Ceramic fiber-cement-based supercapacitor and preparation method thereof

Abstract

The invention firstly provides an application of ceramic fiber in preparation of a cement-based supercapacitor. The inventor accidentally finds that the electrochemical performance of the cement-based supercapacitor prepared by doping a proper amount of ceramic fibers into cement is remarkably improved on the premise of keeping good mechanical properties. Based on the application, the invention also provides a ceramic fiber improved cement-based supercapacitor, which comprises an electrode, a structural phase and an ion phase doped in the structural phase, and the structural phase is a ceramic fiber-cement grade solid electrolyte uniformly doped with a proper amount of ceramic fibers. Wherein the ion phase comprises a lithium salt, and the electrode is a foamed nickel electrode coated with an active substance. The ceramic fiber is doped into a cement matrix, so that the electrochemical performance is remarkably improved, the highest electrochemical performance can reach 922 mF / cm < 2 >, and good mechanical performance is still kept. The invention further provides a preparation method of the cement-based supercapacitor, the preparation process is simple, soaking in an electrolyte is not needed, the operation steps are saved, the cost is low, the difficulty of a method for increasing the ion transmission efficiency in the cement-based electrolyte in the prior art is solved, and the cement-based supercapacitor has important practical application value.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrochemical energy storage, and relates to a cement-based supercapacitor, in particular to a ceramic fiber-cement-based supercapacitor with significantly improved electrochemical performance. BACKGROUND

[0002] Current main electric energy storage technologies include lithium ion batteries, supercapacitors, dielectric capacitors, etc. Compared with batteries, supercapacitors have higher power density and service life; compared with dielectric capacitors, they have higher energy density. These characteristics make supercapacitors have application advantages in energy storage devices. The supercapacitor with cement composite material as electrolyte has the characteristics of stable performance, low price and low maintenance cost, so it gradually stands out among many supercapacitors and becomes a kind of “energy storage / building integrated” device suitable for large building energy storage.

[0003] The essence of the cement-based supercapacitor is to take cement-based material as the core, and mainly realize energy storage through electric double-layer capacitor effect and pseudo-capacitance reaction. Based on the double-layer principle, when an external voltage is applied, a stable and close positive and negative charge layer will be formed at the interface of the electrode and the electrolyte due to the coulomb force or charge migration, which stores energy like two parallel plate capacitors. When the external circuit is closed, these ions quickly leave the interface, and electrons flow through the external circuit, thereby releasing electrical energy. Although there is a pseudo-capacitance reaction, the energy storage process of the supercapacitor is still mainly based on the above-mentioned fast and reversible ion adsorption / desorption, so it has extremely fast charging and discharging speed and super-long cycle life.

[0004] At present, the most common structure of the cement-based supercapacitor includes a separated structure and an integrated structure. Compared with the integrated structure, the separated structure has excellent performance although it is relatively complex to prepare, so it is the most common structure of the cement-based supercapacitor. The structure includes an electrode (active material is loaded on a current collector), a cement separator as a structure phase and an electrolyte as an ion phase; this structure utilizes the cement to form a hard but porous solid after hydration, and the electrolyte is immersed into all pores to provide a medium for ion movement. The cement separator separates the two electrodes to prevent direct short circuit of electrons; but at the same time, the pores in the cement separator allow the ions in the electrolyte to shuttle freely to complete the entire circuit. However, at present, the existing cement-based supercapacitors all have the problems of low voltage window, low energy density and low area loading capacity, which are difficult to meet the needs of building energy storage. Therefore, how to improve the electrochemical performance and mechanical performance of the cement-based supercapacitor is a technical problem to be solved.

[0005] Ceramic fiber is a kind of fibrous lightweight refractory material made of high-purity aluminosilicate and other metal oxides through melting, spinning or blowing, which has excellent properties such as light weight, high temperature resistance, good thermal stability, low thermal conductivity, thermal shock resistance, excellent chemical stability and good electrical insulation. There is no relevant report on the use of ceramic fiber in cement-based supercapacitors and the effects thereof. SUMMARY

[0006] To solve the problem of low energy density of existing cement-based energy storage devices, the present application provides a cement-based supercapacitor with ceramic fiber doped into cement as a solid-state electrolyte. The cement-based supercapacitor uses ceramic fiber with good electrical insulation, and the ceramic fiber is doped into the cement interlayer as a structural phase, which significantly improves the electrochemical performance while maintaining good mechanical properties, and produces unexpected technical effects.

[0007] Technical scheme of the present application:

[0008] The present application first provides the application of ceramic fiber in the preparation of cement-based supercapacitors. The inventors have unexpectedly found that the cement-based supercapacitor prepared by doping an appropriate amount of ceramic fiber into cement significantly improves the electrochemical performance while maintaining good mechanical properties. The amount of ceramic fiber is 0.8-2.0wt% of dry cement. In contrast to the use of electrolyte or conductive polymer to improve the conductivity in the prior art, the ceramic fiber used in the present application has good electrical insulation, which overcomes the technical bias and achieves unexpected technical effects. The inventors speculate that this is due to: (1) the introduction of a large number of small gaps and pores by the doped ceramic fiber, especially in the interface region between the fiber and the cement matrix, these newly formed channels provide more efficient migration paths for ions, resulting in improved overall permeability; (2) the doped ceramic fiber forms a network structure in the cement matrix, which preferentially diffuses ions along the fiber direction, especially at the fiber overlap, forming a "fast channel" to accelerate long-range ion migration and improve ion conductivity, thereby improving the charge and discharge performance. At the same time, the three-dimensional grid formed by the doped ceramic fiber can disperse stress concentration, especially in the direction of partial shear stress and tensile stress, and delay the development of dangerous cracks under pressure after microcracks occur, thereby improving the overall load-carrying capacity of the material.

