Currently used batteries in electric vehicles have cathodes consisting of inorganic materials based on transition metals. Recently an alternative to inorganic cathodes has emerged in the form of organic cathode materials, which benefit from lower costs, higher theoretical capacities, lower environmental impact and the option to use biomass derivates. We synthesized several organic cathode materials based on quinone and pyrazine units and tested them with galvanostatic measurements in a model lithium battery, some of them were also tested in a model magnesium battery. Synthesized 5,14-dihydro-5,7,12,14-tetraazapentacene (DHTAP) based on pyrazine units delivered a specific capacity of 180 mAhg-1 in the first cycles, which is close to its theoretical capacity. With oxidation of DHTAP quinone units have been »added« into the structure, which increased the potential and specific capacity of 5,7,12,14-tetraaza-6,13-pentacenequinone (TAPQ) reaching 324 mAhg-1 in the first discharge of a model lithium battery. Both synthesized materials showed gradual capacity fading due to the dissolution of the active material in the electrolyte. We tried to solve this problem and improve the battery characteristics by incorporating the basic structural unit of DHTAP into a bigger star shaped molecule using a hexaketocyclohexane octahydrate, a derivate of myo-inositol, a compound obtained from waste biomass. Synthesized material showed improved cycling stability delivering a specific capacity of 230 mAhg-1, which remained constant throughout 100 cycles. We employed the same strategy of incorporating quinone units into the star shaped DHTAP analogue through the oxidation process. The oxidation of the material did not bring expected results, as the oxidized material reached specific capacity of 173 mAhg-1 in its first discharge, which is only a half of the capacity of TAPQ. The oxidized material was also soluble in the electrolyte, which was the reason for the observed fast specific capacity fading. We tried to employ a reaction between 2,3-diaminophenazine and 2,5-dihydroxy-1,4-benzoquinone to synthesize a bigger DHTAP analogue. The analysis with MALDI-TOF mass spectrometry showed, that the synthesis did not deliver the expected product, which is probably comprised of the oligomers of 2,3-diaminophenazine. We tested the obtained product in a model lithium battery in which it delivered a specific capacity of 187 mAhg-1 in the 100th cycle with slow capacity fading. Most commonly used strategy to prevent the dissolution of the active material in the electrolyte is the incorporation of the basic structural unit into an oligomer/polymer. In order to employ this strategy, we used a condensation reaction between hexaketocyclohexane octahydrate and tetraamino-p-benzoquinone. Obtained product delivered a lower than expected specific capacity of 120 mAhg-1 in a model lithium battery, without the dissolution of the active material in the electrolyte.
|
