Layered Birnessite Cathode with a Displacement/Intercalation Mechanism for High-Performance Aqueous Zinc-Ion Batteries

<jats:title>Abstract</jats:title><jats:p>Mn-based rechargeable aqueous zinc-ion batteries (ZIBs) are highly promising because of their high operating voltages, attractive energy densities, and eco-friendliness. However, the electrochemical performances of Mn-based cathodes usually suffer from their serious structure transformation upon charge/discharge cycling. Herein, we report a layered sodium-ion/crystal water co-intercalated Birnessite cathode with the formula of Na<jats:sub>0.55</jats:sub>Mn<jats:sub>2</jats:sub>O<jats:sub>4</jats:sub>·0.57H<jats:sub>2</jats:sub>O (NMOH) for high-performance aqueous ZIBs. A displacement/intercalation electrochemical mechanism was confirmed in the Mn-based cathode for the first time. Na<jats:sup>+</jats:sup> and crystal water enlarge the interlayer distance to enhance the insertion of Zn<jats:sup>2+</jats:sup>, and some sodium ions are replaced with Zn<jats:sup>2+</jats:sup> in the first cycle to further stabilize the layered structure for subsequent reversible Zn<jats:sup>2+</jats:sup>/H<jats:sup>+</jats:sup> insertion/extraction, resulting in exceptional specific capacities and satisfactory structural stabilities. Additionally, a pseudo-capacitance derived from the surface-adsorbed Na<jats:sup>+</jats:sup> also contributes to the electrochemical performances. The NMOH cathode not only delivers high reversible capacities of 389.8 and 87.1 mA h g<jats:sup>−1</jats:sup> at current densities of 200 and 1500 mA g<jats:sup>−1</jats:sup>, respectively, but also maintains a good long-cycling performance of 201.6 mA h g<jats:sup>−1</jats:sup> at a high current density of 500 mA g<jats:sup>−1</jats:sup> after 400 cycles, which makes the NMOH cathode competitive for practical applications.</jats:p>