Organic shell wrapped silicon nanowires as an energy storage material

International audienceSilicon nanowires were first produced by lithography or CVD for electronics, sensing and optical applications. Independently, silicon has emerged as highly promising in lithium-ion battery anodes because of its absorbing 10 times more lithium than the standard carbon anodes. Silicon in battery anodes is submitted to intense mechanical constraints due to lithiation-delithiation, that only very small crystals can handle. Silicon nanowires then appeared as particularly efficient as they can withstand such constraints and maintain battery cycling over several hundreds of cycles. However, silicon nanowires grown as thin films do not fit as material for lithium-ion batteries, neither in terms of mass produced nor in terms of production cost: even a coin cell contains several milligrams of anode material, while silicon nanowires are grown at μg/cm$^2$ by CVD.We recently patented [1] a new technology of silicon nanowire synthesis designed for mass production as a powder. The nanowires are grown in a glass or steel reactor at medium temperature (430°C) from metal nanoparticles deposited on an inert support, and from an air-stable organosilane as the silicon source. Table salt (NaCl) is usually used as a support that can be conveniently removed by washing with water after growth. Growth on salt also avoids handling silicon nanowires as a dry powder, preventing risk of inhaling nanoparticles. The synthesis yields silicon nanowires in gram scale, with a yield of 70-80%. Tests of the pure silicon nanowires in lithium-metal batteries show an excellent capacity retention over 1000 cycles