Abstract
Polymeric binders serve to stabilize the morphology of electrodes by providing adhesion and binding between the various components. Successful binders must serve multiple functions simultaneously, including providing strong adhesion, improving conductivity, and providing electrochemical stability. A tradeoff between mechanical integrity and electrochemical performance in binders for lithium-ion batteries is one of the many challenges of improving capacity and performance. In this paper, we demonstrate a self-doped conjugated polymer, poly(9,9-bis(4′-sulfonatobutyl)fluorene-alt-co-1,4-phenylene) (PFP), which not only provides mechanical robustness but also improves electrode stability at temperatures as high as 450 °C. The self-doped PFP polymer is comprised of a conjugated polyfluorene backbone with sulfonate terminated side-chains that serve to dope the conjugated polymer backbone, resulting in stable conductivity. Composite electrodes are prepared by blending PFP with V2O5 in water, followed by casting and drying. Structural characterization with X-ray diffraction and wide-angle X-ray scattering shows that PFP suppresses the crystallization of V2O5 at high temperatures (up to 450 °C), resulting in improved electrode stability during cycling and improved rate performance. This study demonstrates the potential of self-doped conjugated polymers for use as polymeric binders to enhance mechanical, structural, and electrochemical properties.
Highlights
The widespread use and rapidly-growing demand of lithium-ion batteries has raised many researchers’ interests in further improving the lithium storage capacity and its long-term stability and safety [1,2,3,4,5,6,7]
The tradeoff between electrochemical performance and mechanical properties can be potentially overcome by using a multifunctional binder, which provides mechanical robustness, but electronic conductivity as well
The structure of the self-doped polymer PFP is shown in Figure 1A along with an SEM
Summary
The widespread use and rapidly-growing demand of lithium-ion batteries has raised many researchers’ interests in further improving the lithium storage capacity and its long-term stability and safety [1,2,3,4,5,6,7]. Most commonly used binders, such as poly(vinylidene fluoride) (PVDF), poly(tetrafluoroethylene) (PTFE), and carboxy methyl cellulose (CMC), are inactive in terms of ionic or electronic conductivity or electrochemical activity. As such, these binders are added in the lowest possible quantities (typically less than 5 wt % in cathodes) in order to maintain essential mechanical integrity without significantly sacrificing battery capacity. The commercially available conductive polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has been widely studied in device applications, including as a functional binder in carbon black free LiFeO4 cathodes for Li-ion batteries, resulting in improved stability and comparable capacity with conventional electrodes [11]
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