Preparation And Electrochemical Capacitive Characteristic Of Polyaniline Nanofiber By Interfacial Polymerization

Polyaniline (PANI) has enormous development ability as a kind of electrode material of supercapacitor, because of its desirable chemical stability, good conductivity and high faradic pseudo capacitance, as well as low cost advantage. Especially PANI material with one-dimensional nano-structure, in addition to other nano-structure's high specific surface features, also with high long-diameter ratio, high porosity and excellent electrical properties, thus has important research value in the field of supercapacitor.In this paper, PANI nanofiber material was prepared by a novel method of interfacial polymerization. The interfacial polymerization's conditions were investigated and optimized systematically; the behaviors of acquired PANI nanofiber material's electrochemical capacitance in H2SO4 aqueous solution were studied; the electrochemical and capacitive characteristics of the PANI nanofiber of lithium salt doping state in organic electrolyte were studied. On the basis, a novel hybrid capacitor based on the PANI nanofiber of lithium salt doping state and homemade activated carbon was constructed. The main research results and conclusions are as follows:(1) The optimal interfacial polymerization process can prepare Polyaniline nanofiber material with uniform size and good morphology. The material's average diameter is about 50-100 nm and length ranges from 500 nm up to several micrometers. Meanwhile, the process effectively solves the problem brought by crowding effect and improves the Polyaniline nanofiber' yield from 10% to 35%.(2) In H₂SO₄ aqueous solution, acquired PANI nanofiber material can maintain high specific capacitance, good power characteristic and cycle performance. Its single-electrode specific capacitance can reach as high as 317 F/g in discharge current of 5mA, reducing by 5% when discharge current increases from 5mA to 20mA, and the degradation of capacitance is within only 4% during 500 charge-discharge cycles; compared with PANI material with irregular granular morphology prepared by conventional chemical polymerization (electrode capacitance reduces by 11% when discharge current increases from 5mA to 20mA and degradation of capacitance is about 33% during 500 charge-discharge cycles), the advantages of PANI nanofiber material in morphology and structure are fully performed.(3) Lithium salt can dope PANI material in non-doping state fully and effectively, which is similar to the doping of inorganic acid, and may play only a limited and added doping role to PANI material having been doped by acid. Lithium doping increases PANI nanofiber material's capacitance in 1M LiPF₆ organic electrolyte from 49.75F/g to 128.05F/g, and effectively improves recycling stability (degradation of capacitance is within only 30% compared with 70% during 500 charge-discharge cycles) and electricity performance. However, several problems exist, such as excessive voltage drop, low potential ceiling and narrow effective energy storage's potential range.(4) A novel hybrid capacitor based on the PANI nanofiber of lithium salt doping state and homemade activated carbon is constructed. It shows that Et₄NBF₄/PC organic solution is more suitable for the organic electrolyte of the hybrid capacitor compared with organic solution concluding LiPF₆. The effective energy storage's potential range widens from 0-1V to 0-2V and potential ceiling increases from 2.0V to 2.5V under the circumstance of constant capacity, compared with the PANI/PANI symmetric capacitor. At the same time, the discharge voltage drop decreases greatly and cycle performance further improves.