A Bifunctional Bis(trimethylsilyl) Sulfate Additive Improved the Inorganic-Rich Solid Electrolyte Interphase for Lithium Metal Batteries

The solid electrolyte interphase (SEI) is intimately associated with the solvation structure in lithium metal batteries (LMBs), but it is difficult to incorporate the anions into the solvation structure. In this work, bis(trimethylsilyl) sulfate (BTMSS) is introduced as a bifunctional additive to bridge the cation-anion bond to modulate the solvation structure and modify the SEI composition. First, it can simultaneously complex with Li+ and PF6- to form the Li+-BTMSS-PF6- complex, thereby promoting more PF6- to enter the solvation sheath. Moreover, BTMSS has a lower LUMO energy level (-0.58 eV) and thus allows preferential decomposition to generate Li2SO3. The dual function ultimately forms the LiF/Li2SO3-rich SEI. Consequently, the BTMSS-modified electrolyte exhibits stable cycling for more than 600 h in symmetric cells. Furthermore, after 450 cycles at 1 C, the Li//LiFePO4 (7.13 mg cm-2) cell maintains 80% capacity retention. This study presents an effective additive strategy for advancing highly reversible LMBs.