Lithium insertion in carbon-silicon composite materials produced by mechanical milling

Carbons containing nanosize silicon particles were prepared by mechanical milling of graphite and silicon mixtures with different atomic ratios. The microstructure, morphology, and electrochemical performance of ballmilled C1-chiSichi (chi = 0, 0.1, 0.2, 0.25) were analyzed by X-ray diffraction, Raman, high-resolution and transmission electron microscopy, and electrochemical methods. After ballmilling, the crystal size of graphite increased but the size of silicon decreased with increasing content of silicon. Ballmilled C1-chiSichi materials reacted reversibly with lithium, and the reversible specific capacity increased from 437 mAh/g in the ballmilled pure graphite to 1039 mAh/g in ballmilled C0.8Si0.2 materials. The excess capacity due to the Li extraction from silicon appeared at a potential about 0.4 V vs. Li metal. After 20 charge/discharge cycles the reversible capacity of C0.8Si0.2 was 794 mAh/g. This behavior is a result of nanosize silicon particles decreasing the crumbling rate during Li insertion and extraction. These materials appear to be promising candidates for negative electrodes in lithium-ion rechargeable batteries.