Effect of carbon coating on elevated temperature performance of graphite as lithium-ion battery anode material

The effect of carbon-coating on the elevated temperature performance of Ligraphite half-cells is investigated for 1 M LiPF6 in PCECDEC (3:2:5) and 1 M LiBF4 in ECDMC (2:1) electrolytes (PC = propylene carbonate; EC = ethylene carbonate; DEC = diethyl carbonate; DMC = dimethyl carbonate). Carbon-coated graphite is prepared by mixing synthetic graphite particles with polyvinylchloride powders, followed by heating to 1000 °C under a flow of argon gas. For LiPF6-based cells, when pre-cycled cells are stored at 80 °C and then cycled at 30 °C, the loss of charge after storage at elevated temperature is much less with carbon-coated graphite than with untreated graphite electrode. When cycled at 80 °C without pre-cycling, the carbon-coated graphite electrode shows stable cycling behaviour, but untreated graphite results in premature cell failure. It appears that the carbon-coating preserves the graphite electrode even after storage at 60 °C in LiBF4-based electrolyte. From cycling and storage tests, it is concluded that surface modification through carbon-coating is very effective for the improvement of electrochemical performance and thermal stability of graphite electrodes at elevated temperatures.