PVDF-HFP based composite polymer electrolytes for printable smart energy storage system

Energy is a fundamental component of many areas such as the maintenance of modern life, industrial production, transportation, and communication technologies. The growing global population and constantly evolving technology are increasing the demand for energy day by day. In the face of this growing demand, the sustainability and environmental impacts of existing energy sources are being seriously questioned. Today, a large portion of the world's energy needs is still met by fossil fuels. However, these resources cause environmental pollution and, due to their finite nature, do not offer long-term solutions. The greenhouse gases produced by the combustion of fossil fuels bring with them many negative consequences, such as climate change, air pollution, and ecosystem degradation. At the same time, the limited nature of these resources threatens energy supply security and increases energy costs. Therefore, research into environmentally friendly, sustainable, and economically viable energy solutions that can replace fossil fuels has gained momentum. In this context, renewable energy sources have become one of the most discussed alternatives today. Renewable sources such as solar, wind, geothermal, and biomass stand out because they can be obtained continuously from nature and have lower carbon emissions. These types of energy sources contribute to reducing environmental impacts in energy production while also reducing external dependency and contributing to energy security. However, an important feature of renewable energy systems is that their production fluctuates depending on nature, i.e., weather conditions and environmental variables. This fluctuating production profile also poses certain challenges in terms of grid stability and the ability to provide continuous energy to consumers. In order to overcome the above-mentioned challenges, systems capable of balancing the time mismatch between energy production and consumption, i.e., energy storage technologies, are needed. Energy storage systems enable the energy obtained from renewable sources to be used when needed, thereby increasing the continuity and efficiency of the system. In this context, electro-chemical storage systems in particular stand out due to their high energy densities, long cycle lives, and fast response times. Lithium-ion batteries (LIBs) are attracting considerable interest as a promising electrochemical storage solution due to their high energy density, low self-discharge rate, high open-circuit voltage, and long life. The last 25 years have seen the rapid spread of portable electronic devices worldwide, with lithium-ion batteries playing an important role in powering mobile devices such as smartphones, tablets, cameras, and laptops. Nowadays, it is one of the strongest candidates for electric vehicles and energy storage networks. Along with this, LIB chemistry has been continuously developed since it was first commercialized in 1991, reaching a level that can meet the performance requirements of new generation technologies. With the widespread use of lithium-ion batteries, significant developments have also been made in adapting these systems to new generation technologies. In particular, in recent years, there has been growing interest in flexible, lightweight, safe, and user-friendly energy storage solutions to meet energy needs in areas such as wearable devices, flexible electronics, smart textiles, and medical sensors. Such systems are expected not only to be high-performance, but also to demonstrate mechanical flexibility, applicability to different surfaces, and production processes that are economical, fast, and scalable. The traditional battery production methods are insufficient to meet the requirements of these new generation applications. Therefore, it has become inevitable to develop alternative approaches that are both structurally more flexible and more functional in terms of production. Traditional battery manufacturing processes typically involve multiple stages and many standardized steps. These processes include mixing the active material with a solvent to form a slurry, coating this mixture onto a current collector surface, and then drying, calendering, and cutting. In addition, this production method has various disadvantages in terms of cost, material loss, and time. For these reasons, the need for new production techniques that are compatible with flexible surfaces, offer high production speeds, and result in less material waste is increasing day by day. Printable battery systems developed in this direction offer a new perspective in energy storage technologies. Printable batteries are gaining increasing attention in both academic research and industrial applications due to their advantages such as simplicity of production processes, low production costs, environmental friendliness, and easy scalability. The printing techniques used in these systems enable the direct application of patterned electrodes, separators, and electrolyte layers onto different substrates, thereby simplifying the production process and allowing for greater diversity in device design. Although various printing techniques are used in printable battery technologies, screen printing is one of the leading methods in this field. Screen printing is widely used in many industrial sectors due to its low cost, suitability for high-volume production, ability to work with inks of different