Surface modification by coating oxides onto LiMn2O4 is commonly employed to improve cycling stability of LiMn2O4 cathode material for rechargeable lithium-ion batteries. Current fabrications of surface coatings mostly rely on wet chemistry approaches, which lack sufficient flexibility and controllability. The coatings prepared via wet chemistry methods are usually non-uniform and incomplete. This report is the first effort to use atomic layer deposition method for deposition of ultra-thin and highly-conformal Al2O3 coatings onto LiMn2O4 cathodes with precise thickness-control at atomic scale. SEM image of ALD coated cathode shows that the coated particles preserve the original shape of bare particles, indicating that the ALD coating is highly-conformal. XPS technique detects Al on the surface of coated cathodes and thus confirms formation of Al2O3 ALD films on the cathodes. All bare and coated cathodes are cycled at a current density of 240 mA/g in a potential range of -0.3~0.8 V (vs. Ag/Ag+) for electrochemical measurements. The coated cathodes exhibit significantly enhanced capacity retention than bare cathodes over 100 cycles, as the dense and high-quality Al2O3 ALD film separates active material and electrolyte, and retards dissolution of manganese ions from LiMn2O4 particles. In addition, cycling performances of coated cathodes can be optimized by manipulating coating thicknesses which can be easily controlled via varying ALD growth cycles.