A method of iodine-induced lithium intercalation exfoliation of two-dimensional materials

Abstract

This invention relates to a method for iodine-induced lithium intercalation and exfoliation of two-dimensional materials, comprising the following steps: uniformly mixing a target bulk layered material with an inorganic salt to obtain mixture A; the inorganic salt contains lithium iodide; heating mixture A to 280–400°C under a vacuum environment or protective atmosphere, while simultaneously applying ultraviolet light irradiation, and obtaining mixture B through solid-state lithiation treatment; dispersing mixture B in deionized water, and obtaining the two-dimensional material through hydrolysis exfoliation, separation, washing, and drying. This invention uses an inorganic salt containing lithium iodide as the intercalation medium, and through the synergistic excitation of a light field and a thermal field, induces the oxidative decomposition of halide ions and the release of electrons, driving alkali metal ions to intercalate into the interlayer gaps of the bulk layered material to achieve in-situ solid-state intercalation. Then, through hydrolysis exfoliation, an ultrathin two-dimensional material with a large lateral dimension is obtained. The process is safe, has high intercalation efficiency, and good versatility.

Description

Technical Field

[0001] This invention belongs to the field of two-dimensional layered materials, specifically relating to a method for iodine-induced lithium intercalation and exfoliation of two-dimensional materials. Background Technology

[0002] Two-dimensional layered materials, due to their unique electronic, optical, mechanical, and thermal properties, have shown great potential for applications in next-generation electronic devices, energy storage, catalysis, and composite materials. However, achieving the large-scale preparation of high-quality, large-size, and ultrathin two-dimensional nanosheets, especially developing universal preparation methods for various material systems with different chemical stabilizations, remains a major challenge.

[0003] Two-dimensional layered materials are mainly prepared by exfoliation. Common exfoliation methods include mechanical exfoliation, liquid-phase exfoliation, and intercalation exfoliation. Among them, mechanical exfoliation uses adhesive tape to separate layered compound crystals to obtain thin layers, but the yield is extremely low and difficult to scale up. Although common liquid-phase intercalation and solvothermal reactions can achieve exfoliation, they rely on high-temperature and high-pressure closed reactors, which pose a high risk of explosion. In addition, organic solvents tend to produce difficult-to-remove adsorption residues on the surface of two-dimensional nanosheets, which seriously affects the material's performance. Therefore, intercalation-assisted exfoliation has become a research hotspot.

[0004] Among intercalation and stripping methods, electrochemical intercalation is complex and requires sophisticated equipment, while chemical intercalation often uses highly reactive, flammable, and explosive intercalating agents (such as n-butyllithium), posing serious safety risks and environmental pollution problems. Although solid-state intercalation methods have improved safety, existing methods still largely rely on strongly reducing, air-sensitive intercalating agents (such as lithium borohydride), and their industrial scale-up still faces challenges in terms of safety and process stability. Therefore, developing a safe and pure stripping method has significant scientific and industrial value. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned technical deficiencies and provide a method for iodine-induced lithium intercalation and exfoliation of two-dimensional materials, thereby solving the technical problems of unstable intercalating agents and low process safety in the existing technology for intercalation and exfoliation of two-dimensional layered materials.

[0006] To achieve the above-mentioned technical objectives, the technical solution provided by this invention is as follows: In a first aspect, the present invention provides a method for iodine-induced lithium intercalation and exfoliation of a two-dimensional material, comprising the following steps: S1, mixing a target bulk layered material with an inorganic salt to obtain a mixture A; the inorganic salt contains lithium iodide; S2, heating the mixture A to 280-400°C under a vacuum environment or protective atmosphere, while simultaneously applying ultraviolet light irradiation, and obtaining a mixture B through solid-state lithiation treatment; S3, dispersing the mixture B in deionized water, and obtaining a two-dimensional material through hydrolysis, exfoliation, separation, washing, and drying.

