Lithium slag-based polymer microsphere composite phase change energy storage material and preparation method thereof

Abstract

The application provides a composite phase change energy storage material using spodumene lithium extraction tailings (lithium tailings) as a carrier and a preparation method thereof. The geopolymer microspheres are prepared by a dispersion suspension method, and are washed, dried and calcined. Then, through heating and vacuum impregnation, the phase change energy storage material is stably encapsulated in the geopolymer microspheres, and a shaped composite phase change energy storage material is obtained. The application not only provides a phase change energy storage material with large heat storage capacity, excellent encapsulation performance, good chemical stability, strong anti-leakage capacity, strong cycle stability, strong heat conduction capacity and good light-heat conversion capacity, but also provides a new high-value utilization method of spodumene lithium extraction tailings.

Description

Technical Field

[0001] This invention belongs to the field of materials technology and relates to composite phase change energy storage materials with geopolymer microspheres as carriers and their preparation methods. It also proposes a high-value-added resource utilization method for lithium spodumene tailings (lithium slag). Background Technology

[0002] In the development of the new energy industry, lithium salts are key source materials for electrochemical energy storage, primarily derived from spodumene roasted with sulfuric acid. However, this traditional process generates a large amount of residual tailings after lithium extraction, referred to as lithium slag, which not only wastes resources but also causes significant environmental pollution. Therefore, in-depth exploration of the effective recycling and reuse of lithium slag is of great importance. Previous studies on the application of lithium slag have mainly focused on the following: Zhang Hongquan et al. (2021) used lithium slag as the main raw material to prepare a foam ceramic material with uniform pore distribution and suitable pore size, exhibiting a compressive strength of 4.14 MPa and a thermal conductivity of 0.282 W·m. -1 ·K -1 The main chemical elements in lithium slag include Si and Ca. By precisely adjusting the elemental ratios in the raw materials, lithium slag can be transformed into raw materials for cement production, thus realizing the resource utilization of tailings and promoting environmental protection and sustainable development. Quan Zonggang et al. (2022) prepared autoclaved aerated concrete blocks using lithium slag as the main siliceous raw material. They studied the effects of ball milling time, formula, static curing time, and static curing temperature on the dry density and compressive strength of the autoclaved aerated concrete blocks, and finally determined the optimal formula for preparing concrete using lithium tailings. Wu Ji et al. (2021) developed a lithium slag-based insulation board with low thermal conductivity, high strength, adjustable size, and long service life using lithium slag as the main raw material. It has excellent thermal insulation performance and is very lightweight, showing broad application prospects in the field of building materials. The above inventions provide good ideas for the utilization of lithium slag.

[0003] Geopolymers, or geopolymers for short, are amorphous materials with a three-dimensional network structure formed by an alkaline-activated reaction of reactive silica-alumina raw materials. They consist of [SiO4] and [AlO4] linked by O-bridges and are considered a novel, environmentally friendly mineral cementing material. Lithium slag's main chemical components are SiO2 and Al2O3, making it suitable for preparing geopolymers. For example, Lemougna et al. (2020) prepared geopolymers using 20% ​​kaolinite and 80% lithium slag as raw materials. These geopolymers achieved a 7-day compressive strength of nearly 50 MPa and a high-temperature stability of 1100–1200℃, demonstrating excellent performance and functional applications. However, how to leverage the superior properties of geopolymers to achieve high-value utilization of lithium slag remains a significant research focus in lithium slag treatment.

[0004] On the other hand, the energy crisis is one of the most important problems facing human society. Energy storage technology significantly improves energy utilization efficiency by resolving the contradiction between energy supply and demand in time and space, thus becoming one of the important technical means to solve energy and environmental problems. Among them, thermal energy storage is an important method. According to different thermal storage principles, thermal storage technology is divided into sensible thermal storage, latent thermal storage, and chemical thermal storage. Latent thermal storage utilizes the large amount of latent heat absorbed and released during the phase change process of phase change materials to store energy. That is, the thermal storage process is a process of phase change of matter through melting or solidification. Compared with other thermal storage technologies, it has the advantages of high thermal density, recyclability, and environmental friendliness. Phase change energy storage materials refer to materials that can absorb and release a large amount of latent heat during the phase change process, including organic phase change materials and inorganic phase change materials. Among them, organic phase change materials such as paraffin wax and polyethylene glycol have the advantages of high thermal storage efficiency, small temperature change, and low cost, and have a very broad application prospect.

