Composite material for continuous lithium extraction based on photo-thermal synergy, supercooled continuous lithium extraction method and application

Abstract

The invention discloses a composite material for continuous lithium extraction based on photo-thermal synergy, a supercooled continuous lithium extraction method and application, and belongs to the technical field of salt lake lithium extraction and heat energy management. According to the prepared floating type photo-thermal synergistic lithium extraction composite material, through the design of a three-layer composite structure, the synergistic function of temperature regulation and control, lithium ion adsorption and structure supporting is achieved, the problems that a traditional lithium adsorption material is prone to sedimentation and usually needs an additional supporting structure are solved, the density is smaller than that of water, and the composite material can stably float on the surface of salt lake brine; and large-scale deployment and recovery are facilitated.

Description

A composite material for continuous lithium extraction based on photothermal synergy, a method for continuous lithium extraction using supercooling, and its applications. Technical Field

[0001] This invention belongs to the field of lithium extraction and thermal energy management technology in salt lakes, specifically relating to a composite material for continuous lithium extraction based on photothermal synergy, a method for continuous lithium extraction using supercooling, and its applications. Background Technology

[0002] Lithium, dubbed the "white oil of the 21st century," is experiencing a surge in demand in fields such as new energy vehicles and energy storage systems. Global lithium demand is projected to reach 3 million tons of lithium carbonate equivalent by 2030. my country possesses over 60% of the world's lithium reserves in salt lakes, but traditional lithium extraction technologies suffer from long cycles, high energy consumption, and significant susceptibility to climate. Current salt lake lithium extraction technologies primarily include evaporation-precipitation, adsorption, and extraction. Traditional evaporation-crystallization methods require 6-24 months, with a lithium recovery rate of only 30-40%. Adsorption methods offer good selectivity but suffer from slow kinetics and high energy consumption. Direct lithium extraction (DLE) avoids large-area evaporation ponds, but separation efficiency still needs improvement under high magnesium-to-lithium ratios (Mg / Li>20), and often employs pump-driven circulation, resulting in complex processes and energy consumption typically of 3-6 kWh / kgLi₂CO₃. Solar-driven technology can increase adsorption rates by 1-2 times, but it is only effective during the day, lacks thermal management, and cannot operate continuously.

[0003] Lithium manganese oxide (Li 1.6 Mn 1.6 O4, LMO) serves as a spinel-type lithium-ion sieve, with a theoretical adsorption capacity of 50-60 mg / g, and is effective for Li-ion adsorption. + It exhibits good selectivity. However, the following problems exist: (1) the adsorption kinetics are slow at room temperature, requiring 12-24 hours to reach equilibrium; (2) Mn dissolution is severe, with Mn loss reaching 2.0-2.5% after 20 cycles; (3) it requires pump drive and stirring equipment, resulting in high energy consumption; (4) selectivity decreases in brines with high Mg / Li ratios, with a separation factor of only 20-50; (5) powdered LMO is easily lost and difficult to recover. Figure 1 shows the adsorption of lithium ions (S-OH + Li) by the lithium ion sieve in alkaline brine. + → SO Li + H + And the desorption of lithium ions in acidic solutions (SO₄²⁻, Li₂ + H₂O) + → S-OH + Li + The reversible reaction process provides a chemical basis for subsequent "photothermal synergistic lithium extraction".

[0004] Phase change materials (PCMs) have been extensively studied in the field of thermal energy storage. They are ideal thermal management materials because they can absorb or release large amounts of latent heat during phase change, making them particularly suitable for high-altitude salt lake regions with large diurnal temperature variations and abundant solar energy. They can store solar energy during the day and release heat at night to maintain continuous lithium extraction. However, existing PCMs generally suffer from problems such as difficulty in controlling supercooling, phase separation, and insufficient thermal conductivity, making it difficult to achieve long-term stable heat storage and precise on-demand heat release.

[0005] Inorganic hydrated salts such as sodium acetate trihydrate (SAT) and sodium silicate nonahydrate have advantages such as high phase change enthalpy (150-250 kJ / kg) and low cost, but they also have problems such as large supercooling and phase separation. Shin et al. thickened SAT with carboxymethyl cellulose (CMC) and modified it with expanded graphite (EG) to achieve a phase change enthalpy of 230.43 kJ / kg, enabling stable supercooling above 35℃ and improving photothermal conversion efficiency by 85%. Liu et al. introduced borax as a nucleation regulator to control the supercooling of SAT at 15-25℃, achieving controllable triggering release of latent heat, and maintaining the system temperature above the ambient temperature by more than 20℃ for up to 8 hours at night. Zhang et al. developed a eutectic system of SAT and sodium thiosulfate pentahydrate with a phase change temperature of 41-48℃ and a supercooling of >60℃, which can stably store heat for more than 10 days at -20℃. However, these studies mainly focus on building energy conservation and electronic thermal management, and their phase transition temperature and supercooling control targets are not designed for lithium extraction from salt lakes. They also fail to address key issues such as how to integrate with lithium adsorption materials and achieve long-term stable continuous operation in field day-night cycles. Therefore, there is an urgent need to develop a multifunctional material with controllable supercooling characteristics, high heat storage density, excellent photothermal conversion performance, and efficient integration with lithium-ion sieves to achieve continuous day-night lithium extraction.

