Facile formation of Mg-containing interphase on nanosilicon from Agar/MgCO3 precursor for lithium-ion battery anodes

The ultra-high theoretical capacity (4200 mAh g⁻¹) of Silicon anode materials for lithium-ion batteries while which is one of the ideal replacement materials for graphite anodes. However, the poor electrical conductivity and greatly reduces the cycle life of the battery of Silicon material, which suffers from severe volume expansion during charge/discharge cycling leading to electrode pulverization. In this work, Agar/magnesium carbonate-coated silicon nanocomposites were synthesized by utilizing the "self-solidifying" property of agar. The magnesium oxide formed by the decomposition of magnesium carbonate at high temperatures mitigates the volume expansion of nanosilicon together with the derived carbon layer. Moreover, the lithium-magnesium alloy electron-conducting interface layer generated by the reaction between lithium ions and magnesium oxide, which greatly shortens the diffusion length of lithium ions and electrons inside the electrode during the charge-discharge cycle. The first discharge specific capacity was 2060.2 mAh g⁻¹, the Coulombic efficiency as high as 86.28 ​%, and still possesses a reversible specific capacity of 801.5 mAh g⁻¹ after cycling 200 cycles at a high current of 500 ​mA ​g⁻¹ of Agar/magnesium@Si with optimal ratio composite. The composite material used in this work largely suppresses the volume expansion of the silicon anode and contributes to the design of low-cost and high Coulombic efficiency lithium-ion batteries.