Water-soluble-template-derived nanoscale silicon nanoflake and nano-rod morphologies: Stable architectures for lithium-ion battery anodes

Earth abundant and economical rock salt (NaCl) particles of different sizes (< 3 μm and 5–20 μm) prepared by high energy mechanical milling were used as water-soluble templates for generation of Si with novel nanoscale architectures via low pressure chemical vapor deposition (LPCVD). Si nanoflakes (Si_NF) comprising largely amorphous Si (a-Si) with a small volume fraction of nanocrystalline Si (nc-Si), and Si nanorods (Si_NR) composed of a larger volume fraction of crystalline Si (c-Si) and a small volume fraction of a-Si resulted from modification of the NaCl crystals. Si_NF yielded first-cycle discharge and charge capacities of ~2, 830 and 2, 175 mAh·g^–1, respectively, at a current rate of 50 mA·g^–1 with a first-cycle irreversible loss (FIR loss) of ~15%–20%. Si_NR displayed first-cycle discharge and charge capacities of ~2, 980 and ~2, 500 mAh·g^–1, respectively, at a current rate of 50 mA·g^–1 with an FIR loss of ~12%–15%. However, at a current rate of 1 A·g^–1, Si_NF exhibited a stable discharge capacity of ~810 mAh·g^–1 at the end of 250 cycles with a fade rate of ~0.11% loss per cycle, while Si_NR showed a stable specific discharge capacity of ~740 mAh·g^–1 with a fade rate of ~0.23% loss per cycle. The morphology of the nanostructures and compositions of the different phases/phase of Si influence the performance of Si_NF and Si_NR, making them attractive anodes for lithium-ion batteries.