Thin film coatings on lithium-ion battery (LIB) electrode materials have proven to be an effective way to improve the capacity retention, rate capability, and thermal stability of electrode materials. Atomic layer deposition (ALD) is a layer-by-layer thin film coating technique. It consists of a set of sequential reactions that occur only between the gaseous precursors administered to the reactor, and the functional groups present on the surfaces of primary particles. ALD is believed to be an important technique for LIB applications. Currently, most of ALD-LIB research focuses on insulating ALD materials. There is a trade-off between the species transport (increasing capacity) and protection of the particles (expecting long cycle life) using insulating materials. We reported a breakthrough to overcome this trade-off by coating an ultra-thin conformal cerium dioxide (CeO₂) film on the surfaces of LiMn₂O₄ particles. The optimized CeO₂ film (~3 nm) coated particles exhibited a significant improvement in capacity and cycling performance compared to uncoated, Al₂O₃ ALD coated, and ZrO₂ ALD coated samples at room temperature and 55 °C for long cycling numbers. The initial capacity of the 3 nm CeO₂ coated sample showed 24% increment compared to the capacity of the uncoated one, and 96% and 95% of the initial capacity was retained after 1,000 cycles with 1 C rate at room temperature and 55 °C, respectively. Iron oxide films were coated on LiMn_1.5Ni_0.5O₄ particles by ALD for the synergetic effect of performance enhancing by iron doping and conformal iron oxide film coating. With an optimal film thickness of ~0.6 nm, the initial capacity improved by 25% at room temperature and by ~26% at 55 °C at 1C cycling rate. The synergy of doping of LiMn_1.5Ni_0.5O₄ with Fe near surface combined with the conductive and protective nature of the optimal iron oxide film led to high capacity retention (~93% at room temperature and ~91% at 55 °C) even after 1,000 cycles at 1C cycling rate. This work has the potential to produce the foundational knowledge necessary to solve the “capacity-protection” dilemma.