Modifying Specific Li-Sites of LiNH₂ by Na: Study of Multication Hydride Li₃Na(NH₂)₄ in Electrochemical Applications

Optimizing the electrochemical properties of a solid-state electrolyte, for an all-solid-state Li-ion secondary battery, requires understanding the impact of structural modification on the relevant electrochemical properties of the electrolyte. By replacing Li⁺, with Na⁺, from the specific lattice site (2c) of tetragonal LiNH₂, a crystalline multication ionic hydride Li₃Na­(NH₂)₄ is formed which is ordered-variant of LiNH₂ with modified anion and cation dynamics. In comparison to LiNH₂, the modified structure shows improved ionic conductivity (∼10^–5 S/cm at 373 K), and a wide electrochemical operation window (−2 to +5 V) using a Li electrode. The presence of Na⁺, on the specific lattice site of LiNH₂, alters the stability of Li⁺ cations and increases the number of the carrier ions in the multicationic structure of Li₃Na­(NH₂)₄. The study demonstrates the possibility of structural engineering by tuning the site-specific activity in multicationic, stable, lightweight, amide-based hydrides for electrochemical energy-storage applications.