리튬이차전지용 코어-쉘 구조의 Li[Ni0.95Co0.025Mn0.025]O2 양극에 관한 연구

Abstract

A spherical Core-Shell (CS) structured cathode material with an average composition of Li[Ni0.95Co0.025Mn0.025]O2 was synthesized by encapsulating a LiNiO2 core with Li[Ni0.87Co0.065Mn0.065]O2 shell using composition-controlled co-precipitation. The CS cathode exhibited greatly improved capacity retention in a half-cell (corresponding to 90% of its initial capacity after 100 cycles) compared to the LiNiO2 cathode, whose capacity retention was limited to 74.2% after 100 cycles. In a pouch full-cell, representing a prototype LIB, the CS cathode also clearly outperformed the LiNiO2 cathode. The improved cycling performance is mainly attributed to stabilization of the inherently reactive LiNiO2 surface with a Ni-depleted protective shell layer. This stabilization effect of the shell layer was confirmed by differential capacity, electrochemical impedance spectroscopy, and post-cycle structural analysis by HR-TEM. The proposed CS approach allows us to harness the high capacity of LiNiO2 and other extremely Ni-rich NCM compositions with dramatically improved capacity retention, which is an important step toward achieving both the high-energy density and long lifetime required for EV batteries.