Alkali-activated cementitious material for supercapacitors and method of making the same

Abstract

The application belongs to the technical field of concrete, and provides an alkali-activated cementitious material for supercapacitors and a preparation method thereof, the alkali-activated cementitious material is composed of raw materials in the following proportions by weight: fly ash 4-5 parts, slag 1-1.2 parts, alkali-activator 2.5-3 parts; the alkali-activated cementitious material forms zeolite inside after autoclave curing. The alkali-activated cementitious material prepared by the application uses industrial solid waste as raw material, has the advantages of environmental protection and low cost, through optimizing the formula and process of the alkali-activated material, the cycle stability and electrochemical performance of the supercapacitor are significantly improved, the energy storage function of large-volume building materials is realized, and the technical gap of using alkali-activated cementitious material to replace cement-based material to prepare energy storage devices is filled.

Description

Technical Field

[0001] This invention belongs to the field of concrete technology and relates to an alkali-activated cementitious material for supercapacitors and its preparation method. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] As the global energy structure shifts towards renewable energy, the use of energy sources such as solar and wind power is becoming increasingly widespread. The instability of these energy sources necessitates efficient energy storage technologies to balance supply and demand. Concrete supercapacitors, as a novel energy storage technology, can transform large-scale buildings or infrastructure into direct energy storage devices, thereby achieving efficient energy storage and utilization.

[0004] However, the cementitious phase of ordinary concrete is mainly crystalline hydrated calcium silicate, and its electronic conduction mainly relies on the physical contact between aggregates and hydration products, resulting in discontinuous conductive pathways. Alkali-activated cementitious materials, after alkali activation, form an amorphous three-dimensional network of aluminosilicates. In this structure, the disordered connection of silicon-oxygen tetrahedra and aluminum-oxygen tetrahedra generates a large number of oxygen vacancies and mobile alkali metal cations. These cations can freely migrate within the channels, forming "ionic conductive pathways." Furthermore, the amorphous structure reduces the electronic conduction barrier imposed by the crystalline phase, ultimately lowering the volume resistivity of the alkali-activated cementitious material. However, the ion transport efficiency and storage performance of supercapacitors prepared from existing alkali-activated cementitious materials still need improvement.

[0005] Some studies have disclosed a method for preparing fly ash zeolite ceramsite under autoclaving and using fly ash zeolite ceramsite for copper ion adsorption, but the problem of preparing alkali-activated cementitious materials for supercapacitors has not been addressed.

[0006] Therefore, there is an urgent need to develop alkali-activated cementitious materials for supercapacitors that combine superior mechanical strength and electrochemical properties. Summary of the Invention

[0007] To address the aforementioned issues, this invention provides an alkali-activated gelling material for supercapacitors and its preparation method. This invention employs autoclaving to induce the crystallization of amorphous silica-alumina gel in a slag-fly ash-based alkali-activated gel material, generating a zeolite phase. The resulting zeolite has a regular porous structure, which significantly shortens the sodium ion diffusion distance and increases the ion exchange rate constant by 1-2 orders of magnitude. This allows the adsorption-desorption process to be completed in milliseconds, effectively matching the rapid charge-discharge characteristics of supercapacitors and significantly improving the adsorption capacity for sodium ions, thereby optimizing the ion storage capacity and transport efficiency of supercapacitors.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides an alkali-activated cementitious material for supercapacitors.

[0010] The alkali-activated cementitious material is composed of the following raw materials in parts by weight: 4-5 parts fly ash, 1-1.2 parts slag, and 2.5-3 parts alkali activator;

[0011] The alkali-activated cementitious material forms zeolite inside after autoclaving.

[0012] A second aspect of the present invention provides a method for preparing an alkali-activated cementitious material for supercapacitors, comprising:

[0013] Preparation of alkaline activators;

[0014] Mix fly ash and slag evenly to obtain dry material;

[0015] The dry material is mixed evenly with the alkali activator to obtain an alkali-activated gelling material;

[0016] The alkali-activated gelling material is poured into a mold, and then subjected to autoclaving followed by standard curing to obtain the final product.

[0017] Beneficial effects of the present invention

[0018] (1) The fly ash and slag used in this invention are all derived from solid waste in industrial production. Reusing the above-mentioned waste as new building materials in industrial production can not only reduce energy consumption and environmental pollution, but also reduce the material cost of supercapacitors.

[0019] (2) This invention uses fly ash and sodium hydroxide solution as raw materials to make alkali-activated concrete, which makes its performance more stable in high temperature and humid environment. At the same time, it uses alkaline substances to activate the activity of specific materials, which increases the efficiency of electrical energy storage and conversion, thereby achieving the purpose of improving charging and discharging efficiency and cycle stability.

