A novel core-concentration gradient-shelled LiNi0.5Co0.2Mn0.3O2 as high-performance cathode for lithium-ion batteries

Abstract

A novel core-concentration gradient-shelled LiNi_0.5Co_0.2Mn_0.3O₂ was successfully synthesized for the first time by a simple method from core-shelled precursors [(Ni_0.6Co_0.2Mn_0.2)_1/2(Ni_0.4Co_0.2Mn_0.4)_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) LiNi_0.5Co_0.2Mn_0.3O₂. The compositions of core and shell separately were LiNi_0.60Co_0.20Mn_0.20O₂ and LiNi_0.44Co_0.20Mn_0.36O₂, 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 LiNi_0.5Co_0.2Mn_0.3O₂, the CCGS-LiNi_0.5Co_0.2Mn_0.3O₂ presented remarkably improved cycling performance and thermal stability, which can be ascribed to LiNi_0.44Co_0.20Mn_0.36O₂ shell providing structural and thermal stability.