Electrochemical Properties of Nanocrystalline Li4Mn5O12 for Hybrid Capacitor
In such device, different types of materials have been proposed for faradic component. Lithium insertion compounds used in lithium-ion batteries have attracted a lot of interest due to high specific charge. They have been typically used in organic electrolyte but the aqueous solutions are not missing [3,4]. In this work, nanocrystalline Li4Mn5O12 was low-temperature synthesized by sol-gel method with citric acid as a chelating agent. Various initial synthesis conditions were studied such as: pH of solution, the ratio of citric acid to total metal ions, the precursor of lithium salts. The structure, morphology and electrochemical properties of materials are characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM), transmission electronic microscopy (TEM), cyclic voltammetry (CV) and galvanostatic cycling with potential limit (GCPL). The stoichiometric of formula was exactly determined by reduction-oxidation titration and flame atomic absorption spectrophotoscopy (FAAS).
The resulting materials exhibited the particles size of 50 – 100 nm. The electrochemical results showed that Li4Mn5O12 synthesized at pH = 9 and the ratio of citric acid to total metal ions 1:1 exhibited the best electrochemical capacitive performance within potential range of 0 – 1.4 V in 1M Li2SO4. A maximum specific capacitance of 20 F.g-1 during 200 cycles was obtained for hybrid capacitor for AC/Li4Mn5O12 at high discharge rate of 5 A.g-1.
The authors would like to thank Office of Naval Research Global (ONRG) for the grant N62909-13-1-N235. The authors acknowledge funding from VNU-HCM under the grants HS2013-76-01.
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