Nanostructured SiO_x/C composites are promising candidates for high energy density anodes with extended lifespan in next-generation Li-ion batteries (LIBs). However, integrating sustainable precursors for the synthesis of high performance SiO_x/C negative electrodesremains a key challenge. In this study, nanoporous SiO₂ derived from the shells of industrially cultured diatom microalgae is successfully used as a template for synthesizing SiO_x via the magnesiothermic reduction reaction (MgTR), while the effectiveness of different carbon coating (CC) strategies to produce diatom-SiO_x/C from glucose as carbon precursor is thoroughly analyzed. Notably, the original nanostructure of the diatom-SiO₂ frustule is preserved throughout the synthesis process, and it is demonstrated that increasing the heating ramp during MgTR enhances the Si yield, leading to a significant increase in specific capacity of the anodes from 1064 mAh.g⁻¹ (2 °C/min⁻¹) to 1846 mAh.g⁻¹ (20 °C/min⁻¹). A comparative analysis of three synthesis pathways for producing diatom-SiO_x/C composites: 1) MgTR of diatom-SiO₂ followed by CC, 2) CC of diatom-SiO₂ followed by MgTR, and 3) simultaneous reduction of diatom-SiO₂ and glucose precursor, revealed that pathway (1) is most effective for producing highcapacity diatom-SiO_x/C anodes. These findings provide key enablers for developing sustainable SiO_x/C anodes of superior electrochemical performance.