Tungsten Improves Performance of Nickel NCA Cathode

Yang-Kook Sun and others at Hanyang University in South Korea introducing tungsten into Li [Ni_0.95Co_0.04Al_0.01] O₂, NCA cathode to develop high capacity and excellent cycling of nickel-rich layered LiMO2 cathode. Relevant research results have been published in the internationally renowned journal "Energy Storage Materials".

The lithium nickel cobalt aluminum oxides (NCA) are a group of substances comprising metal oxides. Some of them are important due to their application in lithium-ion batteries. NCAs are used as active material on the positive pole (which is the cathode when the battery is discharged). NCAs are mixed oxides comprising the cations of the chemical elements - lithium, nickel, cobalt, and aluminum.

The lithiated nickel-cobalt-aluminum oxide (Li [Ni_0.8Co_0.15Al_0.05] O₂) cathode has become commercialized because it provides high discharge capacity with long cycle life. To further increase the capacity of existing NCA cathodes, the fraction of Ni in the NCA cathode has been progressively increased. However, this approach is limited by the deterioration of capacity and safety concerns.

The superior cycling performances of the W-NCA95 cathode are attributed to the reduction of the anisotropic volume change and the unique long rod-shaped primary particle morphology. The proposed W-NCA95 cathode paves the way for the development of Ni-rich layered LiMO₂ cathodes that can exhibit high capacity, superior cycling stability, and improved thermal stability.

As we all know, increasing the ratio of nickel in the layered lithium transition metal oxide (LiMO₂, where M=Ni, Co, Al, Mn) can increase the capacity of the cathode material and reduce the cost. However, the anisotropic volume change caused by the H2-H3 phase transition will cause the problem of poor battery cycle life.

The harmful phase transition of H2-H3 will produce internal microcracks in the positive electrode particles. These microcracks will accelerate the penetration of the electrolyte into the particles, thereby reacting with the unstable Ni⁴⁺ on the internal primary particles exposed along the microcracks and forming NiO-like. The impurity layer accelerates the degradation of the surface of the primary particles.

Similar to the NCM positive electrode, as the nickel content increases, the capacity retention rate of the high nickel NCA positive electrode will also drop rapidly. Therefore, the development of a nickel NCA positive electrode with excellent structural stability and high performance is particularly important for extending the battery life of secondary lithium batteries.

Recently, the research team of Hanyang University in South Korea modified the existing high-nickel NCA cathode material by using transition metal tungsten elements. The fundamental electrochemical performances of W-doped Li [Ni_0.95Co_0.04Al_0.01] O₂ cathode (W-NCA95) with columnar grains by introducing WS2. The microstructure-modified W-NCA95 delivers a high initial capacity of 242 mAh g-1 (0.1 C) and retains 77.4% of its initial capacity after 1000 cycles, compared to 14.5% for Li [Ni_0.95Co_0.04Al_0.01] O₂ cathode (NCA95). The excellent cycle performance of the W-NCA95 cathode is attributed to the reduction of anisotropic volume change and the unique long rod-like primary particle morphology.

In general, by introducing tungsten into NCA cathode not only has a higher initial capacity but also has better cycle stability, enabling electric vehicles to travel more than 300 miles on a single charge.

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