High-strength cement-based hydrogel electrolyte, rechargeable pool-based battery and preparation method of rechargeable pool-based battery

Abstract

The invention provides a high-strength cement-based hydrogel electrolyte, a rechargeable pool-based battery and a preparation method of the rechargeable pool-based battery, and belongs to the technical field of energy storage. The invention provides a high-strength cement-based hydrogel electrolyte and a preparation method thereof. The invention also provides a high-strength rechargeable pool-based battery and a preparation method thereof. According to the invention, cement is constructed into a layered structure, the basic strength of a cement skeleton is maintained, pores between adjacent cement sheet layers are filled with the PVA-CuSO4 hydrogel, and the adhesion force of the PVA hydrogel enhances the adhesion capacity between a cement material and an electrode, so that the construction of a continuous ion diffusion channel is facilitated, the contact resistance is reduced, and the layered structure can buffer deflection, so that the service life of the electrode is prolonged, and the service life of the electrode is prolonged. The strength and the toughness of the cement are improved, and ions are expected to be quickly transferred through interlayer channels, so that the ionic conductivity is remarkably improved.

Description

Technical Field

[0001] The present invention relates to a high-strength cement-based hydrogel electrolyte, a rechargeable aqueous battery and a preparation method thereof, belonging to the technical field of energy storage. Background Art

[0002] Cement is a basic component of concrete, and concrete is a major building material. However, as a traditional energy-intensive industry, the construction industry accounts for approximately 40% of the total energy consumption, 40% of the atmospheric emissions, 30% of the raw material consumption, and 25% of the water consumption. Due to its large volume, a building often has a large external wall surface area in direct contact with natural resources such as wind energy and solar energy, which also provides good conditions for the large-scale development of the current building photovoltaic industry. However, these clean energies are limited by weather and other reasons and cannot stably output electrical energy. Therefore, the development of energy storage devices is an important factor in the development and utilization of clean energy.

[0003] Currently, the widely used lithium-ion batteries on the market use liquid electrolytes. For safety reasons, researchers generally believe that all-solid-state lithium-ion batteries are the future development direction. The polymer electrolytes that have been commercially applied recently have achieved relatively stable electrochemical performance and cycle life for all-solid-state batteries, and other types of all-solid-state electrolytes are also in the further research or application stage. Cement itself, as an ion conductor, has good electronic insulation and can itself be used as an electrolyte material. On this basis, the development and application of cement-based batteries become possible. At the same time, considering the large surface area and volume of a building, it is of great significance to develop the self-energy storage function of a building for natural energy. In traditional engineering applications, the strength of cement is an important parameter that directly determines the quality and lifespan of a building. When it is used as an electrolyte, the ionic conductivity becomes the key. However, it is difficult for cement to have good mechanical properties and ionic conductivity at the same time. For example, cationic additives (such as KOH and Na2SO4) can improve the ionic conductivity of cement-based electrolytes, but will significantly reduce the strength of cement. Although some polymers can improve the strength and durability of cement, adding them into cement together with cationic compounds cannot simultaneously improve its ionic conductivity and strength. It is obviously very unreasonable to sacrifice the strength and lifespan of cement in pursuit of ionic conductivity. Therefore, the key point in the development of cement-based batteries lies in how to solve the contradiction between the ionic conductivity and strength of cement-based electrolytes.

[0004] Polymer-based hydrogels can enhance the strength and toughness of cement-based batteries due to their inherent ductility. The large amount of water in the gel can also support the self-healing of cementitious materials. Polyvinyl alcohol (PVA) is a common mortar additive that can enhance the bonding strength of cement mortar, reduce the shrinkage rate of cement mortar, reduce cracks and deformations generated during use, improve the durability and anti-aging ability of cement, extend the service life, and increase the toughness and elasticity of cement mortar. By adjusting the water content and chemical reaction rate in cement mortar, the cement mortar can be more evenly distributed in the concrete structure, improving the overall performance and stability. PVA also exhibits good interfacial compatibility with cement, can effectively fill voids and repair cracks, and enhance the adhesion ability between cement materials and electrodes, which is beneficial to constructing a continuous ion diffusion channel and reducing the contact resistance. The pore structure in the PVA skeleton can also improve the adsorption and migration ability of inorganic salt ions, thus significantly increasing the ionic conductivity of cement / polymer composites (Analysis of the mechanism of action of polyvinyl alcohol in high-performance cement-based materials, Journal of Materials Science and Engineering, Article ID: 1673-2812(2008)02-0264-05).

