Unveiling the Stabilities of Nickel‐Based Layered Oxide Cathodes at an Identical Degree of Delithiation in Lithium‐Based Batteries

Abstract Bulk, surface, and interfacial instabilities that impact the cycle and thermal performances are the major challenges with high‐energy‐density LiNi_1−x–yMn_xCo_yO₂ (NMC) cathodes with high nickel contents. It is generally believed that the instabilities and performance losses become exponentially aggravated as the nickel content increases. Disparate from this prevailing belief, it is herein demonstrated that NMC cathodes with higher Ni contents may imply better overall stability than “lower‐Ni” cathodes under an identical degree of delithiation (charging) conditions. With two representative cathodes, LiNi_0.8Mn_0.1Co_0.1O₂ and LiNiO₂, a systematic investigation into their stabilities with control of the degree of delithiation is presented. Electrochemical tests indicate that LiNiO₂ displays better cyclability than LiNi_0.8Mn_0.1Co_0.1O₂ at the same delithiation state. Comprehensive structural and interphase investigations unveil that the inferior cyclability of LiNi_0.8Mn_0.1Co_0.1O₂ predominantly results from aggravated parasitic reactions, and the interphase stability may be more critical than lattice stability in dictating cyclability. Also, LiNiO₂ delivers similar or better thermal behavior than LiNi_0.8Mn_0.1Co_0.1O₂. The findings demonstrate a strong correlation of the stability of NMC cathodes to the degree of delithiation state rather than the Ni content itself, highlighting the importance of reassessing the true implications of Ni content and structural and interphasial tuning on the stabilities of NMC cathodes.