装置 Download PDF

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WO2022193226A1
WO2022193226A1 PCT/CN2021/081516 CN2021081516W WO2022193226A1 WO 2022193226 A1 WO2022193226 A1 WO 2022193226A1 CN 2021081516 W CN2021081516 W CN 2021081516W WO 2022193226 A1 WO2022193226 A1 WO 2022193226A1
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electrolyte
formula
lithium
positive electrode
active material
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PCT/CN2021/081516
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English (en)
French (fr)
Inventor
许艳艳
徐春瑞
郑建明
韩翔龙
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宁德新能源科技有限公司
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Priority to PCT/CN2021/081516 priority Critical patent/WO2022193226A1/zh
Priority to CN202180003379.XA priority patent/CN113841281B/zh
Publication of WO2022193226A1 publication Critical patent/WO2022193226A1/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
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or 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
    • 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 application relates to the field of electrochemical energy storage, in particular to electrolytes, electrochemical devices and electronic devices.
  • electrochemical devices eg, lithium-ion batteries
  • users have also put forward higher and higher requirements for the cycle performance and storage performance of the electrochemical devices.
  • the current technical improvements to electrochemical devices can improve their cycle performance and storage performance to a certain extent, they are still unable to meet the increasingly high usage needs of people, and further improvements are expected.
  • R 1 and R 2 are each independently selected from C 1 -C 5 groups or C1-C5 groups substituted by halogen, and m and n are each independently selected from integers from 0 to 3; R 3 , R 4 , R 5 and R 6 are selected from substituted or unsubstituted methylene, wherein when substituted, the substituent is halogen; the structures represented by R 1 and R 2 can be bridged to form a ring.
  • the C 1 -C 5 groups are selected from alkane groups, alkene groups, oxygen-containing hydrocarbyl groups, silicon-containing hydrocarbyl groups, or cyano-substituted hydrocarbyl groups, or fluoro-substituted alkane groups.
  • the compound represented by formula I includes at least one of formula I-1, formula I-2, formula I-3, formula I-4, formula I-5 or formula I-6:
  • the mass content of the compound represented by formula I is 0.01% to 5% based on the mass of the electrolyte.
  • the electrolyte further includes additives, and the additives include vinyl ester compounds, heterocyclic compounds, sulfonic acid ester compounds, nitrile compounds, fluorine-containing lithium salts, acid anhydride compounds, cyclic ester compounds or chain-like compounds At least one of the ester compounds.
  • the mass content of the additive is 0.01% to 10% based on the mass of the electrolyte.
  • the additives include vinylene carbonate (VC), fluoroethylene carbonate (FEC), vinyl vinyl carbonate (VEC), 1,3-dioxane, 1,4-dioxane Cyclo, Dioxolane, 1,3-Propane Sultone (PS), 1,4-Butane Sultone, Vinyl Sulfate, Methylene Methanedisulfonate (MMDS), Allenyl-1 ,3-Sultone (PES), succinonitrile, glutaronitrile, adiponitrile, 2-methyleneglutaronitrile, dipropylmalononitrile, 1,3,6-hexanetrinitrile ( HTCN), 1,2,6-hexane trinitrile, 1,3,5-pentane methane trinitrile, 1,2-bis(cyanoethoxy)ethane, ethoxy(pentafluoro)cyclotriphosphine Nitrile, Lithium Bistrifluoromethanesulfonimi
  • the electrochemical device includes an electrolyte, a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, wherein the electrolyte is any of the foregoing electrolytes.
  • the positive electrode includes a positive electrode active material layer with a positive electrode active material, the weight percentage of the compound represented by the formula I is X % based on the mass of the electrolyte, and the specific surface area of the positive electrode active material is Y m 2 / The value range of g, Y is 0.1 to 1, and 0.01 ⁇ X/Y ⁇ 7.5 is satisfied.
  • Embodiments of the present application also provide an electronic device, including the above electrochemical device.
  • the compound represented by formula I can form stable interface protection on the surface of the positive and negative electrodes, thereby significantly improving the cycle life and high temperature storage performance of the electrochemical device.
  • electrolyte plays the role of transferring lithium ions between positive and negative electrodes, and is an important guarantee for electrochemical devices to obtain high energy, high rate, long cycle, high safety and other performances.
  • the present application proposes an electrolyte, which can reduce the high-temperature gas production of an electrochemical device and improve the cycle performance and storage performance of the electrochemical device.
  • a kind of electrolyte is provided, and this electrolyte comprises compound shown in formula I:
  • R 1 and R 2 are each independently selected from C 1 -C 5 groups or C1-C5 groups substituted by halogen, m and n are each independently selected from integers from 0 to 3; R 3 , R 4 , R 5 and R 6 are selected from substituted or unsubstituted methylene, wherein when substituted, the substituent is halogen; the structures represented by R 1 and R 2 can be bridged to form a ring.
  • the structures represented by R 1 and R 2 can be bridged to form a ring: R 1 and R 2 can be directly connected to form a bridged ring or R 1 and R 2 can be unconnected.
  • the electrolyte used in the present application can form stable interface protection on the surfaces of the positive and negative electrodes, thereby significantly improving the cycle performance and high-temperature storage performance of the electrochemical device.
  • the acid anhydride compounds of formula I can preferentially decompose by solvent oxidation, forming a dense and stable positive electrode electrolyte interface (CEI) film on the surface of the positive electrode, reducing the contact between the electrolyte and the positive electrode, thereby inhibiting the catalytic decomposition of the electrolyte and reducing the Interface impedance, improved DC resistance (DCR).
  • CEI positive electrode electrolyte interface
  • the compound represented by formula I can be reduced to form a film on the surface of the negative electrode, thereby reducing the reduction and decomposition of the electrolyte solution on the negative electrode.
  • the compound shown in formula I can not only capture a small amount of water and HF in the electrolyte, but also form a stable protective film on the positive electrode and the negative electrode, and can effectively improve the electrochemical device during the continuous charge-discharge cycle process. improved cycling stability and slowed the expansion during cycling.
  • the C1 - C5 groups are selected from alkanes, alkenes, oxygen-containing hydrocarbyls, silicon-containing hydrocarbyls, or cyano-substituted hydrocarbyls, or fluorohydrocarbyls.
  • the compound represented by formula I includes at least one of formula I-1, formula I-2, formula I-3, formula I-4, formula I-5 or formula I-6:
  • the mass content of the compound represented by formula I is 0.01% to 5% based on the mass of the electrolyte. If the mass content of the compound represented by formula I is too small, it is not enough to form good interface protection and the improvement effect on electrochemical devices is relatively limited; if the mass content of the compound represented by formula I is too large, for example, more than 5%, then The enhancement effect of the compound represented by formula I on the stability of the positive electrode interface and the negative electrode interface is no longer significantly improved.
  • the electrolyte may further include additives, the additives include vinyl ester compounds, heterocyclic compounds, sulfonate compounds, nitrile compounds, fluorine-containing lithium salts, acid anhydride compounds, cyclic ester compounds or chain at least one of the ester-like compounds.