[0005] Currently, there are reports (Application No. 202210444065.X, Invention Title: Preparation Method and Application of a Cement-Based-Hydrogel Composite Electrolyte Material) using polyacrylamide (PAM) to compound with alkali or alkali metals (sodium hydroxide, sodium sulfate or sodium chloride) to prepare a cement-based-hydrogel composite electrolyte material and using it as a solid electrolyte for supercapacitors. However, since the crosslinking of PAM is significantly affected by temperature, the exothermic hydration of cement will cause it to undergo self-crosslinking in advance. Therefore, the dried cement specimen is frozen before the hydrogel solution fills the interlayer pores to avoid hydration and heat release; the filling of the interlayer pores with the hydrogel solution also needs to be carried out in an ice-water bath environment to inhibit the hydration reaction of cement and avoid the premature crosslinking of the hydrogel caused by hydration heat release. Such freezing or ice-water bath operations increase the difficulty of condition control, and PAM will also inevitably crosslink at room temperature, resulting in a decrease in the efficiency and quality of PAM penetrating into the interlayer voids of cement. In addition, the conductive substances in the hydrogel in this patent literature are sodium sulfate, sodium chloride or sodium hydroxide, and the preferred conductive substance is sodium chloride, where sodium chloride is at a saturated concentration. However, sodium hydroxide may trigger the alkali-aggregate reaction in cement, is corrosive to some components (such as aluminates) in the cement-based material, may damage the microstructure of cement, significantly reduce the durability of the cement-based material, and cause the cement-based material to expand, crack and its strength to decline. Sodium chloride may accelerate the early hydration reaction of cement, resulting in an increase in early strength, but the late strength growth is slow. High-concentration sodium chloride may inhibit the formation of some hydration products and affect the long-term performance of the cement-based material. Especially, the chloride ion concentration in the saturated sodium chloride solution is extremely high, which will significantly accelerate the corrosion of steel bars and the deterioration of the cement-based material; salt crystals will precipitate under dry conditions, generating crystallization pressure, causing the cement-based material to crack and peel off, and losing its basic mechanical properties.

[0006] There are literature reports on the synthesis of PVA / HPMC / PANI / CuSO4 gel polymer films and their use as flexible electrolytes for batteries (DOl: 10.1016 / j.ssi.2024.116511). Among them, CuSO4 and PANI / [BMIM][BF4] polyionic liquid are used as ionic additives to enhance the ionic conductivity of the electrolyte. The PANI / [BMIM][BF4] polyionic liquid also serves as the solution of the system to enhance the amorphousness and plasticity of the gel electrolyte, making the hydrogel not easily crack after drying into a thin film electrolyte. The ionic conductivity of the ionic liquid is significantly higher than that of CuSO4. Therefore, the improvement of the ionic conductivity of this polymer film mainly relies on the ionic liquid, but ionic liquids are generally quite expensive and not suitable for large-scale use. Summary of the Invention

[0007] In order to improve the strength of the cement-based battery and the ionic conductivity of the hydrogel electrolyte, the present invention provides a high-strength cement-based hydrogel electrolyte, a rechargeable aqueous battery, and a preparation method thereof.

[0008] The present invention provides a high-strength cement-based hydrogel electrolyte, which is prepared from cement, water, water reducing agent, PVA, and CuSO4, and the mass ratio is as follows:

[0009] 50 parts of cement, 1 part of water reducing agent, 17.5 parts of water, 4 - 6 parts of PVA, and 0.04 - 1.6 parts of CuSO4.

[0010] Preferably, the mass ratio is as follows:

[0011] 50 parts of cement, 1 part of water reducing agent, 17.5 parts of water, 5 parts of PVA, and 0.07 parts of CuSO4.

[0012] The present invention provides a preparation method of the above-mentioned cement-based hydrogel electrolyte, which is characterized in that it includes the following steps:

[0013] a. Prepare a cement matrix with a layered structure:

[0014] Take cement and water reducing agent, mix and grind them, add water and mix evenly, pour them into a mold, place them in a wet box for more than 24 hours, demold, cure, and dry.

