리튬 이온 전지 양극 물질로서 리튬니켈망간산화물의 전기화학 특성에 관한 연구

Abstract

Developing cathode electrode materials with high energy densities is required for Li-ion batteries applications in next-generation. In this regard, the LiNi0.5Mn1.5O4 spinel cathodes are one of the most promising materials due to their high energy, arising from a high operating potential (~4.7V vs. Li/Li+). However, there are concerns about the stability of organic electrolytes at the high potential from redox couple (Ni4+/Ni2+). In order to develop the full energy density of LiNi0.5Mn1.5O4 cathodes in next-generation vehicles, it is essential to understand the materials durability or stability at high potential. In this thesis, particular experimental has been introduced to verify reactivity of the materials at high potential. Even if the material electrode were exposed to high potential for long time like 5.3V for 100hours, bulk structure is very stable. Nevertheless, electrochemical behaviors are degraded with large polarization and capacity fading. That’s why there is a passivation layer on the electrode surface, which is caused from electrolyte decomposition at high potential. Next, to solve the problem, the material particles are coated with Al2O3 using atomic layer deposition (ALD). The coated LNMO electrodes with 5ALD cycles deliver 84% capacity retention compared to initial and no polarization. The surface modification contributes to enhancing the stability of materials at high potential.Additionally, to enhance rate capability, modification method is excess lithium doping. Li excess spinel (Li1.1Ni0.45Mn1.5O4) has improved performance because excess lithium has organized some disordering of Ni/Mn arrangement. High power Li excess spinel was synthesized and great performance was achieved by using excess lithium doping.