High-Performance Ni-Rich Cathodes through Precision Control for Electric Vehicle Batteries

Abstract

Li-ion batteries (LIBs) become the main portable energy source for electric vehicles (EVs) owing to their high energy and power densities as compared to those of other forms of secondary batteries. As the overall performance and cost of LIBs are largely determined by the cathode material, recent research has heavily focused on developing high-capacity cathode materials. However, chasing high-energy-density without compromising service life is very challenging. Among the available cathode materials for LIBs, layered Li[Ni1-x-yCox(Mn or Al)y]O2 (NCM or NCA) is the material of choice owing to its high theoretical capacity of 275 mAh g−1. The demand for higher energy density at a lower cost has pushed the Ni content to approach 90% because Ni is in charge of energy density in NCM and NCA cathode. The inclusion of more Ni in the NCM and NCA cathodes has significant benefits in LIB energy density and cost, as it concomitantly reduces the content of expensive Co. However, the increase in Ni content sacrifices cycling and thermal stability due to the high reactivity of Ni. Such a trade-off between energy density and stability becomes increasingly severe with increasing Ni content. Capacity fading of Ni-rich NCM and NCA cathodes, especially above Ni 80%, largely originates from microcracking which exposes a large portion of the cathode interior to deleterious electrolyte attack. To suppress the development of microcracks on cathode materials, Ni-rich cathode materials should guarantee mechanical stability even in highly charged states. In this presentation, Ni-rich layered cathodes through precision control are presented. One approach is an optimization of both the crystal structure and primary particle morphology by introducing high valence ions. Another strategy is to develop concentration gradient (CG) cathodes with rod-shaped primary particles that are elongated along the radial direction. The CG cathodes are further optimized via high-valence ion doping thereby preserving the microstructure until the cathode attains optimal crystal structure via the reduction of cation mixing. These cathodes exhibit outstanding performance in long-term cycling tests.