[0015] b. Prepare a precursor solution of PVA-CuSO4 hydrogel:

[0016] Dissolve PVA in deionized water, the concentration of PVA is 10% - 15% w / w, stir at 90 °C for 1 hour; then dissolve CuSO4 in deionized water to make a CuSO4 solution, and slowly add it to the PVA solution to obtain a precursor solution of PVA-CuSO4 hydrogel.

[0017] c. Composite the cement matrix and the PVA-CuSO4 hydrogel precursor solution:

[0018] Place the dry cement matrix prepared in step a in a vacuum permeation instrument, evacuate the whole system, the vacuum degree reaches about -0.1 MPa, inject the prepared precursor solution in the vacuum state until the solution submerges the aqueous matrix, and keep it for 2 hours in the vacuum state; then use the freeze-thaw cycle method to prepare a cement matrix composite PVA-CuSO4 hydrogel electrolyte.

[0019] Specifically, the mold in step a has a layered structure, and the number of layers is two or more; the bottom cement of the layered structure matrix is connected to each other; the drying method in step a is vacuum drying, the drying temperature is 65 °C, and the drying time is 2 days or more.

[0020] The conditions of the freeze-thaw cycle method described in step c are: freezing at -20°C for 12 h, thawing at room temperature for 6 h, and repeating 3 times.

[0021] The present invention also provides a high-strength rechargeable aqueous battery, which is composed of a cement-based electrode and the cement-based hydrogel electrolyte described above.

[0022] The present invention also provides a preparation method of the high-strength rechargeable aqueous battery described above, which includes the following steps:

[0023] a. Prepare a cement-based electrode;

[0024] b. Prepare a cement-based hydrogel electrolyte;

[0025] c. Place the PVA-CuSO4 hydrogel composite cement electrolyte on the surface of the positive electrode cast with conductive mortar. Subsequently, in a similar manner, pour half of the cement mortar into a mold, cover the lower surface with the PVA-CuSO4 hydrogel composite cement electrolyte, cover the upper surface with a negative metal electrode layer, pour the other half of the cement mortar, cast the negative metal electrode in the conductive mortar, and vibrate the cement material in the mold; place the mold in a wet box, demold after 24 h, and place it in the wet box again for curing.

[0026] Among them, the preparation method of the cement-based electrode described in step a includes the following steps:

[0027] 1) Preparation of the metal electrode: Using Fe and Ni as the metal electrodes, adopt the electroplating method to electroplate the metal onto the carbon fiber and cast it in the cement matrix as the cement-based electrode;

[0028] 2) Cast the metal electrode with conductive mortar:

[0029] Take cement and carbon black, grind and stir, add a water reducer and water, and continue to mix. Pour half of the cement mortar into a mold, cover the surface with a metal electrode layer, pour the other half of the cement mortar, and cast the metal electrode in the conductive mortar; place the mold in a wet box, demold after 24 h, and place it in the wet box again for curing;

[0030] Among them, the mass ratio of cement, carbon black, water reducer, and water is:

[0031] Cement 50 parts, carbon black 2 parts, water reducer 1 part, water 17.5 parts.

[0032] Among them, the electroplating bath solution for Ni plating in step 1) is 300 g / L NiSO4·7H2O, 25 g / L NiCl2·6H2O, and 25 g / L H3BO3, and electroplate at a current of 1.0 A for 3 h; the electroplating bath solution for Fe plating is 200 g / L FeSO4·7H2O, and electroplate at a current of 1.5 A for 3 h.

[0033] Compared with sodium sulfate, sodium chloride, sodium hydroxide, and other commonly used electrolyte materials such as sulfuric acid, which may cause corrosion to cement, copper ions (Cu 2+ ) itself may play an inhibitory role in certain corrosion reactions in cement, especially in certain specific environments, such as high humidity or sulfate-containing environments. Copper ions (Cu 2+ ) may undergo an exchange reaction with calcium ions (Ca 2+ ) released during the cement hydration reaction, forming certain coordination compounds in the cement, affecting the ion exchange performance of the cement, and thus changing the ion conductivity of the cement. In addition, using cement as the structural matrix of the electrolyte can provide the necessary mechanical strength and load-bearing capacity, where the layered micropores are further filled with an ion-conductive hydrogel and act as ion diffusion channels. Therefore, the PVA-CuSO4 hydrogel has high ion conductivity, excellent water retention ability, and cyclic stability, which not only improves the electrochemical performance of the cement but also is beneficial to the hydration of the cement, and is a feasible filling material.