[0007] Compared with the prior art, the beneficial effects of the present invention include: This invention uses an inorganic salt containing lithium iodide as the intercalation medium. Through the synergistic excitation of light and heat fields, halide ions are induced to oxidize and decompose, releasing electrons. This drives alkali metal ions to intercalate into the interlayer spaces of a bulk layered material, achieving in-situ solid-state intercalation. The bulk material is then exfoliated by the gas expansion force generated by the hydrolysis reaction, yielding an ultrathin two-dimensional material with a large lateral dimension. This method avoids the high-pressure hazards and solvent residue problems of solvothermal reactions and overcomes the bottleneck of scalable electrochemical intercalation. It is safe, has high intercalation efficiency, and is highly versatile, suitable for the large-scale preparation of various two-dimensional layered materials. Attached Figure Description

[0008] Figure 1 This is a schematic diagram illustrating the solid-state lithium-ion exfoliation method for preparing ultrathin nanosheets in an embodiment. Figure 2 Raman spectra of the PdTe2 nanosheets prepared in Example 1; Figure 3 AFM images and thickness distribution statistics of the PdTe2 nanosheets prepared in Example 1 are shown; where (a) is the AFM image and (b) is the related thickness distribution statistics. Figure 4 Here is a high-resolution TEM image of the PdTe2 nanosheets prepared in Example 1; Figure 5 EDS image of the PdTe2 nanosheets prepared in Example 1; Figure 6 The images shown are TEM images of the graphene nanosheets prepared in Example 2; where (a) is a low-magnification transmission electron microscope image and (b) is a high-resolution transmission electron microscope image. Figure 7 The yield distribution and average yield of NbTe2 nanosheets of different masses prepared in Example 5; Figure 8 The images shown are SEM and AFM images of PdTe2 nanosheets prepared in Example 6 at different reaction times; where (a)-(d) are SEM images of nanosheets obtained after 0.5h, 1h, 1.5h and 3h of reaction, respectively, and (e)-(h) are AFM images of nanosheets obtained after 0.5h, 1h, 1.5h and 3h of reaction, respectively. Detailed Implementation

[0009] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0010] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the invention, are intended to cover non-exclusive inclusion.

[0011] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0012] To address the shortcomings of current intercalation exfoliation methods for two-dimensional materials, such as unstable intercalating agents and low process safety, this invention provides a method for iodine-induced lithium intercalation exfoliation of two-dimensional materials. This invention uses inorganic salts as intercalating agents, which is highly safe, the reaction byproducts are easy to recover, and the product has high purity. The method of this invention has strong versatility.

[0013] In a first aspect, the present invention provides a method for iodine-induced lithium intercalation and exfoliation of a two-dimensional material, comprising the following steps: S1, solid-phase mixing: The target bulk layered material is mixed uniformly with inorganic salt to obtain mixture A; the inorganic salt contains lithium iodide; S2, Photothermal Synergistic Intercalation: Mixture A is heated to 280-400°C in a vacuum environment or protective atmosphere, while being irradiated with ultraviolet light, and then subjected to solid-state lithiation to obtain mixture B; S3, Hydrolysis and purification: Mixture B is dispersed in deionized water, and after hydrolysis, separation, washing and drying, a two-dimensional material is obtained.

[0014] This invention uses lithium iodide-containing inorganic salts (alkali metal halides) as intercalation media. Through the synergistic excitation of light and heat fields, halide ions are induced to oxidize and decompose, releasing electrons. This drives alkali metal ions to embed into the interlayer spaces of bulk layered materials, achieving in-situ solid-state intercalation. The bulk material is then exfoliated by the expansion force of the gas generated by the hydrolysis reaction (hydrogen bubbles released from the reaction of lithium and water between the layers), yielding ultrathin, large-lateral-size two-dimensional materials (two-dimensional layered nanosheets). This method avoids the high-pressure hazards and solvent residue problems of solvothermal reactions and overcomes the bottleneck of large-scale electrochemical intercalation.

