Layered Oxide Cathodes for Li-Ion Batteries: Oxygen Loss and Vacancy Evolution

Abstract

Loss of oxygen in layered transition-metal oxides is a major reason for the structural degradation and thus the fade of electrochemical performance in the cathodes for Li-ion batteries. Via in situ transmission electron microscopy observations of LiNi 0.80 Co 0.15 Al 0.05 O 2 (NCA), we found that the oxygen loss in the layered cathode is a twostage process with distinct release rates. The initial rapid oxygen loss generates a high concentration of oxygen vacancies, which results in the formation of an amorphized, vacancy-containing rock-salt layer in the surface. In the second stage, the slower rate of oxygen loss allows recrystallization of this defective phase via coalescing of atomic oxygen vacancies, which results in the formation of a cavity-containing surface layer with a crystalline rock-salt structure over the layered phase in the bulk. Comparison of the in situ results with electrochemically cycled NCA cathodes confirms this two-stage process of oxygen loss. These results provide unprecedented microscopic details regarding the structural degradation of layered oxides arising from oxygen loss and have broader implications in manipulating the oxygen activity in the electrode.

Defect and structural evolution under high-energy ion irradiation informs battery materials design for extreme environments

“…13c ). Formation of the spinel phase may indicate oxygen evolution in order to form a cation densified state, according to previously reported literature 57 . Meanwhile at a low temperature (−173 °C), the resistance to amorphization of Na 2/3 Fe 1/2 Mn 1/2 O 2 decreases significantly (Supplementary Fig.…”

“…The preferential defect alignment is likely due to the formation of interstitial-type dislocation loops in the interlayer space between transition metal layers, in which a large free volume is available to accommodate the accumulation of the interstitials. Such dynamics of defect evolution (e.g., the formation and accumulation of vacancies and interstitials) under ion irradiation shares similar attributes to that of defect evolution in layered cathodes on electrochemical cycling (e.g., vacancies and interstitials formation through oxygen evolution and ion migration) 57 , 84 , 85 . Point defects such as vacancies and interstitials can largely influence the electrochemical performance of layered cathodes.…”

Challenges and Strategies to Advance High‐Energy Nickel‐Rich Layered Lithium Transition Metal Oxide Cathodes for Harsh Operation

“…Via in situ transmission electron microscopy observations of delithiated NCA cathode during heating, Zhang et al found that the oxygen loss in the layered cathode is a twostage process with distinct release rates, which includes rapid oxygen loss and formation of oxygen vacancies in the surface and further slow coalescing of atomic oxygen vacancies in the bulk. [32] Besli et al further probed the thermal decomposition, fracture, and oxygen evolution of chemically delithiated NCA particles during heating from room temperature to 450 °C using a number of advanced X-ray and electron probes. They have observed similar phenomenon as that occurred in the electrochemically delithiated NCA cathodes during heating, but further found that the release of oxygen also created numerous mesopores, which could thus provide a pathway for the release of lattice oxygen from the bulk and surface.…”

“…found that the oxygen loss in the layered cathode is a two‐stage process with distinct release rates, which includes rapid oxygen loss and formation of oxygen vacancies in the surface and further slow coalescing of atomic oxygen vacancies in the bulk. [ 32 ] Besli et al. further probed the thermal decomposition, fracture, and oxygen evolution of chemically delithiated NCA particles during heating from room temperature to 450 °C using a number of advanced X‐ray and electron probes.…”

Interfacial Degradation and Optimization of Li‐rich Cathode Materials†

“…Although Li‐rich transition metal oxides offer absorbing features, disadvantages in terms of low initial coulombic efficiency, continuous voltage decay, gas evolution and poor rate capability can't be ignored, which greatly hinder the practical applications of these cathode materials. [ 8‐12 ] The ratio of discharge capacity to charge capacity during the first cycle, namely initial coulombic efficiency, is ascribed to excessive irreversible Li + ions consuming. Transition metal (TM) ions have an increasing tendency to occupy lithium vacancies in high state of charge to form reconstruction, giving rise to the hindrance for lithium diffusion.…”