Electrodeposition of polypyrrole as binder-free and high mass-loading electrodes for flexible supercapacitors

Flexible or bendable energy storage devices have drawn great attention recently due to the great demand for the development of soft portable equipment. Conducting polymers (polypyrrole, polyaniline, polythiophene) are particularly interesting powder form candidates for active materials in such devices. A traditional slurry-based technology with low mass loadings (1 mg/cm2) is usually used. However, poor interparticle or particle-substrate connections influence the performance of devices during bending. Furthermore, increasing the mass loading (10 mg/cm2) of commercial-level electrode materials often has the problems of poor electrical and ionic conductivity, which will hinder their practical applications. The electrodeposition process of conducting polymers provides an alternate useful method to synthesize uniform and binder-free electrodes with high mass loadings. Here, electrochemically synthesized polypyrrole is proposed and investigated to increase the energy storage performance with high mass loadings. The electrodeposition polypyrrole electrode with a mass loading of 10 mg/cm2 demonstrates a competitive gravimetric capacitance of 265 F/g at a current density of 1 A/g. In the case of a symmetrical supercapacitor with E-PPy, the differences in the capacitance obtained with different electrode masses are insignificant (59.1 F/g for 2.4 mg/cm2 and 54.9 F/g for 10 mg/cm2). The assembled supercapacitor also possesses outstanding flexibility (as high as 96.3% capacitance retention at 2 A/g) upon bending to 140° for 10 cycles.