WO2020015234A1 - 金属锂二次电池用电解液以及使用该电解液的金属锂二次电池 - Google Patents

金属锂二次电池用电解液以及使用该电解液的金属锂二次电池 Download PDF

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WO2020015234A1
WO2020015234A1 PCT/CN2018/112571 CN2018112571W WO2020015234A1 WO 2020015234 A1 WO2020015234 A1 WO 2020015234A1 CN 2018112571 W CN2018112571 W CN 2018112571W WO 2020015234 A1 WO2020015234 A1 WO 2020015234A1
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lithium
secondary battery
battery
electrolyte
sulfur
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PCT/CN2018/112571
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English (en)
French (fr)
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王骞
杨程凯
刘�文
申兰耀
周恒辉
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青海泰丰先行锂能科技有限公司
北大先行科技产业有限公司
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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
    • H01M10/0567—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
    • 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
    • H01M12/00—Hybrid cells; Manufacture thereof
    • H01M12/08—Hybrid cells; Manufacture thereof composed of a half-cell of a fuel-cell type and a half-cell of the secondary-cell type
    • 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 invention belongs to the technical field of batteries, and particularly relates to an electrolytic solution for a lithium metal secondary battery containing a sulfur-containing conjugate structure additive and a lithium metal secondary battery using the electrolytic solution.
  • metallic lithium As a negative electrode material with a high capacity density (3860mA h g -1 ), metallic lithium has great application potential in secondary lithium batteries and lithium air batteries. However, metal lithium also has great safety problems due to its active chemical properties. When lithium is deposited, it is very easy to grow dendritic puncture membranes due to concentration polarization and electric fields, which causes a series of safety problems.
  • the current methods mostly focus on the modification of the surface of lithium metal, that is, forming a stable interface protective film on the surface of the lithium negative electrode with high lithium ion conductivity ( SEI (Solid Electrolyte Interphase) membrane).
  • SEI Solid Electrolyte Interphase
  • one method is to form an in-situ LiEI-rich SEI film with high inorganic ion conductivity and high mechanical strength on the surface of the lithium electrode, which can accelerate the deposition and dissolution of lithium and inhibit the growth of lithium dendrites.
  • Ethylene carbonate Angew.Chem.Int.Ed.2018,57,1-6), etc.
  • an organic film to protect metallic lithium.
  • a compound such as pyrrole is used to form a protective film on the surface of metallic lithium to inhibit dendrite growth and enhance anode stability (Patent Document: CN102315420A).
  • Patent Document: CN102315420A Patent Document: CN102315420A.
  • none of the methods mentioned above can fundamentally solve the uneven deposition caused by the concentration gradient in the solution.
  • the formed film is also easily deformed with the deformation of the metal surface, and it is difficult to protect the anode well when the current density is large. Surface, resulting in dendrites. That is, it can only play a role in inhibiting the growth of lithium dendrites, and cannot fundamentally prevent the formation of lithium dendrites.
  • Patent Document CN108054429A
  • the present invention provides an electrolyte for metal lithium secondary batteries containing small molecule sulfur-containing conjugate structure additive, and metal lithium using the electrolyte Secondary batteries can prevent dendrites from occurring in rechargeable lithium batteries at a lower cost.
  • the invention is an electrolytic solution for a metal lithium secondary battery, which contains a lithium salt, a non-aqueous solvent, and a sulfur-containing conjugated structure additive, wherein the concentration of the lithium salt is 0.5-10 mol / L and the sulfur-containing conjugate
  • concentration of the lithium salt is 0.5-10 mol / L
  • sulfur-containing conjugate The ratio of the mass of the structural additive to the volume of the non-aqueous solvent is 0.01 to 100 mg / mL.
  • the lithium salt is one or more of LiPF 6 , LiTFSI, and LiClO 4 .
  • the non-aqueous solvent may be selected from 1,3-dioxolane (DOL), ethylene glycol dimethyl ether (DME), and ethylene carbonate (EC). ), One or more of diethyl carbonate (DEC), dimethyl carbonate (DMC), and propylene carbonate (PC).
  • DOL 1,3-dioxolane
  • DME ethylene glycol dimethyl ether
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • DMC dimethyl carbonate
  • PC propylene carbonate
  • the non-aqueous solvent is a mixed solvent of 1,3-dioxolane (DOL) and ethylene glycol dimethyl ether (DME), and carbonic acid.
  • DOL 1,3-dioxolane
  • DME ethylene glycol dimethyl ether
  • PC propylene carbonate
  • the sulfur-containing conjugated structure additive is one or more of carbonyl sulfur type, thioether type, and sulfone type.
  • the sulfur-containing conjugated structure additive is dithiooxamide, thioacetamide, thiourea, thiophene, carbon disulfide, diphenyl sulfide, Or diphenylthiourea.
  • the sulfur-containing conjugated structure additive does not contain a benzene ring.
  • the ratio of the mass of the sulfur-containing conjugated structure additive to the volume of the non-aqueous solvent is 0.05-50 mg / mL.
  • the ratio of the mass of the sulfur-containing conjugated structure additive to the volume of the non-aqueous solvent is 0.1 to 10 mg / mL.
  • Another aspect of the present invention is a lithium metal secondary battery including the electrolyte for a lithium metal secondary battery of the present invention, a positive electrode, a negative electrode, and a separator.
  • the effective part of the sulfur-containing conjugated structure additive is a sulfur head group and a molecular fragment connected by a conjugated structure, and the entire acting portion exists in a molecular form or is connected to the macromolecule and the substrate as an active group.
  • the sulfur head group can undergo adsorption catalysis on the surface of metallic lithium under the stability of the conjugated structure, promote the deposition of lithium and play a role in leveling.
  • the sulfur head group is adsorbed on the surface of the lithium metal, and the subsequent conjugated group containing a double bond stabilizes the sulfur head group and forms a solvent-soluble component with other organic structures, giving a certain solubility.
  • the sulfur head group gives the growth point of lithium deposition and reduces the growth energy barrier, which is different from the performance of sulfur-containing additives in traditional copper and zinc electroplating.
  • the sulfur-containing conjugate structure additive is suitable for various electrolyte systems such as ethers, esters, ionic liquids, and gel electrolytes, that is, it is used in liquid and condensed lithium secondary batteries and lithium air batteries.
  • Figure 1 shows a scanning electron microscope (SEM) image of a lithium sheet without any treatment at different magnifications.
  • Figure 2a is a scanning electron micrograph of the surface of a lithium electrode after a long cycle in a conventional ether electrolyte
  • Figure 2b is a long cycle performance of a lithium-lithium symmetrical battery in a conventional ether electrolyte at normal temperature (25 ° C) curve.
  • the current density for charging and discharging is 2mA cm -2
  • the amount of lithium metal circulated is controlled to 1mAh cm -2 .
  • FIG. 3a is a scanning electron microscope image of a lithium electrode surface after a long cycle in an ether electrolyte containing dithiooxamide.
  • Fig. 3b Long-cycle performance curve of a lithium-sulfur symmetrical battery in an ether electrolyte containing dithiooxamide at a room temperature (25 ° C) using dithiooxamide as an electrolyte containing a sulfur-containing conjugate structure additive .
  • the current density for charging and discharging is 2mA cm -2 , and the amount of lithium metal circulated is controlled to 1mAh cm -2 .
  • Figure 4a is a lithium-lithium symmetrical battery first cycled in a conventional electrolyte for 20 weeks. After the lithium dendrite is generated, the battery is disassembled, two lithium pieces are taken out, and then the ether electrolyte containing dithiooxamide Scanning electron micrograph of the surface of the lithium electrode after the battery was assembled and cycled for 20 weeks.
  • 4b and 4c show the long-cycle performance of a lithium-lithium symmetrical battery after being disassembled and reassembled in an ether electrolyte containing no dithiooxamide and an ether electrolyte containing dithiooxamide, respectively.
  • the current density for charging and discharging is 2mA cm -2 , and the amount of lithium metal circulated is controlled to 1mAh cm -2 .
  • An embodiment of the present invention is an electrolytic solution for a lithium metal secondary battery, which contains the following lithium salt, a non-aqueous solvent, and a sulfur-containing conjugate structure additive.
  • the lithium salt one or more selected from LiCl, LiF, LiFSI, LiPF 6 , LiTFSI, and LiClO 4 , and preferably one or more selected from LiPF 6 , LiTFSI, and LiClO 4 .
  • LiPF 6 , LiTFSI, and LiClO 4 are used, the surface flatness of the lithium negative electrode and the cycle performance of the lithium-lithium symmetrical battery in the present invention are significantly better than other lithium salts.
  • the added amount of the lithium salt is 0.5-10 mol / L, preferably 1-5 mol / L, and even more preferably 1-3 mol / L.
  • the added amount of the lithium salt is less than 1 mol / L, the lithium ion migration ability of the solution will be reduced, the conductivity of the solution will be affected, and the cycle performance under high current density of the lithium battery will be affected. Above 10mol / L, it will be limited by the solubility of the lithium salt.
  • the lithium salt when the lithium salt is added in an excessive amount, the viscosity of the electrolyte becomes very high, which affects the wettability of the electrolyte to the lithium negative electrode. It will further affect the cycling performance of the battery.
  • the present invention suppresses the growth of lithium dendrites, improves the flatness of the surface of the lithium negative electrode, and further improves the cycle life of the lithium battery.
