Electrochemical properties of non-stoichiometric nanocrystalline Li4Mn5O12 for hybrid capacitors

Non-stoichiometric nanocrystalline Li4Mn5O12 was synthesized using the sol-gel method with citric acid at a low-temperature. The effects of the pH condition on the structure, morphology and electrochemical properties were investigated. X-ray diffraction patterns and scanning electron microscopy images confirmed that all the samples crystallized in spinel structures with a particle size in the nanometric scale. Transmission electron microscopy images showed that particle size varied from 50-100 nm. The Li4Mn5O12 was tested as an electrode material in half-cell Li/Li4Mn5O12 and in full-cell vulcanized carbon/Li4Mn5O12 at a high rate charge-discharge. Among the samples, Li4Mn5O12 (prepared at pH = 9) exhibited the best electrochemical capacitive performance in an aqueous hybrid capacitor full-cell AC/Li4Mn5O12 as well as in an non-aqueous Li/Li4Mn5O12 half-cell. The specific sample delivered a power density of 20 F g(-1) at a high discharge rate of 4 A g(-1) and an energy density of 31.1 Wh g(-1).