Superhalogen-Enhanced Band Gap, Ductility, and Li+-Ion Conductivity in Layered Antiperovskites Li7O2Br2(BH4) and Li7O2(BH4)3

Superhalogens are widely recognized for their ability to modulate the properties of conventional antiperovskites. However, their impact on layered antiperovskites remains unexplored. To address this gap, this study investigates two superhalogen-based layered antiperovskite materials, Li₇O₂Br₂(BH₄) and Li₇O₂(BH₄)₃, which are derived from Li₇O₂Br₃ by substituting Br^– with superhalogen [BH₄]⁻. Using DFT and AIMD simulations, we systematically examine their crystal structures, thermodynamic and mechanical stability, electronic properties, and Li⁺ ion conductivity. The results reveal that both Li₇O₂Br₂(BH₄) and Li₇O₂(BH₄)₃ exhibit high stability. The substitution of [BH₄]⁻ clusters significantly increases the band gap and alters the electronic states, underscoring the intricate interplay between chemical composition and electronic structure. Furthermore, the room-temperature Li⁺-ion conductivity is significantly enhanced compared to Li₇O₂Br₃, primarily due to the rotational dynamics of [BH₄]⁻ clusters, which effectively lower the energy barriers for Li⁺ hopping. Additionally, ductility is improved, as indicated by an increased Pugh’s ratio, facilitating better electrode contact and accommodating volume changes during Li⁺-ion insertion and extraction processes.