Technical Field

Thermoplastic material is made conductive by adding reinforcement and/or filler elements to electrically insulating thermoplastic polymers for use as cathodes of secondary batteries. As an alternative to the cathode source material applied on the traditionally used aluminum sheet, it provides the ability to provide electrical conductivity and cation ions without using the aluminum sheet as the cathode host, allowing the use of cathodes containing a single layer of thermoplastic composite material.

Prior Art

One of the most critical problems of our age is to find environmentally friendly and low-cost resources in energy production and storage in line with technological developments. In recent years, interest in alternative fuel sources and green energies to replace fossil fuels has increased, and an effort has been made to replace traditional fuel sources. The most critical renewable or sustainable energy sources are solar, wind, and hydroelectric. Due to the inability of renewable energy sources to be continuous or stable, the need for energy storage devices increases day by day after electricity is produced.

One of the essential basic materials used for energy storage, batteries, are systems used to convert chemical energy into electrical energy.

The types of batteries commonly used today are primary batteries and secondary batteries. Primary batteries are non-rechargeable, secondary batteries are rechargeable. The secondary batteries can be recharged and reused, and their sensitivity to the environment enables them to be used more widely. An increasing number of research and development projects to develop secondary batteries was carried out on especially lithium-ion (Li-ion) batteries, which stand out in terms of ease of use. In recent years, intensive studies have been conducted on developing new generation composite cathode and anode electrodes with low cost and high efficiency to increase energy efficiency. Almost every individual has portable electronic devices (mobile phones, cameras, computers, etc.) in our age. With the effect of technological developments, most of the electronic devices we use in our daily life have become and continue to be suitable for wireless use. It is inevitable that these devices, which have become wireless, need a portable energy source. Features such as having a high energy density, long service life, being able to be charged in a short time, and having minimum damage to the environment are required from this energy source. In this context, rechargeable secondary batteries are widely used for portable electronic device technology, which will meet the energy need.

Li-ion batteries are the most popular secondary batteries in use today. Li-ion batteries use a lithium source (lithium metal, lithium salt, or organolithium compounds) as the cathode element, carbon-based compounds, ceramic or metallic salts as a host anode element, and an anhydrous organic solution or solidphase electrolyte as the electrolyte.

In the cathode elements used in the current art, LiCoO2, LiMn2O4 or LiFePO4, Lithium Nickel Manganese Cobalt and Lithium Nickel Cobalt Aluminum Oxide are applied on an aluminum collector and used as a source of lithium ions. In addition, Sodium sources materials are used such as sodium cobalt oxide, sodium magnesium oxide, sodium iron phosohate, or sodium titanium oxide. Moreover, calcium metal oxides are examples of cathode active materials used in calcium batteries. The most crucial cathode elements used today are Lithium and Sodium, and the chemical structures of these materials, the redox reactions in the battery, and the substances used to form the battery cell by providing these reactions are explained in the article "2021 roadmap for sodium-ion batteries" for sodium batteries and both lithium and sodium Cathode materials created with additives for energy storage were given in the Journal of Power Sources in an article named "Sodium and lithium incorporated cathode materials for energy storage applications - A focused review" in 2021. While the energy storage mechanisms in the anode material are divided into intercalation, conversion reactions, or alloying, cathode materials store energy by intercalation or conversion reactions. The simultaneous application of these mechanisms is an essential building block that directly affects battery efficiency. Each electrode material group has its advantages and limitations. Therefore, selecting suitable electrode materials is the main issue for battery efficiency and applicability. The limited specific capacity of the cathode materials is one of the major obstacles for improving the energy densities of existing lithium-ion batteries. The production of new secondary batteries with long cycle life and higher energy density is critical to reduce the weight, costs, and environmental impact of portable electronic devices and electric or hybrid vehicles. To improve the performance of the cathode material, studies have been made to widen the thickness of the shield coating on the cathode surface to a point where it can inhibit oxygen discharge at higher temperatures. It is mentioned in the article "Metal oxide-coated cathode materials for Li-ion batteries-A review," published in the Journal of Alloys and Compounds in 2019. One of the basic principles is that the cathode surface, with a coating of sufficient thickness to facilitate the increase in performance, should be ionic and electrically conductive if it increases cell resistance and adversely affects regular battery operation.

