Plasma-Assisted Surface Modification on the Electrode Interface for Flexible Fiber-Shaped Zn-Polyaniline Batteries

A novel flexible fiber-shaped zinc-polyaniline battery (FZPB) is proposed to enhance the electrochemical performance, mass loading, and stability of polyaniline cathodes. To this end, electron-cyclotron-resonance oxygen plasma-modified carbon fibers are employed. During plasma treatment, on the carbon-fiber surface, O₂⁺ plasma breaks the C-C, C-H, and C-N bonds to form C radicals, while the O₂ molecules are broken down to reactive oxygen species (O⁺, O²⁺, O₂⁺, and O₂²⁺). The C radicals and the reactive oxygen species are combined to homogeneously form oxygen functional groups, such as -OH, -COOH, and -C═O. The surface area and total pore volume of the treated carbon fibers increase as the plasma attacks. During electrodeposition, aniline interacts with the oxygen functional groups to form N-O and N-H bonds and π-π stacking, resulting in a homogeneous and high-loading polyaniline structure and improved adhesion between polyaniline and carbon fibers. In an FZPB, the cathode with plasma-treated carbon fibers and a polyaniline loading of 0.158 mg mg_CF^-1 (i.e., 2.36 mg cm_CF^-1) exhibits a capacity retention of 95.39% after 200 cycles at 100 mA g^-1 and a discharge capacity of 83.96 mA h g^-1 at such a high current density of 2000 mA g^-1, which are ∼1.67 and 1.24 times those of the pristine carbon-fiber-based one, respectively. Furthermore, the FZPB exhibits high flexibility with a capacity retention of 86.4% after bending to a radius of 2.5 mm for 100 cycles as a wearable energy device.