Improvement of long-term cycling performance of Li[Ni0.8Co0.15Al0.05]O2 by AlF3 coating

Abstract The surface of a Li[Ni 0.8 Co 0.15 Al 0.05 ]O 2 cathode material was coated by a 50-nm thick AlF 3 layer using a simple dry coating process. Although the initial discharge capacity of pristine and AlF 3 -coated Li[Ni 0.8 Co 0.15 Al 0.05 ]O 2 was nearly same, the AlF 3 -coating significantly improved the electrochemical performances of Li[Ni 0.8 Co 0.15 Al 0.05 ]O 2 in a full cell configuration (graphite anode), especially at an elevated temperature (55 °C). Furthermore, the AlF 3 -coated Li[Ni 0.8 Co 0.15 Al 0.05 ]O 2 had better thermal stability than the pristine electrode. The improved electrochemical performance likely arose from the AlF 3 coating layer which may have retarded the transition metal dissolution from HF attack. Electrochemical impedance spectroscopy and transmission electron microscopy provided direct evidence that the AlF 3 coating layer suppressed the increase in charge transfer resistance and cathode material pulverization during cycling.