Different types of MnO2 recovered from spent LiMn2O4 batteries and their application in electrochemical capacitors

Three types (λ, γ, and β) of MnO2 have been successfully prepared from spent LiMn2O4 electrode materials and utilized as electrode materials for electrochemical capacitors. Experiments show that the obtained λ-MnO2 sample has particle sizes ranging from 0.2 to 3 μm and the as-prepared β-MnO2 and γ-MnO2 samples both exist in nanorods with diameters of about 100 nm. The length of β-MnO2 nanorods varies from 0.2 to 3 μm, while γ-MnO2 nanorods have lengths of 0.2–2 μm. The main results of electrochemical tests indicate that these MnO2 electrodes exhibit good supercapacitive performances which are dependent on their morphology and microstructure. As electrode material, λ-MnO2 sample presents a specific capacitance of 200.55 F g−1, which is higher than those of other two types of MnO2. However, β-MnO2 electrode shows superior long-term cyclic stability and rate performance to other two MnO2 samples. These results indicate that manganese dioxides recycled from spent LiMn2O4 batteries show great potential in application as the active materials for electrochemical capacitors. This study could provide a novel and useful approach to the recovery and reuse of spent LiMn2O4 batteries.