An anion-immobilized composite electrolyte for dendrite-free lithium metal anodes [Chemistry]

Lithium metal is strongly regarded as a promising electrode material in next-generation rechargeable batteries due to its extremely high theoretical specific capacity and lowest reduction potential. However, the safety issue and short lifespan induced by uncontrolled dendrite growth have hindered the practical applications of lithium metal anodes. Hence, we propose a flexible anion-immobilized ceramic–polymer composite electrolyte to inhibit lithium dendrites and construct safe batteries. Anions in the composite electrolyte are tethered by a polymer matrix and ceramic fillers, inducing a uniform distribution of space charges and lithium ions that contributes to a dendrite-free lithium deposition. The dissociation of anions and lithium ions also helps to reduce the polymer crystallinity, rendering stable and fast transportation of lithium ions. Ceramic fillers in the electrolyte extend the electrochemically stable window to as wide as 5.5 V and provide a barrier to short circuiting for realizing safe batteries at elevated temperature. The anion-immobilized electrolyte can be applied in all–solid-state batteries and exhibits a small polarization of 15 mV. Cooperated with LiFePO₄ and LiNi_0.5Co_0.2Mn_0.3O₂ cathodes, the all–solid-state lithium metal batteries render excellent specific capacities of above 150 mAh⋅g⁻¹ and well withstand mechanical bending. These results reveal a promising opportunity for safe and flexible next-generation lithium metal batteries.