Abstract
Recently, rechargeable aqueous zinc–manganese dioxide batteries have attracted extensive attention due to their intrinsic safety and high energy density. However, due to the poor reversibility and substrate-dependent feature of the MnO2 dissolution/deposition reaction, MnO2 is barely cycled at a low areal capacity and short period, which considerably limits its practical applications. Herein, a reversible transformation reaction of an inorganic salt Zn4(OH)6SO4·5H2O (ZHS) was coupled with the dissolution/deposition reaction of layered K- and Na-inserted MnO2 (KNMO) to realize a high areal capacity KNMO–ZHS composite cathode for energy-dense and stable aqueous zinc batteries. During the dissolution (discharging process) and deposition (charging process) of KNMO, ZHS transforms in the opposite direction and plays the role of a pH stabilizer during discharging and an in situ pore former during charging, thus considerably enhancing the reaction kinetics and reversibility of KNMO. The KNMO–ZHS cathode could deliver a high specific capacity of 335 mAh g–1 at 0.1 A g–1 and show stable cycling for 5000 cycles at 6 A g–1. In particular, for the first time, a zinc-ion battery with a record high mass loading of more than 50 mg cm–2 cathode was demonstrated and showed decent capacity retention, which paves the way for practical applications of zinc–manganese dioxide batteries.
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