High-performance LiNi0.8Mn0.1Co0.1O2 cathode by nanoscale lithium sulfide coating via atomic layer deposition

The commercialization of nickel-rich LiNi0.8Mn0.1Co0.1O2 (NMC811) has been hindered by its continuous loss of practical capacity and reduction in average working voltage. To address these issues, surface modification has been well-recognized as an effective strategy. Different from the coatings reported in literature to date, in this work, we for the first time report a sulfide coating, amorphous Li2S via atomic layer deposition (ALD). Our study revealed that the conformal nano-Li2S coating shows exceptional protection over the NMC811 cathodes, accounting for the dramatically boosted capacity retention from ∼11.6% to ∼71% and the evidently mitigated voltage reduction from 0.39 to 0.18 V after 500 charge–discharge cycles. In addition, the Li2S coating remarkably improved the rate capability of the NMC811 cathode. Our investigation further revealed that all these beneficial effects of the ALD-deposited nano-Li2S coating lie in the following aspects: (i) maintain the mechanical integrity of the NMC811 electrode; (ii) stabilize the NMC electrode/electrolyte interface; and (iii) suppress the irreversible phase transition of NMC structure. Particularly, this study also has revealed that the nano-Li2S coating has played some unique role not associated with traditional non-sulfide coatings such as oxides. In this regard, we disclosed that the Li2S layer has reacted with the released O2 from the NMC lattices, and thereby has dramatically mitigated electrolyte oxidation and electrode corrosion. Thus, this study is significant and has demonstrated that sulfides may be an important class of coating materials to tackle the issues of NMCs and other layered cathodes in lithium batteries.