Designing sustainable Li-ion battery systems with redox-active organic materials

Abstract

Lithium-ion batteries (LIBs) store electrical energy via chemical reactions that involve lithium ions and electron transfer. Their high energy density makes them suitable for various applications, from portable devices to large energy storage systems. However, the sustainability of LIBs is limited by irreversible side reactions that occur during repetitive charging and discharging, leading to reduced capacity and insufficient battery life. In this thesis, I propose a design for sustainable LIB systems utilizing the reversible electron transfer reaction of redox-active organic materials (ROMs). Chapter 1 offers a comprehensive overview of the fundamental principles of energy storage in LIBs, exploring the challenges that hinder their efficient and sustainable operation. The chapter further introduces ROMs, highlighting their potential applications in addressing the irreversible reactions in LIBs. Chapter 2 presents a new concept in spent LIB recycling based on the spontaneous charge transfer mechanism. I establish the general criteria for designing a cathode regeneration solution consisting of recyclable electron donors and Li salts to facilitate thermodynamically controlled chemical re-lithiation of spent cathodes. The proposed strategy surpasses the previous methods regarding materials and energy efficiency, universality, eco-friendliness, and process simplicity. Chapter 3 demonstrates a series of ROMs as a new class of mobile catalysts for facile Li2CO3 decomposition. Through a comparative study using characterization techniques combined with in-situ and ex-situ analyses, I provide evidence that selected ROMs facilitate Li2CO3 removal with minimal overpotential while inhibiting reactive singlet oxygen production from the decomposition of electrolyte and electrode. This study is the first example of new possibilities to design multifunctional catalysts to oxidize both Li2O2 and Li2CO3 for ambient air operational lithium-air batteries. Chapter 4 explores how solvent dynamics influence the shuttling effect in organic batteries. The study distinguishes the relationship between the dissolution of ROMs and shuttle effects, revealing the critical role of electron self-exchange reactions between dissolved ROMs. To mitigate the shuttle effect, I used a weak solvent-based electrolyte, simulating the solvation structure of a highly concentrated electrolyte even at low salt concentrations. Using a standard salt concentration, I demonstrated that weak solvent-based electrolytes enhance cycle retention and Coulombic efficiency in organic batteries, outperforming traditional electrolytes that suffer from rapid capacity decay and low energy efficiency due to the intense shuttling effect.