The effect of La~(3+) and F~- co-doping on high rate capability of LiMn_2O_4

Co-doping with La and F lithium manganese oxide LiLa x Mn 2-xFxO4-x (x=0,0.01,0.02,0.05) materials were synthesized by segmented solid-state sintering method. The results showed that co-doping had unobvious effect on the discharge capacity at the current density below or equal to 1C. However,the rate performance from 2 to 10C was significantly improved. Besides,doping amount had great influence on the discharge property at 15C. Especially,when the doping amount was 0. 02,the discharge capacity was increased from only 4% to 56%. The results were supported by means of X-ray diffraction( XRD),cyclic voltammetry( CV) and electrochemical impedance spectroscopy( EIS). When there was no second phase,the charge transfer resistance,the anodic and cathodic polarization decreased and the electrochemical reversibility enhanced gradually with the increase of doping amount. However,when the second phase appeared at x = 0. 05,the charge transfer resistance,anodic and cathodic polarization began to increase.