Recent Progress in Polyaniline and its Composites for Supercapacitors

Polyaniline (PANI) has piqued the interest of nanotechnology researchers due to its potential as an electrode material for supercapacitors. Despite its ease of synthesis and ability to be doped with a wide range of materials, PANI's poor mechanical properties have limited its use in practical applications. To address this issue, researchers investigated using PANI composites with materials with highly specific surface areas, active sites, porous architectures, and high conductivity. The resulting composite materials have improved energy storage performance, making them promising electrode materials for supercapacitors. Here, we provide an overview of recent developments in PANI-based supercapacitors, focusing on using electrochemically active carbon and redox-active materials as composites. We discuss challenges and opportunities of synthesizing PANI-based composites for supercapacitor applications. Furthermore, we provide theoretical insights into the electrical properties of PANI composites and their potential as active electrode materials. The need for this review stems from the growing interest in PANI-based composites to improve supercapacitor performance. By examining recent progress in this field, we provide a comprehensive overview of the current state-of-the-art and potential of PANI-based composites for supercapacitor applications. This review adds value by highlighting challenges and opportunities associated with synthesizing and utilizing PANI-based composites, thereby guiding future research directions.

Improved lithium-ion battery performance by introducing oxygen-containing functional groups by plasma treatment

Metal sulfides are often used as cathode materials for lithium-ion batteries (LIBs) owing to their high theoretical specific capacity; however, excessively fast capacity decay during charging/discharging and rapid shedding during cycling limits their practical application in batteries. In this study, we proposed a strategy using plasma treatment combined with the solvothermal method to prepare cobalt sulfide (Co_1-xS)-carbon nanofibers (CNFs) composite. The plasma treatment could introduce oxygen-containing polar groups and defects, which could improve the hydrophilicity of the CNFs for the growth of the Co_1-xS, thereby increasing the specific capacity of the composite electrode. The results show that the composite electrode present a high discharge specific capacity (839 mAh g^-1at a current density of 100 mA g^-1) and good cycle stability (the capacity retention rate almost 100% at 2000 mA g^-1after 500 cycles), attributing to the high conductivity of the CNFs. This study proves the application of plasma treatment and simple vulcanization method in high-performance LIBs.

Boosting the Utilization and Electrochemical Performances of Polyaniline by Forming a Binder-Free Nanoscale Coaxially Coated Polyaniline/Carbon Nanotube/Carbon Fiber Paper Hierarchical 3D Microstructure Composite as a Supercapacitor Electrode

Nanoscale polyaniline (PANI) is formed on a hierarchical 3D microstructure carbon nanotubes (CNTs)/carbon fiber paper (CFP) substrate via a one-step electrochemical polymerization method. The chemical and structural properties of the binder-free PANI/CNTs/CFP electrode are characterized by field emission scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy. The specific capacitance of PANI/CNTs/CFP tested in a symmetric two-electrode system reaches 731.6 mF·cm^-2 (1354.7 F·g^-1) at a current density of 1 mA·cm^-2 (1.8 A·g^-1). The symmetric supercapacitor device demonstrates excellent cycling performance up to 10,000 cycles with a capacitance retention of 81.4% at a current density of 1 mA·cm^-2 (1.8 A·g^-1). The results demonstrate that the binder-free CNTs/CFP composite is a strong backbone for depositing ultrathin PANI layers at a high mass loading. The hierarchical 3D microstructure PANI/CNTs/CFP provides enough space and transporting channels to form an efficient electrode-electrolyte interface for the supercapacitance reaction. The formed nanoscale PANI film coaxially coated on the sidewalls of CNTs enables efficient charge transfer and a shortened diffusion length. Hence, the utilization efficiency and electrochemical performances of PANI are significantly improved. The rational design strategy of a CNT-based binder-free hierarchical 3D microstructure can be used in preparing various advanced energy-storage electrodes for electrochemical energy-storage and conversion systems.

Novel Lignin-Cellulose-Based Carbon Nanofibers as High-Performance Supercapacitors

In this work, a simple phosphating process was proposed to modify cellulose-acetate (CA) and lignin for a novel energy storage precursor material. The prepared precursor fibers exhibited good thermal stability of lignin and flexibility of CA. Subsequently, the precursor fibers undergo a short preoxidation and carbonization treatment process to obtain the biomass-based carbon fibers (CFs) with complete fibrous morphology, uniform fiber diameter, high surface areas, good flexibility, and excellent power storage capacity. The specific capacitance of 346.6 F/g was obtained by using CFs-5 (prepared with 40% H₃PO₄ content) as a supercapacitor. Simultaneously, the biomass-based CF supercapacitor device delivers a high-energy density of 31.5 Wh/kg at the power density of 400 W/kg. These results indicate that the introduction of H₃PO₄ can effectively reduce the energy consumption of the preoxidation treatment process for the preparation of the biomass-based CFs, while increasing the energy storage properties significantly. This novel strategy showed a successful route for the preparation of high-quality and low-consumption biomass-based CFs.

Multifunctional nanocomposite structural separators for energy storage

Separators in energy storage devices such as batteries and supercapacitors are critical elements between the much-researched anodes and cathodes. Here we present a new "structural separator" comprised of electrically-insulating aligned alumina nanotubes, which realizes a structural, or mechanically robust, function in addition to allowing charge transfer. The polymer nanocomposite structural separator is demonstrated in a supercapacitor cell and also as an interface reinforcement in an aerospace-grade structural carbon fiber composite. Relative to a polymeric commercial separator, the structural separator shows advantages both electrically and structurally: ionic conductivity in the supercapacitor cell is doubled due to the nanotubes disrupting the semi-crystallinity in the polymer electrolyte, and the structural separator creates an interface that is 50% stronger in the advanced composite. In addition to providing direct benefits to existing energy storage devices, the structural separator is best suited to multifunctional structural energy storage applications.

An all-solid-state asymmetric device based on a polyaniline hydrogel for a high energy flexible supercapacitor

3D porous PANI hydrogel and a gel electrolyte were used to fabricate a high performance, all-solid-state, flexible asymmetric supercapacitor with an energy density of up to 6.16 mW h cm⁻³.