Improvement of electrochemical properties of layered LiNi1/3Co1/3Mn1/3O2 positive electrode material by zirconium doping

To improve the electrochemical properties of LiNi1/3Co1/3Mn1/3O2, powders of Zr-doped mixed transition metal oxides, LiNi1/3Co1/3Mn1/3-xZrxO2 (x = 0, 0.01, 0.025, 0.05) (LNCMZ), are synthesized via a thermal polymerization method. Their structure and electrochemical properties are investigated by X-ray diffraction, galvanostatic charge–discharge of LNCMZ/Li half cells, galvanostatic intermittent titration technique (GITT), direct current resistance measurement and AC impedance spectroscopy. All of the prepared LNCMZ samples have a hexagonal α-NaFeO2 structure whose lattice parameters increase monotonously with the Zr content. The Zr doping results in higher lithium diffusion coefficient in LNCMZ and more stable resistance during the electrochemical cycling of LNCMZ/Li cells so that the Zr-doped samples show notable improvement of cycling performance and rate capability. The sample LiNi1/3Co1/3Mn1/3-0.01Zr0.01O2 exhibits the best electrochemical performance with capacity retention of 92.7% during 100 cycles and a capacity of 133.9 mAh g−1 at 8 C rate, corresponding to 71.5% of its capacity at 0.1 C.

Research highlights
► l Cationic substitution of Mn4+ by Zr4+ in the lattice of LiNi1/3Co1/3Mn1/3O2.
► l Zr substitution causes higher diffusion coefficient and better rate performance.
► l Zr-doping stabilizes the lattice structure, resulting in better cycling stability.