Analytical Sciences

Determination of Li⁺ Diffusion Coefficients in the Li_xV₂O₅ (x = 0 – 1) Nanocrystals of Composite Film Cathodes

Dah-Yeon YOO,*1 In-Hyeong YEO,*2 Won Il CHO,*3 Yongku KANG,*4 and Sun-il MHO*1

*1 Division of Energy Systems Research, Ajou University, Suwon 443-749, Korea
*2 Department of Chemistry, Dongguk University, Seoul 100-715, Korea
*3 Energy Storage Research Center, Korea Institute of Science and Technology, Seoul 130-650, Korea
*4 Division of Advanced Materials, Korea Research Institute of Chemical Technology, Daejeon 305-600, Korea

The Li⁺ ion diffusion coefficients (D_Li+) in V₂O₅ (2.12 × 10⁻¹² cm² s⁻¹) and in the intermediate α-, ε-, and δ-Li_xV₂O₅ phases (1.6 × 10⁻¹⁴, 8.0 × 10⁻¹⁵, and 8.5 × 10⁻¹⁵ cm² s⁻¹, respectively), reversibly formed during charging/discharging processes of the crystalline-V₂O₅ and PEDOT (poly-3,4-ethylenedioxythiophene) composite-film electrode, are precisely determined by the galvanostatic intermittent titration technique. The specific surface area of the composite film is estimated to be 13.600 m² g⁻¹, where the external surface area and the nanopore area are 10.704 and 2.896 m² g⁻¹, respectively. The V₂O₅ crystals are coated and interconnected by a conductive polymer network in the composite film, thereby improving the electrode characteristics. V₂O₅ and PEDOT composite-film cathodes showed high specific capacities (290 mA h g⁻¹ at a 1 C rate), excellent rate capabilities (178 mA h g⁻¹ at a 10 C rate), and superior cycling stabilities (ca. 15% degradation after 500 consecutive cycles).

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