Hierarchical Carbon-Coated Ball-Milled Silicon: Synthesis and Applications in Free-Standing Electrodes and High-Voltage Full Lithium-Ion Batteries.

Lithium ion batteries have been regarded as one of the most promising energy storage devices and development of low-cost batteries with high energy density is highly desired so that the cost per watt-hour ($/Wh) can be minimized. In this work, we report using ball-milled low-cost silicon (Si) as the starting material and subsequent carbon coating to produce low-cost hierarchical carbon-coated (HCC) Si. The obtained particles prepared from different Si sources all show excellent cycling performance of over 1000 mAh/g after 1000 cycles. Interestingly, we observed in situ formation of porous Si and it is well confined in the carbon shell based on post-cycling characterization of the hierarchical carbon-coated metallurgical Si (HCC-M-Si) particles. In addition, lightweight and free-standing electrodes consisting of the HCC-M-Si particles and carbon nanofibers were fabricated, which achieved 1015 mAh/g after 100 cycles based on the total mass of the electrodes. Compared with conventional electrodes, the lightweight and free-standing electrodes significantly improve the energy density by 745%. Furthermore, LiCoO2 and LiNi0.5Mn1.5O4 cathodes were used to pair up with the HCC-M-Si anode to fabricate full cells. With LiNi0.5Mn1.5O4 as cathode, energy density up to 547 Wh/kg was achieved by the high-voltage full cell. After 100 cycles, the full cell with LiNi0.5Mn1.5O4 cathode delivers 46% more energy density than that of the full cell with LiCoO2 cathode. The systematic investigation on low-cost Si anodes together with their applications in lightweight free-standing electrodes and high-voltage full cells will shed light on development of high-energy Si-based lithium-ion batteries for real applications.