In Situ Cross‐Linking and Interfacial Engineering via Multifunctional Diamine Additive for High‐Temperature Magnesium Metal Batteries

The electrolyte and its interfacial chemistry are crucial for the development of high-temperature magnesium metal batteries. Here, a robust in situ cross-linked gel polymer electrolyte (MgB@CGPE) and its derived Mg₃N₂-rich (Mg₃N₂ and related Mg─N─H complexes) interphase are obtained by a multifunctional diamine additive. The Mg₃N₂-rich interphase exhibits low magnesium ion migration activation energy and can effectively inhibit the continuous decomposition of electrolyte at the interface under elevated temperatures. Moreover, the MgB@CGPE can enable reversible magnesium deposition and dissolution over a wide temperature range of 30-180 °C. The assembled Mo₆S₈//MgB@CGPE//Mg cells demonstrate stable cycling over 200 cycles at 150 °C with 80% capacity retention. Additionally, these cells also address crucial mechanical and thermal safety concerns, indicating their potential for use under extreme conditions. This work presents a universal and practical strategy for designing polymer electrolytes that operate at elevated temperatures.