Core-Shell Structured CoP@C Cubes as a Superior Anode for High-Rate and Stable Sodium Storage

Abstract

Transition metal phosphides have emerged as a class of promising anode materials of sodium-ion batteries owing to their excellent sodium storage capacity. However, the limited electronic conductivity and significant volume expansion have impeded their further advancement. In this work, we propose a rational design of cube-like CoP @C composites with unique core-shell structure via in situ phosphating and subsequent carbon coating processes. The uniform carbon coating serves as a physical buffering layer that effectively mitigates volume changes during charge/discharge processes, and prevents particle agglomeration and fragmentation, thereby enhancing the structural stability of electrode. Moreover, the nitrogen-rich carbon layer not only provides additional active sites for sodium ion adsorption but also improves the electrode conductivity and accelerates charge transport dynamics. Consequently, the as-synthesized CoP@C exhibits a remarkable capacity retention rate of 94.8 % after 100 cycles at 0.1 A g⁻¹ and achieves a high reversible capacity of 146.7 mAh g⁻¹ even under a high current density of 4.0 A g⁻¹.