[0020] (3) In this invention, the amorphous silica-alumina gel in the slag-fly ash-based alkali-activated gel material is crystallized by autoclaving to generate a zeolite phase. The zeolite has a regular pore structure, which can shorten the diffusion distance of sodium ions and increase the ion exchange rate constant by 1-2 orders of magnitude. This allows the adsorption-desorption process to be completed in milliseconds, effectively matching the fast charge and discharge characteristics of supercapacitors and significantly improving the adsorption capacity of sodium ions, thereby optimizing the ion storage capacity and transmission efficiency of supercapacitors.

[0021] (4) The preparation method of the present invention is simple, practical and easy to promote. Attached Figure Description

[0022] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. Exemplary embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0023] Figure 1 This is a photograph of the actual supercapacitor made of alkali-activated cementitious material of the present invention. Detailed Implementation

[0024] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of skill in the art. The reagents and raw materials used in this invention are readily available through conventional means, and unless otherwise specified, they are used in accordance with conventional methods in the art or product instructions. Similarly, unless otherwise specified, the test methods of this invention are performed in accordance with conventional methods in the art or industry-standard methods or practices. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to the methods of this invention. The preferred embodiments and materials described herein are for illustrative purposes only.

[0026] This invention provides an alkali-activated cementitious material for supercapacitors, which is composed of the following raw materials in parts by weight: 4-5 parts fly ash, 1-1.2 parts slag, and 2.5-3 parts alkali activator;

[0027] The alkali-activated cementitious material forms zeolite inside after autoclaving.

[0028] The type of alkali-activated gelling material affects the structure of the zeolite phase and thus its electrochemical performance. Therefore, this invention studies the composition of alkali-activated gelling materials and finds that, compared with other alkali-activated gelling materials, the zeolite phase induced by slag-fly ash-based alkali-activated gelling materials after autoclaving has a regular pore structure, which can significantly shorten the sodium ion diffusion distance and increase the ion exchange rate constant by 1-2 orders of magnitude. It can be used to prepare solid electrolytes for supercapacitors.

[0029] When preparing alkali-activated gelling materials, attention must be paid to the liquid-to-solid ratio. This invention studies the liquid-to-solid ratio, and preferably, the liquid-to-solid ratio of the alkali-activated gelling material is 0.10-0.20 (wherein, the solid is dry material, water glass, and sodium hydroxide, and the liquid is the solvent of the alkali activator). Within this range, the compressive strength and electrochemical performance of the specimen after solidification are most ideal.

[0030] In the preparation of alkali-activated cementitious materials for supercapacitors, the ratio of the alkali activator is crucial. The alkali activator of this invention is composed of water, water glass, and sodium hydroxide (i.e., prepared by mixing water and solid sodium hydroxide to form a sodium hydroxide solution, then adding water glass and mixing thoroughly). Its ratio needs to be optimized according to the characteristics of the cementitious material used. Therefore, this invention studies the ratio of these two components. Preferably, the alkali activator is composed of water, water glass, and sodium hydroxide, with a molar ratio of water glass to sodium hydroxide of 1.55-1.65:1, to ensure that it can fully activate the coagulation and hardening reaction of the cementitious material, thereby guaranteeing the electrochemical performance and stability of the supercapacitor.

[0031] The function of water glass is to regulate the reaction rate between fly ash and sodium hydroxide solution, thereby controlling the setting time of the material and making it easier to conduct experiments. Therefore, this invention studies the modulus of water glass, preferably with a modulus of 0.5-0.55, to obtain a better setting rate and improve the electrochemical and mechanical properties of the supercapacitor.

[0032] The concentration of sodium hydroxide affects the conductivity of alkali-activated cementitious materials used in supercapacitors. Excessive sodium hydroxide concentration leads to an increase in the internal resistance of the alkali-activated cementitious material. Conversely, excessively low sodium hydroxide concentration results in decreased stability of the alkali-activated cementitious material, affecting the overall performance of the supercapacitor. Therefore, this invention studies the concentration of sodium hydroxide. Preferably, the concentration of sodium hydroxide in the alkali activator is 4.0 mol / L-4.5 mol / L to obtain better electrochemical performance.