[0009] Based on the foregoing applications, the present application also provides a ceramic fiber modified cement-based supercapacitor, comprising an electrode, a structural phase and an ionic phase doped in the structural phase; the structural phase is a ceramic fiber-cement-based solid electrolyte uniformly doped with an appropriate amount of ceramic fiber; the amount of the ceramic fiber is 0.8-2.0 wt% of the dry cement. The diameter of the ceramic fiber is 1-5 μm, and the length of the ceramic fiber is 1-5 mm. The ionic phase comprises a lithium salt, and the electrode is a foam nickel electrode coated with an active substance; the loading amount of the active substance is 8-11 mg / cm 2 By incorporating ceramic fiber into the cement matrix, the electrochemical performance is significantly improved, and the surface capacitance can reach up to 922 mF / cm 2 , and still maintains good mechanical properties.

[0010] Preferably, the lithium salt is lithium triflate, lithium bis(trifluoromethanesulfonyl)imide or lithium perchlorate; when the foam nickel electrode is a negative electrode, the active substance is a capacitive carbon or graphene, and when the foam nickel electrode is a positive electrode, the active substance is manganese dioxide, copper cobalt oxide or nickel cobalt oxide.

[0011] Moreover, the inventors have found that the ceramic fiber modified cement-based supercapacitor has excellent rate performance and cycle stability. Analysis shows that this is because the main components of the ceramic fiber are silicon dioxide and aluminum oxide; when the ceramic fiber is eroded in an alkaline environment, (1) the Si-O-Si bond of the silicon dioxide is broken by the Ca(OH)2 produced by cement hydration, and the silicon-oxygen skeleton is attacked and destroyed by hydroxyl ions, which can cause the surface layer of the ceramic fiber to fall off, and the reaction process is as follows: =Si-O-Si+OH-→=Si-OH+=Si-O-. This causes local erosion of the Ca(OH)2 crystal and the contact point of the fiber, and eventually forms a local hollow or porous tubular structure. This structure provides a fast transport channel for electrolyte ions, significantly shortening the ion diffusion path. (2) The Al2O3 contained in the ceramic fiber can react with the cement hydration product to form C–A–S–H gel, further improving the density and stability of the interface region, and inhibiting the excessive development of alkali corrosion, so that the overall skeleton of the ceramic fiber remains stable, so that the hollow structure has controllability and functionality, rather than being destructive.

[0012] The present application also provides a preparation method of the cement-based supercapacitor as described above, comprising the following steps:

[0013] (1) Preparing ceramic fiber: take an appropriate amount of ceramic fiber with a diameter of 1-5 μm, crush and process it to a length of 1-5 mm to obtain treated ceramic fiber. The ceramic fiber used in the present application is a raw material that can be purchased through commercial channels, which is easy to obtain and low in price, and is conducive to the later application.

[0014] (2) Preparation of electrode: coat appropriate amount of capacitive carbon or graphene on the nickel foam as the negative electrode, and coat appropriate amount of manganese dioxide, copper cobalt oxide or nickel cobalt oxide on the nickel foam as the positive electrode; the active material loading is about 8-11 mg / cm 2 .

[0015] (3) Preparation of capacitor: add appropriate amount of lithium salt, polymer and ceramic fiber treated in step (1) into silicate cement and stir well, then pour into a mold after mixing; insert the electrode prepared in step (2), demold and maintain after shaping, to obtain a ceramic fiber modified cement-based super capacitor; the polymer is polyacrylic acid / polyethylene oxide.

[0016] The amount of lithium salt is 5-10 wt% of dry cement, and the amount of polymer is 2-6 wt% of dry cement; the water-cement ratio of the silicate cement is 0.3-0.5. The specific operation of the maintenance is: 25±5℃ temperature condition, 90±5% humidity condition for 28 days. The electrode sheet is firmly fixed in the cement uncured period by the mold, so that it exists in parallel and vertical state on both sides of the cement electrolyte after demolding, and the structure is more stable, which is beneficial to subsequent charging and discharging.

[0017] Compared with the conventional cement-based capacitor, the preparation method of the cement-based super capacitor only needs to crush the ceramic fiber on the basis of adding lithium salt and polymer, and incorporate it in the preparation of the cement-based electrolyte, which is simple in preparation process; and does not need to be soaked in the electrolyte, saving operation steps, in addition, low cost, solves the difficulty of increasing the ion transmission efficiency of the cement-based electrolyte in the prior art, and has important practical application value.

[0018] The application of the cement-based super capacitor as described above is used in an environment with humidity of 100% or after the super capacitor is soaked in water until adsorption saturation. Since the cement-based super capacitor adds lithium salt, it has good ion transmission efficiency without soaking when the environmental humidity is 100%, and has good electrochemical performance; and when the environmental humidity is low, it only needs to be soaked in water, without the need to prepare an electrolyte solution, which simplifies the operation and reduces the cost.

