WO2023236509A1 - 一种电解液及其制备方法、锂离子电池 - Google Patents

一种电解液及其制备方法、锂离子电池 Download PDF

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WO2023236509A1
WO2023236509A1 PCT/CN2022/141936 CN2022141936W WO2023236509A1 WO 2023236509 A1 WO2023236509 A1 WO 2023236509A1 CN 2022141936 W CN2022141936 W CN 2022141936W WO 2023236509 A1 WO2023236509 A1 WO 2023236509A1
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lithium
electrolyte
lithium salt
film
solvent
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PCT/CN2022/141936
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English (en)
French (fr)
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刘世琦
刘建文
何思聪
王石泉
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湖北万润新能源科技股份有限公司
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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
    • H01M10/0568—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
    • H01M10/052—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
    • H01M10/0567—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
    • H01M10/056—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
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0025—Organic electrolyte
    • H01M2300/0028—Organic electrolyte characterised by the solvent
    • H01M2300/0037—Mixture of solvents

Definitions

  • the present invention relates to the technical field of lithium electronic batteries, and specifically to an electrolyte solution and a preparation method thereof, and a lithium ion battery.
  • Lithium-ion batteries have the advantages of high voltage, high energy density, multiple cycles and green environmental protection.
  • lithium-ion batteries have been widely used in electronic equipment such as mobile phones, laptops, and smart robots, as well as in aerospace, ships, military facilities and other fields.
  • lithium-ion batteries are also widely used as power batteries in electric vehicles.
  • Carbonate solvent is a commonly used electrolyte solvent for lithium-ion batteries. It has the advantages of high conductivity, low cost, and good compatibility with electrodes. However, in high-voltage battery systems, carbonate solvents are extremely easy to decompose. The by-products of the oxidative decomposition of the solvent will be deposited on the electrode surface, greatly increasing the battery impedance and reducing battery performance.
  • the first object of the present invention is to provide an electrolyte that can form an excellent SEI film (solid electrolyte interface) by using a specific type of first lithium salt, inhibit excessive decomposition of the electrolyte solvent, and is beneficial to Intercalation and extraction of lithium ions; by introducing the second lithium salt and using it in conjunction with the first lithium salt, it can participate in SEI film formation while passivating the aluminum foil. Therefore, the electrolyte has high conductivity at low temperatures, and the battery produced has good cycle performance at high voltages. Moreover, by introducing film-forming additives, the present invention can further improve the cycle performance of the lithium-ion battery at high voltage and the conductivity of the electrolyte at low temperatures.
  • the second object of the present invention is to provide a method for preparing an electrolyte, which has the advantages of simple operation, mild conditions, short process flow, and is suitable for mass production.
  • the third object of the present invention is to provide a lithium-ion battery that has both high electrical performance and low-temperature performance.
  • the invention provides an electrolyte, including lithium salt, organic solvent and film-forming additives;
  • the lithium salt includes a first lithium salt and a second lithium salt
  • the first lithium salt includes lithium bistrifluoromethanesulfonyl imide (LiTFSI) and/or lithium bisfluorosulfonyl imide (LiFSI).
  • LiTFSI lithium bistrifluoromethanesulfonyl imide
  • LiFSI lithium bisfluorosulfonyl imide
  • the second lithium salt includes lithium difluoroborate (LiODFB), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ) and lithium bisoxaloborate (LiBOB, also known as lithium dioxalate borate, At least one of lithium dioxalate borate).
  • LiODFB lithium difluoroborate
  • LiBF 4 lithium tetrafluoroborate
  • LiClO 4 lithium perchlorate
  • LiBOB lithium bisoxaloborate
  • the electrolyte provided by the present invention can improve the cycle performance of lithium-ion batteries at high voltage and the conductivity of the electrolyte at low temperatures by using specific types of lithium salts and introducing film-forming additives.
  • the first lithium salt provided by the present invention has a high solubility and can be formulated into a high-concentration electrolyte.
  • high-concentration electrolytes can form an excellent SEI film, mainly due to the decomposition of lithium salts, which can inhibit excessive decomposition of the electrolyte solvent.
  • the SEI film formed by high-concentration electrolyte is mainly lithium-rich compounds and has high conductivity, which is conducive to the insertion and extraction of lithium ions.
  • the present invention can effectively passivate the aluminum foil and prevent the first lithium salt from corroding the aluminum foil under high voltage; and the second lithium salt partially participates in SEI film formation, which can Further improve battery performance.
  • the present invention adds film-forming additives to the electrolyte, which can form an excellent interface protective film on the electrode surface to avoid side reactions between the solvent and the electrode material surface, thereby improving the high-voltage cycle performance of the battery.
  • the second lithium salt includes at least two of lithium difluoroborate, lithium tetrafluoroborate and lithium bisoxaloborate.
  • the molar concentration of the first lithium salt in the electrolyte is 0.8-4mol/L, including but not limited to 0.9mol/L, 1mol/L, 1.2mol/L, 1.4mol/L, 1.5mol /L, 1.8mol/L, 2mol/L, 2.2mol/L, 2.4mol/L, 2.6mol/L, 2.8mol/L, 3mol/L, 3.2mol/L, 3.4mol/L, 3.6mol/L , 3.8 mol/L, or any range value between the two.
  • Using a molar concentration within this range is beneficial to further improving the cycle performance of lithium-ion batteries at high voltages and the conductivity of the electrolyte at low temperatures.
  • the molar concentration of the first lithium salt in the electrolyte is 1 ⁇ 3 mol/L.
  • the molar concentration of the second lithium salt in the electrolyte is 0.05-0.7mol/L, including but not limited to 0.07mol/L, 0.09mol/L, 0.1mol/L, 0.2mol/L, The point value of any one of 0.3mol/L, 0.4mol/L, 0.5mol/L, and 0.6mol/L or the range value between any two.
  • Using a molar concentration within this range is beneficial to further improving the cycle performance of lithium-ion batteries at high voltages and the conductivity of the electrolyte at low temperatures.
  • the molar concentration of the second lithium salt in the electrolyte is 0.1 ⁇ 0.5 mol/L.
  • the film-forming additives include lithium difluorophosphate (LiPO 2 F 2 ), vinylene carbonate (VC, also known as 1,3-dioxol-2-one, ethylene carbonate), sulfuric acid At least one of vinyl ester (DTD), dimethyl sulfate (DMS), butylene sulfite (BS) and fluoroethylene carbonate (FEC).
  • LiPO 2 F 2 lithium difluorophosphate
  • VC vinylene carbonate
  • S dimethyl sulfate
  • BS butylene sulfite
  • FEC fluoroethylene carbonate
  • Film-forming additives can form an excellent interface protective film on the electrode surface to avoid side reactions between the solvent and the electrode material surface.
  • the film-forming additives include lithium difluorophosphate (LiPO 2 F 2 ), vinylene carbonate (VC, also known as 1,3-dioxol-2-one , ethylene carbonate), vinyl sulfate (DTD), dimethyl sulfate (DMS), butylene sulfite (BS) and fluoroethylene carbonate (FEC).