  • the mass content of the additive is 0.01% to 10% based on the mass of the electrolyte. If the mass content of these additives is too small, the improvement effect on the electrochemical device is relatively limited; if the mass content of these additives is too large, for example, more than 10%, the effect on inhibiting the decomposition and heat generation of metal lithium and the electrolyte no longer significantly increased.
  • the use of polynitrile compounds can reduce the viscosity and cost of the electrolyte.
  • the cyclic ester compound can assist in enhancing the film-forming stability of the anode solid-state interface film (SEI).
  • the aforementioned additives include vinylene carbonate (VC), fluoroethylene carbonate (FEC), vinyl ethylene carbonate (VEC), 1,3-dioxane, 1,4-dioxane Hexacyclic, dioxolane, 1,3-propane sultone (PS), 1,4-butane sultone (BS), vinyl sulfate (DTD), methylene methanedisulfonate ( MMDS), propenyl-1,3-sultone (PST), succinonitrile, glutaronitrile, adiponitrile, 2-methyleneglutaronitrile, dipropylmalononitrile, 1,3, 6-Hexanetrinitrile (HTCN), 1,2,6-Hexanetrinitrile, 1,3,5-pentanemethanetrinitrile, 1,2-bis(cyanoethoxy)ethane, ethoxy (Pentafluoro)cyclotriphosphazene, Li
  • VC
  • these compounds have strong antioxidant capacity and are not easily oxidized at the positive electrode.
  • these compounds will be reduced on the surface of metal lithium to form a protective film, which inhibits the decomposition of metal lithium and the electrolyte to generate heat, and further enhances the protection of the negative electrode active material.
  • the electrolyte may also include other non-aqueous organic solvents and lithium salts.
  • the non-aqueous organic solvent may contain at least one of carbonates, carboxylates, ethers or other aprotic solvents.
  • Examples of carbonate-based solvents include dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, Bis(2,2,2-trifluoroethyl) carbonate, etc.
  • carboxylate-based solvents include methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate , ethyl butyrate, propyl butyrate, butyl butyrate, ⁇ -butyrolactone, 2,2-difluoroethyl acetate, valerolactone, butyrolactone, 2-fluoroethyl acetate, 2,2 -ethyl difluoroacetate, ethyl trifluoroacetate, ethyl 2,2,3,3,3-pentafluoropropionate, 2,2,3,3,4,4,4,4-heptafluorobutyric acid Methyl ester, methyl 4,4,4-trifluoro-3-(trifluoromethyl)butyrate, ethyl 2,
  • ether-based solvents include ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, dibutyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, bis(2,2,2-trimethyl ether) Fluoroethyl) ether, etc.
  • the lithium salt of the present application includes at least one of an organic lithium salt or an inorganic lithium salt. In some embodiments, the lithium salt of the present application contains at least one of fluorine, boron, and phosphorus.
  • the lithium salts of the present application include lithium hexafluorophosphate LiPF 6 , lithium difluorophosphate LiPO 2 F 2 , lithium bistrifluoromethanesulfonimide LiN(CF 3 SO 2 ) 2 (LiTFSI), bis(fluorosulfonic acid) Lithium acyl)imide Li(N(SO 2 F) 2 )(LiFSI), Lithium Bisoxalate Borate LiB(C 2 O 4 ) 2 (LiBOB), Lithium Difluorooxalate Borate LiBF 2 (C 2 O 4 )(LiDFOB ), at least one of lithium hexafluoroarsenate LiAsF 6 , lithium perchlorate LiClO 4 , lithium trifluoromethanesulfonate LiCF 3 SO 3 .
  • the concentration of the lithium salt in the electrolyte of the present application is about 0.5 mol/L to 3 mol/L, about 0.5 mol/L to 2 mol/L, about 0.5 mol/L to 1.5 mol/L, or about 0.8mol/L to 1.2mol/L.
  • Embodiments of the present application also provide electrochemical devices.
  • the electrochemical device includes an electrode assembly including a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte.
  • the electrolyte is the electrolyte described above.
  • the negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector.
  • the anode active material layer may be provided on one side or both sides of the anode current collector.
  • the negative electrode current collector may use at least one of copper foil, nickel foil or carbon-based current collector.
  • the anode active material layer may include an anode active material.
  • the anode active material in the anode active material layer includes at least one of lithium metal or silicon-based material.
  • the silicon-based material includes at least one of silicon, silicon oxide, silicon carbon, or silicon alloy.
  • a conductive agent and/or a binder may also be included in the anode active material layer.
  • the conductive agent in the negative active material layer may include at least one of carbon black, acetylene black, Ketjen black, lamellar graphite, graphene, carbon nanotubes, carbon fibers, or carbon nanowires.
  • the binder in the negative active material layer may include carboxymethyl cellulose (CMC), polyacrylic acid, polyacrylate, polyacrylate, polyvinylpyrrolidone, polyaniline, polyimide, At least one of polyamideimide, polysiloxane, styrene-butadiene rubber, epoxy resin, polyester resin, polyurethane resin or polyfluorene.
  • the materials disclosed above are only exemplary, and any other suitable materials may be used for the negative electrode active material layer.
  • the mass ratio of the negative electrode active material, the conductive agent and the binder in the negative electrode active material layer may be (80 to 99):(0.5 to 10):(0.5 to 10). It should be understood that this is only is exemplary and not intended to limit the application.
  • the positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector.
  • the positive electrode active material layer may be located on one side or both sides of the positive electrode current collector.
  • the positive electrode current collector may be aluminum foil, and of course, other positive electrode current collectors commonly used in the art may also be used.
  • the thickness of the cathode current collector may be 1 ⁇ m to 200 ⁇ m.
  • the cathode active material layer may be coated only on a partial area of the cathode current collector.
  • the thickness of the cathode active material layer may be 10 ⁇ m to 500 ⁇ m. It should be understood that these are exemplary only and other suitable thicknesses may be employed.
  • the cathode active material layer includes a cathode active material.
  • the positive active material includes LiCoO 2 , LiNiO 2 , LiMn 2 O 4 , LiCo 1-y My O 2 , LiNi 1-y My O 2 , LiMn 2-y My O 4 , LiNi x Co y Mn z M 1-xyz O 2 , wherein M is selected from at least one of Fe, Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V or Ti, And 0 ⁇ y ⁇ 1, 0 ⁇ x ⁇ 1, 0 ⁇ z ⁇ 1, x+y+z ⁇ 1.
  • the positive active material may include at least one of lithium cobalt oxide, lithium manganate, lithium iron phosphate, lithium iron manganese phosphate, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, or lithium nickel manganate,
  • the above-mentioned positive electrode active material may be subjected to doping and/or coating treatment.
  • the positive active material layer further includes a binder and a conductive agent.
  • the binder in the positive active material layer may include 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, polymethyl methacrylate, polytetrafluoroethylene At least one of vinyl fluoride or polyhexafluoropropylene.
