Geothermal Silica as a Sustainable Source for Lithium-Ion Battery Anodes: Advances, Challenges, and Future Prospects

Geothermal silica has emerged as a promising and underutilised precursor for silicon-based lithium-ion battery anodes. Geothermal silica can be recovered from brines, scales, and solid residues generated during geothermal energy production, creating an opportunity to valorise existing waste streams while mitigating silica-scaling problems. This review examines the formation, availability, and material characteristics of geothermal silica, with particular emphasis on its high silica content, commonly reported in the range of ~50–98 wt% in solid geothermal residues, as well as its generally amorphous nature and porous structure. It then evaluates the main processing steps required to convert geothermal silica into battery-relevant silicon, including extraction, purification, and silica-to-silicon reduction, with particular focus on magnesiothermic reduction. Among the available routes, methods that provide improved impurity control while preserving porous or amorphous precursor structures appear most relevant for achieving favourable electrochemical performance. Recent comparative findings indicate that geothermal silica can, in some cases, be competitive with biomass-derived silica sources in terms of purity, composition, and morphology, although these advantages are not universal and depend on source-specific chemistry, impurity profile, and processing conditions. Reported electrochemical studies further show that geothermal-silica-derived silicon and silica-based composites can deliver electrochemically relevant capacities, in some cases exceeding the theoretical capacity of graphite (~372 mAh g−1), although performance varies significantly across studies. In addition, specific surface areas of ~50–150 m2 g−1 reported for some geothermal silica materials may support further silicon processing and influence electrochemical behaviour. Overall, geothermal silica represents a technically relevant and sustainability-oriented pathway toward silicon-based anode materials; however, further work is needed on source consistency, impurity management, structural control, long-term cycling stability, and scalable production.