Department of Energy Engineering (Energy Engineering)As batteries have been introduced in electric vehicles (EV) and energy storage system (ESS), bi-modal Li[NixCoyMnz] O2 (NCM) cathode materials have been highlighted thanks to their high value of volumetric energy density. However, these commercial applications accompany huge amount of heat release during cycles, therefore, the NCM cathode materials in battery system are rapidly deteriorated by a heat transfer. Therefore, in order to prevent cathode degradation under high temperature, researchers have studied on degradation mechanism of the cathode materials such as phase transition, metal dissolution, cation mixing and intra/intergranular cracks.
However, the studies are limited in a microscopic view, which can explain degradation mechanism in a particle scale. In the case of the commercial LiBs, the electrodes with a high thickness are fabricated for achieving high energy density. In this circumstance, the cathode particles are placed in a variety of environment, and particle degradation also unequally occurs according to the particle arrangement. Therefore, investigation on degradation mechanism of the bi-modal NCM cathode should be conducted in a local scale.
Herein, ex-situ Raman spectroscopy is utilized as a powerful tool to analysis degradation of bi-modal NCM cathode in a local scale. Correlation with ex-situ Raman spectra and XRD spectra shows that ratio of the Raman peak intensity between 597cm-1(A1g, Ni2+O6) and 547cm-1 (A1g, Ni3+O6) is proper as an indicator of electrode degradation. On the basis of our investigation, the main factor of cathode degradation under high temperature related with the degree of particle fraction and the improvements are discussed in detail.clos
