The synthesis, structure, and electrochemical performance of normalLifalse[NixLi1/3−2x/3Mn2/3−x/3false]O2 for 0

Layered sodium manganese bronzes having the P2 structure false(Na2/3false[Li1/6Mn5/6false]O2false) , were used to prepare layered lithium manganese oxides by ion exchange of Na by Li using LiBr in hexanol. X‐ray diffraction and chemical analysis show that layered Li2/3false[Li1/6Mn5/6false]O2 has an O2 type structure. The arrangement of manganese and oxygen atoms in this phase differs fundamentally from that found in layered LiMnO2 (O3 structure), in orthorhombic LiMnO2 , and in spinel Li2Mn2O4 so that conversion to spinel during electrochemical cycling is not expected. Li2/3false[Li1/6Mn5/6false]O2 as well as the related Li2/3false[Li1/18Mn17/18false]O2 and Li2/3false[Mn0.85Co0.15false]O2 have a reversible charge capacity of about 150 mAh/g. During cycling the new cathode materials do not convert to spinel, in contrast to the behavior of layered and orthorhombic LiMnO2 . © 1999 The Electrochemical Society. All rights reserved.

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Li2CraMn2xO4 samples with x = 1.0, 1.25, and 1.5 were prepared by heating sol-gel precursors to elevated temperatures in argon. Three crystalline phases were observed as a function of the final heating temperature and x, and these were plotted on a structure-composition-temperature diagram. The samples lose some oxygen as they are heated, and this is probably part of the cause for the structural changes observed. The structure of Li2CrMnO4 heated to 1000 °C has been determined to be a distorted-hexagonal layered structure, much like that of the layered LiMnO2 phase recently reported by Armstrong and Bruce.'9 This does not agree with previous work by Davidson et al.," who claimed this phase was a tetragonal or orthorhombic distortion of the spinel structure. We show that Davidson's data are better explained by our model. At lower temperatures (e.g., 700 °C), the compounds are isostructural with LiCoO,, with the R-3m space group. Li/Li2CraJvln2_r04 electrochemical cells were made for all the samples and voltage-composition profiles measured. Li,Cr,25Mn,,,04 heated at 700 °C has an attractive voltage profile and a reversible capacity near 150 mAh/g when measured at a low rate of discharge.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 155.69.4.4 Downloaded on 2014-11-05 to IP

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The structure and the electrochemical properties of P2-Na 2/3 ͓Co x Ni 1/3Ϫx/2 Mn 2/3Ϫx/2 ͔O 2 and Li 2/3 ͓Co x Ni 1/3Ϫx/2 Mn 2/3Ϫx/2 ͔O 2 (0 р x р 2/3) are investigated by X-ray and neutron diffraction as well as by electrochemical techniques. Li 2/3 ͓Co x Ni 1/3Ϫx/2 Mn 2/3Ϫx/2 ͔O 2 (0 р x р 2/3) can be considered a solid solution between Li 2/3 1ϩ ͓Ni 1/3 2ϩ Mn 2/3 4ϩ ͔O 2 2Ϫ and Li 2/3 1ϩ ͓Co 2/3 3ϩ Mn 1/3 4ϩ ͔O 2 2Ϫ . Samples with x near 0 and with x near 2/3 adopt the T2 structure, while those with intermediate x show a stacking faulted O2 structure. This paper demonstrates that T2-Li 2/3 ͓Co 2/3 Mn 1/3 ͔O 2 is quite different from T2-Li 2/3 ͓Ni 1/3 Mn 2/3 ͔O 2 in its properties. First, neutron diffraction studies indicate that there is no superlattice ordering of Co and Mn in the transition metal layers of P2-Na 2/3 ͓Co 2/3 Mn 1/3 ͔O 2 or T2-Li 2/3 ͓Co 2/3 Mn 1/3 ͔O 2 , as there is in P2-Na 2/3 ͓Ni 1/3 Mn 2/3 ͔O 2 and T2-Li 2/3 ͓Ni 1/3 Mn 2/3 ͔O 2 . Second, the electrochemical results show that all the lithium can be extracted from T2-Li 2/3 ͓Co 2/3 Mn 1/3 ͔O 2 , unlike T2-Li 2/3 ͓Ni 1/3 Mn 2/3 ͔O 2 , from which only one half the available lithium can be extracted.

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