Open AccessRevisiting Primary Particles in Layered Lithium Transition‐Metal Oxides and Their Impact on Structural Degradation
Author(s) -
Lee SeungYong,
Park GyeongSu,
Jung Changhoon,
Ko DongSu,
Park SeongYong,
Kim Hee Goo,
Hong SeongHyeon,
Zhu Yimei,
Kim Miyoung
Publication year - 2019
Publication title -
advanced science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.388
H-Index - 100
ISSN - 2198-3844
DOI - 10.1002/advs.201800843
Subject(s) - lithium (medication) , materials science , electrochemistry , transition metal , cathode , particle (ecology) , oxide , primary (astronomy) , transmission electron microscopy , crystallite , metal , battery (electricity) , nanometre , chemical engineering , nanotechnology , crystallography , chemistry , composite material , metallurgy , electrode , physics , medicine , biochemistry , oceanography , power (physics) , quantum mechanics , astronomy , geology , engineering , endocrinology , catalysis
Layered lithium transition‐metal oxide materials, e.g., Li(Ni 1− x − y Co x Mn y )O 2 (NCM) and Li(Ni 1− x − y Co x Al y )O 2 , are the most promising candidates for lithium‐ion battery cathodes. They generally consist of ≈10 µm spherical particles densely packed with smaller particles (0.1–1 µm), called secondary and primary particles, respectively. The micrometer‐ to nanometer‐sized particles are critical to the battery performance because they affect the reaction capability of the cathode. Herein, the crystal structure of the primary particles of NCM materials is revisited. Elaborate transmission electron microscopy investigations reveal that the so‐called primary particles, often considered as single crystals, are in fact polycrystalline secondary particles. They contain low‐angle and exceptionally stable special grain boundaries (GBs) presumably created during aggregation via an oriented attachment mechanism. Therefore, this so‐called primary particle is renamed as primary‐like particle. More importantly, the low‐angle GBs between the smaller true primary particles cause the development of nanocracks within the primary‐like particles of Ni‐rich NCM cathodes after repetitive electrochemical cycles. In addition to rectifying a prevalent misconception about primary particles, this study provides a previously unknown but important origin of structural degradation in Ni‐rich layered cathodes.