Ultrathin 2D hexagon CoP/N-doped carbon nanosheets for robust sodium storage

Due to the natural abundance and potential price advantage, sodium-ion batteries (SIBs) have attracted increasing attention as promising alternatives to lithium-ion batteries (LIBs). However, the development of SIBs is severely hampered due to the poor cycling stability and low rate capability resulting from the larger ionic size of Na+ than that of Li+. Herein, 2D hexagon CoP/N-doped carbon (H-CoP@NC) nanosheets have been prepared via solvothermal method combined with the upper gas phase phosphating. Benefiting from the synergistic effect of N-doped carbon layer and ultrathin 2D hexagonal nanosheet structure, the H-CoP@NC as anode materials exhibit superior electrochemical performances in terms of rate capability and cyclic stability, delivering specific capacity of 209.9 mAhg−1 at 2 Ag−1 after 1100 cycles for SIBs, and high Coulombic effciency of approximately 100% over 1100 cycles. Ex-situ XRD were performed to research the structural evolution between Na and CoP during cycling processes. Analysis from the Ex-situ XPS and work function indicates that the enhanced electrochemical property H-CoP@NC might be attributed to the stable SEI film, lower charge-transfer resistance and better electrode kinetics as a result of thinner nanosheet and the presence of carbon layer.