Mn3O4 nanocrystalline@carbon nanotube-carbon nanotube for long-lifetime and excellent rate-capability zinc-ion storage

Rapid capacity decay and inferior rate capability are two main problems that affect the application of Mn3O4 in aqueous zinc-ion batteries (ZIBs). Herein, we synthesize ultrasmall Mn3O4 nanocrystalline on carbon nanotube-carbon nanotube through in-situ growth of ZIF-8 on carbon nanotube, etching by tannin acid, chemical reaction of carbon and KMnO4, and final calcination. It is found that Mn3O4 nanocrystalline tightly embraces the carbon matrix, with 8-10 nm in size, 59% of weight percentage, and 46.3 m2 g−1 of specific surface area. As cathode material for ZIBs, the composite exhibits outstanding electrochemical performance, superior to most of Mn-based composites. It can deliver discharge capacity of 234 mAh g−1 at 1 A g−1 after 400 cycles. At 5 A g−1, the discharge capacity may reach 49 mAh g−1, and recovery ability is still good. Electrochemical mechanism is further studied through various electrochemical kinetics analyses and ex-situ material characterizations. The excellent Zn storage performance mainly benefits from the synergistic effect of the high conductive carbon nanotube-carbon nanotube matrix, the unique composite structure and small size of Mn3O4 nanocrystalline. The work provides a new strategy to construct the long-lifetime and excellent rate-capability Mn-based cathodes for ZIBs.