NEW INSIGHTS INTO THE ROLE OF ALUMINUM IN LiNi_0.8Co_0.15Al_0.05O₂ (NCA) CATHODE MATERIAL VIA ⁷Li AND ²⁷Al MAS NMR SPECTROSCOPY

Lithium battery research is strongly driven by the demand for longer lasting and better performing energy storage for everything from portable electronics to electric cars. A majority of this research is invested in the development of improved electrode (anode and cathode) materials. The layered transition metal oxides, particularly of the form LiMO₂ (M = transition metals), exhibit some of the best properties in terms of energy densities, relative safety and cost. Among these materials, the aluminum-doped lithium nickel cobalt layered oxide, of the form LiNi_0.8Co_0.15Al_0.05O₂, (NCA) stands out. NCA has been in commercial production since 1999 and its excellent electrochemical and technical features made it the cathode material of choice for Elon Musk`s Tesla car. As such, this material has been fairly well-studied by a full range of analytical techniques. However many aspects of the material`s excellent performance remain not fully understood, e.g. the full extent of the role that the dopant aluminum plays. This current work focuses on an as-of-yet unexplored angle, that is a detailed structural analysis of the bulk material via 7Li and 27Al MAS NMR spectroscopy. The results of this study indicate some novel insights into this well-known cathode material, and in particular shed some new light on the structural environment of the dopant aluminum atoms. In addition, further information was gleaned regarding the effect of the presence of the aluminum on the cycling performance of the NCA material, as well as its influence in diminishing some of the undesired side reactions that prove detrimental to the undoped aluminum-free analog material.