[0015] Specifically, this invention uses an inorganic salt containing lithium iodide as an intercalating agent, replacing flammable and explosive organic lithium reagents, and completely eliminates the risk of high-pressure explosion caused by solvent vaporization in solvothermal reactions, resulting in extremely high safety. Furthermore, the reaction byproducts are mainly water-soluble salts, which are easy to clean and recover. The all-solid-phase reaction system avoids the co-intercalation and surface residue of organic solvent molecules, resulting in high product purity. This invention is mainly based on opening physical steric hindrance and weakening interlayer forces, and does not rely on the chemical bonding of specific elements, thus possessing high universality. The reaction kinetics are fast, the intercalation efficiency is high, and the yield is high, making it suitable for industrial production.

[0016] In some embodiments, in step S1, the inorganic salt is a mixed salt of lithium iodide and potassium iodide in a mass ratio of (1.35-1.45):1, more preferably 1.41:1. The present invention uses a mixture of lithium iodide and potassium iodide to form a eutectic salt system. Pure lithium iodide has a melting point as high as 469 °C; excessively high temperatures can cause phase transitions or thermal decomposition in some two-dimensional materials (such as transition metal chalcogenides). Adding potassium iodide to form a eutectic significantly lowers the system's melting point to approximately 280-300 °C, allowing it to form a molten state at a lower temperature. This greatly enhances the contact interface between the salt and the bulk material, improving intercalation kinetics.

[0017] In some embodiments, in step S1, the mass ratio of inorganic salt to target bulk layered material is (10-20):1. In this invention, the mass ratio of target bulk layered material to inorganic salt is crucial for balancing intercalation efficiency and post-processing difficulty. When the ratio is below 10:1, the amount of molten salt is insufficient to completely encapsulate the bulk material, leading to a shortage of intercalating agent and ultimately incomplete peeling. When the ratio is above 20:1, although peeling can be guaranteed, it results in a significant waste of inorganic salt, increasing preparation costs. Therefore, this invention ensures sufficient intercalation kinetics by controlling the mass ratio of inorganic salt to target bulk layered material.

[0018] In some embodiments, in step S1, the target bulk layered material and inorganic salt are mixed uniformly through solid-phase grinding. This invention achieves microscopically uniform mixing through solid-phase grinding.

[0019] In some embodiments, in step S2, the wavelength of the ultraviolet light is 200–280 nanometers. This invention uses short-wavelength ultraviolet light of 200–280 nanometers, whose photon energy can precisely match the oxidation absorption band of iodine ions, serving as the core driving force to excite electron release.

[0020] In some embodiments, the solid-state lithiation treatment time in step S2 is 0.5 to 3 hours. This invention achieves complete intercalation of bulk powder by controlling the solid-state lithiation treatment time.

[0021] In some embodiments, in step S3, mixture B is naturally cooled to room temperature and then dispersed in deionized water.

[0022] In some embodiments, the hydrolysis stripping time in step S3 is 0.5 to 1.5 hours.

[0023] In some embodiments, in step S3, drying is performed at 50–70°C for 1–3 hours.

[0024] In some embodiments, in step S3, the two-dimensional layered material includes one of a single-element layered material, a main group layered material, a transition metal compound, or a transition metal compound alloy system.

[0025] Furthermore, single-element layered materials include graphene, black phosphorus, silicene, or germanene; main group layered materials include hexagonal boron nitride.

[0026] Furthermore, transition metal compounds include transition metal tellurides, transition metal sulfides, or transition metal selenides, such as PdTe2, NbTe2, PdSeTe, etc.

