Advances in Development of New Supercapacitors

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Chemistry Department, Bar-Ilan University, Ramat-Gan, Israel

Considering the growing demand for green and renewable energy sources, electrochemical energy conversion devices are under massive investigation. There are some applications for which energy density is important, whereas for others rate capability (high-power density) and prolonged durability are essential. Batteries address the need for high energy density, while electrochemical capacitors, so called supercapacitors, can be relevant for the high power density purpose. The first part of our work was focused on high voltage supercapacitors with adiponitrile (ADN) as solvent for non-aqueous electrolyte solutions. Voltammetric studies showed that the electrochemical window of ADN solutions with activated carbon electrodes is very wide (more than 5V). We charged our cells to only 3.5V in order to avoid detrimental side reactions. We worked with solutions containing 2 electrolytes: Et4NBF4 and Et4NPF6. The use of Et4NPF6 improves the passivation on the Al current collector, and hence the performance improves. At room temperature an operation of supercapacitor with relatively high energy density, around 42.5Wh/Kg, based on the weight of the electrodes’ active mass was enabled. At the temperature of 60 °C, we charge the cells to 3.3V. The second part of our work focuses on aqueous hybrid Li ion capacitor. Hybrid systems possess intermediate properties between supercapacitors and batteries, thus containing both a capacitive or pseudo capacitive electrode and a battery type electrode. With a good selection of electrodes, it is possible to achieve high-rate capability and durability, and also enhanced specific energy density compare to standard supercapacitors. We explored the performance of Li ion-based hybrid capacitor based on a carbon-based capacitive negative electrode, LiMn2O4 spinel as positive electrode and aqueous solutions with salt as the electrolyte (pH = 7.5). Here, we demonstrate full hybrid devices as a proof of concept. The cell exhibits a potential of 1.5V without side reactions for 1500 cycles with capacity of 60mAh/g.









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