In situ hydrothermal synthesis of double-carbon enhanced novel cobalt germanium hydroxide composites as promising anode material for sodium ion batteries

Germanium (Ge)-based materials are considered to be one of the most promising anode materials for sodium-ion batteries (SIBs). Nevertheless, the practical electrochemical performance is severely hampered by poor cyclability due to volumetric expansion of Ge upon cycling. Herein, double-carbon confined cobalt germanium hydroxide (CGH@C/rGO) composites has been facilely synthesized with the supportion of l-ascorbic acid and graphene oxide (GO) as anode materials for sodium-ion storage. As a result, the CGH@C/rGO anode delivers a high cyclic stability with a reversible capacity of 416 mA h g(-1) after 100 cycles at 100 mA g(-1) and an excellent rate capability of 206 mA h g(-1) at 2000 mA g(-1) compared with CGH, CGH@C and CGH/rGO composites. Besides, the reversible capacity of 266 mA h g(-1) still remained even after 500 cycles at current density of 1 A g(-1). Such outstanding electrochemical performance could be accredited to a strong interaction between CGH, carbon, and graphene, which increases the electronic conductivity, relieves the volume expansion aroused by sodiation/desodiation, shortens the pathway of electron/ion transportation that further improving the reaction kinetics and endowing the material with remarkable cycling capability. Obviously, this in situ hydrothermal synthesis of double carbon coating strategy can be extended to designing other candidates of anode materials for SIBs.

Automated summary

The double-carbon confined cobalt germanium hydroxide (CGH@C/rGO) composites, synthesized with the support of l-ascorbic acid and graphene oxide, exhibit high cyclic stability and excellent rate capability for sodium-ion storage, outperforming other composites. This outstanding electrochemical performance is attributed to the strong interaction between CGH, carbon, and graphene, which improves electronic conductivity, relieves volume expansion, and shortens electron/ion transportation pathways. The in situ hydrothermal synthesis of double carbon coating strategy shows promise for designing other anode materials for SIBs.