Chemical surface treatments for decreasing irreversible charge loss and preventing exfoliation of graphite in Li-ion batteries

Chemical pretreatments modify surface properties of graphite and hence enhance its electrochemical performance in Li-ion battery. Surface modifications ameliorate the solid electrolyte interphase (SEI) layer formed on graphite during first cycle. An effective SEI formation is vital for reversible cycling of graphite in propylene carbonate (PC) based electrolytes, which is advantageous for low temperature applications of Li-ion batteries. For minimum surface layer thickness, the surface groups already existing on graphite were modified by chemical pretreatments. Chemically pre-reduced graphites show less irreversible charge loss, whereas chemically pre-oxidized graphites show more irreversible charge loss. Treatment of graphite by n-butyl lithium resulted in exclusively edge covered particles. This material exhibits low irreversible charge loss, good reversible cycling in PC based electrolyte, as well as homogeneous and flexible SEI. Cyclability of this material in standard electrolyte was optimized by stabilizing the surface chemical composition by use of ethylene carbonate as additive.