소결제 첨가와 수세 공정이 리튬이온전지 양극 소재 단결정 LiNiO2의 구조 및 전기화학 성능에 미치는 영향

Effect of Flux Additives and Post-Synthesis Washing on Structural and Electrochemical Properties of Single-Crystal LiNiO2 Cathodes for Li-Ion Batteries

Single-crystal LiNiO2 (LNO) is a promising cathode material for lithium-ion batteries due to its high capacity and enhanced structural stability, attributed to the absence of grain boundaries. However, its high-temperature synthesis often induces undesired cation mixing. In this study, a minimal-flux solid-state synthesis approach was employed to control the structure and electrochemical behavior of single-crystal LNO using small amounts (0.05 mol) of various flux additives (KOH, NaOH, LiCl, LiNO3, KI). Among them, LiNO3 yielded the best overall performance, with reduced cation mixing, stable lattice structure, and superior cycling stability—without requiring post-synthesis washing. The effect of deionized water washing was also examined. Although washing typically removes residual flux, its impact varied depending on the flux type. KOH-washed samples showed improved layer ordering and higher initial capacity, whereas NaOH and LiCl led to degraded surface structure or lower performance. Notably, all washed samples exhibited extra side reactions during the initial charge, indicating that washing could introduce surface chemical heterogeneity. These findings highlight the coupled effects of flux composition and washing process on the structural and electrochemical properties of LNO. Careful optimization of both factors is essential for developing high-performance single-crystal cathodes.