Remarkable performance improvement of inexpensive ball-milled Si nanoparticles by carbon-coating for Li-ion batteries

• Inexpensive ball-milled Si nanoparticles (BM-Si) are investigated for LIBs.
• BM-Si is much worse than expensive CVD-derived Si-nanoparticles (CVD-Si).
• The key factor is found to be the physical contact between each of Si nanoparticles.
• Carbon-coating and capacity restriction remarkably improve the performance of BM-Si.
• A specific ‘wrinkled’ structure is formed not only in CVD-Si but also in BM-Si.

Si nanoparticles prepared by ball-milling (BM-Si) are expected as practical negative-electrode materials for lithium-ion batteries, but their performance is much lower than those of more expensive Si nanomaterials, such as chemical-vapor-deposition derived Si nanoparticles (CVD-Si) having a tight network structure. It is found that carbon-coating of aggregations of BM-Si forms a quasi-network structure, thereby making the performance comparable to that of CVD-Si under capacity restriction (to 1500 mAh g−1). In this case, the structural transition of BM-Si during charge/discharge cycling is characterized by the formation of a specific ‘wrinkled structure’, which is very similar to that formed in CVD-Si.

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