Anionic redox effect on the electrochemical performance of LLNMC–CeO$_2$–C nanocomposites

Li[Li$_{0.13}$Ni$_{0.2}$Mn$_{0.47}$Co$_{0.2}$]O$_2$–CeO$_2$ composites have been obtained by coprecipitation with CeO$_2$ and by coating with ceria followed by coating with carbon film. STEM analysis revealed the formation of 20–30 nm ceria particles on the surface of LLNMC grains in all cases. Both carbon-coated LLNMC-CeO$_2$ composites and carbon-free LLNMC coated with 1 % CeO$_2$ demonstrated enhanced capacity values that could not be explained by the charge compensation via redox of nickel and cobalt. 5 % CeO$_2$-coprecipitated sample demonstrated the most intense anomaly in CV at U = 4.1–4.5 V associated with redox processes in the anionic sublattice of LLNMC and a larger charge transfer resistance compared to other composites. The maximum values of Li$^+$ diffusion coefficient have been observed for the samples coated with 1 % CeO$_2$. The different electrochemical behavior of these samples could be explained by the different intensity of anionic redox processes in the samples with different amount of nanocrystalline ceria.