Bimodal Porous Carbon-Silica Nanocomposites for Li-Ion Batteries

Bimodal porous carbon-silica (BP-CS) nanocomposites exhibit advantageous properties from a design perspective for low-cost lithium-ion battery anodes. The BP-CS nanocomposites were fabricated using cooperative self-assembly of phenolic resin, tetraethylorthosilicate, and Pluronic F127 via a scalable roll-to-roll method. An etching reaction between molten KOH and silica at high temperature (∼700 °C) introduces micropores and increases the surface area from 446 m²/g to 1718 m²/g without the loss of the ordered mesostructure. This large surface area after etching is generally advantageous for electrochemical energy storage. The carbon framework not only provides electrical conductivity but also constrains the volumetric changes of SiO₂ during Li⁺ insertion and extraction to improve the capacity stability on charge–discharge cycling. The bimodal pores of BP-CS facilitate lithium-ion diffusion (mesopores) while maximizing the contact area between the electrolyte and electrode (micropores) as well as providing stress relief from Li⁺ insertion. These characteristics lead to a discharge capacity of 611 mAh g^–1 after 200 cycles at 200 mA g^–1 with over 99.5% Coulombic efficiency for all discharge cycles. Even when increasing the current rate to 3 A g^–1, a capacity of 313 mAh g^–1 is retained after 1500 cycles, corresponding to <0.005% fade in the capacity per cycle. The combination of a high rate performance, a good cycle stability at a high rate, and a scalable synthesis route with low-cost precursors makes BP-CS a promising inexpensive, carbon/SiO₂-based anode material for long lifetime batteries

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