  • LiPO 2 F 2 lithium difluorophosphate
  • VC vinylene carbonate
  • DTD vinyl sulfate
  • DMS dimethyl sulfate
  • BS butylene sulfite
  • FEC fluoroethylene carbonate
  • the mass fraction of the film-forming additive in the electrolyte is 0.1% to 6%; including but not limited to 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9 A point value of any one of %, 1%, 1.5%, 2%, 3%, 3.5%, 4%, 5%, 5.5% or a range value between any two.
  • film-forming additives in the above dosage range will help further improve the high-voltage cycle performance of lithium-ion batteries.
  • the mass fraction of the film-forming additive in the electrolyte is 0.5% to 5%.
  • the organic solvent includes ether solvents and/or nitrile solvents.
  • Ether solvents have good compatibility with lithium anodes and carbon anodes, and are not prone to side reactions with the anode.
  • Nitrile solvents have high electrical conductivity and can significantly improve the shuttle ability of lithium ions in the electrolyte solvent. At the same time, nitrile solvents have high oxidation resistance. The cyano functional group of nitrile solvents can form a stable complex with the metal ions of the positive electrode, thereby improving the high-pressure stability of the positive electrode.
  • the organic solvent includes a mixture of the ether solvent and the nitrile solvent, and the mass ratio of the ether solvent to the nitrile solvent is 1 to 3:1.
  • the mass ratio of the ether solvent and the nitrile solvent may be 1:1, or 2:1, or 3:1.
  • the ether solvent includes at least one of ethylene glycol dimethyl ether, tetrahydrofuran and dioxolane (also known as 1,3-dioxolane).
  • ethylene glycol dimethyl ether solvent has good compatibility with lithium negative electrode and carbon negative electrode, and is not prone to side reactions with the negative electrode.
  • the nitrile solvent includes at least one, more preferably at least two, of acetonitrile, butyronitrile, succinonitrile, glutaronitrile and adiponitrile.
  • the present invention also provides a method for preparing the electrolyte as described above, which includes the following steps:
  • the preparation method has the advantages of simple operation, convenience, mild conditions, short process flow, and is suitable for mass production.
  • the mixing is performed in an argon-filled glove box.
  • the organic solvent undergoes dehydration and purification. So that the prepared electrolyte does not contain water.
  • the preparation method includes the following steps:
  • the first lithium salt, the second lithium salt and the film-forming additive are added thereto in sequence, and the electrolyte solution is obtained after mixing.
  • the preparation method of the electrolyte specifically includes the following steps: in a glove box filled with argon gas, the ether solvent and the nitrile solvent after dehydration and purification are mixed in proportion (formulation ratio) and mix evenly to obtain a mixed solvent; then, add the first lithium salt therein, and after the first lithium salt is completely dissolved, add the second lithium salt; after the first lithium salt and the second lithium salt are both completely dissolved, Then add a film-forming additive thereto, and after mixing evenly, obtain the electrolyte solution.
  • the present invention also provides a lithium ion battery, including the electrolyte solution as described above, or the electrolyte solution prepared by the electrolyte solution preparation method as described above.
  • the lithium-ion battery has good cycle performance at high voltage and higher energy density; and the electrolyte in the lithium-ion battery has good conductivity at low temperatures and has a high capacity retention rate.
  • the electrolyte provided by the present invention can be formulated into a high-concentration electrolyte by introducing a first lithium salt with high solubility.
  • the high-concentration electrolyte can form an excellent SEI film and can inhibit excessive decomposition of the electrolyte solvent.
  • the SEI film formed by high-concentration electrolyte is mainly lithium-rich compounds and has high conductivity, which is conducive to the insertion and extraction of lithium ions.
  • the electrolyte provided by the present invention can effectively passivate the aluminum foil by introducing a specific type of second lithium salt to be used in conjunction with the first lithium salt, and prevent the first lithium salt from corroding the aluminum foil at high voltage; and, the second Lithium salt participates in SEI film formation, which can further improve battery performance.
  • the electrolyte provided by the present invention can form an excellent interface protective film on the electrode surface by introducing specific types of film-forming additives to avoid side reactions between the solvent and the electrode material surface, thereby improving the high voltage cycle performance of the battery. .
  • the specific type of ether solvent in the electrolyte provided by the present invention has good compatibility with the lithium negative electrode and the carbon negative electrode, and is not prone to side reactions with the negative electrode.
  • the specific type of nitrile solvent in the electrolyte provided by the present invention has high conductivity and can significantly improve the shuttle ability of lithium ions in the electrolyte solvent.
  • nitrile solvents have high oxidation resistance.
  • the cyano functional group of nitrile solvents can form a stable complex with the metal ions of the positive electrode, thus improving the high-voltage stability of lithium-ion batteries.
  • the lithium-ion battery provided by the present invention has the advantages of high energy density and high capacity retention rate.
  • Figure 1 is a comparison chart of battery cycle performance provided by the present invention.
  • the electrolyte provided in this embodiment is composed of lithium salt, organic solvent and film-forming additives.
  • the lithium salt consists of a first lithium salt and a second lithium salt.
  • the first lithium salt is lithium bistrifluoromethanesulfonimide (LiTFSI)
  • the second lithium salt is lithium difluoroxalateborate (LiODFB).
  • the organic solvent consists of an ether solvent and a nitrile solvent with a mass ratio of 3:1.
  • the ether solvent is ethylene glycol dimethyl ether and the nitrile solvent is acetonitrile.
  • the film-forming additive is lithium difluorophosphate (LiPO 2 F 2 ).
  • the molar concentration of the first lithium salt in the electrolyte solution is 1 mol/L.
  • the molar concentration of the second lithium salt in the electrolyte solution is 0.1 mol/L.
  • the mass fraction of the film-forming additive in the electrolyte is 0.5%.
  • the preparation method of the electrolyte provided in this embodiment includes the following steps: in a glove box filled with argon, mix the ether solvent and the nitrile solvent after dehydration and purification evenly according to the above ratio to obtain a mixed solvent; then, Add the first lithium salt to it, wait until the first lithium salt is completely dissolved, then add the second lithium salt; wait until both the first lithium salt and the second lithium salt are completely dissolved, then add a film-forming additive to it, and mix evenly , get the electrolyte.
  • the electrolyte provided in this embodiment is composed of lithium salt, organic solvent and film-forming additives.
  • the lithium salt consists of a first lithium salt and a second lithium salt.
  • the first lithium salt is lithium bistrifluoromethanesulfonimide (LiTFSI)
  • the second lithium salt is lithium difluoroxalateborate (LiODFB).
  • the organic solvent consists of an ether solvent and a nitrile solvent with a mass ratio of 3:1.
  • the ether solvent is ethylene glycol dimethyl ether and the nitrile solvent is butyronitrile.
  • the film-forming additive is lithium difluorophosphate (LiPO 2 F 2 ).
  • the molar concentration of the first lithium salt in the electrolyte solution is 1 mol/L.
  • the molar concentration of the second lithium salt in the electrolyte solution is 0.1 mol/L.
  • the mass fraction of the film-forming additive in the electrolyte is 0.5%.
  • the preparation method of the electrolyte provided in this embodiment is the same as that in Embodiment 1.
  • the electrolyte provided in this embodiment is composed of lithium salt, organic solvent and film-forming additives.
