Formation and effect of orientation domains in layered oxide cathodes of lithium-ion batteries

Abstract

We show that in layered oxidesthat are employed as cathodes in lithium-ion batteries,the cation layers can order on different {111} NaCl planes within a single particle, which makes the lithium layer discontinuous across a particle.Thefindings challenge previous assertions that lithiumundergoes 2-D diffusion in layered oxides and the data provide new insights into the decrease in rate capabilities for some layered oxides. Therefore, it is critically important to understand how these discontinuities form and how the loss of 2-D diffusion impacts the overall performance of the layered oxide cathode materials. EmployingX-ray diffraction (XRD) and aberration-corrected scanning transmission electron microscopy (STEM), we find that as the material transitions from a disordered to an ordered state, it forms four orientation variants corresponding to the four {111} NaCl planes. This transition is not intrinsic to all layered oxides and appears to be more strongly affected by nickel. Furthermore, with energy dispersive spectroscopy(EDS), we show that there is an increase in the nickel concentrationat the interface between each orientation variant.This reduces the rate of lithium diffusion, negatively affects the rate capability, and could be contributing to the overall capacity fade.

Surface Structural and Chemical Evolution of Layered LiNi0.8Co0.15Al0.05O2 (NCA) under High Voltage and Elevated Temperature Conditions

“…Areas with rocksalt contrast can be present in a particle as one of the four orientation variants of the layered structure. 60 These domains are usually marked by domain boundaries where preferential segregation of Ni occurs 61 In the present study, we are describing a separate rocksalt phase, which is different from an orientation domain. It is to be mentioned here that the phases we find in NCA are topotactic and the extended rocksalt phase is found to occur as a result of extensive disordering of the layered structure.…”

A systematic investigation of cycle number, temperature and electric field strength effects on Si anode

“…The RDF obtained from a diffraction measurement contains the important one-dimensional information, and it provides insight into the structure of lithiated Si anode. For the perfect single crystal diamond cubic structure Si, the three peaks in RDF are 2.35 Å, 3.85 Å and 4.65 Å, respectively, corresponding to the distance Si-Si bonds [47]. In Fig.…”

“…shows the first peak of 2.42 Å based on the RDF curve, meaning that the body-centred tetragonal structure Si takes place during the delithiation[47]. Hence, a phase transformation from α-Si to β-Si could occur in the delithiation due to the high compressive stress induced by Li-ion diffusion, which produces the volume expansion and interface mismatch (see,Figs.…”

Determination of Spinel Content in Cycled Li1.2Ni0.13Mn0.54Co0.13O2 Using Three-Dimensional Electron Diffraction and Precession Electron Diffraction

“…Because of this, it is difficult to conclude that a certain change in the structure is due to cycling and not due to the electron beam. Moreover, it has been shown that twins originating from Fm3m rock salt type structure to R3m layered structure (Figure 1d,b) symmetry lowering during synthesis can easily be mistaken for the occurrence of spinel or rock salt phases when relying only on images [11][12][13].…”

“…In contrast to single-crystal X-ray or neutron diffraction, single-crystal electron diffraction can be done on submicronsized crystals, which is the size used in battery cathode materials. When compared to TEM imaging, electron diffraction can readily distinguish whether extra reflections are due to twinning or due to the formation of the spinel phase [11][12][13]. Furthermore, electron diffraction requires lower beam intensities while still giving access to information at the level of atom coordinates, even of the lithium ions [14][15][16][17][18].…”