The influence of the electrolyte on the electrochemical behavior of PTMA as cathodic electrode material

The TEMPO-based polymer PTMA is a standard material for the research of organic radical batteries and displays a high capacity and a high rate stability at elevated currents when used with lithium-ion battery electrolytes. However, these electrolytes are the source of safety concerns and cause the dissolution of the organic electrode active material in the electrolyte, which limits the cycle life and leads to increased self-discharge. The aim of this thesis is to investigate the complex interactions and the resulting electrochemical behavior of PTMA-based electrodes in combination with different alternative electrolytes. The integrated publications establish the important role of the electrolyte for organic active materials and the lack of studies on this topic. Subsequently, the great influence of the electrolyte composition and concentration on the performance of PTMA-based electrodes is highlighted. In particular, a positive effect of highly concentrated electrolytes on the stability and self-discharge of PTMA-based electrodes is revealed. Based on this, the use of aprotic and protic ionic liquids as electrolytes for PTMA is investigated. There, a superior performance for PTMA in FSI--based aprotic ionic liquids is obtained. Lastly, the important aspect of self-discharge of PTMA with respect to current, rest time and electrolyte is studied. It is shown that the self-discharge mechanism strongly depends on the applied charging current, which is affected by the transport properties of the used electrolyte. The results of this dissertation show that the electrochemical behavior of PTMA is significantly affected by the alternative electrolytes. It is evident that with the use of different electrolyte concepts, the performance of PTMA can be optimized in a task-specific manner. In addition, the studies show that the electrolyte of an electrochemical investigation setup can be understood as a tool that can influence and elucidate the processes within the cells.


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