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Cathodes; Density functional theory; Electron energy levels; Electron energy loss spectroscopy; Electron scattering; Electronic structure; Energy dissipation; High resolution transmission electron microscopy; Lithium; Lithium compounds; Scanning electron microscopy; Titanium oxides; Transition metals; X ray absorption spectroscopy; Zirconium compounds, Cathodes material; Layered oxides; Li-rich layered oxide; Lithium-rich layered oxides; Oxygen retention; Rate performance; Specific capacities; Structured oxides; Surface doping; Voltage decay, Oxygen
Abstract:
Li-rich layer-structured oxides are considered promising cathode materials for their specific capacities above 250 mAh·g-1. However, the drawbacks such as poor rate performance, fast capacity fading, and the continuous transition metal (TM) migration into the Li layer hinder their commercial applications. To address these issues, surface doping of Ti and Zr was conducted to the Li- and Mn-rich layered oxide (LMR), Li1.2Mn0.54Ni0.13Co0.13O2. The drop of the average discharge potentials of the Ti- and Zr-doped LMR was reduced by 593 and 346 mV in 100 cycles, respectively. With aberration-corrected scanning transmission electron microscopy and electron energy loss spectroscopy, we clarified that Ti4+and Zr4+ions are located near the surface of the material, anchor the surface oxygen, and stabilize the LMR structure. The difference in the strengths of the Ti-O and Zr-O bonds and the doping-resultant electronic structures were determined with density functional theory (DFT) calculations and soft X-ray absorption spectroscopy (SXAS), responsible for the electrochemical performance of surface-doped materials. These findings verify our modification strategies to enhance the cycling performances of the promising LMR cathode materials. © 2022 American Chemical Society. All rights reserved.
