(632g) Tuning Semi-Conducting Polymers for Binder Applications in Fe3O4 Li-Ion Battery Anodes

Lithium-ion batteries are one of the most important energy storage devices for a variety of applications, but require improvements for future energy needs. Battery electrodes are complex mesoscale systems comprised of an active material, conductive agent, current collector, and polymeric binder. The current active material in anodes, graphite, has a low theoretical capacity, which limits its application use. Future developments require higher capacity materials, such as magnetite (Fe₃O₄), which has three times the theoretical capacity of graphite. However, magnetite suffers from large volume changes during repetitive charging-discharging, which creates challenges with capacity retention. Further research is needed to make magnetite a commercially viable active material.

The majority of electrode material research for Li-ion batteries focuses on the synthesis of active particles, with less focus on polymeric binders. However, the binder plays a crucial role in stability and ensures electrode integrity. The traditional polymeric binder, poly(vinylidene difluoride) (PVDF), fails to accommodate large changes in spacing between particles during cycling. As such, it is believed the role of active material-binder interactions is essential for electrode stability.

This work focuses on utilizing conjugated polymers as binders to aid in electron and ion transport in magnetite-based anodes. The overarching goal of this study is to create a framework of desirable qualities necessary for polymeric binders by investigating how different functional groups aid or hinder electrochemical performance. Conjugated polymers under investigation include poly[3-(potassium-4-butanoate)thiophene] (PPBT), poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) derivatives, and polyacrylic acid (PAA). PPBT in conjunction with a polyethylene glycol (PEG) surface coating for the active material was demonstrated to enhance both electron and ion transport in magnetite based anodes. PEDOT:PSS derivatives showed comparable cycling performance to PPBT over 100 cycles at 0.3 C, demonstrating enhanced capacity retention compared to the traditional PVDF. Rate capability testing revealed similarities between PPBT and PAA. Chemical characterization is expected to reveal further differences between the polymeric binders as a result of their unique interactions with magnetite due to differences in chemical structure.