Enhancement of the High-Rate Performance of an Organic Radical Thin-Film Battery by Decreasing the Grafting Density of Polymer Brushes

A high-rate performance enhancement of a poly(2,2,6,6-tetramethylpiperidin-1-oxy-4-yl methacrylate) (PTMA) brush as a thin-film organic radical cathode is achieved by grafting density reduction. n-Octyltrichlorosilane as a capping agent diluted the surface initiator density on the indium tin oxide (ITO) substrate. Surface initiator-modified ITO substrates (1% and 100%) were grafted with PTMA to yield low (LD) and high (HD) grafting density PTMA brushes (0.11 and 0.26 chains nm–2, respectively). The cyclic voltammetry and AC impedance results showed that the LD PTMA brush has a lower impedance than the HD PTMA brush electrode. The in situ electrochemical atomic force microscopy detected a larger thickness change in the LD PTMA brush during the redox reactions than in the HD PTMA brush. This difference is attributed to the loose packing of the polymer chains in the LD PTMA brush that enhances polymer chain mobility and transportation of ClO4– anions. Furthermore, the thin-film organic radical battery cell with the LD PTMA brush electrode exhibited outstanding high-rate performance (>50% retention at 1500 C) and a good cycle-life performance of 89% retention at 20 C over 400 cycles.