A novel core-concentration gradient-shelled LiNi0.5Co0.2Mn0.3O2as high-performance cathode for lithium-ion batteries

Abstract

A novel core-concentration gradient-shelled LiNi0.5Co0.2Mn0.3O2 was successfully synthesized for the first time by a simple method from core-shelled precursors [(Ni0.6Co0.2Mn0.2)1/2(Ni0.4Co0.2Mn0.4)1/2](OH)2 that were synthesized via a co-precipitation route. Particle size increase of hydroxide precursors from core to shell, in combination with subsequent investigations of Energy Disperse X-ray Spectrum (EDS) on precursors, supported the formation of a core-shelled structure. To obtain concentration gradient layer between core and shell, a high calcined temperature of 900 °C was selected as high temperature calcination gave rise to diffusion of cations in the core-shelled structure. Thus, the prepared precursor powders were then calcined with stoichiometric ratio lithium carbonate (Li/M = 1.05) at 900 °C in air, which resulted in core-concentration gradient-shelled (CCGS) LiNi0.5Co0.2Mn0.3O2. The compositions of core and shell separately were LiNi0.60Co0.20Mn0.20O2 and LiNi0.44Co0.20Mn0.36O2, between which was a concentration gradient layer. X-ray diffraction (XRD) studies show that the prepared material was indexed to a typical layered structure with a Rm space group. Compared to LiNi0.5Co0.2Mn0.3O2, the CCGS-LiNi0.5Co0.2Mn0.3O2 presented remarkably improved cycling performance and thermal stability, which can be ascribed to LiNi0.44Co0.20Mn0.36O2 shell providing structural and thermal stability.