Synthesis of Si/SiO_x from talc and its characteristics as an anode for lithium-ion batteries

A mixture of silicon (Si) and silicon suboxide (SiO_x, x < 2) phases is prepared from talc by magnesio-thermal reduction and acid etching processes. Talc is a clay mineral composed of hydrated magnesium silicate and is one of the most abundant minerals on earth. The reduced Si/SiO_x nanoparticles are found to be porous after acid etching and are closely connected. The Si/SiO_x particles are supported on a carbon layer which imparts them with electronic conductivity and improved durability towards stresses associated with the volume change of Si/SiO_x during cycling. The structural, physical, and electrochemical properties of these electrodes are analyzed through X-ray diffraction, scanning electron microscopy, Fourier transform-infrared spectroscopy, transmission electron microscopy, thermogravimetric analysis, electrochemical impedance spectroscopy and galvanostactic charge-discharge tests. The initial discharge capacity of the carbon-coated Si/SiO_x obtained from talc is measured to be 842 mAh/g at 1 C (1500 mA/g) which decreases to 470 mAh/g after 300 cycles, showing a much higher capacity retention (~55.8%) than pure Si nanoparticles. This superior cycling stability may be attributed to the porous network structure of the magnesio-thermally reduced Si/SiO_x and its endurance towards volume changes during cycling.