MnO₂ Heterostructure on Carbon Nanotubes as Cathode Material for Aqueous Zinc-Ion Batteries

Due to their cost effectiveness, high safety, and eco-friendliness, zinc-ion batteries (ZIBs) are receiving much attention nowadays. In the production of rechargeable ZIBs, the cathode plays an important role. Manganese oxide (MnO₂) is considered the most promising and widely investigated intercalation cathode material. Nonetheless, MnO₂ cathodes are subjected to challenging issues viz. limited capacity, low rate capability and poor cycling stability. It is seen that the MnO₂ heterostructure can enable long-term cycling stability in different types of energy devices. Herein, a versatile chemical method for the preparation of MnO₂ heterostructure on multi-walled carbon nanotubes (MNH-CNT) is reported. Besides, the synthesized MNH-CNT is composed of δ-MnO₂ and γ-MnO₂. A ZIB using the MNH-CNT cathode delivers a high initial discharge capacity of 236 mAh g^-1 at 400 mA g^-1, 108 mAh g^-1 at 1600 mA g^-1 and excellent cycling stability. A pseudocapacitive behavior investigation demonstrates fast zinc ion diffusion via a diffusion-controlled process with low capacitive contribution. Overall, the MNH-CNT cathode is seen to exhibit superior electrochemical performance. This work presents new opportunities for improving the discharge capacity and cycling stability of aqueous ZIBs.