Improved Cycling Stability of LiCoO2 at 4.5 V via Surface Modification of Electrodes with Conductive Amorphous LLTO Thin Film.

The stability issue of LiCoO2 cycled at high voltages is one of the burning questions for the development of lithium ion batteries with high energy density and long cycling life. Although it is effective to improve the cycling performance of LiCoO2 via coating individual LiCoO2 particles with another metal oxides or fluorides, the rate capacity is generally compromised because the typical coating materials are poor conductors. Herein, amorphous Li0.33La0.56TiO3, one of the most successful solid electrolytes, was directly deposited on the surface of made-up LiCoO2 electrodes through magnetron sputtering. Not only the inherent conductive network in the made-up LiCoO2 electrodes was retained, but also the Li+ transport in bulk and across the cathode-electrolyte interface was enhanced. In addition, the surface chemical analysis of the cycled LiCoO2 electrodes suggests that most of the stability issues can be addressed via the deposition of amorphous Li0.33La0.56TiO3. With an optimized deposition time, the LiCoO2 electrodes modified by Li0.33La0.56TiO3 performed a steady reversible capacity of 150 mAh/g at 0.2 C with the cutoff voltage from 2.75 to 4.5 V vs. Li+/Li and an 84.6% capacity gain at 5 C comparing with the pristine one.