  • the non-aqueous solvent may be selected from 1,3-dioxolane (DOL), ethylene glycol dimethyl ether (DME), ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate ( DMC), one or more of propylene carbonate (PC), preferably a mixed solvent of 1,3-dioxolane (DOL) and ethylene glycol dimethyl ether (DME), ethylene carbonate (EC) Mixed solvent with diethyl carbonate (DEC), mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) or propylene carbonate (PC).
  • DOL 1,3-dioxolane
  • DME ethylene glycol dimethyl ether
  • EC ethylene carbonate
  • DMC dimethyl carbonate
  • PC propylene carbonate
  • the surface smoothness of lithium in the present invention is high, and the lithium-lithium symmetrical battery has the longest cycle life.
  • the volume ratio of the mixed solvent is 1: 5-5: 1, preferably 1: 1.
  • DOL 1,3-dioxolane
  • DME ethylene glycol dimethyl ether
  • the sulfur-containing conjugate structure additive one or more selected from the group consisting of carbonyl sulfurs and thioethers, and preferably one or more selected from carbonyl sulfurs, thioethers and sulfones Most preferred are carbonyl sulfurs.
  • carbonyl sulfurs it is preferable that the sulfur-containing conjugated structure additive does not contain a benzene ring.
  • the lithium negative electrode has a relatively flat surface without dendrites, and the cycle performance of the lithium-lithium symmetrical battery is greatly improved.
  • the benzene ring-containing sulfur-containing conjugated structure additive is used, the surface of the lithium negative electrode is relatively uneven and has high and low protrusions. In the subsequent further cycle process, it is easy to cause short-circuit and other behaviors, reducing the lithium-lithium symmetrical battery. Cycle life.
  • carbonyl sulfur examples include carbon disulfide, thiourea, dithiooxamide, thioacetamide, and diphenylthiourea.
  • thioethers examples include thiophene and diphenyl sulfide.
  • the addition amount of the sulfur-containing conjugate structure additive is 0.01 to 100 mg / mL, preferably 0.05 to 50 mg / mL, and more preferably 0.1 to 10 mg / mL with respect to the volume of the non-aqueous solvent.
  • the added amount of the sulfur-containing conjugate structure additive is less than 0.01 mg / mL, the concentration of the additive is too low, and a good result of leveling the surface morphology of the lithium negative electrode may not be achieved, thereby preventing the suppression of lithium.
  • the effect of dendrites when the amount of the sulfur-containing conjugated structure additive is higher than 100 mg / mL, it will be limited by the solubility of the additive, thereby increasing the viscosity of the electrolyte and affecting the lithium being wetted by the electrolyte. Wet capacity, in addition, will cause waste of additives and increase costs.
  • the present invention successfully obtains a dendritic-free smooth lithium negative electrode, which greatly improves the cycle life of a lithium battery.
  • lithium metal secondary battery of the present invention To the electrolytic solution for a lithium metal secondary battery of the present invention, other additives commonly used in the art may be added as needed, such as lithium nitrate, lithium sulfide, fluoroethylene carbonate, vinylene carbonate, and the like.
  • Another embodiment of the present invention is a metal lithium secondary battery including the above-mentioned electrolyte for a metal lithium secondary battery of the present invention, the following positive electrode, negative electrode, and separator.
  • the positive electrode is an electrode having a positive electrode active material layer on a positive electrode current collector.
  • a material capable of occluding and releasing lithium ions during charge and discharge can be used, such as a layered lithium manganate such as LiMnO 2 or LixMn 2 O 4 (0 ⁇ x ⁇ 2), spinel-type lithium manganate, LiCoO 2 , LiNiO 2 , substances in which a part of the transition metal existing in the above-mentioned compound is replaced by other metals, olivine compounds such as LiFePO 4 and LiMnPO 4 , Li 2 MSiO 4 (M is at least one selected from the group consisting of Mn, Fe, and Co), active non-metals such as S, I 2 and various active support forms thereof. They can be used alone or in a combination of two or more.
  • the negative electrode is a lithium sheet or a carrier containing lithium, such as a foamed nickel and a foamed copper carrier.
  • any separator may be used as long as it suppresses the contact between the positive electrode and the negative electrode, makes charge carriers permeable, and has durability in the electrolytic solution.
  • Specific materials suitable for the separator may include polyolefins such as polypropylene or polyethylene microporous membranes, cellulose, polyethylene terephthalate, polyimide, polyvinylidene fluoride, and the like. They can be used in the form of, for example, porous films, woven fabrics, or non-woven fabrics.
  • the lithium metal secondary battery electrolyte of the present invention According to the lithium metal secondary battery electrolyte of the present invention and the lithium metal secondary battery using the lithium metal secondary battery electrolyte, it can be known from the results of the charge and discharge test and SEM test that the lithium metal secondary battery electrolyte of the present invention
  • the surface of the lithium metal negative electrode is flat and free of protrusions, which fundamentally solves the problem of lithium dendrites and improves the cycle life of the lithium battery.
  • the charge and discharge test and SEM test are as follows:
  • Charging and discharging test The lithium-lithium symmetrical battery recognized in the industry is used to characterize the short-circuit behavior of the lithium battery caused by the lithium dendrite, which affects the cycle life of the battery.
  • the test conditions are: a blue battery test system is used to perform a long-term charge and discharge cycle test until the battery is short-circuited, and the cycle time that has been performed when the battery is short-circuited is recorded.
  • the current density for charging and discharging is 2 mA cm -2 , the amount of lithium metal circulated is controlled to 1 mAh cm -2 , and the test temperature is controlled at 25 ° C.
  • the lithium sheets used for testing below are all negative lithium sheets.
  • LiTFSI Lithium bistrifluoromethanesulfonimide
  • DOL 1,3-dioxolane
  • DME ethylene glycol dimethyl ether
  • a double lithium symmetrical battery was assembled with the above-mentioned electrolyte, and the battery was subjected to a charge and discharge test.
  • test current density was 2 mA cm -2 and the amount of lithium metal circulated was controlled to 1 mAh cm -2 .
  • cycle performance is shown in Figure 2b, and the SEM image of the negative lithium sheet of the battery after disassembly is shown in Figure 2a after 20 weeks of cycling.
  • LiPF 6 Lithium hexafluorophosphate
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • the current density was 2 mA cm -2 and the amount of lithium metal circulated was controlled to 1 mAh cm -2 .
  • LiPF 6 Lithium hexafluorophosphate
  • EC ethylene carbonate
  • DMC dimethyl carbonate
  • the current density was 2 mA cm -2 and the amount of lithium metal circulated was controlled to 1 mAh cm -2 .
  • Lithium perchlorate LiClO 4
  • PC propylene carbonate
  • a double lithium symmetrical battery was assembled with the above-mentioned electrolyte, and the battery was subjected to a charge and discharge test. The current density was 2 mA cm -2 and the amount of lithium metal circulated was controlled to 1 mAh cm -2 .
  • Lithium bistrifluoromethanesulfonimide LiTFSI was added to a mixed solvent of 1,3-dioxolane (DOL) -ethylene glycol dimethyl ether (DME) (DOL and DME volume ratio was 1: 1) ), Formulated into an electrolyte of 1 mol / L, and then adding dithiooxamide, stirring and dissolving until a uniform solution is formed (the concentration of the dithiooxamide is 0.1 mg / mL (the concentration of the sulfur-containing conjugate additive The ratio of the mass to the volume of the non-aqueous solvent is the same below)).
  • DOL 1,3-dioxolane
  • DME ethylene glycol dimethyl ether
  • a double lithium symmetrical battery was assembled with the above-mentioned electrolyte, and the battery was subjected to a charge and discharge test.
  • the current density was 2 mA cm -2 and the amount of lithium metal circulated was controlled to 1 mAh cm -2 .
  • Lithium bistrifluoromethanesulfonimide (LiTFSI) was added to a mixed solvent of 1,3-dioxolane (DOL) -ethylene glycol dimethyl ether (DME) (DOL and DME volume ratio was 1: 1) )
  • DOL 1,3-dioxolane
  • DME ethylene glycol dimethyl ether
  • DOL and DME volume ratio was 1: 1)
  • a double lithium symmetrical battery was assembled with the above-mentioned electrolyte, and the battery was subjected to a charge and discharge test. The current density was 2 mA cm -2 and the amount of lithium metal circulated was controlled to 1 mAh cm -2 .
  • Lithium bistrifluoromethanesulfonimide (LiTFSI) was added to a mixed solvent of 1,3-dioxolane (DOL) -ethylene glycol dimethyl ether (DME) (DOL and DME volume ratio was 1: 1) )
  • DOL 1,3-dioxolane
  • DME ethylene glycol dimethyl ether
  • Lithium bistrifluoromethanesulfonimide (LiTFSI) was added to a mixed solvent of 1,3-dioxolane (DOL) -ethylene glycol dimethyl ether (DME) (DOL and DME volume ratio was 1: 1) ), Prepare an electrolyte of 1 mol / L, add dithiooxamide, stir and dissolve until a uniform solution is formed (dithiooxamide concentration is 10 mg / mL).
  • a double lithium symmetrical battery was assembled with the above-mentioned electrolyte, and the battery was subjected to a charge and discharge test. The current density was 2 mA cm -2 and the amount of lithium metal circulated was controlled to 1 mAh cm -2 .
  • Lithium hexafluorophosphate LiPF 6 was added to a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (the volume ratio of EC and DEC was 1: 1) to prepare a 1 mol / L electrolytic solution, and then added to The thiooxamide is stirred and dissolved until a uniform solution is formed (the concentration of the dithiooxamide is 0.1 mg / mL).
