Sodiation–Desodiation Reactions of Various Binary Phosphides as Novel Anode Materials of Na-Ion Battery

Sodiation–desodiation behaviors were investigated for electrodes composed of various binary phosphides, InP, CuP2, GeP, SiP, and LaP, as anode materials of a Na-ion battery. Although LaP electrode did not react with Na, the other electrodes showed reversible sodiation–desodiation reactions in the initial cycles. Rapid capacity decays were observed for CuP2, GeP, and SiP electrodes. In contrast, a better cyclability was attained for the InP electrode. These results indicate that binary phosphides (M–P) require four properties for improving cyclability: (i) low thermodynamic stability of M–P, (ii) high electronic conductivity of M, (iii) low hardness of M, and (iv) reactivity of M with Na.