Utilizing Camphene As an Alternative to NMP Solvent for Casting Redox-Active Organic Cathode Materials
Authors: Vaidyula Rinish Reddy , Brotherton Zachary , Fuller Robert Ferguson , Kawashima Kenta , Wang Ziqing , Lynd Nate , Mullins Charles Buddie 
Published: December 2024

Efficient energy storage systems are imperative for integrating intermittent renewable energy sources into the grid, facilitating the sustainable adoption of electric vehicles, and advancing portable electronic devices.1 While current energy storage systems primarily rely on inorganic metal-based materials containing transition metals like cobalt, manganese, nickel, and iron, their extraction poses environmental hazards and occupational risks.2–4 Additionally, redox-active polymer (RAP)-based organic electrode materials present a versatile alternative for energy storage, as they are not limited to specific counter-ions and can be utilized in various battery systems, including lithium-ion, sodium-ion, multivalent-ion, and dual-ion batteries.5 Composed of carbon, oxygen, nitrogen, and sulfur, RAPs offer advantages such as lower density, greater abundance, reduced cost, and lower environmental impact compared to conventional energy storage systems.6

Despite their promise, conventional electrode preparation methods for RAPs encounter challenges in dispersing polymer active materials with conductive additives and binders, potentially limiting access to active sites and reducing material utilization. Alternative strategies have been explored, including modifying active material morphology during synthesis and utilizing carbon-based current collectors.7 However, metal current collectors, prized for their high electronic conductivity and cost-effectiveness, have garnered special attention.8 Traditionally, N-methyl-2-pyrrolidone (NMP) serves as a solvent for dispersing active materials, conductive additives, and binders in electrode casting. While NMP exhibits excellent compatibility for electrode casting due to its viscosity and solvability, its toxicity renders it less desirable.9 Moreover, the poor dispersibility of large organic polymer chains in this polar solvent may compromise access to active sites.

Here, we propose the use of bio-derived terpene camphene as a solvent for freeze-casting active materials, aiming to enhance dispersion and yield porous electrodes through camphene sublimation during drying. Our study investigates the performance of various redox-active polymer cathodes cast with camphene compared to those cast with NMP. Our results demonstrate superior capacity retention of camphene-cast electrodes even at higher current densities, highlighting the significance of the casting process for RAPs. Additionally, cyclic voltammetry and galvanostatic intermittent titration techniques reveal enhanced ion diffusivity in camphene-cast electrodes, leading to reduced charge transfer and interfacial resistance. We anticipate that these findings will encourage further exploration of this casting process to enhance the performance of organic redox-active batteries.

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