  • a double lithium symmetrical battery was assembled with the above-mentioned electrolyte, and the battery was subjected to a charge and discharge test. The current density was 2 mA cm -2 and the amount of lithium metal circulated was controlled to 1 mAh cm -2 .
  • LiPF 6 Lithium hexafluorophosphate
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • the concentration of the dithiooxamide is 10 mg / mL.
  • a double lithium symmetrical battery was assembled with the above-mentioned electrolyte, and the battery was subjected to a charge and discharge test. The current density was 2 mA cm -2 and the amount of lithium metal circulated was controlled to 1 mAh cm -2 .
  • LiPF 6 Lithium hexafluorophosphate
  • EC ethylene carbonate
  • DMC dimethyl carbonate
  • the thiooxamide is stirred and dissolved until a uniform solution is formed (the concentration of the dithiooxamide is 0.1 mg / mL).
  • a double lithium symmetrical battery was assembled with the above-mentioned electrolyte, and the battery was subjected to a charge and discharge test. The current density was 2 mA cm -2 and the amount of lithium metal circulated was controlled to 1 mAh cm -2 .
  • LiPF 6 Lithium hexafluorophosphate
  • EC ethylene carbonate
  • DMC dimethyl carbonate
  • the thiooxamide is stirred and dissolved until a uniform solution is formed (the concentration of the dithiooxamide is 10 mg / mL).
  • a double lithium symmetrical battery was assembled with the above-mentioned electrolyte, and the battery was subjected to a charge and discharge test. The current density was 2 mA cm -2 and the amount of lithium metal circulated was controlled to 1 mAh cm -2 .
  • Lithium perchlorate LiClO 4
  • dithiooxamide was added and stirred to dissolve until a uniform solution was formed (dithiooxamide concentration was 0.1 mg). / mL).
  • a double lithium symmetrical battery was assembled with the above-mentioned electrolyte, and the battery was subjected to a charge and discharge test. The current density was 2 mA cm -2 and the amount of lithium metal circulated was controlled to 1 mAh cm -2 .
  • Lithium perchlorate LiClO 4
  • dithiooxamide was added and stirred to dissolve until a uniform solution was formed (dithiooxamide concentration was 10 mg / mL).
  • a double lithium symmetrical battery was assembled with the above-mentioned electrolyte, and the battery was subjected to a charge and discharge test. The current density was 2 mA cm -2 and the amount of lithium metal circulated was controlled to 1 mAh cm -2 .
  • An electrolytic solution was prepared in accordance with Examples 1-4, except that the dithiooxamide was replaced with thioacetamide (the concentration of thioacetamide was 0.1, 1, 5, and 10 mg / mL in this order).
  • a double lithium symmetrical battery was assembled with the above-mentioned electrolyte, and the battery was subjected to a charge and discharge test. The current density was 2 mA cm -2 and the amount of lithium metal circulated was controlled to 1 mAh cm -2 .
  • An electrolytic solution was prepared according to Example 5-6, except that the dithiooxamide was replaced by thioacetamide (the concentration of thioacetamide was 0.1, 10 mg / mL in this order).
  • a double lithium symmetrical battery was assembled with the above-mentioned electrolyte, and the battery was subjected to a charge and discharge test. The current density was 2 mA cm -2 and the amount of lithium metal circulated was controlled to 1 mAh cm -2 .
  • An electrolytic solution was prepared in accordance with Examples 7-8, except that the dithiooxamide was replaced with thioacetamide (the concentration of thioacetamide was 0.1 and 10 mg / mL in this order).
  • a double lithium symmetrical battery was assembled with the above-mentioned electrolyte, and the battery was subjected to a charge and discharge test. The current density was 2 mA cm -2 and the amount of lithium metal circulated was controlled to 1 mAh cm -2 .
  • An electrolytic solution was prepared in accordance with Examples 9-10, except that the dithiooxamide was replaced with thioacetamide (the concentration of thioacetamide was 0.1 and 10 mg / mL in this order).
  • a double lithium symmetrical battery was assembled with the above-mentioned electrolyte, and the battery was subjected to a charge and discharge test. The current density was 2 mA cm -2 and the amount of lithium metal circulated was controlled to 1 mAh cm -2 .
  • An electrolyte solution was prepared according to Examples 1-4, except that the dithiooxamide was replaced with thiourea (the concentration of thiourea was 0.1, 1, 5, and 10 mg / mL in this order).
  • a double lithium symmetrical battery was assembled with the above-mentioned electrolyte, and the battery was subjected to a charge and discharge test. The current density was 2 mA cm -2 and the amount of lithium metal circulated was controlled to 1 mAh cm -2 .
  • An electrolytic solution was prepared according to Example 5-6, except that the dithiooxamide was replaced with thiourea (the concentration of thiourea was 0.1 and 10 mg / mL in this order).
  • a double lithium symmetrical battery was assembled with the above-mentioned electrolyte, and the battery was subjected to a charge and discharge test. The current density was 2 mA cm -2 and the amount of lithium metal circulated was controlled to 1 mAh cm -2 .
  • An electrolytic solution was prepared in accordance with Examples 7-8, except that the dithiooxamide was replaced with thiourea (the concentration of thiourea was 0.1 and 10 mg / mL in this order).
  • a double lithium symmetrical battery was assembled with the above-mentioned electrolyte, and the battery was subjected to a charge and discharge test. The current density was 2 mA cm -2 and the amount of lithium metal circulated was controlled to 1 mAh cm -2 .
  • An electrolyte solution was prepared in accordance with Examples 9-10, except that the dithiooxamide was replaced with thiourea (the concentration of thiourea was 0.1 and 10 mg / mL in this order).
  • a double lithium symmetrical battery was assembled with the above-mentioned electrolyte, and the battery was subjected to a charge and discharge test. The current density was 2 mA cm -2 and the amount of lithium metal circulated was controlled to 1 mAh cm -2 .
  • An electrolytic solution was prepared in accordance with Examples 1-4, except that the dithiooxamide was replaced with thiophene (the concentration of thiophene was 0.1, 1, 5, and 10 mg / mL in this order).
  • a double lithium symmetrical battery was assembled with the above-mentioned electrolyte, and the battery was subjected to a charge and discharge test. The current density was 2 mA cm -2 and the amount of lithium metal circulated was controlled to 1 mAh cm -2 .
  • An electrolytic solution was prepared in accordance with Example 5-6, except that the dithiooxamide was replaced by thiophene (the concentration of thiophene was 0.1 and 10 mg / mL in this order).
  • a double lithium symmetrical battery was assembled with the above-mentioned electrolyte, and the battery was subjected to a charge and discharge test. The current density was 2 mA cm -2 and the amount of lithium metal circulated was controlled to 1 mAh cm -2 .
  • An electrolytic solution was prepared in accordance with Examples 7-8, except that the dithiooxamide was replaced by thiophene (the concentration of thiophene was 0.1 and 10 mg / mL in this order).
  • a double lithium symmetrical battery was assembled with the above-mentioned electrolyte, and the battery was subjected to a charge and discharge test. The current density was 2 mA cm -2 and the amount of lithium metal circulated was controlled to 1 mAh cm -2 .
  • An electrolytic solution was prepared in accordance with Examples 9-10, except that the dithiooxamide was replaced with thiophene (the concentration of thiophene was 0.1 and 10 mg / mL in this order).
  • a double lithium symmetrical battery was assembled with the above-mentioned electrolyte, and the battery was subjected to a charge and discharge test. The current density was 2 mA cm -2 and the amount of lithium metal circulated was controlled to 1 mAh cm -2 .
  • An electrolyte solution was prepared in accordance with Examples 1-4, except that the dithiooxamide was replaced with carbon disulfide (the concentration of carbon disulfide was 0.1, 1, 5, and 10 mg / mL in this order).
  • a double lithium symmetrical battery was assembled with the above-mentioned electrolyte, and the battery was subjected to a charge and discharge test. The current density was 2 mA cm -2 and the amount of lithium metal circulated was controlled to 1 mAh cm -2 .
  • An electrolytic solution was prepared in accordance with Example 5-6, except that the dithiooxamide was replaced with carbon disulfide (the concentration of carbon disulfide was 0.1 and 10 mg / mL in this order).
  • a double lithium symmetrical battery was assembled with the above-mentioned electrolyte, and the battery was subjected to a charge and discharge test. The current density was 2 mA cm -2 and the amount of lithium metal circulated was controlled to 1 mAh cm -2 .
  • An electrolyte solution was prepared according to Examples 7-8, except that the dithiooxamide was replaced with carbon disulfide (the concentration of carbon disulfide was 0.1, 10 mg / mL in this order).
  • a double lithium symmetrical battery was assembled with the above-mentioned electrolyte, and the battery was subjected to a charge and discharge test. The current density was 2 mA cm -2 and the amount of lithium metal circulated was controlled to 1 mAh cm -2 .
  • An electrolyte solution was prepared according to Examples 9-10, except that the dithiooxamide was replaced with carbon disulfide (the concentration of carbon disulfide was 0.1, 10 mg / mL in this order).
  • a double lithium symmetrical battery was assembled with the above-mentioned electrolyte, and the battery was subjected to a charge and discharge test. The current density was 2 mA cm -2 and the amount of lithium metal circulated was controlled to 1 mAh cm -2 .
  • An electrolyte solution was prepared according to Examples 1-4, except that the dithiooxamide was replaced by diphenyl sulfide (the concentration of diphenyl sulfide was 0.1, 1, 5, and 10 mg / mL in this order).
