Technical field

[0001 ] The present invention relates to synthetic stones as electrical energy storage. It invention does also disclose a method for manufacturing and using such synthetic stones as electrical energy storage. Thus, the present invention relates to a method capable of manufacturing synthetic stones and to use them as capacitors and batteries so that a new combination of synthetic stones comprising geopolymer/cement composite i.e. geopolymer cementitious composite as an electrolyte in the form of mortar matrix can be used as an electrolyte matrix and two steels as electrodes in said method. The method is both practical and cost-effective.

Background technique

[0002] In the future, structural materials will take on additional functions such as collection and storing power from solar and wind renewable energy sources. This function will not only improve the energy efficiency of structures but also enable better management of excess energy by feeding it to the grid to reduce energy peak demands or using it to power auxiliary systems such as lighting posts, traffic lights, advertising boards, electric vehicle charging stations and structural health monitoring sensors. The development of a novel battery is necessary in order to reduce the cost of fuel and environmental pollution.

[0003] Capacitors offer high power density but limited energy density. Concrete, after water, is the world's most used material. Researchers have been exploring the idea of using concrete to store electricity essentially making buildings that act as giant batteries. Cement is a dielectric material that contains water. In cement, water is present both inside and outside the silicate hydrate crystals. Electrolytes are ionic dielectric materials that conduct electricity through the movement of ions. In other words, an electrolyte is an electronic insulator, but is an ionic conductor. A battery consists of an anode, that is an electrode which is an electronic conductor and which undergoes chemical oxidation during the discharge of the battery, and a cathode, that is an electrode which is an electronic conductor and which undergoes chemical reduction during the discharge of the battery. These two electrodes are separated by an electrolyte. During discharge, a voltage appears between the anode and the cathode.

[0004] In general, the idea is gaining ground as many places come to increasingly rely on renewable energy from the wind and sun. Rechargeable batteries are then necessary when winds die down or darkness falls, but so far, they are often made of toxic substances that are far from environmentally friendly. For this purpose, it is recommended to use environmentally friendly materials instead.

[0005] Experimental concrete batteries have managed to hold only a small fraction of what a traditional battery does. To this end, efforts to increase the capacity of batteries and supercapacitors are the subject of discussion by many researchers. Research into electrical energy storage in civil engineering structures remains scarce and only a few concepts of cement-based structural electrical energy storage systems have been proposed to date. These cement-based energy storage systems use the pore solution in the cement as electrolyte and cement with additives such as graphene, black carbon, zinc and magnesium dioxide as electrodes. The cement-based battery concept can be extended from cement to concrete by the addition of aggregates. Concrete refers to cement that is filled with aggregates. Although the aggregates do not take part in the electrochemical reactions, they are conventionally used in cement-based structures for the purpose of mechanical reinforcement, drying shrinkage reduction and cost decrease. The presence of aggregate(s) in the cement-based electrolyte is expected to cause the thickness of the electrolyte layer to increase. The thickness increase is not desirable, since it will result in a higher resistance in the electrolyte layer in the direction perpendicular to the layer and this resistance contributes to the overall battery resistance. [0006] Nearly 40% of the overall energy consumption of a society is consumed by residential and commercial building for heating and /or cooling and zero-energy buildings attract more and more attention of researchers. In the future, advanced structural materials used on a large scale are expected to provide new intelligent functions, such as building materials for energy storage and electricity storage to reduce pollution by chemical batteries. The use of an inexpensive and abundant material, such as cement and geopolymer, for batteries and supercapacitors enables the development of large storages. Geopolymers are a new cement-free binding material that have been extensively studied to replace Portland cement. Geopolymers are prepared by the reaction of silica- and alumina-rich materials with alkali solutions. The preferred source materials are fly ash, slag and metakaolin, and the most commonly used alkali activators are sodium hydroxide and sodium silicate. These solutions react with active silica (SiO2) and alumina (AI2O3) and form a Si-O-AI network. Cement-based batteries and supercapacitors that utilize a cement-based electrolyte have been disclosed by Burstein et al. In this kind of supercapacitors, two electrodes are immersed into the electrolyte, and two electrodes are separated by a ion permeable membrane which is an electronic insulation to prevent electrical contact.

