6Li MAS NMR Studies of the Local Structure and Electrochemical Properties of Cr-doped Lithium Manganese and Lithium Cobalt Oxide Cathode Materials for Lithium-Ion Batteries

Abstract

6Li magic-angle spinning NMR spectroscopy has been used to probe the lithium local environments in a series of layered compounds, Cr-doped LiCoO2, Co-doped LiCrO2, Cr-doped LiMnO2, and the Li-rich material Li[Li0.2Cr0.4Mn0.4]O2. A series of resonances are seen for LiCrxCo1-xO2 due to Cr3+ occupancy of the first and second cation coordination sphere surrounding Li. The shifts, which are caused by a transferred hyperfine interaction, differ in size and sign, depending on the Li−O−Cr bond angle. The shift of LiCrO2 cannot be directly extrapolated from those measured in the magnetically dilute Cr3+-doped LiCoO2 compounds, and remains constant with temperature (from room to 283 °C). This behavior is ascribed to the strong antiferromagnetic couplings that exist in LiCrO2. The behavior of Cr3+-doped layered LiMn(III)O2 is qualitatively similar to that of Co3+-doped LiCrO2, both compounds showing additional resonances caused by the dopant cations. Dramatically different NMR spectra are seen for Li[Li0.2Cr0.4Mn0.4...