Kazuo Tanno

Structural changes of Nb2O5 and V2O5 as rechargeable cathodes for lithium battery

Abstract The structural changes of T-Nb2O5 and V2O5 cathodes with discharge and recharge were investigated by X-ray photoelectron spectroscopy (ESCA) and X-ray diffractometory etc. ESCA spectra of the discharge products shows that M5+ is reduced to a lower valence state such as M4+ on the discharge, and the chemical bond between Li+ inserted into the oxide and O2− of the oxide exhibits a higher ionic character than that of Li2O. X-ray diffraction measurement shows that T-Nb2O5 gives the reversible structural change accompanying the disorder and order of the atomic arrangement on the charge-discharge cycling. On the other hand, V2O5 takes two discharge steps, within the 1st step of which it gives the reversible lattice change along b-axis caused by the intercalation of Li+ into the oxide layer, whereas within the 2nd step it is considered that the reaction in the charge-discharge takes place in the vicinity of the surface of the oxide particle. In both oxides, ternary phases such as LixM2O5 are produced as discharge products, where x is at least 2 for Nb2O5 and x is at least 3 for V2O5.

Electrochemical characteristics and structural changes of molybdenum trioxide hydrates as cathode materials for lithium batteries

Several characteristics of MoO3·2H2O and MoO3·H2O, such as thermal behaviour and conductivity and the electrochemical behaviour and structural changes associated with discharge and charge have been investigated. The suitability of these substances as new cathode materials for non-aqueous lithium batteries has been assessed. MoO3·H2O, having only one coordinated water molecule, showed a discharge capacity of about 400 Ah kg−1 of acid weight and a discharge potential around 2.5 V vs Li/Li+. This capacity was much higher than the 280 Ah kg−1 of anhydrous MoO3.MoO3·H2O showed good charge-discharge cyclic behaviour at a capacity below l e−/Mo while keeping the original layered lattice on cycling. In addition, the crystal system of MoO3·H2O was found to be changed from a monoclinic system to orthorhombic with lattice parameters ofa=0.5285 nm,b=1.0824 nm,c=0.5237 nm on discharge to 0.5 e−/Mo.

Physical and electrochemical characterization of quaternary Li-Mn-V-O spinel as positive materials for rechargeable lithium batteries

Quaternary Li-Mn-V-O spinels formed from heating mixtures of LiNO{sub 3}, MnCO{sub 3}, and NH{sub 4}VO{sub 3} around 350{degree} have been characterized by electrochemical measurement, X-ray photoelectron spectroscopy, X-ray diffractometry, {sup 7}Li-NMR, and magnetic susceptibility measurements. These results were compared with those for ternary Li-Mn-O spinels prepared at 350 and 850 C. The compositions of the quaternary and ternary spinels formed at 350 C were shown to be x(Li{sub 2}O)Mn{sub 2}O{sub 4} {center_dot} yV{sub 2}O{sub 5} (x = 0.5 {approximately} 1, y = 0 {approximately} 0.4). The cubic a{sub 0}-lattice parameter and specific density of the quaternary spinels increased with increasing vanadium content in the spinel structure. The {sup 7}Li-NMR measurements revealed that the quaternary spinels did not show any Knight shift, while the ternary Li-Mn-O spinels formed at 350 and 850 C had a large Knight shift of 490 {approximately} 535 ppm in reference to LiCl. Furthermore, the measurement of the magnetic susceptibility indicated that the ternary and quaternary spinels formed at 350 C are paramagnetic and the ternary LiMn{sub 2}O{sub 4} prepared at 850 C is antiferromagnetic.

Electrochemical and structural characteristics of niobium(V) oxide in a rechargeable lithium battery

Abstract The discharge behaviour of T-Nb 2 O 5 in various electrolytes is unaffected by the choice of solvent, but is strongly dependent on the crystal radius of the solute cation species. Thermodynamic and structural studies show that this is due to the insertion of unsolvated Li + ions into the crystal lattice. The graphite content of the Nb 2 O 5 electrode has a marked influence on the cycling behaviour on account of the decrease in the oxide conductivity with discharge. Furthermore, the chemical diffusion coefficient of Li + ions in Nb 2 O 5 is about 10 −10 cm 2 s −1 , which is one order of magnitude smaller than that in V 2 O 5 with a layered structure.

The effect of permeated hydrogen on the pitting of type 304 stainless steel

The effect of permeated hydrogen on the pitting behavior of type 304 stainless steel was investigated using a Devanathan type cell. One side of the stainless steel sheet was galvanostatically charged with hydrogen, while the other side was subjected to pitting tests. The permeated hydrogen typically enhanced the pitting susceptibility of the stainless steel; the pitting potential during potentiodynamic polarization became less noble and the induction period for pitting became shorter. However, the permeated hydrogen did not change the critical pitting potential determined potentiostatically. The effect of permeated hydrogen on the pitting potential and the induction period diminished after hydrogen charging was stopped. Analysis by X-ray photoelectron spectroscopy showed that the cationic fraction of chromium in a hydrogen-charged passive film was lower than that in an uncharged film. Thus, the permeated hydrogen is thought to suppress the aging process of the passive film with respect to enrichment of chromium.

