Year

2012

Degree Name

Master of Engineering - Research

Department

Institute for Superconducting & Electronic Materials, Faculty of Engineering

Abstract

As energy initiatives shift away from fossil fuels, research on renewable resources and their energy storage has become vital to the future of energy strategies. Battery technology will have a prominent future in the endeavour towards sustainability. All-polymer based batteries have recently gained renewed interest, mainly due to the possibilities for manufacturing flexible and environmentally friendly devices. To make an all-polymer battery, flexible free-standing electrode materials could be more suitable than electrodes with metal substrates. Basically, conventional lithium batteries typically consist of a positive electrode and a negative electrode spaced by a separator, which is soaked with an electrolyte solution. Each electrode is formed from a metal substrate that is coated with a mixture of an active material, an electrical conductor, a binder, and a solvent. This kind of electrode is not suitable for flexible or bendable batteries, because a metal substrate is used to hold the active materials. The active material layer will be cracked or peeled off from the substrate when they are bent frequently. To avoid these drawbacks, several initiatives have been taken in this Master’s degree work to develop additive–free, flexible, conducting polymer electrodes for all-polymer battery application. In this respect, an all-polymer battery system based on free-standing polypyrrole (PPy)  para (toluene sulfonic acid) (pTS) cathode and polypyrrole (PPy)  indigo carmine (IC) anode was investigated. Highly flexible and bendable PPy-pTS films were prepared using the electropolymerization method. The films are soft, lightweight, mechanically robust, and highly electrically conductive. The films display a cauliflower-like morphology consisting of micron-scale spherical grains, which are related to dopant intercalation in the polymeric chains. The electrochemical behaviour of the free-standing films was examined as cathode against lithium counter electrode. Electrochemical tests demonstrated that the PPy-pTS film with 30 min deposition time exhibited higher discharge capacity (85 mAh g-1) beyond 80 cycles than the PPy-pTS films with 1 h deposition time (76 mAh g-1) and 2 h deposition time (55 mAh g-1) at 0.1 mA cm-2 over a voltage range of 2.5-4.3 V. The free-standing films can be used as potential cathode materials to satisfy the new market demand for flexible and bendable polymer batteries. Flexible free-standing PPy-IC films were designed as additive-free anode material and were produced via the electropolymerization method. The films are soft, lightweight, mechanically robust, and electrically conductive. The films display a cauliflower-like morphology 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 minutes) 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. Such free-standing films can be used as anode materials for polymer batteries that are suitable for the various types of design and power needs of soft portable electronic equipment. Stable and high performance devices based on doped conducting polymers can be developed by employing the right combinations of conducting polymers and dopants. A novel all-polymer battery system based on conducting polymer (polypyrrole, PPy) doped para (toluene sulfonic acid) (pTS) and indigo carmine (IC) was tested. The performance of the systems consisting of PPy-pTS as cathode and PPy-IC as anode in conjunction with polymer electrolyte and 1 M LiPF6 commercial electrolyte were respectively evaluated. For these systems, all the free-standing PPy-pTS and PPy-IC films were directly used without the need for any metal substrate to act as an electrical conductor. Electrochemical measurements demonstrated that the PPy-pTS/PPy-IC (commercial electrolyte) system exhibited a discharge capacity of 36 mAh g-1 at 0.05 mA cm-2 after 50 cycles, which is around 92 % of the initial discharge capacity. In the case of PPy-pTS/PPy-IC (polymer electrolyte), the discharge capacity retention was 16 mAh g-1, which is also 76 % of the initial discharge capacity. In summary, this work deals with the fabrication of a novel all-polymer battery system, with significant advantages in terms of environmental friendliness, resonable capacity, and good cycling stability, which can lead to a future generation of polymer batteries to satisfy new market demand in the field of energy storage devices.

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.