UC Riverside

Driven by the ever-growing energy demand worldwide, lithium-ion batteries (LIBs) continue to be a competitive solution for energy storage systems, ranging from personal electronics to electric vehicles (EVs) and stationary energy storage systems. However, safety continues to be an aspect of high concern and interest for their continued employment and for achieving higher levels of penetration and utilization in the consumer electric market.The main objectives of this dissertation are focus on the development of: 1) gel polymer electrolytes (GPEs) that can alleviate safety concerns borne from the use of liquid electrolytes, and 2) batteries composed of a titanium-based anode material to enable the assembly of full-cell batteries in open-air conditions. Chapter 1 introduces the background of LIBs, specifically, working principles and their compositions (cathode, anode, separator and electrolyte(s)). Chapter 2 discusses the experimental methods and fundamental theory used throughout this dissertation. Chapter 3, focuses on the design of a full coin-cell and the selection of components. Specifically, a titanium-based anode material (Li4Ti5O12, LTO), a lithium transition metal oxide cathode (LiFePO4, LFP), a liquid electrolyte (0.6 m LiBOB), and a gel polymer electrolyte (PEGDA-PC-LiTFSI) are selected based on moisture-resistance and stability in the air criteria needed for the assembly in open-air conditions. Chapter 4 investigates the use of modified GPEs to improve battery characteristics by utilizing additional polymer hosts or lithium salt additives to: 1) strengthen mechanical properties, and 2) to improve the solid electrolyte interphase (SEI). From the study and analysis of charging and discharging profiles, it is concluded that the harder robustness of GPEs with less plasticizer shows more stable cyclic performance. Scanning Electron Microscopy (SEM) imaging taken after cycling testing shows that the cathode electrode is blocked by poor SEI films formed between cathode and electrolyte. Confirmed by SEM characterization, the addition of LiBOB salt improves the quality of SEI films and results in better cycling stability. In addition to the physical and electrochemical characterization, Chapter 3 and Chapter 4, present and discuss the results from flammability tests during electrolyte development. Lastly, the conclusion and remarks are summarized in Chapter 5.