Phosphonium Bromides Regulating Solid Electrolyte Interphase Components and Optimizing Solvation Sheath Structure for Suppressing Lithium Dendrite Growth

Abstract Electrolyte additives play important roles in suppressing lithium dendrite growth and improving the electrochemical performance of long‐life lithium metal batteries (LMBs), however, it is still challenging to design individual additive for adjusting the solid electrolyte interphase (SEI) components and changing lithium ion solvation sheath in the electrolyte at the same time for optimizing electrochemical performance. Herein, alkyl‐triphenyl‐phosphonium bromides (alkyl‐TPPB) are designed as the electrolyte additive to enhance the stability of metallic Li anode under the guidance of multi‐factor principle for electrolyte additive molecule design (EDMD). Both alkyl‐TPP cations and Br − anions produce positive influences on suppressing Li dendrite growth and stabilizing the unstable interphase between metallic Li anode/electrolyte. As expected, the optimized solvation sheath structure, and the stable SEI suppress Li dendrite growth. As a result, the Li||Li 4 Ti 5 O 12 cell reveals a long stable life over 1000 cycles with high Coulombic efficiency (99.9%). This work provides an insight on stabilizing SEI and optimizing solvation sheath structure with novel approach to develop long‐term stability and safety LMBs.