  • the conductive agent in the positive active material layer may include at least one of conductive carbon black, acetylene black, Ketjen black, lamellar graphite, graphene, carbon nanotubes, or carbon fibers.
  • the mass ratio of the positive electrode active material, the conductive agent, and the binder in the positive electrode active material layer may be (70 to 98):(1 to 15):(1 to 15). It should be understood that the above are only examples, and any other suitable materials, thicknesses and mass ratios may be used for the positive electrode active material layer.
  • the weight percentage of the compound represented by the formula I is X %
  • the specific surface area of the positive electrode active material is Y m 2 /g
  • the value of Y ranges from 0.1 to 1, 0.01 ⁇ X/Y ⁇ 7.5 is satisfied.
  • the release membrane includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid.
  • the polyethylene includes at least one selected from high density polyethylene, low density polyethylene or ultra-high molecular weight polyethylene. Especially polyethylene and polypropylene, they have a good effect on preventing short circuit and can improve the stability of the battery through the shutdown effect.
  • the thickness of the isolation film is in the range of about 3 ⁇ m to 500 ⁇ m.
  • the surface of the isolation membrane may further include a porous layer, the porous layer is disposed on at least one surface of the isolation membrane, the porous layer includes at least one of inorganic particles or a binder, and the inorganic particles are selected from aluminum oxide (Al 2 O 3 ), silicon oxide (SiO 2 ), magnesium oxide (MgO), titanium oxide (TiO 2 ), hafnium dioxide (HfO 2 ), tin oxide (SnO 2 ), ceria (CeO 2 ), nickel oxide (NiO), zinc oxide (ZnO), calcium oxide (CaO), zirconium oxide (ZrO 2 ), yttrium oxide (Y 2 O 3 ), silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, At least one of calcium hydroxide or barium sulfate.
  • aluminum oxide Al 2 O 3
  • silicon oxide SiO 2
  • magnesium oxide MgO
  • titanium oxide TiO 2
  • hafnium dioxide HfO
  • the pores of the isolation membrane have diameters in the range of about 0.01 ⁇ m to 1 ⁇ m.
  • the binder of the porous layer is selected from polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyamide At least one of vinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene.
  • the porous layer on the surface of the separator can improve the heat resistance, oxidation resistance and electrolyte wettability of the separator, and enhance the adhesion between the separator and the pole piece.
  • the electrode assembly of the electrochemical device is a wound electrode assembly or a stacked electrode assembly.
  • the electrochemical device is a lithium-ion battery, although the application is not so limited.
  • the positive electrode, the separator, and the negative electrode are wound or stacked in sequence to form an electrode assembly, which is then packaged in, for example, an aluminum-plastic film case, and an electrolyte is injected. Formed and packaged to make lithium-ion batteries. Then, the performance test of the prepared lithium-ion battery was carried out.
  • electrochemical devices eg, lithium ion batteries
  • electrochemical devices eg, lithium ion batteries
  • Other methods commonly used in the art may be employed without departing from the disclosure of the present application.
  • Embodiments of the present application also provide electronic devices including the above electrochemical devices.
  • the electronic device in the embodiment of the present application is not particularly limited, and it may be used in any electronic device known in the prior art.
  • electronic devices may include, but are not limited to, notebook computers, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, headsets, Video recorders, LCD TVs, portable cleaners, portable CD players, mini discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power, motors, automobiles, motorcycles, power-assisted bicycles, bicycles, Lighting equipment, toys, game consoles, clocks, power tools, flashlights, cameras, large-scale household storage batteries and lithium-ion capacitors, etc.
  • the preparation of the positive electrode the positive active material lithium manganate LiMn 2 O 4 , the conductive agent conductive carbon black, and the binder polyvinylidene fluoride (PVDF) are dissolved in N-methylpyrrolidone in a weight ratio of 96:2:2 (NMP) solution to form a positive electrode slurry.
  • NMP binder polyvinylidene fluoride
  • negative electrode active material artificial graphite, conductive agent conductive carbon black, binder styrene-butadiene rubber (SBR), thickener sodium carboxymethyl cellulose (CMC) are mixed in a weight ratio of 96.4: 1.5: 1.6: 0.5 The ratio is dissolved in deionized water to form a negative electrode slurry.
  • a 10 ⁇ m thick copper foil was used as the negative electrode current collector, and the negative electrode slurry was coated on the negative electrode current collector with a coating amount of 9.3 mg/cm 2 , and the negative electrode was obtained after drying, cold pressing and cutting.
  • the isolation film is a polyethylene (PE) isolation film with a thickness of 16 ⁇ m.
  • ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are uniformly mixed in a mass ratio of 3:5:2, and then The additive components were added, and the lithium salt LiPF 6 (final concentration was 1 mol/L) was dissolved in the above-mentioned non-aqueous solvent to obtain an electrolyte solution.
  • the added component was Compound I-1, and the mass content in the electrolyte was 0.1%.
  • Preparation of lithium ion battery stack the positive electrode, the separator and the negative electrode in sequence, so that the separator is placed between the positive electrode and the negative electrode for isolation, and then the electrode assembly is obtained by winding. Place the electrode assembly in the outer packaging aluminum-plastic film, remove the moisture at 80°C, inject the above electrolyte and encapsulate it, and then charge it to 3.3V with a constant current of 0.02C, and then charge it to 3.6V with a constant current of 0.1C. ), degassing, trimming and other technological processes to obtain a lithium ion battery (thickness 3.3mm, width 39mm, length 96mm).
  • Comparative Example 1 no other additive components were added to the electrolyte. In Comparative Example 2, only 3% of PS was added, and the compound represented by formula I was not added. In Examples 2 to 7, the addition amount of the compound of formula I-1 was different from that of Example 1. In Examples 8 to 18, the kinds of compounds represented by formula I added were different from those in Example 1. In Examples 19 to 34, in addition to the compound represented by formula I-1, other additives were also added, wherein the mass content of the compound represented by formula I-1 in Examples 19 to 34 was 1%. In Examples 35 to 41 and Comparative Example 3, the content of the compound represented by Formula I and the specific surface area of the positive electrode active material were different from those in Example 1. The test methods for each parameter of the present application are described below.
  • the lithium-ion battery was placed in a 45°C incubator, and allowed to stand for 30 minutes, so that the lithium-ion battery reached a constant temperature and the initial thickness of the battery was tested.
  • the lithium-ion battery that has reached a constant temperature is charged at a constant current of 0.5C to a voltage of 4.2V, then charged at a constant voltage of 4.2V to a current of 0.05C, and then discharged at a constant current of 1C to a voltage of 3.0V. This is a charge-discharge cycle. . Taking the capacity of the first discharge as 100%, repeat the charge-discharge cycle for 500 times, stop the test, record the cycle capacity retention rate, and measure the battery thickness at the same time.
  • Cycle capacity retention rate capacity at 500 cycles/capacity at first discharge ⁇ 100%.
