Influence of Preparation Conditions of Composite Positive Electrodes for Enhanced Reversible Capacity in All-Solid-State Na/S Batteries

抄録

Sodium-sulfur (Na/S) batteries are promising low-cost next-generation batteries. In particular, all-solid-state Na/S batteries are expected to demonstrate high capacity at room temperature because sulfur has a high theoretical capacity as a positive electrode active material and sulfide solid electrolytes exhibit high ionic conductivity. However, sulfur is insulating and must be mixed with conductive agents to create both ionic and electronic conductive pathways. In addition, sulfur undergoes a large volume change during cycling, and the solid-solid interface connections are easily lost. Therefore, it is necessary to devise a composite positive electrode design that achieves a high capacity by maintaining the solid-solid interface and activating sulfur redox reactions. In this study, sulfur, mesoporous carbon, and Na₃PS₄ or Na₃SbS₄ are used as composite positive electrodes, and the preparation conditions of the composite positive electrodes are investigated by charge–discharge testing and cross-sectional observations. This study clarifies that the type of sulfide solid electrolytes and its degree of dispersion in the composite electrode significantly modify electronic/ionic percolation pathways and interfacial stability, thereby governing sulfur utilization and cycling retention.