Magnesium Substitution in Ni-Rich NMC Layered Cathodes for High-Energy Lithium Ion Batteries

Ni-rich LiNi1-x-yMnxCoyO2 (NMC) layered oxides are promising cathode materials for high-energy density lithium ion batteries but suffer from severe capacity fading upon cycling. Elemental substitution (= doping) with Mg has repeatedly attracted attention in NMC materials to overcome instability problems at reasonable cost, yet rational compositional tuning is needed to guarantee sufficient cycle life without compromising energy density on the material level. Herein, a series of Mg-substituted NMC materials with 90 mol% Ni are investigated regarding key performance metrics in NMC || graphite full-cells benchmarked against LiNi0.80Mn0.10Co0.10O2 and LiNi0.90Mn0.05Co0.05O2 synthetized using the same co-precipitation route. A linear correlation between cycle life and attainable gravimetric capacities is demonstrated, which are directly influenced by the degree of Mg substitution and the amount of Li+ cycled upon (de-)lithiation processes. A Mg content <2 mol% should be considered to take notable benefit from the increase in Ni content from 80 to 90 mol% to achieve a higher energy density. The present study highlights the importance of evaluating the true implications of elemental substitution on cell performance and is expected to be an insightful guideline for the future development of NMC-type cathode materials in particular with high Ni and low Co content.

Automated summary

This study investigates the Mg substitution of Ni-rich LiNi1-x-yMnxCoyO2 (NMC) layered oxides and demonstrates a linear correlation between cycle life and attainable gravimetric capacities, which are influenced by the degree of Mg substitution and the amount of cycled Li+ ions. To achieve a higher energy density, a lower Mg content and higher Ni content should be considered.