The delithiated samples obtained by chemically extracting lithium from a series of O3 type layered (1 2 z) Li[Li 1/3 Mn 2/3 ]O 2 ?(z) Li[Co 12y Ni y ]O 2 solid solution samples by reacting with the oxidizer NO 2 BF 4 in acetonitrile medium have been chemically and structurally characterized. The oxygen loss in the delithiated samples has been found to be determined by the amount of lithium in the transition metal layer of the O3 type layered structure. However, high Mn 4+ content in the samples causes a decrease in oxygen loss and the lithium content in the transition metal layer is sensitively influenced by the tendency of Ni 3+ to get reduced to Ni 2+ and the consequent volatilization of lithium during synthesis. The chemically delithiated samples were found to adopt either the parent O3 type structure or the new P3 or O1 type structures depending upon the composition and synthesis temperature of the parent samples and the proton content inserted into the delithiated sample. For example, a high proton insertion resulting from a good cation ordering or a larger surface area seems to favor the transformation of the initial O3 structure to the P3 or O1 structure. However, such phase transformations were not evident in the electrochemically delithiated solid solution samples.
y ഛ 0.5͒ cathodes belonging to a solid solution series between layered Li͓Li 1/3 Mn 2/3 ͔O 2 and LiCo 1−z Ni z O 2 were synthesized at 900 and 750°C and characterized as cathode materials for lithium-ion batteries. The observed lithium content in the samples decreases with increasing Ni content due to a tendency to form Ni 2+ and volatilization of lithium during synthesis. The first charge and discharge capacities decrease with increasing Ni content. For example, the first discharge capacity drops from 269 mAh/g for the y = 0 sample to 194 mAh/g for the y = 0.5 sample. The decrease in the discharge capacity with increasing Ni content is due to a decrease in the lithium content in the transition metal layer and a consequent decrease in the amount of oxygen lost irreversibly during the first charge as indicated by a structural and chemical characterization of the chemically delithiated samples.
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