All-solid-state Na ion batteries (Na-ASSBs) with an oxide solid electrolyte have been successfully developed using glass ceramic as the cathode active material. Melt flow during the crystallization of the precursor glass enables the cathode to be integrated with a solid electrolyte. Such an integrated cathode/solid electrolyte demonstrates remarkable battery performance.
All-solid-state batteries with oxide solid electrolytes are safer and more thermally stable than conventional lithium-ion batteries with organic liquid electrolytes. There are many potential oxide material candidates for solid electrolytes that conduct sodium ions. The advantages of these materials are that they have stable and high ionic conductivities, and they can utilize ceramics, such as β-alumina, which do not contain rare metals or rare earth, and are already in use. However, even if a solid electrolyte has sufficient ionic conductivity, integrating the electrode active material into the solid electrolyte and operating the battery remain problematic. Oxide solid electrolytes have particularly poor moldability, so although solid electrolytes are safe, integration and forming ionic conduction paths are difficult.
In this work, we focused on Na-ASSBs using Na2FeP2O7 glass ceramic as the cathode active materials. Powdered Na2O-Fe2O3-P2O5 precursor glass, β”-alumina, and acetylene black were mixed to prepare the cathode mixture, which was applied on a β”-alumina substrate; subsequently, heating was performed to sinter and crystallize the glass. Consequently, the solid electrolyte and cathode were successfully integrated. In addition, it was found that the resistance value can be reduced to 1/30 of the previous work by making the positive electrode material finer and increasing the specific surface area of the solid electrolyte substrate.
This integrated Na-ASSB showed rapid charge/discharge performance (2 C rate) even at 30 °C. Furthermore, we have succeeded in operating the device even in a low temperature environment, which is difficult to operate with an all-solid-state battery using an oxide solid electrolyte.
The excellent battery performance allows for the practical application of Na-ASSBs. This presentation focuses on the excellent performance of Na-ASSBs and the manner in which such performance can be achieved.