Takashi Uchida

High ionic conductivity in lithium lanthanum titanate

It has been discovered that the polycrystalline lithium lanthanum titanate Li0.34(1)La0.51(1)TiO2.94(2) shows high ionic conductivity more than 2 × 10−5 S cm−1 (D.C. method) at room temperature, which is compared with that of Li3.5V0.5Ge0.5O4. This compound has cubic perovskite structure whose cell parameter is 3.8710(2) A. By a.c. impedance analysis, the equivalent circuit of the sample could be divided into two parts; bulk crystal and grain boundary. The ionic conductivity of the bulk part is as high as 1 × 10−3 S cm−1 at room temperature. Such a high conductivity is considered to be attributed to the presence of a lot of equivalent sites for lithium ion to occupy and freely move in this perovskite. In addition, this compound is easy to react with lithium metal and the electronic conductivity has become much higher than before being in contact with Li. It can be explained that titanium ion was reduced by ii insertion into a vacant site and then an electron carrier was introduced.

The Spinel Phases LiM y Mn2 − y O 4 (M = Co, Cr, Ni) as the Cathode for Rechargeable Lithium Batteries

To improve the cycle performance of spinel LiMn 2 O 4 as the cathode of 4 V class lithium secondary batteries, the quaternary spinel phases LiM y Mn 2-y O 4 (M = Co, Cr, Ni ; y = 1/12, 1/9, 1/6, 1/3) were prepared at 750°C in air. X-ray diffraction and electrochemical studies were carried out using the Li/Li x M y Mn 2-y O 4 cells. These cathodes were more tolerant to repeated lithium extraction and insertion than a standard LiMn 2 O 4 spinel electrode in spite of a small reduction in the initial capacity. Considering both cycle life and capacity density, LiCo 1/6 Mn 11/6 O 4 showed good cycle performance with an energy density of 370 Wh kg at the 300th cycle. The improvement in cycling performance is attributed to the stabilization in the spinel structure by the doped metal cations.

The spinel phases LiM{sub y}Mn{sub 2{minus}y}O{sub 4} (M = Co, Cr, Ni) as the cathode for rechargeable lithium batteries

To improve the cycle performance of spinel LiMn 2 O 4 as the cathode of 4 V class lithium secondary batteries, the quaternary spinel phases LiM y Mn 2-y O 4 (M = Co, Cr, Ni ; y = 1/12, 1/9, 1/6, 1/3) were prepared at 750°C in air. X-ray diffraction and electrochemical studies were carried out using the Li/Li x M y Mn 2-y O 4 cells. These cathodes were more tolerant to repeated lithium extraction and insertion than a standard LiMn 2 O 4 spinel electrode in spite of a small reduction in the initial capacity. Considering both cycle life and capacity density, LiCo 1/6 Mn 11/6 O 4 showed good cycle performance with an energy density of 370 Wh kg at the 300th cycle. The improvement in cycling performance is attributed to the stabilization in the spinel structure by the doped metal cations.

The spinel phases LiAlyMn2−yO4 (y=0, 1/12, 1/9, 1/6, 1/3) and Li(Al,M)1/6Mn11/6O4 (M=Cr, Co) as the cathode for rechargeable lithium batteries

In order to improve the cycle performance of LiMn2O4, the spinel phases LiAlyMn2−yO4 (y=0, 1/12, 1/9, 1/6, 1/3) and Li(Al,M)1/6Mn11/6O4 (M=Cr, Co) were prepared at 650°C for 24 h in air. By substituting, the cycle performance was improved at the expense of an initial capacity. For LiAl1/12Cr1/12Mn11/6O4, the capacity of the cell maintained 90% of the initial capacity at the 200th cycle. By substituting, the chemical diffusion coefficient of lithium ion in the cathodes increased by one order of magnitude comparing with that of parent LiMn2O4. The phase transition due to the Jahn–Teller distortion caused by Mn3+ was suppressed in these partially substituted spinels.