  • the lithium salt consists of a first lithium salt and a second lithium salt.
  • the first lithium salt is lithium bistrifluoromethanesulfonimide (LiTFSI)
  • the second lithium salt is lithium difluoroxalateborate (LiODFB).
  • the organic solvent consists of an ether solvent and a nitrile solvent with a mass ratio of 3:1.
  • the ether solvent is ethylene glycol dimethyl ether and the nitrile solvent is adiponitrile.
  • the film-forming additive is lithium difluorophosphate (LiPO 2 F 2 ).
  • the molar concentration of the first lithium salt in the electrolyte solution is 1 mol/L.
  • the molar concentration of the second lithium salt in the electrolyte solution is 0.1 mol/L.
  • the mass fraction of the film-forming additive in the electrolyte is 0.5%.
  • the preparation method of the electrolyte provided in this embodiment is the same as that in Embodiment 1.
  • the electrolyte provided in this embodiment is composed of lithium salt, organic solvent and film-forming additives.
  • the lithium salt consists of a first lithium salt and a second lithium salt.
  • the first lithium salt is lithium bistrifluoromethanesulfonimide (LiTFSI)
  • the second lithium salt is lithium difluoroxalateborate (LiODFB).
  • the organic solvent consists of an ether solvent and a nitrile solvent with a mass ratio of 1:1.
  • the ether solvent is ethylene glycol dimethyl ether and the nitrile solvent is butyronitrile.
  • the film-forming additive is lithium difluorophosphate (LiPO 2 F 2 ).
  • the molar concentration of the first lithium salt in the electrolyte solution is 1 mol/L.
  • the molar concentration of the second lithium salt in the electrolyte solution is 0.1 mol/L.
  • the mass fraction of the film-forming additive in the electrolyte is 0.5%.
  • the preparation method of the electrolyte provided in this embodiment is the same as that in Embodiment 1.
  • the electrolyte provided in this embodiment is composed of lithium salt, organic solvent and film-forming additives.
  • the lithium salt consists of a first lithium salt and a second lithium salt.
  • the first lithium salt is lithium bistrifluoromethanesulfonimide (LiTFSI)
  • the second lithium salt is lithium tetrafluoroborate (LiBF 4 ).
  • the organic solvent consists of an ether solvent and a nitrile solvent with a mass ratio of 3:1.
  • the ether solvent is ethylene glycol dimethyl ether and the nitrile solvent is butyronitrile.
  • the film-forming additive is lithium difluorophosphate (LiPO 2 F 2 ).
  • the molar concentration of the first lithium salt in the electrolyte solution is 1 mol/L.
  • the molar concentration of the second lithium salt in the electrolyte solution is 0.1 mol/L.
  • the mass fraction of the film-forming additive in the electrolyte is 0.5%.
  • the preparation method of the electrolyte provided in this embodiment is the same as that in Embodiment 1.
  • composition of the electrolyte provided in this embodiment is basically the same as that in Example 5. The only difference is that lithium tetrafluoroborate is replaced by lithium bisoxaloborate (LiBOB) (but its dosage remains unchanged, that is, the second lithium in the electrolyte The molar concentration of the salt is still 0.1mol/L).
  • the preparation method of the electrolyte provided in this embodiment is the same as that in Embodiment 1.
  • the electrolyte provided in this embodiment is composed of lithium salt, organic solvent and film-forming additives.
  • the lithium salt consists of a first lithium salt and a second lithium salt.
  • the first lithium salt is lithium bistrifluoromethanesulfonyl imide (LiTFSI)
  • the second lithium salt is lithium difluoroxalate borate (LiODFB).
  • the organic solvent consists of an ether solvent and a nitrile solvent with a mass ratio of 3:1.
  • the ether solvent is ethylene glycol dimethyl ether and the nitrile solvent is butyronitrile.
  • the film-forming additive is vinylene carbonate (VC).
  • the molar concentration of the first lithium salt in the electrolyte solution is 1 mol/L.
  • the molar concentration of the second lithium salt in the electrolyte solution is 0.1 mol/L.
  • the mass fraction of the film-forming additive in the electrolyte is 5%.
  • the preparation method of the electrolyte provided in this embodiment is the same as that in Embodiment 1.
  • composition of the electrolyte provided in this embodiment is basically the same as that in Example 7. The only difference is that vinylene carbonate is replaced by fluoroethylene carbonate (FEC) (but its dosage is kept unchanged, that is, the film formation in the electrolyte is The mass fraction of additives is still 5%).
  • FEC fluoroethylene carbonate
  • the preparation method of the electrolyte provided in this embodiment is the same as that in Embodiment 1.
  • the electrolyte provided in this embodiment is composed of lithium salt, organic solvent and film-forming additives.
  • the lithium salt consists of a first lithium salt and a second lithium salt.
  • the first lithium salt is lithium bistrifluoromethanesulfonimide (LiTFSI)
  • the second lithium salt is lithium difluoroxalateborate (LiODFB).
  • the organic solvent consists of an ether solvent and a nitrile solvent with a mass ratio of 3:1.
  • the ether solvent is ethylene glycol dimethyl ether and the nitrile solvent is butyronitrile.
  • the film-forming additive is fluoroethylene carbonate (FEC).
  • the molar concentration of the first lithium salt in the electrolyte solution is 2 mol/L.
  • the molar concentration of the second lithium salt in the electrolyte solution is 0.5 mol/L.
  • the mass fraction of the film-forming additive in the electrolyte is 5%.
  • the preparation method of the electrolyte provided in this embodiment is the same as that in Embodiment 1.
  • composition of the electrolyte provided in this embodiment is basically the same as that in Embodiment 9. The only difference is that the molar concentration of the first lithium salt in the electrolyte is replaced with 3 mol/L.
  • the preparation method of the electrolyte provided in this embodiment is the same as that in Embodiment 1.
  • the electrolyte provided in this embodiment is composed of lithium salt, organic solvent and film-forming additives.
  • the molar concentration of the first lithium salt in the electrolyte solution is 2.5 mol/L.
  • the molar concentration of the second lithium salt in the electrolyte solution is 0.3 mol/L.
  • the mass fraction of the film-forming additive in the electrolyte is 3%.
  • the preparation method of the electrolyte provided in this embodiment is the same as that in Embodiment 1.
  • the electrolyte provided in this embodiment is composed of lithium salt, organic solvent and film-forming additives.
  • the molar concentration of the first lithium salt in the electrolyte solution is 1.5 mol/L.
  • the molar concentration of the second lithium salt in the electrolyte solution is 0.2 mol/L.
  • the mass fraction of the film-forming additive in the electrolyte is 4%.
  • the preparation method of the electrolyte provided in this embodiment is the same as that in Embodiment 1.
  • the electrolyte provided in this comparative example is composed of lithium salt and organic solvent.
  • the lithium salt is lithium hexafluorophosphate (LiPF 6 ).
  • the organic solvent consists of ethylene carbonate, dimethyl carbonate and diethyl carbonate with a mass ratio of 1:1:1.
  • the molar concentration of lithium salt (lithium hexafluorophosphate) in this electrolyte solution is 1 mol/L.
