Porous polyaniline nanofiber/vanadium pentoxide layer-by-layer electrodes for energy storage

Abstract

There has been long-standing interest in hybrid electrodes containing an electronically conductive polymer and an inorganic cathode material for electrochemical energy storage. Conductive polymers such as polyaniline serve to enhance the conductivity of the electrode, and are electrochemically active themselves. Here, we report the layer-by-layer (LbL) assembly of polyaniline (PANI) nanofibers and V₂O₅ to form hybrid electrodes for electrochemical energy storage. The resulting electrode is highly porous and significantly exceeds in performance relative to an analogous electrode assembled with conventional PANI in place of PANI nanofibers. By utilizing PANI nanofibers in place of conventional PANI, significant gains in capacity (3×), specific energy (40×), and specific power (4×) are realized. The growth of the film is investigated using profilometry and quartz crystal microbalance; the thickness of the film increases linearly with respect to the number of layer pairs deposited. It is found that the electrochemical response possesses contributions from both PANI nanofibers and V₂O₅, and that the electrochemical performance of this LbL system is dependent on film thickness. The electrode contains 59 wt% V₂O₅ and stores 0.8 mol Li⁺ per mol of V₂O₅. A film thickness of 1.2 μm yields optimum results, with a discharge capacity of 320 mA h g⁻¹, a power density of 4000 mW g⁻¹, and an energy density of 886 mW h g⁻¹ (per mass of active cathode), depending on discharge current. After 100 cycles, the electrode retains 75% of its initial capacity, and no appreciable volumetric expansion after cycling is observed. These results highlight the promise of porous electrodes made via LbL assembly, where two dissimilar materials can be intimately blended to achieve synergistic properties.