Epitaxial ZrO2 coating on LiMn2O4 nanoparticles using atomic layer deposition (ALD) shows high conformality, uniformity and precise thickness control at atomic scale. The thickness of ZrO2 coating can be precisely tailored at 2Å per ALD cycle. Cycling performance of ZrO2 ALD-modified LiMn2O4 cathode material is optimized by tuning the coating thickness via varying ALD growth cycles. The optimal thickness of ZrO2 coating for maximized electrochemical performance of LiMn2O4 is ∼1.2nm grown via 6 ZrO2 ALD layers. LiMn2O4 nanoparticles coated with 6 ZrO2 ALD layers deliver a very high initial discharge capacity of 136.0mAh/g at 1C at 55°C, significantly higher than that of bare LiMn2O4 (124.1mAh/g). The effect of ZrO2 ALD coating on improving capacity retention of LiMn2O4 is even more distinct at high charge/discharge rate at elevated temperature. LiMn2O4 nanoparticles coated with 6 ZrO2 ALD layers after heat treatment retain a discharge capacity of 90.3mAh/g after 100 cycles at 5C at 55°C, while bare LiMn2O4 nanoparticles exhibit a final capacity of 58.8mAh/g. ZrO2-ALD-modified LiMn2O4 nanoparticles show significantly improved specific capacity and enhanced cycleability at high rate at elevated temperature due to the protective effect of ultrathin and high-quality ALD surface coatings.