Preparation of TEMPO-contained pyrrole copolymer by in situ electrochemical polymerization and its electrochemical performances as cathode of lithium ion batteries

Abstract

Composite electrodes based on the nitroxide free radical-contained pyrrole copolymer (PPy-co-PPy-C-TEMPO) as active material were one-step synthesized by in situ electrochemical polymerization, which was then directly applied as the cathode of lithium ion batteries. The structure, morphology, electrochemical property, and charge-discharge performances of prepared copolymers were characterized by FTIR, SEM, cyclic voltammogram, electrochemical impedance spectroscopy, and galvanostatic charge-discharge testing, respectively. The results demonstrated that PPy-co-PPy-C-TEMPO-based composite cathodes have been successfully prepared by in situ electrochemical method, and the introduction of the nitroxide free radical (TEMPO) could obviously affect the morphology and electrochemical characteristics of the obtained electroactive polymers. And the charge/discharge tests showed that with the introduction of the TEMPO, PPy-co-PPy-C-TEMPO-based composite cathodes exhibited an improved specific capacity of 70.9 mAh g−1 for PPy-co-PPy-C-TEMPO (4:1) and 62.6 mAh g−1 for PPy-co-PPy-C-TEMPO (8:1) as measured at 20 mA g−1 between 2.5 and 4.2 V, which were remarkably higher than that of the pure PPy cathode of 41.0 mAh g−1 under the same experimental conditions. Also, the obtained PPy-co-PPy-C-TEMPO copolymers demonstrated an acceptable cycling stability during the charge-discharge process. These obtained cell performances for the composite cathodes were attributed to the application of the in situ electrochemical polymerization technology, which enhanced the intimate integration between conductive polymer film and electrode. Furthermore, the introduction of TEMPO-contained pyrrole (Py-C-TEMPO) improved the morphology of the composite cathode, which was in favor of the utilization of active materials and the improved electrochemical performances.