A study on the effect of ultrathin Li-rich oxide coating on single crystal Ni-rich cathode for Lithium-ion batteries

다국어 초록 (Multilingual Abstract)

A study on the effect of ultrathin Li-rich oxide coating on single crystal Ni- rich cathode for Lithium-ion batteries Kyoung Eun KIM Department of Energy Engineering The Graduate school Hanyang University Utilizing a single-crystalline LiNixCoyMn1-x-yO2 (SNCM) cathode material with high nickel content (x ≥ 0.8) has the potential to improve both the mechanical characteristics and electrochemical stability when compared to a conventional poly-crystalline Ni-rich NCM. However, unlike poly- crystalline NCM, Ni-rich SNCM cathodes suffer the gradual structural collapse from surface to bulk region in the particle as their main cause for cathode degradation. In this study, we fabricated an electrochemically inert Li-rich Li2MnO3 (LMO) coating on SNCM (x = 0.9) to alleviate the initial surface degradation and prevent the interior structure collapse of particle. An ultrathin LMO coating layer synthesized using amorphous MnO2 and residual Li compounds of SNCM suppressed c-axis lattice shrinkage and expansion of SNCM during the H2–H3 phase transition, leading to a reduction in anisotropic lattice strain and intragranularcracking. Moreover, the monoclinic LMO surface prevented the unfavorable layered to spinel and/or rock-salt phase transition of SNCM while maintaining its layered structure even after repetitive high-voltage (4.5 V) operation. Benefiting from its enhanced structural stability, the LMO-coated SNCM cathode exhibited higher capacity retention (76.2%) after 100 cycles than that of pristine SNCM (61.5%) with a high upper cut-off voltage (4.5 V). This study provides a simple and efficient coating strategy for improving the high- voltage stability of the Ni-rich SNCM cathode and offers insights into the performance-enhancement and degradation mechanisms of Ni-rich layered oxides.

목차 (Table of Contents)

• Chapter 1 Introduction 14
• Chapter 2 Research background 18
• Chapter 3 Experimental 29
• Chapter 4 Result and discussion 38
• Chapter 5 Conclusions 73
• References 74
• 국문요지 83