α-MnO2 nanofibers/carbon nanotubes hierarchically assembled microspheres: Approaching practical applications of high-performance aqueous Zn-ion batteries

Rechargeable Zn-ion batteries (ZIBs) have attracted extensive attention, but their practical application is hindered by the limited cycling life and complicated preparation process of cathode materials. Here, we develop a facile yet scalable chemical precipitation/spray-granulation combined methodology for the fabrication of alpha-MnO2 nanofibers/carbon nanotubes hierarchically assembled microspheres (alpha-MnO2/CNT HMs) as the cathode material for aqueous ZIBs. The alpha-MnO2 evenly anchoring to the CNTs-based framework shows significantly increased tap density compared with pristine alpha-MnO2, which can effectively enhance the electrochemical stability. Owing to the synergistic merits of highly conductive carbon nanotubes network and alpha-MnO2 nanofibers with desirable structure features, within our knowledge, the highest areal energy density of 0.98 Wh cm(-2) at 0.2 A g(-1) and the record cycling stability with 96% capacity retention over 10000 cycles at 3 A g(-1) among the reported cathodes for ZIBs are achieved. Zn2+ and H+ co-insertion reaction mechanism with high reversibility is further revealed. Fast kinetic of the H+ insertion/extraction process renders the cell excellent cycling stability. Facile preparation of nanofibrous alpha-MnO2 based micro-composite, cost benefit of the source materials, and the superior battery performance provide new approaches for the practical applications of ZIBs.