Enabling dual-reinforced stable hybrid interfaces for intercepting lithium dendrite growth and improving the performances of solid-state lithium-metal batteries

Lithium metal batteries (LMBs) with composite solid electrolytes (CSEs) offer a compelling medium for supporting the electrification of the transportation sector, thanks to their high energy density and safety. Various electrode/electrolyte interfacial issues still hinder the performance of LMBs, limiting their cyclability and scalability. To thoroughly understand and mitigate interfacial matters, here we successfully engineered an in-situ formed hybrid solid electrolyte interface (SEI) and cathode electrolyte interface (CEI) using a tri-layer CSE incorporating functional group-rich hexafluorocyclotriphosphazene (TLCSE-HFPN) and lithium difluorooxalatoborate (LiDFOB)/lithium difluorophosphate (LiDFP) dual salt containing liquid electrolyte (LE) additive. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (ToF-SIMS) studies demonstrated that the SEI/CEI layers are rich in fluorine, nitrogen, and phosphorus derivatives due to the decomposition of HFPN and LiDFOB/LiDFP salts. These in-situ engineered SEI/CEI layers synergistically regulated the Li⁺ flux transport, preventing lithium dendrite breeding and electrode degradation during long-term cycling. Consequently, our novel TLCSE-HFPN design exhibits extremely stable Li plating/stripping cycling performance for over 2000 h at 0.2 mA cm⁻². Additionally, the Li-Nf@LFP//Li and Li-Nf@NCM811//Li solid-state lithium metal batteries (SSLMBs) demonstrate impressive long-term electrochemical durability, with 1212 and 300 cycles, respectively, at 0.5C/2C and 0.5C/0.5C, achieving a capacity retention rate of 80.65 % and 84.14 %, respectively. The current work, therefore, provides a viable design for multifunctional CSE, a step forward in realizing the high-performance next-generation SSLMBs.