Nanoscale Sulfide Coatings for Addressing the Issues of Nickel-Rich Metal Oxide Cathodes

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High-nickel (Ni) metal oxides are among the most promising cathodes for high-energy rechargeable batteries, featuring their higher capacity and lower cost than those of the commercialized LiCoO2 cathodes. Among them, Ni-rich lithium nickel manganese cobalt oxides, LiNixMnyCozO2 (NMCs, x ≥ 0.6, x + y + z = 1) are particularly attractive, ascribed to their further improvement in capacity and cost. Unfortunately, Ni-rich NMCs suffer from a series of inherent issues related to performance and safety, which become more and more challenging with increasing Ni contents. To address these issues, a variety of strategies have been employed, such as element doping, surface coating, and new electrolytes and additives. Using atomic layer deposition (ALD), recently, we coated Ni-rich NMC cathodes with sulfide coatings. For the first time, consequently, we found that sulfides are a class of coating materials having special protection effects on NMCs but have not been explored previously. Our recent and on-going studies revealed that sulfide coatings could be converted into sulfites and/or sulfates.1 Such a conversion is favorable for protecting electrolytes from oxidation. Furthermore, the resultant sulfites/sulfates enable better ionic conductivity while fulfill other functions including improving mechanical integrity, mitigating undesirable interface reactions, and inhibiting structural degradation. Additionally, ALD as a coating method provides many benefits, such as conformal and uniform coating coverage, low process temperature, and accurate coating thickness.2-4 Thus, our studies not only opened a new area for surface coating of electrodes but also demonstrated ALD being very beneficial for pursuing high-performance NMCs. Wang, X.; Cai, J.; Ren, Y.; Benamara, M.; Zhou, X.; Li, Y.; Chen, Z.; Zhou, H.; Xiao, X.; Liu, Y.; Meng, X., High-performance LiNi0.8Mn0.1Co0.1O2 cathode by nanoscale lithium sulfide coating via atomic layer deposition. Journal of Energy Chemistry 2022, 69, 531-540.Meng, X.; Yang, X. Q.; Sun, X. L., Emerging applications of atomic layer deposition for lithium-ion battery studies. Adv. Mater. 2012, 24 (27), 3589-3615.Meng, X., Atomic layer deposition of solid-state electrolytes for next-generation lithium-ion batteries and beyond: Opportunities and challenges. Energy Storage Materials 2020, 30, 296-328.Meng, X., Atomic and molecular layer deposition in pursuing better batteries. J. Mater. Res. 2021, 36, 2-25.