[0034] The precursor of the PVA hydrogel is the PVA solution. There is no need to add initiators and cross-linking agents, and there is no additional polymerization process. The gelation of PVA is mainly by the physical cross-linking method, mainly achieved through the freeze-thaw cycle method. The cross-linking process does not require heating, so the hydration heat of the cement will not affect the cross-linking of PVA. There is no need to control the temperature of the cement and the system in stages, and the precursor solution can fill the interlayer pores of the cement at room temperature.

[0035] The preparation of the PVA hydrogel is mainly divided into two methods: physical cross-linking and chemical cross-linking. Chemical cross-linking requires adding additional substances such as cross-linking agents and initiators. The synthesized PVA needs to be washed, and impurities may be introduced into the PVA gel; the physical cross-linking method does not require chemical cross-linking agents. Generally, in the laboratory, it is mainly prepared by the freeze-thaw cycle method. However, the PVA cross-linking requires multiple freeze-thaw cycles, and the preparation time is long. It should be noted that Cu 2+ itself participates in the hydration of the cement, affects the ion exchange performance of the cement, and thus changes the ion conductivity of the cement; CuSO4 can also act as a cross-linking agent or catalyst to affect the gelation process of PVA. Cu 2+ ions can coordinate with the hydroxyl groups (-OH) on the PVA molecular chain to form cross-linking points, promoting the gelation of PVA. This coordination cross-linking effect can enhance the mechanical strength and stability of the PVA hydrogel.

[0036] The beneficial effects of the present invention are:

[0037] In the present invention, cement is constructed into a layered structure. The cement skeleton maintains the basic strength, and the PVA-CuSO4 hydrogel is filled in the pores between adjacent cement lamellae. The adhesion of the PVA hydrogel enhances the adhesion ability between the cement material and the electrode, which is beneficial to constructing a continuous ion diffusion channel and reducing the contact resistance. The pore structure in the PVA skeleton can also improve the adsorption and migration ability of Cu 2+ , thus significantly improving the ionic conductivity of the PVA-CuSO4 hydrogel. In addition, this layered structure can buffer flexure, improve the strength and toughness of the cement, and is expected to promote the rapid transfer of ions through the interlayer channels, thereby significantly improving the ionic conductivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 . (a) Cement matrix structure of the layered structure (b) PVA-CuSO4 hydrogel composite cement-based electrolyte, (c) Hydrogel electrolyte and rechargeable cement-based battery structure;

[0039] Figure 2 Mold for rechargeable water pool-based battery;

[0040] Figure 3 . Influence of PVA concentration on the specific flexural strength and specific compressive strength of PVA hydrogel cement-based electrolyte (without CuSO4);

[0041] Figure 4 . Influence of PVA concentration on the fracture energy of PVA hydrogel cement-based electrolyte (without CuSO4);

[0042] Figure 5 . Specific flexural strength and specific compressive strength of PVA-CuSO4 hydrogel composite cement-based electrolyte at different CuSO4 concentrations;

[0043] Figure 6 . Fracture energy of PVA-CuSO4 hydrogel composite cement-based electrolyte at different CuSO4 concentrations;

[0044] Figure 7 . Impedance spectra of PVA-CuSO4 hydrogel composite cement-based batteries at different CuSO4 concentrations;

[0045] Figure 8 . Charge-discharge current curves of PVA-CuSO4(1M) hydrogel composite cement-based battery. DETAILED DESCRIPTION OF THE INVENTION

[0046] Example 1 Preparation of the cement-based hydrogel electrolyte of the present invention

[0047] (1) Hierarchical cement matrix: 50 g of cement and 1 g of water reducer are mixed in a ceramic bowl and ground and stirred for 3 min. 17.5 g of water (water-cement ratio 0.35) is added and mixed evenly. It is poured into a mold, and the mold is placed in a wet box. After 24 h, it is demolded and placed in the wet box again for curing. The cement at the bottom of the hierarchical cement matrix is interconnected ( Figure 1 a). The cured cement block is placed in a vacuum oven and dried at 65 °C for 2 days to remove the moisture inside the cement.