  • Thickness expansion ratio (battery thickness after 500 cycles-battery initial thickness)/battery initial thickness ⁇ 100%.
  • Table 1 shows the respective parameters and evaluation results of Comparative Example 1 and Examples 1 to 18.
  • the specific surface area of the positive electrode active material of all Examples was 0.5 m 2 /g. It can be seen from Comparative Example 1 and Examples 1 to 18 that the addition of the compound represented by Formula I in the electrolyte can improve the cycle performance, thickness expansion ratio and overdischarge storage performance of the electrochemical device. By comparing Examples 1 to 7, it can be seen that as the content of the compound represented by formula I increases, the degree of improvement in cycle performance, thickness expansion ratio and overdischarge storage performance first increases and then weakens. From Examples 8 to 18, it can be seen that some other compounds I-2, I-3, I-4, I-5, I-6 also showed good performance in the cycle performance, thickness expansion ratio and overdischarge storage performance of electrochemical devices.
  • the improvement of different levels is because the compound shown in formula I can adsorb a small amount of water and HF in the electrolyte, which increases the stability of the electrolyte; at the same time, it is easy to oxidize and form a dense protective film on the positive electrode, reducing the impact of the electrolyte on the electrolyte. The destruction of the positive electrode; and the film is preferentially reduced on the negative electrode during the first charge and discharge, and the film is dense, which inhibits the decomposition reaction of the electrolyte at the negative electrode.
  • the optimal addition amount of the compound represented by formula I was 1%, mainly because it can not only effectively stabilize the electrolyte, but also form excellent interface protection at the positive and negative electrodes at the same time.
  • Table 2 shows the respective parameters and evaluation results of Examples 4 and 19 to 34 and Comparative Examples 1 to 2.
  • Example 4 the specific surface area of the positive electrode active material of all Examples was 0.5 m 2 /g.
  • Example 4 By comparing Examples 19 to 28 with Example 4, it can be seen that after adding the conventional additive PS or VC to the electrolyte containing the compound represented by formula I-1, wherein, based on the quality of the electrolyte, formula I-1 The mass content of the compound is all 1%, which improves the cycle performance of the lithium ion battery, and simultaneously improves the thickness expansion rate and the overdischarge storage performance of the lithium ion battery.
  • the additional additives can not only form a film on the negative electrode to modify the SEI formed by the compound represented by formula I, but also form an excellent interfacial protective film on the positive electrode to alleviate the side reactions of the electrolyte at the positive electrode and the negative electrode.