  • the preparation method of the electrolyte provided in this comparative example includes the following steps: in a glove box filled with argon, mix the ethylene carbonate, dimethyl carbonate and diethyl carbonate that have been dehydrated and purified according to the above ratio. A mixed solvent is obtained; then, lithium hexafluorophosphate is added to it, and after mixing evenly, an electrolyte solution is obtained.
  • the lithium salt is the first lithium salt
  • the first lithium salt is lithium bistrifluoromethanesulfonimide (LiTFSI).
  • the organic solvent consists of an ether solvent and a nitrile solvent with a mass ratio of 3:1.
  • the ether solvent is ethylene glycol dimethyl ether and the nitrile solvent is butyronitrile.
  • the film-forming additive is fluoroethylene carbonate (FEC).
  • the molar concentration of the first lithium salt in the electrolyte solution is 2.5 mol/L.
  • the mass fraction of the film-forming additive in the electrolyte is 5%.
  • the preparation method of the electrolyte provided in this comparative example is basically the same as that of Example 9, except that the second lithium salt is not added.
  • the electrolyte provided in this comparative example consists of lithium salt, organic solvent and film-forming additives.
  • the lithium salt is the second lithium salt
  • the second lithium salt is lithium difluoroxalate borate (LiODFB).
  • the organic solvent consists of an ether solvent and a nitrile solvent with a mass ratio of 3:1.
  • the ether solvent is ethylene glycol dimethyl ether and the nitrile solvent is butyronitrile.
  • the film-forming additive is fluoroethylene carbonate (FEC).
  • the molar concentration of the second lithium salt in the electrolyte solution is 2.5 mol/L.
  • the mass fraction of the film-forming additive in the electrolyte is 5%.
  • the preparation method of the electrolyte provided in this comparative example is basically the same as that of Example 9, except that the first lithium salt is not added.
  • composition of the electrolyte provided in this comparative example is basically the same as that in Example 9. The only difference is that the molar concentration of the first lithium salt in the electrolyte is replaced with 0.5 mol/L, and the molar concentration of the second lithium salt in the electrolyte is changed. The molar concentration is 2mol/L.
  • the preparation method of the electrolyte provided in this comparative example is the same as that in Example 9.
  • the preparation method of the electrolyte provided in this comparative example is the same as that in Example 9.
  • composition of the electrolyte provided in this comparative example is basically the same as that in Example 9, and the only difference is that the mass fraction of the film-forming additive in the electrolyte is replaced with 8%.
  • the preparation method of the electrolyte provided in this comparative example is the same as that in Example 9.
  • composition of the electrolyte provided in this comparative example is basically the same as that in Example 9. The only difference is that the mass ratio of the ether solvent and the nitrile solvent is replaced by 1:3.
  • the preparation method of the electrolyte provided in this comparative example is the same as that in Example 9.
  • Lithium-ion batteries were prepared using the electrolytes prepared in the above embodiments and comparative examples respectively, and electrochemical performance tests were performed on the lithium-ion batteries prepared in each group (3 to 4.4 at -20°C, 0.2C rate Test the electrochemical performance of the battery under V conditions, cycle 150 cycles), and the test results are shown in Table 1 below.
  • the battery preparation method includes: placing the cut positive electrode piece in the center of the positive electrode shell of the button battery, then placing a separator (2320 separator from Celgard Company), and then injecting an appropriate amount of electrolyte (the above embodiments and each pair proportion of the electrolyte), so that the separator is completely wetted. Then place the lithium sheet (as the negative electrode) above the separator, place gaskets and shrapnel above the lithium sheet, and finally cover the negative electrode shell. Use a battery sealing machine to compact the positive and negative electrode shells. After leaving it for 24 hours, you finally get the test result. of lithium-ion batteries.
  • the preparation method of the positive electrode sheet includes: mixing the positive active material LiNi 0.5 Mn 0.3 Co 0.2 O 2 , the conductive agent acetylene black and the binder polyvinylidene fluoride with a mass ratio of 8:1:1. , add the dispersant N-methylpyrrolidone and stir to obtain a uniform positive electrode slurry.
  • the positive electrode slurry is coated on the aluminum foil current collector with a loading of 2 mg/cm 2 , and then dried and sliced to obtain a positive electrode piece.
  • Example 1 Group Capacity retention rate after 150 cycles at -20°C
  • Example 2 81.85%
  • Example 3 81.06%
  • Example 4 80.73%
  • Example 5 81.25%
  • Example 6 81.12%
  • Example 7 81.92%
  • Example 8 81.90%
  • Example 9 87.24%
  • Example 10 88.81%
  • Example 11 76.68%
  • Example 12 78.15% Comparative example 1 44.33% Comparative example 2 56.76% Comparative example 3 53.02%
  • the first lithium salt (LiTFSI) has high conductivity and solubility, and film-forming additives (LiPO 2 F 2 , VC, FEC) can form a good interface film on the electrode surface.
  • film-forming additives LiPO 2 F 2 , VC, FEC
  • the combination of specific types of solvents, lithium salts and additives can significantly improve the discharge capacity retention rate of lithium-ion batteries at low temperatures.
  • ethylene glycol dimethyl ether has good solubility and negative electrode deformability
  • the nitrile solvent has high conductivity and It has good compatibility with the high-voltage cathode.
  • the present invention uses LiTFSI as the main lithium salt (first lithium salt) of the electrolyte, which has the characteristics of high solubility and high conductivity.
  • High-concentration LiTFSI can be decomposed in the solvent to form an excellent SEI film.
  • the second lithium salt also partially participates in SEI film formation.
  • Film-forming additives LiPO 2 F 2 , VC, FEC can form a good SEI film on the electrode surface and suppress side reactions between the electrolyte and the electrode.

