Cationic Effect on the Electrochemical Characteristics 
of the Hydrothermally Grown Manganese Dioxide
Hydrothermal growth of manganese dioxide (MnO2) nanostructures was carried out on indium tin dioxide glass substrates at 95°C for 24 h to study the effect of cations such as K+, Li+, and Na+ on their properties. It was observed that presence of cations affected the MnO2 phase and morphology: amorphous MnO2 (no cations) showed columnar-like structure, ε-MnO2 (K+) presented nanowires, α-MnO2 (Na+) was composed of agglomerates of spherical nanoparticles, while β-MnO2 (Li+) consisted of spherical aggregates of nanoparticles. The different electrochemical performance depending on the structure is expected to be useful for application in Li-ion batteries. As-grown ε-MnO2 exhibited lower charge resistance and higher ionic diffusion rate, providing the electrode with enhanced specific discharge capacity of 910 mAh g−1 and capacity retention of 98% after 500 scans. Hence, K+ can support tunnel structures and stabilize the structure compared with the smaller cations Na+ and Li+.