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Rechargeable aqueous Zn/MnO2 batteries are very attractive large‐scale energy storage technologies, but still suffer from limited cycle life and low capacity. Here the novel adoption of a near‐neutral acetate‐based electrolyte (pH ≈ 6) is presented to promote the two‐electron Mn4+/Mn2+ redox reaction and simultaneously enable a stable Zn anode. The acetate anion triggers a highly reversible MnO2/Mn2+ reaction, which ensures high capacity and avoids the issue of structural collapse of MnO2. Meanwhile, the anode‐friendly electrolyte enables a dendrite‐free Zn anode with outstanding stability and high plating/stripping Coulombic efficiency (99.8%). Hence, a high capacity of 556 mA h g−1, a lifetime of 4000 cycles without decay, and excellent rate capability up to 70 mA cm−2 are demonstated in this new near‐neutral aqueous Zn/MnO2 battery by simply manipulating the salt anion in the electrolyte. The acetate anion not only modifies the surface properties of MnO2 cathode but also creates a highly compatible environment for the Zn anode. This work provides a new opportunity for developing high‐performance Zn/MnO2 and other aqueous batteries based on the salt anion chemistry. [ABSTRACT FROM AUTHOR]

The phase evolution and anion redox behaviours under electrochemical cycling of sodium transition metal layered oxides have both been intensively studied. In this review, we focus on the relationship between them at high voltage states-of-charge, in the context of growing evidence that anion redox begins at an earlier state of charge than previously thought, and that the final structural change can behave in either a biphasic or a pseudo-solid solution manner, depending on the transition metal element. By systematically reviewing major breakthroughs in experimental materials discovery, characterization techniques and theoretical understanding, we tentatively propose a new way to think about the phase transition dynamics and a path to improving the theory of anion redox. • The most updated theories on structural evolution and anion redox are reviewed. • High voltage layered oxides for sodium ion battery cathode materials are examined. • Characterization techniques that can help to build our understanding are suggested. • Shortcomings of the current theories and future perspectives are discussed. [ABSTRACT FROM AUTHOR]