Decorating local Li+ solvation structure and optimizing solid electrolyte interphase with potassium trifluoroacetate for dendrites-free lithium metal anodes

Abstract

Fabricating a stable and robust solid electrolyte interphase to realize the dendrites-free lithium (Li) deposition morphology in the existing commercial electrolytes remains challenging. Here, the cost-effective potassium trifluoroacetate is proposed as an electrolyte additive, in which TFA− anions have the capability to involve in constructing solid electrolyte interphase with abundant inorganic species by modulating local Li+ solvation structure. It is found that TFSI− and NO3− anions in the electrolyte can be recruited into Li+ primary solvent sheath to replace partial solvent molecules confirmed by classical molecular dynamic simulations. This is due to the strong polar interaction between TFA− anions and Li+, which is favorable for weakening the coordination of solvent molecules proved by density functional theory calculation. Besides, with the assistance of electrostatic shielding of K+, the Li deposition morphology is greatly improved. Benefiting from the potassium trifluoroacetate additive, Li+ transference number (tLi+) of 0.68, considerable ionic conductivity (σLi+) of 8.93 × 10−4 S cm−1, and stable cycling over 400 h at 1.0 mA cm−2 are obtained. Moreover, the full cells coupling with LiFePO4 cathode exhibit a low overpotential of 212.41 mV and high capacity retention of 87.67% after 283 cycles under the current density of 1.0 C.