Quantifying TEMPO Redox Polymer Charge Transport toward the Organic Radical Battery

Abstract

To design new and better organic active battery materials in a rational fashion, fundamental parameters of the charge transport must be studied. Herein we report on the electronic conductivity by electron diffusion in a TEMPO-containing redox polymer, and the reorganization energy of the TEMPO self-exchange in an organic solvent is determined for the first time. The electronic conductivity was 8.5 μS/cm at E⁰ and corresponded to a redox hopping mechanism. The apparent electron diffusion coefficient was 1.9 × 10^-9 cm²/s at room temperature, and at short times the ion diffusion was limiting with a diffusion coefficient of 6.5 × 10^-10 cm²/s. The reorganization energy was determined to be 1.01 eV, indicating a rather polar chemical environment for the TEMPO groups. The implications for the usage of this type of materials in organic energy storage are discussed. As conductivity through 10 μm was demonstrated, we show that, if sufficient swellability can be ensured, charge can be transported through several micrometer thick layers in a battery electrode without any conducting additive.

Keywords: TEMPO; electron diffusion; in situ conductivity; redox hopping; redox polymer; reorganization energy.