[0019] Compared with the prior art, the beneficial effects of the present application are:

[0020] (1) The present application provides the application of ceramic fiber in the preparation of a cement-based super capacitor. By increasing the ceramic fiber with good insulation, the conductivity of the cement-based super capacitor is improved, achieving an unpredictable technical effect, while maintaining good mechanical properties, and the technical effect is remarkable.

[0021] (2) Based on the aforementioned applications, this application provides a ceramic fiber modified cement-based supercapacitor. The cement-based supercapacitor not only maintains good mechanical properties but also achieves a significant improvement in electrochemical performance. Furthermore, it can maintain good rate performance and cycle stability as the service life extends.

[0022] (3) This application also provides a method for preparing the ceramic fiber modified cement-based supercapacitor. The preparation method is simple and low in cost, and has important practical application value. Attached Figure Description

[0023] Appendix Figure 1 This is a schematic diagram of the structure of the ceramic fiber-modified cement-based supercapacitor described in this invention.

[0024] Appendix Figure 2 The cement-based supercapacitors prepared in Examples 1-4 and Comparative Example 1 operate at 0.4 mA / cm². 2 Constant current charge-discharge curves at current density.

[0025] Appendix Figure 3 The surface capacitance curves and coulombic efficiency curves of the cement-based capacitors prepared in Examples 1-4 and Comparative Example 1 are shown.

[0026] Appendix Figure 4 EIS resistance curves of cement-based capacitors prepared in Examples 1-4 and Comparative Example 1 are shown.

[0027] Appendix Figure 5 The graphs show the ionic conductivity of the cement-based capacitors prepared in Examples 1-4 and Comparative Example 1.

[0028] Appendix Figure 6 Electrochemical curves of the cement-based capacitor prepared in Example 1 are shown below; (a) constant current charge-discharge curve, (b) electrical impedance curve, (c) CV curve, and (d) surface capacitance curve and coulombic efficiency curve.

[0029] Appendix Figure 7 The total porosity of the cement-based materials prepared in Comparative Examples 1 and 1-4 was determined.

[0030] Appendix Figure 8 The pore size distribution curves are for the cement-based electrolytes prepared in Examples 1-4 and Comparative Example 1.

[0031] Appendix Figure 9 The diagram shows the pore size distribution of the cement-based electrolytes prepared in Examples 1-4 and Comparative Example 1.

[0032] Appendix Figure 10Trends of mechanical properties of cement-based electrolytes prepared in Examples 1~4 and Comparative Example 1, a) flexural strength, b) compressive strength.

[0033] Figure 2 Figure 11 Figure 3: Microstructure morphology of cement-based materials prepared in Examples 1~4 and Comparative Example 1; where (a) Comparative Example 1, (b) Example 1, (c) Example 2, (d) Example 3, (e) Example 4.

[0034] Figure 4 Figure 12 Results of mechanical efficiency η, electrochemical energy storage efficiency η, and multifunctional efficiency η of cement-based structural supercapacitors prepared in Examples 1~4 and Comparative Example 1. m e DETAILED DESCRIPTION

[0035] The application will be further described below with reference to the examples.

[0036] The raw materials used in this example were all purchased through commercial channels: ceramic fibers were purchased from Shanghai Chenqihua Technology Co., Ltd., and the main components were alumina and silicon dioxide; triflic acid was purchased from Shanghai Maclaurin Reagent Co., Ltd., and polyacrylic acid was purchased from Shanghai Maclaurin Reagent Co., Ltd.

[0037] Example 1: Preparation of ceramic fiber modified cement-based supercapacitors

[0038] Ceramic fibers with a diameter of 1-5 μm were crushed into lengths of 1-5 mm with a crusher; 30 g of dry cement was weighed, 0.8 wt% of ceramic fibers were added to the dry cement along with 5 wt% of LiOTF and 6 wt% of PAA, and mixed evenly, then an appropriate amount of water was added according to a water-cement ratio of 0.5, and mixed evenly, then poured into a mold with dimensions of 1 cm x 1 cm x 1 cm as a cement electrolyte. Capacitive carbon, acetylene black, and polytetrafluoroethylene emulsion were coated on a size of 1 cm x 1 cm of foam nickel at a mass ratio of 8:1:1 as the negative electrode, and manganese dioxide, acetylene black, and polytetrafluoroethylene emulsion were coated on the foam nickel as the positive electrode at a mass ratio of 8:1:1; the loading was 11 mg / cm 2 The two electrodes were inserted into the gaps reserved in the mold in parallel and vertically, respectively, so that the electrode sheets were fixed on both sides of the cement-based electrolyte, placed on a vibration table to discharge gas, placed in a curing box with a humidity of 90±5% at 25±5°C for 28 days, demolded, and a ceramic fiber modified cement-based supercapacitor was obtained.

[0039] Example 2: Preparation of ceramic fiber modified cement-based supercapacitors

[0040] Unlike Example 1, the dosage of ceramic fibers was 1.2 wt% of dry cement. ​​

[0041] Example 3: Preparation of ceramic fiber modified cement-based supercapacitor

[0042] The difference from Example 1 is that the dosage of ceramic fiber is 1.6wt% of dry cement.

[0043] Example 4: Preparation of ceramic fiber modified cement-based supercapacitor

[0044] The difference from Example 1 is that the dosage of ceramic fiber is 2.0wt% of dry cement.

