We describe synchroton based X-ray diffraction techniques and issues related to in situ studies of intercalation processes in battery electrodes. We then demonstrate the utility of this technique, through a study of two batches of LiMn2O4 cathode materials. The structural evolution of these spinel materials was monitored in situ during the initial charge of these electrodes in actual battery cells. Significant differences were observed in the two batches, particularly in the intercalation range of x = 0.45 to 0.20. The first-order structural transitions in this region indicated coexistence of two cubic phases in the batch 2 material, whereas the batch 1 material showed suppressed two-phase coexistence. Batch 2 cells also indicated structural evolution in the low-potential region below 3.0 V in contrast to the batch 1 material. Differences in structural evolution between batches of LiMn2O, could have important ramifications in their cycle life and stability characteristics. 466 ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 134.48.29.181 Downloaded on 2014-11-03 to IP 10 x-ray photon energy (keY) 100 ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 134.48.29.181 Downloaded on 2014-11-03 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 134.48.29.181 Downloaded on 2014-11-03 to IP ABSTRACTChemical reactions taking place at elevated temperatures in a polymer-bonded lithiated carbon anode were studied by differential scanning calorimetry. The influences of parameters such as degree of intercalation, number of cycles, specific surface area, and chemical nature of the binder were elucidated. It was clearly established that the first reaction taking place at ca. 120-140 °C was the transformation of the passivation layer products into lithium carbonate, and that lithiated carbon reacted with the molten binder via dehydrofluorination only at T> 300 °C. Both reactions strongly depend on the specific surface area of the electrodes and the degree of lithiation.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 134.48.29.181 Downloaded on 2014-11-03 to IP
One approach to increasing the ionic conductivity of polymer electrolyte is to add plasticizers to the polymer-salt complexes 1. Recently, we have synthesized a new plasticizer, modified carbonate (MC3), by attaching three ethylene oxide units to the 4-position of ethylene carbonate 2. AC impedance studies 2 showed that an ionic conductivity of 5x10"5S em"I could be achieved at room temperature, by adding 50 wt% of MC3 into PEO-LiCFaSO 3 complex. This is two orders of magnitude higher than that found in PEO-I.iCF3SO3 electrolyte without a plasticizer, and one order of magnitude higher than that found when using same amount of propylene carbonate (PC) as plasticizer. Temperature dependent conductivity measurement and thermal analysis show that this new plasticizer increased the ionic conductivity throughout the entire complex system, while the conventional plasticizers only create a high conductivity path way through the plasticizer itself. The samples are free standing films with good mechanical properties. When MC3 is used as a plasticizer, the ionic conductivity increase is much higher than using PC as a plasticizer at high ' DISTRIBUTION OF THIS DOOUIVIENr 15 UNLIMITED 8 temperature (65 "C), implying an increase in the number of charge carriers. Therefore, we believe that MC3 has a stronger ion pair dissociation effect than PC, when used as a plasticizer. The ion pair dissociation effect was studied by Raman, FTIR, and near edge x-ray absorption fine structure (NEXAFS) spectroscopy.
Ge 3 N 4 was investigated for its electrochemical activity with Lithium as a possible negative electrode material for Li-ion batteries. Ge 3 N 4 was found to reversibly react with Li, exhibiting high capacity, 500 mAh/g, and maintaining good cycling stability. The reaction mechanism of Ge 3 N 4 with lithium was investigated in detail using in situ and ex situ X-ray diffraction ͑XRD͒ in reflection, in situ XRD in transmission, ex situ transmission electron microscopy, and selected-area electron diffraction ͑SAED͒. The two phases, ␣-and -Ge 3 N 4 , of the electrode material mostly maintained their respective crystalline microstructure during cycling. A substantial integrated intensity decrease in the XRD Bragg reflections observed during the first lithiation and the concurrent emergence of diffuse rings in SAED suggest the reaction of Ge 3 N 4 with lithium may be limited thereby converting only the outermost shell of the Ge 3 N 4 crystal. The identification of ␣-Li 3 N and Ge at the end of the first delithiation using SAED supports a lithium/metal nitride conversion reaction process. The formation of the Li 3 N matrix was found to be consistent with a 50% irreversible capacity loss in the first cycle.The materials currently used as negative electrodes in commercial rechargeable Li-ion batteries are based on graphite. The intercalation of lithium within the Van der Waals gap existing between graphene planes is reversible. The intercalation of lithium results in an increase of the interlayer spacing but the overall volume change, 9%, is small, resulting in good cycle life. Complete lithiation of graphite to LiC 6 results in a theoretical capacity of 372 mAh/g. Intensive research has been carried out worldwide to develop materials which improve on the performance of graphite. One area of research consists in the development of carbon-based materials exhibiting higher capacity. An alternative revival of the inorganic approach has also garnered much interest. Most work has concentrated on the development of alloys and oxides while nitrides have been investigated less thoroughly.Nishijima et al. first introduced ternary lithium transition metal nitrides, such as Li 3 FeN 2 1 and Li 7 MnN 4 , 2 as candidates for use as negative electrode materials in Li-ion batteries. These nitrides of general formula Li 2nϪ1 MN n exhibit a cubic antifluorite-type structure. A second group of ternary lithium transition metal nitrides, Li 3Ϫx M x N 3-9 where M stands for Cu, Ni, and Co, have also been investigated for their electrochemical properties. These nitrides are isostructural to the hexagonal Li 3 N where the transition metal substitutes for Li in between Li 2 N layers. Li 2.6 Co 0.4 N was reported to exhibit good cycling stability and high capacity, 700 mAh/g. The main drawbacks of these materials are their moisture sensitivity and the requirement of a predelithiation step before use as negative electrodes in Li-ion batteries.Sn 3 N 4 and tin subnitrides, 10,11 InN, and indium subnitrides, 11 Zn 3 N 4 , 10 and silicon tin oxynitr...
The electrochemical lithium-ion extraction/insertion properties of two spinel lithium manganese oxides, stoichiometric Li0.99Mn2O4 and lithium-rich Li1.04Mn1.93O4, were studied. Their voltage profile and cyclic voltammetry all show two-step reaction for lithium-ion extraction/insertion at their 4 V plateau. The high-resolution in situ X-ray diffraction (XRD) studies show both materials experience three cubic phases, cubic I, II, and III, during cycling at 4 V plateaus. Two two-phase coexistence regions were observed. These results show that phase transitions between cubic I and II and between cubic II and III are first-order transitions. The in situ XRD data also reveal that lithium-rich composition does not suppress the phase transitions of spinel between their three cubic phases, but leads to the increase of variation range of the lattice parameters of the cubic phases. This in turn reduces the jumping step of the lattice parameter between adjacent phases and increases the overlap of the adjacent phase. This study shows conclusively that the three-phase process is the intrinsic feature of spinel Li1+yMn2O4 during lithium-ion extraction/insertion on the 4 V plateau. © 2002 The Electrochemical Society. All rights reserved.
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