Probing 3D Evolution and Electrochemical Behavior of Nano Silicon Anodes in Sulfide All-Solid-StateBatteries via Nano X-Ray Tomography and in Operando XAS

Silicon (Si) is one of the most promising anode materials for the next generation Li-ion batteries on account of its ultrahigh specific capacity (3590 mAh g-1) and relatively low working potential of 0.4 V (vs. Li+/Li). The utilization of silicon anode in all-solid-state lithium batteries (ASLBs) can further boost the energy density compared with the conventional graphite anode. Among various ASLBs with different solid electrolytes (SEs), the ASLBs with sulfide SEs delivered remarkable performances because of the excellent ionic conductivity (&gt;1 mS cm^-1) and relative “soft” mechanical properties (compared with oxides SEs) for intimate contact with electrode materials of sulfide SEs. However, the compatibility of Si and sulfide SEs is questioned because of the potential electrochemical decomposition. In addition, the extreme volume change (400%) of Si during cycling also brings great challenges to the structural stability of the ASLBs. Nano-Si (&lt;100 nm in diameter) have a higher structural stability because the smaller geometry size can relieve stress. Therefore, in this study, we systematically analyzed the electrochemical and structural evolution of different nano-Si-based anodes in ASLBs with sulfide SE via <i>in-operando</i> synchrotron X-ray absorption near-edge structure (XANES) spectroscopy and scanning electron microscopy (SEM) combined with X-ray nano-tomography (XnT). Three kinds of nano Si-based anodes (pure nano-Si (Si), nano-Si compositing with SE (Si-SE), nano-Si compositing with SE and carbon (Si-SE-C)) were analyzed. The Operando XANES revealed that the sulfide SE experiences an electrochemical decomposition in the nano-Si anode and the addition of carbon accelerates this process. However, this electrochemical decomposition only occurs at the first lithiation process and the products are stable in the following cycles and has comparable ionic conductivity. The ex-situ SEM and ex-situ XnT exhibit that the addition of SE and carbon in the nano-Si anode benefits the structural stability, which is further explained by a chemo-elasto-plastic modeling framework. Owing to the enhanced reaction kinetics and mechanical structural stability, the Si-SE-C achieved the highest Si utilization, with a lithiation/delithiation capacity of 3288/2917 mAh g^-1 and an initial coulombic efficiency of 88.7%, which are significantly higher than the capacities of 2653/2291 mAh g^-1 and ICE of 86.4% in Si-SE, and the capacities of 2353/1935 mAh g^-1 and ICE of 82.2% in Si. This work indicated that the addition of SE and carbon into nano-Si anode can enhance the reaction kinetics, improve the utilization of Si, and benefit the mechanical structure stability, though the SE shows slight decomposition but the generated chemistry is ionically conductive and stable in the following cycles. Through the comprehensive evaluation between the pros and cons of adding SE and carbon, in terms of improvements in reaction kinetics and structural stability compared with the limited electrochemical decomposition of SE, nano-Si-SE-C composite anode demonstrates the best Si utilization with the highest specific capacities.<br/>&lt;quillbot-extension-portal&gt;&lt;/quillbot-extension-portal&gt;&lt;quillbot-extension-portal&gt;&lt;/quillbot-extension-portal&gt;