Effect of Sn Addition on Anode Properties of SiO<i>_x</i> in Sodium-Ion Batteries (Supporting Information)

<p>Our group has investigated the properties of lithium-ion battery anodes fabricated using Sn/SiO<i>_x</i> (SiO<i>_x</i> is a mixed phase of Si clusters and amorphous SiO₂ matrix). The addition of Sn improves the conductivity of the SiO₂ matrix, while the formation of the Li⁺-conductive Li₂Si₂O₅ phase in the SiO₂ matrix improves Si utilization. The charge–discharge cycle life is also extended. In this study, Sn-doped SiO<i>_x</i> has been used to fabricate the anode of a sodium-ion battery, and its charge–discharge properties are evaluated. The addition of 3 wt% Sn to SiO<i>_x</i> improves the cycle property, as revealed by charge–discharge tests. X-ray diffraction analysis confirmed that the Na⁺-conductive Na₂Si₂O₅ phase is formed during the charging and discharging processes. These results indicate that adding Sn improves the electronic conductivity of SiO₂, and Na₂Si₂O₅ facilitated the movement of Na in the SiO₂ matrix. Thus, the utilization of Si is enhanced, and a high discharge capacity is achieved.</p>