  • Table 3 shows the respective parameters and evaluation results of Examples 35 to 41 and Comparative Example 3.
  • X/Y when X/Y is in the range of 0.1 to 6, with the increase of the ratio, the high-temperature cycle performance of lithium-ion batteries first increases and then decreases, and the thickness expansion rate of lithium-ion batteries first decreases and then increases. There is a large trend, and the over-discharge storage performance of lithium-ion batteries has a trend of first decreasing and then increasing. It can be seen that X/Y should not be too large, preferably in the range of 0.01 to 7.5.

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Abstract

本申请提供了电解液、电化学装置和电子装置。电解液包括式I所示化合物：其中，R1和R2各自独立地选自C1-C5基团或经卤素取代的C1-C5基团，m和n各自独立地选自0至3的整数；R3、R4、R5和R6选自经取代或未经取代的亚甲基，其中经取代时，取代基为卤素；R1和R2所代表的结构可以桥接成环。本申请的实施例通过在电解液中采用式I所示化合物，式I所示化合物能在正负极表面形成稳定的界面保护，从而显著改善电化学装置的循环寿命和高温存储性能。

Description

电解液、电化学装置和电子装置 技术领域
本申请涉及电化学储能领域，尤其涉及电解液、电化学装置和电子装置。
背景技术
随着电化学装置(例如，锂离子电池)的在各类电子产品中的广泛应用，用户对于电化学装置的循环性能和存储性能等也提出了越来越高的要求。虽然目前对电化学装置的技术改进能够在一定程度上提升其循环性能和存储性能，但是仍然无法满足越来人们越来越高的使用需求，期待进一步改进。
发明内容
本申请的实施例中提供了一种电解液，该电解液包括式I所示化合物：
Figure PCTCN2021081516-appb-000001
其中，R 1和R 2各自独立地选自C 1-C 5基团或经卤素取代的C1-C5基团，m和n各自独立地选自0至3的整数；R 3、R 4、R 5和R 6选自经取代或未经取代的亚甲基，其中经取代时，取代基为卤素；R 1和R 2所代表的结构可以桥接成环。
在一些实施例中，C 1-C 5基团选自烷烃基、烯烃基、含氧烃基、含硅烃基或氰基取代的烃基或氟取代烷烃基。在一些实施例中，式I所示化合物包括式I-1、式I-2、式I-3、式I-4、式I-5或式I-6中的至少一种：
Figure PCTCN2021081516-appb-000002
在一些实施例中，基于电解液的质量，式I所示化合物的质量含量为0.01％至5％。在一些实施例中，电解液还包括添加剂，添加剂包括乙烯酯类化合物、杂环化合物、磺酸酯类化合物、腈类化合物、含氟锂盐、酸酐类化合物、环状酯类化合物或链状酯类化合物中的至少一种。在一些实施例中，基于电解液的质量，添加剂的质量含量为0.01％至10％。在一些实施例中，添加剂包括碳酸亚乙烯酯(VC)、氟代碳酸乙烯酯(FEC)、乙烯基碳酸乙烯酯(VEC)、1,3-二氧六环、1,4-二氧六环、二氧戊环、1,3-丙烷磺酸内酯(PS)、1,4-丁烷磺酸内酯、硫酸乙烯酯、甲烷二磺酸亚甲酯(MMDS)、丙烯基-1,3-磺酸内酯(PES)、丁二腈、戊二腈、己二腈、2-亚甲基戊二腈、二丙基丙二腈、1,3,6-已烷三腈(HTCN)、1,2,6-已烷三腈、1,3,5-戊烷甲三腈、1,2-双(氰乙氧基)乙烷、乙氧基(五氟)环三磷腈、双三氟甲烷磺酰亚胺锂、双(氟磺酰)亚胺锂、双草酸硼酸锂(LiB(C 2O 4) 2)、二氟草酸硼酸锂、二氟磷酸锂(LiDPF)、四氟硼酸锂、丁二酸酐、戊二酸酐、柠康酸酐、马来酸酐(MA)、甲基琥珀酸酐、2,3-二甲基马来酸酐或三氟甲基马来酸酐中的至少一种。
本申请的一些实施例还提供了一种电化学装置，该电化学装置包括电解液、正极、负极以及设置在正极和负极之间的隔离膜，其中，电解液为上述任一种电解液。在一些实施例中，正极包括具有正极活性材料的正极活性材料层，基于所述电解液的质量，所述式I所示化合物的重量百分比为X％，正极活性材料的比表面积Y m 2/g,Y的取值范围为0.1至1，满足0.01≤X/Y≤7.5。
本申请的实施例还提供了一种电子装置，包括上述电化学装置。
本申请的实施例通过在电解液中采用式I所示化合物，式I所示化合物能在正负极表面形成稳定的界面保护，从而显著改善电化学装置的循环寿命和高温存储性能。
具体实施方式
下面的实施例可以使本领域技术人员更全面地理解本申请，但不以任何方式限制本申请。
电化学装置采用的大多数正极活性材料(例如，锰酸锂)存在容量衰减，尤其是在高温条件下。电解液作为电化学装置的重要材料，在正负极之间起到传递锂离子的作用，是电化学装置获得高能量、大倍率、长循环、高安全等性能的重要保证。本申请提出一种电解液，可以减少电化学装置的高温产气，改善电化学装置的循环性能和存储性能。
在一些实施例中，提供了一种电解液，该电解液包括式I所示化合物：
Figure PCTCN2021081516-appb-000003
其中，R 1和R 2各自独立地选自C 1-C 5基团或经卤素取代的C1-C5基团， m和n各自独立地选自0至3的整数；R 3、R 4、R 5和R 6选自经取代或未经取代的亚甲基，其中经取代时，取代基为卤素；R 1和R 2所代表的结构可以桥接成环。R 1和R 2所代表的结构可以桥接成环表示：R 1和R 2可以直接相连形成桥环或者R 1和R 2不相连。本申请采用的电解液能够在正负极表面形成稳定的界面保护，从而显著改善电化学装置的循环性能和高温存储性能。在首次充电时，式I结构的酸酐类化合物能够优先溶剂氧化分解，在正极表面形成致密稳定的正极电解质界相(CEI)膜，减少电解液与正极接触，从而抑制电解液的催化分解，降低界面阻抗，改善直流电阻(DCR)。另外，式I所示化合物能够在负极表面还原成膜，减少电解液在负极的还原分解。式I所示化合物作为酸酐类添加剂，既可以捕获电解液中的少量的水及HF，又可以在正极、负极形成稳定的保护膜，在持续充放电循环过程中，可以有效地提升电化学装置的循环稳定性以及减缓循环过程中的膨胀。
在一些实施例中，C 1-C 5基团选自烷烃基、烯烃基、含氧烃基、含硅烃基或氰基取代的烃基或氟代烃基。在一些实施例中，式I所示化合物包括式I-1、式I-2、式I-3、式I-4、式I-5或式I-6中的至少一种：
Figure PCTCN2021081516-appb-000004
