Hollow lithium manganese oxide nanotubes using MnO₂-carbon nanofiber composites as cathode materials for hybrid capacitors

To improve the electrochemical performance of hybrid capacitors, hollow lithium manganese oxide (LiMn₂O₄, LMO) nanotubes (NTs) as cathode materials were synthesized by a solid-state reaction, using MnO₂ coated on a porous carbon nanofiber (PCNF) templates. To determine the optimum shell thickness of hollow LMO, the time of MnO₂ coating on PCNF was adjusted to 10, 30, and 60 min. Among these, hollow LMO NTs, which were synthesized by 30-min coating with MnO₂ on the PCNFs, have superior performance. They exhibited an excellent reversible capacity (∼72.8 mAh g⁻¹) at 1 C, capacity retention of ∼98.4% after 100 cycles, and an excellent high-rate capability. This superior performance can be explained by the hollow structure giving a reduced diffusion distance for Li-ions, the networked structure of one-dimensional NTs allowing fast charge transfer, and the achievement of the optimal stoichiometric ratio of the LMO phase.