Effects of chelators on the structure and electrochemical properties of Li-rich Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 catho
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ORIGINAL PAPER
Effects of chelators on the structure and electrochemical properties of Li-rich Li1.2Ni0.13Co0.13Mn0.54O2 cathode materials A. E. Abdel-Ghany 1 & A. M. Hashem 1 & A. Mauger 2 & C.M. Julien 2 Received: 29 April 2020 / Revised: 29 April 2020 / Accepted: 24 July 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract In this study, carboxylic acids, namely concentrated citric acid and ethylene diamine tetra-acetic acid (EDTA) solution, are used as chelators to synthesize Li-rich layered Li1.2Ni0.13Mn0.54Co0.13O2 (LLNMC) by sol-gel method. We investigate the influence of these chelators on the morphology crystal properties and electrochemical performance of LNMC. Based on XRD data, the synthesized materials can be characterized as a combination of two phases, a rhombohedral R-3m phase (LiNi1/3Mn1/3Co1/3O2) and a monoclinic C2/m phase (Li2MnO3), which, according to the stoichiometry, are xLi2MnO3•(1-x)LiNi1/3Mn1/3Co1/3O2 with x = 0.5. The morphology and local structure were studied using electron microscopy (SEM, TEM and HRTEM) and Raman spectroscopy, respectively. A clear evidence for the effect of chelating agent was observed from electrochemical tests carried out by galvanostatic charge-discharge cycling and electrochemical impedance spectroscopy. The sample prepared via EDTA as organic complexing agent exhibits the best electrochemical properties, with higher capacity and rate capability. Keywords Chelating agent . Li-rich cathode . Lithium-ion batteries . Electrochemical impedance
Introduction The lithium-ion batteries (LIBs) are considered as a key product to the progressive replacement of fossil energy by green energy. Their use in some applications require ever growing energy densities, for instance to increase the driving range of electric vehicles. To satisfy this purpose, intense research is currently done on advanced positive electrode materials, since they are limiting components of LIBs [1, 2]. In particular, layered lithium-rich oxides, represented by xLi2MnO3·(1x)LiNixMnyCo1-x-yO2 (shorted as LLNMC), exhibit a reversible specific capacity of ≥ 250 mAh g−1 and wide operating voltage range (2.0–4.8 V vs. Li+/Li) [3–7]. The performance compares well with the capacity of conventional cathode materials (≤ 200 mAh g − 1 ), such as LiCoO 2 (LCO),
* C.M. Julien [email protected] 1
Inorganic Chemistry Department, National Research Centre, 33 El Bohouth St. (former El Tahrir St.), Dokki, Giza 12622, Egypt
2
Institut de Minéralogie, de Physique des Matériaux et Cosmologie (IMPMC), Sorbonne Université, UMR-CNRS 7590, 4 Place Jussieu, 75752 Paris, France
LiNixMnyCo1-x-yO2 (NMC) and LiNixCo1-x-yAlyO2 (NCA). The remarkably high capacity of LLNMC is obtained when the Li2MnO3 component is activated, which requires a charge potential higher than 4.5 V [8–10]. However, this large potential leads to endangerment for its crystal structure, so that this electrode suffers from a high initial irreversible capacity loss (ICL), a low rate capability and increasing polarization upon
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