Plastic pollution is found everywhere. From lands to oceans and atmosphere, plastic wastes are threatening natural ecosystems and human health. New studies show an alarming increase in the amount of micro and nano-sized plastics found in soil, air, and biomass. With rapid increase in consumption rates of single-use plastics (including masks and gloves due to COVID-19 pandemic) along with a sharp rise of production rates, immediate and sustainable solutions are urgent. To lessen the plastic pollution build-up and keep plastics as a useful and valuable commodity, recycling technologies need to be improved to keep pace with the rising demands. In this work, we investigated the energy storage capability of upcycled Polyethylene Terephthalate (PET) plastic waste. In general, PET has massive utilization in different sectors of industry including textile, packaging, and automotive with nearly a 5% increase in production each year. The pristine upcycled material that was collected via fiberization and controlled carbonization, showed the combination of supercapacitive and pseudocapacitive behaviors. Next, by adding silicon nanoparticles and elemental sulfur, a composite Si-C anode and a S-C cathode were developed, respectively. The generated electrodes were tested in half-cells in a lithium-ion battery setup. We implemented a series of computational, analytical, and electrochemical characterization techniques including DFTB+, Raman, TGA, SEM-EDS, TEM, XRD, BET, CV, GCPL, EIS, and GITT to explore the content of the materials and explain the detected electrochemical performance. The preparation methods are industrially mature and scalable and we hope that this work can bring opportunities for future research and development to tackle plastic pollution and move towards a more sustainable society.