Enhancement in the electrochemical performance of zirconium/phosphate bi-functional coatings on LiNi0.8Co0.15Mn0.05O2 by the removal of Li residuals

Abstract

The effect of bi-functional coatings consisting of Zr and phosphate (P) on the electrochemical performance of Li_1.0Ni_0.8Co_0.15Mn_0.05O₂ (NCM) has been investigated. The presence of various types of Zr and P compounds such as oxides (ZrO₂ and Li₂ZrO₃) and phosphates (Zr₂P₂O₉, ZrP₂O₇ and LiZr₂(PO₄)₃) in the coating was confirmed by experiments as well as density functional theory (DFT) calculations. When the NCM samples were coated with the Zr/P hybrid material, the cycle retention and the amount of removed Li residuals (LiOH, Li₂CO₃) were enhanced by the synergistic effect from Zr and P. The NCM sample coated with a Zr/P layer with a Zr/P ratio of 1 : 1 exhibited an increase in the initial capacity (209.3 mA h g⁻¹) compared to the pristine sample (207.4 mA h g⁻¹) at 0.1C, owing to the formation of the coating layer. The capacity retention of the Zr/P coated sample (92.4% at the 50th cycle) was also improved compared to that of the pristine NCM sample (90.6% at the 50th cycle). Moreover, the amount of Li residuals in the Zr/P coated NCM sample was greatly reduced from 3693 ppm (pristine NCM) to 2525 ppm (Zr/P = 5 : 5).