Bromophenyl-Crosslinked "Rigid yet Compliant" Flame-Retardant Polyether Electrolyte for High-Voltage and Wide-Temperature Lithium Metal Batteries

Abstract

In situ polymerized polymer electrolytes are promising for solid-state lithium metal batteries (SLMBs), yet they face intrinsic trade-offs between thermal resilience and high-voltage stability. Herein, we propose a "rigid yet compliant" molecular design paradigm to construct a cross-linked polyether-based electrolyte via in situ polymerization. This strategy integrates rigid bromophenyl groups-serving as both anion-anchoring and flame-retardant units-with flexible, Li+-conducting ether-oxygen chains within a covalently bonded network. This architectural synergy guides the formation of gradient-structured solid electrolyte interface (SEI) and cathode electrolyte interface (CEI) at both electrodes, featuring a mechanically robust inorganic-rich inner layer and an adaptive organic outer layer. The resulting electrolyte demonstrates superior electrochemical properties, including an ionic conductivity of 0.70 mS cm−1 at 25°C, a high Li+ transference number of 0.81, and a wide electrochemical stability window of 5.7 V. It enables stable Li plating/stripping for over 2800 h and inherent flame-retardant characteristics. Notably, full cells assembled with this electrolyte deliver exceptional cycling stability under high-voltage conditions (e.g., 4.5 V-class LiNi0.8Co0.1Mn0.1 and 4.6 V-class Li-rich Mn-based layered oxides) and across a wide temperature range (−20 to 60°C). The practical viability and safety of the PBDOL system are further validated in pouch cells under severe mechanical and thermal abuse. This work provides a definitive design guideline for highly safe, high-voltage, and wide-temperature quasi-solid-state LMBs.