[0007] U.S. Patent Application 2021/01 19249 A1 published on Apr 22, 2021 describes a source voltage e.g. operating as a secondary battery, i.e. functionalized for electricity or energy storage function, comprising an electrolyte comprising e.g. a cementitious binder composition with a mixture in which the main components comprising aluminium and silicon oxides is formed using alkaline activators, e.g. sodium hydroxide (NaOH), potassium hydroxide (KOH), sodium sulphate (Na2SO4), sodium carbonate (Na2CO3), potassium sulphate (K2SO4), potassium carbonate(K2C03); further comprising fly ash, sand, gravel and additives. The two electrode made of aluminum, chalk carbon and steel.

[0008] Pat. Pub. CN 1 13 436 899 A discloses the geopolymer-based supercapacitor including a geopolymer matrix, a metal electrode and a capacitor wire. The conductive slurry comprises potassium silicate aqueous solution, ferrosilicon powder, chlorinated fly ash, Lithium and sodium fluoride. Modification solution, which is composed of a NaOH solution and a NaHCOs solution. [0009] Pat. Pub. CN 1 13 666 654 A discloses a conductive paste for forming a supercapacitor based on building materials, the paste has modified fly ash, modified alkali excitant and ion reinforcing agent. The modified solution composed of NaOH solution and NaHCOa solution can destroy part of the glassy structure and protective film on the surface of fly ash, so that the structure of modified fly ash becomes looser and more porous than that of ordinary fly ash. Lithium chloride, sodium fluoride, ferrosilicon powder and potassium silicate aqueous incorporates into the geopolymer, and the released lithium ions and fluoride ions, due to their small size, can pass through the silico-aluminum oxide (-Si-) formed in the hardened geopolymer. (O-AI-O-) tetrahedron and directional movement, thereby enhancing the conductivity of the geopolymer. Pat. Pub. CN 1 13 436 907 A describes a geopolymer-based super capacitor comprising a matrix prepared from a conductive slurry; the conductive slurry comprises modified fly ash, modified alkali activator and ion reinforcing agent. The geopolymer matrix is prepared from conductive slurry, the conductive slurry comprises modified fly ash, a modified alkali activator and an ion enhancer, the modified fly ash is prepared from common fly ash, NaOH and NaHCOa, the modified alkali activator is prepared from ferrosilicon powder and a potassium silicate aqueous solution, and the ion enhancer is prepared from lithium chloride and sodium fluoride; and the geopolymer matrix contains a preset number of free ions and can directionally move to generate current. The positive electrode metal and the negative electrode metal are both copper sheets or copper alloy sheets.

[0010] Conducting fillers such as porous and activated carbon (AC), graphene, carbon nanotubes (CNT), carbon fiber and other carbon-based materials are generally used for commercial supercapacitor fabrication to improve the electrical conductivity. However, low volumetric performance, including low energy density (<20 mWh/cm ³ ), low volumetric capacitance (<200 F/cm ³ ) and lower operating voltage(<2.7 V) are major challenges in current supercapacitor research. Therefore, advanced electrode materials with higher capacity, higher voltage and energy densities are an urgent and desirable need for future supercapacitors. Relying on their unique structure, large surface area, high electrical and thermal conductivity, fast ion diffusion, thickness and composition controllability. Incredible associated structures with a layered morphology, fast electron transport and rapid ion diffusion capability, intrinsic high electronic conductivity (up to «24000 S/cm), hydrophilicity, favourable pseudocapacitive performance and enriched surface functionalities of MXene play a significant role in high electrochemical energy storage performance over other 2D materials.

[001 1 ] The effect of MXene on the properties of cement has shown that the early hydration of cement inhibited by MXene. Meanwhile, the total hydration heat of cement hydration is increased with the addition of MXene. It can be concluded that using a small percentage of MXese in conductive mortar can be effective to increase the compressive strength of mortar. Also the addition of MXene can decrease the electrical resistivity. This conductive additive are connected to each other in the cement-based material to form a good conductor path and conduct electricity.

