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    Cobalt-Free Layered LiNi0.8Mn0.15Al0.05O2/Graphene Aerogel Composite Electrode for Next-Generation Li-Ion Batteries
    (Amer Chemical Soc, 2023) Kuruahmet, Deniz; Guler, Aslihan; Yildirim, Sidika; Singil, Mustafa Mahmut; Gungor, Hatice; Uzun, Esma; Alkan, Engin
    In this work, we introduce LiNi0.8Mn0.15Al0.05O2 (NMA), which is cobalt-free and has a high nickel content, and a conductive composite material to NMA by supporting it with a three-dimensional (3D) graphene aerogel (GA). With an easy freeze-drying approach, NMA nanoparticles are properly dispersed on graphene sheets, and GA creates a strong and conductive framework, significantly improving the structure and conductivity. The structure of the pure NMA and NMA/ graphene aerogel (NMA/GA) composite was investigated by X-ray diffraction (XRD) and field emission scanning electron microscopy (FE -SEM). XRD and FE-SEM analyses clearly indicated that ultrapure NMA structures are homogeneously dispersed among the GAs. In addition, the composite structure was examined using transmission electron microscopy (TEM) to determine the dispersion mechanisms. The electrochemical cycling performance of the pure NMA and NMA/GA composite was evaluated by rate capacitance, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The synthesized NMA/GA was able to provide 89.81% specific capacity retention after the 500th cycle at C/2. The average charge/ discharge rates of the obtained cathode show good electrochemical results and exhibit capacities of 190.2,186.3, 185.2, 176.2, 161.2,142.6, and 188.5 mAh g-1 at C/20, C/10, C/5, C, 3C, 5C, and C/20, respectively. EIS data showed an improvement in the impedance of the composite containing GA. According to the results of the electrochemical tests, NMA nanoparticles formed a conductive network with its porous structure thanks to GA, formed a protective layer on the surface, prevented the side reactions between the cathode and the electrolyte, decreased the impedance of the cathode, and increased the redox kinetics. In addition, the changes in the structure were investigated in the NMA/GA composite cathode by XRD, FE-SEM, and Raman analyses at the end of the 50th, 250th, and 500th cycles. In summary, the NMA/GA cathode is expected to play an important role in lithium-ion batteries (LIBs) by taking advantage of its easy synthesis and excellent cycle stability.
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    Graphene aerogel based positive electrode for lithium ion batteries
    (Elsevier, 2024) Kuruahmet, Deniz; Guler, Aslihan; Yildirim, Sidika; Singil, Mustafa Mahmut; Gungor, Hatice; Uzun, Esma; Alkan, Engin
    In this study, a composite of LiNi0.8Mn0.1Co0.1O2 nanoparticles (nNMC-811) supported by three-dimensional (3D) graphene aerogel (GA) was prepared to increase the practical energy density and performance capability of high nickel cathodes. The porous LiNi0.8Mn0.1Co0.1O2 nanoparticle/graphene aerogel (nNMC-811/GA) composite is composed of nNMC-811 and graphene that act as a bridge for electron transfer and acceleration of lithium ion diffusion. nNMC-811 and nNMC-811/GA cathodes characterization data with techniques including X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectra (FT-IR) and X-ray photoelectron spectroscopy (XPS) are discussed. Both Field Emission Scanning Electron Microscopy (FE-SEM) and Transmission Electron Microscopy (TEM) made clear observations of the uniform distribution of the cathode active powders over the 3D graphene aerogel structure. The electrochemical performance of the nNMC-811 and nNMC-811/GA cathodes was evaluated by the galvanostatic charge-discharge measurement between 2.5 V and 4.5 V at room temperature using a computer-controlled battery tester. In addition, variable speed capacity ratios (C-rate), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) analyzes were also performed. nNMC-811/GA hybrid composite structure delivers a specific capacity of 183.15 mAhg(-1) at C/2 after the 500th cycle. It is understood from the FE-SEM images taken after the cycle that there is no deterioration in the structure. According to results, it was observed that the 3D porous structure of the nNMC-811/GA composite facilitated the mobility of Li+ ions, and the excellent electrochemical performances of the cathodes were improved due to the increasing defects as well as the electrical conductivity of GA.