[0033] Preferably, the fly ash is Class I fly ash. Class I fly ash can effectively inhibit alkali-aggregate reaction and reduce the autogenous shrinkage of alkali-activated cementitious materials, thereby improving the crack resistance and carbonation resistance of alkali-activated cementitious materials. Furthermore, these properties are crucial for the long-term stability of alkali-activated cementitious materials used in supercapacitors, especially in complex operating environments (such as humid environments), where they can better improve the durability of alkali-activated cementitious materials.

[0034] Different grades of slag powder vary in terms of activity and particle characteristics, which in turn affect the electrochemical performance, strength, and durability of alkali-activated cementitious materials used in supercapacitors. Therefore, this invention studies the grades of slag, and preferably, the slag is S105 grade slag to obtain better electrochemical performance, strength, and durability.

[0035] The conditions of autoclaving affect the structure and composition of the zeolite phase. Therefore, this invention studies the conditions of autoclaving. Preferably, the conditions are: curing at 40°C for 4-6 hours, followed by curing at 0.2MPa-0.5MPa and 120°C-150°C for 10-12 hours to obtain a regular pore structure, thereby giving the alkali-activated gel material better electrochemical and mechanical properties.

[0036] This invention provides a method for preparing an alkali-activated cementitious material for supercapacitors, comprising:

[0037] Preparation of alkaline activators;

[0038] Mix fly ash and slag evenly to obtain dry material;

[0039] The dry material is mixed evenly with the alkali activator to obtain a slurry;

[0040] The slurry is poured into a mold, first steam-pressed and then cured according to standard conditions to obtain the final product.

[0041] Preferably, the dry material and the alkali activator are mixed by stirring.

[0042] More preferably, the stirring speed is 140-160 r / min.

[0043] To obtain better electrochemical performance, this invention studied the amount of carbon black and PVDF in the negative electrode slurry. Preferably, the mass ratio of carbon black to PVDF in the negative electrode slurry is 9-12:1 to obtain better electrochemical performance.

[0044] To ensure good conductivity of the electrode in alkali-activated gelling materials, care must be taken during electrode preparation. When adding sodium ferric pyrophosphate and conductive carbon black to the electrode, the amounts of sodium ferric pyrophosphate, PVDF, and conductive carbon black are carefully controlled to ensure uniform mixing and a certain level of conductivity in the positive electrode material. This invention has investigated the optimal amounts of sodium ferric pyrophosphate, PVDF, and conductive carbon black. Preferably, the mass ratio of sodium ferric pyrophosphate, PVDF, and conductive carbon black in the positive electrode slurry is (8-10):1:1 to achieve better electrochemical performance.

[0045] The electrodes are inserted after the alkali-activated gel material is poured and compacted. Attention must be paid to the placement distance and orientation of the positive and negative electrodes. Because the hardening of the alkali-activated material affects the conductivity of the supercapacitor, its internal structure becomes denser and the ion transport path more complex. Excessive distance between the electrodes will affect conductivity. Therefore, the electrode positions must be carefully arranged. Preferably, the electrodes are placed in the center of the mold, 5mm from both the left and right long sides and 10mm from both the front and back short sides. The distance between the two electrodes should be controlled between 2.0mm and 2.5mm to maintain a good ion and electron transport channel.

[0046] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are explanations of the present invention and not limitations thereof.

[0047] Unless otherwise specified in this document, "parts" refers to parts by weight.

[0048] The sodium hydroxide used in the examples was all crystalline powder; the fly ash used had a density of 2.1 g / cm³. 3 The specific surface area is approximately 1500 m² / kg; the density of the slag used is 2.8 g / cm³. 3 -3.1g / cm 3 The specific surface area is 500m² / kg - 600m² / kg; the modulus of the water glass used is 0.5, and it is a commercially available product.

[0049] Example 1

[0050] (1) Preparation of negative electrode

[0051] Take several pieces of nickel foam of uniform size, 20mm × 50mm;

[0052] Carbon black and PVDF are mixed uniformly in a ratio of 9:1, and NMP (1% of the total mass of the powder) is added dropwise to the powder to obtain the negative electrode slurry.

[0053] The negative electrode slurry is coated onto nickel foam to obtain the negative electrode;

[0054] The prepared electrodes were dried in a drying oven at 60°C for 4 hours.

[0055] The dried electrodes are then compacted.

[0056] (2) Preparation of positive electrode

[0057] Take several pieces of nickel foam of uniform size, 20mm × 50mm;

[0058] Sodium iron pyrophosphate, PVDF, and conductive carbon black are mixed uniformly in a ratio of 8:1:1. NMP (1% of the total mass of the powder) is added dropwise to the powder to obtain a positive electrode slurry. The positive electrode slurry is then coated onto the surface of an electrode substrate (nickel foam) to obtain a positive electrode.

