Effect of Nb doping on electrochemical properties of LiNi1/3Co1/3Mn1/3O2 at high cutoff voltage for lithium-ion battery

Nb doped cathode materials with the formula LiNi1/3Co1/3Mn1/3−xNbxO2 (x = 0, 0.01, 0.02, 0.03) have been prepared successfully by sol-gel method. The effect of Nb substitution on the crystal structure and electrochemical properties of LiNi1/3Co1/3Mn1/3O2 were studied systematically by X-ray diffraction (XRD) and various electrochemical measurements. The results showed Nb substitution played an important role in the good cycling performance of LiNi1/3Co1/3Mn1/3O2. Charge/discharge tests revealed that LiNi1/3Co1/3Mn1/3-0.02Nb0.02O2 showed a capacity retention of 94.1% at 1 C after 50 cycles in a high cutoff voltage range (3.0-4.6 V), while discharge capacity of LiNi1/3Co1/3Mn1/3O2 remains only 89.4% of that at 1 C. Ex-situ XRD analysis and EIS analysis indicated that the improved electrochemical properties of Nb-doped sample result from the more stable structure and lower resistance during the electrochemical cycling.