[0048] (2) Composite of cement matrix and PVA-CuSO4 hydrogel: 5 g of PVA is dissolved in 40 g of distilled water and stirred at 90 °C for 1 h. Then a certain mass of CuSO4 is dissolved in 5 g of deionized water to make a CuSO4 solution (concentrations of 0 M, 0.05 M, 0.1 M, 0.5 M, 1 M, and 2 M), and it is slowly added to the above PVA solution to obtain a precursor solution of PVA-CuSO4 hydrogel. The PVA-CuSO4 precursor solution is transferred to a petri dish.

[0049] The above-mentioned cured and dried cement specimens are placed in a vacuum permeation instrument, and the whole system is evacuated. When the vacuum reaches about -0.1 MPa, the prepared precursor solution is injected under vacuum until the solution submerges the specimens, and it is kept in this vacuum state for 2 h. Subsequently, the layered cement filled with PVA-CuSO4 solution is frozen at -20 °C for 12 h and thawed at room temperature for 6 h, and this is repeated 3 times. The freeze-thaw cycle is used to catalyze the conversion of the precursor solution into a hydrogel. After removing the excess hydrogel attached to the outside, a cement matrix composite PVA-CuSO4 hydrogel electrolyte is obtained ( Figure 1 b). The cement matrix not only provides strength and mechanical stability but also can serve as a carrier for the hydrogel. The interconnected hydrogel layers promote ion transport and significantly improve the ion transport efficiency.

[0050] Example 2 Preparation of the rechargeable aqueous battery based on the present invention

[0051] (1) Preparation of metal electrodes

[0052] Fe and Ni are used as metal electrodes (Formulas 1 and 2), and redox reactions occur during the charge and discharge processes. The metal electrodes are prepared by electroplating. The metal is electroplated onto carbon fibers and then cast into a cement matrix to form a cement-based electrode. Specifically, the carbon fiber mesh is connected to the negative electrode as the cathode, and the metal is connected to the positive electrode as the anode. During electroplating, metal ions at the anode dissolve and transfer to the surface of the cathode. The selection of the electroplating current and duration determines the thickness and quality of the metal plating until the mesh is completely covered by the coated metal. For the Ni positive electrode, the carbon fiber mesh is used as the positive electrode, and the Ni metal sheet is used as the negative electrode. The electroplating bath solution is 300 g / L NiSO4·7H2O, 25 g / L NiCl2·6H2O, and 25 g / L H3BO3, and electroplating is carried out at a current of 1.0 A for 3 h. For the Fe negative electrode, the carbon fiber mesh is used as the positive electrode, and the Fe metal sheet is used as the negative electrode. The electroplating bath solution is 200 g / L FeSO4·7H2O, and electroplating is carried out at a current of 1.5 A for 3 h. After completing the electrode electroplating, the excess surface of the mesh is cut off and cast into the conductive mortar electrode layer.

[0053] Fe(OH)2 + 2e - →Fe + 2OH - E red = -0.89V Formula 1

[0054] NiOOH + H2O + e - →Ni(OH)2 + OH - E red = +0.52V Formula 2

[0055] (2) Casting the metal electrode in conductive mortar

[0056] 50 g of cement and 2 g of carbon black are mixed in a ceramic bowl and ground and stirred for 3 min. Then, 1 g of water reducer and 17.5 g of water (water-cement ratio 0.35) are added and mixed evenly. Half of the cement mortar is poured into a mold, a metal electrode layer is covered on the surface, and the other half of the cement mortar is poured in to cast the metal electrode in the conductive mortar.

[0057] The mold for casting the metal electrode in conductive mortar and assembling the electrode and electrolyte is a cube mold. As Figure 2 shown, its length and width are restricted, and the height only needs to be higher than the sum of the positive and negative electrodes and the electrolyte. The positive and negative electrodes and the electrolyte are stacked and placed in the mold (where, 1 - light color is the mold, 2 - dark color is the cement matrix)

[0058] Example 3 Screening test of the PVA concentration in the precursor solution of the PVA-CuSO4 hydrogel of the present invention

[0059] Place the PVA-CuSO4 hydrogel composite cement electrolyte on the surface of the positive electrode cast with conductive mortar. Subsequently, using a similar method, pour half of the cement mortar into the mold. Cover the lower surface with the PVA-CuSO4 hydrogel composite cement electrolyte, cover the upper surface with the negative metal electrode layer, pour the other half of the cement mortar, cast the negative metal electrode in the conductive mortar, and vibrate the cement-based material in the mold. Place the mold in a wet box, demold after 24 h, and then place it in the wet box again for curing( Figure 1 c).