Figure PCTCN2021081516-appb-000005
应该理解，这仅是示例性的，而不用于限制，还可以包括其他合适结构的化合物。
在一些实施例中，基于电解液的质量，式I所示化合物的质量含量为0.01％至5％。如果式I所示化合物的质量含量太小，则不足以形成良好的界面保护而对电化学装置的改善作用相对有限；如果式I所示化合物的质量含量太大，例如，大于5％，则式I所示化合物对正极界面和负极界面的稳定性的增强作用不再显著提高。
在一些实施例中，电解液还可以包括添加剂，添加剂包括乙烯酯类化合物、杂环化合物、磺酸酯类化合物、腈类化合物、含氟锂盐、酸酐类化合物、环状酯类化合物或链状酯类化合物中的至少一种。在一些实施例中，基于电解液的质量，添加剂的质量含量为0.01％至10％。如果这些添加剂的质量含量太小，则其对电化学装置的改善作用相对有限；如果这些添加剂的质量含量太大，例如，大于10％，则对抑制金属锂与电解液的分解产热的作用不再显著增加。
在一些实施例中，多腈化合物的使用可以降低电解液的粘度和成本。在一些实施例中，环状酯类化合物可以辅助增强负极固态界面膜(SEI)的成膜稳定性。
在一些实施例中，上述添加剂包括碳酸亚乙烯酯(VC)、氟代碳酸乙烯酯(FEC)、乙烯基碳酸乙烯酯(VEC)、1,3-二氧六环、1,4-二氧六环、二氧戊环、1,3-丙烷磺酸内酯(PS)、1,4-丁烷磺酸内酯(BS)、硫酸乙烯酯(DTD)、甲烷二磺酸亚甲酯(MMDS)、丙烯基-1,3-磺酸内酯(PST)、丁二腈、戊二腈、己二腈、2-亚甲基戊二腈、二丙基丙二腈、1,3,6-已烷三腈(HTCN)、 1,2,6-已烷三腈、1,3,5-戊烷甲三腈、1,2-双(氰乙氧基)乙烷、乙氧基(五氟)环三磷腈、双三氟甲烷磺酰亚胺锂(LiTFSI)、双(氟磺酰)亚胺锂(LiFSI)、双草酸硼酸锂LiB(C 2O 4) 2(LiBOB)、二氟草酸硼酸锂(LiDFOB)、二氟磷酸锂(LiDFP)、四氟硼酸锂(LiBF 4)、丁二酸酐、戊二酸酐、柠康酸酐、马来酸酐(MA)、甲基琥珀酸酐、2,3-二甲基马来酸酐或三氟甲基马来酸酐中的至少一种。一方面这些化合物的抗氧化能力较强，在正极处不易被氧化。另一方面，在负极析锂的情况下，这些化合物会在金属锂表面还原，形成一层保护膜，抑制金属锂与电解液的分解产热，进一步增强对负极活性材料的保护。
在一些实施例中，电解液还可以包括其他非水有机溶剂和锂盐。非水有机溶剂可以包含碳酸酯、羧酸酯、醚类或其他非质子溶剂中的至少一种。碳酸酯类溶剂的示例包括碳酸二甲酯、碳酸二乙酯、碳酸甲乙酯、碳酸甲丙酯、碳酸乙丙酯、碳酸二丙酯、碳酸乙烯酯、碳酸丙烯酯、碳酸丁烯酯、二(2,2,2-三氟乙基)碳酸酯等。羧酸酯类溶剂的示例包括乙酸甲酯、乙酸乙酯、乙酸正丙酯、乙酸正丁酯、丙酸甲酯、丙酸乙酯、丙酸丙酯、丙酸丁酯、丁酸甲酯、丁酸乙酯、丁酸丙酯、丁酸丁酯、γ-丁内酯、乙酸2,2-二氟乙酯、戊内酯、丁内酯、2-氟乙酸乙酯、2,2-二氟乙酸乙酯、三氟乙酸乙酯、2,2,3,3,3-五氟丙酸乙酯、2,2,3,3,4,4,4,4-七氟丁酸甲酯、4,4,4-三氟-3-(三氟甲基)丁酸甲酯、2,2,3,3,4,4,5,5,5,5-九氟戊酸乙酯、2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,9-十七氟壬酸甲酯、2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,9-十七氟壬酸乙酯等。醚类溶剂的示例包括乙二醇二甲醚、二乙二醇二甲醚、四乙二醇二甲醚、二丁醚、四氢呋喃、2-甲基四氢呋喃、双(2,2,2-三氟乙基)醚等。
在一些实施例中，本申请的锂盐包括有机锂盐或无机锂盐中的至少一种。在一些实施例中，本申请的锂盐中含有氟元素、硼元素、磷元素中的至少一种。
在一些实施例中，本申请的锂盐包括六氟磷酸锂LiPF 6、二氟磷酸锂LiPO 2F 2、双三氟甲烷磺酰亚胺锂LiN(CF 3SO 2) 2(LiTFSI)、双(氟磺酰)亚胺锂Li(N(SO 2F) 2)(LiFSI)、双草酸硼酸锂LiB(C 2O 4) 2(LiBOB)、二氟草酸硼酸锂LiBF 2(C 2O 4)(LiDFOB)、六氟砷酸锂LiAsF 6、高氯酸锂LiClO 4、三氟甲磺酸锂LiCF 3SO 3中的至少一种。在一些实施例中，本申请的电解液中的锂 盐的浓度为约0.5mol/L至3mol/L、约0.5mol/L至2mol/L、约0.5mol/L至1.5mol/L或约0.8mol/L至1.2mol/L。
本申请的实施例还提供了电化学装置。电化学装置包括电极组件，电极组件包括正极、负极、设置在正极和负极之间的隔离膜以及电解液。在一些实施例中，电解液为以上描述的电解液。
在一些实施例中，负极可以包括负极集流体和设置在负极集流体上的负极活性材料层。负极活性材料层可以设置在负极集流体的一侧或两侧上。在一些实施例中，负极集流体可以采用铜箔、镍箔或碳基集流体中的至少一种。在一些实施例中，负极活性材料层可以包括负极活性材料。在一些实施例中，负极活性材料层中的负极活性材料包括锂金属或硅基材料中的至少一种。在一些实施例中，硅基材料包括硅、硅氧化合物、硅碳化合物或硅合金中的至少一种。
在一些实施例中，负极活性材料层中还可以包括导电剂和/或粘结剂。负极活性材料层中的导电剂可以包括炭黑、乙炔黑、科琴黑、片层石墨、石墨烯、碳纳米管、碳纤维或碳纳米线中的至少一种。在一些实施例中，负极活性材料层中的粘结剂可以包括羧甲基纤维素(CMC)、聚丙烯酸、聚丙烯酸盐、聚丙烯酸酯、聚乙烯基吡咯烷酮、聚苯胺、聚酰亚胺、聚酰胺酰亚胺、聚硅氧烷、丁苯橡胶、环氧树脂、聚酯树脂、聚氨酯树脂或聚芴中的至少一种。应该理解，以上公开的材料仅是示例性，负极活性材料层可以采用任何其他合适的材料。在一些实施例中，负极活性材料层中的负极活性材料、导电剂和粘结剂的质量比可以为(80至99):(0.5至10):(0.5至10)，应该理解，这仅是示例性的，而不用于限制本申请。
在一些实施例中，正极包括正极集流体和设置在正极集流体上的正极活性材料层。正极活性材料层可以位于正极集流体一侧或两侧上。在一些实施例中，正极集流体可以采用铝箔，当然，也可以采用本领域常用的其他正极集流体。在一些实施例中，正极集流体的厚度可以为1μm至200μm。在一些实施例中，正极活性材料层可以仅涂覆在正极集流体的部分区域上。在一些实施例中，正极活性材料层的厚度可以为10μm至500μm。应该理解，这些仅是示例性的，可以采用其他合适的厚度。
在一些实施例中，正极活性材料层包括正极活性材料。在一些实施例中，正极活性材料包括LiCoO 2、LiNiO 2、LiMn 2O 4、LiCo 1-yM yO 2、LiNi 1-yM yO 2、LiMn 2-yM yO 4、LiNi xCo yMn zM 1-x-y-zO 2，其中M选自Fe、Co、Ni、Mn、Mg、Cu、Zn、Al、Sn、B、Ga、Cr、Sr、V或Ti中的至少一种，且0≤y≤1，0≤x≤1，0≤z≤1，x+y+z≤1。在一些实施例中，正极活性材料可以包括钴酸锂、锰酸锂、磷酸铁锂、磷酸锰铁锂、镍钴锰酸锂、镍钴铝酸锂或镍锰酸锂中的至少一种，上述正极活性材料可以经过掺杂和/或包覆处理。
