Sufficient Utilization of Zirconium Ions to Improve the Structure and Surface properties of Nickel‐Rich Cathode Materials for Lithium‐Ion Batteries

Abstract

We doped Zr⁴⁺ ions in the outer layer of Ni_0.8 Co_0.1 Mn_0.1 (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.