Preparation Of Ammonium-based Ionic Plastic Crystal Solid-state Electrolytes And Their Application In Lithium Secondary Battery

With the rapid development of new energy vehicles,the traditional organic liquid electrolyte can no longer meet the safety requirements of lithium secondary batteries.As a new type of solid plasticizer with excellent thermal and electrochemical properties,ionic plastic crystals can combine with polymer and lithium salt to prepare high safety solid ionic plastic crystal-polymer solid-state electrolytes.Three kinds of ammonium-based ionic plastic crystals with different anions:triethylmethylammonium bis（fluorosulfonyl）imide(N₁₂₂₂FSI),triethyl-methylammonium bis（trifluoromethanesulfonyl）imide(N₁₂₂₂TFSI),and triethylmethyl-ammonium tetrafluoroborate(N₁₂₂₂BF₄)were synthesized.And their composition,thermal properties and ionic conductivity were characterized and analyzed.Among them,the N₁₂₂₂FSI shows the best plasticity and the highest ionic conductivity(30℃,8.33×10^-6 S cm^-1),which is expected to be used as a solid plasticizer in the solid-state electrolyte system.A series of ammonium-based ionic plastic crystal-polymeric ionic liquid solid-state electrolytes were prepared by combining ionic plastic crystal N₁₂₂₂FSI with ionic liquid polymer（P（DADMA）TFSI）)and lithium bis（trifluoromethanesulfonyl）imide（LiTFSI）.It has relatively high ionic conductivity(25℃,2.08×10^-4 S cm^-1),good thermal stability,and electrochemical stability,as well as interface performance.In addition,it was applied in Li/LiFePO₄ batteries under 40℃,and shows high discharge specific capacity,good cycle performance and rate performance.Ionic plastic crystal N₁₂₂₂FSI was combined with poly（vinylidenefluoride-co-hexafluoropropylene）（P（VDF-HFP））and lithium bis（fluorosulfonyl）imide（LiFSI）to prepare a series of ammonium-based ionic plastic crystal-P（VDF-HFP）solid-state electrolytes.It has high ionic conductivity(30℃,8.62×10^-4 S cm^-1),good thermal stability and electrochemical stability.In particular,Li/LiFePO₄ cells employing as-prepared electrolytes exhibit high discharge capacity,favorable cycling and rate performance at 30℃,which is comparable to those using liquid electrolytes.The electrolyte is expected to have great potential for application in lithium secondary batteries.