Method for preparing M-phase vanadium dioxide at low temperature and reducing phase change temperature of M-phase vanadium dioxide

Abstract

The invention discloses a low-temperature preparation method of M-phase vanadium dioxide and a method for reducing the phase change temperature of the M-phase vanadium dioxide. The method comprises the following steps: preparing the M-phase vanadium dioxide by using an oxidant adding proportioning method; and reducing the phase transition temperature of the M-phase vanadium dioxide by using an acid etching method. According to the preparation method, the M-phase vanadium dioxide powder with the phase change temperature close to the room temperature can be rapidly obtained at the low temperature through a proportioning method, and no extra medicine is added in the preparation process; vacancy is introduced through acid liquor etching, and the phase change temperature of M-phase vanadium dioxide is reduced to the room temperature range while the valence state of vanadium is not changed.

Description

Technical Field

[0001] The present invention relates to the technical field of material preparation, and particularly relates to a method for preparing M-phase vanadium dioxide at low temperature and reducing its phase transition temperature. Background Art

[0002] M-phase vanadium dioxide has high hardness, high tensile strength, thermal deformation resistance, and corrosion resistance, and is a necessary product in fields such as aerospace parts, automotive parts, and medical equipment. It also has excellent electrochemical properties and can be used as an electrocatalyst and battery electrode material, showing potential applications in the field of energy storage and conversion. Vanadium dioxide has multiple phase structures, including A-phase, B-phase, R-phase, and M-phase. Generally, vanadium dioxide can only form the M-phase under the coexistence of high temperature (usually above 1000°C), high pressure (usually above 1.5 GPa), and another element (such as oxygen, carbon, nitrogen, or sulfur), and the reaction conditions are relatively harsh. Therefore, it is particularly important to explore other simple and rapid preparation methods for M-phase vanadium dioxide. For example, Chinese Patent No. 202211559919.5 discloses a method for preparing M-phase vanadium dioxide. Vanadyl sulfate is used to prepare vanadyl acetate powder, and then vanadyl acetate powder is used to prepare M-phase vanadium dioxide powder. The whole process is carried out in two steps, and alkaline solutions (such as ammonia water, sodium hydroxide, etc.) are required to adjust the pH, heat and stir, and calcine. The process is relatively cumbersome, and the calcination temperature is high and the time is long. Therefore, developing a method with a simple process flow to prepare M-phase vanadium dioxide at a lower temperature and in a shorter time has great scientific research value.

[0003] In addition, M-phase vanadium dioxide has unique phase transition characteristics, and this characteristic changes abruptly with temperature (the transition time is less than 1 nanosecond), accompanied by significant changes in electrical and optical properties. This makes M-phase vanadium dioxide show great potential in the field of intelligent materials. By regulating its phase transition temperature, devices such as intelligent optical windows and optical switches can be prepared to achieve dynamic regulation of optical properties. However, the phase transition temperature of the existing synthesized vanadium dioxide is often around 68°C, still having a certain distance from the "room temperature phase transition" characteristic required by existing intelligent materials. Therefore, on the basis of the above low-temperature and rapid preparation of M-phase vanadium dioxide, it is necessary to further reduce its phase transition temperature to around room temperature for subsequent development and application. For example, Chinese Patent No. 202411484953 discloses a method for rapidly reducing the phase transition temperature of vanadium dioxide. By adding sodium phosphate and potassium nitrate and introducing oxygen vacancies into the hydrothermal vanadium dioxide powder, vanadium dioxide with a low phase transition temperature is obtained. However, the hydrothermal reaction is not suitable for industrial production, and the reaction kettle temperature is 400 - 600°C, with a relatively high explosion risk. Therefore, it is very necessary to develop a technology for reducing the phase transition temperature of vanadium dioxide that is mild in reaction and can be carried out at room temperature.

[0004] In view of this, improvements should be made to the existing technology. Summary of the Invention

[0005] The main object of the present invention is to provide a method for low-temperature preparation of M-phase vanadium dioxide and reducing its phase transition temperature. By using the proportioning method, M-phase vanadium dioxide powder with a phase transition temperature close to room temperature can be quickly obtained at low temperature, and no additional drugs are required during the preparation process; by etching with dilute sulfuric acid to introduce vacancies, the phase transition temperature of M-phase vanadium dioxide can be reduced to the room temperature range without changing the valence state of vanadium.

[0006] According to one aspect of the present invention, a method for low-temperature preparation of M-phase vanadium dioxide and reducing its phase transition temperature is proposed, which includes the following steps: Preparing M-phase vanadium dioxide by using the method of adding an oxidant in proportion; Reducing the phase transition temperature of M-phase vanadium dioxide by using the acid etching method.

