Synthesis of carbon-modified cobalt disphosphide as anode for sodium-ion storage

Phosphorus-rich metal phosphides have a high theoretical sodium-ion storage capacity. For example, cobalt disphosphide (CoP₂) possesses a theoretical sodium-ion storage capacity of about 1330 mAh g⁻¹, while the theoretical capacity of cobalt phosphide (CoP) is about 893 mAh g⁻¹. However, it is currently challenging to synthesise phosphorus-rich metal phosphides. Herein, we report the synthesis of phosphorus-rich rod-like cobalt disphosphide with a carbon shell (CoP₂@C) by thermal decomposition of polydopamine-coated cobalt oxalate in the presence of sodium hypophosphite. The as-obtained CoP₂@C anode delivered a high sodium-ion storage capacity of ∼550 mAh g⁻¹ at 500 mA g⁻¹ due to its multi pseudocapacitive and intercalation charge storage mechanisms. These preliminary results show that CoP₂@C hold a great promise for developing high-performance electrochemical energy storage devices based on sodium-ion as the charge carrier.