Tomiya Kishi

Structural properties of Li1+xV3O8 upon lithium insertion at ambient and high temperature

Abstract Lithium insertion behaviour of lithium vanadate, Li 1.2 V 3 O 8 , was investigated using both chemical and electrochemical methods at ambient and high temperature of 100°C. Additional Li + ions up to Li 4 V 3 O 8 were accommodated under 2.5 V at 100°C. Each of the cell parameters changed linearly in the single-phase region of x 1+ x V 3 O 8 . A constant value was observed in the two-phase region of 2.0 x x >3.2 lead to an increase in cell volume of the host structure.

Electrochemical Behavior of Silver in 1-Ethyl-3-methylimidazolium Tetrafluoroborate Molten Salt

A room-temperature molten salt, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF 4 ) with adequate purity was obtained simply by the reaction of 1-ethyl-3-methylimidazolium chloride and tetrafluoroboric acid. Silver tetrafluorohorate dissolves up to ∼0.2 mol dm 3 in EMIBF 4 at room temperature Electrochemical deposition and dissolution of silver on a platinum electrode were found possible in EMIBF 4 containing AgBF 4 . The reduction of monovalent silver species is electrochemically irreversible, the rate constant being estimated to be I × 10 -5 cm s -1 . The diffusion coefficient of Ag(I) is calculated to be 6 × 10 -7 cm 2 s -1 , suggesting that Ag(I) exists as a substantially bare cation (Ag . ) in EMIBF 4 .

Lithium insertion and extraction kinetics of Li1 +xV3O8

Abstract Lithium insertion and extraction kinetics of lithium trivanadate, Li1+xV3O8, was investigated by using the electrochemical measurements at various temperatures and current densities. The results showed that the reaction rates of both insertion and extraction were limited by the small diffusivity of Li+ ions in the Li4V3O8 phase formed for x>1.5 upon lithiation. Extraction reaction was also dependent on the thermodynamic factor on the basis of the incomplete reversibility of transformation from the Li4V3O8 phase to the original LiV3O8 one.

Preparation and lithium insertion behaviour of oxygen-deficient Li1+xV3O8-δ

Abstract Oxygen deficient Li 1 + x V 3 O 8 − δ (0.03 δ 1 + x V 3 O 8 with carbon. From infrared spectroscopic (IR) studies, it is found that specific oxygen is removed from the host lattice. Electrochemical measurement reveals that more lithium is inserted in Li 1 + x V 3 O 8 − δ compared with original Li 1 + x V 3 O 8 contrary to a decrease in pentavalent vanadium V(V) by the introduction of oxygen defects. This is probably due to the formation of new sites available for the occupation of Li + ions. During the oxidation process by charging of Li 1 + x V 3 O 8 − δ containing V(IV), Li + ions are extracted from the octahedral sites and inserted at the initial stage of discharge process. These effects result in an increase in the total amount of inserted lithium.

Lithium insertion behaviour of Li1+xV3O8 with different degrees of crystallinity

Lithium insertion behaviour of amorphous Li 1+x V 3 O 8 was compared with that of poorly crystalline and highly crystalline LiV 3 O 8 . This oxide retained the amorphous state during discharge and charge cycle and exhibited electrochemical performance inferior to the crystalline one, i.e., smaller discharge capacity and lower cycle efficiency. The crystallinity of the crystalline Li 1+x V 3 O 8 was one of the primary factors determining the rate of lithium insertion reaction.

Electrochemical insertion of magnesium to Mg0.5Ti2(PO4)3

Abstract Mg0.5Ti2(PO4)3 having NASICON-lattice was prepared by sol–gel method and evaluated as a cathode material for magnesium cells. The crystalline phase could be successfully obtained after heating at 600°C. Electrochemical magnesium insertion from a propylene carbonate solution into this host was found possible and one Mg2+ ion could be accommodated per unit formula. However, the magnesium insertion process was under kinetic control of Mg2+ diffusion due to the low mobility of Mg2+ in this host.

Lithium insertion behaviour of manganese or molybdenum substituted Li1 + xV3O8

Mn(IV) or Mo(VI) substituted single-phase compounds having a nominal composition Li1 + yMnyV3 − yO8 (0 < y < 0.1) and LiMoyV3 − yO8 (0 < y < 0.3), respectively, have been obtained by solid-state reaction. Electrochemical measurements revealed different influences of substitution on the lithium insertion behaviours. While substitution of V(V) with Mn(IV) and introduction of Li(I) into the interlayer decrease the insertion limit of lithium, substitution of V(V) with Mo(VI) shows a featureless discharge curve without changing the insertion limit. The ionic sites available for Li+ occupation between the layers rather than the electronic sites offered by V(V) are considered to determine the insertion limits of lithium into Li1 + xV3O8.

Lithium insertion into Li4V3O8

Abstract The lithium insertion characteristics of lithium vanadate, Li 4 V 3 O 8 , were investigated using LiV 3 O 8 prepared by the precipitation technique as the starting material. The Li 4 V 3 O 8 phase was formed by lithiation over x =1.5 in Li 1+ x V 3 O 8 , and the diffusion of lithium in this phase determined the reaction rate of insertion more than x =1.5. Improvement of insertion kinetics in the Li 4 V 3 O 8 phase extended the lithium insertion limit from x =3.2 to x =4.0, compared with the case of LiV 3 O 8 by conventional high temperature synthesis. Lithium insertion proceeds as the single-phase reaction in the range of 3.2 x

Lithium insertion behaviour of Li1+xV3O8 prepared by precipitation technique in CH3OH

Abstract Li 1+ x V 3 O 8 (LT-M sample) was obtained by the sol-gel method in CH 3 OH. This sample, prepared at 350°C, possessed a smaller grain size and better electrochemical performance than the HT sample prepared by conventional high temperature synthesis. High discharge capacity (372 mAh g −1 : x =4.0) and reversible discharge and charge cycles were attained owing to improvement of insertion and extraction kinetics. When heated at 200°C, CH 3 OH molecules remained in the compound and crystallinity became lower by lithium insertion over x =2.0. The lithium deintercalation was irreversible.

Effect of crystallinity on lithium insertion behaviour of Na1+xV3O8

Abstract The amorphous sodium vanadate, Na 1+ x V 3 O 8 was prepared by quenching of the melt and its lithium insertion behaviour was compared with those of poorly crystalline and highly crystalline ones. The experimental results showed that the crystallinity of Na 1+ x V 3 O 8 determined the role of sodium on moving of lithium upon lithiation and the flexibility of adjacent units in the crystalline host lattice.