Unveiling the Mechanical and Electrochemical Evolution of Nano Silicon Composite Anodes in Sulfide based All-solid-state Batteries

The utilization of silicon (Si) anodes in all-solid-state lithium batteries (ASLBs) provides the potential for high energy density. However, the compatibility of sulfide solid-state electrolytes (SEs) with Si and carbon is often questioned due to potential decomposition. To investigate this, operando X-ray absorption near-edge structure (XANES) spectroscopy, ex-situ scanning electron microscopy (SEM) and ex-situ X-ray nano-tomography (XnT) were utilized to study the chemistry and structure evolution of nano Si composite anodes. Results from XANES demonstrated a partial decomposition of SEs during the first lithiation stage, which was further accelerated by the presence of carbon. But the performance of first three cycles in Si-SE-C was stable, which proved the generated media is ionically conductive. XnT and SEM results showed that the addition of SEs and carbon improved the structural stability of the anode with fewer pores and voids. A chemo-elasto-plastic model revealed that SEs and carbon buffered the volume expansion of Si, thus enhancing mechanical stability. The balance between the pros and cons of SEs and carbon in enhancing reaction kinetics and structural stability enabled the Si composite anode to demonstrate the highest Si utilization with higher specific capacities and better rate than pure Si and Si composite anodes with only SEs.