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

The growing demand for wearable electronics boosts researches on flexible fibrous energy storage devices, such as fibrous Zn-MnO 2 battery. One bottleneck for the capacity of fibrous MnO 2 electrode, especially at high discharge rate, is the inefficient interfacial charge transfer between nano particles within mechanical-mixed MnO 2 aggregates. Herein, nano γ-MnO 2 has been in-situ grafted on nano carbon branches via a mild interfacial oxidation reaction using KMnO 4 -doped MnO 2 sol precursor, to form nano composites of MnO 2 @ 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 MnO 2 electrode based on the composites of MnO 2 @ hierarchical carbon networks is successfully applied to fibrous Zn-MnO 2 battery, by giving a 2.5 times of capacitance promotion and a better charging-discharging cycling stability. [Display omitted] • A rapid δ-to-γ crystal transformation of MnO 2 have been boosted at hierarchical carbon interface. • The rapid crystal transformation takes place by using Mn(VII)-doped MnO 2 precursor as a mild oxidant. • Highly capacitive MnO 2 @HCNW materials have been synthesized via the crystal-transformation reaction. • Efficient fibrous Zn-MnO 2 battery was assembled, and gives a 2.5-times capacitance promotion. [ABSTRACT FROM AUTHOR]