Suppressing growth of lithium dendrites by introducing deep eutectic solvents for stable lithium metal batteries

Abstract

Lithium metal anodes are recognized as one of the most promising anode materials used to increase the energy density of rechargeable lithium batteries. However, some key issues caused by lithium dendrites hinder their practical applications. The deep eutectic solvent (Li⁺[(urea)₃(TFSI⁻)₁]) is introduced into a carbonate electrolyte as an additive in this work to improve the performance of lithium metal batteries (LMBs). Consequently, the lithium symmetrical cell with 1 wt% deep eutectic solvent electrolyte exhibits a stable cycling life of over 1200 hours at a current density of 0.5 mA cm⁻², and the capacity retention of the Li/LiFePO₄ cells is maintained over 92.1% after 1000 cycles at 1C. The experimental and theoretical calculation results indicate that urea is preferentially absorbed on the Li anode surface, which is attributed to the formation of a stable solid electrolyte interphase layer enriched with Li₃N for faster Li⁺ transport. Moreover, the solvation energy of solvated Li⁺ decreases after the introduction of the deep eutectic solvent into the carbonate electrolyte for easy Li⁺ release during the desolvation process. The deep eutectic solvent can regulate the solid electrolyte interface (SEI) layer formation and reduce the lithium plating reaction barrier due to the aforementioned advantages, thus remarkably improving the electrochemical performance of the lithium metal anode.