STUDIES ON MODIFICATION OF LITHIUM MANGANATE PARTICLE SURFACE FOR LITHIUM ION BATTERY WITH METAL OXIDE

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In order to remarkably improve the charge-discharge cycling characteristics at temperatures above 50ィイD1゜ィエD1C of LiMnィイD22ィエD2OィイD24ィエD2 as a positive electrodematerial of lithium ion battery, the oxide was partially modified with cobalt (III) oxide at the particle surface. The method for the modification was as follows : dispersing electrolytic manganese dioxide powder (EMD) in aqueous solution of cobalt (II) nitrate, adding sodium hydroxide solution to it to prepare the powder coated with cobalt hydroxide which was oxidized by oxygen in air, separating the powder from the solution, mixing lithium compounds and the powder at the ratio of (Mn+Co) : Li=2 : 1 and then heating the mixture at 470ィイD1゜ィエD1C for 6h, followed by further heating at 750ィイD1゜ィエD1C for 20h to prepare LiCoィイD2yィエD2MnィイD22-yィエD2OィイD24ィエD2 (y=0.04, 0.08, and 0.16). The samples obtained were confirmed to have spinel structure by XRD and a large part of cobalt (III) ions were found to exist preferentially at the powd … More er surface by EDX analysis. Small amount of the ions were thought to be in the inner part of the particles in dilute concentration due to thermal diffusion of the ions. The samples of LiCoィイD2yィエD2MnィイD22-yィエD2OィイD24ィエD2 were tested on the charge-discharge cycling characteristics at 30 and 60ィイD1゜ィエD1C. Comparison of the characteristics at 30ィイD1゜ィエD1C showed that modification yielded remarkably improved charge-discharge performance, though that of LiMnィイD22ィエD2OィイD24ィエD2 did such a performance that discharge capacity considerably decreased with charge-discharge cycling. But the characteristics at 60ィイD1゜ィエD1C showed that even the modified samples did not provide good performance. In order to change the distribution of cobalt ion in the oxides, LiCoィイD2yィエD2MnィイD22-yィエD2OィイD24ィエD2 samples were heated at 900ィイD1゜ィエD1C for 30m. The samples obtained also did not provide good performance. As a further experiment the surface of EMD was treated using ferrous ion, nickel ion and magnesium ion instead of cobalt ion, and lithium manganate powders including these ions were synthesized. As a result of examining the charge-discharge cycling characteristics of LiMィイD20ィエD2MnィイD21・84ィエD2OィイD24ィエD2 (M=Fe, Ni, Mg) at 60ィイD1゜ィエD1C LiNiィイD20・16ィエD2MnィイD21・84ィエD2OィイD24ィエD2 provided an excellent characteristics. It was found that modification of LiMnィイD22ィエD2OィイD24ィエD2 powder with nickel oxide at the particle surface remarkably improves the charge-discharge cycling characteristics at higher temperature. Less