Determining the electrochemical properties of SiO2 for the rational design of siliconbased active materials in lithium-ion batteries

Abstract SiO 2 is a compound often found in next-generation silicon-based lithium-ion battery anode materials, although it is thought to cause low initial coulombic efficiencies and low reversible capacities. Therefore, precise knowledge of the electrochemical properties of SiO 2 is essential for predictive lithium-ion battery full cell design. However, reliably determining these properties is challenging due to the insulating character of SiO 2 . In this work, a thorough electrochemical characterisation of SiO 2 was enabled through SiO 2 -C composite formation that provided nanostructured conductive pathways within particles. SiO 2 scaffolds derived from the MCM-41 family enabled pore tuning. After filling these pores with carbon, composites with different SiO 2 /C ratios were obtained. Their specific charge values, measured during the initial cycle in a potential window of 5 mV to 1.0 V, was extrapolated to 100% carbon and 100% SiO 2 resulting in a reversible (irreversible) specific charge of 671 mA h g −1 (1069 mA h g −1 ) at an initial coulombic efficiency of 39% for SiO 2 . The reliability of this method was validated by comparing the extrapolated value for carbon to the measured specific charge of an amorphous carbon reference, which consisted of an electrochemically inert porous boron nitride compound filled with carbon. These results demonstrated that SiO 2 was not stable at typical lithium-ion battery anode potentials. SiO 2 transformed into products that were lithiated reversibly, and products that were inert at LIB anode potentials. Post-mortem IR spectroscopy suggested that lithium silicates were contained in the inert products, which ceased to contribute to the electrochemical reactions after the initial cycle. Graphical abstract