Dual strategy with Li-ion solvation and solid electrolyte interphase for high Coulombic efficiency of lithium metal anode

Lithium metal is an ideal anode for high-energy-density rechargeable batteries. However, its practical applications are hindered by the low Coulombic efficiency (CE) caused by the dendrites’ growth and the fragile SEI. Both ionic solvation behavior and SEI formation strongly affect the stability of the Li metal anode in a rechargeable battery. In this paper, 1,3-dioxolane (DOL), the well-known weak solvating capability and good SEI formation, was used as the solvent in its-fluorinated ether (TTE) blends. DOL reduced the cation-solvents interaction but reinforced the cation-anions coordination, lowering the Li plating-stripping overpotential. The addition of TTE significantly reshaped the solvation structure of Li-ion in the mixed solvent of DOL-TTE in comparison to the concentration effect. Specifically, the high TTE contents improved the electrochemical stability of the electrolyte, generated more anion-derived SEI, and resulted in the uniform Li plating-stripping that correlated with the solvation structure of more ionic aggregates less free solvents and anions. Apart from stabilizing Li anode, the decreasing free solvents in DOL-TTE (1:2) electrolytes prevented the rapid capacity decline of Li-SPAN cells from the dissolution and loss of LiPSs, obtaining 92% capacity retention and 99.77% average CE after 100 cycles.