Organic negative electrode materials for Li-ion and Na-ion batteries

This thesis work comprises work on novel organic materials for Liand Nabatteries, involving synthesis, characterization and battery fabrication and performance. First, a method for improving the performance of a previously reported Li-ion battery material (lithium benzenediacrylate) is presented. It is demonstrated that applying freeze drying in combination with carbon coating in the liquid state renders the compound an improved morphology. Moreover, the content of carbon and its influence on electrochemical performance is discussed. The material achieves reasonable capacity values (>150 mAh g) also when cycled at comparatively high C-rates (2C). Second, two novel organic salts, disodium pyrromellitic dimide and disodium benzenediacrylate, are synthesized and investigated as electrode materials for Na-ion batteries and compared with the respective Li-based homologues. While the synthesis is shown to be straightforward, the electrochemical performances display an unexpected degree of complexity. Both Nacompounds experience capacity losses during cycling, either due to decomposition problems (as proven by NMR studies for disodium pyrromellitic diimide), due to dissolution of the active material into the electrolyte, or due to side reactions in the case of the disodium benzenediacrylate. Nevertheless, the compounds still present capacities of 90 mAh g and 50 mAh g, respectively, after 100 cycles. Comparisons of these Na-based organic salts with their Li homologues shows that the research field of organic sodium battery materials still needs further improvements and fundamental insights in order to achieve acceptable capacity from the active materials. The Na compounds, however, display promising coulombic efficiencies (~95 %), which is detrimental for future implementation of the final batteries. The large amount of work carried out on optimizing different Li compounds for Li batteries would in this context be essential to extend also to the Na compounds. Examples include tailoring the carbon content and morphology, or exploring a wider range of electrolytes suitable for these systems.