Novel design of ultra-fast Si anodes for Li-ion batteries: Crystalline Si@amorphous Si encapsulating hard carbon

Nanocrystalline Si (c-Si) dispersed in amorphous Si (a-Si) encapsulating hard carbon (HC) has been synthesized as an anode material for fast chargeable lithium-ion batteries. The HC derived from natural polysaccharide was coated by a thin a-Si layer through chemical vapour deposition (CVD) using silane (SiH₄) as a precursor gas. The HC@c-Si@a-Si anodes showed an excellent cycle retention of 97.8% even after 200 cycles at a 1 C discharge/charge rate. Furthermore, a high capacity retention of ∼54% of its initial reversible capacity at 0.2 C rate was obtained at a high discharge/charge rate of 5 C. Moreover, the LiCoO₂/HC@c-Si@a-Si full-cell showed excellent rate capability and very stable long-term cycle. Even at a rate of 10 C discharge/charge, the capacity retention of the LiCoO ₂/HC@c-Si@a-Si full-cell was 50.8% of its capacity at a rate of 1 C discharge/charge and showed a superior cycle retention of 80% after 160 cycles at a rate of 1 C discharge/charge.