Toward Achieving High Areal Capacity in Silicon-Based Solid-State Battery Anodes: What Influences the Rate-Performance?

Achieving high areal capacity and rate performance in solid-state battery electrodes is challenging due to sluggish charge carrier transport through thick all-solid composite electrodes, as the transport strongly relies on the microstructure and porosity of the compressed composite. Introducing a high-capacity material like silicon for such a purpose would require fast ionic and electronic transport throughout the electrode. In this work, by designing a composite electrode containing Si nanoparticles, a superionic solid electrolyte (SE), and a carbon additive, the possibility of achieving areal capacities over 10 mAh·cm–2 and 4 mAh·cm–2 at current densities of 1.6 mA·cm–2 and 8 mA·cm–2, respectively, at room temperature is demonstrated. Using DC polarization measurements, impedance spectroscopy, microscopic analyses, and microstructure modeling, we establish that the route to achieve high-performance anode composites is microstructure modulation through attaining high silicon/solid electrolyte interface contacts, particle size compatibility of the composite components, and their well-distributed compact packing in the compressed electrode.