Rock-Salt Growth-Induced (003) Cracking in a Layered Positive Electrode for Li-Ion Batteries

Abstract

For the first time, (003) cracking is observed and determined to be the major cracking mechanism for the primary particles of Ni-rich layered dioxides as the positive electrode for Li-ion batteries. Using transmission electron microscopy techniques, here we show that the propagation and fracturing of platelet-like rock-salt phase along the (003) plane of the layered oxide are the leading cause for the cracking of primary particles. The fracturing of the rock-salt platelet is induced by the stress discontinuity between the parent layered oxide and the rock-salt phase. The high nickel content is considered to be the key factor for the formation of the rock-salt platelet and thus the (003) cracking. The (003)-type cracking can be a major factor for the structural degradation and associated capacity fade of the layered positive electrode.

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

“…Ultimately, they will evolve into larger cracks. [186] The presence of Li-site TM cations (rock-salt formation) and a high degree of stacking faults, presumably due to distortion of the oxygen framework (with high vacancy concentration), was also observed by Zhang et al [188] In any case, a (negative) cooperative effect of oxygen vacancies, structural dislocations, cracking, and rock-salt formation is likely to occur. TEM studies [186,187] revealed that intragranular cracking follows a strict crystallographic preference along the (003) plane.…”

Surface/Interface Structure Degradation of Ni‐Rich Layered Oxide Cathodes toward Lithium‐Ion Batteries: Fundamental Mechanisms and Remedying Strategies

“…The formation of intragranular cracks is proposed as an electrochemically driven and diffusion‐controlled process, and characteristically initiates from the grain interior, that is, a consequence of a dislocation‐based crack incubation mechanism (Figure d) . More significantly, the nucleation, growth, and driving force of intragranular cracks is revealed by the atomic observation into cracks at different developing stages using TEM (Figure e) . The intragranular cracks along the (003) planes induced by the formation and fracturing of the platelet‐like rocksalt phase has been demonstrated to be a chief cracking origin in Ni‐rich cathodes.…”

“…e) TEM, HRTEM images and corresponding schematic illustration for a one‐cycle particle with developing (003) crack. Reproduced with permission . Copyright 2017, American Chemical Society.…”

Single-crystal based studies for correlating the properties and high-voltage performance of Li[NixMnyCo1−x−y]O2 cathodes

“…31 Recently, intra-granular cracking resulting from high-voltage cycling of layered oxides was found to progress from the grain interior along the (003) plane, which led to bulk structural degradation and reduced long-term stability. 18,32 In conventional NMC samples, large porous aggregates of secondary particles consist of various sized primary particles. Naturally, material performance is controlled by the physical properties of primary particles as well as the properties of secondary particles, such as the particle size distribution, porosity, grain boundaries, etc.…”