Reversible Li⁺/H⁺ Exchange Impairs Si/C/Li₇La₃Zr₂O₁₂ Mixed Anodes

Silicon is a promising anode material for both liquid- and solid-state batteries due to its high theoretical capacity and low operating voltage. Among solid-state electrolytes, Li7La3Zr2O12 (LLZO) is considered a promising candidate due to its good stability against highly reducible anodes. However, the chemical and electrochemical stabilities of LLZO in silicon-based anodes, particularly in industrially mature aqueous slurries, remains insufficiently explored. In this study, we report that mixing LLZO with silicon in aqueous slurries leads to a reversible Li+/H+ exchange during the lithiation process. This exchange results in a significant influx of protons into the battery, triggering a hydrogen evolution reaction (HER) at low voltage, which severely degrades the silicon-based electrodes and the performance of batteries. To address this issue, we propose a solution by incorporating sulfolane into the electrolyte, which can effectively confine free H+ and mitigate HER. With this modification, the battery retains 22.2% and 10.4% of its capacity at 3C and 5C charge rates, respectively, providing a potential strategy for the application of mixed LLZO in silicon-based anodes.