Fast ion transport at solid–solid interfaces in hybrid battery anodes

Carefully designed solid-electrolyte interphases are required for stable, reversible and efficient electrochemical energy storage in batteries. We report that hybrid battery anodes created by depositing an electrochemically active metal (for example, Sn, In or Si) on a reactive alkali metal electrode by a facile ion-exchange chemistry lead to very high exchange currents and stable long-term performance of electrochemical cells based on Li and Na electrodes. By means of direct visualization and ex situ electrodeposition studies, Sn–Li anodes are shown to be stable at 3 mA cm−2 and 3 mAh cm−2. Prototype full cells in which the hybrid anodes are paired with high-loading LiNi0.8Co0.15Al0.05O2(NCA) cathodes are also reported. As a second demonstration, we create and study Sn–Na hybrid anodes and show that they can be cycled stably for more than 1,700 hours with minimal voltage divergence. Charge storage at the hybrid anodes is reported to involve a combination of alloying and electrodeposition reactions. Solid-electrolyte interphases (SEI) play important roles in battery operations. Here, the authors report hybrid anodes by forming a Sn overlayer on alkali metal electrodes, leading to a robust SEI and consequently improved electrochemical performance.