Cerium fluoride coated layered oxide Li1.2Mn0.54Ni0.13Co0.13O2 as cathode materials with improved electrochemical performance for lithium ion batteries

• Cerium fluoride is used as a novel coating material for Li-rich layered cathode.
• Coated cathode displays enhanced high-rate capability and cycling stability.
• Coating layer suppresses the increase of electrochemical impedance of electrode.

Cerium fluoride (CeF3) coated lithium-rich layered Li1.2Mn0.54Ni0.13Co0.13O2 particles are synthesized using a facile chemical deposition route. The structural and electrochemical properties of pristine and CeF3-coated electrodes are investigated by X-ray diffraction (XRD), thermogravimetric-differential scanning calorimetry (TG-DSC), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), galvanostatic charge/discharge tests, electrochemical impedance spectra (EIS) and cyclic voltammetry (CV). The results indicate that the cathode particles are uniformly covered with a CeF3 layer (∼10 nm thick) after 2 wt.% CeF3 surface coating. The coated electrode shows an enhanced initial coulombic efficiency of 80.8% compared to 75.2% for the pristine electrode. Moreover, the coated electrode demonstrates better cyclic performance, which exhibits capacity retention of 91.7% after 50 cycles compared with only 82.1% for the pristine one. Furthermore, the CeF3-coated electrode delivers a superior high-rate capacity of 103.1 mAh g−1 at 5C, higher than 82.2 mAh g−1 for the pristine one. The remarkably improved cycling stability and high-rate capacity of the surface-modified electrode is ascribed to the presence of a stable and thin CeF3 coating layer which effectively reduces the damage of electrode structure and suppresses the increase of impedance during cycling by preventing direct contact of electrode with electrolyte.