Abstract
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.