High‐Capacity Sub‐Nano Divalent Silicon from Biosilicification

Abstract In terms of high capacity and reliable safety, low‐valent silicon‐based composites with small grain sizes are practicable anode materials for lithium‐ion batteries. However, robust tetravalent silicon precursors make the synthesis hard to be green. Using biosilicification in water hyacinth ( Eichhornia crassipes ), it is found to be a superior natural precursor of low‐valent silicon. The biogenic sub‐nano (0.5 nm) siliceous dots composite (EC‐SiOC) shows a reversible conversion mechanism between Si─O and C─O bonds, unlike previous lithium storage mechanisms associated with alloying reactions. Due to the homogeneous biogenic structure facilitating the solid‐phase reaction, the normalized energy consumption of pyrolytic EC‐SiOC is about 80% lower than the carbothermic reduction of silica, similar to molten salt electrolysis. Statistically, the sampling survey of EC‐SiOC from different regions shows a high average capacity of 749.9 mAh g −1 under a current density of 100 mA g −1 . This study reveals the great potential of biomass precursors for synthesizing Si─O─C materials.