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Abstract

一种电解液及其制备方法、锂离子电池。电解液包括锂盐、有机溶剂和成膜添加剂；锂盐包括第一锂盐和第二锂盐；第一锂盐包括双三氟甲烷磺酰亚胺锂和/或双氟磺酰亚胺锂；第二锂盐包括二氟草酸硼酸锂、四氟硼酸锂、高氯酸锂和双草酸硼酸锂中的至少一种。

Description

一种电解液及其制备方法、锂离子电池
本申请要求2022年6月7日提交的，申请号为202210637294.3，发明名称为“一种电解液及其制备方法、锂离子电池”的中国发明专利申请的优先权，该申请的公开内容以引用的方式并入本文。
技术领域
本发明涉及锂电子电池技术领域，具体而言，涉及一种电解液及其制备方法、锂离子电池。
背景技术
锂离子电池具有高电压、高能量密度、多次循环和绿色环保等优点。目前，锂离子电池已被广泛用于手机、笔记本电脑、智能机器人等电子设备，以及航空航天、船舶、军事设施等领域。此外，锂离子电池作为动力电池在电动汽车中也得到了广泛的应用，随着动力电池商业化规模的不断扩大，需要开发更高效、能量密度更高和安全性能更好的电池。
碳酸酯溶剂是常用的锂离子电池电解液溶剂，其具有电导率高、成本低以及与电极相容性好等优点。然而，在高电压电池体系中，碳酸酯溶剂极其容易分解。而溶剂被氧化分解的副产物会沉积在电极表面，极大增加了电池阻抗，降低了电池性能。
此外，动力电池性能受温度影响很大，电动汽车有时会在极端天气下使用。在超低温情况下，电解液电导率急剧降低，会导致电池容量快速衰减，这阻碍了动力电池的大规模使用。
因此，提供一种同时具有高电压性能和低温性能的动力型锂离子电池电解液具有重要意义。
有鉴于此，特提出本发明。
发明内容
本发明的第一目的在于提供一种电解液，通过采用特定种类的第一锂盐，可以形成优良的SEI膜(固体电解质界面膜，solid electrolyte interface)，抑制电解液溶剂的过度分解，有利于锂离子的嵌入和脱出；通过引入第二锂盐与第一锂盐搭配使用，能够在钝化铝箔的同时参与SEI成膜。因此，该电解液在低温下的电导率高，且其制得的电池在高电压下的循环性能好。并且，本发明通过引入成膜添加剂，能够进一步提高锂离子电池在高电压下的循环性能和电解液在低温下的电导率。
本发明的第二目的在于提供一种电解液的制备方法，该制备方法具有操作简单、条件温和、工艺流程短以及适合大批量生产等优点。
本发明的第三目的在于提供一种锂离子电池，该锂离子电池同时具有高电性能和低温性能。
为了实现本发明的上述目的，特采用以下技术方案：
本发明提供了一种电解液，包括锂盐、有机溶剂和成膜添加剂；
其中，所述锂盐包括第一锂盐和第二锂盐；
所述第一锂盐包括双三氟甲烷磺酰亚胺锂(LiTFSI)和/或双氟磺酰亚胺锂(LiFSI)。
所述第二锂盐包括二氟草酸硼酸锂(LiODFB)、四氟硼酸锂(LiBF 4)、高氯酸锂(LiClO 4)和双草酸硼酸锂(LiBOB，又称双乙二酸硼酸锂、二草酸硼酸锂)中的至少一种。
本发明提供的电解液，通过采用特定种类的锂盐，并引入成膜添加剂，能够提高锂离子电池在高电压下的循环性能和电解液在低温下的电导率。
具体地，本发明提供的第一锂盐的溶解度很高，能够配制成高浓度电解液。高浓度电解液相比于传统电解液，可以形成优良的SEI膜，主要源 自于锂盐的分解，可以抑制电解液溶剂的过度分解。并且，高浓度电解液形成的SEI膜主要是富锂化合物，有较高的电导率，有利于锂离子的嵌入和脱出。
同时，本发明通过引入第二锂盐与第一锂盐搭配使用，能够有效的钝化铝箔，避免第一锂盐在高电压下腐蚀铝箔；并且，第二锂盐部分参与SEI成膜，可以进一步提升电池的性能。
此外，本发明通过在电解液中加入成膜添加剂，其在电极表面可以形成优良的界面保护膜，避免溶剂和电极材料表面发生副反应，从而提升电池的高电压循环性能。
在本发明一些具体的实施方式中，所述第二锂盐包括二氟草酸硼酸锂、四氟硼酸锂和双草酸硼酸锂中的至少两种。
优选地，所述电解液中的所述第一锂盐的摩尔浓度为0.8～4mol/L，包括但不限于0.9mol/L、1mol/L、1.2mol/L、1.4mol/L、1.5mol/L、1.8mol/L、2mol/L、2.2mol/L、2.4mol/L、2.6mol/L、2.8mol/L、3mol/L、3.2mol/L、3.4mol/L、3.6mol/L、3.8mol/L中的任意一者的点值或任意两者之间的范围值。
采用该范围内的摩尔浓度有利于进一步提高锂离子电池在高电压下的循环性能和电解液在低温下的电导率。
更优选地，所述电解液中的所述第一锂盐的摩尔浓度为1～3mol/L。
优选地，所述电解液中的所述第二锂盐的摩尔浓度为0.05～0.7mol/L，包括但不限于0.07mol/L、0.09mol/L、0.1mol/L、0.2mol/L、0.3mol/L、0.4mol/L、0.5mol/L、0.6mol/L中的任意一者的点值或任意两者之间的范围值。
采用该范围内的摩尔浓度有利于进一步提高锂离子电池在高电压下的循环性能和电解液在低温下的电导率。
更优选地，所述电解液中的所述第二锂盐的摩尔浓度为0.1～0.5mol/L。
优选地，所述成膜添加剂包括二氟磷酸锂(LiPO 2F 2)、碳酸亚乙烯酯(VC，又称1,3-二氧杂环戊烯-2-酮、乙烯碳酸酯)、硫酸乙烯酯(DTD)、硫酸二甲酯(DMS)、亚硫酸丁烯酯(BS)和氟代碳酸乙烯酯(FEC)中的至少一种。
成膜添加剂在电极表面可以形成优良的界面保护膜，避免溶剂和电极材料表面发生副反应。
采用上述种类的成膜添加剂有利于进一步提升锂离子电池的高电压循环性能。
在本发明一些具体的实施方式中，所述成膜添加剂包括二氟磷酸锂(LiPO 2F 2)、碳酸亚乙烯酯(VC，又称1,3-二氧杂环戊烯-2-酮、乙烯碳酸酯)、硫酸乙烯酯(DTD)、硫酸二甲酯(DMS)、亚硫酸丁烯酯(BS)和氟代碳酸乙烯酯(FEC)中的至少两种。
优选地，所述电解液中的所述成膜添加剂的质量分数为0.1％～6％；包括但不限于0.2％、0.3％、0.4％、0.5％、0.6％、0.7％、0.8％、0.9％、1％、1.5％、2％、3％、3.5％、4％、5％、5.5％中的任意一者的点值或任意两者之间的范围值。
采用上述用量范围的成膜添加剂有利于更进一步提升锂离子电池的高电压循环性能。
