Biyoatıklardan karbon sentezi ve elektrokimyasal özelliklerinin incelenmesi
Carbon synthesis from bioatic and investigation of electrochemical properties
Yazar: GÜLBİKE YALDIZ
Danışman: DOÇ. DR. MEHMET OĞUZ GÜLER
Sakarya Üniversitesi / Fen Bilimleri Enstitüsü / Metalurji ve Malzeme Mühendisliği Ana Bilim Dalı
Derece: Yüksek Lisans, 2023
Konu: Enerji = Energy ; Metalurji Mühendisliği = Metallurgical Engineering

Özet:
Fosil yakıtların tükenmesi, elektrik enerjisi depolama sistemlerine olan ihtiyacı son derece önemli hale getirmiştir. Kesintili yenilenebilir enerji kaynaklarının (rüzgâr, güneş ve dalga gibi) yoğun olmadığı saatlerde sürekli bir enerji akışı sağlayarak elektrik enerjisi şebekesini stabilize etmek için verimli bir enerji depolama sistemi çok önemlidir. Elektriksel enerji depolama teknolojisinin geliştirilmesinde en çok odaklanılan, pilllerdir. Piller şu anda diğer enerji depolama teknolojilerine kıyasla en geniş uygulama alanına sahiptir. Lityum iyon pillerde kullanılan hammaddelerin hızla artan maliyeti, son zamanlarda araştırmacıları farklı pil teknolojilerine yönlendirmiştir. Sodyum iyon piller düşük maliyeti, doğada bol miktarda bulunması ve çevre dostu olması nedeniyle lityum iyon pillere alternatif olarak kabul edilmektedir. Pillerde kullanılan negatif elektrotta, karbon bazlı malzemeler her zaman alkali iyon piller için temel bir rol oynamıştır. Düşük maliyet ve yüksek spesifik kapasite gibi avantajları nedeniyle sert karbon, sodyum iyon piller için önemli bir aday olarak görülmektedir. Ayrıca sert karbonun yenilenebilir biyo-kaynaklardan elde edilebilmesi maliyeti düşürdüğü için büyük ölçekli üretim ve ticarileştirilme açısından büyük avantaj sağlamaktadır.
Bu tez çalışmada, sodyum iyon pillerde kullanılan anot malzemesi için biyokütle atıklarından yeni karbon anot elektrot geliştirilmiştir. Sakarya ilinde bol bulunması, düşük maliyeti ve sürdürülebilirlikleri nedeniyle ekonomik açıdan önemli tarımsal bir ürün olan fındık kabuğu biyokütle atığı kullanılmıştır. İlk olarak, H3PO4 ile ön işleme tabii tutulan fındık kabuğunun karbonizasyonu yoluyla sentezlenen yeni sert karbon malzemenin morfolojik, kimyasal ve elektrokimyasal özellikleri incelenmiştir. Bu karbon malzemelerin yapısı, dokusu ve bileşimi, X-ışını kırınımı (XRD) analizi, Raman spektrometresi, alan emilsiyonlu taramalı elektron mikroskobu (FESEM) analizi kullanılarak incelenmiştir. Oluşturulan anodun elektrokimyasal performansı ise galvanostatik şarj-deşarj, çevrimsel voltametri (CV) ve empedans analizleri kullanılarak incelenmiştir. Sonuç olarak, elektrot 0,5C'lik bir akım yoğunluğunda 250 çevrim sonra 247.6 mAh g-1'e varan tersinir kapasite değeri ve %74.7'lik kapasite korunumu göstermektedir.  Düşük maliyetli ve sürdürülebilir kaynağa sahip fındık kabuğu biyokütlesi, kolay ve uygun fiyatlı sentez prosedürleriyle birleştirildiğinde, sodyum iyon piller için umut verici bir ham madde olarak görülmektedir.

Abstract:
The depletion of fossil fuels has made the need for electrical energy storage systems extremely important. Since intermittent energy consumption (such as wind, solar, and wave) is not intense, an efficient energy storage system is very important to stabilize the electrical energy grid by releasing uninterrupted energy. Much of the focus on improving electric storage technology has been on battery storage. Batteries currently have the widest application area compared to other energy storage technologies. The type and number of battery storage applications are constantly expanding, mainly in the areas of electric and electric hybrid vehicles, grid energy storage, portable electronics, and the storage of electrical energy produced by renewable sources such as wind and solar generators. A battery essentially consists of one or more electrochemical cells containing a positive electrode (cathode), a negative electrode (anode), a separator, and an electrolyte medium (ion conductor). During battery operation, electron migration through an electronic conductor (electrodes) is accompanied by ion migration in the opposite direction from an ionic conductor (electrolyte), maintaining electro-neutrality. Batteries are divided into primary and secondary batteries according to the reversibility of chemical reactions. Primary batteries, also known as dry cells, are batteries that cannot be recharged when the chemical energy in them is exhausted. There are many types, especially lithium batteries, alkaline batteries and zinc batteries. Secondary batteries are rechargeable batteries that store chemical energy and convert chemical energy into electrical energy when needed. Secondary batteries are used in portable electronic and electrical devices, etc. appears in many fields. There are many types such as nickel cadmium, nickel metalhydride, lithium ion, lithium polymer.