[0012] High conductivity of the electrode material is an important component of supercapacitors. In recent years, 2D electrode materials have been extensively studied due to their high specific surface area, excellent electronic and mechanical properties. Particularly, MXenes, a new large family of 2D materials with metallic conductivity and hydrophilic surfaces.

[0013] The development of MXene based electrodes has achieved remarkable progress in terms of electric performance and it is used in supercapacitors that demonstrated by utilizing such electrodes combined with PVA-H2SO4 polymer as electrolyte.

[0014] Self-restacking of MXene nanosheets gives rise to the increase of “dead” area, results in a fatal loss in available surface area, prevents electrolyte penetration into layers, and limits the electrochemical performance of electrode materials and practical applications. Introducing interlayer spacers between the sheets is an effective strategy to prevent the restacking, simultaneously, increase specific surface area. The electrochemical performance can also be improved via an increase in the electrode/electrolyte interface areas and a decrease in the ion diffusion length within active materials. [0015] Using metal nanoparticles (NPs) as spacers, the MXene-metal nanocomposites showed promising properties as electrode materials for electrochemical capacitors. In particular, silver (Ag) nanoparticles have the highest conductivity among the noble metals, and exhibit large surface area-to-volume ratio at the nanoscale level and hence are excellent nanomaterials for energy storage devices where a large surface area is required. Current research works showed that combining other materials with MXenes to produce MXenes-based composite electrode materials is one of the most effective strategies for energy storage applications.

[0016] There is need to develop a geopolymer based supercapacitor in form of synthetic stone.The present invention provide a supercapacitor stone comprising new conductive filler in mortar and active material on metal electrodes.There is currently no supercapacitor made of an synthetic stone with such an electrode and the field of civil engineering needs to develop the electricity storage.

Object of the invention:

[0017] The purpose of this invention is it to eventually change the structure of similar capacitors and batteries and approaching the stone structure for use in buildings. Another objective of this invention is it to increase efficiencies and lifespan of batteries. In view of the information give above, the technical problem to be solved by the present invention is to provide a synthetic stone supercapacitor which no longer needs chemical supercapacitors and which can be used for building facades of building, and another object of the invention is it to provide a manufacturing process for manufacturing such synthetic stone supercapacitors which is simple, low cost and easy to prepare and execute.

Technical Solution of the invention

[0018] The technical problem is solved by a synthetic stone which comprises a geopolymer-cement matrix and two steel electrodes immersed in the electrolyte matrix of the geopolymer-cement matrix, hereby providing an electricity storage function. This geopolymer-based batteries are superior to cement-based batteries in performance.

[0019] The manufacturing of this synthetic stones comprises these steps: A) Preparing of conductive mortar as a paste,

B) Preparing of MXene & Ag hybrid coated Steel electrodes,

C) Placing two steel electrodes in the mold,

D) Pouring the conductive paste into the mold,

E) Curring the conductive paste for 48 hours for obtaining the solid synthetic stone supercapacitor.

Detailed description

[0020] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawing.

Shown is:

Figure 1 : The typical process of alkaline batteries;

Figure 2: A schematic diagram of the structure of synthetic stones of the present invention.

Technical Theory of Cementitious Composites Battery

[0021 ] Conventional batteries are composed of an anode, cathode, and electrolyte as shown in Figure 1 . In any battery, ions and electrons move through the electrolyte and the circuit from the anode to the cathode respectively. Typical alkaline batteries use zinc as the anode, manganese dioxide as the cathode and a salt solution as the electrolyte. The electrolyte’s ionic conductivity should be high with a low electrical resistance thereby allowing it to carry high current. Liquid electrolytes traditionally perform better due to the high mobility of ions.

[0022] The cementitious composites battery is applied to these general concepts of batteries and is shown schematically in Figure 2. Cement-based batteries that utilize a cement-based electrolyte have been disclosed by Burstein and Speckert and Sakai et al. The use of an inexpensive and abundant material, such as cement, for batteries enables the development of large batteries. Furthermore, by incorporating the cementbased battery as a part of a structure, the battery does not consume extra and that potentially provides large amounts of energy. In other words, the battery becomes integrated with a structure.

