Suppressing High Current Induced Local Compositional Heterogeneity in LiNi_(0.6)Co_(0.2)Mn_(0.2)O_2 By Controlling the Kinetic Parameters

摘要

Understanding the cycling rate-dependent kinetics is crucial for engineering batteries with better performance in high power applications. Although high cycling rate induces phase heterogeneity which is responsible for life-time and rate capability, such dynamics are poorly understood and uncontrollable. In this study, operando X-ray diffraction analysis with high temporal resolution was utilized to investigate phase transition kinetics of LiNi_(0.6)Co_(0.2)Mn_(0.2)O_2 at a high cycling rate. Due to the sluggish Li diffusion at high lithiation levels, highly asymmetric phase transition was observed in charge and discharge. While relatively homogeneous phase transition took place during discharging, strong phase separation was observed during charging. By taking advantage of the dependence of diffusion and redox kinetics on Li composition and tuning the initial lithiation distribution, we were able to manipulate the overall phase transformation kinetics and further induce solid-solution phase transformation at the high C-rate charging. The finite element analysis elucidated the effect of Li content-dependent diffusion kinetics on the phase transition pathway. Our findings suggest a new direction of optimizing fast cycling protocols based on the fundamental understanding of the material properties.