Understanding the relationship of electrochemical properties and structure of microstructure-controlled core shell gradient type Ni-rich cathode material by single particle measurement

Abstract

• Ni-rich core-shell gradient material (CSG) was investigated by quantitative analysis using single particle. • The charge transfer resistances of CSG is more stable conventional NCM during cycle. • The lithium diffusion coefficient of CSG is 10 times higher than that of conventional NCM. To overcome those of drawbacks form Nickel-rich NCM cathode materials about poor cyclability and thermal instability at elevated temperatures and high voltage conditions, CSG (core shell gradient NCM) fabricated with the concentration gradient control has continuous and gradual transition metal composition concentration gradient. It has that the rod-shaped primary particles forming the interior had a directionality toward the center of the secondary particles. The correlation of gradient structure and electrochemical properties has been investigated for this study by single particle measurement. Quantitative evaluation of the electrochemical properties of the active material through single particle measurement showed more clearly the difference in the unique electrochemical properties between CSG which have a unique structure and conventional NCM (LiNi 0.8 Co 0.1 Mn 0.1 O 2 ). The measured initial reversible capacity was measured as 0.52 nAh (NCM, 10.4 um diameter) and 1.34 nAh (CSG, 14 um diameter). In addition, rate capability showed that CSG had higher discharge capacity under the same current density condition. In addition, calculated charge transfer resistance of CSG was lower in all DOD (depth of discharge) regions than NCM by Tafel plot. The calculated by GITT lithium diffusion coefficient in CSG is found to be 10 times higher than conventional NCM in all lithiated states. This suggests that the high diffusion coefficient of CSG not only beneficial for excellent rate capability, but also sagnificantly improves cycle life by suppressing internal stress generated upon cycling.