[0045] Example 5: Preparation of ceramic fiber modified cement-based supercapacitor

[0046] The difference from Example 1 is that,

[0047] The ceramic fiber with a diameter of 1-5 μm is crushed into 1-5 mm in length with a crusher; 30 g of dry cement is weighed, and 0.8wt.% of ceramic fiber is uniformly mixed with 10wt% of lithium bis-trifluoromethanesulfonimide and 5wt% of PAA, and then added to the dry cement to mix uniformly, then an appropriate amount of water is added according to the water-cement ratio of 0.3, and mixed uniformly, then poured into a mold with a size of 1 cm x 1 cm x 1 cm as a cement electrolyte. The graphene, acetylene black, and polytetrafluoroethylene emulsion are coated on the size of 1 cm x 1 cm of foam nickel as the negative electrode at a mass ratio of 8:1:1, and the copper cobalt oxide, acetylene black, and polytetrafluoroethylene emulsion are coated on the foam nickel as the positive electrode at a mass ratio of 8:1:1; the loading amount is 8 mg / cm 2 The two electrodes are respectively inserted into the reserved gap of the mold in parallel and vertically, so that the electrode sheet is fixed on both sides of the cement-based electrolyte, placed on a vibration table to discharge gas, placed in a curing box with 25±5℃ 90±5% humidity for 28 days, demolded, and a ceramic fiber modified cement-based supercapacitor is obtained.

[0048] Example 6: Preparation of ceramic fiber modified cement-based supercapacitor

[0049] The difference from Example 1 is that,

[0050] Ceramic fibers with a diameter of 1-5 μm were ground into 1-5 mm lengths using a grinder; 30 g of cement was weighed, and 0.8 wt.% ceramic fibers were uniformly mixed with 8 wt% lithium perchlorate and 4 wt% PAA, and then added to the cement to mix uniformly, and then an appropriate amount of water was added according to a water-cement ratio of 0.4, and the mixture was uniformly mixed and then injected into a mold with a size of 1 cm x 1 cm x 1 cm to serve as a cement electrolyte. Capacitive carbon, acetylene black, and polytetrafluoroethylene emulsion were coated on a foam nickel with a size of 1 cm x 1 cm at a mass ratio of 8:1:1 to serve as a negative electrode, and manganese dioxide, acetylene black, and polytetrafluoroethylene emulsion were coated on a foam nickel at a mass ratio of 8:1:1 to serve as a positive electrode; the loading was 9 mg / cm 2 The two electrodes were respectively inserted into the gaps reserved in the mold in step 2) in parallel and vertically, so that the electrode sheets were fixed on both sides of the cement-based electrolyte, and were placed on a vibration table to discharge gas, and were placed in a curing box with a humidity of 90±5% at 25±5°C for 28 days, and were demolded, to obtain a ceramic fiber-modified cement-based supercapacitor.

[0051] Example 7: Preparation of a ceramic fiber-modified cement-based supercapacitor

[0052] Different from Example 1, the ceramic fibers were not added for modification.

[0053] Ceramic fibers with a diameter of 1-5 μm were ground into 1-5 mm lengths using a grinder; 30 g of cement was weighed, and 0.8 wt.% ceramic fibers were uniformly mixed with 8 wt% lithium perchlorate and 4 wt% PAA, and then added to the cement to mix uniformly, and then an appropriate amount of water was added according to a water-cement ratio of 0.4, and the mixture was uniformly mixed and then injected into a mold with a size of 1 cm x 1 cm x 1 cm to serve as a cement electrolyte. Capacitive carbon, acetylene black, and polytetrafluoroethylene emulsion were coated on a foam nickel with a size of 1 cm x 1 cm at a mass ratio of 8:1:1 to serve as a negative electrode, and manganese dioxide, acetylene black, and polytetrafluoroethylene emulsion were coated on a foam nickel at a mass ratio of 8:1:1 to serve as a positive electrode; the loading was 9 mg / cm 2 The two electrodes were respectively inserted into the gaps reserved in the mold in step 2) in parallel and vertically, so that the electrode sheets were fixed on both sides of the cement-based electrolyte, and were placed on a vibration table to discharge gas, and were placed in a curing box with a humidity of 90±5% at 25±5°C for 28 days, and were demolded, to obtain a ceramic fiber-modified cement-based supercapacitor.

[0054] Comparative Example 1: Preparation of a cement-based supercapacitor

[0055] Different from Example 1, no ceramic fibers were added for modification. Specifically:

[0056] Take 30 g of cement, mix 5 wt% LiOTF and 6 wt% PAA uniformly, then add to the cement, mix uniformly, then add appropriate amount of water according to water-cement ratio 0.5, mix uniformly, then pour into a mold with size 1 cm x 1 cm x 1 cm, as a cement electrolyte. The positive and negative electrodes prepared above are respectively parallel and vertical inserted into the gap reserved in the mold, so that the electrode sheet is fixed on both sides of the cement-based electrolyte, placed on the vibration table to discharge gas, placed in a curing box with 25±5℃ 90±5% humidity for 28 days, demolded, and a ceramic fiber modified cement-based supercapacitor is obtained.

