新型炭材料

PREFACE

KANG Fei-yu

2011, 26(3)

Abstract(2390)

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Effects of carbonaceous materials on the physical and electrochemical performance of a LiFePO₄ cathode for lithium-ion batteries

KANG Fei-yu, |　MA Jun, LI Bao-hua

2011, 26(3): 161-170. doi: 10.1016/S1872-5805(11)60073-5

Abstract(3119)

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Abstract:
The effects of carbonaceous materials on the physical and electrochemical performance of LiFePO₄/C hybrids are reviewed. The major role, advantages and disadvantages of carbon-based materials in LiFePO₄/carbon hybrids are discussed. The introduction of an in situ grown carbon coating would be beneficial to limiting the LiFePO₄ particle growth and increasing the electric conductivity. The structure and precursors of the in situ grown carbons have a great influence in the rate performance of the hybrids, which can be related to an improved electron and ion transfer rate. Deposition of LiFePO₄ into a carbonaceous matrix such as a templated membrane can increase the contact area between the active materials and the electrolyte, which favors a fast ion transport. The addition of conductive carbon and graphene would only effectively increase the electrical conductivity. In order to achieve an excellent electrochemical performance of LiFePO₄, it is necessary to take advantage of and to combine these approaches to optimize electron and ion transfer rates. Also, it is most important to minimize the carbon content in LiFePO₄/carbon hybrids to increase volumetric energy density and tap density when practical applications in electric vehicles are targeted.

Hierarchical porous carbons: design, preparation, and performance in energy storage

FU Ruo-wen, LI Zheng-hui, LIANG Ye-ru, LI Feng, XU Fei, WU Ding-cai

2011, 26(3): 171-179. doi: 10.1016/S1872-5805(11)60074-7

Abstract(1804)

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Hierarchical porous carbons (HPCs) possess a multimodal pore size distribution of micro-, meso-, and/or macropores, and thus show high electrochemically accessible surface area, short diffusion distance, and high mass transfer rate when used as electrode materials in energy storage devices. Because of this, HPCs show excellent rate capabilities and have attracted considerable attention in recent years. Normally, HPCs are prepared by templating methods or combined templating/activation methods, in which carbons are inverse replicas of the template and the pore structure parameters of HPCs can be easily tuned. Recently, simpler template-free methods have been developed and show a promising future. In this review, we describe the recent advances in design, preparation, and electrochemical performance of HPCs, with particular attention to the main achievements using HPCs developed in our groups since 2008. Finally we give a brief outlook.

The effect of carbon particle morphology on the electrochemical properties of nanocarbon/polyaniline composites in supercapacitors

ZHOU Guang-min, WANG Da-wei, LI Feng, ZHANG Li-li, WENG Zhe, CHENG Hui-ming

2011, 26(3): 180-186. doi: 10.1016/S1872-5805(11)60075-9

Abstract(2617)

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Nanocarbon/polyaniline (PANI) composites were prepared by in situ polymerization of aniline on carbon blacks (CB), carbon nanotubes (CNTs) and graphene nanosheets (GNSs). The GNS/PANI composite has the highest PANI content with high specific capacitance, low internal resistance as well as improved cycling stability and rate capability. Of the three, the GNS/PANI composite shows better performance than CB/PANI and CNT/PANI. This can be attributed to the following three characteristics of GNSs as the PANI support: (a) the two-dimensional planar structure is beneficial to homogeneous nucleation of a large amount of PANI on their surface, giving more active sites for the redox reaction; (b) the planar contact between GNSs and PANI is good for constructing a conductive network with a high electron transfer rate and a low resistance and (c) the layer-by-layer stacks of crumpled GNSs and PANI layers prevent the peeling of PANI from the graphene surface. As a consequence the material can tolerate severe volume changes, swelling and shrinkage of PANI, during charge/discharge.

The electrochemical properties of templated and activated mesoporous carbons produced from coal pitch

ZHOU Ying, SONG Xiao-na, SHU Cheng, QIU Jie-shan

2011, 26(3): 187-191.

Abstract(2186)

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Mesoporous carbons (MCs) were made from coal pitch derived from coal liquefaction residue with silica nanoparticles as template and CO₂ as activation agent. The microstructure and electrochemical properties of the MCs were investigated with TEM, N₂ adsorption, an electrochemical workstation and a Land battery test system. Results show that the specific surface area increases with activation time at 900℃ under a CO₂ flow rate of 100mL · min^-1. The specific surface area of MC activated for 150min is 1360m² · g^-1 while that of the un-activated one is 722m² · g^-1. The specific capacitance of the MC activated for 150min is 135F · g^-1 at a current density of 1000mA · g^-1 and the decrease in its specific capacitance is 7% after being charged and discharged 10000 times.

