LiAlO₂/LiAl₅O₈ Membranes Derived from Flame-Synthesized Nanopowders as a Potential Electrolyte and Coating Material for All-Solid-State Batteries

Recently, γ-LiAlO2 has attracted considerable attention as a coating in Li-ion battery electrodes. However, its potential as a Li+ ceramic electrolyte is limited due to its poor ionic conductivity (<10–10 S cm–1). Here, we demonstrate an effective method of processing LiAlO2 membranes (<50 μm) using nanopowders (NPs) produced via liquid-feed flame spray pyrolysis (LF-FSP). Membranes consisting of selected mixtures of lithium aluminate polymorphs and Li contents were processed by conventional tape casting of NPs followed by thermocompression of the green films (100 °C/10 kpsi/10 min). The sintered green films (1100 °C/2 h/air) present a mixture of LiAlO2 (∼72 wt %) and LiAl5O8 (∼27 wt %) phases, offering ionic conductivities (>10–6 S cm–1) at ambient with an activation energy of 0.5 eV. This greatly increases their potential utility as ceramic electrolytes for all-solid-state batteries, which could simplify battery designs, significantly reduce costs, and increase their safety. Furthermore, a solid-state Li/Li3.1AlO2/Li symmetric cell was assembled and galvanostatically cycled at 0.375 mA cm−2 current density, exhibiting a transference number ≈ 1.