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Öğe 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, EnginIn 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.Öğe Enhancing the Electrochemical Properties of Silicon Nanoparticles by Graphene-Based Aerogels(John Wiley and Sons Inc, 2023) Kuruahmet, Deniz; Şıngıl, Mustafa Mahmut; Güler, Aslıhan; Yıldırım, Sıdıka; Güngör, Hatice; Uzun, Esma; Alkan, EnginHerein, silicon nanoparticles (nSi) are produced by magnesiothermic reduction methods. nSi are then obtained in the form of a 3D graphene aerogel (GA), prepared by a simple one-step freeze-drying process using L-ascorbic acid. By a simple freeze-drying process, nSi is neatly decorated between sheets of graphene. GA forms a conductive structure for nSi whose mechanical mesh acts as a buffer layer. This conductive structure greatly improves the structural integrity and conductivity of the anode material. Nanoparticles silicon/graphene aerogel (nSi/GA) nanocomposite is investigated by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. nSi/GA nanocomposite demonstrates a superior capacity of 550 mAh g?1 after 500th cycle. As a result, the nSi/GA anodes show improvement in cycling stability compared with pure nSi. Tests are conducted at different rate capability to measure the velocity characteristic and the resulting anode exhibits average specific discharge capacities of 1217, 976, 919, 825, 674, and 572 mAh g?1 at charge/discharge rates of C/20, C/10. C/5, 1C, 3C, and 5C, respectively. Benefiting from easy synthesis and excellent cyclic stability, nSi/GA are expected to play an important role in the lithium-ion battery. © 2023 Wiley-VCH GmbH.Öğe 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, EnginIn 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.Öğe Graphene aerogel-supported Na3V2(PO4)3/C cathodes for sodium-ion batteries(Elsevier Science Sa, 2023) Gultekin, Sidika Yildirim; Guler, Aslihan; Kuruahmet, Deniz; Gungor, Hatice; Singil, Mustafa Mahmut; Uzun, Esma; Akbulut, HatemNa3V2(PO4)3 (NVP) is a preferred cathode material for Na-ion batteries due to its good thermal stability and long cycle life, but its low electrical conductivity limits its use. The carbon coating method is widely available in the literature but can solve the problem to a limited extent. Graphene aerogel-based composite materials with lightweight, high surface area and 3-dimensional (3D) porous structure are prepared, and the properties are tried to be improved further. In this study, carbon-coated Na3V2(PO4)3 (NVP/C) and graphene aerogel-carbon-coated Na3V2(PO4)3 (GA-NVP/C) composite have been synthesized. The produced samples have been analyzed using Field emission scanning electron microscopy, X-ray diffraction, Raman spectrum, Thermal Gravity Analysis, Xray photoelectron spectroscopy, Brunauer-Emmett-Teller and Transmission electron microscopy. Then, the effect of graphene aerogel additive on electrochemical performances as cathode materials has been investigated. Even though GA-NVP/C and NVP/C have similar discharge capacities in the first cycle, GA-NVP/C shows high cycle stability when compared to NVP/C after 250 cycles. The GA-NVP/C cathode also has a higher discharge capacity than the NVP/C cathode at different current rates. The diffusion coefficient calculated using the cyclic voltammetry curve of GA-NVP/C is also high, supporting the graphene aerogel's positive results. In conclusion, we show that adding GA with a 3-dimensional porous structure greatly improves the electrochemical properties of the cathode in Na-ion batteries.
