Lityum iyon piller için yazdırılabilir NMC katot mürekkeplerinin sentezi
Synthesis of printable NMC cathodes for lithium ion batteries
Yazar: FATMA SENA TUNCA
Danışman: DOÇ. DR. MAHMUD TOKUR
Sakarya Üniversitesi / Fen Bilimleri Enstitüsü / Metalurji ve Malzeme Mühendisliği Ana Bilim Dalı
Derece: Yüksek Lisans, 2024
Konu: Enerji = Energy ; Metalurji Mühendisliği = Metallurgical Engineering

Özet:
Lityum iyon (Li-ion) piller, yüksek enerji yoğunluğu ve uzun ömrü sayesinde taşınabilir elektronik cihazlardan elektrikli araçlara ve yenilenebilir enerji sistemlerine kadar geniş bir uygulama yelpazesi sunar. Ancak, bu pillerin üretim süreci karmaşıktır ve maliyetleri yüksektir. Aktif malzemelerin açık hava koşullarına duyarlılığı, titiz üretim ortamları gerektirmekte ve bu da üretim maliyetlerini artırmaktadır. Geleneksel elektrot hazırlama süreci, poliviniliden florür (PVDF) bağlayıcısının çözülmesi için N-Metil-2-Pirrolidon (NMP) solventinin kullanılmasını içermektedir. NMP'nin hem pahalı hem de toksik doğası, sağlık riskleri ve çevresel sorunlar oluşturmaktadır.
Yüksek oranda nikel içeren NMC811 katotlar, yüksek voltaj aralıklarında etkili çalışabilmelerine rağmen zamanla yan reaksiyonlar ve katot-elektrolit arayüzü (CEI) kalınlaşması nedeniyle kapasite düşüşleri yaşamaktadır. Bu tez çalışmasında, kapasite kaybını aşmak ve su bazlı katot mürekkeplerinin üretimini mümkün kılmak amacıyla, NMC811 parçacıkları hidrotermal yöntemle indirgenmiş grafen oksit (iGO) ile kaplanmıştır. iGO kaplaması, NMC811 parçacıklarının etrafında koruyucu bir tabaka oluşturarak yan reaksiyonları azaltmakta ve elektrot yapısını stabilize etmektedir. Böylece kapasite kaybını önlenerek pil performansı iyileştirilmiştir.
Katot tabakalarının üretilmesinde kullanılan serigrafi süreci, çok yönlü ve ölçeklenebilir bir tekniktir. Bu yöntem, viskoz mürekkebin bir alt tabakaya desenli bir ağ ekran aracılığıyla uygulanmasını ve ardından kurutulmasını içermektedir. Bu yöntem, uygulanan tabakanın kalınlığı ve homojenliği üzerinde hassas kontrol sağlar, bu da pilin performansı için kritik öneme sahiptir. Serigrafi ayrıca rulodan ruloya üretimle uyumludur, bu da üretim verimliliğini önemli ölçüde artırabilir ve maliyetleri düşürebilir. Serigrafinin çeşitli alt tabakalar ve malzemelere uyarlanabilirliği, büyük ölçekli pil üretimi için çekici bir seçenek haline getirmektedir.
Bu çalışmada kullanılan su bazlı bağlayıcılar, özellikle karboksimetil selüloz (CMC) ve polietilen oksit (PEO), geleneksel PVDF-NMP bağlayıcılarına göre birkaç avantaj sunmaktadır. CMC, selülozdan türetilmiştir ve bu nedenle biyolojik olarak parçalanabilir bir malzemedir. PEO ise mükemmel film oluşturma özellikleri ve mekanik esneklik ile bilinmektedir. Bu bağlayıcılar birleştiğinde, çevrim sırasında katot malzemesinin hacim değişikliklerini karşılayabilen sağlam bir matris sağlar ve böylece pilin dayanıklılığını ve performansını artırır. Bağlayıcı hazırlama sürecinde toksik solventlerin bulunmaması, üretim ortamının güvenliğini artırır ve pil üretiminin çevresel etkisini azaltmaktadır.