在一些实施例中，正极活性材料层还包括粘结剂和导电剂。在一些实施例中，正极活性材料层中的粘结剂可以包括聚偏氟乙烯、偏氟乙烯-六氟丙烯的共聚物、苯乙烯-丙烯酸酯共聚物、苯乙烯-丁二烯共聚物、聚酰胺、聚丙烯腈、聚丙烯酸酯、聚丙烯酸、聚丙烯酸盐、羧甲基纤维素钠、聚醋酸乙烯酯、聚乙烯呲咯烷酮、聚乙烯醚、聚甲基丙烯酸甲酯、聚四氟乙烯或聚六氟丙烯中的至少一种。在一些实施例中，正极活性材料层中的导电剂可以包括导电炭黑、乙炔黑、科琴黑、片层石墨、石墨烯、碳纳米管或碳纤维中的至少一种。在一些实施例中，正极活性材料层中的正极活性材料、导电剂和粘结剂的质量比可以为(70至98):(1至15):(1至15)。应该理解，以上所述仅是示例，正极活性材料层可以采用任何其他合适的材料、厚度和质量比。
在一些实施例中，基于所述电解液的质量，所述式I所示化合物的重量百分比为X％，正极活性材料的比表面积Y m 2/g，Y的取值范围为0.1至1，满足0.01≤X/Y≤7.5。通过使X/Y在上述范围内，可以有效地改善锂离子电池的高温循环性能并减少存储产气，这主要是因为电解液中的式I所示化合物可以形成良好的界面保护且较少地增加阻抗。在合适的X/Y及电解液作用下，可获得较好的锂离子电池性能。而在X/Y过大时，式I所示化合物的比例过高，成膜阻抗较大，进而导致锂离子电池阻抗增加，影响锂离子电池性能。
在一些实施例中，隔离膜包括聚乙烯、聚丙烯、聚偏氟乙烯、聚对苯二甲酸乙二醇酯、聚酰亚胺或芳纶中的至少一种。例如，聚乙烯包括选自高密度聚乙烯、低密度聚乙烯或超高分子量聚乙烯中的至少一种。尤其是聚乙烯和聚丙烯，它们对防止短路具有良好的作用，并可以通过关断效应 改善电池的稳定性。在一些实施例中，隔离膜的厚度在约3μm至500μm的范围内。
在一些实施例中，隔离膜表面还可以包括多孔层，多孔层设置在隔离膜的至少一个表面上，多孔层包括无机颗粒或粘结剂中的至少一种，无机颗粒选自氧化铝(Al 2O 3)、氧化硅(SiO 2)、氧化镁(MgO)、氧化钛(TiO 2)、二氧化铪(HfO 2)、氧化锡(SnO 2)、二氧化铈(CeO 2)、氧化镍(NiO)、氧化锌(ZnO)、氧化钙(CaO)、氧化锆(ZrO 2)、氧化钇(Y 2O 3)、碳化硅(SiC)、勃姆石、氢氧化铝、氢氧化镁、氢氧化钙或硫酸钡中的至少一种。在一些实施例中，隔离膜的孔具有在约0.01μm至1μm的范围的直径。多孔层的粘结剂选自聚偏氟乙烯、偏氟乙烯-六氟丙烯的共聚物、聚酰胺、聚丙烯腈、聚丙烯酸酯、聚丙烯酸、聚丙烯酸盐、羧甲基纤维素钠、聚乙烯呲咯烷酮、聚乙烯醚、聚甲基丙烯酸甲酯、聚四氟乙烯或聚六氟丙烯中的至少一种。隔离膜表面的多孔层可以提升隔离膜的耐热性能、抗氧化性能和电解质浸润性能，增强隔离膜与极片之间的粘接性。
在本申请的一些实施例中，电化学装置的电极组件为卷绕式电极组件或堆叠式电极组件。在一些实施例中，电化学装置为锂离子电池，但是本申请不限于此。
在本申请的一些实施例中，以锂离子电池为例，将正极、隔离膜、负极按顺序卷绕或堆叠成电极组件，之后装入例如铝塑膜壳体中进行封装，注入电解液，化成、封装，即制成锂离子电池。然后，对制备的锂离子电池进行性能测试。
本领域的技术人员将理解，以上描述的电化学装置(例如，锂离子电池)的制备方法仅是实施例。在不背离本申请公开的内容的基础上，可以采用本领域常用的其他方法。
本申请的实施例还提供了包括上述电化学装置的电子装置。本申请实施例的电子装置没有特别限定，其可以是用于现有技术中已知的任何电子装置。在一些实施例中，电子装置可以包括，但不限于，笔记本电脑、笔输入型计算机、移动电脑、电子书播放器、便携式电话、便携式传真机、便携式复印机、便携式打印机、头戴式立体声耳机、录像机、液晶电视、 手提式清洁器、便携CD机、迷你光盘、收发机、电子记事本、计算器、存储卡、便携式录音机、收音机、备用电源、电机、汽车、摩托车、助力自行车、自行车、照明器具、玩具、游戏机、钟表、电动工具、闪光灯、照相机、家庭用大型蓄电池和锂离子电容器等。
下面列举了一些具体实施例和对比例以更好地对本申请进行说明，其中，采用锂离子电池作为示例。
实施例1
正极的制备：将正极活性材料锰酸锂LiMn 2O 4、导电剂导电炭黑、粘结剂聚偏氟二乙烯(PVDF)按重量比96：2：2的比例溶于N-甲基吡咯烷酮(NMP)溶液中，形成正极浆料。采用13μm的铝箔作为正极集流体，将正极浆料涂覆于正极集流体上，涂覆量为18.37mg/cm 2，经过干燥、冷压、裁切后得到正极。
负极的制备：将负极活性材料人造石墨、导电剂导电炭黑、粘结剂丁苯橡胶(SBR)、增稠剂羧甲基纤维素钠(CMC)按重量比96.4：1.5：1.6：0.5的比例溶于去离子水中，形成负极浆料。采用10μm厚度铜箔作为负极集流体，将负极浆料涂覆于负极集流体上，涂覆量为9.3mg/cm 2，干燥、冷压、裁切后得到负极。
隔离膜的制备：隔离膜采用16μm厚的聚乙烯(PE)隔离膜。
电解液的制备：在含水量小于10ppm的环境下，将碳酸乙烯酯(EC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)按照3：5：2的质量比混合均匀，接着加入添加成分，再将锂盐LiPF 6(终浓度为1mol/L)溶解于上述非水溶剂，得到电解液。实施例1中添加成分为化合物I-1，在电解液中的质量含量为0.1％。
锂离子电池的制备：将正极、隔离膜、负极按顺序依次叠好，使隔离膜处于正极和负极中间起到隔离的作用，并卷绕得到电极组件。将电极组件置于外包装铝塑膜中，在80℃下脱去水分后，注入上述电解液并封装，经过化成(0.02C恒流充电到3.3V，再以0.1C恒流充电到3.6V)，脱气，切边等工艺流程得到锂离子电池(厚度3.3mm、宽度39mm、长度96mm)。
其余实施例和对比例是在实施例1步骤的基础上进行参数变更，具体变更的参数如下表所示。
在对比例1中，电解液中未添加其他添加成分。在对比例2中，仅添加了3％的PS，而没有添加式I所示化合物。在实施例2至7中，式I-1化合物的添加量与实施例1不同。在实施例8至18中，添加的式I所示化合物的种类与实施例1不同。在实施例19至34中，除了添加式I-1所示化合物之外，还添加了其他添加剂，其中实施例19至34中式I-1所示化合物的质量含量为1％。在实施例35至41和对比例3中，式I所示化合物的含量和正极活性材料的比表面积与实施例1不同。下面描述本申请的各个参数的测试方法。
45℃循环性能测试：
将锂离子电池置于45℃恒温箱中，静置30分钟，使锂离子电池达到恒温后测试电池初始厚度。将达到恒温的锂离子电池以0.5C恒流充电至电压为4.2V，然后以4.2V恒压充电至电流为0.05C，接着以1C恒流放电至电压为3.0V，此为一个充放电循环。以首次放电的容量为100％，反复进行充放电循环500次，停止测试，记录循环容量保持率，同时测量电池厚度，以容量保持率及厚度膨胀率作为评价锂离子电池循环性能的指标。
循环容量保持率＝循环至500次时的容量/首次放电时的容量×100％。
按下式计算锂离子电池的厚度膨胀率：
厚度膨胀率＝(循环500次后的电池厚度-电池初始厚度)/电池初始厚度×100％。
过放存储性能测试：
