Cell tests demonstrated that the use of an AlF3 coating enabled a LiCoO2 electrode to deliver a higher discharge capacity (208 mAh g-1) at an upper cutoff voltage of 4.54 V. About 94% of the initial capacity was retained after 50 cycles, while the capacity retention of pristine LiCoO2 was only 60% at 4.5 V. The improved electrochemical performance with the AlF3 coating was attributed to the delay of structural degradation of LiCoO2 during cycling. A structural analysis of the cycled LiCoO2 electrode revealed that the pristine LiCoO2 transforms to a cubic spinel phase via an intermediate phase triggered by progressive chemical leaching of Co during cycling. The AlF 3 coating protected LiCoO2 from the chemical attack by HF and thus helped to delay the eventual phase transformation to a spinel phase. By delaying this transformation, the AlF3 coating was able to reduce the charge-transfer resistance and maintain the structural stability when cycled above 4.5 V.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Renewable Energy, Sustainability and the Environment
- Surfaces, Coatings and Films
- Materials Chemistry