Li-ion batteries are used in countless portable electronics and are making their way to larger scale technologies like electric vehicles. To keep up with demand for a higher energy density battery, novel materials are being researched to optimize Li-ion battery performance. However, one often neglected component of Li-ion batteries, the polymer binder used in the electrodes, may hold the key to improved performance. Traditionally the role of the polymer binder has been limited to holding together the two other components of an electrode, the active material and conductive additive. But if beneficial electrical and mechanical properties can be combined into a multi-functional polymer binder, it is possible that the amount of conductive additive can be reduced or removed altogether, increasing the overall energy density of the electrode. In this work, we synthesize a series of conjugated polymer-based binder materials for silicon anodes. The polymers are synthesized through Suzuki-Miyaura polycondensation of a monomer mixture, and a variety of monomers are chosen to impart a specific functionality. Fluorene with di-octyl side-chains improve solubility and processibility, fluorene with oligo(ethylene glycol) side chains improve elasticity and electrolyte uptake, naphthalene diimide units provide redox activity, and methyl benzoate phenyl esters react with lithium to impart conductivity. We process electrodes through flow coating and compare their morphology, performance, mechanical properties, and electrochemical properties to electrodes fabricated with a PEDOT:PSS binder. Our work to date shows that the conductivity of the binder and battery performance is strongly dependent on doping and processing history. Current work is focused on systematic studies of battery performance with varying binder conductivity and investigation of electrode mechanical properties.

Novel conjugated polymer binders and their processing for Si-based Li-ion battery anodes

253rd National Meeting (2017)

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