![]() ![]() Lithium ions intercalate between the layers upon discharging, remaining between the lattice planes until the battery gets charged, at which point the lithium de-intercalates and moves to the anode. NMC materials have layered structures similar to the individual metal oxide compounds lithium cobalt oxide (LiCoO 2) and lithium manganese oxide (LiMn 2O 4). Lithium ions can move in and out between the layers. Displacing nickel from the layered structure can alter the material's bonding characteristics, forming undesirable phases and lowering its capacity. The similar size of Ni 2+ (0.69 Å) and Li + (0.76 Å) facilitates cation mixing. Cation mixing, a process in which Li + substitutes Ni 2+ ions in the lattice, increases as nickel concentration increases as well. Higher nickel content decreases the oxygen generation temperature while also increasing the heat generation during battery operation. Oxygen can generate from the metal oxide at 300☌ when fully discharged, degrading the lattice. Increasing cobalt content comes at the cost of replacing either higher-energy nickel or chemically stable manganese while also being expensive. Most notably, increasing the nickel content in NMC increases its initial discharge capacity, but lowers its thermal stability and capacity retention. Modifying the transition metal stoichiometry changes the material's properties, providing a way to adjust cathode performance. Cobalt and nickel oxidize partially to Co 4+ and Ni 4+ during charging, while Mn 4+ remains inactive and maintains structural stability. įor NMC111, the ideal oxidation states for charge distribution are Mn 4+, Co 3+, and Ni 2+. The general lithium content typically remains around 1:1 with the total transition metal content, with commercial NMC samples usually containing less than 5% excess lithium. Other common compositions are NMC622 and NMC811. A composition of 50% nickel, 30% manganese, and 20% cobalt would be called NMC532 (or NCM523) and have the formula LiNi 0.5Mn 0.3Co 0.2O 2. For example, an NMC molar composition of 33% nickel, 33% manganese, and 33% cobalt would abbreviate to NMC111 (also NMC333 or NCM333) and have a chemical formula of LiNi 0.33Mn 0.33Co 0.33O 2. Three numbers immediately following the NMC abbreviation indicate the relative stoichiometry of the three defining metals. Points in a solid solution phase diagram between the end members LiCoO 2, LiMnO 2, and LiNiO 2 represent stoichiometric NMC cathodes. Furthermore, an increased nickel content provides more capacity within the stable operation window. Reducing the cobalt content in NMC is also a current target, owing to ethical issues with cobalt mining and the metal's high cost. There is a particular interest in optimizing NMC for electric vehicle applications because of the material's high energy density and operating voltage. Lithium ions intercalate into the cathode or anode during charging and discharging. A general schematic of a lithium-ion battery. ![]()
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