Preparation and electrochemical properties of manganese dioxide flexible electrodes for zinc-ion batteries

Manganese dioxide (MnO2), a commonly used cathode material for zinc-ion batteries (ZIBs), has attracted considerable attention owing to its abundant reserves in nature, safety, and high theoretical capacity. One of the key challenges in the preparation of high-performance zinc-ion batteries is the construction of a cathode with a stable microstructure. In this study, a flexible and conductive carbon cloth (CC) was chosen as the substrate onto which manganese dioxide (MnO2) was deposited through either reductive deposition or electrochemical deposition methods to form a carbon cloth@ manganese dioxide (CC@MnO2) cathode. For the reductive deposition method, a precursor solution of KMnO4 and H2SO4 was used, and various concentrations were adopted to synthesize the CC@MnO2 cathode. The synthesized electrode is referred to as the CC@MnO2-reductive deposition cathode. Specifically, KMnO4 solutions with concentrations of 0.25, 0.40, and 0.55 mol·L−1 were mixed with H2SO4 at concentrations of 0.20 mol·L−1 and 0.50 mol·L−1. For the electrochemical deposition method, MnO2 nanoparticles were decorated on CC using a three-electrode system under the potentiostatic mode at a potential of 1.1 V for 1500 s. A depositing electrolyte consisting of 0.1 mol·L−1 MnSO4 + 0.1 mol·L−1 Na2SO4 was used. The synthesized electrode is referred to as the CC@MnO2-electrochemical deposition cathode. The cathodes synthesized under different parameters were comparatively analyzed via scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron microscopy to explore their morphology and microstructure. Furthermore, the prepared CC@MnO2 cathodes were assembled into button-type zinc-ion batteries, and their electrochemical properties, charging/discharging performance, and cycling stability were evaluated. The test results showed that the Zn//CC@MnO2 cells based on the reductive deposition method with a 0.40 mol·L−1 KMnO4 + 0.50 mol·L−1 H2SO4 mixed solution delivered optimal zinc storage performance (providing a discharge-specific capacity of up to 291 mA·h·g−1 at a current density of 0.1 A·g−1), energy density of 293.3 W·h·kg–1), and cycling stability with a capacity retention of 90.48% after 1000 cycles at a current density of 1 A·g−1 and Coulomb efficiency of 99.87%. The superior electrochemical performance of the CC@MnO2-RD cathode compared with that of the CC@MnO2-ED cathode is attributable to the improved structural stability and uniformity of the former. In addition, a reversible two-step insertion storage mechanism involving H+ and Zn2+ in the CC@MnO2 cathode for ZIBs was verified through ex-situ X-ray diffraction and scanning electron microscopy measurements at different charging/discharging states. This paper highlights the optimized preparation process of CC@MnO2 electrodes based on the reductive deposition method, demonstrating advantages such as low cost and ease of fabrication. These findings can serve as a reference for developing high-performance zinc-ion batteries. © 2024 Science Press. All rights reserved.