[0057] Example 8: Electrochemical performance characterization of cement-based supercapacitors prepared in Examples 1-4 and Comparative Example 1

[0058] 1. CHI670F electrochemical workstation was used for testing, and the test conditions were: at room temperature, humidity 100%, two-electrode system was used for testing. The cement-based supercapacitors prepared in Examples 1-7 all have good electrochemical performance and mechanical properties. Among them, the surface capacitance of Example 1 can reach 922 mF / cm 2 , while maintaining a compressive strength of 18.45 MPa and a bending strength of 5.04 MPa. The results of Examples 1 and 5-7 are basically the same, indicating that the most critical factor is the dosage of ceramic fiber. Examples 1-4 and Comparative Example 1 are described in detail below.

[0059] The characterization method specifically includes:

[0060] (1) Cyclic voltammetry (CV): the test object is the cement-based supercapacitor prepared in Example 1. The results are shown in Figure 6 c.

[0061] (2) Galvanostatic charge-discharge curve (GCD): the test object is the cement-based supercapacitor. The results are shown in Figure 2 . According to the GCD curve shown in Figure 2 , the surface capacitance of the supercapacitor is calculated by the formula: C=IΔt / ΔV. The results are shown in Figure 3 .

[0062] (3) EIS test: the test object is the cement electrolyte, and the test frequency is 0.01 Hz-1 MHz; the results are shown in Figure 4 . According to the bulk resistance of the EIS test results, the ionic conductivity of the cement electrolyte is calculated, and the results are shown in Figure 5 . The intersection of the EIS curve of the cement electrolyte and the real axis is taken as the bulk resistance (R s ) of the structure electrolyte, and the ionic conductivity (σ) of the structure electrolyte is calculated by the formula: σ=L / (A·Rs ) calculating the ionic conductivity of the cement electrolyte.

[0063] Figure 2 Galvanostatic charge-discharge curves (GCD) of the cement-based capacitors prepared in Examples 1-4 and Comparative Example 1 were prepared. From Figure 2 it can be seen that (1) the voltage window of the cement-based supercapacitor is 0V-1.5V, which has good electrical performance; (2) the GCD curve of the cement-based supercapacitor is relatively symmetrical triangle; and with the increase of the fiber content, the discharge time becomes shorter and shorter. It is shown that the introduction of an appropriate amount of fiber can greatly improve the electrochemical performance of the cement-based supercapacitor, but excessive incorporation may weaken its reinforcing effect.

[0064] Figure 3 The surface capacitance curve and coulombic efficiency curve of the cement-based capacitors prepared in Examples 1-4 and Comparative Example 1 were prepared. From Figure 3 it can be seen that (1) when the current density is 0.4mA / cm 2 , the surface capacitance of the cement-based capacitor prepared in Comparative Example 1 is 253 mF / cm 2 , and the discharge surface capacitance of the cement-based capacitor prepared in Example 1 is 922 mF / cm 2 , compared with the fiber-free cement-based capacitor of Comparative Example 1, the area specific capacitance is greatly increased; (2) with the increase of the ceramic fiber content, the area specific capacitance of the cement-based capacitor shows a downward trend, wherein the area specific capacitance can reach 850.67 mF / cm 2 when the ceramic fiber content is 1.2wt%, and the area specific capacitance decreases to 474.67 mF / cm 2 when the ceramic fiber content is 1.6wt%, but compared with the cement-based capacitor without adding ceramic fiber, it is still improved by 87.62%, which has significant progress.

[0065] Figure 4 The EIS curves of the cement electrolytes prepared in Examples 1-4 and Comparative Example 1 were prepared. From Figure 4 it can be seen that (1) the EIS curve is a straight line in the low frequency region, which shows that the diffusion migration of the ion conductive phase in the pore structure of the ordinary Portland cement, indicating that the cement electrolyte is an ion conductive material; (2) the EIS curve in the high frequency region is a small semicircle, and the intersection of the EIS curve in the high frequency region with the real axis is the bulk resistance R s of the ion conductive material; in the fiber-free Comparative Example 1, the resistance of the cement electrolyte is 128.25Ω; the EIS curves of the cement electrolytes prepared in Examples 1-4 with ceramic fiber incorporation are overall shifted to the left of the X axis, and the bulk resistance Rs is 70.5Ω-147.9Ω. This shows that compared with the fiber-free cement electrolyte, the bulk resistance Rs of the cement electrolyte improved by an appropriate amount of ceramic fiber is smaller.

[0066] Figure 2 shows the ion conductivity curves of the cement-based supercapacitors prepared in Example 1-4 and Comparative Example 1. Figure 5 Figure 3 shows the electrochemical performance of the cement-based supercapacitor prepared in Example 1. Figure 5 It can be seen that: (1) compared with Comparative Example 1, the ion conductivity of the cement electrolyte with 0.8wt% ceramic fiber (Example 1) increased to 8.48 mS / cm, indicating that adding an appropriate amount of ceramic fiber can improve the ion transport efficiency of the cement electrolyte. (2) When the content of ceramic fiber gradually increased to 2.0wt% (Example 4), the ion conductivity of the cement electrolyte gradually decreased to 4.06 mS / cm. The inventors speculate that this is because too much ceramic fiber incorporation will produce a certain agglomeration, indicating that the ion conductivity of the cement electrolyte reaches a threshold when the content of ceramic fiber is 0.8%,

