How sintering temperature affects the electrochemical performance of ultra-high nickel (Ni > 0.9) cathode material

Abstract

The burgeoning demand for electric vehicles with extended driving ranges has propelled ongoing development efforts for ultra-high nickel (Ni > 0.9) cathode materials. Despite significant ongoing research focused on Ni-rich cathode materials, a more comprehensive foundational understanding of ultra-high nickel cathode materials is essential. In our research, we employed LiNi0.94Co0.06O2 as a model ultra-high nickel cathode material to systematically delve into the interplay between sintering temperature, structural features, and electrochemical behavior. Within a sintering temperature spectrum of 660–720 °C, we discerned that specimens produced at diminished temperatures manifest a reduced initial discharge capacity yet excel in cycling endurance. In stark contrast, their counterparts produced at augmented temperatures behave inversely. Identifying a singular sintering temperature that achieves equilibrium between initial discharge capacity and cycling performance proves elusive. Through X-ray diffraction and high-resolution transmission electron microscopy, it became evident that samples synthesized at lower temperatures exhibit pronounced lithium-nickel mixing and develop a thicker NiO layer on the surface, leading to compromised initial discharge performance and capacity. Utilizing focused ion beam scanning electron microscopy, differential capacity analysis, and in-situ X-ray diffraction, we confirm that samples synthesized at lower temperatures possess smaller particle sizes, enabling them to withstand volumetric expansion stress during cycling, resulting in enhanced cycling performance. In the realm of ultra-high nickel cathode materials, elevating the sintering temperature is a conduit to superior initial discharge efficiency and capacity. Yet, the imperative of preserving diminutive particle dimensions, as a stratagem to bolster cycling performance, stands out as a pivotal research frontier.