FBE- Malzeme Bilimi ve Mühendisliği Lisansüstü Programı
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Malzeme Bilimi ve Mühendisliği Ana Bilim Dalı altında bir lisansüstü programı olup, yüksek lisans ve doktora düzeyinde eğitim vermektedir.
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Yazar "Alpay, Barış Cem" ile FBE- Malzeme Bilimi ve Mühendisliği Lisansüstü Programı'a göz atma
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ÖgeReactor Design, Characterization And Production Of Cathode Active Material Via Co-precipitation Method For Lithium Ion Batteries(Institute of Science And Technology, 2019-12-19) Alpay, Barış Cem ; Keleş, Özgür ; 521171002 ; Material Science and Engineering ; Malzeme Bilimi ve MühendisliğiGreen - ecofriendly energy sources are one of the most researched topics since the global warming and increase in the greenhouse gas is a global concern. However, those renewable energy sources may not be available for every day of a year. Winds may not be able to provide sufficent force to turbines, solar energy may not be used on cloudy days. These problems disrupts the continous usage of renewable sources. However, storage technology can support the output of energy from these sources. In this aspect, lithium – ion batteries (LIBs) are very promising and already on the use energy storage systems. LIBs are still being researched extensively. Electrochemical performance of the LIBs majorly depend on the electrode materials such as anodes and cathodes. However, since commercial anodes are way ahead of the cathodes in the aspect of capacity, majority of the researches are focused on cathode materials. NMC cathode materials are very promising and currently being used in electrical vehicles and consumer electronics but they still require improvement. NMC mainly consists of nickel, cobalt and manganese. Commercialized NMC is the NMC 111. Numbers indicate that cathode material contains transition metal at the ratio of 1:1:1 respectively Ni:Mn:Co. There are many NMC stoichiometries such as NMC 433, NMC 532, NMC 622 and NMC 811. Main idea is to increase nickel content of the material while reducing the cathode content as much as possible. However, increasing nickel content also increases the reactivity of cathode active material. This situation not also distrupts electrochemical performance of the battery, it also jeopardises the safety of battery. To be able to produce NMC 811 with high capacity with no safety issues requires optimization of synthesis methods. Co-precipitation is the mainly used NMC synthesis method for commercial materials and for scientific researches. Main mechanism of this method is to precipitate transition metals together in hydroxide form very well controlled conditions. Even though preparations are simple for this method, parameter optimization plays a critical role for high quality final product. There are numereous studies on the optimization of reaction temperature, level of pH, molarity of chemical reagents, reaction time, and feed rate of chemicals and so on. However, there are very few researches on how mixing paramaters affect precipitates as well as mixing quality such as providing homogenous mixing of chemicals. In most of the studies done on co-precipitation, only given information is the mixing rate. This study consists of three main parts. First, via COMSOL Multiphysics software a series of simulations with different impeller geometries (type) at different configurations is done. Knowing that for the best homogeneity, a single loop must be formed in the reactor, it is found that propeller type impeller is the best among the other blades which are hydrofoil blade, pitched blade and rushton turbine. It provides single loop with the lowest possible mixing time. Moreover, impeller diameter should be smaller than 0.55 T (T = reactor tank diameter). Following the first part findings, in the second part the impellers geometries used in the simulations are 3D printed and used to produce NMC 811 cathode material. All parameters kept constant apart from the impeller type and configuration in each experiment. The output of co-precipitation process, powders are structurally and morphologically analysed suing XRD and SEM, respectively. XRD results show that impeller type does not significantly affect the crystal strucuture of the synthesized Ni0.8Co0.1Mn0.1(OH)2 samples. They all are indexed as hexagonal β-Ni(OH)2 structure. However, after the calcination, main effect of the impeller was observed. Rietvield analysis of heat treated crystalline LiNi0.8Co0.1Mn0.1O2 samples showed different cation mixing levels, which is attributed to the usage of different impellers during their precursor synthesis stage. Effect on the morphology could not be investigated since the reaction time did not allow for complete morphological development. This will be investigated in future studies. However, average particle size is investigated for each impeller type. It is found that average particle size decreases with increasing big loop to small loop ratio (RL) for the pitched blade and hydrofoil impeller type. On the contrary, average particle size increases with increasing RL for the propeller type impeller. Last, using the powders, electrodes that produced as cathodes have been preapared and analysed electrochemically to see their half-cell test results for lithium ion batteries. For the electrochemical performance analyses, cyclic voltammetry, galvanostatic and impedance tests are conducted. As a result, it is understood that the impeller type has an effect on the cation mixing and oxidation states of transition metals in the crystal. This situation directly affects the electrochemical properties of the material. Powders produced from the precursor that is synthesized with rushton turbine impeller, which has the lowest homogeneity, showed the worst electrochemical performance with an inital discharge capacity of 102.68 mAh/g. The propeller type impeller, which reached the highest level of homogeneity, also showed the best performance in the 2.8 - 4.3 V range with an initial discharge capacity of 177.70 mAh/g at C/20 rate with a 75.62% capacity retention.