Study On Electrochemical Performance Of Iron Difluoride Cathode In Ionic Liquid Electrolyte

Lithium ion battery has obvious advantages such as high working voltage,high energy density and environmental protection.It is widely used in 3C products,electric vehicles,aerospace and other important fields.Metallic iron based fluoride（Fe F₂ or Fe F₃）,whose theoretical specific capacity is three to four times higher than that of the existing conversion cathode materials,is expected to replace the current commercial disembedded cathode materials,and its superior properties can be used as the first choice of the next generation cathode materials.However,the poor conductivity,large volume change during charging and discharging,large voltage lag and irreversi.（1）Using 1-ethyl-3-methyl-imidazolbis（trifluoromethanesulfonyl）imide（EMIMTFSI）,1-butyl-1-methylpiperidinbis（trifluoromethanesulfonyl）imide(PP₁₄TFSI),n-methyl-n-propylpy rrolidinbis（trifluoromethanesulfonyl）imide(PYR₁₃TFSI)as substrate,The conductivity of electrolyte added with different Li TFSI lithium concentration（0.5 M,1.0 M,1.5 M,2.0 M）at room temperature and high temperature（60℃）is better than that at room temperature by comparison.Further comparison of the electrochemical performance of different lithium concentrations at high temperature（60℃）shows that the capacity of PP₁₄TFSI matrix electrolyte is only 20 m Ah g^-1 after 150 cycles of charge and discharge,while the capacity of PYR₁₃TFSI and EMIMTFSI electrolyte after 250 cycles is 230 m Ah g^-1 and 200 m Ah g^-1,respectively:Esters（FEC）and ether（DME）add can be found,ethers electrolyte is more conducive to form stable in the process of long cycle CEI:through exploring polyacrylonitrile（PAN）modified coated ferrous fluoride can be found that after coated ferrous fluoride avoids direct contact with the electrolyte,alleviate the electrolyte of ferrous fluoride dissolution.PYR13TFSI and EMIMTFSI ionic liquids were selected for further study.（2）Using glucose doped modified ferrous fluoride as the positive electrode,PYR₁₃TFSI and EMIMTFSI as the matrix electrolyte,the influence of binary blend electrolyte and ether（DME）organic electrolyte on its electrochemical performance was investigated.The results show that the binary blend electrolyte exhibits excellent thermal stability,the thermal decomposition temperature is close to 380℃,and the electrochemical window width is 5.3 V.Appropriate EMIMTFSI can inhibit the decomposition of PYR₁₃TFSI ionic liquid on the positive electrode surface,and the electrode material modified by glucose doping has better reversible capacity in the blend electrolyte.The addition of ether（DME）organic electrolyte significantly improved the wettability of binary blend electrolyte,which was beneficial to improve the migration ability of Li⁺,and formed a more stable CEI under its action,and optimized the cycle performance and service life of the battery.（3）The electrochemical performance of ferrous fluoride anode in ionic liquid composite polymer electrolyte was studied.With polymer-polyvinyl oxide（PEO）as the matrix,sodium salt（Na TFSI）as the salt addition,different volumes（0 m L,0.3 m L,0.6 m L）ionic liquid PYR₁₄TFSI as the modification additive.The addition of ionic liquid not only improves the performance of polymer solid electrolyte,but also does not reduce its safety.Ionic liquid itself has high conductivity,good stability and other characteristics,so that the crystallinity of PEO electrolyte decreases.The thermal stability and electrical conductivity of PEO were improved.By comparison,it can be found that the conductivity of 0.6m L PYR₁₄TFSi reaches 1.03×10^-3S cm^-1 and the oxidation potential reaches 5.3V at 60℃.The reversible capacity of ferrous fluoride anode material reaches 198 m Ah g^-1 after 150 cycles in ionic liquid composite polymer PEO electrolyte.