Black phosphorus as a high-capacity and formable negative electrode material: applications in all-solid-state sodium batteries

In the development of sodium secondary batteries, the negative electrode materials face challenges in terms of their reversibility and energy density. In this study, phosphorus was explored as a negative electrode material in all-solid-state sodium batteries combined with stable solid electrolytes, such as Na 3 BS 3 glass, Na 3 Zr 2 Si 2 PO 12 , and β-alumina. The all-solid-state sodium cells exhibited a capacity of 2000 mAh g −1 and high reversibility for over 100 cycles, with high capacity retention of 99%. Despite significant volume expansion, intimate interfaces between the solid electrolyte and active materials were achieved during charge–discharge cycles, facilitated by the high formability and electronic and ionic conductivity of the produced phosphide. Phosphorus acts as a bifunctional material and serves as both an electrode and an electrolyte component. These promising properties support the use of phosphorus-based negative electrodes with both sulfide and oxide solid electrolytes in all-solid-state sodium batteries, thereby facilitating easier cell fabrication with enhanced capacity and cycle life.