  • a double lithium symmetrical battery was assembled with the above-mentioned electrolyte, and the battery was subjected to a charge and discharge test. The current density was 2 mA cm -2 and the amount of lithium metal circulated was controlled to 1 mAh cm -2 .
  • An electrolyte solution was prepared according to Example 5-6, except that the dithiooxamide was replaced by diphenyl sulfide (the concentration of diphenyl sulfide was 0.1, 10 mg / mL in this order).
  • a double lithium symmetrical battery was assembled with the above-mentioned electrolyte, and the battery was subjected to a charge and discharge test. The current density was 2 mA cm -2 and the amount of lithium metal circulated was controlled to 1 mAh cm -2 .
  • An electrolyte solution was prepared in accordance with Example 7-8, except that the dithiooxamide was replaced by diphenyl sulfide (the concentration of diphenyl sulfide was 0.1, 10 mg / mL in this order).
  • a double lithium symmetrical battery was assembled with the above-mentioned electrolyte, and the battery was subjected to a charge and discharge test. The current density was 2 mA cm -2 and the amount of lithium metal circulated was controlled to 1 mAh cm -2 .
  • An electrolyte solution was prepared according to Examples 9-10, except that the dithiooxamide was replaced by diphenyl sulfide (the concentration of diphenyl sulfide was 0.1, 10 mg / mL in this order).
  • a double lithium symmetrical battery was assembled with the above-mentioned electrolyte, and the battery was subjected to a charge and discharge test. The current density was 2 mA cm -2 and the amount of lithium metal circulated was controlled to 1 mAh cm -2 .
  • An electrolytic solution was prepared in accordance with Examples 1-4, except that the dithiooxamide was replaced with diphenylthiourea (the concentration of diphenylthiourea was 0.1, 1, 5, and 10 mg / mL in this order).
  • a double lithium symmetrical battery was assembled with the above-mentioned electrolyte, and the battery was subjected to a charge and discharge test. The current density was 2 mA cm -2 and the amount of lithium metal circulated was controlled to 1 mAh cm -2 .
  • An electrolytic solution was prepared according to Example 5-6, except that the dithiooxamide was replaced with diphenylthiourea (the concentration of diphenylthiourea was 0.1, 10 mg / mL in this order).
  • a double lithium symmetrical battery was assembled with the above-mentioned electrolyte, and the battery was subjected to a charge and discharge test. The current density was 2 mA cm -2 and the amount of lithium metal circulated was controlled to 1 mAh cm -2 .
  • An electrolytic solution was prepared according to Examples 7-8, except that the dithiooxamide was replaced with diphenylthiourea (the concentration of diphenylthiourea was 0.1, 10 mg / mL in this order).
  • a double lithium symmetrical battery was assembled with the above-mentioned electrolyte, and the battery was subjected to a charge and discharge test. The current density was 2 mA cm -2 and the amount of lithium metal circulated was controlled to 1 mAh cm -2 .
  • An electrolytic solution was prepared in accordance with Examples 9-10, except that the dithiooxamide was replaced with diphenylthiourea (the concentration of diphenylthiourea was 0.1, 10 mg / mL in this order).
  • a double lithium symmetrical battery was assembled with the above-mentioned electrolyte, and the battery was subjected to a charge and discharge test. The current density was 2 mA cm -2 and the amount of lithium metal circulated was controlled to 1 mAh cm -2 .
  • Example 5 LiPF 6 EC / DEC Dithiooxamide 0.1mg / mL ⁇ 250
  • Example 6 LiPF 6 EC / DEC Dithiooxamide 10mg / mL ⁇ 500
  • Example 7 LiPF 6 EC / DMC Dithiooxamide 0.1mg / mL ⁇ 230
  • Example 8 LiPF 6 EC / DMC Dithiooxamide 10mg / mL ⁇ 480
  • Example 9 LiClO 4 PC Dithiooxamide 0.1mg / mL ⁇ 200
  • Example 10 LiClO 4 PC Dithiooxamide 10mg / mL ⁇ 400
  • Example 11 LiTFSI DOL / DME Thioacetamide 0.1mg / mL ⁇ 500
  • Example 12 LiTFSI DOL / DME Thioacetamide 1mg / mL ⁇ 1200
  • Example 13 LiTFSI DOL / DME Thi
  • Example 49 LiClO 4 PC Carbon disulfide 0.1mg / mL ⁇ 500
  • Example 50 LiClO 4 PC Carbon disulfide 10mg / mL ⁇ 900
  • Example 51 LiTFSI DOL / DME Diphenyl sulfide 0.1mg / mL ⁇ 300
  • Example 52 LiTFSI DOL / DME Diphenyl sulfide 1mg / mL ⁇ 500
  • Example 53 LiTFSI DOL / DME Diphenyl sulfide 5mg / mL ⁇ 800
  • Example 54 LiTFSI DOL / DME Diphenyl sulfide 10mg / mL ⁇ 1000
  • Example 55 LiPF 6 EC / DEC Diphenyl sulfide 0.1mg / mL ⁇ 250
  • Example 56 LiPF 6 EC / DEC Diphenyl sulfide 10mg / mL
  • Lithium bistrifluoromethanesulfonimide (LiTFSI) was added to a mixed solvent of 1,3-dioxolane (DOL) -ethylene glycol dimethyl ether (DME) (DOL and DME volume ratio was 1: 1) ), Prepared as an electrolyte of 1 mol / L, and recorded as electrolyte 1. Thereafter, dithiooxamide was added to the electrolytic solution 1, and the solution was stirred and dissolved until a uniform solution was formed (the concentration of the dithiooxamide was 1 mg / mL), and was referred to as electrolytic solution 2. The electrolytic solution 1 was used to assemble a double lithium symmetrical battery, and the battery was subjected to a charge and discharge test.
  • DOL 1,3-dioxolane
  • DME ethylene glycol dimethyl ether
  • the current density was 2 mA cm -2 and the amount of lithium metal circulated was controlled to 1 mAh cm -2 .
  • disassemble the battery in the glove box After a 20-week cycle, disassemble the battery in the glove box, reassemble the circulated lithium chip with electrolyte 1 and electrolyte 2, respectively, and perform the charge and discharge test again.
  • the current density is 2mA cm -2 .
  • the amount of lithium metal was controlled to 1 mAh cm -2 .
  • a comparison of the cycle performance is shown in FIG. 4b.
  • the SEM image of the lithium sheet of the battery after disassembling it after 20 weeks of circulation in electrolyte 1 and 20 weeks in electrolyte 2 is shown in FIG. 4a.
  • the addition of sulfur-containing conjugate structure additives can improve the cycle life of lithium-ion batteries, and lower or higher than this concentration range will not achieve the expected effect. If the concentration is lower than 0.01mg / mL, the effect of leveling the surface of the lithium electrode will not be achieved. If it is higher than 100mg / mL, during the long cycle of the battery, with the decomposition of the electrolyte, there will be some additive particles on the lithium surface. Precipitation will affect the cycle life of the battery.
  • the battery will form small protrusions, that is, dendrites, under pure electrolyte. After a long cycle, lithium is preferentially deposited on the protrusions, thereby The dendrite grows indefinitely.
  • the cycle of adding dithiooxamide raised dendritic lithium chips have been produced. After 20 weeks of cycling under the dithiooxamide environment, the surface of the lithium chip appears obvious. Leveling and repair phenomena. This smooth lithium surface proves that the additive dithiooxamide can repair the uneven dendrites on the surface of the lithium sheet, which fundamentally inhibits the formation of dendrites, thereby effectively improving the cycle life of the lithium battery.