[0007] According to an embodiment of the present invention, preparing M-phase vanadium dioxide by using the method of adding an oxidant in proportion includes: After uniformly mixing a solid of vanadium with a high valence containing ammonia and vanadium pentoxide by grinding to obtain a mixed powder, sintering the mixed powder under vacuum conditions to obtain M-phase vanadium dioxide powder.

[0008] According to an embodiment of the present invention, reducing the phase transition temperature of M-phase vanadium dioxide by using the acid etching method includes: Placing the M-phase vanadium dioxide powder in an acid solution at a predetermined ratio, ultrasonically dispersing and then stirring and soaking, washing and drying the soaked M-phase vanadium dioxide powder to obtain M-phase vanadium dioxide powder with a low phase transition temperature.

[0009] According to an embodiment of the present invention, the solid of vanadium with a high valence containing ammonia includes one or more of ammonium metavanadate and ammonium polyvanadate.

[0010] According to an embodiment of the present invention, the molar ratio of the solid of vanadium with a high valence containing ammonia to vanadium pentoxide is (1-2):1.

[0011] According to an embodiment of the present invention, the vacuum conditions include a vacuum degree ≤ -0.09 MPa, a sintering heating rate of 2-10 °C / min, a reaction temperature of 300-500 °C, and a heat preservation time of 15-120 min.

[0012] According to an embodiment of the present invention, the acid solution includes a sulfuric acid solution.

[0013] According to an embodiment of the present invention, the ratio of the M-phase vanadium dioxide powder to the sulfuric acid solution ≤ 50 g / L.

[0014] According to an embodiment of the present invention, the concentration of the sulfuric acid solution is 0.1-0.5 mol / L, and the stirring and soaking time is 0.5-2 h.

[0015] According to an embodiment of the present invention, stirring is carried out by a magnetic stirrer.

[0016] In a method for low-temperature preparation of M-phase vanadium dioxide according to an embodiment of the present invention and reducing its phase transition temperature, M-phase vanadium dioxide powder with a phase transition temperature close to room temperature can be rapidly obtained at low temperature by a proportioning method, and no additional drug addition is required during the preparation process; vacancies are introduced by acid etching, and while not changing the valence state of vanadium, the phase transition temperature of M-phase vanadium dioxide is reduced to the room temperature range. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0018] Figure 1 Shows a process flow diagram of a method for low-temperature preparation of M-phase vanadium dioxide and reducing its phase transition temperature according to an exemplary embodiment of the present invention; Figure 2 Shows an SEM image of a method for low-temperature preparation of M-phase vanadium dioxide and reducing its phase transition temperature according to an exemplary embodiment of the present invention; Figure 3 Shows an XRD image of a method for low-temperature preparation of M-phase vanadium dioxide and reducing its phase transition temperature according to an exemplary embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] The following detailed description of the embodiments is used to exemplarily illustrate the principle of the present invention, but cannot be used to limit the scope of the present invention. The present invention can be implemented in many different forms, not limited to the specific embodiments disclosed in the text, but including all technical solutions falling within the scope of the claims.

[0020] These embodiments of the present invention are provided to make the present disclosure thorough and complete, and to fully convey the scope of the present invention to those skilled in the art. It should be noted that: unless otherwise specifically stated, the relative arrangements of components and steps, the components of materials, numerical expressions and values set forth in these embodiments should be construed as merely exemplary, rather than as limitations.

[0021] It should be noted that in the description of the present invention, unless otherwise specified, the meaning of "a plurality" is greater than or equal to two; the orientation or positional relationship indicated by the terms "upper", "lower", "left", "right", "inner", "outer", etc. is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0022] It should also be noted that in the description of the present invention, unless otherwise clearly specified and limited, the terms "mounted", "connected", and "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected, or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances. When it is described that a specific device is located between a first device and a second device, there may or may not be an intermediate device between the specific device and the first device or the second device.

[0023] All terms used in the present invention have the same meanings as those understood by ordinary skilled artisans in the field to which the present disclosure pertains, unless otherwise specifically defined. It should also be understood that terms defined in a general dictionary, such as, should be interpreted to have a meaning consistent with their meaning in the context of the relevant art, and should not be interpreted in an idealized or overly formal sense, unless specifically defined as such herein.

[0024] Technologies, methods, and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but in appropriate cases, these technologies, methods, and devices should be regarded as part of the specification.