[0006] Solar-enhanced lithium extraction technology has attracted attention in recent years. The solar-enhanced interfacial evaporation-ion adsorption system developed by Guo et al. can extract lithium... + The recovery capacity increased from 12.4 mg / g to 28.7 mg / g, and the adsorption rate doubled. The floating solar evaporator designed by Xu et al. achieved an evaporation rate of 1.5 kg·m³ under 1 day of sunlight. -2 ·h -1 Li + The concentration is enriched by 3-5 times. However, these technologies rely entirely on real-time light, are only effective during the day, and lack effective heat management, resulting in drastic temperature fluctuations in the system (the temperature difference between day and night can reach 30-40℃). This makes it impossible to achieve continuous and stable lithium extraction at night or on cloudy or rainy days, which seriously restricts the overall extraction efficiency and equipment utilization.

[0007] In summary, while existing technologies have made progress in lithium-ion sieves, phase change energy storage, and solar thermal energy, they have failed to achieve organic integration of these three technologies. In particular, there is a lack of solutions for utilizing controllable supercooled phase change materials to store daytime solar energy and precisely release it at night to maintain the adsorption temperature. Therefore, existing technologies cannot simultaneously meet the industrialization requirements of lithium extraction from salt lakes, which demand continuous day and night operation, precise temperature control, and simplified, low-consumption processes. Summary of the Invention

[0008] To address the aforementioned shortcomings in existing technologies, this invention provides a composite material for continuous lithium extraction based on photothermal synergy, a method for continuous lithium extraction under cooling, and its applications. This effectively solves the technical defects in existing technologies for lithium extraction from salt lakes, such as easy sedimentation of lithium adsorbent materials, large temperature fluctuations, low photothermal conversion efficiency, and poor day-night cycle stability.

[0009] To achieve the above objectives, the technical solution adopted by the present invention to solve its technical problems is as follows: The purpose of the present invention is to provide a composite material based on photothermal synergistic continuous lithium extraction, which includes a temperature control layer, a support layer, and an adsorption layer located between the two; the temperature control layer is a thermochromic composite phase change material, which has reversible color change characteristics and a supercooling effect, providing heat for the adsorption layer to adsorb lithium; the adsorption layer uses a core-sheath bicomponent polymer with floating characteristics and hydrophilic properties as the substrate, on which lithium ion sieve particles are fixed; the support layer is a thermoplastic film.

[0010] The technical principle of this invention is as follows: The continuous lithium extraction technology operates based on the supercooling effect and day-night temperature regulation: during the day, the photothermal conversion and heat storage characteristics of the thermochromic phase change material are used to maintain a suitable lithium adsorption temperature; at night, the supercooling characteristics of the phase change material are used to delay the heat release during the solidification process, thereby effectively extending the time the system temperature remains within the ideal adsorption temperature range. According to the thermophysical parameters of Dyn PCM material, this supercooling effect can delay the exothermic process for several hours to more than ten hours, providing thermal support for continuous lithium extraction at night, thus achieving continuous day-night operation.

[0011] Furthermore, the total thickness of the temperature control layer, the adsorption layer, and the support layer is 2~8mm, of which the thickness of the temperature control layer is 0.5~3mm; the thickness of the adsorption layer is 1~3mm; and the thickness of the support layer is 0.3~1.5mm.

[0012] Furthermore, the total thickness of the temperature control layer, the adsorption layer, and the support layer is 3~5mm, of which the thickness of the temperature control layer is 1~2mm; the thickness of the adsorption layer is 1.5~2.5mm; and the thickness of the support layer is 0.3~1.5mm.

[0013] Furthermore, the support layer is a polypropylene film or a polyethylene film.

[0014] Further, the preparation method of the temperature control layer is as follows: (1) Mix and heat the electron donor, electron acceptor and solvent to obtain a thermochromic agent solution; the mass ratio of electron donor, electron acceptor and solvent is 1~3:3~6:90~96; (2) Heat and melt the phase change matrix material and add it to the thermochromic agent solution, stir evenly and then cool and solidify to obtain a thermochromic composite phase change material; the mass ratio of phase change matrix material to thermochromic agent solution is 1~10:1.

[0015] Furthermore, the electron donor is a fluorane compound; the electron acceptor is a phenolic compound; and the solvent is a long-chain ester compound.

[0016] Furthermore, the mass ratio of electron donor, electron acceptor, and solvent is 2.3:4.7:93.

[0017] Furthermore, the electron donor is 2-phenylamino-3-methyl-6-dibutylaminofluorane; the electron acceptor is 2,2-bis(4-hydroxyphenyl)propane; and the solvent is 4-benzyloxyphenylethyl decanter.

[0018] Furthermore, the mass ratio of the phase change matrix material to the thermochromic agent solution is 3~7:1.

