A design of MnO-CNT@C₃N₄ cathodes for high-performance aqueous zinc-ion batteries

Manganese oxides have been regarded as one of the most promising candidates in rechargeable aqueous zinc ion batteries due to their high specific capacity, high operating voltage, low cost and no-toxicity. Nevertheless, the grievous dissolution of manganese and the sluggish Zn²⁺ ions diffusion kinetics deteriorate the long cycling stability and the rate performance. Herein, we propose a combination of hydrothermal and thermal treatment strategy to design a MnO-CNT@C₃N₄ composite cathode material where MnO cubes are coated by carbon nanotubes (CNTs) and C₃N₄. Owing to the enhanced conductivity by CNTs and the alleviation of the dissolution of Mn²⁺ from the active material by C₃N₄, the optimized MnO-CNT@C₃N₄ exhibits an excellent rate performance (101 mAh g^-1 at a large current density of 3 A g^-1) and a high capacity (209 mAh g^-1 at a current density of 0.8 A g^-1), which is much better than its MnO counterpart. The energy storge mechanism of MnO-CNT@C₃N₄ is confirmed to be the co-insertion of H⁺/Zn²⁺. The present work provides a viable strategy for the design of advanced cathodes for high-performance zinc ion batteries.