Evolution of Local Structural Ordering and Chemical Distribution upon Delithiation of a Rock Salt–Structured Li_1.3Ta_0.3Mn_0.4O₂ Cathode

Abstract

Lithium-rich disordered rock-salt oxides have attracted great interest owing to their promising performance as Li-ion battery cathodes. While experimental and theoretical efforts are critical in advancing this class of materials, a fundamental understanding of key property changes upon Li extraction is largely missing. In the present study, single-crystal synthesis of a new disordered rock-salt cathode material, Li 1.3 Ta 0.3 Mn 0.4 O 2 (LTMO), and its use as a model compound to investigate Li concentration-driven evolution of local cationic ordering, charge compensation, and chemical distribution are reported. Through the combined use of 2D and 3D X-ray nanotomography, it is shown that Li removal accompanied by oxygen oxidation is correlated with the development of morphological defects such as particle cracking. Chemical heterogeneity, quantified by subparticle level distribution of Mn valence state, is minimal during Mn redox, which drastically increases upon the formation of cracks during oxygen redox. Density functional theory and bond valence sum mismatch calculations reveal the presence of local short-range ordering in the pristine oxide, which gradually disappears along with the extraction of Li. The study suggests that with cycling the transformation into true cation-disordered state can be expected, which likely impacts the voltage profile and obtainable energy density of the oxide cathodes.

Automatic 3D image registration for nano-resolution chemical mapping using synchrotron spectro-tomography

“…We present our approach for handling the 3D imaging results on Li x Ta 0.3 Mn 0.4 O 2 battery cathode particles that tilted slightly during the acquisition of the spectro-tomographic data (Kan et al, 2019). We focused on the Mn K edge because the redox activity of the Mn cation in this material is one of the major charge-compensation mechanisms for the cathode during battery operation.…”

“…The sample was then washed with acetonitrile several times and dried overnight. For more details, we refer to the published literature (Kan et al, 2019).…”

Emerging X-ray imaging technologies for energy materials

“…In contrast, the structural failure in Li-ion battery mainly occurs during the Li-ion extraction process when an enormous particle pulverization takes place, as shown in Figure 6 Similar to 2D TXM, tomography can be combined with XAS technique in order to obtain a 3D chemical mapping. In a recent 3D XANES study, tomography measurements with 30 nm resolution were conducted to study the delithiation of micro-sized Li1.3Ta0.3Mn0.4O2 (LTMO) cathode particles [68]. The imaging data was collected at more than 100 energy points across the Mn K-edge to create a 3D chemical map, as shown in Figure 7 (a).…”

Impact of Local Separation on the Structural and Electrochemical Behaviors in Li2MoO3LiCrO2 Disordered Rock‐Salt Cathode Material

“…[18] Kan et al have reported a continuous decrease in the short-range order of Ta during delithiation of Li 1.3 Ta 0.3 Mn 0.4 O 2 cathode material, implying the existence of a certain driving force that increases a degree of disorder in multi-component Li-excess systems. [19] Although further study is needed, one possible answer may reside in the local separation that induces significant inhomogeneous strain and concentration of stress within the crystallite, which may have facilitated the cation-disorder process.…”