[0019] Furthermore, the mass ratio of the phase change matrix material to the thermochromic agent solution is 5:1.

[0020] Furthermore, the phase change matrix material is an organic phase change material.

[0021] Furthermore, the phase change matrix material is paraffin, fatty acids, etc.

[0022] The thermochromic composite phase change material prepared above has supercooling characteristics, and can remain in a liquid state below the phase change temperature during the cooling process, thus prolonging the heat release time; it appears dark in the solid low temperature and has strong light absorption ability; it appears transparent or translucent in the liquid high temperature and has high light transmittance; the solid-solid phase change temperature is 20~25℃, and the solid-liquid phase change temperature is 35~45℃, preferably 38~42℃.

[0023] Further, the preparation method of the adsorption layer is as follows: S1, Select a core-sheath bicomponent fiber made of polyolefin as the substrate, form a fiber web, then make a needle-punched felt substrate, and finally perform hydrophilic treatment with silicone oil to obtain a fiber substrate with floating characteristics and hydrophilic properties; S2, calcine the lithium manganese oxide precursor to obtain spinel structured lithium ion sieve particles, and then add water to form an LMO suspension with a mass concentration of 5~15wt%; S3, Immerse the fiber substrate obtained in S1 into the LMO suspension. After the fiber substrate has absorbed the LMO, take it out and freeze-dry it. Then heat it to soften the sheath layer in the fiber substrate and fix the lithium ion sieve particles. Finally, activate it by acid treatment to obtain a direct lithium extraction felt.

[0024] Furthermore, in the core-sheath bicomponent fiber, the volume ratio of the core layer to the sheath layer is 40~60:60~40, wherein the melting point of the core layer polyolefin is higher than that of the sheath layer polyolefin.

[0025] Furthermore, in the core-sheath bicomponent fiber, the volume ratio of the core layer to the sheath layer is 50:50.

[0026] Furthermore, the core layer polyolefin is polypropylene, and the sheath layer polyolefin is polyethylene.

[0027] Furthermore, the areal density of the needle-punched felt substrate is 80~120 g / m². 2 Preferably 90~100g / m 2 .

[0028] Furthermore, the silicone oil treatment time is 12~48h, and the water contact angle of the treated fiber substrate is less than 90°.

[0029] Furthermore, the water contact angle of the hydrophilic fiber substrate is 20~50°.

[0030] Furthermore, the lithium manganese oxide precursor is lithium manganese oxide powder, which is calcined at a temperature of 400~500℃ for 3~6h in an air or oxygen atmosphere.

[0031] Furthermore, the heating temperature in S3 is 120~140℃, and the heat treatment time is 10~25min.

[0032] Furthermore, the acid treatment activation is carried out at room temperature, with a soaking time of 2 to 8 hours, and the acid used is hydrochloric acid with a concentration of 0.05 to 0.2 M.

[0033] Furthermore, the acid concentration was 0.1M, and the soaking time was 4-6 hours.

[0034] Furthermore, the density of the obtained direct lithium extraction felt is less than that of water, preferably 0.90~1.00 g / cm³. 3 It can float stably on the water surface; wherein, the mass percentage of lithium ion screen particles is 5~15wt%, preferably 7~10.5wt%.

[0035] Another objective of this invention is to provide a method for preparing the above-mentioned composite material based on photothermal synergistic continuous lithium extraction. Specifically, the method involves heating the temperature control layer to a molten state, coating it onto the surface of the adsorption layer, cooling and solidifying it, then composited with a support film. After preheating at 60°C for 10 minutes, the temperature control layer material is bonded to the adsorption layer in a slightly molten state through hot-pressing.

[0036] Furthermore, the hot-pressing composite temperature is 120–140℃, the pressure is 0.3–0.8MPa, and the time is 30–90s.

[0037] Another object of the present invention is to provide the use of the above-mentioned composite material based on photothermal synergistic continuous lithium extraction in the preparation of lithium extraction devices.

[0038] Another object of the present invention is to provide the use of the above-described composite material or the above-described lithium extraction device based on photothermal synergy in continuous lithium extraction based on supercooling.

[0039] Another objective of this invention is to provide a lithium extraction device for salt lakes, comprising a salt lake brine pool, a composite material for continuous lithium extraction based on photothermal synergy, a temperature monitoring system, and a lithium ion collection system; wherein the composite material for continuous lithium extraction based on photothermal synergy floats on the surface of the salt lake brine, and achieves continuous lithium extraction day and night through natural sunlight irradiation and supercooling effect.

[0040] Another objective of this invention is to provide a continuous lithium extraction method based on supercooling, specifically as follows: in an alternating light and dark environment, lithium is extracted from salt lake brine using the aforementioned composite material based on photothermal synergistic continuous lithium extraction, or a lithium extraction device.

[0041] The beneficial effects of this invention are as follows: 1. This invention utilizes the supercooling characteristics of thermochromic composite phase change materials to prolong the heat release time during the nighttime cooling process, effectively maintaining the suitable temperature for lithium adsorption. This breaks through the limitation of traditional lithium extraction technology, which can only work under daylight conditions, and provides a solution for achieving efficient continuous day and night lithium extraction, greatly improving lithium extraction efficiency and equipment utilization.

