Modified natural flake graphite with high cycle performance as anode material in lithium ion batteries

Natural flake graphite was mild-expanded and then carbon coated to enhance its cycle performance. The sample was investigated by scanning electron microscopy (SEM), powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). The interlayer distance of graphite was slightly increased and many defects were introduced into graphite to form a porous structure. The mild-expanded graphite with pyrolysis carbon coating could accommodate up to 378 mAh g−1 capacity and keep 100% capacity after 100 cycles. A mechanism is proposed that the increased interlayer distance and porous structure act as buffer for the change of graphite's volume in cycles, which greatly enhances the cycle stability. Porous structure also increases the capacity remarkably according to the micro-porous storage mechanism.