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

https://www.jstage.jst.go.jp/article/ieejfms1972/105/6/105_6_329/_pdf

Electrical Properties of Highly Ordered Graphite Fibers-Potassium Intercalations

The importance of the effective temperature factor in X-ray analysis was shown by presenting the results of measurement of the effective Debye parameter Be f f on some crystalline samples.Calcium fluoride precipitated from Ca (OH) 2 by HF had three times larger value of Be f f than the commercial reagent grade one.This value corresponded to the value after grinding of reagent grade CaF2 for more than 20 hrs.Rutile formed by the phase transformation from anatase with very fine grain was found to have relatively large value of Be f f at the beginning of transformation.It was shown that very large error in the quantity of the crystalline phase might be introduced from the neglect of the effective temperature factor if intensity of the diffraction line at high angle side was used.It was also shown to obtain more reliable results on the ion distribution in spinels (GeCo2O4 and CoAl2O4) by finding the one gave the best linearity between log (Iobs/Icalc) and (sin 2θ/λ2).By this revised method, the effect of the difference in the effective temperature factor from specimen to specimen on the conclusion can be neglected.

Accuracy and Effective Temperature Factor in X-ray Analysis

By the heat treatments at 1700°-2000°C under 5 kbar, the sintered graphite disks were prepared from various starting materials, such as graphitizing polyvinylchloride coke, graphitized fine powder, non-graphitizing phenol resin char and carbon beads, fluid and gilsonite cokes with onion-like texture, and the powder of PAN fibre.From the polyvinylchloride coke and PAN fibre, the disks with high degrees of graphitization and orientation were obtained. The graphitized fine powders, phenol resin char, 1000°C-pre-heated carbon beads and fine powders of fluid coke gave the sintered disks with similar values of orientation degree, which being a little lower than that of the polyvinylchloride coke. The fluid coke and gilsonite coke gave relatively low degree of orientation. The 2000°C-pre-heated carbon beads gave the disks with high degree of graphitization, very low degree of orientation and high bulk density.

Sintering and Graphitization of Various Garbons under Pressure

Summary and prospects

Charcoals were prepared under various conditions of carbonization from three kinds of plants: balsa (Ochroma lagopus Sw), giant ipil-ipil (Leucaena leucocephala (Lam.) de Wit) and mousou chiku (Phyllostachys pubescens). The pore structure of the various charcoals was observed on fractured cross-sections under SEM and was evaluated utilizing mercury porosimetry. The sorption capacity of the charcoals for A-grade heavy oil was determined by direct soaking in oil. It was found that the pore structure of the charcoals depended strongly on, not only, the precursor plants but also carbonization conditions, particularly heating rate. Balsa charcoals prepared with a heating rate of 50°C/min. under vacuum gave a relatively high sorption capacity for A-grade oil, approximately 30g/g of charcoal. The other two charcoals, derived from giant ipil-ipil and Mousou chiku, had a considerably lower capacity, approximately 1.5g/g-carbon. The dependence of pore occupancy, the ratio of volume of oil sorbed to total pore volume, on the average pore radius indicated that pores with a diameter above 1μm were largely responsible for heavy oil sorption.

https://www.jstage.jst.go.jp/article/jsms1963/53/7/53_7_818/_pdf

Michio Inagaki

Papers

Electrical Properties of Highly Ordered Graphite Fibers-Potassium Intercalations

Accuracy and Effective Temperature Factor in X-ray Analysis

Sintering and Graphitization of Various Garbons under Pressure

Summary and prospects

Effect of Preparation Condition on Pore Structure and Heavy Oil Sorption of Charcoals