Binder free 2D aligned efficient MnO₂ micro flowers as stable electrodes for symmetric supercapacitor applications

Herein, δ-MnO₂ micro-flower thin films are grown directly onto a stainless steel mesh via a simple rotational chemical bath deposition technique. Moreover, the influence of the concentration of precursor ratio of MnSO₄:KMnO₄ is investigated and the obtained samples are designated as M1 (KMnO₄:MnSO₄ = 3:1), M2 (KMnO₄:MnSO₄ = 3:2) and M3 (KMnO₄:MnSO₄ = 3:3). The concentration of MnSO₄ as a starting material has a significant influence on the reaction kinetics, which subsequently alters the morphology and also the electrochemical performance. Among these three electrodes, the M1 electrode exhibits a high specific capacitance of 376 F g^-1 at a current density of 5 mA cm^-2 and a high specific energy of 52 W h kg^-1, which is higher than M2 (specific capacitance 312 F g^-1 and specific energy 43 W h kg^-1) and M3 (specific capacitance 283 F g^-1 and specific energy 39 W h kg^-1) electrodes. Due to the interesting performance of the M1 based electrode, the symmetric device is fabricated using two electrodes M1 (3:1) and represented as SSM/M1//M1/SSM. The device provides a maximum specific capacitance of 87 F g^-1 and specific energy density of 32 W h kg^-1 at a current density of 5 mA cm^-2. In addition, the symmetric device of the M1 electrode also exhibits good cycle stability showing 138% capacitance retention up to 2500 cycles. The enhanced electrochemical performance could be attributed to the direct growth of micro-flowers of MnO₂ on a stainless steel mesh, which provides more pathways for easy diffusion of electrolyte ions into the electrode. This study provides new insight and pathways for the development of low-cost and high-performance energy storage devices.