Nb 2 O 5 exhibits various crystal systems, such as orthorhombic ͑o͒, tetragonal ͑t͒, and monoclinic ͑m͒, among which Nb 2 O 5 synthesized at 900-1000°C is commercially used as a cathode material of the 2-V lithium ion battery. The battery performances depended on the structure of Nb 2 O 5 , and the t-Nb 2 O 5 synthesized at 1000°C exhibited an excellent cycling performance with a large discharge capacity of 190 mAh ͑g oxide͒ −1 . The structural variations of Nb 2 O 5 during electrochemical reaction were examined. The in situ synchrotron radiation-X-ray diffraction ͑XRD͒ measurement indicated that o-and t-Nb 2 O 5 maintain their original crystal lattices, accompanying a small change in the cell volume even after the Li intercalation. The in situ X-ray absorption fine structure ͑XAFS͒ analysis of o-and t-Nb 2 O 5 revealed that the continuous variation from Nb 5+ to Nb 4+ took place during the intercalation process. A significant rearrangement of the Nb-O octahedra accompanied by the change of Nb-O and Nb-Nb interactions occurred in both structures with Li intercalation. XRD and XAFS data suggests that the two-dimensional layer structure of t-Nb 2 O 5 seems to be more flexible regarding the Li intercalation compared with the three-dimensional structure of o-Nb 2 O 5 . This may account for the better cyclic performance of the former material as the electrode material.

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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The electrochemical reaction in a lithium rechargeable battery includes intercalation (charge process) and deintercalation (discharge process) of the lithium ion accompanied by the redox reaction of the transition metals in a cathode material, which often undergoes complex structural transformation. X-ray Absorption Fine Structure (XAFS) is suitable for the analysis of the electrochemical reactions because it affords local structural information of an absorber atom in a powder material of unknown structure. Chemical states and structural changes accompanying the electrochemical Li deintercalation of Li1-x(Mn,M)2O4 (M=Ni,Cr,Co) were revealed by the in situ XAFS technique utilizing an in situ cell composed of a thin film cathode, a liquid electrolyte and a lithium foil anode. XAFS measurements were carried out at BL-10B and 12C, PF, Tsukuba in a transmission mode at various stages of the charge process. XANES analyses of Mn and M as a function of x showed that the origin of the high voltage (ca.5 V) +2 P2O7+2HCl+3H2O Crystallization was initiated by spontaneous nucleation and the rate of nucleation was controlled by gradual rise of temperature. These crystals exhibit vitreous to subvitreous luster having a size of 0.5-3 mm with less twinning. Structural Characterization: Single crystal X-ray diffraction structural data were collected. The unit cell parameters were obtained using the method of short vectors followed by least squares refinement of 22-28 reflections are as follows: Na2COP2O7 a=6. It can be visualized from the 3-dimensional structures of these compounds that they are ideal for ionic mobility.The ionic conductivity measurements were carried out which confirmed that they exhibit ionic conductivity with values ranging from 10 -5 to 10 -3 Ohm cm 2 at 593°K with Ea=0.63 to 1.2eV. Much effort has been made in our research in Uppsala to understand through single-crystal XRD methods lithium insertion-extraction mechanisms in a number of different cathode materials used in secondary lithium-ion (polymer) batteries. An electrochemical method is used to vary the lithium content of our samples in a reversible manner. Diffraction studies on series of compounds with varying lithium content reveal lithiation induced structural changes. In favorable cases it is also possible to follow the charge redistribution in the materials with deformation electron density studies. A general feature is beginning to emerge; namely, the formation of superlattices during these processes. These can be described as a combination of displacive and compositional modulations of the parent structures. There are examples of both commensurate and incommensurate modulations. Further, the resulting sequences of structural changes and corresponding rearrangements in electron density combine to suggest a high degree of co-operativity in the processes. These ideas will be illustrated for V6O13 and LiMn2O4 -and some general conclusions drawn relating to the more precise nature of this co-operativity. Microcrystalline quartz as agates and flint ...

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