NMC811 parçacıklarının iGO ile kaplanması, elektrotun elektriksel iletkenliğini ve yapısal stabilitesini artırır. Bu yöntem, elektrolit ile aktif malzeme arasındaki doğrudan teması azaltarak yan reaksiyonları en aza indirir ve katotun genel performansını  
iyileştirir. Su bazlı bağlayıcılar, toksik solvent içermediğinden üretim ortamının güvenliğini artırır ve çevresel etkileri azaltır. Ayrıca, serigrafi teknolojisi, tabaka kalınlığı ve homojenliği hassas şekilde kontrol etme avantajı sunar ve rulodan ruloya üretimle uyumludur, bu da üretim verimliliğini artırır.
CMC ve PEO bağlayıcıları su bazlı hazırlanmış ve bu bağlayıcıların geleneksel PVDF-NMP bağlayıcılarıyla karşılaştırılması yapılmıştır. CMC ve PEO bağlayıcıları, çevre dostu bir alternatif sunmaktadır ve bu bağlayıcıların kullanımı, 2.8-4.6 V voltaj aralığında 50 çevrim sonrası %75 elektrokimyasal stabilite sağlamıştır. Bu sonuç, su bazlı bağlayıcıların yüksek performanslı lityum iyon piller için etkili bir seçenek olduğunu göstermektedir.
Su bazlı üretim sürecinin çevresel ve ekonomik faydaları azımsanamayacak kadar fazladır. Toksik solventlerin ortadan kaldırılması, atık yönetimini basitleştirir ve maliyetleri düşürür. Ayrıca, bu üretim yöntemleri küresel tedarik zincirine bağımlılığı azaltabilir ve çevre dostu üretim süreçlerinin benimsenmesini teşvik edebilir. Sosyo-ekonomik olarak, bu yöntemler işçi sağlığını iyileştirir ve toplum sağlığına katkıda bulunur, bu da kamu destek ve kabulünü artırabilir.
Bu araştırmanın bulguları, gelecekteki yenilikler için önemli bir temel sağlamakta ve enerji depolama endüstrisinde sürdürülebilirliği ve verimliliği artırmaya yönelik önemli adımlar sunmaktadır. Su bazlı katot mürekkepleri ve serigrafi teknikleri, yüksek performanslı ve çevre dostu lityum iyon pillerin üretiminde büyük potansiyele sahiptir. Bu öncü yaklaşım, hem mevcut zorlukları ele almakta hem de gelecekteki ihtiyaçları öngörmektedir, böylece lityum iyon pillerin sürdürülebilir enerji çözümlerinin temel taşı olarak kalmasını sağlamaktadır.

Abstract:
Lithium-ion (Li-ion) batteries are a life-saving energy storage technology. They are indispensable in various applications ranging from portable electronics to electric vehicles and renewable energy systems due to their high energy density, long cycle life, and reliability. However, the manufacturing process of Li-ion batteries remains complex and costly. The sensitive nature of active materials to open atmosphere conditions necessitates stringent manufacturing environments, contributing to high production costs. The meticulous care needed to handle these materials significantly increases the complexity and cost of the manufacturing process, making it less accessible for large-scale production and application.
The conventional electrode preparation process involves the use of N-Methyl-2-Pyrrolidone (NMP) as a solvent for dissolving Polyvinylidene fluoride (PVDF), a common binder. NMP is not only expensive but also poses serious health risks to workers due to its volatile and toxic nature. Exposure to NMP can lead to respiratory issues, skin irritation, and long-term health problems. The environmental impact of NMP is also concerning, as it is difficult to dispose of safely and can contaminate water and soil. The reliance on such hazardous chemicals not only contributes to unsafe working conditions but also raises significant concerns about the sustainability and environmental impact of the battery production process.
