Oxygen Vacancy Diffusion and Condensation in Lithium‐Ion Battery Cathode Materials

Abstract

Oxygen vacancies (OV) are native defects in transition metal (TM) oxides and their presence has a critical effect on the physicochemical properties of the oxide. Metal oxides are commonly used in lithium‐ion battery (LIB) cathodes and there is still a lack of understanding of the role of OVs in LIB research field. Here, we report on the behavior of OVs in a single‐crystal LIB cathode during the non‐equilibrium states of charge and discharge. We found that microcrack evolution in a single crystal occurs due to OV condensation in specific crystallographic orientations generated by the continuous migration of OVs and TM ions. Moreover, understanding the effects of the presence and diffusion of OVs in metal oxides enables the elucidation of most of the conventional mechanisms of capacity fading in LIBs and provides new insights for new electrochemical applications.

Revealing Mechanism of Li3PO4 Coating Suppressed Surface Oxygen Release for Commercial Ni-Rich Layered Cathodes

“…Recently, some leading companies have tried to marketize the Ni-rich layered Li[Ni 0.8 Co 0.1 Mn 0.1 ]O 2 (hereafter referred to as NCM 811 ) due to the high capacity (∼210 mA h g −1 ). 6,7 However, the wide commercialization of NCM 811 has been largely hindered by its poor cycling stability and the terrible safety issue in its fully charged state, particularly at elevated temperatures. 8,9 At a deeply delithiated state between 4.15 and 4.3 V, the structure of NCM 811 is unstable because of the formation of substantial highly reactive Ni 4+ , which is easily reduced to the rock-salt like phase on the surface.…”

“…Recently, some leading companies have tried to marketize the Ni-rich layered Li­[Ni 0.8 Co 0.1 Mn 0.1 ]­O 2 (hereafter referred to as NCM 811 ) due to the high capacity (∼210 mA h g –1 ). , However, the wide commercialization of NCM 811 has been largely hindered by its poor cycling stability and the terrible safety issue in its fully charged state, particularly at elevated temperatures. , At a deeply delithiated state between 4.15 and 4.3 V, the structure of NCM 811 is unstable because of the formation of substantial highly reactive Ni 4+ , which is easily reduced to the rock-salt like phase on the surface. , The process of layered structure transforming to rock-salt like phase usually induces irreversible oxygen release from the surface of the NCM 811 , resulting in a violent exothermic reaction, and finally resulting in the thermal runaway of the battery. , More importantly, the oxygen release can easily damage the crystal structure, thus decreasing the capacity of NCM 811 . In industrial production, the thermal runaway caused by oxygen release in LIBs has already become an urgent issue.…”

High-Voltage LiCoO2 Material Encapsulated in a Li4Ti5O12Ultrathin Layer by High-Speed Solid-Phase Coating Process

“…As shown in Figure a and Figure b, wide range cross-sectional SEM images of the bare LCO and 0.15% LTO@LCO-800 electrode suggest that the LCO particles in the cycled bare LCO electrode exhibited obvious crack and fracture, whereas most LCO particles in 0.15% LTO@LCO-800 electrode remained intact. Microcracking in a single crystal is an acknowledged reason for the capacity fading in transition metal oxide cathodes . Such comparative result directly proved the role of the continuous LTO coating in protecting and stabilizing the LCO microspheres during the cycling process at high voltage.…”

“…Micro- cracking in a single crystal is an acknowledged reason for the capacity fading in transition metal oxide cathodes. 46 Such comparative result directly proved the role of the continuous LTO coating in protecting and stabilizing the LCO microspheres during the cycling process at high voltage.…”

Intragranular Fracture Mechanism of Highly Crystalline Lithium Manganese Oxide during Lithium Insertion/Extraction Reactions

“…Stress corrosion cracking progresses during initial crack-formation and subsequent crack-growth processes. According to TEM observations of the crack-formation process at the atomic level, oxygen defects play an important role in crack nucleation . In general, large particles contain more defects; therefore, particle fracturing is more pronounced.…”