科研之友
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摘要
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.Mn-2(0).(2))(1/2)(Ni-0.Co-4(0).Mn-2(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 degrees 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 degrees 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 R (3) overbar m 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.