Therefore, exploring safer and more environmentally friendly production techniques is urgently necessary. Within the scope of this thesis study, a novel approach was investigated: the production of water-based LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode inks using the screen-printing method. Screen printing is widely utilized in the fabrication of sensors and electronic devices due to its practical applications and potential for low-cost production. The method's simplicity, scalability, and cost-effectiveness make it a promising candidate for battery manufacturing. By replacing NMP with water as the solvent, the process becomes significantly safer and more environmentally friendly, addressing some of the critical issues associated with traditional Li-ion battery production.
Despite their suitability for operation at high voltage ranges, NMC811 cathodes typically exhibit rapid capacity drops over time. This degradation is primarily due to side reactions and the thickening of the Cathode-Electrolyte Interphase (CEI), which impedes the flow of lithium ions and reduces the battery's overall efficiency. To overcome the capacity drop issue and enable the production of water-based cathode inks, NMC811 particles were encapsulated with reduced graphene oxide (rGO) via a hydrothermal method. Encapsulation with rGO provides a protective layer around the NMC811 particles, mitigating side reactions and stabilizing the electrode structure. This approach helps maintain the integrity of the cathode material, thus enhancing the battery's performance and longevity.
The study also involved comparing water-based Carboxymethyl cellulose (CMC) - Polyethylene oxide (PEO) binders with conventional PVDF-NMP binders. CMC-PEO binders are not only environmentally friendly but also exhibit promising electrochemical stability. Experimental results demonstrated that the water-based cathode inks maintained 75% of their initial capacity after 50 cycles within a high voltage range of 2.8-4.6 V. This performance is comparable to, if not better than, that of electrodes prepared with traditional PVDF-NMP binders, indicating the viability of water-based binders for high-performance Li-ion batteries.
The water-based novel cathode ink presented in this study is not only well-suited for advancing the development of printed batteries but also represents a significant stride towards more eco-friendly production processes. By replacing toxic NMP with water, the process becomes safer for workers and reduces the environmental impact of battery manufacturing. Moreover, screen printing technologies offer strategic importance by lowering the investment cost of battery production, making it more accessible and scalable for widespread application.
The findings of this thesis highlight the potential of water-based production techniques and screen-printing technology in revolutionizing Li-ion battery manufacturing. As the demand for sustainable and efficient energy storage solutions continues to grow, the development of safer, cost-effective, and environmentally friendly production methods becomes increasingly crucial. The innovative approaches explored in this study pave the way for future research and development in the field, promising a greener and more sustainable future for energy storage technology. The successful implementation of water-based cathode inks could lead to a paradigm shift in battery manufacturing, making high-performance Li-ion batteries more accessible and environmentally responsible.
In detail, the encapsulation process of NMC811 particles with reduced graphene oxide (rGO) involved a hydrothermal synthesis method. This method not only ensures a uniform coating of rGO on the particles but also enhances the electrical conductivity and structural stability of the cathode material. The hydrothermal method is advantageous due to its ability to produce high-quality materials with controlled morphology and composition. The rGO encapsulation helps in reducing the direct contact between the electrolyte and the active material, thus minimizing side reactions and improving the overall electrochemical performance of the cathode.
The water-based binders used in this study, specifically CMC and PEO, offer several benefits over traditional PVDF-NMP binders. CMC is derived from cellulose, making it a renewable and biodegradable material. PEO, on the other hand, is known for its excellent film-forming properties and mechanical flexibility. When combined, these binders provide a robust matrix that can accommodate the volume changes of the cathode material during cycling, thereby enhancing the durability and performance of the battery. The absence of toxic solvents in the binder preparation process not only improves the safety of the manufacturing environment but also reduces the environmental footprint of battery production.
The screen-printing process employed for fabricating the cathode layers is a versatile and scalable technique. It involves the deposition of a viscous ink onto a substrate through a patterned mesh screen, followed by drying and curing. This method allows for precise control over the thickness and uniformity of the deposited layer, which is crucial for the performance of the battery. Screen printing is also compatible with roll-to-roll manufacturing, which can significantly increase the production throughput and reduce costs. The adaptability of screen printing to various substrates and materials makes it an attractive option for large-scale battery manufacturing.
