Kinetic Stability of Bulk LiNiO₂ and Surface Degradation by Oxygen Evolution in LiNiO₂‐Based Cathode Materials

Abstract

Capacity degradation by phase changes and oxygen evolution has been the largest obstacle for the ultimate commercialization of high‐capacity LiNiO2‐based cathode materials. The ultimate thermodynamic and kinetic reasons of these limitations are not yet systematically studied, and the fundamental mechanisms are still poorly understood. In this work, both phenomena are studied by density functional theory simulations and validation experiments. It is found that during delithiation of LiNiO2, decreased oxygen reduction induces a strong thermodynamic driving force for oxygen evolution in bulk. However, oxygen evolution is kinetically prohibited in the bulk phase due to a large oxygen migration kinetic barrier (2.4 eV). In contrast, surface regions provide a larger space for oxygen migration leading to facile oxygen evolution. These theoretical results are validated by experimental studies, and the kinetic stability of bulk LiNiO2 is clearly confirmed. Based on these findings, a rational design strategy for protective surface coating is proposed.

Enhanced Electrochemical and Thermal Stabilities of Li[Ni0.88Co0.09Al0.03]O2 Cathode Material by La4NiLiO8 Coating for Li–Ion Batteries

“…This result indicates that there is a thermodynamic driving force for Ni atoms transport, while the migration of oxygen atoms from the NCA lattice in the surface regions are depressed to a great extent due to the formation the stable La 4 NiLiO 8 layer. Because oxygen evolution is limited in surface regions of the Ni‐rich layered oxides, the detrimental transition from layered to rock‐salt structure is expected to reduce during electrochemical cycling in this case.…”

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

“…It is due to the formation of oxygen vacancy that the migration of Ni ions can be obviously reduced and new migration paths for TM ions will be opened, resulting in the subsequent layered‐spinel‐rocksalt phase transformation . To unravel this, Cho and co‐workers provide the reasonable model to examine the Ni ions migration from the original octahedral sites in TM layers to neighboring tetrahedral sites in the Li layer ( Figure a), and corresponding calculated migration barriers with and without oxygen vacancies are also plotted (Figure b) . Their findings demonstrate that the formation of oxygen vacancies can remarkably cut down the diffusion barrier, indicative of low resistance for the Ni ion migration.…”

“…Aside from the above‐mentioned reasons, the formation of oxygen vacancy is also mainly responsible for the layered structure disordering . It is due to the formation of oxygen vacancy that the migration of Ni ions can be obviously reduced and new migration paths for TM ions will be opened, resulting in the subsequent layered‐spinel‐rocksalt phase transformation .…”

Nonflammable Lithium Metal Full Cells with Ultra-high Energy Density Based on Coordinated Carbonate Electrolytes

“…It is known that upon charging process (i.e., delithiation from cathode), oxygen defect formation and release from NCM-based cathode occur (Kong et al, 2019), thereby accelerating interfacial side reactions (including exothermic reactions) between the cathode active material and electrolyte components. The interfacial exothermic reaction of delithiated NCM811 with 4 M LiFSI-PC/FEC (and 1 M LiTFSI-DOL/DME) was therefore examined by differential scanning calorimetry ( Figure 3E).…”