Electrochemical Impedance Analysis of V₂O₅ and PEDOT Composite Film Cathodes

Abstract

Composite films of nanobeam V 2 O 5 and poly-3,4-ethylenedioxythiophene (PEDOT) were grown using an electrochemical polymerization method. PEDOT in the composite film connects the isolated V 2 O 5 nanobeams and gives rise to a conductive network, improved Li-ion accessibility and transport pathways in the electrode. The nanobeam-V 2 O 5 /PEDOT composite film cathodes have high capacities, excellent rate capabilities and cycling stabilities at various C rates: their specific capacities were 262 mAh g À1 at 0.1 C, 239 mAh g À1 at 1 C, 186 mAh g À1 at 10 C, and 141 mAh g À1 at 100 C. After testing the battery for more than 150 battery cycles at a rate of 10 C, the degradation rate was found to be approximately 9 %. The diffusion coefficient of the nanobeam-V 2 O 5 crystalline electrode was calculated to be approximately 4.6 10 À8 ; and those of a-, e-, and d-Li x V 2 O 5 crystalline phases, were estimated to be in the range of (2.1-9.8) 10À10 . Under the conditions of PEDOT coating and networking in the composite film, the diffusion coefficients of each phase of Li x V 2 O 5 that reversibly formed during the discharging and charging processes were able to be estimated.

Determination of Li+ Diffusion Coefficients in the LixV2O5 (x = 0 − 1) Nanocrystals of Composite Film Cathodes

“…1,2 Layered V2O5 demonstrates a high capacity and structural flexibility for the reversible insertion and release of Li ions as a novel cathode material. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] The crystallinity and morphology of V2O5 can play a key role in determining the electrochemical properties of this material. [3][4][5][6][7][8][9][10][11][12][13][14][15] Elongated-rectangular-plate-shape (beam-shaped) V2O5 crystals were prepared by a hydrothermal method and the plate-like morphology reflects the intrinsic properties of layered structure.…”

“…15,16 Conductive polymers have redox properties, and can also be used in the electrodes of secondary batteries and capacitors. [15][16][17][18][19][20] Composite films containing the V2O5 nanocrystal and conductive polymer network can be grown by an electrochemical polymerization method in a solution containing a monomer and dispersed V2O5 particles. In electrochemically polymerized composite films, the polymer can coat the V2O5 particle surfaces and interconnect the isolated nanoparticles within the polymer network.…”

“…The composite film cathodes offer the prospect of improved performance for rechargeable Li batteries due to the enhanced ionic accessibility, transport characteristics, and electronic conductivity of electrode materials. [15][16][17][18] Poly-3,4-ethylenedioxythiophene (PEDOT) is a promising conjugated conductive polymer, because it shows high thermal stability, oxidation resistance over a relatively wide potential range, and mechanical flexibility. 19,20 The Li-ion diffusion coefficient (DLi+), an important parameter for electrochemical kinetics, has been determined by various methods, such as cyclic voltammetry, 8 electrochemical impedance spectroscopy, 16,23 and galvanostatic/potentiostatic intermittent titration techniques.…”

Vanadium-oxide-based electrode materials for Li-ion batteries

“…The Cu0.04V2O5 nanobelts demonstrated a much better rate capability than that of the V2O5 nanobelts. The Cu0.04V2O5 nanobelts delivered specific discharge capacities of 258,196,175,147,104, and 68 mAh g The Cu0.04V2O5 nanobelts exhibited great improvements in both cycling stability and rate performance, compared to the V2O5 nanobelts. The improvements of battery performance were closely associated with nanobelt structures and Cu doping.…”

“…[187] Therefore, designing hybrid composites of V2O5 with conducting polymers can realize great improvements in the battery performance of V2O5 for LIBs. There are three conducting polymers widely used in developing V2O5-based cathode materials, such as polypyrrole (PPy), [188][189][190][191] polyaniline (PANI), [192][193][194] and polythiophene, [195][196][197][198] The easy synthesis and the commercial availability of both polymers and monomers are the driving forces for the extensive research on these conducting polymers.…”