Layered δ-MnO2 as positive electrode for lithium intercalation

Layer structured δ-MnO2 was synthesized by a microwave-assisted hydrothermal method. The morphology of the product consists of flower-like spheres that range from about 200 nm to 3 μm in diameter and are composed of sheets about 5–10 nm in thickness. When tested in the voltage range of 2 to 4.5 V vs. Li+/Li in coin cells, the separator is blocked, handicapping Li+ conductivity and leading to cell failure. When tested in the voltage range of 2 to 4 V in ethylene carbonate/dimethyl carbonate (EC/DMC), the δ-MnO2 delivers an initial reversible capacity of 143.7 mAh g−1 and can maintain 120 mAh g−1 at the 60th cycle. The δ-MnO2 electrode shows good cycling stability at different current densities and delivers a discharge capacity of about 90 mAh g−1 at 1 C, indicating that it is a promising cathode material for lithium ion batteries.