In current solution techniques, there is generally a trend towards composite materials containing polymeric composite, ceramic composite, metallic composite, or carbon-derived nanoparticles or reinforcements with known electrical conductivity in line with the articles mentioned above. The desired discharge capacity, energy density, and cycle number gain in the cathode materials are studied in this context. However, problems have been experienced in putting them on the market due to depleted lithium resources, the difficulty of producing alternative raw materials, and the production track's cost.

As a result of the researches, it was concluded that there is no thermoplastic-based single-layer cathode used in secondary batteries.

Purpose of the Invention

It is essential to reduce environmental pollution, meet the demands of the industry and develop materials with excellent properties while designing recyclable and economical materials.

New materials must overcome existing challenges such as high cost, recyclability, reliability, and energy consumption.

Thermoplastics have become one of the most widely used materials of modern life in recent years, thanks to their superior mechanical properties, thermal stability, workability, and recyclability. Thermoplastics are polymers that can be softened and melted by applying heat and processing in the softened state (e.g., thermoforming) or melted (e.g., extrusion and injection molding). Thermoplastic polymers can be repeatedly processed by heat and directly recycled to make new products. Typical manufacturing processes used to make thermoplastic parts are injection molding, blow molding, and thermoforming.

In addition to the recycling advantage, thermoplastics have high ductility and impact resistance. They can also be joined by various welding techniques such as resistance welding, vibration welding, and ultrasonic welding. Also, cycle times for thermoplastic parts are pretty low.

In recent years, composite materials, especially polymer-based composite materials, have been increasing their popularity in many sectors due to their versatile use, ease of preparation, availability of raw materials, environmental friendliness, improved mechanical properties for desired products, low density, and low cost.

Polymers are often reinforced with other materials to form composites so that the material adequately has the properties required for optimal performance in various fields. Thermoplastic-based composites are gaining increasing attention due to their advantages: lower production cost, high strength, low moisture content, no curing, rework flexibility, and high-temperature resistance. Thermoplastic-based composites are obtained by combining organic or inorganic polymers as a matrix and reinforcement, additives, and/or filling materials in a specific ratio.

It has been concluded that thermoplastic materials, widely studied and widely used globally, have not been tried before as a cathode tool used for energy storage in secondary batteries. As mentioned in the current situation, it is predicted that thermoplastic-based composite materials are suitable for intercalation reaction due to the molecular structure of thermoplastics and can be a cathode material due to their high charge-discharge capacity.

Thermoplastic-based composite materials are quickly done by the extrusion method. Compared to the current cathode production method, the extrusion method is practical and faster. Also, since thermoplastics are easy to shape, they pave the way for using quickly, various, and more accessible methods during processing after they are produced as cathode material. In addition, the recycling of thermoplastic materials is easier and faster than existing cathode materials.

The advantages of thermoplastic-based composite material as the cathode material of secondary batteries are as follows.

• To improve the functioning of the cathode as a lithium source, increasing the discharge capacity, energy capacity, and number of cycles of the anode,

• To standardize and facilitate the process in the production of the cathode and to reduce production costs,

• To prevent the safety problems of Lithium-ion batteries (explosion, heating, flaming, etc.)

• Recycling,

• Developing the cathode with a new method and providing ease of use with a single-layer structure.

Detailed Description of the Invention

The main reason why thermoplastic materials cannot be used as electrode cells alone is that plastics are electrical insulators by nature. With the studies carried out, thermoplastic-based composite materials are suitable for electrical conduction and energy storage. Within the scope of these studies, electrical conductivity, energy storage, and thermal properties are improved by adding metal/metal mineral/organometallic compounds to thermoplastic materials, as well as carbonderived reinforcement and/or filler elements.

