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

Silicon oxide (SiO x ) 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 x restricts high performance. In this study, we prepared M /SiO x active materials consisting of SiO x 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 SiO 2 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 SiO 2 . As a result, we confirmed that SiO x has a nanostructure of nanocrystalline Si dispersed in an amorphous-like SiO 2 matrix and that the third element M exists not in the nanocrystalline Si but in the SiO 2 matrix. The electron conductivity of SiO x was improved by the addition of B and Sn. However, it was not improved by the addition of Al. This is because Al 2 O 3 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 SiO 2 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.