Solid State and Intercalation Chemistry of Nickel-Tellurate Cathodes for Lithium and Sodium Batteries

Abstract

Layered AMO2 oxides have been exhaustively researched over the past 40 years. This process was accelerated by the advent and commercial success of the Li-ion battery. With many AMO2 chemistries approaching their theoretical limit in terms of performance, it is important to continue the search for new material compositions and structures. This search will continue to advance our understanding of the solid state and intercalation chemistry in novel cathode materials for design principles that can aid in making new chemistries feasible or result in the discovery of new solid state electrochemical phenomenon.The nickel-tellurate system has been seldom explored for lithium and sodium positive electrode materials. The presence of Te6+ in the structure allows for a wide range of compositions within a structural family. The cation ratio of A+:Ni2+ can be varied to tailor the amount of vacancies in the structure. In this study, novel compositions in the A+-Ni2+-Te6+-O (A=Li or Na) phase space have been synthesized and characterized with X-ray diffraction, solid-state nuclear magnetic resonance spectroscopy, and electrochemical techniques to elucidate the structure-electrochemical property relationships in these materials. Experimental characterization methods are coupled with density functional theory (DFT) calculations to probe the local atomistic structure and reaction mechanisms. Our findings have led to the identification of unusual structural features for both lithium and sodium cathode materials. For the layered sodium nickel-tellurates, the introduction of excess Na into the MO2 layers led to superior electrochemical performance via the suppression of correlated Na+-ion motion and MO2 layer gliding in the layered NaxMO2 structure.[1] For lithium, the structural nuances have led to poor electrochemical performance, but can nevertheless be used as guiding principles for the exploration of novel cathode chemistries.[2]