The effect of the microstructure of mesophase-pitch-based activated carbons on their electrochemical performance for electric double layer capacitors

LI Bao-hua, WANG Guan, ZHAI Deng-yun, DU Hong-da|　KANG Fei-yu

2011, 26(3): 192-196.

Abstract(2554)

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Activated carbons (ACs) prepared from mesophase pitch and carbonized mesophase pitch by KOH activation were used to fabricate electrodes for electric double layer capacitors. Nitrogen adsorption at 77K was used to characterize the specific surface area and pore structure of the ACs, which showed a bimodal pore size distribution. The performance of the ACs in an organic electrolyte (1mol/L of Et₄NBF₄ in propylene carbonate) was investigated with voltage sweep cyclic voltammetry and constant current charge-discharge cycling. Results show that the capacitance of the ACs not only depends on the surface area and pore size distribution, but also on carbonization treatment. SEM images show that the AC particles from carbonized pitch are formed by stacking of layered slices, which favors an infiltration of solvent into the inner surface of the carbon and improves the capacitance per unit area of micropores.

A comparative study of nitrogen-doped hierarchical porous carbon monoliths as electrodes for supercapacitors

HAO Guang-ping, MI Juan, LI Duo, QU Wen-hui, WU Ting-jun, LI Wen-cui, LU An-hui

2011, 26(3): 192-196. doi: 10.1016/S1872-5805(11)60076-0

Abstract(3651)

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Two nitrogen-doped carbon monoliths with hierarchical porosity over a large size range were prepared by polymerization of resorcinol and formaldehyde in the presence of an organic amine, L-lysine, and an inorganic base, ammonium hydroxide under ambient conditions. Their physical and chemical features were characterized by N₂ sorption, transmission and scanning electron microscopy, and elemental analysis. Their electrochemical properties as the electrodes of supercapacitors were evaluated under both a three-electrode system and a two-electrode system. Results show that the two types of nitrogen-doped carbon possess similar pore structures, but have distinct electrochemical performances. The L-lysine incorporated carbon monolith has a high nitrogen content, a high specific capacitance of 199F · g^-1, and a 1.6% loss in the specific capacitance after 1000 charge-discharge cycles, indicating a long-term cycling stability.

The influence of nitric acid oxidation on the electrochemical performance of asphaltene-based ordered mesoporous carbon

WANG Liu-ping, ZHOU Ying, QIU Jie-shan

2011, 26(3): 204-210.

Abstract(1956)

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Asphaltene-based ordered mesoporous carbon (OMC) was oxidized with 5mol/L nitric acid at 40-100℃. The influence of nitric acid oxidation treatment on its textural properties and electrochemical performance as a supercapacitor electrode material was investigated and the ionic transport behavior in relation to surface chemical structure was discussed. The pore structures and electrochemical performance were examined using XRD, nitrogen adsorption and an electrochemical workstation. Results indicate that electrochemical performance can be improved with nitric acid treatment under mild conditions. The regular mesostructure can be retained, and the surface areas and pore volumes vary slightly when oxidation temperature is below 60℃. A capacitor assembled with the OMC sample oxidized at 60℃ exhibits excellent electric double layer behavior, improved frequency response characteristics and a fast charge-discharge rate with a time constant of 6s. The gravimetric specific capacitance and energy density of OMC oxidized at 60℃ are 138F · g^-1 and 3.9Wh · kg^-1 respectively at a scanning rate of 5mV · s^-1. These values are respectively 57% and 63% greater than for the un-treated one.

Preparation and electrochemical properties of boron-doped mesoporous carbons

ZHAI Xiao-ling, SONG Yan, ZHI Lin-jie, SHI Jing-li, GUO Quan-gui

2011, 26(3): 211-216.

Abstract(2283)

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Boron-doped mesoporous carbons were prepared by an evaporation-induced self-assembly method using boric acid-modified phenol-formaldehyde resin as carbon precursor. The samples were characterized by nitrogen adsorption, small angle X-ray scattering and transmission electron microscopy. Their electrochemical properties were tested by a three-electrode system. The influence of the boron content on the pore structure and electrochemical properties is discussed. Results show that the pore diameter of the mesoporous carbons decreased and the degree of pore order decreased with the increasing boron content. When the boron mass fraction was 0.3%, the specific capacitance per unit area of the sample reached 0.51F · m^-2 at a current density of 75mA · g^-1, which was 1.9 times that of the undoped one and its ordered pore structure was retained.

