Structure and thermal stability of LiNi0.8Co0.15Al0.05O2 after long cycling at high temperature

Abstract

LiNi0.8Co0.15Al0.05O2 (NCA) is widely used as cathode material in commercialized high energy density lithium ion battery due to its high specific capacity. However, the structure and thermal stability of NCA after long electrochemical cycles are remained unclear. Herein, we investigate the structure and thermal stability of aged NCA at both lithiated and delithiated states using in-situ charge/discharge and high temperature X-ray diffraction and transmission electron microscopy images. The thermal stability of delithiated NCA cathode after 400 cycles at 1C is obviously inferior to the lithiated and pristine one. The particle surface of aged NCA changes from layered to spinel phase, while the bulk area maintains the layered structure. The temperature inducing structure change of aged NCA is much lower than that of pristine NCA and the delithiated state of NCA is more vulnerable at high temperature. The drastic structure transformation of aged NCA occurs at 250 °C during heating, which accompanies with oxygen loss and the formation of intergranular cracks in the NCA secondary particles. Thus, this work provides significant information of structure stability of cycled NCA at high temperature for optimizing its surface structure to achieve excellent cycling performance under extreme conditions.