The electrochemical performance of the water-based cathode inks was evaluated through a series of tests, including cyclic voltammetry, galvanostatic charge-discharge cycling, and impedance spectroscopy. These tests revealed that the water-based cathodes exhibited excellent rate capability and cycling stability. The capacity retention of 75% after 50 cycles within a high voltage range is a promising result, indicating the potential of these materials for practical applications. The improved performance can be attributed to the synergistic effects of rGO encapsulation and the use of CMC-PEO binders, which together enhance the structural integrity and electrochemical stability of the cathode.
Furthermore, the environmental and economic benefits of the water-based production process cannot be overstated. The elimination of hazardous solvents like NMP not only makes the production process safer for workers but also simplifies the waste management and disposal processes. The use of water as a solvent reduces the need for expensive solvent recovery systems and lowers the overall production costs. The environmental impact is significantly reduced, making the production process more sustainable and compliant with increasingly stringent environmental regulations.
The broader implications of this research extend to the global supply chain for battery materials. Traditional Li-ion battery manufacturing relies heavily on specific raw materials and chemicals, some of which are sourced from regions with unstable geopolitical climates or significant environmental concerns. By transitioning to water-based production methods and utilizing more abundant, less toxic materials, the dependency on these critical and often problematic supply chains can be reduced. This shift not only enhances the sustainability of battery production but also improves the resilience of the supply chain, making it less vulnerable to disruptions and ensuring a more stable supply of essential components for various industries.
In addition to the technical and environmental benefits, the adoption of water-based cathode inks and screen-printing techniques also has significant socio-economic implications. The safer working conditions associated with the elimination of hazardous solvents like NMP can lead to improved worker health and safety, reducing the incidence of occupational illnesses and injuries. This improvement in workplace safety can result in higher worker satisfaction and productivity, contributing to a more positive and sustainable working environment. Moreover, the reduction in environmental pollutants aligns with broader societal goals of protecting public health and preserving natural ecosystems, thereby garnering greater public support and acceptance of battery manufacturing operations.
Finally, the successful demonstration of this innovative approach to Li-ion battery production sets a precedent for future advancements in the field. It encourages further exploration and optimization of eco-friendly materials and manufacturing techniques, fostering a culture of sustainability and innovation in the energy storage industry. As researchers and manufacturers build upon these findings, the potential for continuous improvement in battery performance, cost-effectiveness, and environmental impact grows, paving the way for a new generation of green technologies. This forward-thinking approach not only addresses current challenges but also anticipates future needs, ensuring that Li-ion batteries remain a cornerstone of sustainable energy solutions for years to come. The adoption of these innovative techniques could revolutionize the battery manufacturing industry, leading to a greener and more sustainable future for energy storage technology. By addressing the critical challenges of safety, cost, and environmental impact, this research provides a pathway for the widespread adoption of high-performance, eco-friendly Li-ion batteries.
Furthermore, the transition to water-based production methods opens up opportunities for greater community and stakeholder engagement. Companies can leverage the environmental and safety benefits of these new processes to enhance their corporate social responsibility (CSR) profiles, potentially attracting more investments and partnerships. Local communities may also benefit from reduced environmental hazards and improved health outcomes, fostering a more positive relationship between battery manufacturers and the communities in which they operate.
In the long term, the advancements in water-based cathode inks and screen-printing techniques could influence regulatory standards and industry practices. As more companies adopt these safer and more sustainable methods, there could be a push towards stricter environmental regulations that mandate the use of non-toxic materials and eco-friendly production processes. This shift could drive further innovation in the industry, as companies strive to comply with new standards while maintaining competitive performance and cost advantages.
Finally, the educational impact of this research cannot be ignored. The findings and methodologies developed in this study can be integrated into academic curricula and training programs for future engineers and scientists. By exposing students to cutting-edge, sustainable technologies, educational institutions can prepare the next generation of professionals to contribute to the ongoing evolution of the energy storage industry. This knowledge transfer is crucial for maintaining the momentum of innovation and ensuring that future advancements continue to prioritize safety, sustainability, and efficiency.