Electrochemical Aging Protocol Governed Capacity Losses and Structure Degradations in Layered LiNi_0.8 Co_0.1 Mn_0.1 O₂...

The comparatively poor endurance of Ni-rich cathode materials restricts their application in high-energy lithium-ion batteries. A thorough understanding of the degradation characteristics of such materials under complex electrochemical aging protocols is required to further improve their reliability. In this work, the irreversible capacity losses of LiNi_0.8 Mn_0.1 Co_0.1 O₂ under different electrochemical aging protocols are quantitatively evaluated via a well-designed experiment. In addition, it is discovered that the origin of irreversible capacity losses is highly related to electrochemical cycling parameters and can be divided into two types. Type I is heterogeneous degradation caused by low C-rate or high upper cut-off voltage cycling and features abundant capacity loss during H2-H3 phase transition. Such capacity loss is attributed to the irreversible surface phase transition that limits the accessible state of charge during the H2-H3 phase transition stage via the pinning effect. Type II is fast charging/discharging induced homogeneous capacity loss that occurs consistently throughout the whole phase transition time. This degradation pathway shows a distinctive surface crystal structure, which is dominated by a bending layered structure rather than a typical rock-salt phase structure. This work offers detailed insight into the failure mechanism of Ni-rich cathodes and provides guidance on designing long-cycle life, high-reliability electrode materials.