Porous Amorphous Co2P/N,B-Co-doped Carbon Composite as an Improved Anode Material for Sodium-Ion Batteries

Sodium-ion batteries (SIBs) represent a promising alternative to lithium-ion batteries, owing 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, owing 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 offer a more stable framework for the uptake of Na. To address these issues, a porous composite composed of amorphous Co2P and N,B-co-doped carbon (A-Co2P/CxNyBz-650) is prepared by controlling the annealing temperature at 650 °C after freeze-drying the precursors. As-prepared A-Co2P/CxNyBz-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 the fact that the amorphous framework can provide easier Na+ accessibility and better strain accommodation, originating from 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 electrolyte.