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

A series of compounds Li[La x Zn y Mn2−x−y ]O4 (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.