Understanding the Effects of Ultra-Thin Al2O3 Coatings Prepared By Atomic Layer Deposition on Lithium Ion Battery Cathode Materials

Abstract

Although various cathode materials possessing high capacity have been developed to date, most of them are still suffering from early capacity fading. Several strategies such as doping, surface treatment and coating have been adopted to minimize this problem. Among a variety of coating strategies, atomic layer deposition (ALD) is regarded as the best technique for coating of cathode materials. ALD is a thin-film growth technique that offers the unique capability to coat complex, three-dimensional objects with precise, conformal layers by atomic-level control over thickness and composition. Over the last decade, ALD has emerged as an effective strategy for coating cathode materials to enhance the overall performance Li-ion batteries. ALD Al2O3 coatings prepared using trimethyl aluminum (TMA) and H2O have been evaluated previously on cathodes including LiCoO2 (LCO), LiMn2O4 (LMO), and Li(NixMnyCoz)O2 (NMC), and the effect of the coating on cycling stability was found to vary between these different materials. Moreover, our recent study of TMA/H2O chemistry on LMO revealed a unique nucleation mechanism leading to unexpected products and altered electrochemical behavior. In an effort to better understand these observations, we are exploring Al2O3 ALD using a range of aluminum precursors (TMA, tris(dimethylamido) aluminum, aluminum trichloride, dimethyl aluminum isopropoxide, and aluminum triisopropoxide) and a variety of cathode materials (LCO, LMO, and several NMCs). We discovered that the ALD aluminum precursor reduces cations on the cathode surface, and the degree of reduction depends on the relative Lewis acidity of the precursor ligands, and on the composition of the cathode surface. In this presentation we will elaborate on these findings and describe the correlations between the chemistry of the ALD-modified cathode surface and the resulting electrochemical behavior and cycling performance.