Reduction of the Calcination Temperature for Improvement of Ni-Rich Single-Crystal Cathode

Abstract

Synthesizing a high-performance single-crystal cathode with a Ni-rich composition for use in Li-ion batteries is a difficult task. This is because sintering of particles requires calcination at high temperatures, but performing calcination at very high temperatures can damage Ni-rich layered cathode materials. Therefore, finding ways to reduce the calcination temperature required for the synthesis of single-crystal cathodes can improve the cathode's performance. In this research, a Ce dopant was introduced to successfully synthesize a Ni-rich single-crystal cathode with the composition Li[Ni0.9Co0.05Mn0.05]O2 (NCM90) at a calcination temperature that was 50°C lower than its optimal temperature. Dopants affect the growth and sintering behavior of cathode materials during calcination depending on their properties. For example, W retards the growth and sintering of grains, preventing the formation of single-crystal particles, while Ce promotes the formation of single-crystal particles. Taking advantage of Ce's ability to promote single-crystal particle formation, a Ce-doped NCM90 cathode was synthesized at a calcination temperature of 800°C, while the undoped NCM90 cathode remained polycrystalline at this temperature. The Ce-doped NCM90 cathode showed an initial capacity of 199.7 mAh g−1 at 0.1 C, and after 100 cycles at 0.5 C, it retained 80.5% of its initial capacity, demonstrating better cycling stability than the undoped NCM90 cathode. The Ce dopant protracted the detrimental H2-H3 phase transition, which reduced capacity loss as revealed by differential capacity analysis. Additionally, the presence of Ce in the cathode improved its thermal stability.