Flexible Free-Standing Hierarchical Carbon-Coated CoP₂ Nanosheets for High-Performance Lithium-Ion Batteries

CoP2 has a high theoretical specific capacity of 1330.4 mA h g–1 based on the formation of Li3P, which is higher than the capacity of cobalt oxides and the cobalt sulfides. Hence, the free-standing CoP2@C nanosheets were synthesized by combining electrodeposition and red phosphorus phosphating to reveal the electrochemical behaviors of CoP2. The discharge and charge plateaus of CoP2 are 0.6 and 1.2 V, respectively, and the specific capacity of the overall electrodes is 487.6 mA h g–1 within 0.05–2.0 V after 100 cycles. The particle accumulating structure of CoP2@C would benefit lithium ion diffusion, which boosts the rate capability. N-doped carbon coatings enhance the structure stability and conductivity while introduce more capacitive behaviors and the initial Coulombic efficiency decrease slightly. To minimize the influence of graphene foams, the voltage range of 0.2–3.0 V was employed and CoP2@C delivers a high specific capacity of 1048.7 mA h g–1 after 100 cycles. From theoretical simulation, the interaction between CoP2 and carbon can effectively improve the conductivity of the electrodes, and inhibit the volume effect of CoP2 in the process of charging and discharging, which can improve the stability. The three-dimensional hierarchical structure can improve the conductivity of the composites and avoid the separation of CoP2 during charging and discharging.