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.