Lithium Nickel Manganese Cobalt Oxides

Lithium Nickel Manganese Cobalt Oxides are a family of mixed metal oxides of lithium, nickel, manganese and cobalt. Nickel is known for its high specific energy, but poor stability. Manganese has low specific energy but offers the ability to form spinel structures that allow low internal resistance.

• Ni-rich NMC has a high discharge capacity
• Mn-rich compositions maintain better cycle life and thermal safety
• Co-rich compositions provide excellent rate capability.

These are lithium ion cell chemistries known by the abbreviation NMC or NCM.

• NMC and NCM are the same thing.
• Lithium-Nickel-Manganese-Cobalt-Oxide (LiNiMnCoO₂)
• Voltage range 2.7V to 4.2V with graphite anode.
• OCV at 50% SoC is in the range 3.6 to 3.7V
• NMC333 = 33% nickel, 33% manganese and 33% cobalt
• NMC622 = 60% nickel, 20% manganese and 20% cobalt
• NMC955 = 90% nickel, 5% manganese and 5% cobalt
• Capacity ~ 154 to 203mAh/g (practical)
• Trend is to reduce Cobalt based on cost and increased capacity
• Higher Nickel content => higher capacity, more heat and faster capacity fade
• Energy density at cell level ~280Wh/kg (2021)
• Maximum energy density at cell level with graphite anode ~350Wh/kg

NMC Composition can be difficult to understand at first and so here is a walk through the compositions and what they actually mean.

The 33%,33%,33%, in NMC111 is the composition of Ni, Mn, Co among themselves rather than the compound (Li Ni_x Mn_y Co_z O₂) as a whole.   

The general formula is LiNi_xMn_yCo_zO₂

• LiNi _0.333Mn_0.333Co _0.333O₂ is abbreviated to NMC111 or NMC333
• LiNi_0.8Mn_0.1Co_0.1O₂ is abbreviated to NMC811

Note that these ratios are not hard and fast. eg NMC811 can be 83% Nickel.

As we move from NMC333 to NMC811 the nickel content increases. As the Nickel content increases the Manganese and Cobalt decrease.

• The thermal stability of the charged NMC decreases with increasing nickel content.
• The more nickel, the lower the onset temperature of the phase transition (i.e., thermal decomposition), and the sharper the peak of the oxygen release.
• Increasing nickel leads to increased structural degradation due to nickel mixing with lithium sites.
• Manganese is the most thermally stable element, which can improve thermal stability.
• Mn-rich cathodes have a reduced capacity because of an ample supply of inactive Mn⁴⁺ species.
• Cobalt also plays an important role in maintaining good thermal stability.

This all means that there is a wide design space available for NMC chemistries and that is expanded further once we look at the anode combinations.

References

• Seong-Min Bak et al, “Structural Changes and Thermal Stability of Charged LiNi_xMn_yCo_zO₂ Cathode Materials Studied by Combined In Situ Time-Resolved XRD and Mass Spectroscopy“, Applied Materials and Interfaces, ACSJCA
• NMC Tapes – NEI Corporation
• NMC as a State-of-the-Art Cathode Material, National Battery Research Institute

NMC 9.5.5 for Li Ion Batteries

Synthesis, Scale up, and Optimisation of NMC 9.5.5 for Li-Ion Batteries.

• Lithium loss during firing and cation mixing disorder can be reduced at larger firing loads.
• Reduction in lithium loss results in improved cathode capacity and cycle life Flux additives can also be used to improve the specific capacity.
• Optimising the firing time and temperature can further improve the cycle life of the NMC 955 material.