Achieving low hardness and high ionic conductivity in anion-substituted Li-rich anti-perovskites for sintering-free all-solid-state batteries

The anti-perovskite-type Li 2 OHBr is recognized as an oxide-based solid electrolyte with relatively high plasticity; however, its low ionic conductivity necessitates further enhancement for practical applications. This study reports a novel mixed-anion lithium-rich anti-perovskite (LiRAP), Li 2+ x ( OH ) 1- x S x Br 1- y F y (LHSBF), designed to synergistically balance high ionic conductivity with superior mechanical deformability. These electrolytes were synthesized via mechanical milling, where the co-substitution of S 2- and F - into the Li 2 OHBr lattice successfully enhanced both transport properties and mechanical plasticity. These improvements are attributed to the B-site occupation of larger S 2- ions that expands the ionic conduction pathways, alongside the moderate F - incorporation that accommodates local lattice strain and increases polarizability, effectively reducing the energy barrier for Li + migration. The enhanced deformability enabled the fabrication of sintering-free, all-solid-state batteries through room-temperature cold pressing, achieving a reversible capacity of approximately 100 mAh g − 1 at 60 ° C . This study provides a breakthrough pathway for developing practical, easily processable, oxide-based battery systems.