Nucleation of dislocations and their dynamics in layered oxide cathode materials during battery charging

Abstract

Defects and their interactions in crystalline solids often underpin material properties and functionality 1 as they are decisive for stability 1-5 , result in enhanced diffusion 6 , and act as a reservoir of vacancies 7 . Recently, lithium-rich layered oxides have emerged among the leading candidates for the next-generation energy storage cathode material, delivering 50 % excess capacity over commercially used compounds. Oxygen-redox reactions are believed to be responsible for the excess capacity 8 , however, voltage fading has prevented commercialization of these new materials. Despite extensive research the understanding of the mechanisms underpinning oxygen-redox reactions and voltage fade remain incomplete. Here, using operando three-dimensional Bragg coherent diffractive imaging 2,9 , we directly observe nucleation of a mobile dislocation network in nanoparticles of lithium-rich layered oxide material. Surprisingly, we find that dislocations form more readily in the lithium-rich layered oxide material as compared with a conventional layered oxide material, suggesting a link between the defects and the

Revealing the Atomic Origin of Heterogeneous Li‐Ion Diffusion by Probing Na

“…Such highly strained lattice could act as a high speed pipe for ion diffusion according to the literature report that expanded lattice can significantly increase ion transport kinetics . It is also consistent with the dislocation mediated fast ion migration observed in other materials . For the first time, these speculations were visualized at atomic‐scale resolution.…”

“…Bragg coherent diffraction study may be good to reveal the effect of dislocation strain field on the lithiation/delithiation kinetics . In this regard, we performed Geometric phase analysis (GPA) on the dislocation region in Figure g.…”

Rechargeable Lithium Metal Batteries with an In‐Built Solid‐State Polymer Electrolyte and a High Voltage/Loading Ni‐Rich Layered Cathode

“…The gradual capacity fading observed in Figure 2a, particularly after cycle 50, is attributed not only necessarily to the AlF 3 ‐Poly‐DOL electrolyte, but to other failure modes, including cathode phase transition, increased internal resistances, or Li metal consumption. Among these, the failure modes of changes in NCM structure have been reported previously as a prominent phenomenon after charge–discharge cycling at potentials in the range used in the study 40,48,49. XRD was used to analyze lattice distortion of LiNi 0.6 Co 0.2 Mn 0.2 O 2 (Figure S17, Supporting Information).…”

Chemical, Structural, and Electronic Aspects of Formation and Degradation Behavior on Different Length Scales of Ni‐Rich NCM and Li‐Rich HE‐NCM Cathode Materials in Li‐Ion Batteries

“…However, even if all of the Li 2 MnO 3 is activated, the measured capacity (activated MnO 2 plus NCM) would not be sufficient to account for the "anomalously" large reversible discharge capacities achieved using this material class. A large variety of structural and/or electronic changes are associated with the irreversible changes during the initial activation process, e.g., reversible oxidation of oxygen species [159] and probably condensation to peroxide-like units, [159] transition metal migration into tetrahedral sites [81,160] and formation of a spinel-like surface layer, [161] formation of lithium/transition metal dumbbells, [70,162] Li + /H + exchange, [163] formation of dislocations [164] etc. [67][68][69]118,156] During the initial charge cycle of the pristine material (up to about 4.8 V), there is, at first, an s-shape-like voltage profile that is attributed to the oxidation of Ni and Co from +II and +III, respectively, to +IV.…”