[0005] However, organic phase change materials (PCMs) often suffer from poor thermal conductivity and liquid leakage during thermal energy storage and release, making them unsuitable for direct use alone. They typically require shaped-structured PCM technology, which combines organic PCMs with high thermal conductivity and high stability encapsulation materials to create shaped composite PCMs. Currently, the main methods for preparing composite PCMs include microencapsulation, porous inorganic carrier methods, sol-gel methods, pressing and sintering methods, and melt blending methods, which can effectively solve the leakage problem of organic PCMs. Among these, the porous inorganic carrier method mainly utilizes the large specific surface area of ​​porous media, the capillary effect of the pore structure, and the high thermal conductivity of its own solid framework to achieve effective encapsulation and support of the PCM. Currently, there are no research reports on the use of geopolymer microspheres as carriers for the preparation of composite PCMs.

[0006] This invention employs lithium slag to first prepare porous geopolymer microspheres, and then uses high thermal conductivity materials such as nanoscale graphite, carbon nanotubes, and graphene as thermal conductivity modifiers to enhance the heat transfer effect of the geopolymer microspheres. The prepared geopolymer microspheres are then used to encapsulate organic phase change materials to prepare shaped composite phase change thermal storage materials. This is not only significant for the resource utilization of lithium slag and the solution of environmental problems, but also holds promise for important applications in the field of new energy materials. Summary of the Invention

[0007] In this invention, lithium slag-based polymer microspheres are first prepared, and then combined with phase change thermal storage materials to prepare a composite phase change energy storage material of lithium slag-based polymer microspheres / organic phase change material, thereby significantly improving the heat transfer performance and thermal stability of the composite phase change material. Furthermore, graphite-modified lithium slag-based polymer microspheres can be prepared by adding 0.5% graphite to the lithium slag to further improve the thermal conductivity of the composite phase change energy storage material.

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

[0009] Lithium slag base polymer microspheres ------------------------ 30wt%~50wt%

[0010] Phase change materials --------------------------------- 50wt%~70wt%

[0011] The phase change material is characterized in that it is an organic phase change material, an inorganic phase change material, or a composite phase change material of organic and inorganic materials. Organic phase change materials include paraffin, stearic acid, lauric acid, polyols, etc.; inorganic phase change materials include CaCl2·6H2O, Na2SO4·10H2O, MgCl2·6H2O, Al(NO3)3·6H2O, etc. The phase change material can be one of these materials or any combination thereof.

[0012] This invention also relates to a method for preparing the above-mentioned lithium slag-based composite phase change energy storage material, wherein the preparation method and its features are as follows:

[0013] Step 1: Add 12-16 parts by mass of lithium slag, 1-4 parts by mass of thermally conductive modifier and 6-10 parts by mass of water to 15-20 parts by mass of 10-13 mol / L NaOH solution. After stirring evenly, add 6-10 drops of H2O2 solution with a concentration of 10wt%-30wt%. Stir for 1 minute at a speed of 500-1000 r / min to prepare a uniform slurry. It should be noted that in this system, if the concentration and mass of the NaOH solution and the mass of the lithium slag are too high or too low, the viscosity of the slurry will be correspondingly high or low, which is not conducive to the formation of microspheres. The addition of H2O2 solution is to enable foaming and the formation of more pores in the microspheres. If too much H2O2 solution is added, it will not be conducive to the formation, and the strength of the resulting material will be too low to be usable. If too little H2O2 solution is added, it will result in low porosity of the geopolymer, thereby reducing the loading effect of the geopolymer microspheres. The thermal conductivity modifier mentioned can be one or a combination of several of the following: nanoscale graphite, carbon nanotubes, and graphene. This is because carbon-based nanomaterials are mainly non-polar, which is conducive to the dispersion of bubbles in the spheres. Too much addition is not conducive to the formation, while too little addition will result in poor thermal conductivity.

