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

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+ trans-ference number (tLi+) of 0.68, considerable ionic conductivity (sLi+) of 8.93 x 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.& COPY; 2023 Elsevier Ltd. All rights reserved.

Automated summary

A cost-effective electrolyte additive, potassium trifluoroacetate, is proposed to fabricate a stable solid electrolyte interphase for dendrites-free lithium deposition. TFA- anions can interact with Li+ and form a solid electrolyte interphase with abundant inorganic species. Molecular dynamic simulations show that TFSI- and NO3- anions in the electrolyte can replace solvent molecules and participate in the Li+ solvation sheath. This is attributed to the strong polar interaction between TFA- anions and Li+, which weakens the coordination of solvent molecules. With the assistance of electrostatic shielding of K+, the Li deposition morphology is significantly improved.