Carbon coated Si(Si/C) composites with a high Si content of 81wt% are synthesized byone-potcarbo- nization of the mixture containing commercial Si particles and polyvinylidene fluoride (PVDF) at an optimized temperature.The Si/Celectrodesdeliverahighcycliccapacityof2003mAhg-1 at 0.5Ag-1 after 50 cycles and an enhanced rate capability of 750 mAhg-1 at 4Ag-1 for over200cycles.The effect of ultrathin carbon coating on lithiation mechanisms of Si particles is evaluated using the in-situ transmission electronmicroscopy(TEM).It is revealed that the carbon-coated Si particles under go an isotropic to anisotropic transition during the initial lithiation,where as such transitionis not observed for the uncoated Si particle.The lithiation rate of Si/C is 3–4.5 times faster than that of un-coated Si with the same diameter, at estament to high ratecapacities of Si/C inreal batteries.The flexible,amorphous carbon coating favorably alters the damage mode of Si particles from pulverization by multiple cracking to fracture by a single crack.The above findings offer fundamental understanding and practical guideline for designing carbon coatings of Si-based electrodes with much enhanced electrochemical performance.

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