[0060] As Figure 3 shown, the specific flexural strength of the PVA hydrogel generally increases with the increase of the PVA concentration. Because the gel network formed by the high-concentration PVA solution is denser, the intermolecular hydrogen bonds and crystalline regions increase, and the ability to resist bending deformation is enhanced. However, when the concentration is too high, it may lead to excessive crosslinking, the material becomes brittle, and the flexural fracture strain decreases, showing a significantly reduced specific flexural strength at a concentration of 25%. In addition, high-viscosity solutions are prone to introducing air bubbles or uneven crosslinking, resulting in local stress concentration and reducing the effective strength. The compressive strength also increases with the increase of the PVA concentration, mainly because the high-concentration gel has a high chain density, and the ability of the chains to resist deformation during compression is stronger. However, when the concentration is too high, the gel may change from ductile compression to brittle fracture, reducing the energy absorption efficiency.

[0061] As Figure 4 shown, when the PVA concentration is low, the crosslinking density of the PVA hydrogel is low, and the molecular chains are easy to slip; when the PVA concentration is in the range of 10% - 15%, it has a moderate crosslinking density and chain entanglement, balancing the energy dissipation and network strength, and has a high fracture energy. However, when the PVA concentration is greater than 15%, although the high crosslinking density and chain entanglement will inhibit the crack propagation, it may also lead to brittle fracture, the fracture energy decreases, and the brittleness of the material increases, significantly affecting the mechanical properties of the material. Therefore, the optimal PVA concentration is between 10% - 15%.

[0062] The beneficial effects of the present invention are demonstrated by experiments below.

[0063] Test Example 1 Test on the flexural and compressive properties of the PVA-CuSO4 hydrogel composite cement electrolyte of the present invention

[0064] Based on the structure of the rechargeable cement-based battery, this test studies the influence of the CuSO4 concentration on the crosslinking effect of the PVA hydrogel, especially on the mechanical properties of the PVA-CuSO4 hydrogel composite cement-based electrolyte.

[0065] The PVA-CuSO4 hydrogel composite cement-based electrolyte and ordinary cement block (without hydrogel modification) were processed into specimens with a size of 40*15*8mm by a cutting machine and a grinding and polishing machine. The mechanical properties were tested by a universal testing machine for a three-point bending test, and the bending load was applied perpendicular to the direction of the cement sheet. The specific flexural strength and specific compressive strength of the traditional casting cement and the PVA-CuSO4 hydrogel composite cement at different CuSO4 concentrations were compared, as shown in the figure. Figure 5 As shown in the figure, with the increase of CuSO4 concentration, the PVA-CuSO4 hydrogel composite cement showed a significant improvement in both specific flexural strength and specific compressive strength. This is mainly due to the good interfacial compatibility between PVA and cement, which can effectively fill gaps and repair cracks and enhance the adhesion of cement materials. 2+ It has a strong polarization ability, which can attract the electron cloud of oxygen atoms and weaken the silicon-oxygen bond (Si-O), thereby causing the bridging oxygen to break and convert into non-bridging oxygen. PVA hydrogel also increases the proportion of non-bridging oxygen, resulting in a shorter silicon chain in the main structure. In this process, due to the presence of lone pairs of electrons and the reduction of bonding electrons, the electronegativity of oxygen atoms becomes stronger, resulting in a stronger bond interaction between Ca in cement and O in hydrogel, thereby enhancing the connection between PVA hydrogel and cement layer, so that cement and hydrogel have a stable interface connection. Therefore, the PVA-CuSO4 hydrogel composite cement electrolyte exhibits good bending and compression resistance.

[0066] Test Example 2 Mechanical properties test of PVA-CuSO4 hydrogel composite cement electrolyte of the present invention

[0067] The three-point bending test was also used to evaluate the effect of CuSO4 concentration on the brittleness of PVA-CuSO4 hydrogel composite cement-based electrolyte. A sharp notch (7 mm long) was prefabricated in the middle of the above 40*15*8 mm specimen, and a load was applied in the middle of the sample at a constant rate (usually 0.5 mm / min) until the sample broke. The load-displacement curve was recorded.

