Authors: Chunyang Wang | Rui Zhang | Huolin L. Xin
Source: Microscopy and Microanalysis (article, 2023-07-22)
Field: Materials Science — Surfaces, Coatings and Films

Atomic-Scale Understanding of New Phase Transition Pathway and Phase Boundary Structures in Layered Oxide Cathodes for Lithium-Ion Batteries High-nickel-content layered oxides are one of the most promising lithium-ion battery (LIB) cathode materials for electric vehicle applications.A fundamental understanding of the working/failure modes as well as the structure-performance relationship of current high-nickel layered oxide cathodes will provide theoretical guidance [1, 2] and foster the design and development of nextgeneration cathode materials for high energy-density and long-life lithium-ion batteries.In the past few years, by coupling in-situ atomic-resolution imaging, electron diffraction, electron tomography and artificial-intelligence-enhanced TEM, we systematically elucidated the lattice-shear induced O3→O1 phase transition, O3-O1 phase boundary structure and the degradation pathway of O1 phase.We first captured the atomic structures of delithiation-induced O1 phase and related misfit defect/crack nucleation at O1-O3 interface in LiNiO 2 [3].Also, we first reported the existence of O1 phase in commercial NMC-811 cathode and elucidated the intra-layer structural transition motifs at O1-O3 interfaces aided by deep-learning-based super-resolution TEM [4].By using in-situ TEM, the stability and evolution of O1 phase were investigated and a new phase transformation mechanism, that is O1→rock salt transformation was discovered [5].We demonstrated for the first time that O1 phase provides a highway for oxygen loss (meaning lower energy barrier for cation mixingtransition metal migration from transition metal layers to Li layers) and deactivation of layered cathodes.Later on, we extended our study to both single-crystalline and polycrystal NMC-811 and ultrahigh-Ni cathodes and demonstrated how O1 phase transformation and evolution could influence the battery's electrochemical performance [6,7].Most recently, we discover that severe chemomechanical deformation during battery operation triggers O3→O1 phase transformation as well as the formation of bending bands and kinks in layered cathodes [8].Distinct from conventional O3→O1 phase transformation which is driven by delithiation-induced self-destabilization, the deformation-induced O3→O1 phase transformation is driven by delithiation coupled with local stress concentration.The new failure mechanism uncovers the connection between mechanical degradation and phase transformation in layered oxides for the first time.With the fundamental insights gained from the systematic TEM study, we successfully designed a zero-strain high-Ni and cobalt-free cathode through compositionally complex doping strategy [9].The new knowledge is expected to applicable to layered oxide cathodes in general and will offer important guidance for optimization of current layered cathodes as well as for the design of new cathode materials in the future [10]. Lithium (medication) ; Engineering physics ; Scale (ratio) ; Atomic units ; Phase transition ; Nanotechnology ; Physics ; Chemistry ; Materials science ; Condensed matter physics ; Psychology Electron and X-Ray Spectroscopy Techniques ; Advancements in Battery Materials ; Advanced Electron Microscopy Techniques and Applications