Different types of MnO_2 recovered from spent LiMn_2O_4 batteries and their application in electrochemical capacitors

摘要

Three types (λ, γ, and β) of MnO_2 have been successfully prepared from spent LiMn_2O_4 electrode materials and utilized as electrode materials for electrochemical capacitors. Experiments show that the obtained λ-MnO_2 sample has particle sizes ranging from 0.2 to 3 μm and the as-prepared β-MnO_2 and γ-MnO_2 samples both exist in nanorods with diameters of about 100 nm. The length of β-MnO_2 nanorods varies from 0.2 to 3 μm, while γ-MnO_2 nanorods have lengths of 0.2-2 μm. The main results of electrochemical tests indicate that these MnO_2 electrodes exhibit good supercapacitive performances which are dependent on their morphology and microstructure. As electrode material, λ-MnO_2 sample presents a specific capacitance of 200.55 F g~(-1), which is higher than those of other two types of MnO_2. However, β-MnO_2 electrode shows superior long-term cyclic stability and rate performance to other two MnO_2 samples. These results indicate that manganese dioxides recycled from spent LiMn_2O_4 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 LiMn_2O_4 batteries.