Carbon-Coated, Diatomite-Derived Nanosilicon as a High Rate Capable Li-ion Battery Anode

Abstract

Silicon is produced in a variety of ways as an ultra-high capacity lithium-ion battery (LIB) anode material. The traditional carbothermic reduction process required is expensive and energy-intensive; in this work, we use an efficient magnesiothermic reduction to convert the silica-based frustules within diatomaceous earth (diatomite, DE) to nanosilicon (nanoSi) for use as LIB anodes. Polyacrylic acid (PAA) was used as a binder for the DE-based nanoSi anodes for the first time, being attributed for the high silicon utilization under high current densities (up to 4C). The resulting nanoSi exhibited a high BET specific surface area of 162.6 cm² g^-1, compared to a value of 7.3 cm² g^-1 for the original DE. DE contains SiO₂ architectures that make ideal bio-derived templates for nanoscaled silicon. The DE-based nanoSi anodes exhibit good cyclability, with a specific discharge capacity of 1102.1 mAh g^-1 after 50 cycles at a C-rate of C/5 (0.7 A g_Si^-1) and high areal loading (2 mg cm^-2). This work also demonstrates the fist rate capability testing for a DE-based Si anode; C-rates of C/30 - 4C were tested. At 4C (14.3 A g_Si^-1), the anode maintained a specific capacity of 654.3 mAh g^-1 - nearly 2x higher than graphite's theoretical value (372 mAh g^-1).