Functional Gel Polymer Electrolytes for Antiflammable High-Energy Density Lithium-based Batteries

Abstract

Safety and stability are the key concepts running throughout this dissertation. The current battery market is continuously striving to achieve higher energy density to meet the growing demand for electric vehicles. For example, high nickel oxide cathode materials, silicon or lithium metal were used. However, these improvements increase the risk of battery explosions. To address this, various strategies have been implemented, modifying components such as cathodes and electrolytes. This dissertation focuses on a gel polymer electrolyte (GPE) formed through in-situ gelation with only 2 wt. % of polymer content. The GPE introduced here aims to mitigate leakage and safety issues while exhibiting excellent electrochemical properties. The addition of functional groups effectively enhanced both safety and stability. Firstly we introduce GPE designed to enhance the non-flammability of lithium- ion batteries (LIBs) by inhibiting radical chain reactions that lead to thermal runaway. We modified previously studied PVA-CN GPEs by attaching fluoroalkyl chains to inhibit battery combustion. Modified to fluoroalkyl, the GPE prevented flammable gases generation from electrolytes and stabilized highly reactive radical. Secondly, we also address the challenges of transition metals dissolution from the cathode. The introduction of chelating moieties into the PVA-CN resolved these issues. Transition metal dissolution and side reactions occurred when employing Ni-rich cathode materials to achieve high energy density and utilizing redox reactions in the high-voltage operation range. Chelating moieties attached to the PVA-CN enhanced the structural stability of the cathode and reduced dissolved metal crosstalk to the anode side. Therefore, battery performance was improved at high-voltage operation up to 4.6 V. Additionally, this dissertation covers the control of gelation speed and the simultaneous modification of PVA-CN by a bi- functional initiator. Steric hindrance from bulky substituents slowed down the gelation process. Delayed gelation at high temperatures degraded the battery performance. To overcome the disturbing of bulky functional groups, we utilized a bi-functional initiator. This strategy has enhanced the versatility and broader application of GPEs.