[0042] 2. This invention uses a thermochromic composite phase change material as a temperature control layer, which has unique reversible color-changing characteristics and can automatically adjust the position of the photothermal interface according to the temperature, significantly improving the photothermal conversion efficiency and heat charging rate, and realizing efficient solar energy utilization and temperature stability.

[0043] 3. By utilizing the heat storage and heat release characteristics of phase change materials, this invention effectively regulates system temperature fluctuations, stabilizes the operating temperature within a suitable lithium adsorption temperature range, significantly reduces temperature fluctuation amplitude, significantly improves lithium adsorption efficiency, and maintains continuous and stable lithium extraction capability during day and night cycles.

[0044] 4. The floating photothermal synergistic lithium extraction composite material prepared by this invention achieves synergistic functions of temperature regulation, lithium ion adsorption and structural support through a three-layer composite structure design. It overcomes the problems of traditional lithium adsorption materials being prone to settling and usually requiring additional support structures. Its density is less than that of water, so it can float stably on the surface of salt lake brine, which is convenient for large-scale deployment and recycling.

[0045] 5. The direct lithium extraction felt of the present invention is prepared by combining core sheath fiber and lithium ion sieve particles, which maintains good flexibility and mechanical strength, and has excellent hydrophilicity. The hydrophilic porous structure can drive water to be transported upward, and while providing lithium ion adsorption, it can regulate the temperature through evaporation and cooling, and can also realize the self-cleaning function of surface salt crystals.

[0046] 6. The preparation process of this invention is simple and low-cost, requiring no additional energy equipment or complex control systems. It is entirely driven by natural solar energy, making it suitable for large-scale application in remote salt lakes. After long-term day-night cycle testing in outdoor environments, the material retains excellent phase change heat storage capacity and thermochromic function, demonstrating excellent long-term stability and weather resistance. Attached Figure Description

[0047] Figure 1 is a schematic diagram of the lithium-ion sieve suspension impregnation and heat treatment fixation process of the adsorption layer in Examples 1-3 of the present invention; Figure 2 is a schematic diagram of the chemical structure and color-changing mechanism of the thermochromic agent in Example 4 of the present invention, including the molecular structure of the electron donor and electron acceptor, the comparison of the chemical structure before and after color change, and the schematic diagram of the donor-acceptor interaction; Figure 3 is a flowchart of the mixed preparation of paraffin and thermochromic agent in Example 4 of the present invention; Figure 4 is a schematic diagram of the structure and operation of the thermochromic composite phase change material in Example 4 of the present invention; Figure 5 is a differential scanning calorimetry curve of the thermochromic composite phase change material in Examples 4-8 of the present invention; Figure 6 is a transmission spectrum of the thermochromic composite phase change material in Examples 4-8 of the present invention; Figure 7 is a schematic diagram of the floating three-layer composite lithium extraction film structure in Example 9 of the present invention; Figure 8 is a schematic diagram of the lithium-ion adsorption-desorption reaction principle and solar-driven lithium extraction operation in Examples 9-10 of the present invention; Figure 9 is a time series diagram of the camera in Example 11 of the present invention; Figure 10 is a temperature-time curve of Example 11 of the present invention during the day-night cycle. Detailed Implementation

[0048] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0049] Example 1: A method for preparing a solar-driven floating adsorption mat for lithium extraction from salt lakes, comprising the following steps (see Figure 1): Step 1: Preparation of the hydrophilic fiber substrate. Polypropylene / polyethylene (PP / PE) core-sheath bicomponent fibers are selected as the substrate. The core layer of the PP / PE core-sheath fiber is polypropylene (PP), and the sheath layer is polyethylene (PE), with a core-sheath volume ratio of 50:50. The PP / PE core-sheath fibers are processed by a carding machine to form a fiber web with an areal density of 96 g / m². 2 Subsequently, the fiber web was consolidated using a needle-punching process to obtain a needle-punched felt substrate. The needle-punched felt substrate was then immersed in a ternary silicone oil K-994 solution (diluted 300 times) for 24 hours for hydrophilication treatment. After removal, it was dried in a 60°C oven to obtain a hydrophilic fiber substrate with a water contact angle of approximately 35°.

[0050] Step 2: Preparation of Lithium-ion Sieve Particles. Lithium manganese oxide (LiMnO2) powder was placed in a muffle furnace and calcined at 450°C in air for 4 hours. After natural cooling to room temperature, Li-ion particles with a spinel structure were obtained. 1.6 Mn 1.6 O4(LMO) lithium-ion sieve particles, which are dark brown in color.

[0051] Step 3: Preparation of LMO suspension. Weigh the LMO particles prepared in step 2, add them to deionized water, and stir with a magnetic stirrer at room temperature to obtain an LMO suspension with a mass concentration of 10 wt%.