更优选地，所述电解液中的所述成膜添加剂的质量分数为0.5％～5％。
优选地，所述有机溶剂包括醚类溶剂和/或腈类溶剂。
醚类溶剂与锂负极和碳负极相容性很好，不易与负极发生副反应。
腈类溶剂具有很高的电导率，能够显著提高锂离子在电解液溶剂中的穿梭能力。同时，腈类溶剂有很高的耐氧化能力，腈类溶剂的氰基官能团可以与正极的金属离子形成稳定的络合，从而提高正极高压稳定性。
更优选地，所述有机溶剂包括所述醚类溶剂和所述腈类溶剂的混合，且所述醚类溶剂和所述腈类溶剂的质量比为1～3：1。
在本发明一些具体的实施方式中，所述醚类溶剂和所述腈类溶剂的质量比为可以为1：1，或者2：1，或者3：1。
采用上述质量比的醚类溶剂和腈类溶剂，有利于进一步提高电解液的电导率。
优选地，所述醚类溶剂包括乙二醇二甲醚、四氢呋喃和二氧戊环(又称1,3-二氧五环)中的至少一种。
其中，乙二醇二甲醚溶剂与锂负极和碳负极相容性很好，不易与负极发生副反应。
优选地，所述腈类溶剂包括乙腈、丁腈、丁二腈、戊二腈和己二腈中的至少一种，更优选为至少两种。
本发明还提供了如上所述的电解液的制备方法，包括以下步骤：
将锂盐、有机溶剂和成膜添加剂混合均匀。
该制备方法具有操作简单、方便、条件温和、工艺流程短以及适合大批量生产等优点。
在本发明一些具体的实施方式中，所述混合在充满氩气的手套箱中进行。
在本发明一些具体的实施方式中，所述有机溶剂经过脱水纯化处理。以使制得的电解液中不含有水。
优选地，所述制备方法包括以下步骤：
将醚类溶剂和腈类溶剂混合均匀后，向其中依次加入第一锂盐、第二锂盐和成膜添加剂，混匀后得到所述电解液。
在本发明一些具体的实施方式中，所述的电解液的制备方法具体包括 以下步骤：在充满氩气的手套箱中，将经过脱水纯化处理后的醚类溶剂与腈类溶剂按比例(配比)混合均匀，得到混合溶剂；然后，向其中加入第一锂盐，待第一锂盐溶解完全后，再加入第二锂盐；待第一锂盐和第二锂盐均溶解完全后，再向其中加入成膜添加剂，待混合均匀后，得到所述电解液。
本发明还提供了一种锂离子电池，包括如上所述的电解液，或者，如上所述的电解液的制备方法所制得的电解液。
该锂离子电池在高电压下的循环性能好，能量密度更高；并且该锂离子电池中的电解液在低温下的电导率好，容量保持率高。
与现有技术相比，本发明的有益效果为：
(1)本发明提供的电解液，通过引入溶解度很高的第一锂盐，能够配制成高浓度电解液，高浓度电解液可以形成优良的SEI膜，可以抑制电解液溶剂的过度分解。并且，高浓度电解液形成的SEI膜主要是富锂化合物，有较高的电导率，有利于锂离子的嵌入和脱出。
(2)本发明提供的电解液，通过引入特定种类的第二锂盐与第一锂盐搭配使用，能够有效的钝化铝箔，避免第一锂盐在高电压下腐蚀铝箔；并且，第二锂盐参与SEI成膜，可以进一步提升电池的性能。
(3)本发明提供的电解液，通过引入特定种类的加入成膜添加剂，其在电极表面可以形成优良的界面保护膜，避免溶剂和电极材料表面发生副反应，从而提升电池的高电压循环性能。
(4)本发明提供的电解液中的特定种类的醚类溶剂与锂负极和碳负极相容性很好，不易与负极发生副反应。
(5)本发明提供的电解液中的特定种类的腈类溶剂具有很高的电导率，能够显著提高锂离子在电解液溶剂中的穿梭能力。并且，腈类溶剂有很高的耐氧化能力，腈类溶剂的氰基官能团可以与正极的金属离子形成稳定的络合，从而提高了锂离子电池的高压稳定性。
(6)本发明提供的锂离子电池具有能量密度高和容量保持率高的优点。
附图说明
为了更清楚地说明本发明具体实施方式或现有技术中的技术方案，下面将对具体实施方式或现有技术描述中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图是本发明的一些实施方式，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据这些附图获得其他的附图。
图1为本发明提供的电池循环性能的对比图。
具体实施方式
下面将结合附图和具体实施方式对本发明的技术方案进行清楚、完整地描述，但是本领域技术人员将会理解，下列所描述的实施例是本发明一部分实施例，而不是全部的实施例，仅用于说明本发明，而不应视为限制本发明的范围。基于本发明中的实施例，本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他实施例，都属于本发明保护的范围。实施例中未注明具体条件者，按照常规条件或制造商建议的条件进行。所用试剂或仪器未注明生产厂商者，均为可以通过市售购买获得的常规产品。
实施例1
本实施例提供的电解液由锂盐、有机溶剂和成膜添加剂组成。
其中，锂盐由第一锂盐和第二锂盐组成，第一锂盐为双三氟甲烷磺酰亚胺锂(LiTFSI)，第二锂盐为二氟草酸硼酸锂(LiODFB)。有机溶剂由质量比为3：1的醚类溶剂和腈类溶剂组成，醚类溶剂为乙二醇二甲醚，腈类溶剂为乙腈。成膜添加剂为二氟磷酸锂(LiPO 2F 2)。
该电解液中的第一锂盐的摩尔浓度为1mol/L。该电解液中的第二锂盐的摩尔浓度为0.1mol/L。该电解液中的成膜添加剂的质量分数为0.5％。
本实施例提供的电解液的制备方法包括以下步骤：在充满氩气的手套箱中，将经过脱水纯化处理后的醚类溶剂与腈类溶剂按上述配比混合均匀，得到混合溶剂；然后，向其中加入第一锂盐，待第一锂盐溶解完全后，再加入第二锂盐；待第一锂盐和第二锂盐均溶解完全后，再向其中加入成膜添加剂，混合均匀后，得到电解液。
实施例2
本实施例提供的电解液由锂盐、有机溶剂和成膜添加剂组成。
其中，锂盐由第一锂盐和第二锂盐组成，第一锂盐为双三氟甲烷磺酰亚胺锂(LiTFSI)，第二锂盐为二氟草酸硼酸锂(LiODFB)。有机溶剂由质量比为3：1的醚类溶剂和腈类溶剂组成，醚类溶剂为乙二醇二甲醚，腈类溶剂为丁腈。成膜添加剂为二氟磷酸锂(LiPO 2F 2)。
该电解液中的第一锂盐的摩尔浓度为1mol/L。该电解液中的第二锂盐的摩尔浓度为0.1mol/L。该电解液中的成膜添加剂的质量分数为0.5％。
本实施例提供的电解液的制备方法与实施例1相同。
实施例3
本实施例提供的电解液由锂盐、有机溶剂和成膜添加剂组成。
其中，锂盐由第一锂盐和第二锂盐组成，第一锂盐为双三氟甲烷磺酰亚胺锂(LiTFSI)，第二锂盐为二氟草酸硼酸锂(LiODFB)。有机溶剂由质量比为3：1的醚类溶剂和腈类溶剂组成，醚类溶剂为乙二醇二甲醚，腈类溶剂为己二腈。成膜添加剂为二氟磷酸锂(LiPO 2F 2)。
