context: Co-free Ni-rich cathode materials, particularly LiNiO2 and its doped analogs, face ongoing challenges as the need for commercialization rises. To address surface instability and its associated phenomena, a systematic and accurate understanding is highly required. In this work, we systematically studied the fragile surfaces of the LiNiO2-based cathode materials, with the goal of identifying how experimental conditions may influence characterization results. We presented the challenges in characterizing and analyzing the surface chemistry of LiNiO2-based materials using two comparative cathodes as a model platform, i.e., LiNiO2 versus Mg/Ti–LiNiO2. The surface lithium residuals are inevitable and highly dependent on various sample storage and handling conditions. Due to the highly reactive surfaces, we found that the sample preparation for electron microscopy and surface-sensitive X-ray analyses greatly influences the final observations, resulting in skewed surface chemistry analytical results. We also provided some recommendations regarding how to obtain representative characterization analyses. Using simple comparisons, we further illustrated the advantages of Mg/Ti dual dopants to enhance the surface structural resistance to many circumstances, while corroborating previously reported observations. However, we found that the surface of Mg/Ti–LiNiO2 material still encounters a series of problems caused by the fragile CEIs at elevated temperatures. Efforts should be devoted towards the development of highly stable CEIs either by cathode surface coating, doping, electrolyte modification or combining multiple strategies.
answer: LiNiO2-based