Enhanced Electrochemical Performance of Li-Rich Cathode Materials by Organic Fluorine Doping and Spinel L1-xNiyMn2-yO4 Coating

This study employed a novel modification strategy to overcome the intrinsic poor rate performance, large initial irreversible capacity, and low cycling stability of Li-rich layered oxide (LLO) cathode materials. The strategy involved simultaneous in situ spinel Li1+xNiyMn2-yO4 coating using Mn-TFBDC (TFBDC: 2,3,5,6-tetrafluoro-1,4-benzenedicarboxylic acid) as the precursor and organic fluorine doping agent. Uniform Li1+xNiyMn2-yO4 coating of the LLO surface was easily achieved via the coordination of the carboxylic acid ligands with the manganese ions and subsequent heat treatment. TFBDC-assisted treatment rendered significantly enhanced electrochemical performance to LLO. The first discharge specific capacity of LLO modified by TFBDC-assisted treatment (TA-LLO) was enhanced to 302.1 mAh g(-1), and the capacity retention significantly increased from 80.8 to 98.9% after 100 cycles at 1C, compared with that of the pristine LLO (PLLO). Electrochemical impedance spectroscopy and the galvanostatic intermittent titration technique confirmed that TA-LLO had a lower charge transfer resistance and higher ion diffusion coefficient than PLLO. These results suggest that the use of organic fluorine is an effective strategy to carry out fluorine doping simultaneously with spinel Li1+xNiyMn2-yO4 coating for fast Li+ ion diffusion and significantly improved electrochemical properties of LLOs.