[0027] The main mechanism of action and advantages of this invention are as follows: (1) such as Figure 1 As shown, the target bulk layered material is uniformly mixed with an inorganic salt, specifically a molten salt containing lithium iodide. In this molten salt environment, short-wave ultraviolet light excitation and heating work together to oxidize iodide ions into iodine molecules, releasing electrons. These released electrons reduce lithium ions in the molten salt to highly reactive zero-valent metal atoms. Due to the extremely small radius of lithium atoms, they can easily diffuse into the van der Waals interlayers of various layered materials, unrestricted by the chemical composition of the host material, achieving universal in-situ interlayer lithiation. When the intercalated compound is placed in water, the interlayer lithium metal reacts violently with the water, releasing hydrogen gas. The instantaneous expansion of the hydrogen bubbles in the interlayer generates a huge exfoliation force, opening and peeling apart the layered stacked structure, thus obtaining single-layer or few-layer two-dimensional nanosheets.

[0028] (2) High universality: The mechanism of this invention is based on the opening of physical steric hindrance and the weakening of interlayer forces, and does not depend on the chemical bonding of specific elements. Therefore, this method is successfully applied to a variety of materials such as transition metal tellurides / sulfides / selenides, main group layered materials (h-BN) and alloy systems.

[0029] (3) Process safety and environmental protection: Lithium iodide is used as an intercalating agent, which replaces the flammable and explosive organic lithium reagents and completely eliminates the risk of high pressure explosion caused by solvent vaporization in the solvothermal reaction, making it extremely safe; and the reaction byproducts are mainly water-soluble salts, which are easy to clean and recycle, in line with the principles of green chemistry; in addition, the all-solid phase reaction system avoids the co-intercalation of organic solvent molecules and surface residues, resulting in higher product purity.

[0030] (4) High yield and large scale: The reaction kinetics are fast, the intercalation efficiency is high, and it has industrial-grade expansion capability. The single preparation amount can reach hundreds of grams (up to 200 grams or more, which is a significant improvement compared to the traditional milligrams or a few grams). It maintains a high yield for various layered materials (generally up to 80%) and has the potential to be directly connected to industrial production lines.

[0031] The present invention will be further described in detail below through specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments used that do not specify the manufacturer are all conventional products that can be obtained commercially.

[0032] Example 1 A method for iodine-induced lithium intercalation exfoliation of a two-dimensional material includes the following steps: (1) Place 0.3 g of PdTe2 bulk powder, 2.55 g of lithium iodide (LiI) and 1.81 g of potassium iodide (KI) in a mortar and grind them thoroughly to obtain mixture A.

[0033] (2) The mixture A was transferred to a quartz glass reactor, sealed, and then the reactor was evacuated to remove air. The reactor was then placed on a heating platform and the mixture A inside the reactor was irradiated with a short-wavelength ultraviolet lamp with a wavelength of 254 nm. At the same time, the heating platform was heated to 300 °C and kept at this temperature for 1.5 hours to complete the solid-state lithiation process and obtain mixture B.

[0034] (3) After the reaction is complete, turn off the heating stage and the ultraviolet lamp, and allow the reaction system to cool naturally to room temperature. Add an appropriate amount of deionized water to the reaction vessel to hydrolyze and peel off mixture B. Vigorous gas bubbles (hydrogen) can be observed being released at this time. After standing for 1 hour, centrifuge and filter the mixture, and wash it with a large amount of deionized water to completely remove residual lithium salt, potassium salt and iodine. Place the washed nanosheet powder in a vacuum drying oven and dry it at 60 °C for 2 hours to finally obtain high-purity, ultrathin two-dimensional layered PdTe2 nanosheet powder.

[0035] The Raman spectrum of the PdTe2 nanosheets prepared in Example 1 is shown below. Figure 2 As shown in the figure, two distinct characteristic peaks consistent with PdTe2 nanosheets can be seen, and there are no impurity peaks, indicating that the prepared PdTe2 nanosheets have a pure phase and high crystal quality.

