LITHIUM MAS NMR STUDIES OF LITHIUM ION ENVIRONMENT AND ION DYNAMIC PROCESS IN LITHIUM IRON AND MAGNESIUM PYROPHOSPHATE AS NEW SERIES OF CATHODE MATERIALS FOR LITHIUM ION BATTERIES

Abstract

<p>Lithium-ion batteries provide a more cost-effective and non-toxic source of reusable energy compare to other energy sources. Several research studies have lead to production of some more promising cathode components for lithium ion batteries. Recently, a new series of pyrophosphate-based composition Li₂FeP₂O₇ and Li₂MnP₂O₇ has been reported as cathode materials. They have shown a 3D framework structure and the two Lithium-ions in the three-dimensional tunnel structure make it possible that more than one lithium ion be extracted during cycling. Lithium solid state nuclear magnetic resonance (NMR) is an effective technique to study this cathode material, not only for analyzing local structure, but also for investigation of the microscopic processes that take place in the battery.</p> <p>In this work, Li₂FeP₂O₇ and Li₂MnP₂O₇ have been synthesized. The lithium environment of these materials is studied using 1D ^6,7Li NMR. Assignment of Li₂MnP₂O₇ spectrum has been made based on Fermi-contact interaction and crystal structure. Both variable temperature experiment and 1D selective inversion NMR are used to establish Li-ion pathways as well as Li hopping rates for Li₂MnP₂O₇. Also, ⁷Li MAS NMR measurements are used to characterize Li environments in LixFeP₂O₇after being electrochemically cycled to different points, and preliminary results regard to changes to ion mobility in LixFeP₂O₇at different electrochemical cycled points are presents here, solid-solution (de)lithetiation process is confirmed for this material.</p>