viscosities, and applicability to various surfaces. In this technique, ink applied to a screen or stencil is spread evenly across the surface using a printing blade, and then when the stencil is removed, the desired pattern is transferred directly to the substrate. It is highly suitable for mass production because it allows multiple components to be printed simultaneously. In addition, the rheological properties of the ink, which is one of the key factors determining print quality, play a critical role in terms of pattern resolution and layer integrity. Success in screen printing depends largely on the rheological properties of the ink used. Parameters such as ink viscosity, flow behavior, and spreadability directly affect print quality and pattern consistency. However, this technique is not suitable for liquid electrolytes with low viscosity and volatile structures. Therefore, there is a need for stable and safe electrolyte systems that are compatible with screen printing. At this point, polymer-based electrolytes emerge as an important alternative. In addition to their suitability for the printing process thanks to their adaptable viscosity, they also offer safer and structurally integrated solutions, making them an attractive option. Polymer electrolyte inks formulated for screen printing offer strong potential in terms of both performance and manufacturability in the production of flexible energy storage devices. Polymer electrolytes were first introduced by Fenton and his colleagues in 1973, and the importance of this structure in technological applications was recognized in the early 1980s. Over the past thirty years, research on the development of polymer electrolytes has continued due to their potential applications in electrochemical energy production, storage, and conversion systems. Polymer electrolyte (PE) is a membrane formed by the dissolution of salts in a high molecular weight polymer matrix. In the preparation of PE, at least one main (host) polymer matrix is required as the basic building block before any additives are added. For this purpose, different types of polymer matrices can be used. At this point, poly(vinylidene fluoride) (PVDF), which has a semi-crystalline structure, stands out as the primary polymer matrix due to its high dielectric constant (ε = 8.4) and the presence of strong electron-withdrawing -C-F functional groups, which facilitate the dissolution of lithium salts and thus support high ion carrier concentrations. In addition, the copolymer obtained by incorporating hexafluoropropylene (HFP) into the PVDF matrix has been widely preferred in electrolyte systems due to its structural advantages. The amorphous HFP phase in the structure of this copolymer enables the retention of a high amount of liquid electrolyte, while the crystalline PVDF phase provides mechanical support to the polymer matrix. However, the high crystalline structure of the poly(vinylidene fluoride hexafluoropropylene) (PVDF-HFP) skeleton limits the mobility of lithium ions, which causes a decrease in performance in practical applications. Increasing the ionic conductivity of PVDF-HFP-based polymer electrolytes is a fundamental problem that still needs to be solved. Studies conducted in this direction have revealed that this problem can be overcome by incorporating inorganic nano-filler materials into polymer electrolyte systems. In addition, incorporating two-dimensional (2D) fillers such as graphene oxide and boron nitride into polymer electrolytes is an effective method for improving the mechanical properties and ionic conductivity of PEs. In recent years, MXene compounds, which are metal carbide and nitride compounds with a 2D layered structure, have been widely used as functional materials in energy storage and conversion systems. These materials are particularly noteworthy as additives for improving the electrochemical performance of polymer electrolytes. However, there are only a limited number of studies in the literature on the application of MXenes in PE systems, and research in this area is still ongoing. Within the scope of this thesis study, a composite electrolyte system was developed by incorporating Ti₃C₂Tx-MXene into a PVDF-HFP-based polymer matrix, aiming to achieve multifunctional performance criteria such as high ionic conductivity, electrochemical stability, and compatibility with printing technologies. The studies were conducted with MXene contributions at different ratios (5%, 10%, 15%, 20%, and 25% by weight), and the effect of the contribution ratio on electrolyte performance was systematically investigated. The findings reveal that performance is directly related not only to the presence of MXene but also to the precise control of its amount. As a result of physical, rheological, and electrochemical characterization studies conducted in this direction, the optimum performance-providing additive ratio has been determined. This additive ratio has provided a wide electrochemical window along with high ionic conductivity values. Additionally, it has been tested in a half-cell configuration with an NMC811 cathode and demonstrated remarkable electrochemical stability, retaining a high percentage of its capacity after 100 cycles. Rheological analyses have also confirmed that the viscosity and flow properties of this electrolyte are compatible with the printing process. These findings demonstrate that the developed structure can be produced using screen printing and has practical potential for energy storage applications.