将锂离子电池置于25℃恒温箱，静置30分钟，使锂离子电池达到恒温后测试电池初始厚度。然后以0.5C恒流放电至3.0V，静置30分钟，继续以0.1C放电至3.0V，最后以0.01C放电至1.0V。将放电后锂离子电池置于60℃恒温箱中，存储观察并测试电池厚度变化情况。以厚度膨胀率作为评价锂离子电池过放存储性能的指标。厚度膨胀率＝(存储60天电池厚度-电池初始厚度)/电池初始厚度×100％。
表1示出了对比例1、实施例1至18的各个参数和评估结果。
表1
Figure PCTCN2021081516-appb-000006
表1中，所有实施例正极活性材料的比表面积为0.5m 2/g。通过对比例1、实施例1至18可知，电解液中的式I所示化合物的添加可以改善电化学装置的循环性能、厚度膨胀率和过放存储性能。通过比较实施例1至7可知，随着式I所示化合物的含量的增加，循环性能、厚度膨胀率和过放存储性能的改善程度先增加，然后减弱。由实施例8至18可知，其他一些化合物Ⅰ-2、Ⅰ-3、Ⅰ-4、Ⅰ-5、Ⅰ-6在电化学装置的循环性能、厚度膨胀率和过放存储性能方面也表现出不同层次的改善，这是由于，式I所示化合物可以吸附电解液中的少量的水及HF，增加了电解液的稳定性；同时易于氧化并在正极形成致密的保护膜，减少电解液对正极的破坏；且在首次充放电时优先在负极还原成膜，成膜致密，抑制了电解液在负极的分解反应。实施例1至14筛选了式I所示化合物的最佳添加量为1％，主要是因为既能有效地稳定电解液，又能够同时在正负极形成优异的界面保护，过高的比例成膜阻抗较大，进而导致锂离子电池阻抗增加，会影响锂离子电池性能； 过低的比例则不足以形成好的界面保护，改善锂离子电池的循环性能的作用有限。
表2示出了实施例4和19至34以及对比例1至2的各个参数和评估结果。
表2
Figure PCTCN2021081516-appb-000007
表2中，所有实施例正极活性材料的比表面积为0.5m 2/g。通过比较实施例4和对比例1或比较实施例22和对比例2可知，相对于未添加式I所示化合物的实施例，在添加式I所示化合物之后，电化学装置的循环性能、厚度膨胀率和过放存储性能得到显著改善。通过比较实施例19至28与实施例4可以看出，在含有式I-1所示化合物的电解液中加入常规添加剂PS或者VC后，其中，基于电解液的质量，式I-1所示化合物的质量含量均为1％，提升了锂离子电池的循环性能，同时改善了锂离子电池的厚度膨胀率和过放存储 性能。这主要是因为额外的添加剂不仅可在负极成膜修饰由式I所示化合物形成的SEI，同时在正极形成优异的界面保护膜，缓解电解液在正极、负极的副反应。过高的PS、VC加入并未带来性能的显著提升，主要是因为成膜阻抗过大造成的，而过少的PS、VC加入也未带来电池性能的提升，来自于成膜不充分。因此，联合使用合适含量的上述添加剂，可以进一步改善锂离子电池的循环性能、厚度膨胀率和过放存储性能。由实施例29至实施例34可以看出，验证的其他常用添加剂(如LiDFP,HTCN,MA,FEC)也能够显著提升电池的循环性能及过放存储性能，主要原因同PS、VC。
表3示出了实施例35至41和对比例3的各个参数和评估结果。
表3
Figure PCTCN2021081516-appb-000008
通过比较实施例35至41和对比例3可以得知，当式I所示化合物的含量X％与正极活性材料的比表面积Y m 2/g的比值(X/Y)过大时，例如，为10时，锂离子电池的循环性能、厚度膨胀率和过放存储性能降低。另外，当X/Y在0.1至6的范围内时，可以有效地改善锂离子电池的高温循环性能并减少存储产气，这主要是因为电解液中的式I所示化合物可以形成良好的界面保护且较少地增加阻抗。在合适的X/Y及电解液作用下，可获得较好的锂离子电池性能。此外，当X/Y在0.1至6的范围内时，随着比值的增大，锂离子电池的高温循环性能存在先提升后降低的趋势，锂离子电池的厚度膨胀 率存在先减小后增大的趋势，并且锂离子电池的过放存储性能存在先减小后增大的趋势。由此可知，X/Y不宜过大，优选地在0.01至7.5的范围内。
以上描述仅为本申请的较佳实施例以及对所运用技术原理的说明。本领域技术人员应当理解，本申请中所涉及的公开范围，并不限于上述技术特征的特定组合而成的技术方案，同时也应涵盖由上述技术特征或其等同特征进行任意组合而形成的其它技术方案。例如上述特征与本申请中公开的具有类似功能的技术特征进行互相替换而形成的技术方案。

Claims (10)

  1. 一种电解液，其包括式I所示化合物：
    Figure PCTCN2021081516-appb-100001
    其中，R 1和R 2各自独立地选自C 1-C 5基团或经卤素取代的C1-C5基团，m和n各自独立地选自0至3的整数；R 3、R 4、R 5和R 6选自经取代或未经取代的亚甲基，其中，经取代时，取代基为卤素；R 1和R 2所代表的结构可以桥接成环。
  2. 根据权利要求1所述的电解液，其中，所述C 1-C 5基团选自烃基、卤代烃基、含氧烃基、含硅烃基或氰基取代的烃基。
  3. 根据权利要求1所述的电解液，其中，所述式I所示化合物包括式I-1、式I-2、式I-3、式I-4、式I-5或式I-6中的至少一种：
    Figure PCTCN2021081516-appb-100002
    Figure PCTCN2021081516-appb-100003
  4. 根据权利要求1所述的电解液，其中，基于所述电解液的质量，所述式I所示化合物的质量含量为0.01％至5％。
  5. 根据权利要求1所述的电解液，其中，所述电解液还包括添加剂，所述添加剂包括乙烯酯类化合物、杂环化合物、磺酸酯类化合物、腈类化合物、含氟锂盐、酸酐类化合物、环状酯类化合物或链状酯类化合物中的至少一种。
  6. 根据权利要求5所述的电解液，其中，基于所述电解液的质量，所述添加剂的质量含量为0.01％至10％。
  7. 根据权利要求5所述的电解液，其中，所述添加剂包括碳酸亚乙烯酯、氟代碳酸乙烯酯、乙烯基碳酸乙烯酯、1,3-二氧六环、1,4-二氧六环、二氧戊环、1,3-丙烷磺酸内酯、1,4-丁烷磺酸内酯、硫酸乙烯酯、甲烷二磺酸亚甲酯、丙烯基-1,3-磺酸内酯、丁二腈、戊二腈、己二腈、2-亚甲基戊二腈、二丙基丙二腈、1,3,6-已烷三腈、1,2,6-已烷三腈、1,3,5-戊烷甲三腈、1,2-双(氰乙氧基)乙烷、乙氧基(五氟)环三磷腈、双三氟甲烷磺酰亚胺锂、双(氟磺酰)亚胺锂、双草酸硼酸锂、二氟草酸硼酸锂、二氟磷酸锂、四氟硼酸锂、丁二酸酐、戊二酸酐、柠康酸酐、马来酸酐、甲基琥珀酸酐、2,3-二甲基马来酸酐或三氟甲基马来酸酐中的至少一种。
  8. 一种电化学装置，其包括电解液、正极、负极以及设置在所述正极和所述负极之间的隔离膜，其中，所述电解液为根据权利要求1至7中任一项所述的电解液。
  9. 根据权利要求8所述的电化学装置，其中，所述正极包括具有正极活性材料的正极活性材料层，基于所述电解液的质量，所述式I所示化合物的 重量百分比为X％，所述正极活性材料的比表面积Y m 2/g，Y的取值范围为0.1至1，满足0.01≤X/Y≤7.5。
  10. 一种电子装置，包括根据权利要求8或9所述的电化学装置。
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