[0014] Step 2: Using a dropper, drip the slurry from Step 1 into silicone oil at a rate of 50-90 drops per minute, which is stirred at 600-1200 rpm at a temperature of 70-85°C and a viscosity of 1000-2000 cs. After the slurry is dispersed into microspheres by the silicone oil and solidifies, place the entire mixture in an oven at 75-90°C for curing for 24-72 hours. In this step, it should be noted that if the slurry is dripped too quickly, adhesion will occur; if the dripping speed is too slow, the temperature of the silicone oil will decrease, thus reducing sphericity. When the silicone oil temperature is too low, the alkali-activated reaction rate decreases, which is not conducive to the formation of geopolymer microspheres. When the silicone oil temperature is too high, the previously dissolved reaction components will rapidly depolymerize and condense to form geopolymer gel covering the unreacted raw material particles, which is not conducive to further alkali-activated reaction. If the viscosity of the silicone oil is too high or too low, it will not be conducive to the formation of lithium slag-based geopolymer microspheres. The prepared lithium slag-based geopolymer microspheres must be spherical, with a particle size preferably of 100-400 μm and a pore size preferably of 0-10 nm. This is because poor sphericity will reduce the loading effect on the phase change material; if the particle size or pore size of the geopolymer microspheres is too large, leakage is likely to occur; if the particle size is too small, it will affect the loading efficiency of the phase change material.

[0015] Step 3: Filter out the microsphere product obtained in Step 2, wash it with 75%-95% ethanol solution, and dry it at 120℃ for 4-8 hours to remove the silicone oil adhering to the surface.

[0016] Step 4: Calcine the product obtained after drying in step 3 at 500℃ for 1-5 hours to fully remove excess silicone oil from the surface and internal pores of the microspheres.

[0017] Step 5: Load excess phase change material into the load device and melt it completely within a temperature range 10-20℃ higher than the melting temperature of the selected phase change energy storage material. Completely immerse the geopolymer microspheres obtained in Step 4 into the device containing excess molten liquid phase change material. Under the conditions of device pressure of -0.05 to -0.1 MPa and temperature of 60 to 150℃ (the specific temperature is adjusted according to the phase change material itself), continuously pump the vacuum pump for 15-30 minutes, then turn off the vacuum pump and maintain this state for 2-4 hours to promote the molten phase change material to fully enter the pores of the geopolymer microspheres. Open the vent valve to restore the internal pressure of the vacuum device to normal, thereby initially obtaining the composite phase change energy storage material.

[0018] Step 6: Place the product obtained in Step 5 on filter paper and perform leakage treatment in an oven at a temperature near the phase change temperature of the phase change material to remove excess phase change material that is not stably encapsulated in the geopolymer microspheres. Continuously replace the filter paper until obvious marks appear on the filter paper. After the treatment is completed, a composite phase change energy storage material product with lithium slag geopolymer microspheres as the carrier can be obtained.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] This invention presents a novel method for utilizing lithium spodumene tailings resources; based on this method, the prepared geopolymer microspheres have a surface area of ​​11.36 m². 2 / g, with an average pore size of 28.376nm, rich pore structure, and excellent encapsulation ability; the composite phase change energy storage material prepared by using graphite-modified lithium slag-based polymer microspheres has excellent thermal storage performance, with significantly improved thermal conductivity and stability. Attached Figure Description

[0021] Figure 1 A stereomicroscopic photograph of the lithium slag-based polymer microspheres used in Example 1;

[0022] Figure 2 The mercury intrusion curves and pore size distribution of the lithium slag-based polymer microspheres used in Example 1 are shown in Figure 1.

[0023] Figure 3 The XRD patterns of the composite phase change energy storage prepared in Examples 1 and 2 are shown.

[0024] Figure 4 Infrared spectra of the composite phase change energy storage prepared in Examples 1 and 2;

[0025] Figure 5 The thermal analysis curves are those of the composite phase change energy storage materials prepared in Examples 1 and 2. Detailed Implementation

[0026] Example 1: Preparation of composite phase change thermal storage materials using geopolymer microspheres loaded with polyethylene glycol 4000

[0027] (1) Geopolymer microspheres were prepared by dispersion suspension method. 20g of lithium slag and 12g of water were added to 25g of 11mol / L NaOH solution and stirred evenly. Then, 8 drops of H2O2 solution were added and stirred for 1min at 1000r / min to form a uniform slurry. The slurry was then rapidly dripped into 85℃ silicone oil stirred at 800r / min at a rate of 60 drops per minute. The slurry was dispersed into microspheres under the shear force of the silicone oil and solidified rapidly. The silicone oil containing the slurry was then placed in an 85℃ oven for 72h. The resulting product was filtered, washed, dried at 120℃ for 8h, and then calcined at 500℃ for 5h to remove excess silicone oil from the surface and internal pores of the microspheres. Finally, the microspheres were sieved to obtain geopolymer microspheres with a diameter of 100-400μm.

