Biodegradable batteries as sustainable power sources for portable devices

Resumen

This thesis presents the development of biodegradable batteries aligned with the sustainability principles of circular economy. These energy sources are focused on reducing the exorbitant quantity of electronic waste caused by the accelerated growth of electronic devices. The present work has been developed at the Institute of Microelectronics of Barcelona, IMB-CNM (CSIC). The batteries presented in this thesis have been completely constructed from organic materials and can be manufactured by economic methods with low energy consumption. This thesis is composed of six chapters: the introductory chapter 1 and five experimental chapters. Chapter 2 of this work is dedicated to the exploration of different redox species appropriate for the development of ecological power sources. In this chapter, the electrochemical characterization of various redox and electrolyte species that met the requirements for the projected batteries was carried out. The selection of the redox species was based on their potential for oxidation, solubility, storage in the solid state and their low toxicity. The third chapter presents the PowerPAD concept, the development of the first biodegradable degradable battery made of paper, carbon electrodes, organic redox species and beeswax. The battery is biotically degradable, that is, the microorganisms present in soils and waters, can degrade the battery to basic compounds with minimal environmental impact. This new class of portable, biodegradable redox flow batteries is ideal for powering the upcoming generation of green electronics devices. Chapter 4 of this thesis is devoted to the development of a capillary-based flow battery. This flow cell has been designed as an effort to optimize the PowerPAD device and has used the same natural materials. A cellulose absorbent pad has been incorporated at the end of the device to provide a quasi-steady flow of the redox species. The electrochemical evaluation of the cell was carried out at different capillary flow rates and electrode reaction areas. In this way, the device presents an optimized faradaic efficiency. In the fifth chapter, a new approach to develop biodegradable batteries is presented. The synthesis and evaluation of biopolymer electrolyte membranes (BioPEMs). These BioPEMs have been manufactured based on natural polymers and organic compounds, such as chitosan, lyophilized cellulose and glycerol as a plasticizer. During this chapter it was possible to carry out the synthesis of two membranes with low toxicity and low manufacturing cost that presented adequate ionic conductivity and low migration of redox species, suitable characteristics for their use in primary flow batteries. Chapter 6 of this thesis presents the development of a primary button cell battery based on lyophilized cellulose hydrogels, chitosan and redox species. This device has been manufactured using porous carbon electrodes, which have been impregnated by the redox hydrogel matrix and uses a BioPEM to separate anode and cathode. The result is a powerful button cell battery in harmony with the environment. Finally, the general conclusions of this thesis are presented highlighting the most remarkable aspects of this work and some of the proposed future work in this research line.