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

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 Li_0.33La_0.56TiO₃, 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 Li_0.33La_0.56TiO₃. With an optimized deposition time, the LiCoO₂ electrodes modified by Li_0.33La_0.56TiO₃ 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.