Effect of Silicon-Based Electrolyte Additive on the Solid-Electrolyte Interphase of Rechargeable Mg Batteries

The unstable solid-electrolyte interface (SEI) poses a major obstacle to the widespread use of rechargeable magnesium batteries (RMBs) as high-volumetric-capacity next-generation energy storage systems. This issue is effectively mitigated by adding 3 wt.% tris(trimethylsilyl) borate (TMSB, C9H27BO3Si3) to a state-of-the-art Cl-free magnesium tetrakis(hexafluoroisopropyloxy)borate in dimethoxyethane (Mg[B(hfip)₄]₂/DME) non-aqueous electrolyte. The modified electrolyte enables stable Mg||Mo₆S₈ (Chevrel phase, CP) full cell operation for up to 1000 cycles at a 1C rate. Tip-enhanced Raman spectroscopy (TERS) reveals that TMSB scavenges degraded electrolyte components and facilitates the formation of a uniform and thin SEI on the magnesium anode. Reflection anisotropy spectroscopy (RAS) further demonstrates that TMSB transforms the interfacial structure, creating a more isotropic and robust SEI during the initial stripping and plating process, thereby extending electrochemical cycling stability. This approach presents a compelling pathway for practical RMB development by stabilizing the SEI and optimizing magnesium electrolyte formulations.