[0025] As Figure 1 shown, the present invention provides a method for low-temperature preparation of M-phase vanadium dioxide and reducing its phase transition temperature, which includes the following steps: Preparing M-phase vanadium dioxide by using the method of adding an oxidant in a proportion; Reducing the phase transition temperature of M-phase vanadium dioxide by using the acid etching method.

[0026] In the method for low-temperature preparation of M-phase vanadium dioxide and reducing its phase transition temperature according to an embodiment of the present invention, M-phase vanadium dioxide powder with a phase transition temperature close to room temperature can be rapidly obtained (in 15 minutes) at low temperature by the proportioning method, and no additional drug addition is required during the preparation process; vacancies are introduced by acid etching, and the phase transition temperature of M-phase vanadium dioxide is reduced to the room temperature range without changing the valence state of vanadium.

[0027] The self-decomposition of ammonium metavanadate will produce a certain amount of vanadium pentoxide and reducing ammonia gas. The purpose of adding an additional oxidant, vanadium pentoxide, is to adjust the ratio of the oxidant (vanadium pentoxide) to the reductant (ammonia gas) to produce the desired product.

[0028] The method of adding an oxidant ratio is mainly used to prepare M-phase VO2 to ensure that the material has the correct crystal structure and phase transition characteristics.

[0029] The acid etching method is to perform surface modification on the prepared M-phase VO2 to reduce its phase transition temperature by regulating the surface structure or chemical state.

[0030] The method of adding an oxidant ratio determines the initial properties of VO2 (such as phase transition temperature, crystal structure, etc.), while the acid etching method further optimizes these properties, especially reducing the phase transition temperature to meet the actual application requirements (such as smart windows, optoelectronic switches, etc.).

[0031] The method of adding an oxidant ratio can initially regulate the phase transition temperature of VO2 by doping (such as W, Mo, etc.), while the acid etching method further finely regulates it through surface modification.

[0032] Carrying out the rapid preparation of M-phase vanadium dioxide at low temperature and reducing the phase transition temperature together can more flexibly regulate the properties of VO2.

[0033] For example, introducing a doping element (such as W) through the method of adding an oxidant ratio to initially reduce the phase transition temperature, and then further optimizing the surface structure through the acid etching method to achieve a lower phase transition temperature and higher performance stability.

[0034] In some specific embodiments, the preparation of M-phase vanadium dioxide using the method of adding an oxidant ratio includes: After mixing and grinding the ammonia-containing high-valent vanadium solid and vanadium pentoxide evenly to obtain a mixed powder, the mixed powder is evenly spread on the bottom of a flat crucible and sintered under vacuum conditions to obtain M-phase vanadium dioxide powder.

[0035] The ammonia-containing high-valent vanadium solid (such as NH4VO3) will decompose during the sintering process to produce ammonia gas (NH3) and reducing gas (such as H2). These gases can effectively reduce V2O5 to VO2 under vacuum conditions, promoting the formation of M-phase VO2. The most important role of the vacuum condition is to ensure the reducing atmosphere generated by the decomposition of ammonium metavanadate, and it can also prevent the further oxidation of vanadium oxides to higher valence states. Mixing and grinding can make the two precursors fully contact, improve the reaction uniformity, and avoid side reactions caused by local composition inhomogeneity. The grinding process can refine the particles, increase the reaction activity, and is beneficial to the formation of M-phase VO2 at a lower temperature.

[0036] Based on the above embodiments, the method of using the acid etching method to reduce the phase transition temperature of M-phase vanadium dioxide includes: Place the M-phase vanadium dioxide powder in an acid solution in a predetermined ratio, stir and soak it after ultrasonic dispersion, and wash and dry the soaked M-phase vanadium dioxide powder with deionized water to obtain the M-phase vanadium dioxide powder with a low phase transition temperature.

[0037] Acid treatment can modify the surface of VO2 powder, change its surface chemical state and electronic structure, thereby reducing the phase transition temperature. Acid etching may introduce defects (such as oxygen vacancies) on the surface of VO2, and these defects can regulate the phase transition behavior of the material, shifting its phase transition temperature towards a lower temperature. Ultrasonic treatment can effectively disperse VO2 powder, prevent particle agglomeration, and increase the specific surface area and reaction activity of the powder. The combination of ultrasonic dispersion and stirring immersion ensures sufficient contact between the acid solution and VO2 powder, achieving uniform surface modification. Acid etching treatment can remove unstable parts on the surface and improve the cycle stability of VO2 powder during the phase transition process.