[0052] Step 4: Preparation of Direct Lithium Extraction Felt (DEF) The hydrophilic fiber substrate obtained in Step 1 is completely immersed in the LMO suspension prepared in Step 3; after removal, it is placed in a freeze dryer for freeze drying to remove all moisture; then the sample is placed in an oven and heat-treated at 130℃ for 18 min to soften the PE sheath and fix the LMO particles; after natural cooling to room temperature, a direct lithium extraction felt, denoted as DEF-9, is obtained, in which the mass percentage of LMO in DEF is 9 wt%.

[0053] Step 5: Acidification and activation of DEF. The DEF-9 obtained in Step 4 is immersed in a 0.1M hydrochloric acid solution at room temperature to activate the Li in the LMO particles. + Extracted and converted into H + After removal, rinse repeatedly with deionized water until neutral, and dry in a 60℃ oven to obtain activated DEF-9 for later use.

[0054] The DEF-9 material prepared in this embodiment has the following characteristics: surface density of approximately 120 g / m³. 2 It has a thickness of approximately 2mm and a density of approximately 0.95g / cm³. 3 (less than the density of water, 1 g / cm³) 3It can float on water; LMO particles are firmly attached to the surface of PP / PE core-sheath fibers; the material is dark brown and has high light absorption in the wavelength range of 250-1500 nm. These characteristics indicate that DEF-9 material has successfully achieved self-floating properties (density <1 g / cm³). 3 Its good hydrophilicity (contact angle <90°) lays the foundation for its photothermal adsorption application on the water surface.

[0055] Example 2 The preparation method of the direct lithium extraction felt in this example is different from that in Example 1, except that the mass concentration of LMO suspension in step 3 and the soaking process conditions in step 4 are adjusted. Finally, a direct lithium extraction felt with an LMO mass percentage of 7wt% is obtained, which is denoted as DEF-7.

[0056] Example 3 The preparation method of the direct lithium extraction felt in this example is different from that in Example 1, except that the mass concentration of LMO suspension in step 3 and the soaking process conditions in step 4 are adjusted. Finally, a direct lithium extraction felt with an LMO mass percentage of 10.5 wt% is obtained, which is denoted as DEF-10.5.

[0057] Comparative Example 1 This comparative example uses pure LMO particle powder as lithium adsorbent material without any carrier loading treatment, and is referred to as Pure-LMO.

[0058] In the lithium adsorption performance comparison experiment, the DEF-7, DEF-9, and DEF-10.5 samples prepared in Examples 1-3, and Pure-LMO powder loaded with an equal mass of LMO active ingredient, were placed in 100 mL of alkaline lithium solution (pH = 11) for testing to compare their adsorption performance. The results showed that under 1-2 sun irradiation, the lithium adsorption rate of DEF-9 reached approximately 9.37 mg / (g·h), significantly higher than that of the Pure-LMO powder that settled at the bottom (approximately 2.5 mg / (g·h)), with an adsorption efficiency improvement of over 40%.

[0059] The physical properties of the composite materials prepared in the embodiments of the present invention were characterized by testing. Specifically, the water contact angle was measured using a contact angle measuring instrument via the static drop method; the areal density was calculated based on the mass per unit area; the thickness was measured using a thickness measuring instrument (such as a micrometer); the density was obtained by the displacement method or by theoretical calculation based on the component density; and buoyancy was determined by observing the sample while it was still on the water surface.

[0060] Table 1 shows the material performance parameters of Examples 1-3 and Comparative Example 1, as detailed below: Table 1 Comparison of Physical Properties of DEF Materials in Different Examples

[0061] As shown in Table 1, the densities of the DEF materials prepared in Examples 1-3 are all less than 1.0 g / cm³. 3 It can float stably on the water surface, while the density of Pure-LMO in Comparative Example 1 is 3.86 g / cm³. 3 It sinks directly to the bottom of the water. The water contact angle of DEF material is between 35-42°, exhibiting good hydrophilicity.

[0062] Example 4: A method for preparing a thermochromic composite phase change material for lithium extraction from salt lakes, comprising the following steps (see Figures 2 and 3): Step 1: Preparation of thermochromic agent. Using an analytical balance, 0.083 g of 2-phenylamino-3-methyl-6-dibutylaminofluorane was weighed as an electron donor, and 0.169 g of 2,2-bis(4-hydroxyphenyl)propane was weighed as an electron acceptor; then 3.348 g of 4-benzyloxyphenylethyl decanter was placed in a beaker as a solvent, mixed evenly on a magnetic stirrer, and heated to 80°C to fully dissolve, to obtain a thermochromic agent solution, wherein the mass ratio of electron donor, electron acceptor and solvent was 2.3:4.7:93.

[0063] Step 2: Preparation of composite phase change material. 18.0g of paraffin wax is heated and stirred in a water bath at 80°C until completely melted. 3.6g of the thermochromic agent solution prepared in Step 1 is added, and stirring is continued for 30min until completely dissolved to obtain thermochromic composite phase change material. The mass ratio of paraffin wax to thermochromic agent is 5:1.