[0068] The fracture energy G is calculated according to formula 3:

[0069]

[0070] Where W is the area under the load-displacement curve (i.e., the energy absorbed during the fracture process); A is the effective area of the fracture surface (notch length a×sample thickness t)

[0071] Figure 6That is the fracture energy of the PVA-CuSO4 hydrogel composite cement-based electrolyte at different CuSO4 concentrations. As the CuSO4 concentration gradually increases, the fracture energy of the PVA-CuSO4 hydrogel composite cement-based electrolyte generally shows a downward trend. This is mainly because as the CuSO4 concentration increases, the cross-linking effect of PVA increases, the cross-linking density of the hydrogel increases, and the structure becomes more compact, resulting in a decrease in the water content of the hydrogel. While the rigidity increases, the brittleness also increases. Therefore, it is necessary to select an appropriate CuSO4 concentration to ensure that the PVA-CuSO4 hydrogel composite cement-based electrolyte has appropriate mechanical properties. When the CuSO4 concentration is in the range of 0.05 - 0.1 M, although the specific flexural strength and specific compressive strength of the electrolyte increase as the CuSO4 concentration increases, and the ionic conductivity also increases, the fracture energy will decrease significantly, increasing the brittleness of the electrolyte and instead reducing its mechanical properties.

[0072] Experimental Example 3 Electrochemical Test of the PVA-CuSO4 Hydrogel Composite Cement Electrolyte of the Present Invention

[0073] The PVA-CuSO4 hydrogel composite cement-based electrolyte and the cement-based electrode are further assembled into a cement-based battery and subjected to electrochemical tests. Figure 7 Figure [ID number] shows the impedance spectra of the PVA-CuSO4 hydrogel composite cement-based battery at different CuSO4 concentrations. Compared with the PVA hydrogel composite cement-based battery without adding CuSO4, the pore structure in the PVA skeleton can improve the adsorption and migration ability of CuSO4 ions. The layered micropores in the cement matrix are further filled with the PVA-CuSO4 hydrogel and act as ion diffusion channels, thus significantly improving the ionic conductivity of the PVA-CuSO4 hydrogel composite cement. The PVA-CuSO4 hydrogel composite cement-based shows more excellent ionic conductivity. In addition, since the CuSO4 concentration directly affects the ionic concentration and ionic conductivity in the cement matrix, the internal resistance (Rs), charge transfer resistance (Rct), and ion migration rate of the cement-based battery increase as the CuSO4 concentration increases. At the same time, as the CuSO4 concentration increases, the water content of the PVA hydrogel decreases, and the bonding effect with the cement matrix enhances, which may promote ion migration. However, the higher the CuSO4 concentration is not necessarily better. As shown by the mechanical property test results, as the CuSO4 concentration increases, it may have a negative effect on the mechanical properties of the cement matrix. Further, Figure 8The current curve of the PVA-CuSO4 hydrogel composite cement-based battery during charge and discharge cycles. During the 900-hour cycle test, the charge and discharge current of the cement-based battery remained relatively stable, indicating that the PVA-CuSO4 hydrogel composite cement-based battery has good charge and discharge performance and cycle stability. The pore structure in the PVA skeleton can improve the adsorption and migration ability of CuSO4 ions, thus significantly increasing the ionic conductivity of the PVA-CuSO4 hydrogel composite cement.

[0074] In summary, the PVA-CuSO4 hydrogel has high ionic conductivity, excellent water retention ability and cycle stability. It not only improves the electrochemical performance of cement, but also is beneficial to the hydration of cement. It is a feasible filling material. Among them, CuSO4 not only changes the ionic conductivity of cement; it also affects the gelation process of PVA as a cross-linking agent or catalyst, promotes the gelation of PVA, and enhances the mechanical strength and stability of the PVA hydrogel. Therefore, at different CuSO4 concentrations, the PVA-CuSO4 hydrogel exhibits different mechanical and electrochemical properties. By adjusting the CuSO4 concentration, the synergistic improvement of the mechanical and electrochemical properties of the PVA-CuSO4 hydrogel composite cement-based battery can be achieved, and a high-strength rechargeable cement-based battery with excellent performance can be obtained. Considering the mechanical and electrochemical properties comprehensively, 0.1M PVA-CuSO4 is the best. Although the electrochemical performance is good when it exceeds 0.1M, the brittleness increases and it is more prone to fracture.

Claims

1. A high-strength cement-based hydrogel electrolyte, characterized in that: It is prepared from cement, water, water reducer, PVA, and CuSO4, and the mass ratio is as follows: Cement 50 parts, water reducer 1 part, water 17.5 parts, PVA 4 - 6 parts, CuSO4 0.04 - 1.6 parts.

