We investigated the applicability of ionic-liquid electrolytes to FeSi 2 / Si composite electrode for lithium-ion batteries. In conventional organic-liquid electrolytes, a discharge capacity of the electrode rapidly faded. In contrast, the electrode exhibited a superior cycle life with a reversible capacity of 1000 mA h g(Si) −1 over 850 cycles in a certain ionic-liquid electrolyte. The difference in the cycle life was explained by surface film properties. In addition, the rate performance of the FeSi 2 /Si electrode improved in another ionic-liquid electrolyte. Remarkably, lithiation of only Si in FeSi 2 /Si composite electrode occurred whereas each FeSi 2 -and Si-alone electrode alloyed with Li in the ionic-liquid electrolyte. FeSi 2 certainly covered the shortcomings of Si and the FeSi 2 /Si composite electrode exhibited improved cycle life and rate capability compared to Sialone electrode.

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Annealed Ni–P–coated Si (Ni–P/Si) anodes for lithium-ion batteries have shown a superior cycle life with discharge capacity of 1000 mA h g−1 over 1100 cycles in some ionic-liquid electrolytes. However, the annealing temperature has yet to be optimized for Ni–P/Si electrodes. We investigated the electrochemical performance of Ni–P/Si electrode annealed at various temperatures in this study. The Ni–P/Si electrodes annealed at 800 ± 20 °C exhibited a superior cycle life with a reversible capacity of 1000 mA h g−1 over 1000 cycles, whereas the capacity of the electrodes annealed at temperatures of 750 °C and 850 °C faded at approximately 500 cycles. At 800 °C, a newly formed NiSi2 phase was theorized to significantly contribute to improving adhesion between the Ni–P coating layer and the Si particles. The Ni–P coating particles tended to aggregate at 850 °C, leading to a reduction in the coating effect, that is, a decline in their reactivity with Li+, acceleration of electrode disintegration, and a reduction in electrical conductivity. On the other hand, Ni–P/Si electrodes annealed at 850 °C exhibited a superior rate performance. The amount of available NiSi2 which ultimately contributed to higher reactivity with Li should increase.

performance and safety but are expensive. To reduce the use 2 of ionic-liquid electrolytes, we investigated the 3 charge/discharge properties of Si-based electrodes in an 4 organic-liquid electrolyte, where the electrode surface was 5 pre-coated with a film derived from an ionic-liquid 6 electrolyte. No improvement in the electrode performance 7 was observed compared to that of a nonmodified Si 8 electrode. Once the modified film was broken down, a 9 stable surface film could not be reformed in the organic-10 liquid electrolyte.

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