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Layered LiNi 0.5 Mn 0.5-x Ti x O 2 was prepared by an emulsion drying method. Solid solution of LiNi 0.5 Mn 0.5-x Ti x O 2 (R3 hm, space group) was formed to x e 0.3, and when x > 0.3, the layered structure transformed to the simple cubic structure. Rietveld refinement of X-ray diffraction data clearly showed that a small amount of Ti doping into LiNi 0.5 Mn 0.5 O 2 structure resulted in reduced cation mixing in the Li layer, and the stronger Ti-O bond relative to the Mn-O one would stabilize the crystal structure. Consequently, charge-discharge capacity and Li + chemical diffusion of Li/LiNi 0.5 Mn 0.5-x Ti x O 2 cells were enhanced by the improvement of physical properties in the oxide matrix. For a higher level of Ti doping, the obtained capacity decreased because a large amount of electro-inactive Ti 4+ (d 0 ) depressed the conduction of electrons in the oxide. The cyclability of Li/LiNi 0.5 Mn 0.5-x Ti x O 2 (x ) 0-0.3) cells was also dependent on the amount of Ti because of a different degree of cation mixing. In situ XRD observation confirmed that the variation in c-axis was different by increasing the Ti doping amount. That is, the Ti doping resulted in a smaller variation in the c-axis, which would be ascribed to the improvement of structural integrity by the stronger bond of Ti-O in the oxide matrix, compared to the Ti-free one. The Ti-doped LiNi 0.5 Mn 0.5-x Ti x O 2 materials also have good thermal safety characteristics at a highly oxidized state, as confirmed by differential scanning calorimetry.

A wide solid solution of lithium manganese chromium oxides, LiMn x Cr 1Ϫx O 2 (0 р x р 0.6), having the layered ␣-NaFeO 2 structure, was synthesized by employing the emulsion drying method, and the Mn and Cr oxidation states of the prepared powders were identified by combination of the Rietveld analysis of the X-ray diffraction ͑XRD͒ data and X-ray absorption near edge spectroscopic ͑XANES͒ analysis. A reversible structural change of LiMn 0.6 Cr 0.4 O 2 was observed using the in situ XRD technique after the first charge. With increasing Mn contents, the reversible capacity increased due to the redox couples of Mn 3ϩ/4ϩ and Cr 3ϩ/6ϩ , as observed by the XANES spectra measured as a function of the Li contents during the first cycle. The rechargeable capacity for LiMn 0.6 Cr 0.4 O 2 was about 140 mAh g Ϫ1 between 4.3 and 2.7 V vs. Li for 30 cycles. The measured chemical diffusion coefficient for LiMn 0.6 Cr 0.4 O 2 was much higher than those for LiAl x Mn 2Ϫx O 4 and LiAl x Co 1Ϫx O 2 . This emulsion drying synthesis is an excellent powder preparation alternative method of high capacity cathode materials to be used in a Li-ion secondary battery.The Li-Mn-Cr-O system has been studied extensively by several research groups. 1-7 Earlier studies have shown that the partial substitution of the Mn sites of the tetragonal spinel Li 2 Mn 2 O 4 by Cr produced a continuous solid solution of Li 2 Cr x Mn 2Ϫx O 4 . 1-3 The final products of this system depend on the Cr doping amount and calcination conditions; different Cr doping amounts resulted in different crystal systems, such as tetragonal (I4 1 /amd), distorted hexagonal (C2/m), and hexagonal (R3 m). 2,3 The corresponding electrochemical properties of the prepared powders were also quite different. For example, a lower Cr doping level in the tetragonal Li 2 Cr x Mn 2Ϫx O 4 showed a two-step Li ϩ deintercalation/intercalation during cycling with two potential plateaus at 3 and 4 V, which were mainly caused by the effect of the Jahn-Teller ion, Mn 3ϩ . A dilution of the effect was achieved by higher level Cr 3ϩ doping in Li 2 Cr x Mn 2Ϫx O 4 where crystallization occurred to produce a distorted hexagonal system. A much higher level doping led to increased symmetry from distorted hexagonal (C2/m) to hexagonal (R3 m) where the cooperative Jahn-Teller distortion was absent. Obviously, the layered compounds showed simple S-shaped charge/ discharge curves and stable cycling behavior. According to the obtained capacity, one is able to postulate that both the Mn 3ϩ and Cr 3ϩ elements were electrochemically active. Unfortunately, the pure hexagonal structured compound, LiCr 0.75 Mn 0.25 O 2 , delivered a capacity of about 100 mAh g Ϫ1 ͑current density: 3.6 mA g Ϫ1 at 25°C͒.Li 3 MnCrO 5 ͑can also be written as Li 1.2 Cr 0.4 Mn 0.4 O 2 ) is a solid solution series, Li 2 MnO 3 -LiCrO 2 . 4,5,7 Obviously, both compounds are famous as electrochemically inactive materials. Nonetheless, once Li 1.2 Cr 0.4 Mn 0.4 O 2 is formed, the hexagonal structured layer compound provides excellent cap...

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