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Abstract

本发明公开了一种含有含硫共轭结构添加剂的金属锂二次电池用电解液以及使用该电解液的金属锂二次电池。所述金属锂二次电池用电解液由锂盐、非水溶剂和含硫共轭结构添加剂构成，所述含硫共轭结构添加剂的质量相对于非水溶剂体积的比值为0.01-100mg/mL。本发明通过选取含有特定量的特定添加剂成分的电解液，能够有效的抑制金属锂二次电池中锂枝晶的生长，从而起到提高金属锂二次电池循环性能和安全性的作用。

Description

金属锂二次电池用电解液以及使用该电解液的金属锂二次电池 技术领域
本发明属于电池技术领域，具体涉及一种含有含硫共轭结构添加剂的金属锂二次电池用电解液以及使用了该电解液的金属锂二次电池。
背景技术
近些年来，环境污染及其引发的雾霾已成为威胁国民健康的重大隐患，其中相当一部分污染来自于化石燃料的燃烧。为解决化石燃料产生的环境问题，各种绿色能源逐渐走进人们的视野。其中，绿色能源锂电池由于其能量密度高、自放电小等特点已经在储能、通讯和交通运输领域得到广泛应用。在锂电池中，传统负极材料石墨因为较低的容量密度(372mA h g -1)，有限制锂电池进一步发展的趋势。因此，企业和学者们纷纷寻求更高能量密度的负极材料。
金属锂作为一种高容量密度的负极材料(3860mA h g -1)，在二次锂电池、锂空气电池中均有很大的应用潜力。但是金属锂也由于其化学性质活泼存在很大的安全问题，当锂沉积时受到浓度极化和电场影响极容易生长枝晶穿刺隔膜，引发一系列安全问题。
为了增强具有金属锂负极的金属锂二次电池的安全性，目前的方法大多集中在锂金属表面的修饰，即在锂负极表面形成一层稳定的，具有高导锂离子能力的界面保护膜(SEI(Solid electrolyte interphase)膜)。如一种方法是在锂电极表面原位形成无机的导离子能力高、机械强度高的富含LiF的SEI膜，加速锂的沉积溶解能力和抑制锂枝晶生长，比如在电解液中添加氟代碳酸乙烯酯(Angew.Chem.Int.Ed.2018,57,1–6)等来形成富含F元素的无机的SEI膜，从而稳定锂负极，抑制枝晶生长。再如，另一种方法则是使用有机膜去保护金属锂，比如使用吡咯等化合物在金属锂表面形成保护膜抑制枝晶生长，增强阳极稳定性(专利文献：CN102315420A)。但是，上面提到的方法都并不能根本上解决溶液中浓度梯度引起的不均匀沉积，同时所形成的膜也容易随着金属表面变形发生变形，在电流密度较大时难以较好的保护阳极表面，从而产生枝晶。也即只能起到抑制锂枝晶的生长效果，而不能从根本上去防止锂枝晶的形成。
此外，还有方法是加入其它复杂的大分子添加剂，提升锂的嵌入脱出效率，从而防止高电流密度下的短路行为。然而这种复杂的添加剂分子合成困难，制备过程繁琐，成本昂贵，很难去实际应用(专利文献：CN108054429A)。
发明内容
为了从根本上克服现有的锂金属表面枝晶生长的问题，本发明提供一种含有小分子的含硫共轭结构添加剂的金属锂二次电池用电解液以及使用了该电解液的金属锂二次电池，能够以较低成本防止可充金属锂电池产生枝晶。
本发明的为一种金属锂二次电池用电解液，其含有锂盐、非水溶剂和含硫共轭结构添加剂，其中，所述锂盐的浓度为0.5-10mol/L，含硫共轭结构添加剂的质量相对于非水溶剂体积的比值为0.01-100mg/mL。
本发明的所述金属锂二次电池用电解液中，优选的，所述锂盐为LiPF 6、LiTFSI和LiClO 4中的一种或多种。
本发明的所述金属锂二次电池用电解液中，作为非水溶剂，可选自1,3-二氧戊环(DOL)、乙二醇二甲醚(DME)、碳酸乙烯酯(EC)、碳酸二乙酯(DEC)、碳酸二甲酯(DMC)、碳酸丙烯酯(PC)中的一种或多种。
本发明的所述金属锂二次电池用电解液中，优选的，所述非水溶剂为1,3-二氧戊环(DOL)和乙二醇二甲醚(DME)的混合溶剂、碳酸乙烯酯(EC)和碳酸二乙酯(DEC)的混合溶剂、碳酸乙烯酯(EC)和碳酸二甲酯(DMC)的混合溶剂或碳酸丙烯酯(PC)。
本发明的所述金属锂二次电池用电解液中，优选的，所述含硫共轭结构添加剂为羰基硫类、硫醚类和砜类中的一种或多种。
本发明的所述金属锂二次电池用电解液中，优选的，所述含硫共轭结构添加剂为二硫代草酰胺、硫代乙酰胺、硫脲、噻吩、二硫化碳、二苯硫醚、或二苯硫脲。
本发明的所述金属锂二次电池用电解液中，优选的，所述含硫共轭结构添加剂不含有苯环。
本发明的所述金属锂二次电池用电解液中，优选的，所述含硫共轭结构添加剂的质量相对于非水溶剂体积的比值为0.05-50mg/mL。
本发明的所述金属锂二次电池用电解液中，优选的，所述含硫共轭结构添加剂的质量相对于非水溶剂体积的比值为0.1-10mg/mL。
本发明的另一个方面为一种金属锂二次电池，其具备本发明的金属锂二次电池用电解液、正极、负极和隔膜。
本发明中，含硫共轭结构添加剂中的有效部位为硫头基和以共轭结构连接的分子片段，整个作用部分以分子形式存在或作为活性基团连接到大分子和基底中。进一步，硫头基在共轭结构稳定下可以在金属锂表面发生吸附催化，促进锂的沉积并起到整平作用。其中硫头基 吸附在金属锂表面，后续含有双键的共轭基团稳定硫头基并与其他有机结构组成亲溶剂成分，给予一定溶解能力。硫头基给予锂沉积的生长点，降低其生长的能垒，这一点不同于含硫添加剂在传统铜、锌电镀中的表现。所述含硫共轭结构添加剂适用于醚类、酯类、离子液体和凝胶电解质等多种电解质体系，即在液态、凝聚态锂二次电池和锂空气电池中均有应用。
附图说明
图1示出了未经过任何处理的锂片在不同放大倍数下的扫描电镜(SEM)图。
图2a是在常规的醚类电解液中长循环后的锂电极表面的扫描电镜图；图2b是在常温(25℃)下，锂锂对称电池于常规的醚类电解液中的长循环性能曲线。充电以及放电的电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。
图3a是在含有二硫代草酰胺的醚类电解液中长循环后的锂电极表面的扫描电镜图。图3b是以二硫代草酰胺作为电解液的含硫共轭结构添加剂，在常温(25℃)下，锂锂对称电池于含有二硫代草酰胺的醚类电解液中的长循环性能曲线。充电以及放电的电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。
图4a是锂锂对称电池先一步在常规的电解液中循环20周，产生锂枝晶后，拆开电池，取出两个锂片，之后再在含有二硫代草酰胺的醚类电解液中组装电池并循环20周后的锂电极表面的扫描电镜图。图4b和图4c是拆开又重新组装后的锂锂对称电池分别在不含有二硫代草酰胺的醚类电解液和含有二硫代草酰胺的醚类电解液中的长循环性能。充电以及放电的电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。
具体实施方式
下面对本发明的具体实施方式进行说明。
本发明一个实施方式为一种金属锂二次电池用电解液，其含有下述锂盐、非水溶剂和含硫共轭结构添加剂。
(1)锂盐
作为锂盐，可选自LiCl、LiF、LiFSI、LiPF 6、LiTFSI、LiClO 4中的一种或多种，优选的是，选自LiPF 6、LiTFSI、LiClO 4中的一种或多种。当使用LiPF 6、LiTFSI、LiClO 4时，本发明中锂负极的表面平整度和锂锂对称电池的循环性能明显优于其他锂盐。
所述锂盐的添加量为0.5-10mol/L，优选为1-5mol/L，进一步优选为1-3mol/L。当所述锂盐的添加量低于1mol/L时，会导致溶液的锂离子迁移能力下降，影响溶液电导率，从而影响锂电池高电流密度下的循环性能，当所述锂盐的添加量高于10mol/L时，会受限制于锂盐的溶解度，此外，当锂盐的添加量过高时，电解液的粘度变的很高，从而又影响了电解液 对锂负极的浸润性，进一步会影响电池的循环性能。通过采用特定量的上述锂盐，本发明抑制了锂枝晶的生长，提高了锂负极表面的平整度，进一步提高了锂电池的循环寿命。
(2)非水溶剂
作为非水溶剂，可选自1,3-二氧戊环(DOL)、乙二醇二甲醚(DME)、碳酸乙烯酯(EC)、碳酸二乙酯(DEC)、碳酸二甲酯(DMC)、碳酸丙烯酯(PC)中的一种或多种，优选为1,3-二氧戊环(DOL)和乙二醇二甲醚(DME)的混合溶剂、碳酸乙烯酯(EC)和碳酸二乙酯(DEC)的混合溶剂、碳酸乙烯酯(EC)和碳酸二甲酯(DMC)的混合溶剂或碳酸丙烯酯(PC)。当使用1,3-二氧戊环(DOL)和乙二醇二甲醚(DME)的混合溶剂时，本发明中锂的表面平整度高，锂锂对称电池有着最长的循环寿命。
混合溶剂的体积比例为1:5-5:1，优选为1:1，当使用体积比为1:1的1,3-二氧戊环(DOL)和乙二醇二甲醚(DME)的混合溶剂时，本发明中抑制锂枝晶的效果最好，锂的表面最为平整，锂锂对称电池的循环寿命最高。
(3)含硫共轭结构添加剂
作为含硫共轭结构添加剂，可为选自羰基硫类、硫醚类中的一种或多种，优选的是，选自羰基硫类、硫醚类和砜类中的一种或多种，最优选为羰基硫类。其中，优选所述含硫共轭结构添加剂不含有苯环。当使用羰基硫类时，本发明中，锂负极得到了一个较为平整的无枝晶的表面，而且锂锂对称电池的循环性能得到了大的提升。当使用含苯环的含硫共轭结构添加剂时，会导致锂负极的表面较为不平整，有高低的凸起，在后续的进一步循环过程中，容易导致短路等行为，降低锂锂对称电池的循环寿命。
作为羰基硫类，可列举二硫化碳、硫脲、二硫代草酰胺、硫代乙酰胺、二苯硫脲等。
作为硫醚类，可列举噻吩、二苯硫醚等。
作为含硫共轭结构添加剂的添加量，相对于所述非水溶剂的体积为0.01-100mg/mL，优选为0.05-50mg/mL，进一步优选为0.1-10mg/mL。当所述含硫共轭结构添加剂的添加量低于0.01mg/mL时，会因为添加剂的浓度太低，起不到很好的整平锂负极表面形貌的结果，从而达不到抑制锂枝晶产生的效果，当所述含硫共轭结构添加剂的添加量高于100mg/mL时，则会受限制于添加剂溶解度的影响，从而增加了电解液的粘度和影响锂被电解液的润湿能力，此外，又会造成添加剂的浪费，增加成本。通过采用特定量的上述含硫共轭结构添加剂，本发明成功的得到了一个无枝晶的光滑的锂负极，极大程度上提高了锂电池的循环寿命。
