Controllable Pulse Reverse Electrodeposition of Mesoporous Li xMnO2 Nano/Microstructures with Enhanced Electrochemical Performance for Li-Ion Storage.

Given the ever-growing demand of electric vehicles and renewable energies, addressing the poor cyclic stability of lithium manganese dioxide is an urgent challenge. In this study, pulse reverse current as the driving force of a one-pot anodic electrodeposition was exploited to design the physicochemical and electrochemical characteristics of lithium manganese dioxides as cathode materials of Li-ion battery. The pulse reverse parameters, including the span of anodic and cathodic current application ( ta and tc) and frequency ( f'), were systematically modulated to determine the optimized values through monitoring the physicochemical properties using X-ray diffraction, thermogravimetric analysis/differential scanning calorimetry, field emission scanning electron microscopy, transmission electron microscopy, energy-dispersive spectrometry, Raman spectroscopy, N2 adsorption-desorption isotherms, and inductively coupled plasma-optical emission spectroscopy, as well as the electrochemical properties using cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge-discharge at different currents. Based on the results, Li0.65MnO2 synthesized using ta = 95 ms, tc = 5 ms, and f' = 8.33 Hz at the constant magnitude of anodic peak current density of 1 mA dm-2 was determined as the optimized sample. The optimized lithium manganese dioxide rendered superior electrochemical performance with the initial discharge capacity of 283 mAh g-1, which accounts for 96.4% of the theoretical discharge capacity, preserving 88.3% of this capacity after 300 cycles at 0.1 C and, in the meantime, was able to release a discharge capacity of 115 mAh g-1 even after cycling at a higher current of 10 C. The superior electrochemical behavior of Li0.65MnO2 was attributed to the exclusive hierarchical urchin-like morphology as well as mesoporous nano/microstructures having a notably high Brunauer-Emmett-Teller surface area of 320.12 m2 g-1 alongside mixed-phase α/γ structure owing to the larger 2 × 2 tunnels, which offer more facile Li+ diffusion.