Incorporation of phosphorus into the surface of natural graphite anode for lithium ion batteries

A new chemical approach for obtaining excellent cycleability of natural graphite is designed and introduced for use as an anode in lithium ion batteries. Here, we evaluate the electrochemical properties of natural graphite after surface modification with ammonium hexafluorophosphate (NH4PF6) to elucidate a correlation between surface structure and its electrochemical performance. The outstanding cyclic retention of 94.9% was obtained by NH4PF6 at the fiftieth cycle, even without the functional additives such as vinylene carbonate (VC) and fluoroethylene carbonate (FEC). Such improvement could be attributed to the introduction of phosphorus into the surface of natural graphite. The electrochemical measurements combined with structural analyses indicate that the phosphorus incorporation could make the surface more stable and reinforce the SEI during cycles. Our findings indicate that surface modification by phosphorus incorporation is effective to modify the physicochemical properties of the SEI and improve the electrochemical properties of natural graphite.