Li-rich and Ni-rich transition metal oxides: Coating and core-shell structures

In this work, we consider influence of synthesis procedures, applying coatings, and formation of core-shell structures on the electrochemical performance of Ni-rich and Li-rich oxides. Li-rich Li1.2Mn0.54Ni0.13Co0.13O2 cathode materials synthesized by different synthesis procedures exhibit different electrochemical behavior, especially those obtained by sol-gel combustion method. The TEM findings reveal the presence of monoclinic and trigonal phases in the Li-rich materials synthesized. TEM/ED/EDX microanalysis shows that the C2/m monoclinic phase appears to have a variable composition Li2[M]O3, where [M] = (Mn, Ni, Co). Whence, on the basis of monoclinic phase we can observe a restricted solid solution with 4 h-Wyckoff Mn-cation positions potentially being occupied by the mixture of three 3d-metal cations [M] = (Mn, Ni, Co). The cyclability of Li-rich oxides is improved by thin alumina films deposited by ALD directly on porous electrodes. The better capacity retention of modified electrodes is explained by suppressing reactions with electrolyte accompanied by growth of SEI film on cathode. The core-shell structures with Ni-rich core and gradient shell enriched with Mn were obtained by coprecipitation and applying the shell material onto LiNi0.8Co0.15Al0.05O2 as received. These structures show better cyclability and rate capability in the extended voltage range of 2.5–4.4 V than the core materials.