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In this work, polypyrrole/graphene doped by p-toluenesulfonic is prepared as an active material for supercapacitors, and its capacitance performance is investigated in various aqueous electrolytes including HCl, LiCl, NaCl, and KCl with a concentration of 3 M, respectively. A rising trend of capacitance is observed according to the cationic mobility (Li(+) < Na(+) < K(+) < H(+)), which is due to its effect on the ionic conductivity, efficient ion/charge diffusion/exchange and relaxation time. On the other hand, long-term cycling stability is in the following order: KCl < NaCl < LiCl < HCl, corresponding to the decreasing tendency of cation size (K(+) > Na(+) > Li(+) > H(+)). The reason can be attributed to the fact that the insertion/de-insertion of large size cation brings a significant doping level decrease and an over-oxidation increase during the charging-discharging cycles. Hence, we not only obtain good capacitance performance (280.3 F g(-1) at 5 mV s(-1)), superior rate capability (225.8 F g(-1) at 500 mV s(-1)) and high cycling stability (92.0% capacitance retention after 10,000 cycles at 1 A g(-1)) by employing 3 M HCl as an electrolyte, but also reveal that the electrolyte cations have a significant effect on the supercapacitors' electrochemical performance.

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Polyaniline (PANI) with high crystallinity degree was facilely synthesized on the surface of stainless steel net by galvanostatic method. The effect of polymerization current density on the characteristics of morphology and structure had been investigated by field emission scanning electron microscopy (FE-SEM), Fourier transforms infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). FE-SEM observations disclosed that PANI was deposited as nanofibers and their diameters decreased with the polymerization current density. FTIR studies revealed that degree of oxidation increased in order PANI-2 < PANI-6 < PANI-10. XPS measurements displayed that PANI polymerized at 6 mA cm 22 (PANI-6) exhibited much higher doping level of 77.8%, which favored the conductivity. XRD analysis discovered that the obtained PANI showed high crystallinity degree in which PANI-6 possessed highest crystallinity degree (X cr ) up to 67%. Electrochemical performances of PANI as electrode materials were studied via cyclic voltammetry. The results presented that PANI-6 possessed greater discharge capacity and better reversibility.In this study, PANI with high crystallinity degree was synthesized by galvanostatic method on the basis of several points of view: the production is purer and more homogeneous, the devices are facile, and different thickness films could be obtained by controlling polymerization time and/or current density. The data about its spectral properties, structure, conductivity, and electrochemical properties were presented. The effect of polymerization current density on the structure, degree of oxidation (DO), doping level (DL), and crystallinity degree was investigated. The relationship between structure and electric properties was discussed. EXPERIMENTAL ReagentsAniline (C 6 H 7 N, analytical grade from Xi'an Chemical Industry, China) was distilled under reduced pressure before use.

Although Li4Ti5O12 (LTO) is considered as promising anode material for high-power Li-ion battery with high safety, the sluggish Li-ion diffusion coefficient restricts its wide application. In this work, oxygen vacancy was successfully incorporated into LTO by an eco-friendly and cost-effective plasma process. The deficient LTO delivers much higher capacity of 173.4 mAh g-1 at 1 C rate after 100 cycles and 140.5 mAh g-1 at 5 C after 1000 cycles than those of the pristine LTO. Meanwhile, even at high rate of 20 C it displays an ultrahigh capacity of 133.1 mAh g-1 after 500 cycles with a Coulombic efficiency of 100%. Detailed analysis discovers that the lithium storage mechanisms in the oxygen-deficient LTO, especially at high rate, were dominated by the insertion behavior and dual-phases conversion due to the fast ion diffusion ability, rather than the widely reported surface capacitance by other approaches. This work highlights that the defect generation by plasma in nanomaterials is an effective way to promote the ion mobility, especially at high rate, thus can be extended to other electrode materials for advanced energy-storage applications.

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