Geopolymer battery and supercapacitor

[0023] Currently, there is a growing interest in combined monitoring and maintenance technologies, in particular through the application of ‘smart cements’. These cements can act as repairs for concrete structures and simultaneously undergo measureable changes in electronic impedance in response to environmental conditions. Geopolymers are synthesized by mixing solid waste (rich alumino-silicate reactive materials such as ground granulated blast furnace slag (GGBFS), fly-ashes) with an alkaline activator (strong alkaline solution such as NaOH or KOH), and then curing at room or high temperature. Geopolymers possess the following advantages over cement: (a) low fuel consumption and CO2 emissions during manufacture; (b) better mechanical properties; (c) rapid hardening; and (d) greater resistance to fire and acid attack. Geopolymers have shown promise in energy storage field as they offer high durability, a versatile range of physical properties, and endurance to extreme environmental conditions. Over the years, geopolymers have been exploited as protective coating materials for marine concrete and transportation infrastructures. One of the challenges of applying geopolymers in the field, however, is that they are typically cured at elevated temperatures above 40 °C. In this invention, it used geopolymeric cementitious composites are formed by alkali activation of alumino silicate materials. The fly ash mortar was used as geopolymer source.

[0024] According to the present invention, the geopolymer-cement matrix is made of conductive mortar, the conductive mortar comprising fly ash, cement, gravel and sand, alkali activator (KOH and SiO2), and some additives of synthetic stone compounds are being added such as one or more of a selection of poly carboxylate ether, retarder, lignosulfonate, ethylene-vinyl acetate, hydroxypropyl methyl cellulose and pigment. Carbon black and MXene can be added to the mortar in order to improve and increase the output, particularly as to current and longevity. [0025] This mortar and this matrix utilize the pore solution in cement and geopolymer, and the pore aqueous solution contains a preset number of freely movable ions which can store energy.

[0026] In this invention, it used MXene as electrode coating and an electrolyte addetive. MXenes are a novel two-dimensional ceramic material, composed of transition metal carbides or carbonitrides with the formula M _n +iX _n T _x . MXene is composed of n + 1 (n = 1-3) layers of early transition metals (M) interwoven with n layers of carbon or nitrogen (X), with the general formula is M _n +iX _n T _x , where M refers to a transition metal such as Sc, Ti, Zr, V, Nb, Cr, or Mo; X refers to C or N elements and Tx indicates the surface termination group (-OH, =0, and/or -F). These fascinating surface groups can inherently provide a large number of active sites with great potential for surface modification and efficient loading of active materials. MXenes possess good electrical and thermal conductivity, high strength, light weight, good thermal stability, and easy processability. MXenes can be one of the compounds Ti3C2T _x , Ti2CT _x , TiaCNTx, TiNbCTx, Ta4CaT _x , Mo2CT _x , Mo2TiC2T _x , Mo2Ti2C3T _x , Nb4C3T _x , Nb2CT _x , (Vo.5 Cro.5)3C2T _x , V ₂ CT _X , Zr3C2T _x , Hf3C2T _x , etc.

[0027] The preparation for manufacturing such synthetic stones does involve these following steps,

A) Preparing of conductive mortar,

B) Preparing of MXene & Ag hybrid coated Steel electrodes,

C) Placing two steel electrodes in the mold,

D) Pouring the conductive paste into the mold,

E) Curring for 48 hours for obtaining the solid synthetic stone supercapacitor.

[0028] The preparing of the conductive mortar can be done, by the below given detailed example, by :

A1 ) Preparing alkaline activator consisting of potassium silicate (faSiOs) solution with SiO2 = 7.98 grams, KOH = 9.21 grams and H2O = 15 grams,

A2) Preparing an additive solution containing poly carboxylate ether = 0.25 gram, retarder = 0.01 gram, lignosulfonate= 0.2 gram, ethylene-vinyl acetate = 0.2 gram, hydroxypropyl methyl cellulose = 0.1 gram and pigment = 0.5 gram. All additives are being stirred in 5 grams de-ionized water for 30 minutes,

A3) 1 .44 grams carbon black is sonicated with probe in water,

A4) 0.08 gram MXene was ultrasonically dispersed in 5 grams water for 5 minutes.

