Lithium-ion batteries (LIBs) stand as the predominant storage technology in various applications from portable devices to stationary purposes. Nevertheless, with their increasing integration in distinct sectors like mobility, there is a constant press for batteries with boosted energy density and enhanced safety. The energy density of the existing LIBs is limited by the electrode materials and their main safety concern is arisen from the inflammable organic liquid electrolytes. Silicon with a theoretical capacity ten times higher than the currently used graphite is envisioned as the alternative anode for the next-generation LIBs. High abundance and low working potential (<0.4 V vs. Li/Li⁺) are the other benefits added to its palette, making Si a promising and viable anode electrode.¹ However, mediocre cyclability due to significant volume change over (de)lithiation and consequential Li loss has so far hindered the Si penetration as a dominant active material into commercial cells. Integration of Si electrodes with solid electrolytes has recently been opened new horizons for a combined improved cyclability and safety of Si-based energy-dense batteries.² Yet the alloying reaction with solid electrolytes and the parameters governing and influencing the charge storage and failure mechanisms need to be understood; these include particle size, electrode microstructure and composition, pressure evolution during assembly and operation, among others.

This communication presents the first study on pure Si NW electrodes, produced by a slurry-free method without carbon or binders,^3,4 as anodes in integration with argyrodite LPSCl solid electrolyte, achieving a high capacity of > 2.5 Ah/g even at relatively high mass loading of 1.7 mg/cm² (e.g., ~5 mAh/cm²), demonstrating their sufficient mixed electronic and ionic conductivities. Electro-chemo-mechanical properties of the electrodes over (de)lithiation were probed through electrochemical impedance spectroscopy, ex-situ microscopy, and in-situ pressure regulation measurements. The Si NW electrode/solid electrolyte interface was found to be electrochemically stable even when fully lithiated. Cross-sectional microscopy at various states-of-charge confirmed the buffering effect of the anode porosity, resulting in preservation of the electrode’s thickness after the first lithiation. Furthermore, the ex-situ microscopies over cycling suggested that the capacity fading is caused through significant porosity loss over the first delithiation. This work not only presents an extensive electrochemical study of the pure Si NW electrodes in integration with argyrodite Li₆PS₅Cl solid electrolyte, but also provides a better understanding of the electrode structure effect on its performance. Accordingly, we believe that the overall cycling properties could be significantly improved by mitigating the electrode shrinkage after the first delithiation, calling for innovative strategies to reinforce the electrode mechanical structure/porosity in its initial cycles.