[0028] (2) Load excess polyethylene glycol 4000 into the loading device and melt it at a temperature of 70°C.

[0029] (3) The treated geopolymer microspheres were completely immersed in a liquid phase device containing excess molten polyethylene glycol 4000, and then placed in a vacuum drying oven. The device was continuously evacuated for 15 minutes at 70°C and then left to stand for 2 hours at -0.09 MPa and 70°C before being removed.

[0030] (4) Leakage: The sample was placed on filter paper and leaked in an 85°C oven. During this process, the filter paper was continuously replaced until no more polyethylene glycol 4000 was precipitated. Finally, the prepared geopolymer microsphere-polyethylene glycol 4000 composite phase change energy storage material was obtained.

[0031] The performance indicators of the obtained samples are as follows: the pore structure and pore size distribution of the lithium slag-based polymer microspheres after treatment are as follows: Figure 1 and Figure 2 As shown, the prepared geopolymer microspheres exhibit good sphericity and uniform particle size distribution (100–400 μm). The pore size of the microspheres is mainly distributed in the range of 0–10 nm, exhibiting microporous and mesoporous structures, with a few macropores also present. The specific surface area is 11.36 m². 2 / g, with an average pore size of 28.376nm. The X-ray diffraction results of the packaged sample are as follows: Figure 3 As shown, the sample's phases are LiAlSi2O6 and polyethylene glycol 4000, indicating that polyethylene glycol 4000 was successfully loaded into lithium slag-based polymer microspheres; the infrared spectrum of the encapsulated sample is shown below. Figure 4 As shown, the infrared spectrum of the sample mainly originates from lithium slag and polyethylene glycol 4000, indicating that polyethylene glycol 4000 was successfully loaded into the lithium slag-based polymer microspheres. The loading rate of polyethylene glycol 4000 on the lithium slag-based polymer microspheres is 42.16%, with a latent heat of fusion of 79.28 J / g and a maximum latent heat of solidification of 71.84 J / g. The prepared material was tested using a heat flow meter thermal conductivity meter, and the obtained sample thermal conductivity was 0.0611 W·m. -1 ·K -1 .

[0032] Example 2: Preparation of composite phase change thermal storage materials using graphite-modified geopolymer microspheres loaded with polyethylene glycol 4000

[0033] (1) Preparation of microspheres: 20g of lithium slag, 0.45g of graphite and 12g of water were added to 25g of 11mol / L NaOH solution. After stirring evenly, 8 drops of H2O2 solution were added and stirred for 1min at 1000r / min to form a uniform slurry. The slurry was then rapidly dripped into 85℃ silicone oil stirred at 800r / min at a rate of 60 drops per minute. The slurry was dispersed into microspheres under the shear force of the silicone oil and solidified rapidly. The silicone oil with the slurry was then placed in an 85℃ oven for 72h. The resulting product was filtered, dried at 120℃ for 8h, and then calcined at 500℃ for 5h to remove excess silicone oil from the surface and internal pores of the microspheres. Finally, the microspheres were sieved to obtain graphite-modified geopolymer microspheres of 100-400μm.

[0034] (2) Load excess polyethylene glycol 4000 into the loading device and melt it at a temperature of 70°C.

[0035] (3) The treated graphite-modified geopolymer microspheres were completely immersed in a liquid phase device containing excess molten polyethylene glycol 4000, and then placed in a vacuum drying oven. The oven was continuously evacuated for 15 minutes at 70°C, and then left to stand for 2 hours at -0.09 MPa and 70°C before being removed.

[0036] (4) Leakage: The sample was placed on filter paper and leaked in an 85°C oven. During this process, the filter paper was continuously replaced until no more polyethylene glycol 4000 was precipitated. Finally, the graphite-modified geopolymer microsphere-polyethylene glycol 4000 composite phase change energy storage material was obtained.

