Unraveling the deposition/dissolution chemistry of MnO2 for high-energy aqueous batteries†
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Quan-Hong
Yang
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Abstract
Aqueous rechargeable batteries based on the deposition/dissolution of MnO2 are drawing significant attention because of their record-high theoretical capacity and redox potential in addition to their low cost and high safety. However, the deposition/dissolution chemistry of MnO2 remains elusive, which must be overcome for it to be used in batteries. Herein, we used an in situ electrochemical quartz crystal microbalance technique to reveal the deposition/dissolution process, and unequivocally identified that it has pH-dependent Mn(III)-intermediates (MnOOH and Mn3+). In particular, the dissolved Mn3+ results in a loss of active species and thus greatly decreases the discharge capacity, Coulombic efficiency and cycling stability. As proof of this new understanding, introducing some redox mediators into the electrolyte effectively addresses this problem in a prototype Cu//MnO2 battery. Our work provides a new and significant insight into the deposition/dissolution chemistry of MnO2, which will promote the further exploration of high-energy aqueous batteries.
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