Hydrogen Isotope Effects on Aqueous Electrolyte for Electrochemical Lithium‐Ion Storage

As two stable hydrogen isotopes, protium and deuterium show magnified isotope effects in physicochemical properties due to the significantly varied atomic masses. In this work, aqueous electrolytes based on heavy water (D₂ O) and light water (H₂ O) were prepared to reveal the electrochemical isotope effects between the hydrogen isotopes. The covalent hydrogen-oxygen bond and intermolecular hydrogen bond in D₂ O are much stronger than those in H₂ O, making them thermodynamically more stable. Compared with the H₂ O-based electrolyte, the D₂ O-based electrolyte shows a broader electrochemical window, a higher percentage of coordinated water and a longer lifetime of hydrogen bond. Because of the above electrochemical isotope effects, the D₂ O-based electrolyte shows high anodic stability against operation of high-voltage layered oxide cathode materials including LiCoO₂ and LiNi0.8 Co0.1 Mn0.1 O₂ , which enables long cycle life and favorable rate performance of aqueous Li-ion batteries.