Building a Long‐Cycle‐Life Rechargeable Daniel Cell from Solvent Isotope Effect of Hydrogen

ABSTRACT High‐performance, long‐cycle‐life aqueous rechargeable metal batteries have shown promises for the next‐generation sustainable electrochemical energy storage. In this work, we elucidated, from an isotopic view, the fundamental mechanisms for metal electrodeposition reactions in a zinc–copper Daniel cell at a subatomic scale, an aqueous primary battery that has been studied for almost two centuries. Benefiting from the hydrogen solvent isotope effect, markedly reduced desolvation Gibbs free energy changes (Δ G des‐ ) of metal cations were identified for the D 2 O‐based electrolytes due to a stronger H‐bond network, which facilitated hydrated cation desolvation and improved the reaction kinetics. A lower Δ G des‐ also helped to increase bare cation concentration and suppress water‐involved parasitic reactions at the interface. Consequently, electroplating of Zn/Cu metal in the D 2 O‐based electrolytes showed lower nucleation overpotentials, more homogeneous deposition morphology and higher average Coulombic efficiencies (Cu: ca. 99.8%, Zn: ca. 99.7%), so that Zn/Cu electrodes exhibited longer operation lifespans (Cu: ca. 3,500 h; Zn: ca. 3,000 h). A rechargeable Daniel cell was built from the D 2 O‐based electrolytes and operated stably for over 2,500 cycles under a voltage‐cutoff testing condition, shedding lights on rational design of high‐performance, low‐cost aqueous rechargeable metal batteries.