A melatonin-inspired coating as an electrolyte preservative for layered oxide cathode-based lithium batteries

Layered transition metal oxides are key cathode materials for obtaining high energy density lithium batteries by virtue of their high specific capacities and operating voltages. However, harmful active species (e.g. reactive oxygen and free radicals) give rise to severe electrolyte decomposition during high-voltage cycling, and subsequently result in rapid battery capacity decay. Inspired by the reactive species-cleanup activity of melatonin, we first build up an endogenous chemically protective cathodic polymer coating as a preservative to relieve electrolyte decomposition. This coating is prepared by casting the homopolymer of 2,2,6,6-tetramethyl-4-piperidyl methacrylate on the cathode via a spin-coating method. Detailed experimental and simulation studies reveal that the as-casted coating can efficiently capture reactive species, sequentially favorable construct compatible cathode/electrolyte interface. Moreover, it is demonstrated that electrolyte solvent decomposition routes can be tuned by this chemically protective coating, compared with traditional Al2O3 coating. Resultantly, the polymer coating-based LiNi0.8Co0.1Mn0.1O2 cathode shows 85% capacity retention after 700 cycles in half cells under 2.7–4.5 V at 1C, evidently outperforming that (35%) of the pristine one. Notably, this polymer coating is also effective for other layered oxide cathode-based lithium batteries. This chemical protection design strategy marks an important milestone to address electrolyte decomposition involving reactive species in rechargeable batteries.