Hierarchical nickel valence gradient stabilizes high-nickel content layered cathode materials

High-nickel content cathode materials offer high energy density. However, the structural and surface instability may cause poor capacity retention and thermal stability of them. To circumvent this problem, nickel concentration-gradient materials have been developed to enhance high-nickel content cathode materials’ thermal and cycling stability. Even though promising, the fundamental mechanism of the nickel concentration gradient’s stabilization effect remains elusive because it is inseparable from nickel’s valence gradient effect. To isolate nickel’s valence gradient effect and understand its fundamental stabilization mechanism, we design and synthesize a LiNi0.8Mn0.1Co0.1O2 material that is compositionally uniform and has a hierarchical valence gradient. The nickel valence gradient material shows superior cycling and thermal stability than the conventional one. The result suggests creating an oxidation state gradient that hides the more capacitive but less stable Ni3+ away from the secondary particle surfaces is a viable principle towards the optimization of high-nickel content cathode materials.

Electrochemical Properties of High Nickel Content Li(Ni0.7Co0.2Mn0.1)O2 with an Alumina Thin-Coating Layer as a Cathode Material for Lithium Ion Batteries

The cathode material, high Nickel content Ni0.7Co0.2Mn0.1 (NCM), was synthesized by coprecipitation with NH4OH used as a complexing agent. The prepared materials are made in the formation of spherical particles of Li(Ni0.7Co0.2Mn0.1)O2 of several micrometers in diameter. Al2O3 was coated by an impregnation method and its content was gradually increased to 1, 2 and 5 wt%. As a result, 1 wt% coated Al2O3 compared to pristine NCM exhibited 82% and 80% retention rates at 5 C and 1 wt% Al2O3 coated NCM recovery at 0.2 C after 5 C showed 100%. In addition, capacity retention of 1 wt% NCM+Al gently decreased in 100 cycle life characteristics, and capacity retention of 95% or more was confirmed.