[0059] The prepared electrodes were dried in a drying oven at 60°C for 6 hours.

[0060] The dried electrodes are then compacted.

[0061] (3) Alkali-activated cementitious materials

[0062] Sodium hydroxide was first dissolved in pure water to prepare a 4.4 mol / L sodium hydroxide solution. Then, this solution was mixed with water glass (water glass modulus of 0.5) at a molar ratio of 1.55:1 to form an alkali activator.

[0063] Weigh out 4 parts fly ash, 1 part slag, and 2.5 parts alkali activator. Mix the fly ash and slag evenly to obtain dry powder. Mix the dry powder and alkali activator with a liquid-solid ratio of 0.10. Stir slowly (speed is 140 r / min, stirring time is 120 seconds). Scrape off the wall material with a scraper and stir quickly to obtain slurry.

[0064] The slurry was poured into a rectangular mold, compacted by vibration, and then positive and negative electrodes were inserted. The electrodes were placed in the middle of the mold, 5 mm from the two long sides and 10 mm from the two short sides, with a spacing of 2.0 mm between them. The mold was then placed in an autoclave and cured at 40°C for 4 hours, followed by curing at 0.5 MPa and 120°C for another 10 hours, for a total curing time of 14 hours. After zeolite formation inside, the mold was cured for 3 days, then demolded to obtain an alkali-activated cementitious supercapacitor.

[0065] (4) Performance test results of alkaline-excited supercapacitor test block

[0066] The alkali-excited supercapacitor test block, after 3 days of standard curing, was tested according to ASTM-638. The 3-day tensile strength was 3.8 MPa and the compressive strength was 60 MPa. Using the Blue Electric CT2001A, the initial discharge specific capacity at 0.1C rate was 96 mAh / g, and the capacity retention rate was 95% after 5000 cycles.

[0067] Example 2

[0068] The difference from Example 1 is that the composition of the alkali-activated cementitious material is: 5 parts fly ash, 1.2 parts slag, and 3 parts alkali activator, with the sodium hydroxide concentration in the alkali activator being 4.0 mol / L.

[0069] The alkali-activated supercapacitor specimens, after 3 days of standard curing, were tested according to ASTM-638. The tensile strength was 3.2 MPa and the compressive strength was 48 MPa after 3 days. Using the Blue Electric CT2001A, the initial discharge specific capacity at 0.1C rate was 83 mAh / g, and the capacity retention rate was 89% after 5000 cycles.

[0070] Example 3

[0071] The difference from Example 1 is that the composition of the alkali-activated cementitious material is 4.5 parts fly ash, 1.1 parts slag, and 2.75 parts alkali activator, and the concentration of sodium hydroxide in the alkali activator is 4.5 mol / L.

[0072] The alkali-excited supercapacitor specimens, after 3 days of standard curing, were tested according to ASTM-638 specifications. The tensile strength was 3.5 MPa and the compressive strength was 51 MPa after 3 days. Using the Blue Electric CT2001A, the initial discharge specific capacity at 0.1C rate was 86 mAh / g, and the capacity retention rate was 90% after 5000 cycles.

[0073] Comparative Example 1

[0074] The only difference from Example 1 is that ordinary silicate cement (grade 42.5) is used instead of the alkali-activated cementitious material of the present invention, while the electrode material remains the same as in Example 1.

[0075] The raw material composition of the solid electrolyte is: 100 parts of ordinary silicate cement, 35 parts of pure water, 160 parts of standard sand, and 0.2 parts of water-reducing agent (PC-303 polycarboxylate high-performance water-reducing agent).

[0076] The preparation process includes the following steps:

[0077] a. Mix ordinary silicate cement with pure water for 3 minutes to obtain a neat slurry. Add standard sand and water-reducing agent, and use a mortar mixer to slowly mix at 140 r / min for 120 seconds, and then quickly mix for 120 seconds.

[0078] b. Pour the mixed mortar into the mold, place it on the vibrating table and vibrate for 2 minutes until compacted to remove internal air bubbles;

[0079] c. Prepare electrodes according to the method of Example 1 and insert them vertically into the mortar (the insertion position is the same as in Example 1, that is: 5mm from the left and right long edges of the mold and 10mm from the front and back short edges).

[0080] d. After the test blocks are placed at standard room temperature (25℃, relative humidity 60%) for 24 hours, they are demolded and transferred to a curing chamber (temperature 20±2℃, relative humidity above 95%) for standard curing for 3 days.

