Global warming is one of the most significant challenges of our generation. An essential element in mitigating this is the drastic reduction of anthropogenic greenhouse gas emissions. In this respect, the political authorities' efforts are directed towards expanding the use of renewable energy. For example, essential targets and objectives have been set in the Paris Climate Agreement or the European Green Deal. This transformation requires massive regulatory and, above all, technological change in all sectors. Lithium-ion batteries (LIB) play a crucial role in achieving these goals, as they are largely used in electromobility and energy supply. Due to the resulting growing demand for the raw materials required, such as lithium, phosphorus, nickel, and cobalt, sustainable materials management through a comprehensive circular economy is essential. Within the scope of the presented doctoral thesis, a novel pyrometallurgical recycling approach, the so-called InduRed reactor concept, was further developed and optimized by researching the underlying processes and phenomena. Initially, the pre-pilot plant InduMelt, operated in batch mode, was improved, and currently commercially used cathode materials were investigated in this reducing process. In the experiments carried out, a promising recovery rate of the valuable metals into a metal alloy was demonstrated, as well as the transfer of lithium and phosphorus into the gas phase. The latter makes it easier to utilize these elements, which are declared as critical raw materials and represent an absolutely unique selling point in pyrometallurgy. Furthermore, it could be shown that the revised reactor design allows a better reproducible test performance. However, neither the originally used crucible material made of Al2O3 nor the new one made of MgO is suitable for continuous operation. In order to drive this technology towards industrial maturity, further research efforts must be made to find an optimum refractory material. However, the waste stream resulting from LIB is composed not only of the cathode material but also of the anode material and other components of the battery assembly incompletely separated in the pretreatment. For this reason, the next step was to investigate the influence of copper and aluminum from the electrode conductor foils and graphite from the anode on the high-temperature behavior under reducing conditions. In the process, a contour model was created, enabling a more straightforward and less experimental application in the InduRed reactor concept in the future. This provides a basis for communication with the pretreatment process operators and is also essential for efficiently developing an overall recycling process. Based on this, a possible process combination of hydromechanical pretreatment, flotation, and pyrometallurgical treatment in the InduMelt plant of a LIB waste stream was investigated. Even if the productivity has to be increased further with optimization measures, a remarkable lithium removal rate of more than 98% and a high product quality of the metal alloy could also be demonstrated in this application. This research activity thus confirms that the InduRed reactor concept is a promising technology for valuable metal recovery from spent lithium-ion batteries. Profound R&D activities in basic research, plant construction, or pre- and post-treatment of the products still have to be carried out to enable a rapid and efficient upscaling of the reactor concept to an industrial application, the execution of which concludes this thesis.