In this critical review, metal oxides-based materials for electrochemical supercapacitor (ES) electrodes are reviewed in detail together with a brief review of carbon materials and conducting polymers. Their advantages, disadvantages, and performance in ES electrodes are discussed through extensive analysis of the literature, and new trends in material development are also reviewed. Two important future research directions are indicated and summarized, based on results published in the literature: the development of composite and nanostructured ES materials to overcome the major challenge posed by the low energy density of ES (476 references).

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A review of electrode materials for electrochemical supercapacitors

Li-ion battery materials: present and future

Herein we report on the synthesis of two-dimensional transition metal carbides and carbonitrides by immersing select MAX phase powders in hydrofluoric acid, HF. The MAX phases represent a large (>60 members) family of ternary, layered, machinable transition metal carbides, nitrides, and carbonitrides. Herein we present evidence for the exfoliation of the following MAX phases: Ti2AlC, Ta4AlC3, (Ti0.5,Nb0.5)2AlC, (V0.5,Cr0.5)3AlC2, and Ti3AlCN by the simple immersion of their powders, at room temperature, in HF of varying concentrations for times varying between 10 and 72 h followed by sonication. The removal of the “A” group layer from the MAX phases results in 2-D layers that we are labeling MXenes to denote the loss of the A element and emphasize their structural similarities with graphene. The sheet resistances of the MXenes were found to be comparable to multilayer graphene. Contact angle measurements with water on pressed MXene surfaces showed hydrophilic behavior.

Two-dimensional transition metal carbides.

Graphene oxide: preparation, functionalization, and electrochemical applications.

Capacitive energy storage is technologically attractive because of its short charging times and its ability to deliver more power than batteries. The capacitive charge-storage properties of mesoporous films of MoO3 with iso-oriented grains now lead to pseudocapacitive materials that offer increased energy density while still maintaining high power density.

Ordered mesoporous [alpha]-MoO3 with iso-oriented nanocrystalline walls for thin-film pseudocapacitors

Degradation of carbon materials by intercalation

Ba 1-x Pb x TiO 3 powder with a fixed composition was prepared by the reaction of BaTiO 3 powders with molten PbCl 2 at various PbCl 2 /BaTiO 3 molar ratios at 600° and 800°C in a nitrogen atmosphere. When 0.1 μm powder was used, the reaction was finished when x=0.9. Two phases of BaTiO 3 and a solid solution of Ba 1-x Pb x TiO 3 coexisted, but the final phase gave a solid solution of Ba 1-x Pb x TiO 3 at 800°C. When 0.5 μm powder was used, the two phases coexisted in the products at 600°C at PbCl 2 /BaTiO 3 = 1.0. A sintered compact of Ba 1-x Pb x TiO 3 powders solid solution was prepared by hot isostatic pressing, and its dielectric constant was measured in the temperature range 20°-550°C.

Molten‐Salt Synthesis of Ba1–xPbxTiO3 in the System BaTiO3–PbCl2

The electrical resistivity of carbon blacks was measured under compression (up to 9 kilobars) at room temperature using a pressure vessel of the piston-cylinder type. The slope of the logρ vs. logP relation was about −0.5 for all the carbon black specimens except the original channel black. For the thermal blacks heat-treated above 2100°C, i. e., the graphitized thermal blacks, the linear relation between logarithms of resistivity, ρ, and of pressure, P, broke at about 2.5—4.5 kilobars. After the break the slope of the logρ vs. logP relation for the graphitized thermal blacks had the same value as that for natural graphite. The original channel black had a value of the slope as high as −0.9, but the 1300°C-treated channel black had a value similar to that of the other samples. This was probably due to the removal of the high-resistance film on the particle surface by the heat treatment. The first stage of the decrease in electrical resistivity with an increase in the pressure seems to be due to the yieldi...

The Electrical Resistivity of Carbon Black under Compression

Polyimides of various chemical structures were prepared from pyromellitic dianhydride (PMDA), biphenyltetracarboxylic dianhydride (BPDA), oxydianiline (ODA), and p-phenylenediamine (PDA). The cold-drawn polyimide films were prepared and carbonized. The electrical conductivity of the carbonized films enhanced linearly with the draw ratio. The effect of cold-drawing on the electrical conductivity is more remarkable with the rigid polyimides such as PMDA/PDA and BPDA/PDA than the flexible polyimides such as PMDA/ODA and BPDA/ODA. The tendency is well in accord with the effect of cold drawing on the improvement of modulus of polyimides. With the rigid polyimides, the higher alignment of polymer chain is supposed to be achieved by the cold-drawing. © 1994 John Wiley & Sons, Inc.

Michio Inagaki

Papers

Degradation of carbon materials by intercalation

Molten‐Salt Synthesis of Ba1–xPbxTiO3 in the System BaTiO3–PbCl2

The Electrical Resistivity of Carbon Black under Compression

Carbonization of polyimide films: Effect of cold‐drawing and chemical structure

Energy dispersive X-ray analysis on supported metallic clusters generated by redox processes on graphite intercalation compounds