(4)其他添加剂
本发明的金属锂二次电池用电解液中还可以根据需要添加其他本领域常用的添加剂，例 如硝酸锂、硫化锂、氟代碳酸乙烯酯、碳酸亚乙烯酯等。
本发明的另一个实施方式为一种金属锂二次电池，其具备本发明的上述金属锂二次电池用电解液，下述正极、负极和隔膜。
(1)正极
正极是在正极集电器上具有正极活性物质层的电极。作为用于正极活性物质层中的正极活性物质，可以使用在充放电期间能够吸藏和放出锂离子的物质，例如层状型锂锰酸盐如LiMnO 2或LixMn 2O 4(0<x<2)、尖晶石型锂锰酸盐、LiCoO 2、LiNiO 2、其中存在于上述化合物中的过渡金属的一部分被其他金属置换的物质、橄榄石化合物如LiFePO 4和LiMnPO 4、Li 2MSiO 4(M为选自Mn、Fe和Co中的至少一种)、活性非金属如S、I 2及其各种活性负载形式等。它们可单独使用或以两种以上组合的方式使用。
(2)负极
负极为锂片或者含有锂的载体，如泡沫镍、泡沫铜载体等。
(3)隔膜
可以使用任意隔膜，只要其抑制正极与负极的接触、使得电荷载流子可透过、并在电解液中具有耐久性即可。适用于隔膜的具体材料可以包括聚烯烃如聚丙烯或聚乙烯类微孔膜、纤维素、聚对苯二甲酸乙二醇酯、聚酰亚胺、聚偏二氟乙烯等。它们可作为诸如多孔膜、织物或无纺布的形式使用。
根据本发明的金属锂二次电池电解液以及使用了该金属锂二次电池电解液的金属锂二次电池，由充放电测试、SEM测试的结果可知，本发明的金属锂二次电池电解液使得锂金属负极表面平整无凸起，从根本上解决了锂枝晶的问题，提高了锂电池的循环寿命。充放电测试和SEM测试如下：
充放电测试：采用行业内公认的锂锂对称电池来表征由锂枝晶引起的锂电池发生短路行为，进而影响电池的循环寿命问题。测试条件为：采用蓝电电池测试系统，进行长时间的充放电循环测试，直到电池发生短路，记录电池发生短路时已经进行的循环时间。充电以及放电的电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2，测试温度控制在25℃。
SEM测试：采用日本生产的Hitachi S-4800扫描电镜进行锂的表面形貌的观察，测试电压为10kV,电流为10微安，由观察结果得到整平效果的评价，评价标准为：◎：表面平整度优异；○：表面平整度良好；△：表面平整度不佳；×：表面平整度差。
实施例
以下结合实施例，进一步阐述本发明。但这些实施例仅限于说明本发明而不用于限制本 发明的保护范围。需要理解的是，如未特别指明，以下用于测试的锂片均为负极锂片。
对比例1
对未经过任何处理的锂片在组装电池前进行SEM测试，结果如图1所示。将双三氟甲烷磺酰亚胺锂(LiTFSI)加入到1,3-二氧戊环(DOL)-乙二醇二甲醚(DME)的混合溶剂中(DOL和DME体积比为1:1)，配制成1mol/L的电解液，搅拌溶解至形成均一的溶液。用上述的电解液组装成双锂对称电池，并且对电池进行充放电测试。测试电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。循环性能如图2b所示，20周循环后拆开电池的负极锂片的SEM图如图2a所示。
对比例2
将六氟磷酸锂(LiPF 6)加入到碳酸乙烯酯(EC)和碳酸二乙酯(DEC)的混合溶剂中(EC和DEC体积比为1:1)，配制成1mol/L的电解液，搅拌溶解至形成均一的溶液。用上述的电解液组装成双锂对称电池，并且对电池进行充放电测试。电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。
对比例3
将六氟磷酸锂(LiPF 6)加入到碳酸乙烯酯(EC)和碳酸二甲酯(DMC)的混合溶剂中(EC和DMC体积比为1:1)，配制成1mol/L的电解液，搅拌溶解至形成均一的溶液。用上述的电解液组装成双锂对称电池，并且对电池进行充放电测试。电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。
对比例4
将高氯酸锂(LiClO 4)加入到碳酸丙烯酯(PC)溶剂中，配制成1mol/L的电解液，搅拌溶解至形成均一的溶液。用上述的电解液组装成双锂对称电池，并且对电池进行充放电测试。电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。
实施例1
将双三氟甲烷磺酰亚胺锂(LiTFSI)加入到1,3-二氧戊环(DOL)-乙二醇二甲醚(DME)的混合溶剂中(DOL和DME体积比为1:1)，配制成1mol/L的电解液，再加入二硫代草酰胺，搅拌溶解至形成均一的溶液(二硫代草酰胺的浓度为0.1mg/mL(所述浓度为含硫共轭添加剂的质量相对于非水溶剂体积的比值，以下同))。用上述的电解液组装成双锂对称电池，并且对电池进行充放电测试。电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。
实施例2
将双三氟甲烷磺酰亚胺锂(LiTFSI)加入到1,3-二氧戊环(DOL)-乙二醇二甲醚(DME)的混 合溶剂中(DOL和DME体积比为1:1)，配制成1mol/L的电解液，再加入二硫代草酰胺，搅拌溶解至形成均一的溶液(二硫代草酰胺的浓度为1mg/mL)。用上述的电解液组装成双锂对称电池，并且对电池进行充放电测试。电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。循环性能如图3b所示，20周循环后拆开电池的锂片的SEM图如图3 a所示。
实施例3
将双三氟甲烷磺酰亚胺锂(LiTFSI)加入到1,3-二氧戊环(DOL)-乙二醇二甲醚(DME)的混合溶剂中(DOL和DME体积比为1:1)，配制成1mol/L的电解液，再加入二硫代草酰胺，搅拌溶解至形成均一的溶液(二硫代草酰胺的浓度为5mg/mL)。用上述的电解液组装成双锂对称电池，并且对电池进行充放电测试。电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。
实施例4
将双三氟甲烷磺酰亚胺锂(LiTFSI)加入到1,3-二氧戊环(DOL)-乙二醇二甲醚(DME)的混合溶剂中(DOL和DME体积比为1:1)，配制成1mol/L的电解液，再加入二硫代草酰胺，搅拌溶解至形成均一的溶液(二硫代草酰胺的浓度为10mg/mL)。用上述的电解液组装成双锂对称电池，并且对电池进行充放电测试。电流密度是2mA cm -2，循环的锂金属的量控制为1mAhcm -2。
实施例5
将六氟磷酸锂(LiPF 6)加入到碳酸乙烯酯(EC)和碳酸二乙酯(DEC)的混合溶剂中(EC和DEC体积比为1:1)，配制成1mol/L的电解液，再加入二硫代草酰胺，搅拌溶解至形成均一的溶液(二硫代草酰胺的浓度为0.1mg/mL)。用上述的电解液组装成双锂对称电池，并且对电池进行充放电测试。电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。
实施例6
将六氟磷酸锂(LiPF 6)加入到碳酸乙烯酯(EC)和碳酸二乙酯(DEC)的混合溶剂中(EC和DEC体积比为1:1)，配制成1mol/L的电解液，再加入二硫代草酰胺，搅拌溶解至形成均一的溶液(二硫代草酰胺的浓度为10mg/mL)。用上述的电解液组装成双锂对称电池，并且对电池进行充放电测试。电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。
实施例7
将六氟磷酸锂(LiPF 6)加入到碳酸乙烯酯(EC)和碳酸二甲酯(DMC)的混合溶剂中(EC和DMC体积比为1:1)，配制成1mol/L的电解液，再加入二硫代草酰胺，搅拌溶解至形成均一的溶液(二硫代草酰胺的浓度为0.1mg/mL)。用上述的电解液组装成双锂对称电池，并且对电 池进行充放电测试。电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。
实施例8
将六氟磷酸锂(LiPF 6)加入到碳酸乙烯酯(EC)和碳酸二甲酯(DMC)的混合溶剂中(EC和DMC体积比为1:1)，配制成1mol/L的电解液，再加入二硫代草酰胺，搅拌溶解至形成均一的溶液(二硫代草酰胺的浓度为10mg/mL)。用上述的电解液组装成双锂对称电池，并且对电池进行充放电测试。电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。
实施例9
将高氯酸锂(LiClO 4)加入到PC溶剂中，配制成1mol/L的电解液，再加入二硫代草酰胺，搅拌溶解至形成均一的溶液(二硫代草酰胺的浓度为0.1mg/mL)。用上述的电解液组装成双锂对称电池，并且对电池进行充放电测试。电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。
实施例10
将高氯酸锂(LiClO 4)加入到PC溶剂中，配制成1mol/L的电解液，再加入二硫代草酰胺，搅拌溶解至形成均一的溶液(二硫代草酰胺的浓度为10mg/mL)。用上述的电解液组装成双锂对称电池，并且对电池进行充放电测试。电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。
实施例11-14
仿照实施例1-4制备电解液，只是将其中的二硫代草酰胺替换为硫代乙酰胺(硫代乙酰胺的浓度依次为0.1、1、5、10mg/mL)。用上述的电解液组装成双锂对称电池，并且对电池进行充放电测试。电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。
实施例15-16
仿照实施例5-6制备电解液，只是将其中的二硫代草酰胺替换为硫代乙酰胺(硫代乙酰胺的浓度依次为0.1、10mg/mL)。用上述的电解液组装成双锂对称电池，并且对电池进行充放电测试。电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。
