Enhanced Cycleability of LiMn2O4 Cathodes by Atomic Layer Deposition of Al2O3 Coatings

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.