Enhanced Performance of All-Solid-State Na-Ion Batteries

Abstract

All-solid-state Na-ion batteries (Na-ASSBs) with an oxide solid electrolyte have been successfully developed using crystallized glass 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 a effectively integrated cathode/solid electrolyte shows excellent battery performance and high cycling stability. All-solid-state batteries with an oxide solid electrolyte are more thermally stable and safer than conventional lithium-ion batteries with an organic liquid electrolyte. In addition, owing to the use of Na, which is abundant natural resources, Na-ASSBs can be manufactured stably without the risk of resource shortage. Therefore, we believe that Na-ASSBs are among the most promising next-generation energy storages with high safety and large capacity. β”-alumina is a common oxide solid electrolyte with high ion conductivity comparable to the organic liquid electrolyte. If β”-alumina can replace organic electrolytes, safer Na-ASSBs operating over a wide temperature range can be fabricated. However, it is difficult to establish effective contact between the cathode material and the oxide solid electrolyte. In this work, we focused on Na-ASSBs using Na2FeP2O7 crystallized glass as the cathode. [1,2] Na2O-Fe2O3-P2O5 precursor glass powder, β”-alumina powder, and acetylene black were mixed to prepare a cathode mixture, which was applied on a β”-alumina substrate, followed by heating to sinter and crystallize the glass. As a result, the solid electrolyte and cathode were successfully integrated. Then, Na metal was attached to the counter side as the anode. The Na-ASSB with such effective integration showed rapid charge/discharge performance (10C) even at room temperature, which in turn enabled the motor to be operated at room temperature (Fig. 1). Furthermore, the cycle performance test at 10C rate and 30°C showed that the capacity retention after 1000 cycles was 94%. The excellent battery performances allow for the practical application of Na-ASSBs. This presentation will focus on the performance of Na-ASSBs and the manner in which it can be realized.