[0064] Step 3: Cooling and Curing. After holding the thermochromic composite phase change material obtained in Step 2 at a certain temperature for 1 hour, it is naturally cooled to room temperature to obtain the thermochromic composite phase change material, denoted as Dyn PCM5. In the Dyn PCM5 material prepared in this embodiment, the mass percentage of paraffin is 83.3 wt%, and the mass percentage of thermochromic agent is 16.7 wt%.

[0065] The molecular composite structure and solid-liquid phase change behavior of the thermochromic composite phase change material are shown in Figure 4.

[0066] Thermochromic Mechanism Explanation: As shown in Figure 2, the color change process of the thermochromic agent is a reversible electron transfer process. At low solid-state temperatures, the lactone ring in the electron donor 2-phenylamino-3-methyl-6-dibutylaminofluorane opens, combining with the hydroxyl group of the electron acceptor 2,2-bis(4-hydroxyphenyl)propane to form a large conjugated system, resulting in a black color. At high liquid-state temperatures, the hydroxyl group of the electron acceptor is in a free state, while the lactone ring in the electron donor closes, resulting in a transparent system. This reversible change from transparent to black allows the material to automatically regulate the position of the photothermal interface during the phase transition, ensuring the photothermal interface closely follows the melt front. The Dyn PCM temperature control layer material used in this process achieves a 260% higher heat charge rate compared to pure paraffin.

[0067] Example 5 The preparation method of the thermochromic composite phase change material in this example is different from that in Example 4, the only difference is that the mass ratio of paraffin to thermochromic agent in step 2 is 1:1. The thermochromic composite phase change material is finally obtained, which is denoted as Dyn PCM1.

[0068] Example 6 The preparation method of the thermochromic composite phase change material in this example is different from that in Example 4, the only difference is that the mass ratio of paraffin to thermochromic agent in step 2 is 2:1. The thermochromic composite phase change material is finally obtained, which is denoted as Dyn PCM2.

[0069] Example 7 The preparation method of the thermochromic composite phase change material in this example is different from that in Example 4, the only difference is that the mass ratio of paraffin to thermochromic agent in step 2 is 3:1, and the thermochromic composite phase change material is finally obtained, which is denoted as Dyn PCM3.

[0070] Example 8 The preparation method of the thermochromic composite phase change material in this example is different from that in Example 4, the only difference is that the mass ratio of paraffin to thermochromic agent in step 2 is 4:1. The thermochromic composite phase change material is finally obtained, which is denoted as Dyn PCM4.

[0071] Table 2 shows the phase change performance parameters of the composite phase change materials in Examples 4-8, as detailed below: Table 2 Comparison of thermophysical properties of composite phase change materials in different examples

[0072] Note: Dyn PCM6 data is not listed in Table 2 because the thermochromic agent content of the sample with this ratio (approximately 85.7 wt% paraffin content) was too low during the preparation process, resulting in an insignificant color-changing effect, which does not meet the design requirements of this invention, and therefore it was not included as a preferred embodiment.

[0073] As shown in Figure 5, the DSC curves reveal that the thermochromic composite phase change materials prepared in Examples 4-8 exhibit two stages: a solid-solid phase transition and a solid-liquid phase transition. The melting point of the solid-solid phase transition is between 22.9 and 23.5 °C, while that of the solid-liquid phase transition is between 39.3 and 39.7 °C. With increasing paraffin content, the enthalpy of fusion (ΔH) increases. m () Gradually increase.

[0074] As shown in Figure 6(f), the transmittance of the material in the ultraviolet and visible light range (250-800 nm) increases with the increase of paraffin mass fraction (corresponding to samples from DynPCM1 to DynPCM5). In the infrared range (800-2200 nm), the curve shows no obvious linear change. When the paraffin content is 83.3 wt% (DynPCM5), the total transmittance in the transparent state reaches 91.2%, which is basically equivalent to that of pure paraffin (92.0%). This proves that the composite system of the present invention can achieve high transmittance similar to that of paraffin while maintaining high enthalpy.

[0075] To evaluate the optical properties of the substrate materials themselves, Figure 6 further compares the transmittance of various common phase change materials at nanometer-scale thicknesses (5 nm and 10 nm). Transmittance data under these thickness conditions can reflect the intrinsic optical properties of the materials. As shown in Figure 6, paraffin wax exhibits a transmittance greater than 95% at both thicknesses. In contrast, sodium silicate nonahydrate has a transmittance of 78-75% at the corresponding thicknesses, and erythritol has 85-80%. The high intrinsic transmittance of paraffin wax allows the resulting composite material, when combined with a thermochromic agent, to maintain high transmittance even in the liquid state.

[0076] Example 9: Construction of a Three-Layer Composite Membrane After completing the preparation of the two functional materials described above, to further enhance the overall photothermal conversion and temperature control capabilities of the system, this invention further proposes a three-layer composite membrane structure, as shown in Figure 7. This structure includes: Layer 1 (Temperature Control Layer): The Dyn PCM5 thermochromic composite phase change material prepared in Example 4 is used as the temperature control layer. This layer has a transparent-to-black reversible color-changing characteristic; in its solid state, it is black and strongly absorbs sunlight, while in its liquid state, it is transparent and allows light to pass through.

