In-situ encapsulating flame-retardant phosphate into robust polymer matrix for safe and stable quasi-solid-state lithium metal batteries

Solid-liquid hybrid electrolytes (SLHEs) are promising electrolyte candidates for Li-metal batteries. However, most of the components of SLHE are flammable, posing safety risks. Here, a non-flammable SLHE was proposed by in-situ encapsulating a flame-retardant liquid phosphate into a robust solid polycarbonate matrix. The in-situ solidified SLHE simultaneously features high Li+ conductivity (4.4 mS cm−1), Young's modulus (12.4 GPa), Li+ transference number (0.76) and a wide electrochemical window (0-4.9 V vs. Li+/Li), which help to effectively suppress dendrites and unfavorable side reactions at the anode and provide compatibility with the high-voltage cathode. By employing non-flammable SLHE, a prototype Li||LiNi0.8Co0.1Mn0.1O2 cell retains 87.7% of the initial capacity after 200 cycles, and the Ah level Li||LiNi0.8Co0.1Mn0.1O2 pouch cells showed enhanced safety by passing the nail test by authorized third parties. This study inspires the optimal design of SLHEs towards practical realization of safe and stable Li-metal batteries.