Resistance characteristics depending on the structure of Ni-rich cathode materials

Abstract

With the growing concern over global warming, the electric vehicle market is experiencing accelerated growth. Consequently, lithium-ion batteries, a crucial component of electric vehicles, have garnered significant attention. Particularly, high- nickel cathode oxides are being recognized as next-generation cathode materials due to their high energy density. However, high-nickel cathode materials face challenges such as capacity degradation and stability issues over long-term use, prompting extensive research efforts to address these issues. In this study, I synthesized cathode materials by adjusting 1) calcination conditions, 2) structure of precursor, and analyzed their electrochemical performance and structural characteristics. Through various analyses, including X-ray diffraction (XRD) and scanning electron microscopy (SEM), alongside electrochemical tests like Hybrid Pulse Power Characterization (HPPC) and Galvanostatic Intermittent Titration Technique (GITT), I found that calcination temperature significantly affects both structural and electrochemical properties. Interestingly, Li/Ni mixing phenomena were found to impact initial charging state resistance more than lithium layer thickness. To understand the impact of structural differences in precursors on the cathode materials, I synthesized materials using three high-nickel precursors with slightly different specific surface areas but the same composition. Through XRD, Neutron diffraction (ND), and SEM analyses, along with HPPC and GITT tests, I investigated the structural and electrochemical performance of the cathode materials. The results showed that cathodes with lower Li/Ni mixing phenomena tended to exhibit better resistance characteristics at the initial charging state. However, samples with higher Li/Ni mixing showed better performance in terms of lifespan and rate capability. This suggests that while Li/Ni mixing phenomena may have a negative impact on resistance, they can have a positive effect on structural stability. Through these two studies, I found that Li/Ni mixing may have a negative impact on resistance characteristics during the initial cycles but can be advantageous in terms of lifespan.