A5) The obtained solution is added to 20 grams of fly ash, 25 grams of cement and 5 grams of gravel and sand, then stirred evenly and then left standing quietly to obtain a mixed solution.

[0029] The preparation method of MXene coated steel electrode can be done, by the below given detailed example, by :

B1 ) The Mxene (d-Ti3C2T _x ) suspension was prepared by adding 0.8 gram of Li F to 10 mL of 9 M HCI with stirring for about 5 min.

B2) 0.5 g of Ti3AIC2 was slowly added to the mixture about 5 min, and the reaction was conducted under stirring by for 24 h at 35°C.

B3) The MXene suspension was performed by sonication using a tip sonicator for 1 h. B4) The MXene suspension was followed by centrifuge processing at 3500 rpm for 30 min. The supernatant was collected and used as MXene suspension.

B5) Ag NPs (0.03 mg/mL) were added into the MXene suspension with vigorous stirring, and the solution was stirred for another 30 min.

B5) Steel was cut to dimensions of 70 mm x 60 mm x 20 mm. The obtained suspension was sprayed 7 times onto an as-cut mesh along with a polyethylene terephthalate) film that was pre-baked on a hot plate at 50°C.

[0030] Advantageously, the steel electrodes 2, 3 are being placed in a rectangular mold 1 as shown in figure 2, and the the distance between the positive electrode 2 and the negative electrode 3 is kept in the range of 8 mm.

[0031 ] The implementation of the present invention has the following beneficial effects: The matrix in the synthetic stone supercapacitor of the present invention contains a number of free ions. The pores in the mortar of this artificial stone carry ions to the electrodes and are a factor for energy storage. So this matrix can be a solid electrolyte and it can prevent electrical contact. These artificial stones can be connected to an external power supply to complete a charging, and later connected to an electrical appliance to complete a discharge. The can used for building facades, thereby realizing an electricity storage function of the building material and saving a lot of energy.

[0032] According to this invention, geopolymeric cementitious composites are being used and formed by alkali activation of alumino silicate materials such as fly ash. In the chemical method of this invention, alkaline activators consist of a mixture of silicate (SiC ) and potassium hydroxide (KOH). Depending on the Si/AI molar ratio, after reaction under controlled temperature, the resulting geopolymeric frameworks can be in the form of potassium-poly(sialate-siloxo) (KPSS) to create ionic conductivity in the mortar.

[0033] According to this invention, the synthetic stone matrix contains the new material MXene, which has been able to give the stone good electrical properties and compressive strength.

[0034] According to this invention, steel electrodes in this supercapacitor contain MXene layer (Ti3C2T _x ) that had shown great potential in electrical energy storage.

[0035] The synthetic stone supercapacitors offer a practical and cost-effective method for storing energy. They provide a green and environment-friendly power storage method, and they can be used for building facades and make it possible for the buildings to be more versatile. In addition, this kind of supercapacitors allow a building structure to deliver power on demand, so this demand does not have to rely totally on power at all times that is delivered from a distance. In intermediate storage is provided which can be charged in times of overproduction of electrical energy and from which energy can be drawn when there is a shortage.

