Manipulating Zn2+ solvation environment in poly(propylene glycol)‐based aqueous Li+/Zn2+ electrolytes for high‐voltage hybrid ion batteries

Abstract Compared with aqueous single‐ion batteries, rechargeable aqueous hybrid ion batteries, especially Li+/Zn2+hybrid ion batteries, are receiving extensive interest owing to their low cost, high operating voltage, and energy density. However, their working voltage and lifespan are limited by the decomposition of water and the growth of Zn dendrites. Herein, detrimental side reactions induced by the water reduction and the Zn dendrite growth are successfully suppressed by a poly(propylene glycol) (PPG)‐based hybrid ion electrolyte [(1 m Zn(TFSI)2 + 10 m LiTFSI) in PPG/H2O]. The addition of PPG in the electrolyte can not only enhance the bonding strength of hydrogen‐bond in water but also tailor the solvation sheath of Zn2+ as revealed by synchrotron X‐rays. The participated solvation of PPG with Zn2+ can weaken Zn−H2O interactions and redistribute Zn2+ flux on the surface of the Zn anode, thus inducing favorably even deposition of Zn. In addition, the decomposition of TFSI− contributes a ZnF2 ‐enriched solid electrolyte interface at the Zn anode to further prevent water decomposition and restrain Zn dendrites. The PPG‐based electrolyte enables 2.1 V LiMnO2//Zn batteries to deliver high specific capacities (121.7 mAh g−1 for a coin cell and 90 mAh g−1 for a pouch cell), and maintain 80% of the capacity over 700 cycles at 0.5 C, suggesting a promising pathway for highly reversible aqueous hybrid ion batteries.