Enhanced Interfacial Kinetics and High Rate Performance of LiCoO 2 Thin-Film Electrodes by Al Doping and In Situ Al 2 O 3 Coating.

The structure and surface-interface instability of LiCoO 2 thin-film electrodes during charge-discharge cycles are one of the main factors leading to the deterioration of electrochemical performance. Element doping and surface coating are effective strategies to tackle this issue. In this work, Al-doped and in situ Al 2 O 3 -coated LiCoO 2 composite thin-film electrodes are prepared by magnetron sputtering. The results show that the resultant composite thin-film electrodes exhibited excellent cycling stability, with a discharge specific capacity of 40.2 μAh um -1 cm -2 after 240 cycles at 2.5 μA cm -2 , with a capacity retention rate of 94.14%, compared to a discharge capacity of the unmodified sample of only 37.7 μAh um -1 cm -2 after 110 cycles, with a capacity retention rate of 80.04%. In addition, the rate performance of the prepared LiCoO 2 film is significantly improved, and the discharge specific capacity of the Al-doped sample reaches 43.5 μAh um -1 cm -2 at 100 μA cm -2 , which is 38.97% higher than that of the unmodified sample (31.3 μAh um -1 cm -2 ). The enhancement of electrochemical performance is mainly attributed to the synergistic effect of Al doping and in situ Al 2 O 3 coating. The metal Al forms a conductive network in the film, while part of the Al will enter the LiCoO 2 lattice to form a LiAl y Co 1- y O 2 solid solution, promoting the transport of lithium ions and improving the stability of the electrode structure. The in situ continuous deposition of the coating optimizes the active material coating-electrolyte interface.