Electrochemical and Structural Investigation on Ultrathin ALD ZnO and TiO2 Coated Lithium-Rich Layered Oxide Cathodes

Ultrathin coatings (1.5 ± 0.3 nm) of titanium dioxide and zinc oxide were deposited on lithium-rich layered oxide cathodes (Li1.2Mn0.6Ni0.2O2, LLO) by atomic layer deposition (ALD). The structures, electrochemical performances, and thermal stabilities of these coatings were investigated. An ultrathin uniform coating was obtained for TiO2 but not for ZnO because of differences in the layer growth mechanism. Regarding the initial charge–discharge curves under a current density of 0.04 C rate, the TiO2 coated samples exhibited a higher discharge capacity, 242 mAhg–1, compared with the ZnO coated samples, 220 mAhg–1, or the pristine samples, 228 mAhg–1. Both coated samples exhibited more stable cycling performance and thermal stability than the pristine samples. After 80 cycles under 0.5 C rate, the TiO2 and ZnO coated samples were found to have higher capacity retention (∼94% and 78%, respectively) than the pristine samples (68%). The reaction temperature of the exothermic peak of the TiO2 and ZnO coated sam...