该电解液中的第一锂盐的摩尔浓度为1mol/L。该电解液中的第二锂盐的摩尔浓度为0.1mol/L。该电解液中的成膜添加剂的质量分数为0.5％。
本实施例提供的电解液的制备方法与实施例1相同。
实施例4
本实施例提供的电解液由锂盐、有机溶剂和成膜添加剂组成。
其中，锂盐由第一锂盐和第二锂盐组成，第一锂盐为双三氟甲烷磺酰亚胺锂(LiTFSI)，第二锂盐为二氟草酸硼酸锂(LiODFB)。有机溶剂由质量比为1：1的醚类溶剂和腈类溶剂组成，醚类溶剂为乙二醇二甲醚，腈类溶剂为丁腈。成膜添加剂为二氟磷酸锂(LiPO 2F 2)。
该电解液中的第一锂盐的摩尔浓度为1mol/L。该电解液中的第二锂盐的摩尔浓度为0.1mol/L。该电解液中的成膜添加剂的质量分数为0.5％。
本实施例提供的电解液的制备方法与实施例1相同。
实施例5
本实施例提供的电解液由锂盐、有机溶剂和成膜添加剂组成。
其中，锂盐由第一锂盐和第二锂盐组成，第一锂盐为双三氟甲烷磺酰亚胺锂(LiTFSI)，第二锂盐为四氟硼酸锂(LiBF 4)。有机溶剂由质量比为3：1的醚类溶剂和腈类溶剂组成，醚类溶剂为乙二醇二甲醚，腈类溶剂为丁腈。成膜添加剂为二氟磷酸锂(LiPO 2F 2)。
该电解液中的第一锂盐的摩尔浓度为1mol/L。该电解液中的第二锂盐的摩尔浓度为0.1mol/L。该电解液中的成膜添加剂的质量分数为0.5％。
本实施例提供的电解液的制备方法与实施例1相同。
实施例6
本实施例提供的电解液的组成与实施例5基本相同，区别仅在于，将四氟硼酸锂替换为双草酸硼酸锂(LiBOB)(但保持其用量不变，即电解液中的第二锂盐的摩尔浓度仍为0.1mol/L)。
本实施例提供的电解液的制备方法与实施例1相同。
实施例7
本实施例提供的电解液由锂盐、有机溶剂和成膜添加剂组成。
其中，锂盐由第一锂盐和第二锂盐组成，第一锂盐为双三氟甲烷磺酰 亚胺锂(LiTFSI)，第二锂盐为二氟草酸硼酸锂(LiODFB)。有机溶剂由质量比为3：1的醚类溶剂和腈类溶剂组成，醚类溶剂为乙二醇二甲醚，腈类溶剂为丁腈。成膜添加剂为碳酸亚乙烯酯(VC)。
该电解液中的第一锂盐的摩尔浓度为1mol/L。该电解液中的第二锂盐的摩尔浓度为0.1mol/L。该电解液中的成膜添加剂的质量分数为5％。
本实施例提供的电解液的制备方法与实施例1相同。
实施例8
本实施例提供的电解液的组成与实施例7基本相同，区别仅在于，将碳酸亚乙烯酯替换为氟代碳酸乙烯酯(FEC)(但保持其用量不变，即电解液中的成膜添加剂的质量分数仍为5％)。
本实施例提供的电解液的制备方法与实施例1相同。
实施例9
本实施例提供的电解液由锂盐、有机溶剂和成膜添加剂组成。
其中，锂盐由第一锂盐和第二锂盐组成，第一锂盐为双三氟甲烷磺酰亚胺锂(LiTFSI)，第二锂盐为二氟草酸硼酸锂(LiODFB)。有机溶剂由质量比为3：1的醚类溶剂和腈类溶剂组成，醚类溶剂为乙二醇二甲醚，腈类溶剂为丁腈。成膜添加剂为氟代碳酸乙烯酯(FEC)。
该电解液中的第一锂盐的摩尔浓度为2mol/L。该电解液中的第二锂盐的摩尔浓度为0.5mol/L。该电解液中的成膜添加剂的质量分数为5％。
本实施例提供的电解液的制备方法与实施例1相同。
实施例10
本实施例提供的电解液的组成与实施例9基本相同，区别仅在于，将电解液中的第一锂盐的摩尔浓度替换为3mol/L。
本实施例提供的电解液的制备方法与实施例1相同。
实施例11
本实施例提供的电解液由锂盐、有机溶剂和成膜添加剂组成。
其中，锂盐由第一锂盐和第二锂盐组成，第一锂盐为双氟磺酰亚胺锂(LiFSI)，第二锂盐为二氟草酸硼酸锂(LiODFB)。有机溶剂由质量比为3：1的醚类溶剂和腈类溶剂组成，醚类溶剂为乙二醇二甲醚，腈类溶剂为丁腈。成膜添加剂为氟代碳酸乙烯酯(FEC)。
该电解液中的第一锂盐的摩尔浓度为2.5mol/L。该电解液中的第二锂盐的摩尔浓度为0.3mol/L。该电解液中的成膜添加剂的质量分数为3％。
本实施例提供的电解液的制备方法与实施例1相同。
实施例12
本实施例提供的电解液由锂盐、有机溶剂和成膜添加剂组成。
其中，锂盐由第一锂盐和第二锂盐组成，第一锂盐为双三氟甲烷磺酰亚胺锂(LiTFSI)，第二锂盐为二氟草酸硼酸锂(LiODFB)。有机溶剂由质量比为3：1的醚类溶剂和腈类溶剂组成，醚类溶剂为乙二醇二甲醚，腈类溶剂为丁二腈。成膜添加剂为氟代碳酸乙烯酯(FEC)。
该电解液中的第一锂盐的摩尔浓度为1.5mol/L。该电解液中的第二锂盐的摩尔浓度为0.2mol/L。该电解液中的成膜添加剂的质量分数为4％。
本实施例提供的电解液的制备方法与实施例1相同。
对比例1
本对比例提供的电解液由锂盐和有机溶剂组成。
其中，锂盐为六氟磷酸锂(LiPF 6)。有机溶剂由质量比为1：1：1的碳酸乙烯酯、碳酸二甲酯和碳酸二乙酯组成。该电解液中的锂盐(六氟磷酸锂)的摩尔浓度为1mol/L。
本对比例提供的电解液的制备方法包括以下步骤：在充满氩气的手套 箱中，将经过脱水纯化处理后的碳酸乙烯酯、碳酸二甲酯和碳酸二乙酯按上述配比混合均匀，得到混合溶剂；然后，向其中加入六氟磷酸锂，混合均匀后，得到电解液。
对比例2
本对比例提供的电解液由锂盐、有机溶剂和成膜添加剂组成。
其中，锂盐为第一锂盐，第一锂盐为双三氟甲烷磺酰亚胺锂(LiTFSI)。有机溶剂由质量比为3：1的醚类溶剂和腈类溶剂组成，醚类溶剂为乙二醇二甲醚，腈类溶剂为丁腈。成膜添加剂为氟代碳酸乙烯酯(FEC)。
该电解液中的第一锂盐的摩尔浓度为2.5mol/L。该电解液中的成膜添加剂的质量分数为5％。
本对比例提供的电解液的制备方法与实施例9基本相同，区别仅在于，不加入第二锂盐。
对比例3
本对比例提供的电解液由锂盐、有机溶剂和成膜添加剂组成。
其中，锂盐为第二锂盐，第二锂盐为二氟草酸硼酸锂(LiODFB)。有机溶剂由质量比为3：1的醚类溶剂和腈类溶剂组成，醚类溶剂为乙二醇二甲醚，腈类溶剂为丁腈。成膜添加剂为氟代碳酸乙烯酯(FEC)。
该电解液中的第二锂盐的摩尔浓度为2.5mol/L。该电解液中的成膜添加剂的质量分数为5％。
本对比例提供的电解液的制备方法与实施例9基本相同，区别仅在于，不加入第一锂盐。
对比例4
本对比例提供的电解液的组成与实施例9基本相同，区别仅在于，将电解液中的第一锂盐的摩尔浓度替换为0.5mol/L，并将电解液中的第二锂盐的摩尔浓度为2mol/L。