[0036] like Figure 3As shown in the AFM images of the PdTe2 nanosheets prepared in Example 1, the PdTe2 nanosheets have a small thickness, mainly concentrated in the range of 2-5 nanometers, and a lateral size of about 5-20 micrometers.

[0037] High-resolution TEM images of the PdTe2 nanosheets prepared in Example 1 are shown below. Figure 4 As shown in the figure, the prepared PdTe2 nanosheets have good crystal quality, and the lattice spacing of ~0.202 nm corresponding to the PdTe2(110) crystal plane can be clearly observed. like Figure 5 The figure shows the EDS spectrum of the PdTe2 nanosheets prepared in Example 1; it can be seen from the figure that the material contains two elements, Pd and Te, and they are evenly distributed.

[0038] Example 2 A method for iodine-induced lithium intercalation exfoliation of a two-dimensional material includes the following steps: (1) Place 0.3 g of graphite powder, 2.55 g of lithium iodide (LiI) and 1.81 g of potassium iodide (KI) in a mortar and grind them thoroughly to obtain mixture A.

[0039] (2) The mixture A was transferred to a quartz glass reactor, sealed, and then the reactor was evacuated to remove air. The reactor was then placed on a heating platform and the mixture A inside the reactor was irradiated with a short-wavelength ultraviolet lamp with a wavelength of 254 nm. At the same time, the heating platform was heated to 300 °C and kept at this temperature for 1.5 hours to complete the solid-state lithiation process and obtain mixture B.

[0040] (3) After the reaction is complete, turn off the heating stage and the ultraviolet lamp, and allow the reaction system to cool naturally to room temperature. Add an appropriate amount of deionized water to the reaction vessel to allow mixture B to undergo hydrolysis and exfoliation. Vigorous gas bubbles (hydrogen) can be observed being released at this time. After standing for 1 hour, centrifuge and filter the mixture, and wash it with a large amount of deionized water to completely remove residual lithium salt, potassium salt and iodine. Place the washed nanosheet powder in a vacuum drying oven and dry it at 60 °C for 2 hours to finally obtain high-purity, ultrathin two-dimensional layered graphene nanosheet powder.

[0041] TEM images of the graphene nanosheets prepared in Example 2 are shown below. Figure 6 As shown in the figure, the prepared graphene nanosheets have ultrathin characteristics and good crystal quality, and the lattice spacing of ~0.21 nm corresponding to the graphene (100) crystal plane can be clearly observed.

[0042] Example 3 A method for iodine-induced lithium intercalation exfoliation of a two-dimensional material includes the following steps: (1) Place 0.3 g of BN block powder, 2.55 g of lithium iodide (LiI) and 1.81 g of potassium iodide (KI) in a mortar and grind them thoroughly to obtain mixture A.

[0043] (2) The mixture A was transferred to a quartz glass reactor, sealed, and then the reactor was evacuated to remove air. The reactor was then placed on a heating platform and the mixture A inside the reactor was irradiated with a short-wavelength ultraviolet lamp with a wavelength of 254 nm. At the same time, the heating platform was heated to 300 °C and kept at this temperature for 1.5 hours to complete the solid-state lithiation process and obtain mixture B.

[0044] (3) After the reaction is complete, turn off the heating stage and the ultraviolet lamp, and allow the reaction system to cool naturally to room temperature. Add an appropriate amount of deionized water to the reaction vessel to hydrolyze and peel off the mixture B. Vigorous gas bubbles (hydrogen) can be observed being released at this time. After standing for 1 hour, centrifuge and filter the mixture, and wash it with a large amount of deionized water to completely remove residual lithium salt, potassium salt and iodine. Place the washed nanosheet powder in a vacuum drying oven and dry it at 60 °C for 2 hours to finally obtain high-purity, ultrathin two-dimensional layered BN nanosheet powder.

