Study On The Effect Of Surfactant On The Supercapacitor Behavior Of Polyaniline Matrix Composites

Supercapacitor, appropriate for the large current charge/discharge and with long cycling life, is a new energy storage device with performance between electrolytic condenser and battery. Its market is promising. Consequently, it is a research focus in the field of new energy storage. Electrode is a core component of supercapacitor. At present, the main research of supercapacitor is developing electrode materials with high energy density and steady performance.Polyaniline (PANI) is the most outstanding conducting polymer among supercapacitor electrode materials due to good electrochemical performance, better environmental stability, cheap reactants and simple synthesis process. Ascribing to its unique doping behavior and bulk phase reaction mechanism, it is of good redox reversibility and high pseudocapacitance. Nevertheless, the comparatively low conductivity and poor cycling stability limit its wide range application. Coupling PANI with carbon materials is an effective way to improve capacitance performance of PANI based electrodes. On the one hand, carbon materials could provide composite with good electrical conductivity, especially when PANI is of neutral state. On the other hand, high mechanical strength of carbon materials could weaken the volume expansion and contraction of PANI during continuous charge/discharge process, resulting in better cycling performance. In recent years, the development of new diversity of carbon materials (high surface area activated carbon, carbon nanotubes, graphene (GN) etc.), with wide range of raw material sources, provides more chance to fabricate high performance PANI/carbon based composite electrode.However, carbon are prone to agglomerate and of poorly soluble in solvents. Simple compositing PANI with carbon materials is hard to take full advantages of two single components and their synergistic effect. Based on this, we proposed to use surfancants to enhance the wettability of carbon and reduce its agglomeration. Meanwhile, surfactants can act as structure-directing agent to improve composites microtopography and further optimize its capacitive performance. According to XPS, SEM, TEM, low temperature N2 adoption and electrical tests, we systemically investigated the influence and function mechanism of different amounts surfactants on PANI based electrode materials morphology, structure and capacitive performance. Specific contents and conclusions are as follows:(1) With the assistance of nonionic surfactant P123, GN/PANI composites are fabricated by one-step in situ polymerization in acid solution. Results indicate that composites are of sandwich structure (PANI nanofibers coated PANI nanoparticle coated GN). P123 with different amounts have no influence to composites crystal structure but effectively control its morphology, particle size and capacitance performance. When the molar ratio of P123 to ANI is 0.0108 (GP-P3), the mixing degree between GN and PANI is the most optimal. The composite is of the highest specific surface area, pore volume, average pore size and of best capacitance performance. At the current density of 500 mA g-1 (similarly hereinafter), specific capacitance of GP-P3 is up to 215.8 Fg-1, increased by 82.0% in comparison with composites without P123 assisted. After 1000 charge-discharge cycles, its capacity retention is up to 91.8%.(2) With the assistance of anionic surfactant SDBS, PANI/CC flexible electrodes were prepared by a simple chemical oxidation in acid solution. SDBS could act as structure-directing agent and dopant at the same time to affect composites performance. According to our study, PANIs synthesized are all amorphous and in their doped state. Suitable SDBS (nSDBS/nANI= 0.011) is conducive to enhancing PANI interchain space and conjugated degree, improving the regularity of its main-chain structure and microstructure of composites (good three-dimensional networked structure). As for capacitance behavior, when the molar ratio of SDBS to ANI is 0.011, composites (PANI/CC-1) obtain the highest specific capacitance (up to 537 F g-1) and the optimal rate capability. After 1000 cycles, its capacity retention is up to 83.4%, showing the best cycle stability. When its power density is 0.25 kW kg-1, its energy density is up to 74.5 Wh kg-1. Additionally, PANI/CC-1 obtains the lowest charge transfer resistance (1.21 Ω) and Warburg resistance (1.21 Ω).