Field of the Invention

The present invention relates to an expanded graphite-based flexible electrode developed by the electroless Ni-B coating method for use in supercapacitors and batteries, and to the production method thereof. The subject of the present invention includes functional materials developed by electroless Ni-B coating of papers obtained by pressing expanded graphite particles.

State of the Art

Today, high-performance flexible electrodes are produced using carbon-derived materials.

Many nanostructured carbon-based materials such as amorphous carbon, carbon nanotube (CNT) and graphene are emphasized, especially for use in supercapacitors in the state of the art. These carbon-based electrodes have high storage capacity and improved electrochemical properties. Thus, it provides high charge-discharge stability and exhibits better flexibility compared to nickel-based electrodes. However, the production of carbon-derived nanostructures is costly. This leads to difficulties in applications. For these reasons, developments are required in the production, and properties of flexible electrodes, and the production of high-performance carbon-derived materials suitable for mass production with a lower cost.

As a result, due to the abovementioned disadvantages and the insufficiency of the current solutions regarding the subject matter, development is required to be made in the relevant technical field.

Brief Description of the Invention

The present invention relates to a flexible electrode and production method thereof which fulfills the abovementioned requirements, eliminates all disadvantages, and brings some additional advantages. The main aim of the invention is to develop a flexible electrode with high performance and lower cost compared to the state of the art though it contains carbon-derived material.

A similar aim of the present invention is to develop a flexible electrode which exhibits excellent charge-discharge stability with its high energy storage capacity when used in supercapacitors, exhibits better flexibility than the widely used nickel-based electrodes with its excellent electrochemical properties.

The aim of the invention is to develop a flexible electrode that has high mechanical stretching properties because it contains Expanded Graphite (EG), provides high energy storage, has low cost, high electrical/thermal conductivity, is lightweight due to its low density, suitable for mass production, hierarchical pore structure.

Another aim of the invention is to develop a flexible electrode with reduced production cost by applying the Ni-B coating on ultra-thin EG papers by an electroless coating method.

Another aim of the invention is to develop a flexible electrode that can be easily adapted to mass production, thanks to its ability to produce environmentally friendly, high-capacity, and fast Ni-B electroless coating layer applied on EG papers.

In order to fulfill the above-mentioned aims, the inventive flexible electrode comprises the following; nickel chloride, sodium borohydride, ethylenediamine, potassium hydroxide, thallium acetate, and expanded graphite, the inventive production method comprises the following steps; obtaining substrate from EG powders, applying Ni-B coating on EG substrate with electroless coating method and washing and drying of the obtained coated substrates.

The structural and characteristic features of the present invention will be understood clearly by the following detailed description and therefore the evaluation shall be made by taking the detailed description into consideration.

Detailed Description of the Invention

In this detailed description, the inventive flexible electrode and the production method thereof are described only for clarifying the subject matter in a manner such that no limiting effect is created. The inventive flexible electrode mainly contains expanded graphite, nickel chloride, sodium borohydride, ethylenediamine, potassium hydroxide and thallium acetate as carbon derivatives. The preferred, and usable amounts by weight of the components constituting the subject of the invention are presented in Table 1 as percentages.

Table 1. The percentages of the components of the invention by weight

The production method developed for obtaining the inventive flexible electrode mainly comprises the following steps; obtaining paper (backing) from EG powders, applying Ni-B coating on EG paper with electroless coating method, and washing and drying of the resulting coated electrodes. Herein, first of all, EG particles are cold-pressed in a pressure range of 5-20 MPa, preferably in a steel mold, and EG paper is obtained. Afterward, obtained graphite papers are coated by heating and stirring in an electroless Ni-B coating solution containing nickel chloride, sodium borohydride, ethylenediamine, sodium hydroxide, thallium acetate in a preferred embodiment of the invention. This solution contains nickel chloride in the range of 5-30 g/lt, sodium borohydride in the range of 0.5-2 g/lt, ethylenediamine in the range of 15-90 g/lt, sodium hydroxide in the range of 10-50 g/lt, thallium acetate in the range of 5-20 mg/lt. In this step, the pH level is between 10 - 14, the temperature is between 90-96 G, the mixing speed is between 250-400 rpm and the processing time is between 5-30 minutes. Herein, glass beaker and magnetic stirrerheater are preferably used as equipment. The EG substrates with the coating obtained after this process are washed several times in ethyl alcohol so as to eliminate foreign chemical waste materials. Finally, the coated EG substrates are dried, preferably in an oven, at 70-90G for 5 hours. Thus, the inventive E G -based flexible electrode is obtained.

Coatings containing metallic elements applied on graphite paper in the state of the art, palladium chloride, which is usually poisonous and quite expensive, is used in the activation of graphite surfaces. However, Ni-P coatings are obtained without performing a surfactant process in the method of the invention. Therefore, a positive approach is considered in terms of both environmental and human health. The current source is not required in electroless coating processes; coating can only be performed by using the coating element source, reducing agents and complexing agents. Simple glass beakers and stirrers are sufficient for the processes. These are all very important for the simplicity, and speed of operation. Besides, large investment-related costs for devices and similar equipment are not required herein.

Ultra-thin EG papers with a high electrical and thermal conductivity, as well as very good flexibility, are produced by pressing EG particles within the scope of the invention. Ni-B coatings are applied on these papers that can be applied easily, easily adapts to industrial-scale production without the need for production devices that require investment costs and are harmless to nature, environmentally friendly with electroless coating, which is a coating method that does not require high labor and is easily adaptable to mass production with its high capacity and fast production. It is expected that the surface activities of the materials to be used as substrates will be high and their electrical conductivity will be high during the electroless coating processes. For this reason, coating of graphite-based materials with metal-based coatings can be performed by activating the surfaces with solutions containing usually palladium chloride. However, palladium chloride solution, which is very expensive and has a negative impact on the environment and human health, is not used for the metallization/activation of graphite substrate surfaces in the present invention. Alternatively, copper or silver wires with high electrical conductivity are dipped into the solution during the coating of graphite substrates, thus creating a conductivity bridge that triggers the coating. On the other hand, it is very important to adjust the coating parameters specified in the previous section in the formation of electroless Ni-B coatings. In particular, the temperature and pH balance should be controlled with high precision devices. Lastly, the trapping of the H ₂ gas that will come out of the chemical solution in the beaker in the coating solution during electroless coating is the triggering aspect for the coating process. Therefore, when the desired temperature is reached, the mouth of the beaker should be closed and kept closed until the coating process begins.

The subject of the invention also includes functional materials developed by using the papers obtained by pressing EG particles in elements such as supercapacitors or batteries by obtaining functional materials developed by coating electroless Ni-B.