[0045] Example 4 A method for iodine-induced lithium intercalation exfoliation of a two-dimensional material includes the following steps: (1) Place 0.3 g of PdSeTe bulk powder, 2.55 g of lithium iodide (LiI) and 1.81 g of potassium iodide (KI) in a mortar and grind them thoroughly to obtain mixture A.

[0046] (2) The mixture A was transferred to a quartz glass reactor, sealed, and then the reactor was evacuated to remove air. The reactor was then placed on a heating platform and the mixture A inside the reactor was irradiated with a short-wavelength ultraviolet lamp with a wavelength of 254 nm. At the same time, the heating platform was heated to 300 °C and kept at this temperature for 1.5 hours to complete the solid-state lithiation process and obtain mixture B.

[0047] (3) After the reaction is complete, turn off the heating stage and the ultraviolet lamp, and allow the reaction system to cool naturally to room temperature. Add an appropriate amount of deionized water to the reaction vessel to allow mixture B to undergo hydrolysis and exfoliation. Vigorous gas bubbles (hydrogen) can be observed being released at this time. After standing for 1 hour, centrifuge and filter the mixture, and wash it with a large amount of deionized water to completely remove residual lithium salt, potassium salt and iodine. Place the washed nanosheet powder in a vacuum drying oven and dry it at 60 °C for 2 hours to finally obtain high-purity, ultrathin two-dimensional layered PdSeTe alloy nanosheet powder.

[0048] Example 5 To rigorously verify the reproducibility of the method of this invention, exfoliation experiments were conducted on NbTe2 bulk powders of different masses (1 g, 5 g, 30 g, 120 g, and 236.4 g). The specific steps included: (1) Different masses of NbTe2 bulk powder and lithium iodide (LiI) and potassium iodide (KI) in the same proportion (0.3:2.55:1.81) were placed in a mortar and ground and mixed thoroughly to obtain mixture A.

[0049] (2) The mixture A was transferred to a quartz glass reactor and sealed. The reactor was then evacuated to remove air. The reactor was then placed on a heating platform and irradiated with a short-wavelength ultraviolet lamp with a wavelength of 254 nm. At the same time, the heating platform was heated to 300 °C and kept at this temperature for 1.5 hours to complete the solid-state lithiation process and obtain mixture B.

[0050] (3) After the reaction is complete, turn off the heating stage and the ultraviolet lamp, and allow the reaction system to cool naturally to room temperature. Add an appropriate amount of deionized water to the reactor to hydrolyze and peel off mixture B. Vigorous gas bubbles (hydrogen) can be observed being released at this time. After standing for 1 hour, centrifuge and filter the mixture, and wash it with a large amount of deionized water to completely remove residual lithium salt, potassium salt and iodine. Place the washed nanosheet powder in a vacuum drying oven and dry it at 60 °C for 2 hours to finally obtain high-purity, ultrathin two-dimensional layered NbTe2 nanosheet powder.

[0051] Example 5: Average yield of NbTe2 stripping of different qualities as shown in Figure 5. Figure 7 As shown, the average yield of NbTe2 blocks of different masses obtained by peeling is 85.7%, indicating that the two-dimensional materials prepared by the peeling method of the present invention have high yield and reproducibility.

[0052] Example 6 To investigate the optimal reaction conditions, exfoliation experiments were conducted using PdTe2, which has the highest interlayer bonding energy, as an example. Since the lithium iodide / potassium iodide mixed salt can completely melt at 300 °C, exfoliation control experiments were performed for different durations (0.5 h, 1 h, 1.5 h, and 3 h) under UV irradiation and a reaction temperature of 300 °C. The specific steps included: (1) Place 0.3 g of PdTe2 bulk powder, 2.55 g of lithium iodide and 1.81 g of potassium iodide in a mortar and grind them thoroughly to obtain mixture A.

