No one loves NMC as much as me

Cathode Material LiNi_xMn_yCo_1−x−yO₂ (NMC)

Lithium nickel manganese cobalt oxide (LiNi_xMn_yCo_1−x−yO₂ or NMC) is a commonly used lithium-ion cathode material due to its improved structural stability at low SOC compared to LCO, high practical capacity, and high energy. Initial research on NMC materials featured LiNi_1/3Mn_1/3Co_1/3O₂ (NMC111) sometimes referred to as NMC333 and sometimes even NCM (don’t be that guy), where the three numbers represent the ratio of transition metals present.

NMC is a layered material, hexagonal in structure with space group R3̅m, with the structure displayed in Figure 1. NMC is understood to be a solid solution of LiCoO₂, LiMnO₂, LiNiO₂, and LiNi_½Mn_½O₂.

Ni-rich NMC materials, where x > y, have generated significant interest in recent years due to higher capacity and further reduction of cobalt and therefore cost.  LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811), LiNi_0.6Mn_0.2Co_0.2O₂ (NMC622), LiNi_0.5Mn_0.3Co_0.2O₂  (NMC 532), and other variations have been predominantly used and studied.

Increasing nickel content of NMC, while positively affecting the energy density, shows increased lithium-nickel site disorder. Octahedral Ni²⁺ and Li⁺ have similar ionic radii (0.61Å and 0.76 Å respectively) allowing them to switch crystallographic sites, negatively impacting the electrochemistry by slowing lithium diffusion and reducing the rate capability of the cell. Ni-rich NMC also suffers from larger volumetric changes during delithiation, decreased thermal stability, and decreased capacity retention compared to NMC111.

Some Resources We Love :

• The Quilty paper on NMC622 is one of my all time favorites for the materials science behind NMC

• This Gasteiger Group publication has a figure explaining the effects of water washing in NMC811 and it’s truly 10/10