Indigo carmine (IC) doped polypyrrole (PPy) as a free-standing polymer electrode for lithium secondary battery application
Flexible free-standing polypyrrole-indigo carmine (PPy-IC) films were designed as additive-free anode material for lithium secondary batteries and were produced via the electropolymerization method. The films are soft, lightweight, mechanically robust, and electrically conductive. The films display a cauliflower-like structure consisting of micron-scale spherical grains, which are related to dopant intercalation in the polymeric chains. The morphologies and electrochemical behaviour of the free-standing PPy-IC films were affected by the electropolymerization conditions. Electrochemical tests demonstrated that the discharge capacity and initial coulombic efficiency increased as the thickness of the films decreased. The PPy-IC films prepared at lower deposition time (30 min) and lower deposition current density (0.4 mA cm−2) exhibited higher discharge capacity (83 mAh g−1 beyond 100 cycles) in the voltage range of 0.01–3.0 V. These free-standing films can be used as possible anode materials to satisfy the new market demand for flexible/bendable lithium polymer or polymer batteries that are suitable for roll-up displays, wearable devices, and implanted medical devices used in biological and biomedical systems.