Water-in-polymer Salt Electrolyte (WIPSE) for Sustainable Lignin Batteries

Abstract: Organic electrolytes are widely used in energy storage technologies, but they are known to have safety, cost, and eco friendliness concerns. Water based electrolytes do not have those issues but are limited by their narrow range potential range of operation to 1.2V. Above that voltage, significant side reactions lead to gas evolution, side reaction and high selfdischarge rate in organic batteries. Because of their superior ionic conductivities, which are critical for reducing device resistance and improving power; as well as their cost-effective ness and non-flammability, researchers have had a second look at water-based electrolyte and found out that super concentrated aqueous solutions behave differently, and their electrochemical stability window can be widened.In this thesis, polyacrylate (PAAK) based "water in polymer salt" electrolyte (WIPSE) has been identified as a promising solution for large-scale energy storage devices. This new family of "water in salt" electrolytes offers a broad electrochemical stability window of up to 3V, a high ionic conductivity (100 mS/cm) and is non-flammable, making it ideal for high power electrochemical storage devices. However, little is known about the matter transport in PAAK based WIPSE and in "water in salt" electrolytes in general. Therefore, this thesis also aims to investigate the properties of PAAK using spectroscopic techniques such as Raman spectroscopy and diffusion NMR to understand the behavior of water and the mechanism of ionic transport in relation to water and polymer chain dynamics. Since the electrolyte only transports cations, it is suitable for use in "cation rocking chair" batteries that utilize two types of polymeric quinones, lignin, and polyimide redox polymers, as positive and negative electrodes, respectively. The electrochemically active redox polymers with K+ ions at neutral pH are ions at neutral pH are advantageous for avoiding corrosion in metal collectors. Further for understanding the fundamental of self-discharge mechanism, the impact of some critical chemical and physical parameters on performance of lignin-based batteries have been investigated.The final chapter of the thesis introduces a novel approach to address the challenges associated with Zn-ion batteries by utilizing the "water-inpolymer salt" electrolyte concept modified by salt additives. The goal is to enable the use of lignin-carbon (L-C) electrodes in a Zinc battery. Lignin, carbon and zinc are among the most affordable, environmentally friendly and sustainable options for energy storage for energy storage. By incorporating WIPSE electrolytes these batteries can offer additional benefits, such as improved safety and the prevention of dendrite formation. Our findings demonstrate that acrylate groups in the electrolyte stabilize the flux on the zinc electrode surface, promoting parallel deposition and significantly reducing dendritic formation through vertical growth. The assembled Zn-lignin battery delivers a maximum energy of 23 Wh/kg and a maximum power of 610 W/kg, with an exceptional 82% retention after 8000 cycles. With the reduced expected environmental impact of green and the cost- effectiveness of these polymer electrolytes, the resulting battery shows great promise in the battery market. Its emergence has opened a new avenue in the pursuit of safe and efficient batteries, which has been a major area of focus within the energy storage industry.