[0038] In some specific embodiments, the ammonia-containing high-valent vanadium solid includes one or more of ammonium metavanadate and ammonium polyvanadate. As precursors, the decomposition products of these two reactants can act as reducing agents without the need for additional addition of reducing agents, simplifying the process flow, and they can decompose and release reducing gases at a relatively low temperature, thereby reducing the temperature required for reduction and saving energy. In a reducing atmosphere, the formation of other vanadium oxides (such as V2O5, V6O 13 etc.) can be inhibited to ensure that the target product is formed.

[0039] Ammonium metavanadate and ammonium polyvanadate have different chemical structures and thermal decomposition behaviors, and the morphology (such as nanowires, nanosheets, etc.) and crystal structure of the product can be regulated by selecting different precursors.

[0040] In some specific embodiments, the molar ratio of the ammonia-containing high-valent vanadium solid to vanadium pentoxide is (1~2):1.

[0041] The reaction formula for heating ammonium metavanadate in an air atmosphere is: 2NH4VO3→V2O5+2NH3+H2O (the final product is vanadium pentoxide) The reaction formula for heating ammonium metavanadate in a reducing atmosphere is: 2NH4VO3→V2O5+2NH3+H2O (the intermediate product is vanadium pentoxide) 3V2O5+2NH3→6VO2+3H2O+N2 (the final product is vanadium dioxide) Therefore, the total reaction formula for generating VO2 is: 6NH4VO3→6VO2+4NH3+6H2O+N2 Obviously, ammonia is in excess, and an oxidizing agent needs to be added to consume ammonia. The obtained equation is: 2NH4VO3+2V2O5→6VO2+4H2O+N2 Therefore, the molar ratio of NH4VO3 to V2O5 is 1:1.

[0042] In some embodiments, to ensure complete reaction, an excessive amount of vanadium(V) oxide containing ammonia solid is added.

[0043] Among them, VO2 (B phase) can be obtained without adding an oxidant. The advantage of adding an oxidant is to fully utilize NH3, have a low temperature, and obtain M-phase VO2 with phase change function.

[0044] Based on the above embodiments, the vacuum condition includes a vacuum degree ≤ -0.09 MPa, the sintering heating rate is 2 - 10 °C / min, the reaction temperature is 300 - 500 °C, and the heat preservation time is 15 - 120 min.

[0045] In some specific embodiments, the acid solution includes sulfuric acid solution. Common acid etchants include dilute hydrochloric acid (HCl), dilute sulfuric acid (H2SO4), and nitric acid (HNO3). A mixed acid (such as HCl - HNO3) can be tried to improve the etching effect. Acid etching can remove surface defects, improve the cycle stability and durability of the material, and the acid solution treatment process is simple and easy to operate, suitable for large-scale production.

[0046] Based on the above embodiments, the ratio of M-phase vanadium dioxide powder to sulfuric acid solution is ≤ 50 g / L. The concentration of the sulfuric acid solution is usually selected between 0.1 mol / L and 1 mol / L. Too low a concentration may result in an insignificant reaction effect, and too high a concentration may over-etch the material. Determine the mass of VO2 powder according to the experimental scale. The specific surface area of VO2 powder will affect the efficiency of acid treatment. Nanoscale VO2 powder has a larger specific surface area and requires more acid solution for sufficient reaction.

[0047] Determine the optimal ratio through experiments. For example, a ratio of 50:1 (1 g of VO2 powder uses 50 mL of sulfuric acid solution) can be tried first, and then adjusted according to the reaction effect.

[0048] After the reaction, conduct experiments according to the preliminarily determined ratio (such as 50:1) and observe the reaction effect.

[0049] Use means such as XRD, SEM, XPS to characterize the treated VO2 powder and analyze its crystal structure, surface chemical state, and phase change temperature.

[0050] Adjust the ratio of sulfuric acid solution to VO2 powder according to the characterization results until the expected effect is achieved.

[0051] Based on the above embodiments, the concentration of the sulfuric acid solution is 0.1 - 0.5 mol / L to avoid over-etching and causing damage to the material structure. The stirring and soaking time is 0.5 - 2 h to ensure sufficient reaction.

[0052] On the basis of the above embodiments, stirring is carried out by a magnetic stirrer. The magnetic stirrer generates eddy currents in the solution by rotating the magnetic rotor (stirring bar), ensuring the uniform dispersion of VO2 powder in the acid solution and avoiding too high or too low local concentration. VO2 powder is prone to agglomeration in the solution, and magnetic stirring can effectively break the agglomeration, increase the contact area between the powder and the acid solution, and enhance the reaction efficiency.

[0053] The following specifically illustrates the present application through embodiments.

