Dissertation Defense: Ye Shi

Rational Design of 3D Nanostructured Conductive Polymer Gels for Electrochemical Energy Storage and Responsive Electronic Device

Ye Shi
Supervised by: Dr. Guihua Yu

This work presents the rational design and synthesis of conductive polymer gels (CPGs) using doping molecules as crosslinkers. Molecules with multiple functional groups are used to crosslink the conductive polymer chains, leading to CPGs with 3D networked structures. These dopant molecules crosslinked CPGs exhibit both high electrical and ionic conductivities since they construct heavily doped and interconnected polymer network for electron transport and hierarchically porous structure for ions diffusion. The chemical and physical properties of dopant molecules crosslinked CPGs can be facilely tuned by controlling the dopants and synthetic conditions.

With improved electrochemical properties, CPGs have been applied as electrode material in supercapacitors and binder material in lithium ion batteries. CPGs establish a continuous network to promote the transport of electrons, provide short ion diffusion path and large surface area for redox reactions, and construct a porous architecture with intrinsic elasticity to accommodate the volume change, thus showing high capacitance and rate capability as supercapacitor electrode materials. CPGs with structure derived elasticity further enable highly flexible supercapacitor. CPGs were also adopted as bifunctional binder materials for lithium ion battery electrodes, acting as both polymeric binder and conductive additive. The gel framework based electrode exhibits greatly improved rate and cyclic performance owing to improved electronic and ionic transport. In addition, both inorganic and organic components are uniformly distributed within the electrode due to the polymer coating. The robust framework further provides mechanical strength to support active electrode materials and improves the long-term electrochemical stability.

Based on conductive polymer gels and a thermoresponsive electrolyte system, electrochemical energy storage devices with thermal self-protection behavior are developed. The smart electrolyte system is achieved by employing a commercially available thermoplastic elastomer, Pluronic, which shows a fast sol-gel transition process upon heating. The gelation of Pluronic solution based electrolytes significantly inhibits the migration of ions, leading to a nearly 100% decrease in specific capacitance. The responsive behavior is highly reversible and tunable. Various electrode materials and conductive ions are compatible with this system.

Finally, multifunctional hybrid gel materials based on CPGs are developed by introducing a second responsive polymeric network, forming interpenetrating double network structure. A highly thermoresponsive and conductive hybrid gel is synthesized by in situ polymerization of CPGs within PNIPAM matrix and a room-temperature self-healing hybrid gel is prepared by introducing a supramolecular gel into PPy gel framework.