Lithium nickel cobalt aluminium oxides

The most important manufacturer of NCA batteries is Panasonic or Panasonic's cooperation partner Tesla,[1] as Tesla uses NCA as active material in the traction batteries of its car models.[2][3] In Tesla Model 3[4] and Tesla Model X, LiNi_0,84Co_0,12Al_0,04O₂ is used.[5] With a few exceptions, current electric cars as of 2019 use either NCA or alternatively lithium nickel manganese cobalt oxides (NMC).[4] In addition to use in electric cars, NCA is also used in batteries for electronic devices, mainly by Panasonic, Sony and Samsung.[6] Cordless vacuum cleaners are also equipped with NCA batteries.[7]

The usable charge storage capacity of NCA is about 180 to 200 mAh/g.[11] This is well below the theoretical values; for LiNi_0,8Co_0,15Al_0,05O₂ this is 279 mAh/g.[1] However, the capacity of NCA is significantly higher than that of alternative materials such as lithium cobalt oxide LiCoO₂ with 148 mAh/g, lithium iron phosphate LiFePO₄ with 165 mAh/g and NMC 333 LiNi_0,33Mn_0,33Co_0,33O₂ with 170 mAh/g.[1] Like LiCoO₂ and NMC, NCA belongs to the cathode materials with layer structure.[11] Due to the high voltage, NCA enables batteries with high energy density. Another advantage of NCA is its excellent fast charging capability.[11] Disadvantages are the high costs and the limited resources of cobalt and nickel.[11]

The two materials NCA and NMC have related structures, quite similar electrochemical behaviour and show similar performance, in particular relatively high energy densities and relatively high performance. It is estimated that the NCA battery of Model 3 contains between 4.5 and 9.5 kg of cobalt and 11.6 kg of lithium.[12]

Lithium nickel oxide LiNiO₂, which is closely related to NCA, or nickel oxide NiO₂ itself, cannot yet be used as a battery material because they are mechanically unstable, shows a rapid loss of capacity and have safety issues.[4]

NCAs LiNi_xCo_yAl_zO₂ with x ≥ 0.8 are called nickel rich;[13] those compounds are the most important variants of the substance class. The nickel-rich variants are also low in cobalt and therefore have a cost advantage, as cobalt is relatively expensive. Furthermore, as the nickel content increases, so does the voltage and thus the energy that can be stored in the battery. However, as the nickel content increases, the risk of thermal breakdown and premature aging of the battery also increases. When a typical NCA battery is heated to 180 °C, it will thermally run away.[14] If the battery was previously overcharged, thermal run away can occur already at 65 °C.[14] The aluminium ions in NCA increase stability and safety, but they reduce capacity because they do not participate in oxidation and reduction themselves.

To make NCA more resistant, in particular for batteries that need to operate at temperatures above 50 °C, the NCA active material is usually coated. The coatings demonstrated in research may comprise fluorides such as aluminium fluoride AlF₃, crystalline oxides (e.g. CoO₂, TiO₂, NMC) or glassy oxides (silicon dioxide SiO₂) or phosphates such as FePO₄.[1]