Which of the nickel-rich NCM and NCA is structurally superior as a cathode material for lithium-ion batteries?

Abstract

As two typical layered nickel-rich ternary cathode materials, NCA and NCM are expected to be commercialized in lithium-ion power batteries. However, there is still a lack of systematic research on the pros and cons of these two nickel-rich materials in industry. Herein, LiNi_0.85Co_0.1Al_0.05O₂ and LiNi_0.8Co_0.1Mn_0.1O₂ were synthesized by the co-precipitation method. It is found that LiNi_0.85Co_0.1Al_0.05O₂ delivers a better cycling stability than LiNi_0.8Co_0.1Mn_0.1O₂, even with a higher nickel content. Characterization of the internal structure and the chemical composition of materials after cycles indicated serious Mn dissolution in LiNi_0.8Co_0.1Mn_0.1O₂ during the long cycles. The Mn dissolution will lead to more serious Li/Ni mixing and Ni dissolution, which would finally cause the worse structural stability of LiNi_0.8Co_0.1Mn_0.1O₂. Besides, first principles calculations were used to calculate the difficulty of generating oxygen vacancies in LiNi_0.85Co_0.1Al_0.05O₂ and LiNi_0.8Co_0.1Mn_0.1O₂ during cycling, and the result showed that the formation energy of vacancy defects of O adjacent to the dopant atoms in the Al doped structure is higher than that of the Mn doped structure. The existence of oxygen vacancies provides a channel for the migration and dissolution of transition metal atoms. Finally, it is calculated and proved that the Al–O bonding stability under the TM–O octahedral coordination system is much greater than the Mn–O bonding stability.