Effect of a ZrO_2 Coating on the Structure and Electrochemistry of Li_x CoO_2 When Cycled to 4.5 V

摘要

Recently, Cho et al. studied the effects of a ZrO_2 coating on the electrochemical behavior of Li/Li_xCoO_2 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 LiCoO_2. They suggested that the thin coating suppressed the lattice expansion of Li_xCoO_2 during cycling, leading to improved behavior. Our results on LiCoO_2 coated with ZrO_2, reported here, confirm the improved cycling behavior. X-ray diffraction (XRD) patterns collected with long counting times show that the coated material is nanocrystalline ZrO_2. In situ XRD results indicate that the lattice of coated Li_xCoO_2 expands and Contracts in exactly the same way as uncoated Li_xCoO_2 during charge and discharge. These results prove that the ZrO_2 coating does not affect the lattice expansion of LiCoO_2, 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 LiCoO_2 and electrolyte.