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This paper reports on the improvement on the capacitive properties of Co-Al layered double hydroxide (Co-Al LDH) by adding hexacyanoferrate(II) and (III) solely or jointly into 1 M KOH aqueous solution. Owing to the high reversibility, the Fe(CN)(6)(3-)/Fe(CN)(6)(4-) ion pair acts as an electron relay at the electrode/electrolyte interface during charge and discharge by coupling in the redox transition of Co(II)/Co(III) in the Co-Al LDH electrode. Electrochemical impedance spectra and Tafel curves provide direct evidences with decreased charge-transfer resistance and increased exchange current density in the alkaline solution containing hexacyanoferrate ions, respectively.

An in situ synthesis method for carbon-coated LiFePO 4 powders has been investigated in detail using inexpensive FePO 4 as an iron source and polypropylene as a reductive agent and carbon source. Thermogravimetric and differential thermal analysis of the precursor mixture indicated that the pyrolysis of polypropylene and the combination reaction of LiFePO 4 could be processed synchronously at a synthesis temperature between 500 and 800°C. X-ray diffraction analyses and scanning electron microscopy observations showed that LiFePO 4 /C composites with fine particle sizes and homogeneous carbon coating could be directly synthesized by the in situ method. The electrochemical performances of the carbon-coated LiFePO 4 powder synthesized at 700°C were evaluated using an electrochemical model cell by galvanostatic charge/discharge and cyclic voltammetry measurements. The in situ synthesized LiFePO 4 /C composite had a high electrochemical capacity of 164 mA h g Ϫ1 at the 0.1C rate, and possessed a favorable capacity cycling maintenance at the 0.3 and 0.5C rates. The good electrochemical properties of the LiFePO 4 /C composite are suggested to originate from the good crystallinity, the fine particle sizes, and the efficient electronic conductive coating layer of the material.

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