Lityum iyon pillerde metal ile katkılandırılmış grafitlerin anot özelliklerinin ve pil performanslarının incelenmesi

Reliable and sustain energy storage is crucial for modern portable electronics, such as mobile phones, laptop computers, MP3 players, other electronic devices, and potential applications for automobile industry. In this sense, lithium ion batteries provide an attractive solution. In addition, the later will bring significant contribution to reduce greenhouse gas emission and address global warming. Even though, lithium ion batteries offer advantages, there is a constant demand for higher energy density, higher power density, longer cycle life batteries which has motivated research into new battery materials for next generation of advanced lithium ion batteries. In lithium ion batteries, graphite is the most widely used anode materials. Even though, metallic materials like silicon, tin, boron etc. have higher specific capacity, due to severe volume changes during charge/discharge, graphite is preferred more compared to metallic materials. However, specific capacity of graphite needs to be improved which is only 372 mAh/g. Intensive researches continue on developing new anode materials with graphite and metals to improve cyclability and specific capacity of lithium ion batteries. This thesis mainly focused on development of metal mixed anode material for lithium ion batteries and assessment of their electrochemical and structural characteristics. The materials investigated are graphite and metals such as silicon dioxide, aluminum, boron and tin. For material characterization, scanning electron microscopy and thermogravimetric analyses were applied. For electrochemical characterization, galvanostatic measurements have been conducted. Compared to carbon based material, silicon has higher theoretical capacity, which is around 4200 mAh/g. Considering its high capacity, silicon is promising material to be used as composite for anode material for lithium ion battery. However, during intercalation/de-intercalation process with lithium, composite structure is changed during large volume expansion/contraction of Si. In this work, to minimize the volume expansion, silicon dioxide was used with graphite. Moreover, additives like tin and magnesium oxide were used to enhance to battery performance. After fabrication of coin lithium ion batteries, galvanostatic measurements were examined. According to results, it can be concluded that even though the initial discharge capacity of battery was improved compared to artificial graphite, due to loss of active matter and SEI formation at the initial cycles, stable discharge capacity cannot be met for all samples. Tin has also higher theoretical capacity, which is 992 mAh/g, compared to graphite. In this study, to improve the battery performance tin/graphite composites, which were prepared with different mass ratios, were used as anode material. Furthermore, addition of silver nitrate to composites were investigated. At the galvanostatic measurement of Sn mixed graphite, no reading can be recorded resulting from using a mean diameter of about 600 µm particle sized Sn powder, which leads flaking at every coating of the tin mixed slurry. Since the diameter of the tin particles could not be reduced further with agate mortar, the qualitative research of tin mixed graphite could not be performed. Recent studies showed that cycling could be improved by addition of aluminum and aluminum oxide to anode material. Even though, aluminum reacts with one lithium atom with moderate volume increase where tin reacts with 4.4 lithium atoms, gravimetric capacity of aluminum (990 mAh/g) is comparable versus tin (990 mAh/g). To enhance battery performance, aluminum or aluminum oxide/graphite composite were also investigated. Furthermore, silicon was used as additive in the composites to utilize and to maintain good capacity during cycle. Prepared samples showed higher initial discharge capacity compared to artificial graphite. However, none of the samples showed proper running battery profile due to the irreversible capacity losses during first cycle. Recent researchers also showed that boron addition to anode material has increase the discharge capacity and decrease the irreversible capacity of lithium ion battery. In this study, different boron additions were examined to find out optimum addition level of boron mixed graphite. In the battery performance analysis of boron mixed graphite, it can be clearly observed that all samples showed superior initial capacity compared to that of artificial graphite. In addition to that, after irreversible capacity loss at the first cycle, the capacity stayed stable at the following cycles with minor changes.