Fast crystal transformation of nano MnO2 induced by mild interfacial oxidation on hierarchical carbon networks for assembling efficient fibrous MnO2 electrode

Abstract

The growing demand for wearable electronics boosts researches on flexible fibrous energy storage devices, such as fibrous Zn-MnO2 battery. One bottleneck for the capacity of fibrous MnO2 electrode, especially at high discharge rate, is the inefficient interfacial charge transfer between nano particles within mechanical-mixed MnO2 aggregates. Herein, nano γ-MnO2 has been in-situ grafted on nano carbon branches via a mild interfacial oxidation reaction using KMnO4-doped MnO2 sol precursor, to form nano composites of MnO2@ hierarchical carbon networks. The grafting reaction selectively takes place at defective sites with a mixed bonding state on the surface of the carbon branches, during which a rapid δ-to-γ crystal transformation is largely boosted, instead of traditional slow δ-to-α crystal transformation. An efficient fibrous MnO2 electrode based on the composites of MnO2@ hierarchical carbon networks is successfully applied to fibrous Zn-MnO2 battery, by giving a 2.5 times of capacitance promotion and a better charging-discharging cycling stability.