Tailoring Polymer Polarity to Regulate Disulfide Accessibility in Redox-Active Particles for Organic Batteries

This study seeks to explore the relationship between particle polarity and the electrochemical accessibility of organo-disulfide-based redox-active particles. Micron-sized poly(glycidyl methacrylate) (PMGA) particles were synthesized and subsequently cross-linked with thiadiazole disulfide to produce redox-active particles (DS-RAPs). The residual glycidyl units underwent reactions with various side chains to modulate the polarity of the DS-RAPs. These side chains vary from nonpolar aliphatic N-methylbutylamine (MBA) to the more polar oligoethylene glycol amine (EGA) and glycidyl carbonate (GC) moieties. Cyclic voltammetry reveals that functionalization with polar side chains enhances electrochemical accessibility, with DS-RAP(GC) demonstrating the highest accessibility in both acetonitrile and tetraglyme-based electrolytes. Testing the DS-RAP derivatives as cathode electrodes in a lithium cell with a LiTFSI/tetraglyme electrolyte indicates that DS-RAP(GC) yields the highest specific capacities, energy efficiency, and best kinetics at 0.1C. Conversely, C-rate dependence measurements show that DS-RAP(EGA) has higher specific capacities at faster C-rates and is more resilient to mass transport limitations compared to DS-RAP(GC) and DS-RAP(MBA). This is attributed to greater electrolyte swelling in DS-RAP(EGA) and higher ion diffusivity, as evidenced by galvanostatic intermittent titration technique (GITT) measurements. Lastly, long-term cycling tests at 0.1C indicate minimal degradation, with the resulting capacity fade attributed to charge trapping during the continuous reversible oxidation/reduction of disulfides. Overall, these findings contribute significantly to the development of effective RAPs for energy storage applications, highlighting the pivotal role of chemical modifications via side chain engineering in controlling particle polarity to enhance charge transport and overall electrochemical performance.