Study on the Electrochemical Features of Carbon-Coated GeS2 and GeSe2 Anodes toward Application in Sodium-Ion Battery

Sodium-ion batteries (SiBs) are highly promising to substitute lithium-ion batteries (LiBs) in wide applications, such as energy storage. The metal sulfide or selenium are candidate anodes for high-energy density SiBs resulting from their theoretically higher initial coulombic efficiency, higher conductivity, and lower voltage polarization. Herein, we found that GeSe2 is more favorable than GeS2 for Na ion storage. The first-principle calculation revealed that the formation energy of GeSe2 is 54.997 kJ mol–1 less than that of GeS2, Ge–Se bonds are easier to rebuild than Ge–S bonds, and Na2Se is easier to decompose than Na2S. The experimental investigation proved that all Na ions are reversible in a GeSe2/Na battery system when the operated voltage window was fixed in 0.01–3 V, which is not realized in a GeS2/Na battery. With galvanization discharge/charge voltage fixed in 0.01–2.5 V, the reversible capacity of GeSe2/C in the 1st, 2nd, 50th, and 100th cycles was 638, 540, 481, and 427 mAh g–1 at 100 mA g–1, while the corresponding values of GeS2/C were only 987, 408, 213, and 162 mA g–1, respectively. The rate charge capacity of GeSe2/C was about 416, 344, 317, 263, 215, 188, 165, and 458 mAh g–1 at 0.5, 1, 2, 3, 4, 5, 6, and 0.2 A g–1, and the corresponding capacity of GeS2 is 294, 228, 200, 159, 128, 110, 98, and 282 mAh cm–1, respectively. The research possibly provides a designable route for the preparation of high-energy density and high-reversibility SiB anodes; i.e., MxSey may be more favorable than MxSy for Na ion storage.