Nanolaminated ZnO–TiO2 coated lithium-rich layered oxide cathodes by atomic layer deposition for enhanced electrochemical performances

The surfaces of the lithium-rich layered oxide cathodes (Li1.2Mn0.6Ni0.2O2, LLO) were modified with nanolaminated ZnO–TiO2 ultra-thin films (1.7 ± 0.4 nm) by atomic layer deposition (ALD) with various coating sequences. The layered oxide cathodes were coated with (I) ALD TiO2, followed by ZnO (P@T@Z), (II) ALD ZnO, followed by TiO2 (P@Z@T), and (III) ALD TiO2, followed by ZnO and TiO2 (P@T@Z@T). Among the nanolaminated coatings, a uniform coating was only obtained for the P@Z@T samples due to the outer layer-like growth of ALD TiO2. Surprisingly, the P@Z@T samples exhibited superior electrochemical performances and thermal stabilities to the other samples. The samples possessed a higher initial specific discharge capacity of 123 mAh g−1 at 1 C, and a capacity retention of 97% after 80 charge-discharge cycles, in comparison with the pristine samples, which were 100 mAh g−1 and 68%, respectively. When the current density increased to 5 and 10 C rate, the samples possessed the specific discharge capacities of 134 and 103 mAh g−1, but the capacities were absent for the pristine samples. The samples charging at 4.8 V withstood a higher decomposition temperature of 267 °C and a lower heat release of 62.4 J/g compared to the pristine samples, 260 °C with 253.6 J/g. The enhanced rate capability and cyclability of the P@Z@T samples were related to the decreased resistance from 1894 to 847 Ωcm−2 and less side reactions. This was due to the uniform surface and complete protection of the nanolaminated film.