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.