实施例17-18
仿照实施例7-8制备电解液，只是将其中的二硫代草酰胺替换为硫代乙酰胺(硫代乙酰胺的浓度依次为0.1、10mg/mL)。用上述的电解液组装成双锂对称电池，并且对电池进行充放电测试。电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。
实施例19-20
仿照实施例9-10制备电解液，只是将其中的二硫代草酰胺替换为硫代乙酰胺(硫代乙酰 胺的浓度依次为0.1、10mg/mL)。用上述的电解液组装成双锂对称电池，并且对电池进行充放电测试。电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。
实施例21-24
仿照实施例1-4制备电解液，只是将其中的二硫代草酰胺替换为硫脲(硫脲的浓度依次为0.1、1、5、10mg/mL)。用上述的电解液组装成双锂对称电池，并且对电池进行充放电测试。电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。
实施例25-26
仿照实施例5-6制备电解液，只是将其中的二硫代草酰胺替换为硫脲(硫脲的浓度依次为0.1、10mg/mL)。用上述的电解液组装成双锂对称电池，并且对电池进行充放电测试。电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。
实施例27-28
仿照实施例7-8制备电解液，只是将其中的二硫代草酰胺替换为硫脲(硫脲的浓度依次为0.1、10mg/mL)。用上述的电解液组装成双锂对称电池，并且对电池进行充放电测试。电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。
实施例29-30
仿照实施例9-10制备电解液，只是将其中的二硫代草酰胺替换为硫脲(硫脲的浓度依次为0.1、10mg/mL)。用上述的电解液组装成双锂对称电池，并且对电池进行充放电测试。电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。
实施例31-34
仿照实施例1-4制备电解液，只是将其中的二硫代草酰胺替换为噻吩(噻吩的浓度依次为0.1、1、5、10mg/mL)。用上述的电解液组装成双锂对称电池，并且对电池进行充放电测试。电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。
实施例35-36
仿照实施例5-6制备电解液，只是将其中的二硫代草酰胺替换为噻吩(噻吩的浓度依次为0.1、10mg/mL)。用上述的电解液组装成双锂对称电池，并且对电池进行充放电测试。电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。
实施例37-38
仿照实施例7-8制备电解液，只是将其中的二硫代草酰胺替换为噻吩(噻吩的浓度依次为0.1、10mg/mL)。用上述的电解液组装成双锂对称电池，并且对电池进行充放电测试。电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。
实施例39-40
仿照实施例9-10制备电解液，只是将其中的二硫代草酰胺替换为噻吩(噻吩的浓度依次为0.1、10mg/mL)。用上述的电解液组装成双锂对称电池，并且对电池进行充放电测试。电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。
实施例41-44
仿照实施例1-4制备电解液，只是将其中的二硫代草酰胺替换为二硫化碳(二硫化碳的浓度依次为0.1、1、5、10mg/mL)。用上述的电解液组装成双锂对称电池，并且对电池进行充放电测试。电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。
实施例45-46
仿照实施例5-6制备电解液，只是将其中的二硫代草酰胺替换为二硫化碳(二硫化碳的浓度依次为0.1、10mg/mL)。用上述的电解液组装成双锂对称电池，并且对电池进行充放电测试。电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。
实施例47-48
仿照实施例7-8制备电解液，只是将其中的二硫代草酰胺替换为二硫化碳(二硫化碳的浓度依次为0.1、10mg/mL)。用上述的电解液组装成双锂对称电池，并且对电池进行充放电测试。电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。
实施例49-50
仿照实施例9-10制备电解液，只是将其中的二硫代草酰胺替换为二硫化碳(二硫化碳的浓度依次为0.1、10mg/mL)。用上述的电解液组装成双锂对称电池，并且对电池进行充放电测试。电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。
实施例51-54
仿照实施例1-4制备电解液，只是将其中的二硫代草酰胺替换为二苯硫醚(二苯硫醚的浓度依次为0.1、1、5、10mg/mL)。用上述的电解液组装成双锂对称电池，并且对电池进行充放电测试。电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。
实施例55-56
仿照实施例5-6制备电解液，只是将其中的二硫代草酰胺替换为二苯硫醚(二苯硫醚的浓度依次为0.1、10mg/mL)。用上述的电解液组装成双锂对称电池，并且对电池进行充放电测试。电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。
实施例57-58
仿照实施例7-8制备电解液，只是将其中的二硫代草酰胺替换为二苯硫醚(二苯硫醚的浓 度依次为0.1、10mg/mL)。用上述的电解液组装成双锂对称电池，并且对电池进行充放电测试。电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。
实施例59-60
仿照实施例9-10制备电解液，只是将其中的二硫代草酰胺替换为二苯硫醚(二苯硫醚的浓度依次为0.1、10mg/mL)。用上述的电解液组装成双锂对称电池，并且对电池进行充放电测试。电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。
实施例61-64
仿照实施例1-4制备电解液，只是将其中的二硫代草酰胺替换为二苯硫脲(二苯硫脲的浓度依次为0.1、1、5、10mg/mL)。用上述的电解液组装成双锂对称电池，并且对电池进行充放电测试。电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。
实施例65-66
仿照实施例5-6制备电解液，只是将其中的二硫代草酰胺替换为二苯硫脲(二苯硫脲的浓度依次为0.1、10mg/mL)。用上述的电解液组装成双锂对称电池，并且对电池进行充放电测试。电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。
实施例67-68
仿照实施例7-8制备电解液，只是将其中的二硫代草酰胺替换为二苯硫脲(二苯硫脲的浓度依次为0.1、10mg/mL)。用上述的电解液组装成双锂对称电池，并且对电池进行充放电测试。电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。
实施例69-70
仿照实施例9-10制备电解液，只是将其中的二硫代草酰胺替换为二苯硫脲(二苯硫脲的浓度依次为0.1、10mg/mL)。用上述的电解液组装成双锂对称电池，并且对电池进行充放电测试。电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。
将对比例1-4和实施例1-70的充放电测试结果和整平效果示于下表1中。
表1
编号 锂盐 有机溶剂 添加剂种类 添加剂浓度 整平效果 循环时间/h
对比例1 LiTFSI DOL/DME / / × 100
对比例2 LiPF 6 EC/DEC / / × 80
对比例3 LiPF 6 EC/DMC / / × 85
对比例4 LiClO 4 PC / / × 70
实施例1 LiTFSI DOL/DME 二硫代草酰胺 0.1mg/mL △ 300
实施例2 LiTFSI DOL/DME 二硫代草酰胺 1mg/mL ○ 1000
实施例3 LiTFSI DOL/DME 二硫代草酰胺 5mg/mL ○ 2000
实施例4 LiTFSI DOL/DME 二硫代草酰胺 10mg/mL ◎ 3000
实施例5 LiPF 6 EC/DEC 二硫代草酰胺 0.1mg/mL △ 250
实施例6 LiPF 6 EC/DEC 二硫代草酰胺 10mg/mL ○ 500
实施例7 LiPF 6 EC/DMC 二硫代草酰胺 0.1mg/mL △ 230
实施例8 LiPF 6 EC/DMC 二硫代草酰胺 10mg/mL ○ 480
实施例9 LiClO 4 PC 二硫代草酰胺 0.1mg/mL △ 200
实施例10 LiClO 4 PC 二硫代草酰胺 10mg/mL ○ 400
实施例11 LiTFSI DOL/DME 硫代乙酰胺 0.1mg/mL ○ 500
实施例12 LiTFSI DOL/DME 硫代乙酰胺 1mg/mL ◎ 1200
实施例13 LiTFSI DOL/DME 硫代乙酰胺 5mg/mL ◎ 1800
实施例14 LiTFSI DOL/DME 硫代乙酰胺 10mg/mL ◎ 3000
实施例15 LiPF 6 EC/DEC 硫代乙酰胺 0.1mg/mL △ 300
实施例16 LiPF 6 EC/DEC 硫代乙酰胺 10mg/mL ○ 500
实施例17 LiPF 6 EC/DMC 硫代乙酰胺 0.1mg/mL △ 280
实施例18 LiPF 6 EC/DMC 硫代乙酰胺 10mg/mL ○ 500
实施例19 LiClO 4 PC 硫代乙酰胺 0.1mg/mL △ 260
