Showing papers by "Dominique Larcher published in 1997"

Electrochemically Active LiCoO2 and LiNiO2 Made by Cationic Exchange under Hydrothermal Conditions

Abstract: The layered LiMO{sub 2} (M = Co, Ni) compounds, which are of potential interest for Li-ion batteries, were synthesized at low temperatures by treatment under hydrothermal conditions of LiOH{center_dot}H{sub 2}O aqueous solutions containing powdered H{sub x}MO{sub 2} phases. The authors studied the reaction mechanism and the influence of temperature, pressure, water dilution, and precursor ratio on the degree of progress of the ion exchange process. Single-phase LiMO{sub 2} can be obtained in 48 h at 160 C under an air pressure of 60 bars from an MOOH/LiOH{center_dot}H{sub 2}O/H{sub 2}O mixture. The degree of advancement of the exchange reaction for M = Co was monitored in situ using an autoclave which allows the withdrawal of samples in the course of the reaction. From transmission electron microscopy coupled with x-ray diffraction studies the authors conclude that the reaction occurs by surface H{sup +}/Li{sup +} exchange and is accompanied by a progressive breaking of the particles due to an interfacial collapse phenomenon. Infrared studies indicate that the LiCoO{sub 2} and LiNiO{sub 2} phases obtained are contaminated by carbonates that can more easily be eliminated in the case of LiCoO{sub 2} by water washing and post-heating treatments under primary vacuum at 200 C formore » 2 days. Once the ion-exchange parameters are controlled, the LiMO{sub 2} products exhibit electrochemical performances comparable to those of high-temperature made phases.« less

Low‐Temperature Synthesis of LiNiO2 Reaction Mechanism, Stability, and Electrochemical Properties

Abstract: A thorough study was made concerning the formation of LiNiO{sub 2} by a low-temperature ion-exchange reaction under hydrothermal conditions. LiNiO{sub 2} with a low degree of cationic mixing and good electrochemical performance was prepared either from pure {beta}-NiOOH, {gamma}-NiOOH, or a mixture of both where the {gamma} phase was the majority. The synthesized product (LT-LiNiO{sub 2}) presents electrochemical properties similar to LiNiO{sub 2} prepared by conventional powder synthesis (HT-LiNiO{sub 2}) in spite of the difference in Brunauer, Emmett, and Teller (BET) surfaces, around 20 m{sup 2}/g for LT-LiNiO{sub 2} and 0.7 m{sup 2}/g for HT-LiNiO{sub 2}. This moisture instability was found (1) to be intrinsic to LiNiO{sub 2}, since ground HT-LiNiO{sub 2} samples presented a similar behavior, (2) to be enhanced by decreasing the LiNiO{sub 2} particle size, and (3) to be much larger than that of LiCoO{sub 2}. In view of electrochemical applications, cobalt-substituted products should be used in order to ensure the stability against both reduction-delithiation and hydrolysis.

A PROCESS FOR SYNTHESIZING LixMnyO4 INTERCALATION COMPOUNDS

Abstract: A novel process for making LixMnyO4 intercalation compounds, wherein 0∫x≤2 and 1.7≤y≤2, comprises the steps of: 1) synthesizing a lithiated manganese oxide precursor by reacting lithium hydroxide, manganese dioxide, and one or more polyhydric alcohols; and 2) heat-treating the lithiated manganese oxide precursor. The intercalation compounds are effectively employed as active components of positive electrodes in rechargeable lithiated intercalation battery cells.