A Robust Dual-Layered Solid Electrolyte Interphase Enabled by Cation Specific Adsorption-Induced Built-In Electrostatic Field for Long-Cycling Solid-State Lithium Metal Batteries

Solid-state lithium (Li) metal batteries (SSLMBs) are considered as one of the most promising next-generation battery technologies due to their high energy density and intrinsic safety. However, interfacial issues such as side reactions and Li dendrite growth severely hinder the practical application of SSLMBs. In this contribution, we proposed a cationic built-in electrostatic field to drive the generation of an anion-derived dual-layered solid electrolyte interphase (SEI). The specific adsorption of tributylmethyl-phosphonium bis(trifluoromethanesulfonyl)imide (TMPB) cations onto negatively charged Li anode surface significantly prevents interfacial side reactions between vulnerable polyethylene oxide (PEO) and Li metal. More importantly, the formed cationic built-in electrostatic field induces the targeted trapping of Li-salt anions onto the Li metal surface, leading to the generation of an anion-derived dual-layered SEI, composed of a mechanically flexible organic-rich surface layer and a Li-ion conductive inorganic-rich bottom layer. As a result, the Li||Li cell demonstrated an extended lifespan of over 1900 hours with the reduced polarization voltage. The Li||LiFePO₄ full cell also exhibited excellent cycling stability, maintaining an average Coulombic efficiency of 99.7 % over 200 cycles at 0.5 C. This work provides valuable insights into mitigating interfacial degradation and promoting uniform Li deposition through surface electrostatic field regulation.