부산대학교 도서관

Layered lithium–nickel–cobalt–manganese oxide (NCM) materials have emerged as promising alternative cathode materials owing to their high energy density and electrochemical stability. Although high reversible capacity is achieved for Ni-rich NCM materials when charged beyond 4.2 V vs. Li+/Li, full lithium utilization is hindered by the pronounced structural degradation and electrolyte decomposition. Herein, we present the unexpected realization of sustained working voltage as well as improved electrochemical performance upon electrochemical cycling at a high operating voltage of 4.9 V in the Ni-rich NCM LiNi0.895Co0.085Mn0.02O2. The improved electrochemical performance at high working voltage at 4.9 V is attributed to the removal of the resistive Ni2+O rock-salt surface layer, which stabilizes the voltage profile and improves retention of the energy density during electrochemical cycling. The manifestation of the layered Ni2+O rock-salt phase along with the structural evolution related to the metal dissolution are probed using in-situ X-ray diffraction, neutron diffraction, transmission electron microscopy, and X-ray absorption spectroscopy. Our findings help unravel the structural complexities associated with high working voltage and offer insight for the design of advanced battery materials, enabling the realization of fully reversible lithium extraction in Ni-rich NCM materials.In Chapter 1, we studied basic knowledge of lithium secondary battery overview, types and properties of cathode materials. In the second chapter, we have studied the surface stabilization of Ni rich NCM induced at high voltages.