Structural Transformation and Cycling Improvement of Nanosized Flower-like γ‑MnO2 in a Sodium Battery

In this paper, we prepared nanostructured γ-MnO2 and used it as the cathode material in a sodium battery. X-ray diffraction (XRD), inductively coupled plasma spectroscopy (ICP), a first-principles calculation, and other tests were carried out to study the structural changes of γ-MnO2 during Na+ (de)­intercalation. A phase transformation of γ-MnO2 to NaMnO2 was found during the first discharge. However, the capacity decayed quickly in EC-based electrolytes due to the dissolution of Mn2+. By replacing the electrolyte with ionic liquid­(IL), Mn2+ dissolution can be effectively alleviated and the cycling of γ-MnO2 can be improved. The capacity is as high as ∼150 mAh/g after 100 cycles in the ionic liqiud.