[0067] In order to further evaluate the electrochemical performance of the cement-based supercapacitor prepared in Example 1, the present application also carried out constant current charge-discharge, electrochemical impedance spectroscopy, and cyclic voltammetry curve research. Figure 6 Figure 3 shows the electrochemical performance of the cement-based supercapacitor prepared in Example 1. Figure 6 a is the constant current charge-discharge curve. From Figure 6 a it can be seen that the GCD curve of the supercapacitor of this structure is relatively symmetrical triangular; and as the current density increases from 0.4 mA / cm 2 to 1.5 mA / cm 2 , the discharge time becomes shorter and shorter, indicating that the energy output is faster. Figure 6 b is the electrochemical impedance curve. From Figure 6 b it can be seen that the intersection of the EIS curve with the real axis in the high frequency region is 70.72Ω, which is consistent with Figure 4 . Figure 6 c is the CV curve. From Figure 6 c it can be seen that the CV curve of the cement-based supercapacitor in the range of 0~1.5V is a symmetrical half-rectangular shape. When the scan rate increases from 1 mV / s to 50 mV / s, the current peak value of the CV curve increases, and the closed integral area also increases. This indicates that the charge accumulation and release capacity is enhanced as the scan rate increases. Figure 6 d is the surface capacitance curve and the coulombic efficiency curve. From Figure 6 d it can be seen that when the current density is 0.4 mA / cm 2 , the surface capacitance of the supercapacitor is 922 mF / cm 2 ; as the current density increases to 1.5 mA / cm 2 , the surface capacitance of the supercapacitor of this structure gradually decreases to 500 mF / cm 2 . It can be known that when the current density increases by 5 times, the surface capacitance retention rate of the supercapacitor of this structure is 54.23%.

[0068] In summary, the amount of ceramic fiber added is a key factor affecting cement-based supercapacitors. The cement-based supercapacitors prepared in Examples 1-7 of this application, by adding an appropriate amount of ceramic fiber, achieved a significant improvement in electrochemical performance (especially areal capacitance), realizing unexpected technical effects and representing a significant advancement compared to existing technologies.

[0069] Example 9: Structural characterization of cement-based capacitors prepared in Examples 1-4 and Comparative Example 1

[0070] (1) Pore structure analysis

[0071] The specific method is as follows: The pore structure of cement-based materials is tested using a mercury porosimeter. After curing and drying, the sample is placed in the mercury porosimeter, and mercury is forced into the pores by gradually increasing the pressure. The relationship between the indentation force and the intrusion volume is recorded.

[0072] Appendix Figure 7 The total porosity is the total porosity of the cement-based materials prepared in Examples 1-4 and Comparative Example 1. Figure 7 It can be observed that the total porosity of Comparative Example 1 is 14.39%, while the total porosity of Example 1 is 19.72%, an increase of nearly one-third compared to Comparative Example 1. This indicates that incorporating an appropriate amount of ceramic fiber increases the total porosity of the cement-based electrolyte.

[0073] Appendix Figure 8 The figures show the pore size distribution curves of the cement-based electrolytes prepared in Examples 1-4 and Comparative Example 1. Figure 8 As can be seen, the pore size distribution of the cement-based electrolytes prepared in Examples 1-4 and Comparative Example 1 is mainly unimodal, with the most probable pore size (MPS) representing the most frequently occurring pores. Specifically, the cement electrolyte prepared in Comparative Example 1 exhibits a strong pore peak near 50 nm. In the cement electrolyte prepared in Example 1, although the strong pore peak only shifts slightly to the left, the peak value increases significantly, indicating that the pore size distribution is more concentrated in the 50 nm pores, resulting in a denser pore structure. With further increases in fiber content, the strong pore peaks of the cement electrolytes prepared in Examples 2-4 gradually shift to the right, and the peak values ​​of the pore peaks all decrease, indicating that the pore size distribution is biased towards larger sizes.

[0074] To further compare the pore size distribution of cement-based materials, the inventors divided the pore size range into intervals of <50 nm (harmless pores), 50~100 nm, 100~200 nm, and >200 nm (harmful pores). (See attached...) Figure 9 This refers to the pore size distribution diagrams of the cement-based electrolytes prepared in Examples 1-4 and Comparative Example 1. Figure 9It can be seen that, compared with Comparative Example 1, the cement electrolyte prepared in Example 1 has more micropores and mesopores, which is more conducive to ion transport during the charging and discharging process. It is worth noting that the content of mesopores and micropores reaches its maximum in Example 1, with the content of pores with a diameter smaller than 50 nm reaching 62.65%. After the fiber content exceeds 0.8%, the mesopores and micropores in the samples of Examples 2-4 gradually decrease. Figure 8 This consistency explains the significant impact of appropriate ceramic fiber content on ion transport in the electrolyte. Specifically, when the ceramic fiber content increased to 1.2 wt%, the content of pores with a diameter greater than 200 nm in the cement electrolyte reached its maximum, while the content of pores with a diameter less than 50 nm decreased to its minimum. Specifically, the content of pores with a diameter less than 50 nm decreased to 51.14%, while the content of pores with a diameter greater than 200 nm increased to 29.27%. This indicates that excessive fiber can lead to uneven distribution in cement-based materials, forming a loose transition zone at the fiber-matrix interface, resulting in a more porous matrix structure. Therefore, while appropriate incorporation of ceramic fiber is beneficial for improving the ion transport capacity of cement-based electrolytes, excessive addition is detrimental; it should be added within the range described in this application to achieve the best results.