[0077] Layer 2 (Adsorption Layer): The DEF-9 floating adsorption mat prepared in Example 1 or LMO particles can be used directly as the lithium ion adsorption layer. This layer is responsible for selectively adsorbing lithium ions from the brine of the salt lake.

[0078] Layer 3 (Support Layer): A polypropylene (PP) film or a polyethylene (PE) film is used as the support layer to provide mechanical strength and structural stability.

[0079] The preparation method is as follows: Dyn PCM5 is heated to a molten state (about 60°C) and uniformly coated onto the surface of DEF-9 or LMO adsorption layer using a coating or casting process, with the coating thickness controlled to be about 250μm; after cooling and solidification, a PP or PE support film is laminated at the bottom. After preheating at 60°C for 10 minutes, the temperature and pressure of the hot pressing are optimized so that the temperature control layer material is combined with the adsorption layer in a slightly molten state, which not only ensures the interlayer bonding strength but also avoids damaging the porous hydrophilic structure of the adsorption layer, thus achieving three-layer integrated integration.

[0080] The structural parameters of the three-layer composite membrane are as follows: The total thickness of the composite membrane is approximately 3-5 mm, of which Layer 1 (temperature control layer, DynPCM5 thermochromic composite phase change material) is approximately 1-2 mm thick, Layer 2 (adsorption layer, DEF-9 floating adsorption felt) is approximately 2 mm thick, and Layer 3 (support layer, PP or PE membrane) is approximately 0.5-1 mm thick. The overall density of the composite membrane is <1.0 g / cm³, allowing it to float stably on the surface of salt lake brine.

[0081] Figure 8 clearly illustrates the three-layer integrated structure of this floating composite membrane: the top temperature control layer is black (solid) or transparent (liquid) and is responsible for receiving solar radiation; the middle adsorption layer is a dark brown LMO particle-supported layer with a good hydrophilic porous structure; and the bottom support membrane ensures the overall mechanical strength and floating stability. This structural design achieves an organic unity of lightweight, buoyancy, and multifunctional integration. In this three-layer composite structure, a stable interfacial bond is formed between the temperature control layer and the adsorption layer. The phase transition process of the temperature control layer does not affect the hydrophilic porous channels of the adsorption layer, ensuring that water and ions can be continuously transported upwards to the adsorption sites.

[0082] Example 10: Photothermal Synergistic Mechanism of Composite Membrane As shown in Figure 8, the working mechanism of the three-layer composite membrane in the diurnal cycle of lithium extraction from salt lake is as follows: Daytime: In the early morning or at the beginning of sunlight, due to the nighttime cooling, Dyn PCM5 is in a solid black state, strongly absorbing sunlight and converting it into heat energy; as the temperature rises to the phase transition temperature (39.5℃), Dyn PCM5 gradually melts and becomes a transparent liquid, allowing light to penetrate to the LMO adsorption layer. The LMO layer continues to absorb heat and adsorb lithium ions; the hydrophilic porous structure of DEF-9 continuously drives the upward transport of water, evaporating and carrying away excess heat, maintaining a stable system temperature. The evaporation and cooling process of DEF-9, combined with the dynamic photothermal interface advancement of the temperature control layer, enables the system to maintain a stable operating temperature under illumination conditions.

[0083] Nighttime: Dyn PCM5 solidifies from a transparent liquid to a black solid, releasing stored heat, slowing down the system temperature drop, and maintaining a suitable lithium adsorption temperature; DEF-9 adsorbs moisture on its surface, dissolving the salt crystals that precipitate during the day, thus achieving self-cleaning.

[0084] This synergistic mechanism enables the dynamic volume absorption effect of the photothermal interface to automatically track the melt front, achieving a solar energy utilization efficiency of 71.5%. Experimental data show that the system equipped with the Dyn PCM5 temperature control layer has a 260% higher heat charging rate compared to pure paraffin, with temperature fluctuations controlled within the range of 38-46℃, which is as close as possible to the optimal temperature range for lithium ion adsorption. The lithium adsorption efficiency is more than 40% higher than that of traditional methods.

[0085] Example 11: Day and Night Cycle Environmental Test for Lithium Extraction from Salt Lake. The three-layer composite membrane prepared in Example 9 was floated in simulated salt lake brine, and daytime solar irradiance was simulated using a solar simulator (energy flux density 0.3 kW / m³). 2 The ambient temperature was set to 25℃ to simulate the diurnal cycle of lithium extraction from a salt lake. Thermocouples and infrared thermal imagers were used to monitor system temperature changes and to determine lithium adsorption and evaporation rates.

[0086] Test conditions: 12 hours of light exposure, 12 hours of darkness, repeated for 30 consecutive days. Brine composition: Na. + Concentration approximately 10.8 g / L, Li + The concentration is approximately 170 μg / L, and the pH value is 11.

