Silicon‐Germanium Solid Solutions with Balanced Ionic/Electronic Conductivity for High‐Rate All‐Solid‐State Batteries

Abstract Silicon (Si) is a promising anode for all‐solid‐state batteries (ASSBs) due to its high capacity, but it suffers from low initial Coulombic efficiency (ICE) and poor rate performance. Here, a series of Si–Ge solid solution anodes is synthesized via high‐energy ball milling. Incorporating isomorphous Ge, which has a lower band gap and larger atomic radius, enhances electronic conductivity and induces lattice distortion to broaden Li ⁺ diffusion pathways. The optimized Si ₇ Ge anode achieves balanced electron/ion conductivities (3.4 × 10 ⁻⁵ /2.34 × 10 ⁻⁵ S cm ⁻¹ ), which are markedly superior to those of pure Si (8.1 × 10 ⁻⁸ /3.13 × 10 ⁻⁶ S cm ⁻¹ ). This dual enhancement enables efficient lithiation/delithiation and stable interfacial contact. As a result, the Si ₇ Ge anode delivers a high ICE of 89.4%, a reversible capacity of 2631 mAh g ⁻¹ , and favorable rate performance (2024 mAh g ⁻¹ at 3 C). In full cells with a LiCoO ₂ cathode, an ICE of 88.0% and 100 mAh g ⁻¹ at 2 C are achieved. An all‐solid‐state pouch cell with the Si ₇ Ge anode demonstrates stable cycling over 100 cycles at 0.33 C, highlighting its potential for practical ASSBs applications. This work offers a promising route to overcome Si anode limitations through rational alloy engineering.