Fig. 3: Structure evolution during charge and discharge.

a In situ XRD patterns corresponding to the charge and discharge curves of Na_0.612K_0.056MnO₂. Schematic illustration of phase transitions along with the content change of Na⁺ in Na_0.612K_0.056MnO₂ (b) and Na₀₇₀₆MnO₂ (c) in cycles of charge and discharge.