实施例20 LiClO 4 PC 硫代乙酰胺 10mg/mL ○ 470
实施例21 LiTFSI DOL/DME 硫脲 0.1mg/mL ◎ 800
实施例22 LiTFSI DOL/DME 硫脲 1mg/mL ◎ 2000
实施例23 LiTFSI DOL/DME 硫脲 5mg/mL ◎ 3000
实施例24 LiTFSI DOL/DME 硫脲 10mg/mL ◎ 4000
实施例25 LiPF 6 EC/DEC 硫脲 0.1mg/mL ○ 750
实施例26 LiPF 6 EC/DEC 硫脲 10mg/mL ◎ 1000
实施例27 LiPF 6 EC/DMC 硫脲 0.1mg/mL ○ 600
实施例28 LiPF 6 EC/DMC 硫脲 10mg/mL ◎ 800
实施例29 LiClO 4 PC 硫脲 0.1mg/mL ○ 500
实施例30 LiClO 4 PC 硫脲 10mg/mL ◎ 800
实施例31 LiTFSI DOL/DME 噻吩 0.1mg/mL ○ 500
实施例32 LiTFSI DOL/DME 噻吩 1mg/mL ◎ 800
实施例33 LiTFSI DOL/DME 噻吩 5mg/mL ◎ 1000
实施例34 LiTFSI DOL/DME 噻吩 10mg/mL ◎ 2000
实施例35 LiPF 6 EC/DEC 噻吩 0.1mg/mL ○ 300
实施例36 LiPF 6 EC/DEC 噻吩 10mg/mL ○ 500
实施例37 LiPF 6 EC/DMC 噻吩 0.1mg/mL ○ 250
实施例38 LiPF 6 EC/DMC 噻吩 10mg/mL ○ 400
实施例39 LiClO 4 PC 噻吩 0.1mg/mL ○ 300
实施例40 LiClO 4 PC 噻吩 10mg/mL ○ 600
实施例41 LiTFSI DOL/DME 二硫化碳 0.1mg/mL ○ 1000
实施例42 LiTFSI DOL/DME 二硫化碳 1mg/mL ◎ 2500
实施例43 LiTFSI DOL/DME 二硫化碳 5mg/mL ◎ 3000
实施例44 LiTFSI DOL/DME 二硫化碳 10mg/mL ◎ 4000
实施例45 LiPF 6 EC/DEC 二硫化碳 0.1mg/mL △ 500
实施例46 LiPF 6 EC/DEC 二硫化碳 10mg/mL ○ 1000
实施例47 LiPF 6 EC/DMC 二硫化碳 0.1mg/mL △ 550
实施例48 LiPF 6 EC/DMC 二硫化碳 10mg/mL ○ 1200
实施例49 LiClO 4 PC 二硫化碳 0.1mg/mL △ 500
实施例50 LiClO 4 PC 二硫化碳 10mg/mL ○ 900
实施例51 LiTFSI DOL/DME 二苯硫醚 0.1mg/mL △ 300
实施例52 LiTFSI DOL/DME 二苯硫醚 1mg/mL △ 500
实施例53 LiTFSI DOL/DME 二苯硫醚 5mg/mL △ 800
实施例54 LiTFSI DOL/DME 二苯硫醚 10mg/mL △ 1000
实施例55 LiPF 6 EC/DEC 二苯硫醚 0.1mg/mL △ 250
实施例56 LiPF 6 EC/DEC 二苯硫醚 10mg/mL △ 500
实施例57 LiPF 6 EC/DMC 二苯硫醚 0.1mg/mL △ 200
实施例58 LiPF 6 EC/DMC 二苯硫醚 10mg/mL △ 300
实施例59 LiClO 4 PC 二苯硫醚 0.1mg/mL △ 150
实施例60 LiClO 4 PC 二苯硫醚 10mg/mL △ 300
实施例61 LiTFSI DOL/DME 二苯硫脲 0.1mg/mL △ 600
实施例62 LiTFSI DOL/DME 二苯硫脲 1mg/mL △ 900
实施例63 LiTFSI DOL/DME 二苯硫脲 5mg/mL △ 950
实施例64 LiTFSI DOL/DME 二苯硫脲 10mg/mL △ 1000
实施例65 LiPF 6 EC/DEC 二苯硫脲 0.1mg/mL △ 300
实施例66 LiPF 6 EC/DEC 二苯硫脲 10mg/mL △ 400
实施例67 LiPF 6 EC/DMC 二苯硫脲 0.1mg/mL △ 350
实施例68 LiPF 6 EC/DMC 二苯硫醚 10mg/mL △ 450
实施例69 LiClO 4 PC 二苯硫醚 0.1mg/mL △ 280
实施例70 LiClO 4 PC 二苯硫醚 10mg/mL △ 320
效果实施例1
将双三氟甲烷磺酰亚胺锂(LiTFSI)加入到1,3-二氧戊环(DOL)-乙二醇二甲醚(DME)的混合溶剂中(DOL和DME体积比为1:1)，配制成1mol/L的电解液，记为电解液1。之后，向电解液1中加入二硫代草酰胺，搅拌溶解至形成均一的溶液(二硫代草酰胺的浓度为1mg/mL)，记为电解液2。用电解液1组装成双锂对称电池，并且对电池进行充放电测试，电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。经过20周的循环后，在手套箱中拆开电池，重新将循环过的锂片分别和电解液1、电解液2组装电池，再次进行充放电测试，电流密度是2mA cm -2，循环的锂金属的量控制为1mAh cm -2。循环性能对比如图4b所示，先于电解液1中循环20周，后于电解液2中循环20周后拆开电池的锂片的SEM图如图4a所示。
由上述结果可知：
1.在控制锂离子电池电解液中其他条件一致的前提下，加入含硫共轭结构添加剂二硫代草酰胺、硫代乙酰胺、硫脲、二硫化碳、噻吩、二苯硫脲、二苯硫醚的实施例1-70中，双锂对称电池的循环寿命都比相同条件下对比例1-4中不含添加剂的双锂对称电池的循环寿命长得多。
2.在一定浓度范围内，加入含硫共轭结构添加剂可以提高锂锂电池的循环寿命，低于或者高于这个浓度范围则达不到预期的效果，当加入的含硫共轭结构添加剂的浓度低于0.01mg/mL，将起不到整平锂电极表面的效果，若高于100mg/mL，在电池的长循环过程中，伴随着电解液的分解，锂表面局部会有添加剂颗粒的析出，又会影响电池的循环寿命。
3.将实施例和对比例1的电性能循环数据(即循环时间)对比后发现，在本发明提到的锂二次电池用电解液中使用的含硫共轭结构添加剂中，含有羰基硫类的添加剂在提高双锂对称电池循环寿命上的效果明显高于硫醚类的添加剂。而且，对比实施例中几种含有羰基硫类的添加剂的整平效果和电化学性能，发现含有大苯环类的添加剂分子在整平效果以及提高电池的循环寿命上作用不如小的添加剂分子，这是因为位阻大的苯环等会影响添加剂分子中S原子与锂电极表面的结合。
4.对比图1、对比例1的循环性能图2以及实施例2的循环性能图3，发现电解液在没有加入二硫代草酰胺时，电池的循环寿命很短，而且经过20周循环后锂表面有很多的小的凸起，这些凸起将在随后的长循环中进一步生长，形成锂枝晶，刺穿隔膜，影响锂电池的循环寿命和安全性能。相反，实施例2中，在含有二硫代草酰胺添加剂的电解液中，经过20周循环后，锂负极的表面非常光滑、清洁，没有任何的凸起现象，这有效地提高了电池的循环寿命和安全性能，这说明了二硫代草酰胺在整平电极表面的作用。对比长循环的电池测试结果，发现在含有含硫共轭结构添加剂的电解液中，双锂对称电池的循环寿命得到了非常大的提高。
5.对比图2和效果实施例1的图4，发现，电池在纯的电解液下会形成小的凸起，也即枝晶，在长的循环后，锂优先沉积在凸起处，从而枝晶无限放大生长，然而在加入二硫代草酰胺的循环中，已经产生凸起的枝晶状锂片，在二硫代草酰胺的环境下循环20周后，锂片的表面出现了明显的整平和修复现象。这一光洁的锂表面，证明添加剂二硫代草酰胺可以修复锂片表面的不平整枝晶现象，从根本上抑制了枝晶的生成，从而有效的提高了锂电池的循环寿命。
上述实施例仅是本发明的优选实施方案，但本发明并不仅限于上述实施例，在不脱离本发明原理的前提下进行的相应变型，也视为本发明的保护范围。

Claims (10)

  1. 一种金属锂二次电池用电解液，其含有锂盐、非水溶剂和含硫共轭结构添加剂，其中，所述锂盐的浓度为0.5-10mol/L，含硫共轭结构添加剂的质量相对于非水溶剂体积的比值为0.01-100mg/mL。
  2. 根据权利要求1所述的金属锂二次电池用电解液，其中，所述含硫共轭结构添加剂为羰基硫类、硫醚类和砜类中的一种或多种。
  3. 根据权利要求1所述的金属锂二次电池用电解液，其中，所述含硫共轭结构添加剂为二硫代草酰胺、硫代乙酰胺、硫脲、噻吩、二硫化碳、二苯硫醚、和二苯硫脲中的一种或多种。
  4. 根据权利要求1～3中任一项所述的金属锂二次电池用电解液，其中，所述含硫共轭结构添加剂不含有苯环。
  5. 根据权利要求1～3中任一项所述的金属锂二次电池用电解液，其中，所述含硫共轭结构添加剂的质量相对于非水溶剂体积的比值为0.05-50mg/mL。
  6. 根据权利要求1～3中任一项所述的金属锂二次电池用电解液，其中，所述含硫共轭结构添加剂的质量相对于非水溶剂体积的比值为0.1-10mg/mL。
  7. 根据权利要求1所述的金属锂二次电池用电解液，其中，所述锂盐为LiPF 6、LiTFSI和LiClO 4中的一种或多种。
  8. 根据权利要求1所述的金属锂二次电池用电解液，其中，所述非水溶剂为选自1,3-二氧戊环(DOL)、乙二醇二甲醚(DME)、碳酸乙烯酯(EC)、碳酸二乙酯(DEC)、碳酸二甲酯(DMC)、碳酸丙烯酯(PC)中的一种或多种。
  9. 根据权利要求1或8所述的金属锂二次电池用电解液，其中，所述非水溶剂为1,3-二氧戊环(DOL)和乙二醇二甲醚(DME)的混合溶剂、碳酸乙烯酯(EC)和碳酸二乙酯(DEC)的混合溶剂、碳酸乙烯酯(EC)和碳酸二甲酯(DMC)的混合溶剂、或碳酸丙烯酯(PC)。
  10. 一种金属锂二次电池，其具备权利要求1～9中任一项所述的金属锂二次电池用电解液、正极、负极和隔膜。
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