Aluminum Interdiffusion into LiCoO₂ Using Atomic Layer Deposition for High Rate Lithium Ion Batteries

Here, as with previous work, atomic layer deposition (ALD) has been used to deposit Al₂O₃ on positive electrode active materials, LiCoO₂, to create a protective barrier layer, suppress the high potential phase transition, and thus reduce the subsequent Co dissolution. However, in this study it was found that it also resulted in the reduction of the charge transfer resistance at the positive electrode–electrolyte interface, thus enhancing the performance of the battery. Energy-dispersive X-ray spectroscopy, in conjunction with transmission electron microscopy, shows that a discrete Al₂O₃ shell was not formed under the selected growth conditions and that the Al diffused into the bulk LiCoO₂. The resulting active oxide material, which was significantly thicker than the nominally ALD growth rate would predict, is proposed to be of the form LiCoO₂:Al with amorphous and crystalline regions depending on the Al content. The cells consisting of the modified electrodes were found to have good cycling stability and discharge capacities of ∼110 mA h g^–1 (0.12 mA h cm^–2) and ∼35 mA h g^–1 (0.04 mA h cm^–2) at 50 and 100 C, respectively