The commercialization of nickel-rich LiNi0.8Mn0.1Co0.1O2 (NMC811) has been hindered by the continuous loss of practical capacity and a reduction in the average working voltage. Performance degradation is related to Li/Ni cation mixing, irreversible layer-spinel-rocksalt phase transition, oxygen evolution, microcracking, and transition metal (TM) ion dissolution. Surface modification, elemental doping, and electrolyte additives are among the various strategies investigated to address these challenges. Among these, surface modification has proven to be a facile and effective strategy. Wet chemistry is widely used to coat powders onto nickel manganese cobalt (NMC) cathodes; however, controlling the coating quality and complete removal of undesired residuals is challenging. Over the past decade, atomic layer deposition (ALD) has emerged as a vapor-phase alternative to wet chemical methods. ALD uniquely enables high-quality conformal and uniform films over either electrode powders or prefabricated electrodes. In addition, ALD features a low process temperature ( ≤ 200 °C) that accurately controls film growth to a desirable crystallinity and thickness at the atomic level.
To date, many different coatings have been reported to modify NMCs via wet chemistry and ALD, including oxides like aluminum oxide (Al2O3), titanium oxide (TiO2), tungsten oxide (WO3), zirconium oxide (ZrO2) cobalt (II, III) oxide (Co3O4), and lithium metal oxides (LMO), phosphates, and fluorides. These coatings aim to address some of the problems highlighted earlier and ultimately improve the performance of the NMC cathodes. However, oxygen evolution still occurs during charging. Therefore, the suppression of oxygen evolution is essential for developing and commercializing Ni-rich NMC and other layered oxide cathode materials.
Recently, Professor Xiangbo Meng at the University of Arkansas, Scientist Yuzi Liu at Argonne National Laboratory, Scientist Xianghui Xiao at Brookhaven National Laboratory, and coworkers published a study entitled “High-performance LiNi0.8Mn0.1Co0.1O2 cathode by nanoscale lithium sulfide coating via atomic layer deposition” in the Journal of Energy Chemistry.
In this study, the authors reported a sulfide coating, amorphous Li2S via ALD. The study showed that the conformal nano-Li2S coating protected the NMC811 cathode and consequently improved the capacity retention, rate performance, and mitigated voltage reduction. The nano-Li2S coating also removed the O2 released from the NMC cathode during the charging process, a unique outcome, considering that traditional non-sulfide coatings do not exhibit this behavior.
The analyses further revealed that the ALD coatings should have the following beneficial effects: (i) improve the mechanical integrity of the NMC811 electrode and NMC powders themselves, (ii) stabilize the interface between the NMC electrode and the electrolyte, (iii) mitigate the structural phase transition of NMC materials, and (iv) remove O2 released from NMC lattices. All these beneficial effects of ALD Li2S coatings are significant for addressing the technical issues of NMC811 electrodes and improving the design of high-performance lithium-ion batteries (LIBs).
Thus, this study has demonstrated that sulfides may be an essential class of coating materials for tackling the performance challenges of NMCs and other layered cathodes in lithium-ion batteries. These findings may encourage future studies by other researchers to investigate a variety of sulfides as new coating films for high-performance NMCs and other cathodes.
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The Journal of Energy Chemistry is a publication that mainly reports on creative researches and innovativeapplications of chemical conversions of fossil energy, carbon dioxide, electrochemical energy and hydrogen energy,as well as the conversions of biomass and solar energy related with chemical issues to promote academicexchanges in the field of energy chemistry and to accelerate the exploration, research and development of energyscience and technologies.
Journal of Energy Chemistry
High-performance LiNi0.8Mn0.1Co0.1O2 cathode by nanoscale lithium sulfide coating via atomic layer deposition
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