Development of New Pyrazole-Based Lithium Salts for Battery Applications – Do Established Basic Design Concepts Really Work?

This work is focused on applying structural concepts and basic chemical principles to model two N-heterocyclic lithium salts, based on trifluoromethyl substituted pyrazolide anions. An easily upscalable preparation method without difficult purification steps was also developed. In a comparative study, the physicochemical properties of the two new lithium salts were investigated, particularly the effect of an additional BF3-group at the nitrogen atom. In comparison to non-substituted lithium pyrazolide, the BF3-addition led to a strong improvement of thermal and electrochemical stability, ionic conductivity, as well as better C-rate and cycling performance. Furthermore, the anodic stability of Al current collectors was investigated and compared to commercial lithium salts, namely LiPF6 and lithium bis((trifluoromethyl)sulfonyl)imide (LiTFSI). Possible mechanisms that lead to the presented improvements are discussed.