Understanding Local Structure-Activity Relation in Lithium-Ion Cathodes with Solid State NMR: Effect of Dopants, Synthesis and Electrochemical Cycling

Abstract

Listen

Translate article

As the need for research and development efforts to enable alternative, sustainable lithium-ion cathode material is increasing, fine-tuning of the cathode composition and local structure has been focused on the use of dopants/ coatings and varying synthesis conditions such as annealing temperature and time. While changing these parameters has been shown to have significant effect on materials performance, the relation of synthesis parameters with local structure and composition and electrochemical activity is an ongoing focus area1. Solid state NMR is an important characterization technique for LIB systems as 6Li and 7Li solid state NMR can directly “see and follow” the Li cations within the structure, providing crucial information on domain structures, lithium local order changes and metal segregation. A multinuclear NMR approach is also crucial to track the dopants and study how/ if the dopants are diffusing into the bulk or remain on the surface as unintended coatings. This work covers an overview of how multinuclear solid-state NMR can be utilized to understand cathode local structure changes with synthesis, and electrochemical cycling, how dopants play a role in transition metal segregation and cathode interphase, and they affect materials performance. The NMR characterization studies focus on lithium-ion cathodes systems including lithium and manganese rich transitional metal oxide cathodes, lithium nickel oxide and nickel manganese cobalt oxides and are assisted by density functional theory calculations in providing a better understanding of the experimental characterization data and therefore local environments, domain structures and dopant effects.