[0053] (2) The mixture A was transferred to a quartz glass reactor, sealed, and then evacuated to remove air. The reactor was then placed on a heating platform, and the mixture A inside the reactor was irradiated with a short-wavelength ultraviolet lamp with a wavelength of 254 nm. At the same time, the heating platform was heated to 300 °C, and the mixture was kept at this temperature for 0.5 hours, 1 hour, 1.5 hours, and 3 hours respectively to complete the solid-state lithiation process and obtain mixture B.

[0054] (3) After the reaction is complete, turn off the heating stage and the ultraviolet lamp, and allow the reaction system to cool naturally to room temperature. Add an appropriate amount of deionized water to the reactor to allow mixture B to undergo hydrolysis and exfoliation. Vigorous gas bubbles (hydrogen) can be observed being released at this time. After standing for 1 hour, centrifuge and filter the mixture, and wash it with a large amount of deionized water to completely remove residual lithium salt, potassium salt and iodine. Place the washed nanosheet powder in a vacuum drying oven and dry it at 60 °C for 2 hours to finally obtain high-purity two-dimensional layered PdTe2 nanosheet powder obtained by exfoliation for different durations.

[0055] Example 6: SEM and AFM images of PdTe2 obtained by stripping at different solid-state lithiation times are shown below. Figure 8 As shown, shorter reaction times (0.5 h, 1 h) yielded thicker PdTe2 nanosheets. Extending the exfoliation time to 1.5 h resulted in more thinner PdTe2 nanosheets. Doubling the exfoliation time (3 h) revealed that the thickness and yield of the exfoliated PdTe2 nanosheets were close to those obtained with the 1.5 h exfoliation time. Therefore, it can be demonstrated that 300 °C for 1.5 h are the optimal exfoliation conditions.

[0056] The above embodiments demonstrate that the method of the present invention is applicable to various two-dimensional layered materials, with a simple and safe process, high yield, and good quality nanosheets, possessing the potential for large-scale production. Furthermore, the preferred solid-state lithiation conditions in this invention are a temperature of 300 ℃, an ultraviolet wavelength of 254 nm, and a reaction time of 1.5 hours. The 300 ℃ temperature is slightly higher than the melting point of the LiI-KI eutectic salt, ensuring a suitable melting reaction environment while avoiding material heat loss. The photon energy of the 254 nm ultraviolet light precisely matches the oxidation absorption band of iodine ions, serving as the core driving force for exciting electron release. 1.5 hours is the optimal balance point for achieving complete intercalation of the bulk powder; too short a time results in insufficient internal intercalation (residual unexfoliated bulk material), while too long a time yields little difference in exfoliation effect compared to 1.5 hours.

[0057] Comparative Example 1 Compared with Example 1, the only difference is that lithium iodide is removed in step S1, while the other steps and conditions are the same as in Example 1.

[0058] The results showed that the target two-dimensional layered material could not be obtained due to the lack of lithium intercalation.

[0059] Comparative Example 2 Compared with Example 1, the only difference is that potassium iodide is removed in step S1, while the other steps and conditions are the same as in Example 1.

[0060] The results showed that, due to the inability to lower the melting point, even under the combined effects of heating at 300°C and illumination, the amount of metallic lithium entering the interlayer was still insufficient, resulting in a low yield of the final two-dimensional layered material.

[0061] Comparative Example 3 Compared with Example 1, the only difference is that the ultraviolet wavelength in step S2 is adjusted to 320nm, while the other steps and conditions are the same as in Example 1.

[0062] The results showed that when long-wave ultraviolet light was used, the matching degree between it and the oxidation absorption band of iodide ions decreased, resulting in insufficient lithium reduction and affecting the yield and size of the obtained two-dimensional layered material.

[0063] Comparative Example 4 Compared with Example 1, the only difference is that ultraviolet light irradiation is removed in step S2, while the other steps and conditions are the same as in Example 1.

[0064] The results showed that the yield of the obtained two-dimensional layered material further decreased compared with Comparative Example 3 after removing ultraviolet light irradiation. As can be seen from Example 1 and Comparative Examples 3-4, the present invention uses light field and thermal field to generate synergistic excitation effect.