[0081] The results showed that the 3-day compressive strength was 30 MPa, the tensile strength was 0.8 MPa, the initial discharge specific capacity was 55 mAh / g, and the capacity retention rate after 5000 cycles was 45%.

[0082] This indicates that the hydration products of silicate cement cannot form a zeolite phase with a regular pore structure, resulting in a significant decrease in the mechanical and electrochemical properties of supercapacitors.

[0083] Comparative Example 2

[0084] The only difference from Example 1 is that only the water glass modulus and sodium hydroxide concentration in the alkali activator are adjusted, while the proportions of the other components remain unchanged.

[0085] Among them, the water glass modulus of the alkaline activator is 0.6, and the sodium hydroxide concentration is 4.6 mol / L.

[0086] Testing revealed that due to excessive sodium hydroxide concentration and water glass modulus, the 3-day compressive strength was 44 MPa and the tensile strength was 1.7 MPa. Microcracks of 0.1 mm to 0.2 mm appeared on the surface of the test block, damaging its structural integrity. The initial discharge specific capacity at 0.1 C rate was 80 mAh / g, and the capacity retention rate after 5000 cycles was 62%. Non-conductive NaFeO2 (sodium metaferrate) was generated during the charge and discharge process.

[0087] Therefore, it can be seen that excessive sodium hydroxide concentration and water glass modulus will affect the formation of zeolite phase, thereby significantly reducing the mechanical and electrochemical performance of supercapacitors.

[0088] Comparative Example 3

[0089] The only difference from Example 1 is that Grade I fly ash is replaced with Grade II fly ash (density 1.7-2.5 g / cm³, specific surface area 1200-1400 m² / kg, carbon content 8%), while the other proportions remain unchanged.

[0090] The results showed that the supercapacitor prepared using Class II fly ash with alkali-activated cementitious material had a 3-day compressive strength of 37 MPa, a tensile strength of 2.0 MPa, an initial discharge specific capacity of 85 mAh / g at 0.1C rate, and a capacity retention rate of 75% after 5000 cycles.

[0091] As can be seen from the comparison between Example 1 and Comparative Example 3, using Grade I fly ash can better improve the mechanical and electrochemical properties of supercapacitors.

[0092] Comparative Example 4

[0093] The difference from Example 1 is that no autoclaving was performed. Its 3-day compressive strength is 32 MPa, tensile strength is 1.5 MPa, initial discharge specific capacity at 0.1C rate is 68 mAh / g, and capacity retention after 5000 cycles is only 58%.

[0094] As can be seen from the comparison between Example 1 and Comparative Example 4, the formation of zeolite phase with regular pore structure significantly improves the mechanical and electrochemical performance of supercapacitors.

[0095] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An alkali-activated cementitious material for supercapacitors, characterized in that, The alkali-activated cementitious material is composed of the following raw materials in parts by weight: 4-5 parts fly ash, 1-1.2 parts slag, and 2.5-3 parts alkali activator; After being steam-cured, the alkali-activated cementitious material forms zeolite inside, and the zeolite has a regular channel structure. The alkaline activator is composed of water, water glass, and sodium hydroxide, with a molar ratio of water glass to sodium hydroxide of 1.55-1.65:1; the modulus of the water glass is 0.5-0.55; and the concentration of sodium hydroxide is 4.0 mol / L-4.5 mol / L. The fly ash is Class I fly ash; The conditions for autoclaving are as follows: after curing at 40℃ for 4-6 hours, continue curing at 0.2MPa-0.5MPa and 120℃-150℃ for 10-12 hours.

2. The alkali-activated cementitious material for supercapacitors as described in claim 1, characterized in that, The liquid-to-solid ratio of the alkali-activated gelling material is between 0.10 and 0.

20.

3. The alkali-activated cementitious material for supercapacitors as described in claim 1, characterized in that, The slag is S105 grade slag.

4. A method for preparing an alkali-activated cementitious material for supercapacitors according to any one of claims 1-3, characterized in that, include: Preparation of alkaline activators; Mix fly ash and slag evenly to obtain dry material; The dry material is mixed evenly with the alkali activator to obtain an alkali-activated gelling material; The alkali-activated gelling material is poured into a mold, and then subjected to autoclaving followed by standard curing to obtain the alkali-activated gelling material for supercapacitors.

5. The preparation method of the alkali-activated cementitious material for supercapacitors as described in claim 4, characterized in that, The dry material and the alkali activator are mixed by stirring.

6. The preparation method of the alkali-activated cementitious material for supercapacitors as described in claim 5, characterized in that, The stirring speed is 140-160 r / min.

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