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  • Author or Editor: M. Wakihara x
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Abstract  

The enthalpy of formation for LiMyMn2–yO4 (M=Co, Cr, Li, Mg, Ni) was measured by a Tian-Calvet type high temperature isothermal microcalorimeter. The standard enthalpy of formation for LiMn2O4 at 876 K was evaluated to be H f 0=–1404.2±6.4 kJ mol–1. The partial substitution of Co and Ni for Mn decreased the absolute H f 0 value, while that of Cr and Mg for Mn increased the absolute H f 0 value. In the case of the partial substitution of Li for Mn, no marked change in H f 0 could be observed.

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The phase diagram of the La-S-O system at 1073 K was established with the vacuum seal technique. Six phases exist at this temperature: La2O3 (B-type), LaS2, La2S3, La2O2SO4, La2O2S and La2O2S2. The thermodynamic functions for the reaction La2O2SO4=La2O3+SO2+1/2 O2 were determined by using the emf method at temperatures from 1123 to 1373 K. The mechanisms of the oxidation reactions in the La-S-O system under different partial pressures of oxygen (−4.4 < log <−0.7) were also investigated by means of DTA, TG and powder X-ray diffractometry.

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Enthalpy increment HT-H289K measurements have been made on iron Chevrel phase sulphide Fe2Mo6S7.8, in the temperature range 300 to 500 K by the drop method using a hightemperature Calvet-type twin calorimeter. The first-order phase transition of this sulphide from a triclinic (low-temperature phase) to a rhombohedral (high-temperature phase) occurred at 375 K, and the enthalpy was evaluated to be 6.0 kJ/mol. The heat capacities of iron Chevrel phase sulphide Fe2Mo6S7.8 were also calculated before and after the phase transition.

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Journal of Thermal Analysis and Calorimetry
Authors: M. Tachibana, T. Tojo, H. Kawaji, T. Atake, N. Morita, H. Ikuta, Y. Uchimoto, and M. Wakihara

Abstract  

Heat capacity of spinel LiCr1/6Mn11/6O4-d (d=0, 0.0184)was measured between 5 and 300 K. Both compounds showed no anomaly in the measured temperature range, especially around the room temperature where a structural phase transition is reported for the parent compound LiMn2O4. The non-stoichiometric compound LiCr1/6Mn11/6O3.9816 has greater heat capacity than that of the stoichiometric LiCr1/6Mn11/6O4. Molecular dynamics study on the vibrational property of LiMn2O4-d revealed that the lattice defects in the non-stoichiometric compound increase the low frequency phonons compared with the stoichiometric compound. It should be related to the greater heat capacity of the non-stoichiometric compound LiCr1/6Mn11/6O3.9816.

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Abstract  

We have focused on the poly(ethylene glycol) (PEG)-borate ester as a new type plasticizer for solid polymer electrolyte for lithium ion secondary battery. Adding the PEG-borate ester into the electrolyte shows the increase in the ionic conductivity of the polymer electrolyte. By measuring the glass-transition temperature of the polymer electrolytes with DSC, it is found that the increase in ionic conductivity of the polymer electrolyte is due to the increase in ionic mobility. By investigating the temperature dependence of the ionic conductivity of the polymer electrolytes using William-Landel-Ferry type equation, we considered that the PEG-borate ester does not have any influence for dissociation of Li-salt.

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