The Research Of High Voltage Electrolyte For 5V Li-ion Batteries

In recent years,the market demand for power battery power is growing because of the faster development of the electric vehicles and the hybrid electric vehicles.A general approach is to use high-voltage platform of Lithium ion battery,which has high energy density and power density.But it is hindered by the lack of matched electrolytes,because the traditional commercial carbonate electrolyte can easily decompose under high-voltage.So,the research for high-voltage electrolyte is of great significance.In this paper,we use functional additive and lithium salts to explore their effects on high-voltage electrolyte.On additive,ethyl methoxyethoxyethyl sulfone?EMEES?was synthesized.EMEES was used as additive,to explore its affect on the electrochemistry performance of the Li/Li Ni_0.5Mn_1.5O₄ battery.On lithium salts,the aluminum foil corrosion by Lithium bis?trifluoromethanesulfonyl imide??LiTFSI?under high-voltage was studied.By adding lithium difluoro?oxalate?borate?LiODFB?to suppress the corrosion and the working mechanism was analyzed.The electrochemical performance of the Li/Li Ni_0.5Mn_1.5O₄ batteries using LiTFSI-Li ODFB-based electrolyte were studied.Considering the practical application of LiTFSI-LiODFB-based electrolyte,the compatibility between the mixed salts electrolyte and commercial anode materials of lithium iron phosphate?LiFePO₄?and of lithium cobalt oxides?LiCoO₂?was studied.First of all,ethyl methoxyethoxyethyl sulfone?EMEES?was synthesized through three steps.The product of each step have been characterized by FT-IR and NMR analysis.Then EMEES was used as additive,to explore its affect on the electrochemistry performance of the Li/LiNi_0.5Mn_1.5O₄ battery.The result shows that for Li/Li Ni_0.5Mn_1.5O₄ battery,the optimal addition of EMEES was 0.5 wt%,which can improve the cycle performance of the battery.Secondly,the aluminum foil corrosion by LiTFSI was studied after constant voltage charging for 7 days at 25? 4.2 V,60? 4.2 V,25? 4.95 V,60? 4.95 V.By adding LiODFB to suppress the corrosion and to explore the effects of LiODFB indifferent addition amount on suppressing the corrosion.Besides,the working mechanism was analyzed.The result shows that B-O compounds from LiODFB may be the main participants to suppress the corrosion of aluminum foil.Then,the electrochemical performance of the Li/Li Ni_0.5Mn_1.5O₄ batteries using Li TFSI-LiODFB-based electrolyte were studied.The result shows that the LiTFSI_0.5-LiODFB_0.5-based electrolyte batteries have the best cycle stability,which are superior to lithium hexafluoride phosphate?LiPF₆?based electrolyte batteries.Finally,the electrochemical performance of Li/Li FePO₄ and Li/LiCoO₂ using Li TFSI-Li ODFB-based electrolyte were studied at 25? and 60?.The result shows that the Li FSI_0.6-LiODFB_0.4-based electrolyte batteries have the best cycle stability at 25? and the LiTFSI_0.4-LiODFB_0.6-based electrolyte batteries have the best cycle stability at 60?,which were superior to LiPF₆-based electrolyte batteries.