Highly Reversible Cycling of Zn-MnO 2 Batteries Integrated with Acid-Treated Carbon Supportive Layer.

Zn-MnO 2 battery with mild-acid electrolytes has been considered as a promising alternative to Li-ion battery for safe and cost-effective energy storage systems (ESSs), and for full electrification. However, the governing mechanism of MnO 2 electrochemistry has not been fully elucidated, hindering further advances in highly reversible MnO 2 cathodes. Eventual Mn 2+ ion dissolution into the electrolyte adversely triggers the irreversible loss of Mn 2+ ions and the excessive precipitation of zinc hydroxyl sulfate (Zn 4 SO 4 (OH) 6 ·xH 2 O, ZHS), leading to irreversible capacity loss upon prolonged cycling. To overcome these drawbacks, a rationally renovated cell structure is proposed by integrating an acid-treated carbon supportive layer (aCSL) in the MnO 2 cathode, which can play multifunctional roles rendering the additional reaction sites for the reversible formation/decomposition of ZHS and re-utilization of the dissolved Mn 2+ ions. Furthermore, the improved affinity of the aCSL toward the electrolyte is beneficial for increasing active surface area and facilitating charge transfer at the cathode side. Benefiting from these features, compared to the conventional cell configuration, the aCSL-integrated Zn-MnO 2 cell exhibits superior cycling over 3000 cycles with negligible capacity decay (85.6% retention) at a current of 3 A g -1 .