Thermal, structural, morphological, functional group and first cycle charge/discharge study of Co substituted LiNi1−x-0.02Mg0.02CoxO2 (x = 0.00, 0.02, 0.04, 0.06, and 0.08) cathode material for LIBs

Abstract

LiNi1−x-0.02Mg0.02CoxO2 compounds with x = 0.0, 0.02, 0.04, 0.06, and 0.08 compositions are prepared by the solid-state method. Their thermal, structural, morphological, functional, and first cycle charge/discharge studies were carried out with the help of thermogravimetric analysis (TGA)/differential thermal analysis (DTA), XRD, SEM, FTIR, and a biologic galvanostat respectively. The TGA/DTA analysis shows their structural stability up to 800 °C. α-NaFeO2 with a layered hexagonal-rhombohedral structure with lattice parameters a = 2.868 Å and c = 14.217 Å and the space group R3̄m was found with the help of their XRD pattern. The intensity ratio is close to 1.2 or more, which indicates that there is no cation-mixing. The structure factor (R) is less than 0.5, indicating their structural stability. The particles are fine and homogeneously distributed with the capacity of cyclability and charge/discharge. The grain size is found to be 3.19, 2.78, 4.83, 4.13, and 5.09 µm for x = 0.0, 0.02, 0.04, 0.06, and 0.08, respectively. The frequency of stretching and bending increased with Co doping and changed the covalency of the M–O bond. The sample with cobalt concentration x = 0.02 is found to be the most efficient one (∼90% capacity retention and 176.61/174.17 mA h g−1 charge/discharge capacity) among the five. Hence, cobalt substitution of an appropriate amount in combination with magnesium, a cheaper element, is still a more exotic cathode material in Ni-rich lithium-ion batteries.