We doped Zr4+ ions in the outer layer of Ni0.8 Co0.1 Mn0.1 (OH)2 by coprecipitation. The distribution of Zr4+ in the final cathode materials showed a gradient distribution because of ion migration during the thermal treatment. The doped layer was confirmed by using various analysis methods (energy-dispersive X-ray spectroscopy, XRD, X-ray photoelectron spectroscopy, and TEM), which implies that Zr4+ can not only occupy both the transition metal slabs and Li slabs but also form a Li2 ZrO3 layer on the surface as a highly ion-conductive layer. The doped Zr4+ in the transition metal slabs can stabilize the crystal structure because of the strong Zr-O bond energy, and the doped Zr4+ in the Li slabs can act as pillar ions to improve the structural stability and reduce cation mixing. The gradient doping can take advantage of the "pillar effect" and restrain the "blocking effect" of the pillar ions, which reduces irreversible capacity loss and improves the cycling and rate performance of the Ni-rich cathode materials. The capacity retention of the modified sample reached 83.2 % after 200 cycles at 1C (200 mA g-1 ) at 2.8-4.5 V, and the discharge capacity was up to 164.7 mAh g-1 at 10C. This effective strategy can improve the structure stability of the cathode material while reducing the amount of non-electrochemical active dopant because of the gradient distribution of the dopant. In addition, the highly ion-conductive layer of Li2 ZrO3 on the surface can improve the rate performance of the cathode.
Keywords: batteries; doping; lithium; nickel; zirconium.
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