The corrosion inhibition of carbon steel in lithium bromide solution by hydroxide and molybdate at moderate temperatures

The corrosion inhibition of carbon steel by OH− and MoO42− was studied in LiBr solutions of 1–23 m (mol kg−1-H2O) at 120 and 160°C. Both inhibitors were effective in reducing corrosion, but pitting was likely to occur in the LiBr solutions of low and intermediate concentrations. In the highly concentrated solutions only simultaneous use of OH− and MoO42− was effective for passivation, otherwise heavy general corrosion was observed. Passive films were always composed of magnetite. The depth profiles of the films were analyzed by XPS, a.c. impedance and corrosion potential were monitored under some conditions. The results are discussed in terms of competitive actions between Br− and OH− in several processes such as adsorption, formation of complex ions, acceleration of breakdown and the formation of passive films.

Electrochemical and structural characteristics of molybdic acid as a new cathode material for nonaqueous lithium batteries

Abstract Some characteristics of molybdic acid, prepared by acidification of an ammonium molybdate solution, and its heated products were examined by chemical and thermal analyses, X-ray diffractometry and scanning electron microscopy. The compositions of the acid as prepared and the products formed on heating up to 350°C were shown as x {(NH 4 ) 2 }O·MoO 3 · y (H 2 O) ( x = 0.075∼0.042, y = 0.400∼0.043). Discharge and charge-discharge cyclic characteristics of the acid cathodes were examined in an electrolytic solution of 1 M LiClO 4 -propylene carbonate at 25°C. The acid cathodes showed a discharge capacity of 390 ∼ 460 Ah/Kg of acid weight and a discharge potential around 2 V vs Li/Li + at a current density of 0.2 mA cm −2 . The capacities obtained were approximately double that of anhydrous MoO 3 . On the charge-discharge cyclings at 0.5 mA cm −2 , however, the discharge capacities of the acids decreased considerably as the cycling number increased 10–30 times. Furthermore, the discharge mechanism of the acid cathode was examined from X-ray diffraction and ir spectrum results. These results revealed that a discharge product shown as Li n {(NH 4 ) 2 O} x ·MoO 3 ·(H 2 O) y , where n may be a constant value of 3, is formed.

The corrosion of carbon steel in lithium bromide solution at moderate temperatures

Abstract The corrosion of carbon steel was studied in various LiBr solutions of 1–25 m (mol kg−1-H2O) at 100–160°C in relation to absorption refrigeration and heat pump systems. Increase in temperature suppressed corrosion slightly in 2 m solution, whereas it promoted corrosion in 23 m solution. The increase in LiBr concentration decreased corrosion slightly at 100°C, while it accelerated it at 160°C. Mixed behaviour was observed in intermediate conditions of temperature and concentration. The corrosion morphology was general. Magnetite particles adhered on the surface. These complicated features of the corrosion process are described in relation to the properties of the solution, such as the activities of the bromide ion and water, the viscosity of the solution, as well as the adhered corrosion products.

Synthesis of hexagonal form of tungsten trioxide and electrochemical lithium insertion into the trioxide

Abstract The tungsten trioxide hydrate, WO 3 · y H 2 O ( y = 0.8−1.1) with the hexagonal tungsten bronze (HTB) structure has been prepared by acidification of lithium tungstate solution with strong acid at a concentration of 0.5–1 M and at a temperature of 100 °C. On the other hand, hydrothermal synthesis of an acidified lithium tungstate solution at temperatures of 150–200 °C leads to the formation of x Li 2 O · WO 3 · y H 2 O ( x = 0.25−0.30, y = 0.6−0.8) having the HTB structure. The dehydration of WO 3 · y H 2 O and x Li 2 O · WO 3 · y H 2 O around 350 °C leads to the dehydrated trioxides, hexagonal WO 3 and x Li 2 O · WO 3 with the HTB structure, respectively. The tungsten trioxides prepared have been characterized by X-ray diffractometry, thermogravimetric analysis and electrochemical method. The cyclic voltammetric and galvanostatic measurements revealed that a reversible lithium intercalation into the crystal lattice of hexagonal WO 3 takes place with charge-discharge cycling.

Intercalation of lithium in r.f.-sputtered niobium oxide film as electrode material for lithium-ion batteries

Vanadium oxide films were prepared by r.f.-sputtering using an argon sputter gas and a V2O5 target. The films were characterized by scanning electron microscopy, atomic force microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and electrochemical techniques. The oxide film as deposited is amorphous; they are heat-treated in the range 300–700°C in oxygen atmosphere and are composed of orthorhombic V2O5 crystals. At higher heat-treatment temperatures (600–700°C) the crystallization of the oxide proceeded significantly with ab-direction parallel to the substrate. The oxide film undergoes a reversible lithium intercalation and deintercalation process. The kinetics of the intercalation process of lithium into amorphous V2O5 film was studied using an a.c. impedance method. Furthermore, a rocking-chair type V2O5 film/LixV2O5 film cell could be charge–discharge cycled over 300 times at a current of 10μA at 25°C.