Improvement of the Anode Properties of Lithium-Ion Batteries for SiO with a Third Element

Silicon oxide (SiO ) has been placed into practical use as an anode active material for next-generation Li-ion batteries because it has a higher theoretical capacity than graphite anodes. However, the synthesis method is typically vapor deposition, which is expensive, and the poor electron conductivity of SiO restricts high performance. In this study, we prepared M/SiO active materials consisting of SiO and a third element (M = Al, B, Sn) using a low-cost mechanical milling (MM) method and investigated their electrode properties as Li-ion battery anodes. Also, the authors added a third element to improve the conductivity of the SiO₂ matrix. Al, B, and Sn were selected as elements that do not form a compound with Si, exist as a simple substance, and can be dispersed in SiO₂. As a result, we confirmed that SiO has a nanostructure of nanocrystalline Si dispersed in an amorphous-like SiO₂ matrix and that the third element M exists not in the nanocrystalline Si but in the SiO₂ matrix. The electron conductivity of SiO was improved by the addition of B and Sn. However, it was not improved by the addition of Al. This is because Al₂O₃ was formed in the insulator due to the oxidization of Al. The charge-discharge cycle tests revealed that the cycle life was improved from 170 cycles to 330 or 360 cycles with the addition of B or Sn, respectively. The improvement in electron conductivity is assumed to make it possible for SiO₂ to react with Li ions more uniformly and form a structure that can avoid the concentration of stress due to the volume changes of Si, thereby suppressing the electrode disintegration.