Abstract
The use of silica as an active material within a lithium-ion battery requires a pre-treatment. The electrochemical reduction between silica and lithium is partially irreversible and is postulated to produce silicon as a reaction product. The silicon formed can reversibly react with lithium to produce stable capacities, higher than current graphite materials. However, both the electrochemical reduction pathway and the electrochemical reduction products are unknown, thereby hampering the design, optimisation and use of such systems. Here we uncover the pathway for the electrochemical reduction and, for the first time, identify elemental silicon as a product of the reduction. We discovered new methods for studying the electrochemical reduction reaction – they are based on monitoring and analysing the capacity increase and the current flow as the material is reduced. Our results conclusively show that silica must be reduced to introduce reversible capacity and that this reduction reaction time can be greatly reduced using a constant load discharge at elevated temperature. Characterisation with total scattering X-ray pair distribution function shows the reduction products are amorphous in nature and confirmed why previous diffraction characterisation attempts were unsuccessful. Our results can help better understand the electrochemical reduction of any silica material. We anticipate these results can be used as a starting point for the development of a scaled-up synthesis route for in-situ reduced silica anodes and their incorporation into lithium-ion full cells.