[0036] The synthetic stone supercapacitor of the invention as presented above does offer, at a voltage of 1 volt, a capacity of 35 mF. With the connection of 3 such artificial stone supercapacitors in series, the voltage can be increased to 2.3 volts. In summary, this rechargeable Nano-polymer artificial stone-based supercapacitor reaches an energy density of approximately 13-14 Wh/kg which is the equivalent of 0.014 KWh/kg), and this is the highest value ever achieved. The largest electric car batteries currently available store about 100 kilowatt hours. With a consumption of 15 to 25 kilowatt hours per 100 kilometres, electric vehicles such as the Tesla Model S/X, the Jaguar l-Pace or the Audi e-tron can travel between 400 and 600 kilometres on one battery charge. Consequently, it takes 7’142 kg of the rechargeable Nano-polymer artificial stone-based supercapacitor in order to store this amount of electrical energy. Generally, weight of brick wall of one meter hight is ranging between 190 kg to 440 kg per square meter, 190 kg for a tickness of 100 mm and 440 kg for a tickness of 230 mm. Take an outer wall of 230 mm thickness with a hight of 2.5 m. Such wall weights 440 kg x 2.5 m per meter length, that is 1 ‘100 kg/m. In other words. 7‘142 kg : 1 ‘100 kg/m = 6.49 m. Therefore, a 6.5 meter long outer wall of 2.5 m height and 230 mm thickness will store the charge of 100 kWh!

[0037] Again referring to figure 2, a synthetic stone supercapacitor provided by the present invention includes matrix mortar 1 , a positive electrode 2 and a negative electrode 3. The matrix mortar includes geopolymer 1 1 , cement 12, alkali activator 13, stone additive 14, Carbon black 15 and Mxene 16. The matrix mortar 1 contains a preset number of free ions, which can move directionally to generate electric current. The positive electrode 2 and negative electrode 3 are coated with MXene and placed in concrete mortar in a distance of each other of 8 mm.

[0038] The preparation method of complete synthetic stone as capacitor includes these steps :

A1 ) Preparing an alkaline activator consisting of potassium silicate (K2SiO3) solution with SiO2 = 7.98 grams, KOH =9.21 grams and H2 = 15 grams,

A2) Preparing an additive solution containing poly carboxylate ether = 0.25 gram, retarde r= 0.01 gram, lignosulfonate = 0.2 gram, ethylene-vinyl acetate = 0.2 gram, hydroxypropyl methyl cellulose = 0.1 gram and pigment = 0.5 gram, and stirring all additive in 5 grams of deionized water for 30 minutes,

A3) Sonicating 1 .44 gram carbon black in the with the probe in 5 grams water, A4) 0.08 gram MXene was ultrasonically dispersed in 5 grams water for 5 minutes. A5) Adding then entire solution to fly ash and cement and gravel and sand, that is 20 grams fly ash, 25 grams of cement and 5 grams of gravel and sand, and stirring evenly, [0039] The preparation method of MXene coated steel electrode can be done, by the below given detailed example, by :

B1 ) The Mxene (d-Ti3C2T _x ) suspension was prepared by adding 0.8 gram of Li F to 10 mL of 9 M HCI with stirring for about 5 min.

B2) 0.5 gram of Ti3AIC2 was slowly added to the mixture about 5 min, and the reaction was conducted under stirring by for 24 h at 35°C.

B3) The MXene suspension was performed by sonication using a tip sonicator for 1 h. B4) The MXene suspension was followed by centrifuge processing at 3500 rpm for 30 min. The supernatant was collected and used as MXene suspension.

B5) Ag NPs (0.03 mg/mL) were added into the MXene suspension with vigorous stirring, and the solution was stirred for another 30 min.

B6) Steel was cut to dimensions of 70mm x 60mm x 20 mm. The obtained suspension was sprayed 7 times onto an as-cut mesh along with a polyethylene terephthalate) film that was pre-baked on a hot plate at 50°C.

C) Placing a positive steel electrodes 2 and a negative steel electrode 3 into the rectangular mold and fixing them by a distance of 8 mm from each other,

D) Poring the prepared mortar into the mold,

E) Leaving the solution stand still for obtaining a mixed solid solution.