Properties of polyaniline/ordered mesoporous carbon composites as electrodes for supercapacitors

LIU Wen-xiao, LIU Na, SONG Huai-he, CHEN Xiao-hong

2011, 26(3): 217-223. doi: 10.1016/S1872-5805(11)60077-2

Abstract(2017)

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Polyaniline (PANI)/ordered mesoporous carbon (OMC) composites were prepared by in situ polymerization of aniline. The effects of PANI loading on the electrochemical properties were tested by galvanostatic charge/discharge, cyclic voltammetry, and AC impedance. It was found that the composites showed higher specific capacitances than pure OMC or PANI. They also had good charge-discharge cycling stability. The capacitance of the composite containing 60% PANI could reach 409F · g^-1 at a current density of 0.1A · g^-1.

The effect of carbonyl, carboxyl and hydroxyl groups on the capacitance of carbon nanotubes

LI Li-xiang, LI Feng

2011, 26(3): 224-228. doi: 10.1016/S1872-5805(11)60078-4

Abstract(2336)

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Concentrated H₂SO₄∶HNO₃ mixed acids, air, nitric acid and potassium permanganate were used to oxidize carbon nanotubes (CNTs) to introduce surface functional groups (SFGs) and the effects of the type and amount of SFGs on the electrochemical properties of CNT supercapacitors were investigated. XPS analysis shows that the mixed acid oxidation produces carbonyl (C=O) and the carboxyl (O-C=O) groups, the air oxidation results in hydroxyl and the smallest amount of carbonyl and carboxyl groups, and both the nitric acid and potassium permanganate treatments result in a moderate amount of carbonyl and carboxyl groups. It was found that the specific surface area and pore structures of the four samples are similar and carbonyl and carboxyl groups contribute the most to pseudo-capacitance through a Faradic reaction. In particular, the carbonyl group has a proportional relationship to the capacitance of CNTs. However, the hydroxyl group does not lead to an obvious increase of pseudo-capacitance, but can increase the electric double layer capacitance. The carbonyl and the carboxyl groups are advantageous for fast Faradic reactions to introduce pseudo-capacitance, owing to their lower charge transfer resistance than that of the hydroxyl group.

The electrocatalytic properties of (Pt/Sn)-CNT hybrids

YAN Xue-jie, CHANG Dong-jun, LI Zhi-hui, WANG Yan, WANG Xiao-min

2011, 26(3): 229-236.

Abstract(2057)

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(Pt/Sn)-CNT hybrids with different Pt/Sn atom ratios were prepared by impregnation using a mixed solution of chloroplatinic acid and stannous chloride using carbon nanotubes (CNTs) as the supporting material, and ethylene glycol and sodium formate as reducing agents. X-ray diffraction and transmission electron microscopy were used to characterize the microstructure of the materials and showed that Pt, Sn particles were highly dispersed on CNTs with a particle size range between 3.5-6.5nm. Sn existed both in a Pt-Sn alloy and also as SnO₂. Cyclic voltammetry analysis indicated that the atomic ratios of Pt/Sn in the materials with the best electro-catalytic activity and anti-toxic abilities were between 2.5∶1 and 3.5∶1. CNTs helped improve the electrocatalytic activity for methanol oxidation.

Preparation of mesoporous carbon microsphere/activated carbon composite for electric double-layer capacitors

TANG Li, ZHAN Liang, YANG Guang-zhi, YANG Jun-he, WANG Yan-li, QIAO Wen-min

2011, 26(3): 237-240. doi: 10.1016/S1872-5805(11)60079-6

Abstract(1837)

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Mesoporous carbon microspheres (MCMs) with specific surface area and diameter of 1850m²/g and 1μm, respectively, were synthesized using the solvothermal method. When mass fraction 20% of these were added to a high surface area-activated carbon (HSAC: 3200m²/g) its interfacial resistance and ion diffusion resistance decreased significantly. The specific capacitance of the composite electrode is 230F/g in 6mol/L KOH electrolyte, whereas those of pure HSAC and MCMs are only 190 and 148F/g, respectively, at a high current density of 12A/g. The improvement in electrochemical performance of the HSAC electrode at high current densities is attributed to the small particle diameter, mesoporous structure and high specific surface area of the added MCMs.

2011 Vol. 26, No. 3

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