[0037] The performance indicators of the obtained samples are as follows: the graphite-modified geopolymer microspheres have a loading rate of 42.16% for polyethylene glycol 4000, with a maximum latent heat of fusion of 79.28 J / g and a maximum latent heat of solidification of 71.84 J / g. By utilizing graphite to enhance the heat transfer effect of the geopolymer microspheres, the overall thermal conductivity of the geopolymer microspheres was successfully increased by 46.15% to 0.0893 W·m⁻¹·K⁻¹.

[0038] In summary, this invention uses lithium slag to prepare geopolymer microspheres and graphite-modified geopolymer microspheres as carriers, and prepares composite phase change energy storage materials by loading phase change materials. The porous spherical phase change materials prepared by vacuum impregnation method have high loading rate, excellent thermal stability, good thermal conductivity, high latent heat of melting, and high latent heat of solidification.

[0039] The present invention has been described in detail above with reference to preferred embodiments and exemplary examples. However, it should be noted that these specific embodiments are merely illustrative explanations of the invention and do not constitute any limitation on the scope of protection of the invention. Various improvements, equivalent substitutions, or modifications can be made to the technical content and embodiments of the present invention without departing from the spirit and scope of protection of the invention, and all such modifications fall within the scope of protection of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A composite phase change energy storage material with lithium slag-based polymer microspheres as carriers, characterized in that The raw materials include the following weight parts: Lithium residue based polymer microspheres 30wt%-50wt%, Phase change material 50wt%-70wt%; The lithium residue based polymer microspheres have a spherical shape, a particle size of 100-400 μm, and a pore size of 0-10 nm; the phase change material is PEG4000; the thermal conductive modifier used in the lithium residue based polymer microspheres can be one or a combination of several of nanoscale graphite, carbon nanotubes, and graphene; The lithium residue based polymer microspheres are prepared by the following steps: Step 1.

1. 12-16 parts by mass of lithium residue, 1-4 parts by mass of a thermal conductive modifier, and 6-10 parts by mass of water are added to 15-20 parts by mass of a 10-13 mol / L NaOH solution, which is stirred uniformly. Then, 6-10 drops of a 10wt%-30wt% H2O2 solution are added, and the mixture is stirred at a speed of 500-1000 r / min for 1 min to form a uniform slurry. Step 1.

2. The slurry obtained in step 1.1 is dropped into silicon oil with a viscosity of 1000 cs-2000 cs at a temperature of 70-85℃ and a stirring speed of 600-1200 r / min at a rate of 50-90 drops per minute using a rubber head dropper. After the slurry is dispersed into microspheres and solidified, the whole is placed in an oven at a temperature of 75-90℃ for 24-72 h. Step 1.

3. The microspheres obtained in step 1.2 are filtered out and washed with a 75%-95% ethanol solution, and then dried at 120℃ for 4-8 h to remove excess silicon oil on the surface of the microspheres. Step 1.

4. The lithium residue based polymer microspheres obtained after drying in step 1.3 are calcined at 500℃ for 5 h to remove excess silicon oil on the surface and in the pores of the microspheres, and finally obtain the lithium residue based polymer microspheres.

2. The method of claim 1, wherein the lithium slag-based polymer microspheres are prepared by the steps of: The steps include the following: ​ Step 2.

1. Excess phase change material is loaded into a loading device and completely melted at a temperature 10-20℃ higher than the melting temperature of the selected phase change energy storage material. The obtained polymer microspheres are completely immersed in a device containing excess molten liquid phase phase change material. The device is maintained at a pressure of -0.05 to -0.1 MPa and a temperature of 60-150℃, and the specific temperature is adjusted according to the phase change material itself. A vacuum pump is used to continuously extract for 15 min, the vacuum pump is turned off and the state is maintained for 2 h, which promotes the molten phase change material to fully enter the pores of the microspheres. The air valve is opened to restore the internal pressure of the vacuum device to normal, thereby obtaining a preliminary composite phase change energy storage material. Step 2.2, place the product obtained in step 2.1 on filter paper, and perform leakage treatment in an oven at a temperature near the phase change temperature point of the phase change material, remove the excess phase change material not stably encapsulated in the geopolymer microspheres, continuously replace the filter paper until no obvious marks are left on the filter paper, and the composite phase change energy storage material product with lithium residue geopolymer microspheres as the carrier is obtained after the treatment is completed.

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