A new coating for improving the electrochemical performance of cathode materials

• LiNi0.4Mn0.4Co0.2O2 is simultaneously coated with alumina and amorphous carbon layer.
• SAED reveals an epitaxial growth of α-Al2O3 on basal {001} facets of the structure.
• However, side-view facets, like {010}, remain free for Li-ion diffusion into cathode.
• Coated cathode samples show both improved high-rate capability and cycling stability.
• Alumina/carbon-coated samples show better rate capability than alumina-coated those.

The layered LiNi0.40Mn0.40Co0.20O2 compound was synthesized and modified with a mixed alumina–carbon coating by a simple soft chemical route. The simultaneous presence of alumina and carbon on the surface of coated samples was proved by ICP-AES, chemical analysis, XP spectroscopy, SEM microanalysis and local electron diffraction. For the first time, we show that the alumina epitaxial layer is formed on basal {001} facets of cathode grains, whereas side-view facets, like {010}, remain free from crystalline α-Al2O3, thus leaving them easy for Li-ion diffusion into cathode structure. An amorphous carbon film was used here for better conductivity of the coating layer and prevention of the electrical contact loss between cathode grains. Electrochemical tests revealed that the mixed alumina-carbon coating applied on LiNi0.40Mn0.40Co0.20O2 stabilizes the surface structure and improves the cycling performance (3–4.5 V) and rate capability of cathodes on their basis compared with the pristine and alumina-coated LiNi0.40Mn0.40Co0.20O2 samples.