Three-Dimensional Manganese Oxide@Carbon Networks as Free-Standing, High-Loading Cathodes for High-Performance Zinc-Ion Batteries

Zinc-ion batteries (ZIBs), which are inexpensive and environmentally friendly, have a lot of potential for use in grid-scale energy storage systems, but their use is constrained by the availability of suitable cathode materials. MnO2-based cathodes are emerging as a promising contenders, due to the great availability and safety, as well as the device's stable output voltage platform (1.5 V). Improving the slow kinetics of MnO2-based cathodes caused by low electrical conductivity and mass diffusion rate is a challenge for their future use in next-generation rapid charging devices. Herein, the aforementioned challenges are overcome by proposing a sodium-intercalated manganese oxide (NMO) with 3D varying thinness carbon nanotubes (VTCNTs) networks as appropriate free-standing, binder-free cathodes (NMO/VTCNTs) without any heat treatment. A network construction strategy based on CNTs of different diameters is proposed for the first time to provide high specific capacity while achieving high mass loading. The specific capacity of as-prepared cathodes is significantly increased. The resulting free-standing binder-free cathodes achieve excellent capacity (329 mAh g(-1) after 120 cycles at 0.2 A g(-1) and 225 mAh g(-1) after 200 cycles at 1 A g(-1)) and long-term cycling stability (158 mAh g(-1) at 2 A g(-1) after 1000 cycles).

Automated summary

Zinc-ion batteries (ZIBs) have potential for use in grid-scale energy storage systems, but suitable cathode materials are needed. MnO2-based cathodes are emerging as promising contenders due to their availability, safety, and stable output voltage. However, their slow kinetics caused by low electrical conductivity and mass diffusion rate are a challenge for rapid charging devices. This study proposes a sodium-intercalated manganese oxide (NMO) with 3D varying thinness carbon nanotubes (VTCNTs) networks as free-standing, binder-free cathodes, which overcome the challenges and achieve excellent capacity and long-term cycling stability.