[0087] Temperature Field Monitoring and Dynamic Analysis: To intuitively reveal the spatiotemporal temperature distribution characteristics of the system during operation, an infrared thermal imager was used to continuously monitor the floating three-layer composite film. As shown in Figure 9, the continuous thermal imaging time series (0s to 360s) clearly records a complete heating and phase transition triggering process: In the initial stage of illumination (0-90s), the material surface temperature rises uniformly and rapidly; during 90-240s, when the temperature reaches the phase transition point (approximately 39.5℃), a clear phase transition front can be observed advancing from the surface inwards, and the high-temperature region (red) in the thermal image gradually expands, while the overall material temperature remains at a stable plateau. This directly confirms the significant buffering and storage effect of the latent heat of phase transition on heat; in the subsequent time (240-360s), the system enters a stable liquid working region with excellent temperature uniformity. The above temperature field evolution process is consistent with the temperature-time curve shown in Figure 10, quantitatively characterizing the temperature control capability of the Dyn PCM5 material.

[0088] As shown in Figure 10, the temperature-time curves reveal that the system equipped with the three-layer composite membrane maintained a stable maximum temperature of around 42°C during the day, while the control group without the PCM layer reached a maximum temperature exceeding 58°C. During the nighttime cooling process, the composite membrane system exhibited a significantly slower temperature decrease rate than the control group, effectively delaying the temperature drop.

[0089] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A composite material based on photothermal synergistic continuous lithium extraction, characterized in that, It includes a temperature control layer, a support layer, and an adsorption layer located between the two; the temperature control layer is a thermochromic composite phase change material, which has reversible color change characteristics and a supercooling effect, providing heat for the adsorption layer to adsorb lithium; the adsorption layer uses a core-sheath bicomponent polymer with floating characteristics and hydrophilic properties as the substrate, on which lithium ion sieve particles are fixed; the support layer is a thermoplastic film.

2. The composite material based on photothermal synergistic continuous lithium extraction according to claim 1, characterized in that, The total thickness of the temperature control layer, adsorption layer and support layer is 2~8mm, of which the thickness of the temperature control layer is 0.5~3mm; the thickness of the adsorption layer is 1~3mm; and the thickness of the support layer is 0.3~1.5mm.

3. The composite material based on photothermal synergistic continuous lithium extraction according to claim 1 or 2, characterized in that, The preparation method of the temperature control layer is as follows: (1) Mix and heat the electron donor, electron acceptor and solvent to obtain a thermochromic agent solution; the mass ratio of the electron donor, electron acceptor and solvent is 1~3:3~6:90~96; (2) Heat and melt the phase change matrix material and add it to the thermochromic agent solution, stir evenly and then cool and solidify to obtain a thermochromic composite phase change material; the mass ratio of the phase change matrix material to the thermochromic agent solution is 1~10:

1.

4. The composite material based on photothermal synergistic continuous lithium extraction according to claim 3, characterized in that, The electron donor is a fluorane compound; the electron acceptor is a phenolic compound; and the solvent is a long-chain ester compound.

5. The composite material based on photothermal synergistic continuous lithium extraction according to claim 3, characterized in that, The phase change matrix material is an organic phase change material.

6. The composite material based on photothermal synergistic continuous lithium extraction according to claim 1 or 2, characterized in that, The preparation method of the adsorption layer is as follows: S1. Select a core-sheath bicomponent fiber made of polyolefin as the substrate, make it into a fiber web, then make it into a needle-punched felt substrate, and finally perform hydrophilic treatment with silicone oil to obtain a fiber substrate with floating properties and hydrophilic properties. S2. Calcining the lithium manganese oxide precursor to obtain spinel-structured lithium-ion sieve particles, and then adding water to form an LMO suspension with a mass concentration of 5~15wt%; S3. Immersing the fiber substrate obtained in S1 into the LMO suspension. After the fiber substrate has absorbed the LMO, it is taken out and freeze-dried, and then heated to soften the sheath layer in the fiber substrate and fix the lithium-ion sieve particles. Finally, it is activated by acid treatment to obtain a direct lithium extraction felt.

7. The composite material based on photothermal synergistic continuous lithium extraction according to claim 6, characterized in that, In the core-sheath bicomponent fiber, the volume ratio of the core layer to the sheath layer is 40~60:60~40, wherein the melting point of the core layer polyolefin is higher than that of the sheath layer polyolefin.

8. The use of the composite material based on photothermal synergistic continuous lithium extraction as described in any one of claims 1 to 7 in the preparation of a lithium extraction device.

9. The use of the composite material based on photothermal synergistic continuous lithium extraction as described in any one of claims 1 to 7 or the lithium extraction device as described in claim 8 in continuous lithium extraction based on supercooling.

10. A continuous lithium extraction method based on supercooling, characterized in that, In an alternating light and dark environment, lithium is extracted from salt lake brine using the composite material based on photothermal synergistic continuous lithium extraction as described in any one of claims 1 to 7, or the lithium extraction device as described in claim 8.

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