Ultrathin surface coatings to enhance cycling stability of LiMn2O4 cathode in lithium-ion batteries

Spinel LiMn₂O₄ suffers from severe dissolution when used as a cathode material in rechargeable Li-ion batteries. To enhance the cycling stability of LiMn₂O₄, we use the atomic layer deposition (ALD) method to deposit ultrathin and highly conformal Al₂O₃ coatings (as thin as 0.6–1.2 nm) onto LiMn₂O₄ cathodes with precise thickness control at atomic scale. Both bare and ALD-coated cathodes are cycled at a specific current of 300 mA g^?1 (2.5 C) in a potential range of 3.4–4.5 V (vs. Li/Li⁺). All ALD-coated cathodes exhibit significantly improved cycleability compared to bare cathodes. Particularly, the cathode coated with six Al₂O₃ ALD layers (0.9 nm thick) shows the best cycling performance, delivering an initial capacity of 101.5 mA h?g^?1 and a final capacity of 96.5 mA h?g^?1 after 100 cycles, while bare cathode delivers an initial capacity of 100.6 mA h?g^?1 and a final capacity of only 78.6 mA h?g^?1. Such enhanced electrochemical performances of ALD-coated cathodes are ascribed to the high-quality ALD oxide coatings that are highly conformal, dense, and complete, and thus protect active material from severe dissolution into electrolytes. Besides, cycling performances of coated cathodes can be easily optimized by accurately tuning coating thickness via varying ALD growth cycles.