2. The cement-based hydrogel electrolyte according to claim 1, characterized in that: The mass ratio is as follows: Cement 50 parts, water reducer 1 part, water 17.5 parts, PVA 5 parts, CuSO4 0.07 part.

3. A method for preparing the cement-based hydrogel electrolyte according to claim 1 or 2, characterized in that: It includes the following steps: a. Prepare a cement matrix with a layered structure: Take cement and water reducer, mix and grind them, add water and mix evenly, pour them into a mold, place it in a wet box for more than 24 hours, demold, cure, and dry. b. Prepare a precursor solution of PVA - CuSO4 hydrogel: Dissolve PVA in deionized water, with the concentration of PVA being 10% - 15% w / w, stir at 90 °C for 1 hour; then dissolve CuSO4 in deionized water to make a CuSO4 solution, and slowly add it to the PVA solution to obtain a precursor solution of PVA - CuSO4 hydrogel. c. Composite the cement matrix and the PVA - CuSO4 hydrogel precursor solution: Place the dried cement matrix prepared in step a in a vacuum permeation instrument, evacuate the whole system, with the vacuum degree reaching about -0.1 MPa, inject the prepared precursor solution in the vacuum state until the solution submerges the water pool matrix, and keep it in the vacuum state for 2 hours; then use the freeze - thaw cycling method to prepare a cement matrix composite PVA - CuSO4 hydrogel electrolyte.

4. The preparation method of the cement - based hydrogel electrolyte according to claim 3, characterized in that: The mold in step a has a layered structure, and the number of layers is two or more; the cement at the bottom of the layered structure matrix is connected to each other. The drying method in step a is vacuum drying, the drying temperature is 65 °C, and the drying time is 2 days or more.

5. The preparation method of the cement-based hydrogel electrolyte according to claim 3, characterized in that: The conditions of the freeze - thaw cycling method in step c are: freeze at -20 °C for 12 hours, thaw at room temperature for 6 hours, and repeat 3 times.

6. A high-strength rechargeable aqueous-based battery, characterized in that: It is composed of a cement - based electrode and the cement - based hydrogel electrolyte described in claim 1 or 2.

7. A method for preparing the high-strength rechargeable aqueous-based battery according to claim 6, characterized in that: It includes the following steps: a. Prepare a cement - based electrode; b. Prepare a cement - based hydrogel electrolyte; c. Place the PVA - CuSO4 hydrogel composite cement electrolyte on the surface of the positive electrode poured with conductive mortar. Subsequently, in a similar way, pour half of the cement mortar into a mold, cover the lower surface with the PVA - CuSO4 hydrogel composite cement electrolyte, cover the upper surface with a negative - electrode metal electrode layer, pour the other half of the cement mortar, pour the negative - electrode metal electrode into the conductive mortar, and vibrate the cement material in the mold; place the mold in a wet box, demold after 24 hours, and place it in the wet box again for curing.

8. The preparation method of the high-strength rechargeable aqueous-based battery according to claim 7, characterized in that: The preparation method of the cement - based electrode described in step a includes the following steps: 1) Preparation of the metal electrode: Use Fe and Ni as metal electrodes, and adopt the electroplating method to electroplate the metal onto the carbon fiber and pour it into the cement matrix as the cement - based electrode. 2) Pour conductive mortar on the metal electrode: Take cement and carbon black, grind and stir them, add water reducing agent and water, and continue to mix. Pour half of the cement mortar into the mold, cover the surface with a metal electrode layer, pour in the other half of the cement mortar, and pour the metal electrode into the conductive mortar. Place the mold in a wet box, demold after 24 hours, and place it in the wet box again for curing. Among them, the mass ratio of cement, carbon black, water reducing agent and water is: 50 parts of cement, 2 parts of carbon black, 1 part of water reducing agent, and 17.5 parts of water.

9. The preparation method of the high-strength rechargeable aqueous-based battery according to claim 8, wherein: In step 1), the electroplating bath solution for Ni plating is 300 g / L NiSO4·7H2O, 25 g / L NiCl2·6H2O and 25 g / L H3BO3, and electroplate for 3 hours at a current of 1.0 A; the electroplating bath solution for Fe plating is 200 g / L FeSO4·7H2O, and electroplate for 3 hours at a current of 1.5 A.

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