Self-Driven SiO2/C Nanocomposites from Cultured Diatom Microalgae for Sustainable Li-Ion Battery Anodes: The Role of Impurities

Nanostructured SiO₂ shells from diatom microalgae are a promising feedstock for the production of high-performance SiO₂ anodes for next-generation lithium-ion batteries (LIBs), and diatom biomass has been proposed as a carbon source for producing SiO₂/C nanocomposites of improved cyclability. A standard approach before implementing diatoms as an anode material involves an acid washing step for removing minor impurities from diatom shells. In this work, we perform the first comprehensive analysis on the effect of minor chemical species present on diatom shells on the electrochemical properties of diatom-SiO₂/C anodes. Unwashed and acid-washed single species cultured diatoms containing their original biomass content were subjected to thermal treatments at 600, 700, 800, and 900 °C, and the resulting SiO₂/C composites were fully characterized by XRD, BET, TGA, Raman, SEM/EDX, and TEM techniques. The electrochemical performance of the resulting anodes reveals the key role of impurities in improving the cycling properties. While acid-washed SiO₂/C composites displayed higher surface area, their electrochemical performance was comparable to non-coated SiO₂. On the other hand, unwashed SiO₂/C anodes exhibited a specific capacity up to twice that of SiO₂. The best-performing SiO₂/C anode was the unwashed diatom-SiO₂ heat-treated at 800 °C, showing a specific capacity of 661 mAh·g^–1 after 100 cycles at a current density of 200 mA·g^–1. Results on the beneficial effects of impurities on SiO₂/C anodes are crucial for an effective implementation of diatoms in LIB technology.

Nanostructured carbon-coated SiO₂ from biomass-derived diatom microalgae are promising candidates for high-performance next-generation lithium-ion battery anodes.