Sodium Cyclopentadienide as a New Type of Electrolyte for Sodium Batteries

Owing to the low cost and high abundance of sodium, sodium‐based batteries, especially those employing metallic sodium anodes, are considered for post‐lithium energy storage. In order to develop high‐performance and long‐lasting sodium‐metal batteries, however, the reversible Na‐metal stripping and plating challenge must be addressed. Most organic electrolytes suffer from non‐uniform and continuous formation of the solid electrolyte interphase as well as unfavorable dendritic growth. The use of sodium cyclopentadienide dissolved in tetrahydrofuran as the electrolyte reveals an improved reversibility of sodium dissolution and electrodeposition combined with an electrochemical stability window of around 2.2 V vs. Na/Na+ and an ionic conductivity of 1.36 mS cm−1 at 25 °C. Furthermore, the plated electrodes showed a remarkable morphology of the Na deposits, that is, no dendrite formation, whereby the above‐mentioned electrolyte could overcome the aforementioned cycling issues, thus suggesting suitability for further studies.