For economic and environmental considerations, organic cathode materials are attracting more attention. Particularly, conducting polymers, such as polythiophene, polyphenylene, polypyrrole, etc., are excellent candidates for lithium-ion batteries with high conductivity, structural designability, and unique anion intercalation/deintercalation mechanism. In this work, an electrodeposition approach to synthesize dense and additive-free polypyrrole film electrodes with p-toluenesulfonic acid as a dopant for lithium-ion batteries was provided. For uniform directional growth layer by layer, a thin PPy film (432 nm) cathode delivered a much higher discharge capacity (188.1 mAh g–1 at 85 mA g–1) and capacity retention (87.0% after 300 cycles) than those of thick films (542 and 866 nm). Unlike the gravimetric capacities, different thicknesses of PPy films had similar volumetric capacity, which was around 40 times higher than that of PPy powder materials, providing a direction for the fabrication of large-capacity microbatteries. Surprisingly, the capacities of the batteries would be further increased after leaving alone for a long time, demonstrating advantages for the application of organic materials.

To address the existing problems of commercial inorganic cathodes, including relatively low capacity, poor rate performance, structural instability, and low conductivity, it is critical to introduce a conductive matrix accompanied with electrochemical activity. Conductive polymers have great potential as electrodes with good conductivity, high redox activity, and potential. In this study, carbon-coated lithium iron phosphate (C-LiFePO4) nanoparticles were effectively dispersed in a polypyrrole (PPy) matrix by in situ pulverization. PPy, as an active nanostructure, significantly improves conductivity and accelerates Li+ diffusion. To further explore the synergy and symbiosis mechanism of PPy and C-LiFePO4 (hereinafter called C-LFP in the composite), the nanoparticle dispersion, carburization dependence, and heat treatment preference were investigated. Therefore, a reasonable amount of PPy (25 wt %) hybridization, a moderately wrapped carbon buffer layer (5.3 wt %), and a suitable heat treatment (100 °C) were employed to prepare the (C-LFP)0.75(PPy)0.25 nanocomposite. With a smaller particle size, uniformly dispersed morphology, and good synergy effect between PPy and C-LiFePO4, (C-LFP)0.75(PPy)0.25 delivers a high discharge capacity (209.1 mAh g–1 at 0.1C), a superior rate capability (86.1 mAh g–1 at 10C), and an outstanding capacity retention (83.5% of the initial values after 500 cycles at 0.5C).