Effect of a ZrO2 coating on the structure and electrochemistry of LixCoO2 when cycled to 4.5 V

Recently, Cho et al. studied the effects of a ZrO2 coating on the electrochemical behavior of Li/LixCoO2 cells. They found that the capacity retention to 4.4 V was significantly improved for cells having electrodes incorporating coated material compared to those with uncoated LiCoO2. They suggested that the thin coating suppressed the lattice expansion of LixCoO2 during cycling, leading to improved behavior. Our results on LiCoO2 coated with ZrO2, reported here, confirm the improved cycling behavior. X-ray diffraction (XRD) patterns collected with long counting times show that the coated material is nanocrystalline ZrO2. In situ XRD results indicate that the lattice of coated LixCoO2 expands and contracts in exactly the same way as uncoated LixCoO2 during charge and discharge. These results prove that the ZrO2 coating does not affect the lattice expansion of LiCoO2, in contrast to the results reported by Cho et al. We believe that the improved cycling behavior is caused by a reduction in the contact area between LiCoO2 and electrolyte. (C) 2002 The Electrochemical Society.