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Ni-rich lithium nickel manganese cobalt oxides (LiNixMnyCo1–x–yO2, x ≥ 0.5, NMCs) are high-capacity cathode materials for Li-ion batteries, but they exhibit limited cycling stability under high cutoff potentials. Various aspects, including transition metal dissolution, structural disordering, particle cracking, surface film thickening, etc., have already been investigated in terms of their performance degradation in the battery research community. Interestingly, these phenomena were primarily observed at the surface layer of the cathode material, implying that they may also be facilitated by some interfacial parasitic reactions between the delithiated NMC electrode and the non-aqueous electrolyte. In this study, LiNi0.6Mn0.2Co0.2O2 (NMC 622) electrodes chemically modified with TiO2 via atomic layer deposition were used as a model system to demonstrate the criticalness of the interfacial parasitic reactions. The suppression of the interfacial parasitic reactions effectively reduced the hike of the cathodic surface film resistance, decreased the level of dissolution of transition metals, decreased the level of particle fragmentation, and mitigated the cation mixing of NMC 622. All of these results demonstrated that careful design of the interfacial layer by surface modifications is a key approach for improving the durability of Ni-rich NMCs under high-voltage cycling.
Gao et al. (Fri,) studied this question.