Oxygen Release Induced Chemomechanical Breakdown of Layered Cathode Materials

Abstract

Chemical and mechanical properties interplay on the nanometric scale and collectively govern the functionalities of battery materials. Understanding the relationship between the two can inform the design of battery materials with optimal chemomechanical properties for long-life lithium batteries. Herein, we report a mechanism of nanoscale mechanical breakdown in layered oxide cathode materials, originating from oxygen release at high states of charge under thermal abuse conditions. We observe that the mechanical breakdown of charged LiNiMnCoO materials proceeds via a two-step pathway involving intergranular and intragranular crack formation. Owing to the oxygen release, sporadic phase transformations from the layered structure to the spinel and/or rocksalt structures introduce local stress, which initiates microcracks along grain boundaries and ultimately leads to the detachment of primary particles, i.e., intergranular crack formation. Furthermore, intragranular cracks (pores and exfoliations) form, likely due to the accumulation of oxygen vacancies and continuous phase transformations at the surfaces of primary particles. Finally, finite element modeling confirms our experimental observation that the crack formation is attributable to the formation of oxygen vacancies, oxygen release, and phase transformations. This study is designed to directly observe the chemomechanical behavior of layered oxide cathode materials and provides a chemical basis for strengthening primary and secondary particles by stabilizing the oxygen anions in the lattice.

Simultaneously Dual Modification of Ni‐Rich Layered Oxide Cathode for High‐Energy Lithium‐Ion Batteries

“…Compared to the cells cycled at room temperature, these aggressively tested cells exhibit worse capacity retention. This is because high temperature would lead to the release of molecular oxygen from the NCM host lattice, accelerating structural degradation . As shown in Figure b, the capacity of the NCM drops from 195.6 to 85.2 mAh g −1 after 150 cycles, with capacity retention of 43.55%, While the LT1 maintains 159.9 mAh g −1 after 150 cycles with capacity retention of 83.28%.…”

“…The electrode/electrolyte interface of Ni‐rich materials is much less stable at a highly delithiated state. The transformation from the original layered to rock‐salt phase (NiO) accompanied by the release of oxygen leads to the thermal runaway and induce potential safety issues . In addition, bulk structural degradation is another vital factor that deteriorates the electrode capacity.…”

Fracture behavior in battery materials

“…The origin of intra-and intergranular cracks in intercalation cathodes is concentration gradient induced stress and two-phase-coherency stress on particles. In layered oxide cathode materials, oxygen release and phase transformation from layered to spinel and/or rocksalt phases generates a large strain during charging process [23]. Intragranular cracks are linked to material defects, such as vacancy and dislocation.…”

Long-term chemothermal stability of delithiated NCA in polymer solid-state batteries

“…5,22,27,43,44 Cathode materials that are at a high delithiation state are especially prone to this phase transition. 44,45 The chemically delithiated Li 0.3 NCA at elevated temperatures undergoes structural transformations involving oxygen evolution and reduction of nickel. Our results indicate that the phase transformation, and the associated nickel reduction, starts at the surface and propagates into the bulk material with increased aging time, in accordance with the literature.…”