Browsing by Author "Lutkenhaus, Jodie"

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    Self-Doped Conjugated Polymeric Binders Improve the Capacity and Mechanical Properties of V2O5 Cathodes
    (MDPI, 2019) Li, Xiaoyi; An, Hyosung; Strzalka, Joseph; Lutkenhaus, Jodie; Verduzco, Rafael
    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.
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    Side‐Chain Engineering for High‐Performance Conjugated Polymer Batteries
    (Wiley, 2021) Li, Xiaoyi; Li, Yilin; Sarang, Kasturi; Lutkenhaus, Jodie; Verduzco, Rafael
    Conjugated polymers are attractive for energy storage but typically require significant amounts of conductive additives to successfully operate with thin electrodes. Here, side‐chain engineering is used to improve the electrochemical performance of conjugated polymer electrodes. Naphthalene dicarboximide (NDI)‐based conjugated polymers with ion‐conducting ethylene glycol (EG) side chains (PNDI‐T2EG) and non‐ion‐conducting 2‐octyldodecyl side chains (PNDI‐T2) are synthesized, tested, and compared. For thick (20 µm, 1.28 mg cm−2) electrodes with a 60 wt% polymer, the PNDI‐T2EG electrodes exhibit 66% of the theoretical capacity at an ultrafast charge–discharge rate of 100C (72 s per cycle), while the PNDI‐T2 electrodes exhibit only 23% of the theoretical capacity. Electrochemical impedance spectroscopy measurements on thin (5 µm, 0.32 mg cm−2), high‐polymer‐content (80 wt%) electrodes reveal that PNDI‐T2EG exhibits much higher lithium‐ion diffusivity (DLi+ = 7.01 × 10−12 cm2 s−1) than PNDI‐T2 (DLi+ = 3.96 × 10−12 cm2 s−1). PNDI‐T2EG outperforms most previously reported materials in thick, high‐polymer‐content electrodes in terms of rate performance. The results demonstrate that the rate performance and capacity are significantly improved through the incorporation of EG side chains, and this work demonstrates a route for increasing the rate of ion transport in conjugated polymers and improving the performance and capacity of conjugated‐polymer‐based electrodes.