Boosting solid-state sodium battery performance via Co-sintering of layered iron, manganese based oxide cathode and NASICON electrolyte

Solid-state sodium batteries gain recognition as promising candidates for energy storage applications, offering enhanced safety and performance. However, their overall efficiency is limited by poor interfacial contact between the cathode active material (CAM) and the solid electrolyte (SE), as well as by interfacial instability. This underscores the imperative of establishing a chemically and electrochemically stable CAM/SE interface to ensure efficient charge transfer and long-term electrochemical performance. Herein, we report the optimization of the co-sintering process between Na 3 Zr 2 Si 2 PO 12 NZSP, (SE), and Na 0.67 Fe 0.5 Mn 0.5 O 2 NFMO, (CAM). A co-sintering temperature of 900 °C, which is suboptimal, yields a sodium-conducting interface that promotes intimate interfacial contact while preserving the bulk properties of both components, thereby enhancing interfacial compatibility. Thermal expansion mismatch between NFMO and NZSP is found to be minimal (<5 × 10 −6 K −1 ), reducing the risk of crack formation during cooling. The full-cell assembled using Na 3 Zr 2 Si 2 PO 12 and Na 0.67 Fe 0.5 Mn 0.5 O 2 composite cathode exhibits superior electrochemical performance with an initial discharge capacity of 149 mA h g −1 at 0.1 C with the capacity retention of 70 % after 200 cycles. This excellent cycling stability is attributed to the well-engineered CAM/SE interface, which ensures efficient charge-transfer kinetics. This study provides guidance on the optimization of the co-sintering mechanism in the realm of achieving intimate electrode/electrolyte contact and can be a cornerstone for future research. TOC Graphic. • Intimate electrode/electrolyte contact are key in solid-state batteries. • Optimized thermal processing enhances contact in composite cathode materials. • Nevertheless, the detailed investigation required during thermal/co-sintering process. • Full cell designed by using optimized co-sintered cathode. • Full cell retains 70 % capacity after 200 cycles.