Effect of Zn2+ doping on thermal, structural, morphological, functional group, and electrochemical properties of layered LiNi0.8Co0.1Mn0.1O2 cathode material

Abstract

The sol–gel method was used to synthesize Zn2+ doped LiNi0.8−xZnxCo0.1Mn0.1O2 (0 ≤ x ≤ 0.05) cathode materials with crystallite sizes ranging from 20.36 to 56.25 nm. The thermal stability of all cathodes were characterized by using thermogravimetric analysis (TGA) and quantity of heat needed is calculated by differential thermal analysis (DTA). Their structural, morphological and functional group analysis by XRD, FE-SEM, and FT-IR spectroscopy respectively. The electrochemical properties of two selected cathodes were also investigated via constant voltage, galvanostatic charge/discharge testing, and electrochemical impedance spectroscopy. The TGA/DTA analysis identified the reaction, weight loss, and phase transformation regions of the precursors. The XRD analysis revealed that all the synthesized cathodes possessed a rhombohedra-hexagonal system with a layered crystalline phase (R3̄m space group). The formation of layered-type structures in all cathodes was also revealed by FT-IR analysis. The content of Zn2+ ions in LiNi0.8−xZnxCo0.1Mn0.1O2 had a significant impact on the structural parameters, such as lattice constants, cell volume, and crystallite size of LiNi0.8Co0.1Mn0.1O2. The level of cation mixing and layered structure of all samples were found to be 1.22–1.38 and 4.9827–5.0195, respectively, indicating that all samples possessed minimal cation mixing and a well-defined layered structure. Such behaviors are important for obtaining improved cyclic performance from these kinds of cathode materials. Agglomerated and porous structure morphology with a grain size from 200 to 320 nm was observed via FE-SEM. The initial discharge capabilities for the LiNi0.8Co0.1Mn0.1O2 and LiNi0.77Zn0.03Co0.1Mn0.1O2 cathodes were found to be 214.84 and 233.57 mAh g−1, respectively, at a 0.1 C current rate between 3.0 and 4.6 V. This revealed that the discharge capacity of the pristine LiNi0.8Co0.1Mn0.1O2 cathode was significantly increased by doping Zn2+ with an x = 0.03 content, which is higher than the previously reported LiNi0.33Co0.33Mn0.33O2 cathode.