Enhanced rate capabilities in a glass-ceramic-derived sodium all-solid-state battery

An all-solid-state battery (ASSB) with a new structure based on glass-ceramic that forms Na₂FeP₂O₇ (NFP) crystals, which functions as an active cathode material, is fabricated by integrating it with a β″-alumina solid electrolyte. Two important factors that influence the rate capability of this ASSB were optimised. First, the particle size of the precursor glass powder from which the NFP crystals are formed was decreased. Consequently, the onset temperature of crystallisation shifts to a lower temperature, which enables the softening of NFP crystals and their integration with β″-alumina at a low temperature, without the interdiffusion of different crystal phases or atoms. Second, the interface between the β″-alumina solid electrolyte and cathode active materials which consisted of the NFP-crystallised glass and acetylene black used as a conductive additive, is increased to increase the insertion/release of ions and electrons from the active material during charge/discharge processes. Thus, the internal resistance of the battery is reduced considerably to 120 Ω. Thus, an ASSB capable of rapid charge/discharge that can operate not only at room temperature (30 °C) but also at -20 °C is obtained. This technology is an innovative breakthrough in oxide-based ASSBs, considering that the internal resistance of liquid electrolyte-based Li-ion batteries and sulphide-based ASSBs is ~10 Ω.