Electrochemical capacitors (ECs) are unique energy storage devices capable of delivering high power compared to rechargeable batteries e.g., lithium-ion batteries. In addition, due to the mainly physical charge storage, ECs can be charged and discharged millions of times without substantial performance loss. Therefore, ECs find a number of applications, for example in regenerative braking of a hybrid vehicle where they save fuel up to 30% as estimated by the manufacturers. The spectrum of ECs applications could be further enhanced by improving the energy performance of these devices. For this purpose, project titled “Charge transfer at the electrified carbon/iodide interface and its application for the development of high energy hybrid electrochemical capacitors” is proposed. In this work, hybrid ECs will be developed where one electrode operates as battery-type (very high capacity) and the other as capacitor-type one. These hybrid ECs will utilize safe, environmentally friendly and high conductivity aqueous electrolytes with benefit to dissolve redox active species such as iodides in order to get additional charge storage by faradaic processes.
The basic research target of the project is to investigate the charge transfer at the carbon/iodide interface which depends on whether the iodide species are introduced in carbon pores by physical methods or under electrochemical polarization. In situ electrochemical techniques, Resonance Raman Spectroscopy and Mӧssbauer Spectroscopy will be used to investigate the interactions of polyiodide species confined within the carbon materials. The optimized high capacity positive carbon electrodes will be combined with capacitive negative electrodes to develop hybrid ECs while using highly concentrated neutral aqueous salt solutions in order to prevent deleterious oxidation of carbon materials during long-term operation at wide temperature range. The evolution of oxygenated functional groups on carbon electrode surface during aging tests will be investigated by thermogravimetry, mass spectrometry and electrochemical techniques.
The final deliverable of the project will be a better understanding of carbon/iodide interface under electrochemical treatments and of polyiodide species formed under confinement in pores or upon interaction with carbon surface, which might be different from the compounds known until now. This knowledge will enable to develop new electrode and electrolyte materials for obtaining high energy and power hybrid ECs in environmentally friendly and low cost aqueous electrolyte.