Amorphous MoS2 as the cathode of lithium secondary batteries

Amorphous MoS2(a-MoS2) was synthesized by the thermal decomposition of (NH4)2MoS4 in a hydrogen gas flow at temperatures from 150 to 300 °C. The a-MoS2 synthesized at 150 and 200 °C were almost amorphous. However, those prepared at 250 and 300 °C showed very small and broad peaks in powder X-ray diffraction patterns. Discharge/charge cycling measurements, revealed that the sample prepared at 150 °C showed the highest cycle capacity (100 Ah/kg) at the 100th cycle. The chemical diffusion coefficients of lithium were also highest for a-MoS2 prepared at 150 °C, and the D values fell in the range of −10

Chemical Diffusion Coefficient of Lithium in Carbon Fiber

In order to obtain safer and more reversible negative electrodes for lithium secondary batteries, intensive research on various carbon materials, such as pyrolytic carbon, polyacrylonitrile- (PAN) based carbon, petroleum coke-based carbon, pitch-based carbon, etc., has been carried out in recent years. Electrochemical investigations on coal pitch-based carbon fiber (heat-treated at 2,800 C) were carried out. The open-circuit voltages of the Li{vert_bar}Li{sub x}C{sub 6} cell were lower than 0.15 V vs. Li/Li{sup +} in the range of 0.15 0.2.«xa0less

Chemical diffusion coefficients of lithium in LiMyMn2 − yO4 (M = Co and Cr)

Chemical diffusion coefficients of lithium ions for LiMn2O4 and LiMyMn2 − yO4 (M = Co and Cr) were measured using the current pulse relaxation technique at room temperature. The D values for LiMn2O4 were between 10−9 and 10−10 cm2 · s−1, while those for LiMyMn2 − yO4 were at least one order of magnitude larger than those of the original LiMn2O4. An order-disorder phase transition near x = 0.5 for LixMyMn2 − yO4 seems to accelerate the diffusion of lithium ions in the spinel structure.

A new method of sulfur vapor pressure control and its application to the V-S system

A new apparatus for obtaining partial pressure of sulfur was devised by using liquid sulfur and carrier gas of nitrogen. This successfully works in the range of ∼10−4 to ∼1 atm of Ps2 at any temperature higher than about 400°C up to about 1000°C. As an application of it, the equilibrium study of V-S system was done at 800°C. Two phases V3S4 and V5S8, each having homogeneity range, were found while no existence of the V2S3 phase could be detected thermodynamically and X-ray crystallogrpahically at this temperature. The standard free energy of following reaction, VS43 + 215S2 = VS85, was calculated by considering the transition-Ps2 and the activities aVS85 and aVS43 · ΔG° (1073K) = −1150 cal·mole−1was obtained with an estimated uncertainty of ± 100 cal to the above reaction.

A rechargeable lithium battery employing iron Chevrel phase compound (Fe1.25Mo6S7.8 as the cathode

Abstract Powder of iron Chevrel phase compound (Fe 1.25 Mo 6 S 7.8 ) was used as the cathode for lithium secondary battery. 1 M LiClO 4 in PC was used as an electrolyte. The discharge and discharge—charge cycling properties were measured galvanostatically at a constant current density from 7.5 μA cm −2 to 0.7 mA cm −2 . A theoretical energy density of 217 W h kg −1 (only the weight of the cathode and incorporated lithium was considered for the estimation) was obtained at the first discharge when C.D. was fixed at 0.3 mA cm −2 (cut-off 1.0 V). A good rechargeability of more than 1100 times was observed in the case of relatively shallow discharge—charge experiment. Lattice expansion with intercalation of lithium ions in the iron Chevrel phase compound was less than that in copper Chevrel phase compounds which had been investigated previously.

Phase relationship on Mo-S system at high temperatures

Abstract Changing the partial pressure of sulfur Ps 2 at temperatures of 750° and 950°C, phase equilibria on the Mo-S system by solid-gas reaction were investigated. Hexagonal 2H-MoS 2 and monoclinic Mo 2 S 3 phases were identified from the x-ray powder diffraction pattern. The 2H-MoS 2 had a slight homogeneity range, i.e. MoS 1.978 to MoS 2.0 at 950°C, MoS 1.983 to MoS 2.0 at 750°C. No remarkable variation of lattice parameters for the MoS 2 was observed. The composition of the Mo 2 S 3 phase was not stoichiometric MoS 1.5 but MoS 1.457 at 950°C. At 750°C the composition of the Mo 2 S 3 phase could not be determined since it was quite difficult to establish the equilibrium state between the gas and the condensed phases. This finding agreed well with the result of Morimoto and Kullerud.