Investigation on the Carbonyl Redox of Polyimide Based on Bridged Dianhydride as Electrode in Lithium-Ion Battery

In lithium-ion batteries, carbonyl redox of polyimides based on bridged dianhydride as electrodes exhibit a low electrochemical activity. In order to explain this phenomenon, we selected three previously reported bridged dianhydride including BTDA, BPDA and ODPA combined with p-PDA to form polyimides noted as PI-1, PI-2 and PI-3, respectively as electrode materials, and polyimide PI-4 composed of NTCDA and p-PDA as contrast. Galvanostatic charge/discharge test was measured in 1 M LiPF6 mixed carbonate electrolyte at 1.2 to 3 V vs Li+/Li, the results showed that PI-1, PI-2 and PI-3 have severe polarization and poor reversibility. Electrochemical impedance spectroscopy (EIS) of the electrodes indicated that the polarization was mainly caused by the much smaller lithium ion diffusion coefficients of PI-1, PI-2 and PI-3 than PI-4. Further research on the cyclic voltammetry of the model compounds dissolved in 1 M LiPF6 or 0.1 M TBAPF6 mixed carbonate electrolyte proved that strong interaction existed between the reduction products and lithium ions was the main reason for poor reversibility and small lithium ion diffusion coefficient of PI-1, PI-2 and PI-3. The data in this work can provide a reference for the future research of polyimide electrode materials.