The rapidly increasing cost of raw materials used in lithium-ion batteries has recently led researchers to different battery technologies. Sodium-ion batteries are considered an alternative to lithium-ion batteries due to their low cost, abundance in nature, and environmental friendliness. At the same time, the working principle of sodium-ion batteries is very similar to lithium-ion. A sodium ion battery consists of two sodium insertion materials, the negative (anode) and positive (cathode) electrodes, divided by the separator, and a sodium salt electrolyte. The sodium-ion battery is used sodium ions as charge carriers, which can move reversibly between the cathode and anode via the electrolyte as a pure ionic conductor between the electrodes during discharge and charging. During the discharge process, electrons are released from the anode, causing the oxidation reaction, and transferred to the cathode, where reducing chemical reactions take place, via the external circuit. The reverse transfer of electrons takes place during the charging process. The electrolyte has high ionic conductivity and low electrical conductivity, which acts as an insulator for electrons and plays the main role as a transport medium between anode and cathode for alkaline ions. In a complete battery cell, the cathode plays an important role both in terms of electrochemical performance and overall cost of manufacture for advanced commercial products. Therefore, the development of promising cathode materials for SIP technology is crucial. So far, high-performance cathode materials have been used in layered systems of types O3 and P2, as well as polyanionic compounds, Prussian blue analogues, organic compounds, etc. is shown. 
In the negative electrode used in batteries, carbon-based materials have always played a fundamental role in alkali-ion batteries. Due to its advantages such as low cost and high specific capacity, hard carbon is seen as an essential candidate for sodium-ion batteries. Hard carbons, as the name suggests, offer a significant degree of mechanical stiffness. It is often found in the structural properties of these materials that retain a high degree of precursor morphology. Hard carbons are generally obtained by precursors that do not allow the formation of graphite structures even after high-temperature processing, presenting a strongly cross-linked structure, and giving the end product an isotropic structure. In addition, the availability of hard carbon from renewable bio-resources provides a great advantage in terms of large-scale production and commercialization, as it reduces the cost.
According to the literature, hard carbon materials derived from different biomasses offer specific capacities ranging from 100 mAh g-1 to 350 mAh g-1 at low current densities. Compared to commercial precursors such as glucose, sucrose, and polymers, biomass waste can represent an ideal carbon source. Indeed, various biomass wastes such as banana peels, pomelo peels, rice hulls, ox horns, and peanut shells have been investigated. Of course, biomass waste is not a pure chemical. In fact, it consists of several components but is usually free if not subsidized (disposal of industrial biowaste often carries additional costs). In general, the main component of plant-derived biomass is cellulose. Cellulose molecules align to form microfibrils, which are themselves aligned and attached to macro fibrils by a matrix of hemicellulose, pectin, or lignin. Consequently, cellulose-based biomass can be simplified into three subclasses pectin, hemicellulose, and lignin-based materials. Thus, a comparative study was conducted between hard carbons obtained from waste materials belonging to three different subclasses: peanut shells (lignin-based), corncob (hemicellulose-based), and apples (pectin-based).
In this thesis, a new carbon anode electrode was developed from biomass waste for the anode material used in sodium ion batteries. Hazelnut shell biomass waste, which is an economically important agricultural product due to its abundance, low cost and sustainability in Sakarya province, was used. First, the morphological, chemical and electrochemical properties of the new hard carbon material synthesized by carbonization of hazelnut shell pretreated with H3PO4 were investigated. The structure, texture and composition of these carbon materials have been studied using X-ray diffraction (XRD) analysis, Raman spectrometry, and field emission scanning electron microscopy (FESEM) analysis. The electrochemical performance of the formed anode was investigated using galvanostatic charge-discharge, CV and impedance analyses.
This thesis study provides a new idea for the high-value functional use of biomass waste. In the present study, hazelnut shells were finely ground and pretreated with H3PO4 and then heat treated at 800 °C in an inert atmosphere. The electrochemical performance of electrodes made of hard carbon obtained from hazelnut shells was investigated in Na cells. This concept will guide the design and synthesis of carbons for the latest generation of advanced sodium-ion batteries. This resource-rich and low-cost carbon material for sodium-ion batteries are easily prepared from biomass by direct carbonization at 800 oC. Thanks to the large micropores, the hard carbon electrodes from the hazelnut shell offer a high reversible capacity of 247.6 mAh g-1, which is almost stable even after 250 cycles, together with excellent cycling performance. Hard carbons derived by H3PO4 pretreatment of hazelnut shells have a greater number of active sites to store Na ions; these may be defects and/or voids in the hard carbon as prepared. As a result, the anode electrode offers a high reversible capacity of 247.6 mAh g-1 even after long cycles between samples prepared here. Low-cost and sustainably sourced nutshell biomass, combined with easy and affordable synthesis procedures, is seen as a promising raw material for sodium-ion batteries.