Amorphous-Co₂P/N,B-codoped-Carbon Composite As An Improved Anode Material For Sodium Ion Batteries

Sodium ion batteries（SIBs）represent a promising alternative to lithium ion batteries due to the much higher abundance and lower cost of sodium resources in comparison with lithium.However,the electrode materials of SIBs usually suffer from more severe issues,such as low specific capacity and poor cyclability,due to the much larger Na+ diameter and drastic volumetric variations during sodiation/desodiation.Hence,it is still a huge challenge to develop superior electrode materials for reversible Na storage.In comparison with the crystalline materials conventionally used in batteries,amorphous ones may have more stable framework to uptake Na.To address these issues,a porous composite composed of amorphous-Co₂ P and N,B-codoped-carbon（A-Co₂P/CxNyBz-650）is prepared via controlling the annealing temperature at 650 oC after freeze-drying the precursors.The as-prepared A-Co₂P/C_xN_yB_z-650 exhibits much better Na-storage properties in terms of higher Na-storage capacity,longer cycling stability and excellent rate performance compared with the crystalline counterparts.These may benefit from that,amorphous framework can provide easier Na⁺ accessibility and better strain accommodation originated from the volumetric variations during sodiation/desodiation.More importantly,the electrolyte for all of the electrochemical tests are NaPF₆-based,which is more accessible for practical applications because of its higher safety compared with the commonly used NaClO₄-based one.