[0065] In summary, the method of this invention is a general solid-state exfoliation strategy based on photothermal synergistic decomposition of iodine-induced lithium intercalation, which can be used for the large-scale preparation of two-dimensional materials. This method utilizes an inorganic salt including lithium iodide as an intercalating agent. Under the synergistic effect of short-wavelength ultraviolet irradiation and thermal activation, iodine ions are induced to oxidize and release iodine vapor and electrons, driving lithium ions to intercalate in situ into the van der Waals interlayers of various layered materials, achieving efficient solid-state lithiation. Subsequently, through a hydrolysis reaction, the expansion force generated by the release of interlayer hydrogen gas achieves efficient material exfoliation. This method avoids the high-pressure hazards and solvent residue problems of solvothermal reactions and overcomes the bottleneck of the difficulty in scaling up electrochemical intercalation. This method has the capability of preparing nanosheets at the hundred-gram scale, and the obtained nanosheets have atomic-level thickness (2-5 nm), large lateral dimensions (5-20 μm), and excellent crystal quality, providing a general solution for the industrial application of two-dimensional materials.

[0066] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for iodine-induced lithium intercalation exfoliation of two-dimensional materials, characterized in that, Includes the following steps: S1, Mix the target bulk layered material with inorganic salts evenly to obtain mixture A; the inorganic salts contain lithium iodide; S2, In a vacuum environment or protective atmosphere, mixture A is heated to 280-400°C while being irradiated with ultraviolet light, and then subjected to solid-state lithiation treatment to obtain mixture B; S3, Disperse mixture B in deionized water, and obtain the two-dimensional material by hydrolysis, peeling, separation, washing and drying.

2. The method for iodine-induced lithium intercalation exfoliation of two-dimensional materials according to claim 1, characterized in that, In step S1, the inorganic salt is a mixed salt of lithium iodide and potassium iodide mixed in a mass ratio of (1.35~1.45):

1.

3. The method for iodine-induced lithium intercalation and exfoliation of two-dimensional materials according to claim 1, characterized in that, In step S1, the mass ratio of the inorganic salt to the target bulk layered material is (10-20):

1.

4. The method for iodine-induced lithium intercalation exfoliation of two-dimensional materials according to claim 1, characterized in that, In step S1, the target block layered material and inorganic salt are mixed evenly through solid-phase grinding.

5. The method for iodine-induced lithium intercalation exfoliation of two-dimensional materials according to claim 1, characterized in that, In step S2, the wavelength of the ultraviolet light is 200–280 nanometers.

6. The method for iodine-induced lithium intercalation exfoliation of two-dimensional materials according to claim 1, characterized in that, In step S2, the solid-state lithiation treatment takes 0.5 to 3 hours.

7. The method for iodine-induced lithium intercalation exfoliation of two-dimensional materials according to claim 1, characterized in that, In step S3, the mixture B is naturally cooled to room temperature and then dispersed in deionized water; And / or, The hydrolysis and stripping time is 0.5–1.5 h; The drying process involves drying at 50–70°C for 1–3 hours.

8. The method for exfoliating two-dimensional materials with iodine-induced lithium intercalation according to claim 1, characterized in that, In step S3, the two-dimensional layered material includes one of the following: single-element layered material, main group layered material, transition metal compound, or transition metal compound alloy system.

9. The method for exfoliating two-dimensional materials with iodine-induced lithium intercalation according to claim 8, characterized in that, The single-element layered material includes graphene, black phosphorus, silicene, or germanene; the main group layered material includes hexagonal boron nitride.

10. The method for iodine-induced lithium intercalation exfoliation of two-dimensional materials according to claim 8, characterized in that, The transition metal compounds include transition metal tellurides, transition metal sulfides, or transition metal selenides.

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