Enhanced electrochemical performance of La- and Zn-co-doped LiMn2O4 spinel as the cathode material for lithium-ion batteries

Aseries of compounds Li[LaxZnyMn2-x-y] O-4 (x = y = 0.01-0.05) is synthesized by doping the pure spinel LiMn2O4 with lanthanum and zinc ions. These cathode materials are characterized by X-ray powder diffractometry, inductively coupled plasma optical emission spectrometry, scanning electron microscopy, transmission electron microscopy, cyclic voltammetry, galvanostatic charge-discharge studies, and electrochemical impedance spectroscopy (EIS). The particle sizes range from 42 to 140 nm. The results reveal that the pristine LiMn2O4 delivers a discharge capacity of 122.3 mAh g(-1) at 0.1C while at 5C the reversible capacity reduces to 51 mAh g(-1) that is about 41 % of the initial discharge capacity. Among all the doped samples, LiLa0.01Zn0.01Mn1.98O4 is the best composition that delivers a discharge capacity of 118 mAh g(-1) with the low capacity fade of 0.18 mAh g(-1) cycle(-1) over the investigated 100 cycles. At a high current rate of 5C, 78 % of the initial discharge capacity in the first cycle is retained, while 95 % of the discharge capacity is recovered when the current density is reduced back to 0.1C. Our results demonstrate that the lanthanum and zinc co-doping has stabilized the structural integrity of the spinel host by suppressing the Jahn-Teller distortion and also provides short distances for Li+ diffusion as is clear from the EIS results.