A spontaneously evolving multifunctional interphase enables durable cycling in solid-state lithium metal batteries.

NASICON-type Li1.3Al0.3Ti1.7(PO4)3 (LATP) is a highly attractive solid electrolyte for solid-state lithium batteries, yet direct contact with Li metal readily induces Ti4+ reduction, electron leakage, heterogeneous interphase growth, and stress concentration, which collectively trigger interfacial degradation and dendrite penetration. Herein, a PVDF coating loaded with modified AlN is introduced at the LATP|Li interface to address the intrinsic interfacial instability of LATP|Li. Through PVDF defluorination, the coating forms an F-N bifunctional inorganic filler framework anchored within the PVDF matrix. Upon in situ reaction with Li metal, this framework yields an F-N bifunctional mosaic-structured interphase composed of coordinated LiF/Li x Al and Li3N/Li x Al heterogeneous microdomains, synergistically blocking electron leakage, facilitating Li+ transport, homogenizing interfacial charge distribution, regulating Li deposition, and accommodating mechanical stress. Consequently, the modified interface delivers durable cycling performance in LFP full cells, achieving 141.8 mA h g-1 after 800 cycles with 96.62% capacity retention at 0.5C. Notably, the evolved interphase integrates electrochemical and chemo-mechanical functions to enable stable cycling of NCM811 full cells, delivering an initial discharge capacity of 186.5 mA h g-1 at 0.5C with 82.14% capacity retention after 150 cycles. This work provides a design strategy for constructing durable cooperative interphases for solid-state batteries.