Nitroxide Radical Polymer-Solvent Interactions and Solubility Parameter Determination

Nitroxide radical polymers such as poly(2,2,6,6-tetramethylpiperidinyloxy-4-ylmethacrylate) (PTMA) are electrode materials of interest for organic batteries. They exhibit a reversible capacity (111 mAh/g theoretical), high redox potential (3.6 V vs Li/Li⁺), and rapid charging. One major consideration for the design and processing of organic batteries is the interaction between the polymer and solvent, such as the electrolyte. For example, linear PTMA may dissolve in the electrolyte solution, which leads to capacity fade during long-term cycling. To predict these polymer-solvent interactions, the Flory-Huggins interaction parameter, the Hildebrand and Hansen solubility parameters of PTMA are determined using group contribution calculations and experimental methods. Using calculated and measured solubility parameters, the Flory-Huggins interaction parameter for PTMA is estimated for common battery electrolyte systems. Membrane osmometry is used to confirm the PTMA Flory-Huggins interaction parameter. Once confirmed, the PTMA Flory-Huggins interaction equation is used to recommend new electrolyte solvents to improve battery performance.