Nb-Cl co-doping improved the electrochemical performance of LiNi0.6Co0.2Mn0.2O2 cathode materials

LiNi0.6Co0.2Mn0.2O2 cathode material has been widely studied by researchers due to its high capacity, but its further development is restricted by low rate capacity, poor interface stability, and poor structural stability. Nb-Cl co-doped LiNi0.6Co0.2Mn0.2O2 cathode materials were prepared by solid-phase method. Structural analysis revealed that Nb and Cl elements were uniformly incorporated into the crystal structure. Electrochemical results show that the optimal co-doping amounts of Nb and Cl are 1% and 2%, and the modified LiNi0.6Co0.2Mn0.2O2 cathode material exhibits higher discharge capacity and cycle stability. At 0.5 C, the capacity retention rate was 90.80% after 100 cycles at a cut-off voltage of 3.0-4.6 V, much higher than that of the pristine sample which was 81.17%. In addition, the modified sample can still maintain a reversible capacity of 148.0 mAh g(-1) even at 5 C. This is attributed to the synergistic effect of anion-cation co-doping, which effectively inhibits the phase transition process on the surface of the material in a highly delithiated state, slows down the structural collapse during cycling, and promotes the reversible intercalation/extraction of Li+. EIS and GITT tests also proved that Nb-Cl co-doping reduces the charge transfer resistance (R-ct) and effectively increases the lithium ion diffusion rate.