Thermoplastic-based composite material with electrical conductivity and energy storage properties is used as active cathode material in secondary batteries. As a thermoplastic matrix in polymer-based composite material; Polyethylene (PE), Polypropylene (PP), Polystyrene (PS), Polyethylene terephthalate (PET or PTFE), Polyamide (PA) (Nylon), Polyvinyl chloride (PVC), Polycarbonate (PC), Acrylonitrile butadiene styrene (ABS), Polyvinylidene chloride (PVDC), Polybutylene Terephthalate (PBT), Polyphenylene Sulfide (PPS), At least one of the thermoplastic matrix material types such as Syndiotactic Polystyrene (SPS), Polyether ether ketone (PEEK), Polyketones (POK) is used. The thermoplasticbased composite recipe is created by adding metal, metal salts (Metal minerals), organometallic compounds, and carbon derivatives (graphite, graphene, carbon nanotube, carbon fiber, etc.) materials to electrically insulating polymers to provide conductivity.

Twin-screw extruder is used in the production of thermoplastic-based composite material.

During the production of thermoplastic composite material with twin-screw extruder, metal and/or metal salt, organometallic compounds and carbon derivative, primary and secondary antioxidants, compatibilizing side feeders are added into the molten thermoplastic matrix material. This molten material is passed through water bath and cut into granules with the help of a pelletizer.

The main mechanisms involved in an extrusion process are feeding, melting, and homogeneous mixing. The ratio of screw length to diameter (L/D ratio) affects the mixing and homogeneity of the output. The exit velocity of the material from the extruder depends on the screw speed, barrel temperature, screw configuration, and melt viscosity.

In line with these parameters, 30 - 80% by weight of thermoplastic matrix material is used in the thermoplastic-based composite material produced by the extrusion method. Lithium, Sodium, Calcium, Magnesium compounds and/or derivatives that can be a source of cations at a rate of 20-60% by weight as reinforcement and/or filler, 3-15% by weight of metal and/or 10-30% by weight of metal mineral and/or by weight of It is used with 10-30% organometallic compounds and/or 1-15% by weight binder additives and/or 1-15% by weight conductivity increasing additives. These materials are turned into granules or extrudates as a result of the extrusion process.

Firstly, thermoplastic-based composite materials of extrudates that are granulated or extruded directly are filmed with a plastic film machine. The thickness of these shaped film materials should be in the range of 0.10 - 1.00 mm. Depending on the type of thermoplastic material to be used, it should only be added with a binder or by extrusion using additional chemicals, and the single-layer cathode should be ready as a material to be used directly in the battery.

The steps for the use of thermoplastic-based composite material as a cathode in Li-ion batteries, which are one of the secondary batteries, are given below;

• In order to be a single-layer cathode of thermoplastic-based composite materials, 30 - 80% by weight of thermoplastic matrix material is used. Lithium, Sodium, Calcium, Magnesium compounds and/or derivatives that can be a source of cations at a rate of 20-60% by weight as reinforcement and/or filler, 3-15% by weight of metal and/or 10-30% by weight of metal mineral and/or by weight of It is prepared for the extruder method by using 10-30% organometallic compounds and/or 1-15% by weight binder additives and/or 1-15% by weight conductivity enhancing additives.

• During the extrusion method, the single-layer cathode is formed into a film and/or sheet form by injection molding directly from the granule, or a flexible structure is gained by drawing the extrudates as films and/or sheets after the direct extrusion process.

• After these processes, the single-layer cathode material is cut and shaped according to the desired battery type (pen battery, button cell, etc.).

• Water and oxygen are removed from the single-layered cathode by keeping it in an inert gas atmosphere in order to remove any moisture that may have remained inside the shaped single-layered cathode, and then the process is completed with the battery closure process.

The thermoplastic-based composite material, which is the subject of the invention, can be produced in different secondary battery types suitable for all kinds of sectors (for example, automotive, electrical-electronics, defense, aerospace industry, etc.) where energy storage applications are used.