Insights on the Degradation Behavior of Diatom SiO2 Anodes for Lithium-ion Batteries

SiO2 is a promising material for developing high-capacity anodes for lithium-ion batteries (LIBs). However, degradation behavior of SiO2 anodes upon prolonged electrochemical cycling remains unexplored. In this work, the causes leading to capacity fade on SiO2 anodes are investigated and simple strategies to attenuate anode degradation are explored. Nanostructured SiO2 from diatomaceous earth was integrated into anodes containing different quantities of conductive carbon in the form of either a conductive additive or a nanometric coating layer. Galvanostatic cycling was conducted for 200 cycles and distinctive trends on capacity fade were identified. A thorough analysis of the anodes at selected cycle numbers was performed using a toolset of characterization techniques, including electrochemical impedance spectroscopy, FIB-SEM cross-sectional analysis and TEM inspections. Significant fragmentation of SiO2 particles surface and formation of filigree structures upon cycling are reported for the first time. Morphological changes are accompanied by an increase in impedance and a loss of electroactive surface area. Carbon-coating was found to restrict particle fracture and increase capacity retention to 66% compared to 47% for uncoated samples after 200 cycles. Results provide valuable insights to improve cycling stability of SiO2 anodes for next-generation LIBs.