ZnO-coated MnO2 Nanorods with Enhanced and Stabilized Charge Transfer Performance as a Cathode Material for Aqueous Zinc-Ion Batteries

In this work, ZnO-coated MnO2 nanorods are synthesized by a two-step hydrothermal reaction. The MnO2 nanorods have a length greater than 1 mu m and a diameter of 30-50 nm. The thin ZnO coating on the surface of the MnO2 nanorods is 2-3 nm thick. ZnO-coated MnO2 nanorods exhibit enhanced and stabilized charge transfer performance relative to uncoated MnO2 nanorods. At a current density of 0.1 A g(-1), ZnO-coated MnO2 nanorods deliver capacity of 346 mAh g(-1) after 50 cycles, and at a high current density of 1 A g(-1), they deliver capacity of 210 mAh g(-1) even after 1000 cycles, with no capacity decay during cycling. In contrast, the capacity of uncoated MnO2 nanorods rapidly decreases to 61 mAh g(-1) at a current density of 0.1 A g(-1) after 50 cycles. The improved electrochemical performance of the ZnO-coated MnO2 nanorods can be attributed to the following factors: the ZnO/MnO2 interface rich in defects increases the electrochemical reaction sites for Zn storage, while the ZnO coating suppresses large volume changes of the MnO2 nanorods, prevents direct contact between MnO2 nanorods and electrolyte, and improves the conductivity of the MnO2 nanorods.