Effect of lithium to zirconium ratio on microstructure and electrochemical performances of LZO modified LiNi0.8Co0.1Mn0.1O2 cathode materials

Lithium zirconate (LZO) coatings were routinely applied to NCM cathode materials in industry to improve cyclability and stability, but their working principles remain some elusive. Li/Zr molar ratios for coating preparation in sol-gel route always shows random variations in literature, due to vaporization of lithium source, solid-state diffusion of Zr4+ and formation of residue lithium. In this work, LZO coatings were prepared via a sol-gel route, and chemical compositions and amounts of Zr4+ doping were studied with varying Li/Zr molar ratios. It was found that, the surface composition of LZO was dominated by Li2ZrO3 at a low Li/Zr molar ratio of 2.1, and then Li6Zr2O7 and residue lithium increased with a rising Li/Zr molar ratio. As for the ion doping, Zr4+ preferred to enter crystal lattices of NCM811 at a low Li/Zr molar ratio. The best electrochemical performance was ach-ieved for the LZO modified NCM811 with a Li/Zr ratio of 2.4 (NCM811-LZO2.4), and the reasons could be attribute to modification processes introduced moderate Zr4+ doping and the multiphase LZO (Li2ZrO3 and Li6Zr2O7) coating onto the NCM811, which reduced the surface residue lithium and enhanced transport rate of charge carriers. As a result, the NCM811-LZO2.4 delivers a high coulombic efficiency of 91.4% in the initial cycle, outstanding capacity retention after 500 cycles (193 mAh g-1 at 0.2 C), and a good rate capacity of 155.9 mAh g-1 at 10 C. This work provides a method of tailoring chemical compositions of LZO protective coatings to improve the electrochemical performance of NCM811 materials.