Thermal oxidation enables stable microsized mesoporous silicon anode for lithium-ion batteries

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Silicon (Si) has been considered the most promising next-generation anode material for lithium-ion batteries (LIBs) due to its high theoretical capacity (3579 mAh/g) and safe potential (0.45 V vs Li/Li+). However, it suffers from a quick capacity fading caused by the large volume changes (300%) during the lithiation/delithiation process. Silicon oxides (SiOx) show less volume expansion/contract compared to elemental Si. The oxygen of SiOx can also react with Li+ to form inactive Li2O and conductive lithium silicates during the initial lithiation process, which are beneficial for buffering the volume expansion and maintaining the electrode structural stability during cycling, thus improving the electrochemical cycling stability. However, the specific capacity of SiOx is lower compared to Si. Based on this background, it is possible to combine the advantages of Si and SiOx by constructing their composite material. The Si/ SiOx might be a promising choice to realize stable battery cycling with high reasonable capacity. In the present study, we prepared mesoporous Si/SiOx composite (Si with a SiOx surface layer) by thermally oxidizing microsized mesoporous Si at different temperatures (300, 450, 650, 700, 750, 800, 1100 oC) in air. The initial mesoporous Si was prepared by electrochemical etching from silicon wafers and then milled with a planetary ball mill into the micrometer range for further oxidation. Material characterization and coin cell tests were performed to investigate the effects of the different oxygen content on electrode performance. The results show that the electrode can deliver a charge capacity of over 2000 mAh/g but the capacity is fading fast when the oxygen content is less than 50 at.%. The optimal sample (PSi-700) with 54 at.% oxygen content shows the highest initial Coulumbic efficiency (ICE) of 78 % and a stable cycling performance for over 180 cycles with a limited capacity of 800 mAh/g at a current density of 200 mA/g. The research indicated that the approach to combine Si and SiOx with an appropriate oxygen content can enable a high-performance microsized mesoporous Si anode for lithium-ion batteries.

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