In recent years, rechargeable aqueous zinc‐ion batteries (ZIBs) have received much attention. However, the disproportionation effect of Mn2+ seriously affects the capacity retention of ZIBs during cycling. Here, the capacity retention of the Mn3O4 cathode is improved by effective valence engineering. The valence engineering of Mn3O4 is caused by bulk oxygen defects, which are in situ derived from the Mn‐metal organic framework during carbonization. Bulk oxygen defects can change the (MnO6) octahedral structure, which improves structural stability and inhibits the dissolution of Mn2+. The ZIB assembled from bulk oxygen defects Mn3O4@C nanorod arrays (Od‐Mn3O4@C NA/CC) exhibits an ultra‐long cycle life, reaching 84.1 mAh g−1 after 12 000 cycles at 5 A g−1 (up to 95.7% of the initial capacity). Furthermore, the battery has a high specific capacity of 396.2 mAh g−1 at 0.2 A g−1. Ex situ characterization results show that initial Mn3O4 is converted to ramsdellite MnO2 for insertion and extraction of H+ and Zn2+. First‐principles calculations show that the charge density of Mn3+ increases greatly, which improves the conductivity. In addition, the flexible quasi‐solid‐state ZIB is successfully assembled using Od‐Mn3O4 @ C NA/CC. Valence engineering induced by bulk oxygen defects can help develop advanced cathodes for aqueous ZIB.

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The severe shuttling behavior in the discharging–charging process largely hampers the commercialization of lithium–sulfur (Li–S) batteries. Herein, we design a bifunctional separator with an ultra-lightweight MnO2 coating to establish strong chemical adsorption barriers for shuttling effect alleviation. The double-sided polar MnO2 layers not only trap the lithium polysulfides through extraordinary chemical bonding but also ensure the uniform Li+ flux on the lithium anode and inhibit the side reaction, resulting in homogeneous plating and stripping to avoid corrosion of the Li anode. Consequently, the assembled Li–S battery with the MnO2-modified separator retains a capacity of 665 mA h g–1 at 1 C after 1000 cycles at the areal sulfur loading of 2.5 mg cm–2, corresponding to only 0.028% capacity decay per cycle. Notably, the areal loading of ultra-lightweight MnO2 coating is as low as 0.007 mg cm–2, facilitating the achievement of a high energy density of Li–S batteries. This work reveals that the polar metal oxide-modified separator can effectively inhibit the shuttle effect and protect the Li anode for high-performance Li–S batteries.

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