[0075] (2) Microstructure analysis

[0076] The microstructure and morphology of the cement-based solid electrolytes in Examples 1-4 and Comparative Example 1 were analyzed using scanning electron microscopy at an accelerating voltage of 5 kV. The test results are as follows: Figure 11 As shown; where: (a) Comparative Example 1, (b) Example 1, (c) Example 2, (d) Example 3, (e) Comparative Example 4. Each is represented by... Figure 11 a and Figure 11 As can be seen from the comparison, the microstructure of the cement-based solid electrolyte without ceramic fibers in Comparative Example 1 mainly consists of calcium silicate hydrate (CSH) gel, voids, and cracks; while the cement-based solid electrolyte with ceramic fibers in Example 2 has a looser microstructure with a greater number of small pores, which provides a transport channel for conductive ions and water molecules, promotes the migration of conductive ions in the cement-based solid electrolyte, and accelerates the transport of conductive ions at the electrode / electrolyte interface.

[0077] Depend on Figure 11 As shown in b, some cracks appeared on the surface of the ceramic fiber. This is because the cement hydration near the ceramic fiber surface produced Ca(OH)2 crystals, which eroded and broke the Si-O-Si bonds of silicon dioxide in the ceramic fiber. The silicon-oxygen skeleton was attacked and destroyed by hydroxide ions, leading to local erosion at the contact point between the ceramic fiber and the Ca(OH)2 crystals. Debonding occurred between the cement and the fiber, and radial cracks formed inside the ceramic fiber (reaction process: =Si-O-Si=+OH-→=Si-OH+=Si-O-), ultimately forming a locally hollow or porous tubular structure. FromFigure 11 It is found that the alumina in the ceramic fiber can react with the hydration product to form C-A-S-H gel to further improve the compactness and stability of the interface. Thus, water can penetrate into the interior of the ceramic fiber and drive ion diffusion, and such a structure is more conducive to the rapid transmission of electrolyte ions; thus, the cement-based supercapacitor prepared in the present application can still maintain good rate performance and cycle stability as the use cycle is prolonged.

[0078] Example 10: Mechanical property characterization of the cement-based supercapacitors prepared in Examples 1-4 and Comparative Example 1

[0079] (1) Mechanical property test method: the mechanical properties of the cement electrolyte were tested by using a JES-300 universal material testing machine, the loading rate for the compressive strength test was 2.4 kN / s, and the loading rate for the bending strength test was 50 N / s.

[0080] Figure 10 The mechanical property test graphs (compressive strength, bending strength) of the cement-based electrolyte materials prepared in Examples 1-4 and Comparative Example 1 are shown. Figure 10 It can be seen that, compared with the cement electrolyte material prepared in Comparative Example 1 without fiber content, the mechanical properties of the cement electrolyte materials prepared in Examples 1-4 show a trend of first decreasing, then increasing, and then decreasing and tending to be stable with the increase of the fiber content, but basically do not affect the mechanical properties.

[0081] Table 1 is the mechanical property characterization results of the cement electrolyte materials prepared in Comparative Example 1 and Examples 1-4. As can be seen from Table 1, the compressive strength and bending strength of the cement electrolyte prepared in Comparative Example 1 are 23.70 Mpa and 4.52 Mpa, respectively; the compressive strength of the cement electrolyte material prepared in Example 1 decreases to 18.45 Mpa but the bending strength increases to 5.04 Mpa. The inventors believe that this is because: the ceramic fiber can effectively bridge the cracks at a low content, improve the crack propagation energy absorption, and significantly enhance the bending resistance and toughness. The compressive strength of the cement electrolyte material prepared in Example 2 (the fiber content is 1.2%) increases to 35.17 Mpa; this is because, as the surface of the fiber is hydroxylated (Si–OH, Al–OH) in the alkaline environment and participates in the reaction with Ca²⁺, a local C–A–S–H / gel phase may be generated at the fiber / matrix interface, and the local densification improves the compressive bearing capacity. The compressive strength of the cement electrolyte materials prepared in Examples 3-4 gradually decreases; this is because, as the ceramic fiber increases, the interfaces between the fibers and between the fibers and the matrix are too many, and the interface becomes a potential weak point, which is prone to produce microcracks under pressure, resulting in a gradual decrease in the compressive strength.

[0082] Table 1 Mechanical property characterization results of the cement electrolyte materials prepared in Comparative Example 1 and Examples 1-4

[0083] Test sample Ceramic fiber content (wt%) Flexural strength (MPa) Compressive strength (MPa) Comparative Example 1 0 4.52 23.70 Example 1 0.8 5.04 18.45 Example 2 1.2 3.92 35.17 Example 3 1.6 4.74 25.06 Figure 3 2 4.60 23.73

[0084] Example 11: Analysis of the multifunctionality of cement-based supercapacitors prepared in Examples 1-4

[0085] The multifunctional performance of structural supercapacitors is a crucial performance indicator. Generally, the multifunctional performance (multifunctional efficiency) of structural supercapacitors is evaluated using a mathematical analysis model. This analytical method comprehensively considers the electrochemical energy storage efficiency of the electrochemical energy storage component. e (The ratio of the surface capacitance of the fabricated structural supercapacitor to the half-surface capacitance of a single electrode in a three-electrode system) and the mechanical efficiency of the structural components. m (The ratio of compressive strength between cement-based supercapacitors and pure cement-based supercapacitors). Specifically, according to... Figure 12 η can be obtained from the surface capacitance data of the mid-plane and the surface capacitance data of the electrode plates. e Based on the compressive strength data in Table 1, η can be obtained. m The surface capacitance of the electrode prepared by this invention was measured to be 1.21 F / cm. 2 .

