Monday, 30 May 2022
West Ballroom B/C/D (Vancouver Convention Center)
G. Hwang, T. Kim, D. Lee, H. Kang, Y. Lee, J. H. Moon (Korea Advanced Institute of Science and Technology), and E. Cho (Korea Advanced Institute of Science and Technology (KAIST))
Due to the recent increase in the public interest and market size of electric vehicles, the demand for lithium-ion batteries has also risen in parallel. However, current LiCoO2 based/LiFePO4 cathode batteries do not meet the desired energy densities for the electric vehicle market. To solve this issue, lithium-rich layered oxides have been proposed as the next evolution of cathode materials. Lithium-rich layered oxides are known to undergo oxygen redox reactions at high voltages, leading to their characteristic high capacity and energy density. However, charging to the upper voltage limits may lead to a high concentration gradient of lithium ions due to its slow diffusion rate. In the layered structures of lithium-rich layered oxides, such concentration gradients will cause non-uniform volume change. This generates internal stress within the material and can lead to the formation of dislocations if accumulated past the critical point. Thus, internal stress within primary particles degrade lithium ion diffusion rate and in turn degrade the cycle stability of the cathode.
In this research, the cycle stability of Lithium-rich layered oxide cathodes was improved by reducing internal stress through primary particle size control using a simple molten salt method. Reducing the primary particle size shortens the diffusion path of lithium, thereby mitigating the concentration gradient of lithium ions generated during charging and discharging. Accordingly, it is possible to effectively suppress the formation of dislocations by reducing the stress caused in the particles, which in turn reduces the deterioration of electrode performance. However, when the size of primary particles is reduced, side reactions on the surface become severe due to the increase in surface area, causing problems such as reduction of coulombic efficiency and the lifetime of the battery. In this study, an additional coating process was performed to mitigate the side effects of particle size reduction.