[0040] Specifically, in step E, the mixed solution is dried for 24 hours at ambient temperatures then placed in an oven at 50°C for 24 hours. Specifically, the ordinary fly ash is a first-grade fly ash and the cement is a Portland cement type 2. The alkali activator is made of potassium hydroxide powder and silicon dioxide powder. Preferably, based on parts by mass, the alkali activator is made from 30.7 parts of potassium hydroxide powder and 26.6 parts of silicon dioxide powder. Specifically, additives are being stirred in water for 30 minutes. Preferably, carbon black is sonicated for 5 minutes with probe. Specifically, the MXene is d-Ti3C2T _x . Preferably, MXene was sonicated for 5 minutes with probe. Specifically, the steel electrode was coated with Mxene and Ag hybrid. Specifically, the steel electrode includes a positive steel electrode 2 and a negative steel electrode 3 that are being fixed in the mortar matrix 1 . The negative electrode 3 and positive electrode 2 are being fixed in a distance of 8mm to each other. Example 1 :

[0041 ] Hereinafter, this artificial stone capacitor is described in more detail and specifically with reference to the examples which however are not intended to limit the present invention. This stone was prepared by mixing fly ash and cement into the alkaline activator with fly ash-cement and gravel and sand, that is 20 grams fly ash, 25 grams cement and 5 gram gravel and sand. The alkaline activator does consist of potassium silicate (faSiOa) solution with SiO2 = 7.98 grams, KOH = 9.21 grams and H2O = 15 grams. In the stone combination some additives were added such as poly carboxylate ether = 0.25 gram, retarder = 0.01 gram, lignosulfonate = 0.2 gram, ethylene-vinyl acetate = 0.2 gram, hydroxypropyl methyl cellulose = 0.1 gram and pigment = 0.5 gram, carbon black = 1.44 grams and Mxene= 0.08 gram, Ag nanoparticle solution = 0.03 mg/ml. All additives were stirred in 5 grams of water for 30 minutes and carbon black was sonicated for 5 minutes with probe. MXene was ultrasonically dispersed in 5 grams water for 5 minutes and added with alkaline solution to cement and fly ash. All component were mixed for 3 minutes with a mixer. After mixing, the paste was poured into plastic molds to form the capacitor in the shape of a rectangular plastic brick. Two steel mesh electrodes 2, 3 with dimensions of 70mm x 60mm x 20 mm have been used. They were first washed with soap, water and acetone, then coated with Mxene and Ag hybrid and inserted into capacitor and the sample was vibrated to ensure good contact between the electrodes and the matrix. The distance between the electrodes was 8 mm. The fabricated capacitor was cured at room temperature for 24 h. Then it was cured in oven at 50 °C for 24 h in vacuum oven.

[0042] To prepare steel electrode coated with Mxene and Ag hybrid film, 0.8 gram LiF was added to 10 mL of 9 M HCI with stirring for about 5 min. Then 0.5 gram of TiaAIC2 was added to the mixture about 5 min, and the reaction was conducted under stirring by for 24 h at 35°C. The MXene suspension was performed by sonication using a tip sonicator for 1 h. Then it was followed by centrifuge processing at 3500 rpm for 30 min. The supernatant was collected and used as MXene suspension. Ag NPs (0.03 mg/mL) were added into the MXene suspension with vigorous stirring, and the solution was stirred for another 30 min. Steel was cut to dimensions of 70 mm x 60 mm x 20 mm. The obtained suspansion was sprayed 7 times onto an as-cut mesh along with a polyethylene terephthalate) film that was pre-baked on a hot plate at 50°C.

[0043] The supercapacitor of this example 1 offers a rated voltage of 1 .1 Volt and the capacity for it was also calculated and this was 35 mF. A series of circuit operations were carried out in order to increase voltage. Three capacitors were connected in series. It can be able to charge 2.3 V in 24 hours. Also the total capacity of this capacitor was calculated to be 89 mF.

[0044] What is disclosed above is only a preferred embodiment of the present invention, which of course cannot be used to limit the scope of rights of the present invention. Therefore, equivalent changes made according to the claims of the present invention still fall within the scope of the present invention.

[0045] These synthetic stones with their capability to store electrical energy offer unique opportunities, e.g. for erecting buildings and thereby using the building for providing the capacity for intermediate storing of electrical energy and releasing electrical energy on demand. E.g. LEDs for can be powered for enlighting streets and buildings. Or 4G connections and higher can be powered in remote areas. Such synthetic stones can also be used for paring with solar panels to power sensors built into concrete structures such as long bridges or highways.