In Situ Synchrotron X-Ray Diffraction Studies of the Phase Transitions in Li[sub x]Mn[sub 2]O[sub 4] Cathode Materials

Abstract

In situ X-ray diffraction studies of Li x Mn 2 O 4 spinel cathode materials during charge-discharge cycling were carried out using a synchrotron as the X-ray source. Lithium-rich (x = 1.03-1.06) spinel materials, obtained from two different sources, were studied. Three cubic phases with different lattice constants were observed during charge-discharge cycles in all of the samples when a sufficiently low charge-discharge rate (≤C/10) was used. There were two regions of two-phase coexistence, which indicates that both phase transitions are first order. The separation of the Bragg peaks representing these three phases varied from sample to sample and also depended on the charge-discharge rate. These results show that the deintercalation of lithium in lithium-rich spinel cathode materials proceeds through a series of phase transitions from a lithium-rich phase to a lithium-poor phase and finally to a λ-MnO 2 -like cubic phase, rather than through a continuous lattice constant contraction in a single phase.The Li x Mn 2 O 4 spinel is one of the most promising cathode materials for lithium rechargeable batteries because of its low cost and low toxicity. Recent studies have focused on the problem of capacity fading of this material during cycling, especially at elevated temperature. This fading has been attributed to two sources, the dissolution of Mn 2+ into the nonaqueous electrolytes 1 and the inhomogeneity of the spinel local structure. 2,3 Early ex situ X-ray diffraction studies of Li x Mn 2 O 4 were performed by Ohzuku et al. 4 They found that two cubic phases coexist for 0.60 > x > 0.27, and a single cubic phase is present for 1.0 > x >0.6. Xia and Yoshio 5 reported in their studies that the two-phase coexistence was suppressed in cathode materials which were prepared lithium rich (x = 1.04) or oxygen rich. They also claimed that the two-phase coexistence is one of the key factors for the capacity fading during cycling. By suppressing this phase transition, the capacity fading of the lithium-rich cathode materials was significantly improved at the expense of lower initial capacity. In their later X-ray diffraction (XRD) studies, 6 an in situ technique was used, and the same conclusion that there was a onephase structure for lithium-rich spinel was presented. This interesting work raised an important issue: the relationship between the structural change and the capacity fading of these spinel materials during cycling. However, there are experimental data published by other research groups that show two-phase coexistence in lithiumrich spinels. For example, Richard et al. 7 have reported their in situ XRD studies with the observation of two-phase coexistence in the 0.60 > x > 0.27 range for Li x Mn 2 O 4 material, where the x value before charge was similar to that in the studies of Ref. 5 (x = 1.02 vs. x = 1.04). The main difference between these two studies is the charge rate (C/40 in Ref. 7 vs. C/3 in Ref. 5). The first issue to address in this article is whether the two-phase coexistence region is being suppre...

Effect of the electrode potential on the surface composition and crystal structure of LiMn2O4 in aqueous solutions

“…Given that the binding energy position of the 3p peak changes with oxidation state and that the 3p 3/2 and 3p 1/2 doublet is not resolved then the Mn(III) and Mn(IV) components could each be fitted with a single peak [31] extracting or inserting Li + , the crystal structure undergoes several phase transitions between different cubic structures depending on the lithium content [38]. In-situ X-ray studies demonstrated that two phase transitions occur between three cubic phases [39].…”

Tuning charge–discharge induced unit cell breathing in layer-structured cathode materials for lithium-ion batteries

“…The expansion of c is considered to be caused by the increased repulsive force between the MO 2 layers resulting from the reduced number of Li ions in the Li layer. LiMn 2 O 4 spinel with cubic structure shows a contraction in all three dimensions during delithiation 12 (003), (101), (104), (107), (108) and (110) ARTICLE For most of the intercalation compounds as cathode materials for lithium batteries, the contraction of the unit cell volume is a 'normal' trend during delithiation. It can be generally explained by the shrinking cation radius that resulted from the transition metal oxidation.…”

“…This type of structural changes is called 'unit cell breathing'. For LiMn 2 O 4 spinel materials with cubic structure, the unit cell breathing is similar but the lattice parameters contract (during charge) and expand (during discharge) simultaneously in all three directions 12 . When a significant amount of Lis were removed from the layer-structured material during high voltage charging (for example, 50% for LiCoO 2 ), the change of parameter c reversed course from expanding to contracting and can reach values even shorter than the pristine, if charged to voltages close to or higher than 5 V (ref.…”

Re-Deposition of Aluminum Species after Dissolution to Improve Electrode Performances of Lithium Manganese Oxide

“…3b). That is, two peaks in the discharge dQ/dV plots, which are associated with the lithiation reactions of spinel LMO, 29 are observed at 4.10 and 3.93 V before storage (Fig. 3a), but move down to 3.91 and 3.78 V after storage.…”