[0086] Therefore, the multifunctional efficiency η of the structural supercapacitor can be calculated by the following formula:

[0087] Ƞ = Ƞ 𝑒 + Ƞ m

[0088] Appendix Figure 12 The results show the multifunctional efficiency of the cement-based supercapacitors prepared in Examples 1-4 and Comparative Example 1. ​ As shown: (1) The electrochemical energy storage efficiency ηe of the cement-based supercapacitor does not increase completely with the increase of the ionic conductivity of the cement electrolyte doped with ceramic fibers; this indicates that the capacitance of the cement-based supercapacitor is not only related to the capacitance characteristics of the composite electrode and the cement electrolyte, but also to the compatibility between the composite electrode and the cement electrolyte. (2) The mechanical efficiency Ƞm of the fiber cement-based supercapacitors prepared in Examples 1-4 of this application is in the range of 0.78 to 1.48, and the electrochemical energy storage efficiency Ƞe is in the range of 0.09 to 1.52. Therefore, the multifunctional efficiency Ƞ is calculated to be in the range of 1.09 to 2.88, which is better than the structural supercapacitors reported in the prior art. This indicates that the cement electrolyte prepared in Examples 1-4 of this application has better multifunctionality and is an excellent structural electrolyte for cement-based supercapacitors.

[0089] In summary, the present application first reports the introduction of ceramic fibers into cement materials to prepare cement-based structural supercapacitors. The cement-based supercapacitors show a good combination of electrochemical energy storage performance and mechanical performance, achieving significant improvement in electrochemical performance while maintaining good mechanical performance. Moreover, the cement-based supercapacitors can still maintain good rate performance and cycle stability as the use cycle is prolonged. More importantly, the ceramic fiber modified cement-based supercapacitors have a simple preparation process and low cost, and have important practical application value. Therefore, the ceramic fiber doped polymer cement electrolyte assembled cement-based structural supercapacitors described in the present application have potential material advantages and important practical application value in the field of structural energy storage integration.

Claims

1. Use of ceramic fiber in preparation of cement-based supercapacitor.

2. Use according to claim 1, characterized in that: The amount of the ceramic fiber is 0.8-2.0 wt% of dry cement.

3. A ceramic fiber modified cement-based supercapacitor comprising an electrode, a structural phase, and an ionic phase doped in the structural phase; characterized in that: The structural phase is a ceramic fiber-cement-based solid electrolyte uniformly doped with an appropriate amount of ceramic fiber; the amount of the ceramic fiber is 0.8-2.0 wt% of dry cement.

4. The cement-based ultracapacitor of claim 3, wherein: The diameter of the ceramic fiber is 1-5 μm, and the length of the ceramic fiber is 1-5 mm.

5. The cement-based ultracapacitor of claim 3 or 4, wherein: The ionic phase comprises a lithium salt, the electrode is an active material-coated foam nickel electrode; the loading of the active material is 8-11 mg / cm 2 .

6. The cement-based ultracapacitor of claim 5, wherein: The lithium salt is lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonyl)imide or lithium perchlorate; when the foam nickel electrode is a negative electrode, the active substance is a capacitive carbon or graphene, and when the foam nickel electrode is a positive electrode, the active substance is manganese dioxide, copper cobalt oxide or nickel cobalt oxide.

7. The method of making a cement-based ultracapacitor according to any one of claims 3-6, wherein: The method comprises the following steps: (1) Preparing ceramic fiber: taking an appropriate amount of ceramic fiber with a diameter of 1-5 μm, crushing the ceramic fiber to have a length of 1-5 mm to obtain treated ceramic fiber; (2) Preparation of electrode: coat appropriate amount of capacitive carbon or graphene on the nickel foam as the negative electrode, and coat appropriate amount of manganese dioxide, copper cobalt oxide or nickel cobalt oxide on the nickel foam as the positive electrode; the active material loading is about 8-11 mg / cm 2 ; (3) Preparing supercapacitor: adding an appropriate amount of lithium salt, polymer and treated ceramic fiber of step (1) into Portland cement and stirring thoroughly, then pouring the mixture into a mold; inserting the electrode prepared in step (2), demolding and curing to obtain a ceramic fiber improved cement-based supercapacitor.

8. The method of claim 7, wherein: In step (3), the amount of lithium salt is 5-10 wt% of dry cement, and the amount of polymer is 2-6 wt% of dry cement; the water-cement ratio of the Portland cement is 0.3-0.5; and the polymer is polyacrylic acid / polyethylene oxide.

9. The method of claim 7, wherein: In step (4), the curing is performed at a temperature of 25±5 °C and a humidity of 90±5% for 28 days.

10. Use of a cement-based supercapacitor according to any one of claims 3-6, characterized in that: The application is used under the condition of a humidity of 100% or after the supercapacitor is soaked in water until saturated adsorption.

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