本对比例提供的电解液的制备方法与实施例9相同。
对比例5
本对比例提供的电解液的组成与实施例9基本相同，区别仅在于，将氟代碳酸乙烯酯(FEC)替换为亚硫酸亚乙酯(ES)(但保持其用量不变，即电解液中的成膜添加剂的质量分数仍为5％)。
本对比例提供的电解液的制备方法与实施例9相同。
对比例6
本对比例提供的电解液的组成与实施例9基本相同，区别仅在于，将电解液中的成膜添加剂的质量分数替换为8％。
本对比例提供的电解液的制备方法与实施例9相同。
对比例7
本对比例提供的电解液的组成与实施例9基本相同，区别仅在于，将醚类溶剂和腈类溶剂的质量比替换为1：3。
本对比例提供的电解液的制备方法与实施例9相同。
实验例1
分别采用以上各实施例和各对比例制得的电解液制得锂离子电池，并对各组制得的锂离子电池分别进行电化学性能测试(在-20℃，0.2C倍率下3～4.4V条件下测试电池的电化学性能，循环150圈)，测试结果如下表1所示。
其中，电池的制备方法包括：将分切好的正极极片放置在扣式电池正极壳正中，再垫上隔膜(Celgard公司的2320隔膜)，然后注入适量的电解液(以上各实施例和各对比例制得的电解液)，使隔膜完全浸润。再将锂片(作为负极)放置在隔膜上方，在锂片上方放置垫片和弹片，最后盖 上负极壳，使用电池封装机将正负极壳压实，静置24h后，最终得到待测试的锂离子电池。
其中，所述正极极片的制备方法包括：将质量比为8:1:1的正极活性材料LiNi 0.5Mn 0.3Co 0.2O 2、导电剂乙炔黑和粘结剂聚偏二氟乙烯混合均匀后，向其中加入分散剂N-甲基吡咯烷酮搅拌，得到均匀的正极浆料。将该正极浆料涂覆于铝箔集流体上，载量为2mg/cm 2，然后烘干切片，得到正极极片。
表1 各组锂离子电池的电化学性能测试结果
组别 -20℃循环150圈后的容量保持率
实施例1 80.21％
实施例2 81.85％
实施例3 81.06％
实施例4 80.73％
实施例5 81.25％
实施例6 81.12％
实施例7 81.92％
实施例8 81.90％
实施例9 87.24％
实施例10 88.81％
实施例11 76.68％
实施例12 78.15％
对比例1 44.33％
对比例2 56.76％
对比例3 53.02％
对比例4 60.28％
对比例5 48.17％
对比例6 65.38％
对比例7 58.43％
同时，实施例1、实施例9、实施例10和对比例1的电池循环性能对比图如图1所示。
结合表1和图1的数据可以看出，乙二醇二甲醚和腈类溶剂混合可以提高电解液的耐氧化能力和电导率。第一锂盐(LiTFSI)有很高的电导率和溶解度，成膜添加剂(LiPO 2F 2、VC、FEC)可以在电极表面形成良好的界面膜。特定种类的溶剂、锂盐和添加剂搭配使用可以显著提高锂离子电池在低温下的放电容量保持率。
可见，本发明所提供的具有高压低温性能的用于锂离子电池的电解液，其中的乙二醇二甲醚有很好的溶解性能和负极形容性，腈类溶剂有很高的电导率且与高压正极相容性好，这两种溶剂按照一定的比例混合后，提高了电池的高压循环性能和在低温下放电容量保持率。
并且，本发明通过采用LiTFSI作为电解液的主要锂盐(第一锂盐)，具有高溶解性和高电导率的特点，高浓度的LiTFSI可以在溶剂中分解形成优良的SEI膜。同时，第二锂盐除起到钝化铝集流体的作用，还部分参与SEI成膜。成膜添加剂(LiPO 2F 2、VC、FEC)可以在电极表面形成良好的SEI膜，抑制电解液和电极的副反应。
尽管已用具体实施例来说明和描述了本发明，然而应意识到，以上各实施例仅用以说明本发明的技术方案，而非对其限制；本领域的普通技术人员应当理解：在不背离本发明的精神和范围的情况下，可以对前述各实施例所记载的技术方案进行修改，或者对其中部分或者全部技术特征进行等同替换；而这些修改或者替换，并不使相应技术方案的本质脱离本发明各实施例技术方案的范围；因此，这意味着在所附权利要求中包括属于本发明范围内的所有这些替换和修改。

Claims (10)

  1. 一种电解液，其特征在于，包括锂盐、有机溶剂和成膜添加剂；
    其中，所述锂盐包括第一锂盐和第二锂盐；
    所述第一锂盐包括双三氟甲烷磺酰亚胺锂和/或双氟磺酰亚胺锂；
    所述第二锂盐包括二氟草酸硼酸锂、四氟硼酸锂、高氯酸锂和双草酸硼酸锂中的至少一种。
  2. 根据权利要求1所述的电解液，其特征在于，所述电解液中的所述第一锂盐的摩尔浓度为0.8～4mol/L；
    优选地，所述电解液中的所述第一锂盐的摩尔浓度为1～3mol/L。
  3. 根据权利要求1所述的电解液，其特征在于，所述电解液中的所述第二锂盐的摩尔浓度为0.05～0.7mol/L；
    优选地，所述电解液中的所述第二锂盐的摩尔浓度为0.1～0.5mol/L。
  4. 根据权利要求1所述的电解液，其特征在于，所述成膜添加剂包括二氟磷酸锂、碳酸亚乙烯酯、硫酸乙烯酯、硫酸二甲酯、亚硫酸丁烯酯和氟代碳酸乙烯酯中的至少一种。
  5. 根据权利要求1所述的电解液，其特征在于，所述电解液中的所述成膜添加剂的质量分数为0.1％～6％；
    优选地，所述电解液中的所述成膜添加剂的质量分数为0.5％～5％。
  6. 根据权利要求1～5任一项所述的电解液，其特征在于，所述有机溶剂包括醚类溶剂和/或腈类溶剂；
    优选地，所述有机溶剂包括所述醚类溶剂和所述腈类溶剂的混合，且所述醚类溶剂和所述腈类溶剂的质量比为1～3：1。
  7. 根据权利要求6所述的电解液，其特征在于，所述醚类溶剂包括 乙二醇二甲醚、四氢呋喃和二氧戊环中的至少一种；
    优选地，所述腈类溶剂包括乙腈、丁腈、丁二腈、戊二腈和己二腈中的至少一种。
  8. 如权利要求1～7任一项所述的电解液的制备方法，其特征在于，包括以下步骤：
    将锂盐、有机溶剂和成膜添加剂混合均匀。
  9. 根据权利要求8所述的电解液的制备方法，其特征在于，所述制备方法包括以下步骤：
    将醚类溶剂和腈类溶剂混合均匀后，向其中依次加入第一锂盐、第二锂盐和成膜添加剂，混匀后得到所述电解液。
  10. 一种锂离子电池，包括如权利要求1～7任一项所述的电解液，或者，如权利要求8或9所述的电解液的制备方法所制得的电解液。
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