Investigation of interfaces in flexible lithium ion batteries

Flexible and stretchable solid electrolyte-based lithium-ion batteries (LIBs) can potentially revolutionize our lives. They have wide range of applications, including flexible screen displays, wearable sensors, stretchable electronics, among others. Solid polymer electrolytes (SPEs) offer many advantages such as thermal and chemical stability, appropriate mechanical behavior, wide electrochemical window, safety, flexibility and low cost. However, SPE development faces several challenges, mainly, low ionic conductivity and problems pertaining to the interface between the electrodes and solid electrolytes. A stable and highly (ion) conductive interfacial layer is of utmost importance in LIB charge/discharge, rate capability, cyclability, and safety. This dissertation investigates the interface between SPE and electrodes in flexible and stretchable batteries. Several techniques to enhance the interfaces are explored including additives, specifically, tryptic soy broth (TSB) biomaterial and fluoroethylene carbonate (FEC), and enhanced SPE fabrication strategies (multi-layer fabrication method and hot-pressing). SPE-based LIB capacity improved significantly using 0.5 wt% TSB biomaterial due to the enhanced electrode-electrolyte interface. Furthermore, due to improved stable interfacial layer formation, flexible LIBs capacity more than doubled by using the FEC additives. Our flexible LIBs were shown to power light-emitting diode (LED) under 180 degree bending angles. Furthermore, spiral stretchable LIBs were demonstrated to work under 6000% out-of-plane stretching deformation. The investigation of interfacial phenomena and solid electrolytes in LIBs can provide deeper understanding of engineering strategies to improve LIBs properties and performance. The developed SPE-based flexible and stretchable LIBs can be promising for high safety and high-capacity energy applications.