[0054] Example 1 S1. Put 1 g of ammonium metavanadate and 1.56 g of vanadium pentoxide into a quartz mortar and mix and grind them evenly. Then spread the mixed powder on a corundum crucible and place it in the center of a tube furnace. Then evacuate to make the pressure in the tube ≤ -0.09 MPa; S2. Raise the temperature of the furnace cavity to 300 °C at a heating rate of 5 °C / min, keep it warm for 15 min, and naturally cool to room temperature to obtain M-phase vanadium dioxide powder; S3. Take 1 g of the obtained vanadium dioxide powder, put it into 50 ml of 0.1 mol / L sulfuric acid solution, ultrasonically disperse it evenly, and then place it on a magnetic stirrer and stir for 1 h; S4. Wash and dry the M-phase vanadium dioxide powder soaked in sulfuric acid above to obtain an M-phase vanadium dioxide with a low phase transition temperature, and its phase transition temperature is 31 °C.

[0055] As Figure 2 and 3 shown, are the SEM image and XRD image of the M-phase vanadium dioxide in this embodiment.

[0056] Example 2 S1. Put 5 g of ammonium metavanadate and 7.78 g of vanadium pentoxide into a quartz mortar and mix and grind them evenly. Then spread the mixed powder on a corundum crucible and place it in the center of a tube furnace. Then evacuate to make the pressure in the tube ≤ -0.09 MPa; S2. Raise the temperature of the furnace cavity to 500 °C at a heating rate of 8 °C / min, keep it warm for 60 min, and naturally cool to room temperature to obtain M-phase vanadium dioxide powder; S3. Take 3 g of the obtained vanadium dioxide powder, put it into 200 ml of 0.3 mol / L sulfuric acid solution, ultrasonically disperse it evenly, and then place it on a magnetic stirrer and stir for 0.5 h; S4. Wash and dry the M-phase vanadium dioxide powder soaked in sulfuric acid above to obtain an M-phase vanadium dioxide with a low phase transition temperature, and its phase transition temperature is 29 °C.

[0057] Example 3 S1. Place 10 g of ammonium metavanadate and 15.6 g of vanadium pentoxide into a quartz mortar and mix and grind them evenly. Then spread the mixed powder flat in a corundum crucible and place it in the center of a tubular furnace. Then evacuate to make the pressure in the tube ≤ -0.09 MPa; S2. Raise the furnace chamber temperature to 400 °C at a heating rate of 10 °C / min, hold for 120 min, and naturally cool to room temperature to obtain M-phase vanadium dioxide powder; S3. Take 2 g of the obtained vanadium dioxide powder and place it in 100 ml of 0.5 mol / L sulfuric acid solution. After ultrasonic dispersion, place it on a magnetic stirrer and stir for 2 h; S4. Wash and dry the M-phase vanadium dioxide powder soaked in sulfuric acid with deionized water to obtain an M-phase vanadium dioxide with a low phase transition temperature, and its phase transition temperature is 26 °C.

[0058] After the implementation of this application, it has at least the following beneficial effects: (1) The method of adding an oxidant ratio can inhibit the generation of impurity phases, obtain high-purity M-phase vanadium dioxide, and improve the performance stability of the material; (2) The acid etching method can further reduce its phase transition temperature by modifying the surface structure of vanadium dioxide or introducing defects (such as oxygen vacancies), making it more suitable for applications such as smart windows and optoelectronic switches; (3) Acid etching can remove impurities or oxides on the surface of vanadium dioxide, improve its surface chemical state and electronic structure, thereby improving the optical and electrical properties of the material; (4) The method of adding an oxidant ratio controls the crystal structure and phase transition characteristics of vanadium dioxide from the source of material preparation, while the acid etching method further optimizes its performance from the perspective of surface modification. The combination of the two can achieve multi-level and all-round performance regulation; (5) By initially reducing the phase transition temperature by the method of adding an oxidant ratio and then further optimizing by the acid etching method, the phase transition temperature of vanadium dioxide can be reduced to near room temperature (~25 - 30 °C), meeting the application requirements of smart windows and other applications; (6) The combination of the two methods can not only regulate the phase transition temperature, but also improve the optical, electrical and thermal properties of vanadium dioxide, making it have a wider application prospect in the fields of smart windows, optoelectronic switches, thermochromic coatings, etc.

[0059] The above are exemplary embodiments disclosed by the present invention. The order of disclosure of the above embodiments of the present invention is only for description and does not represent the superiority or inferiority of the embodiments. However, it should be noted that the discussion of any above embodiment is only exemplary and is not intended to imply that the scope of disclosure of the embodiments of the present invention (including the claims) is limited to these examples. Without departing from the scope defined by the claims, various changes and modifications can be made. The functions, steps, and / or actions of the method claims according to the disclosed embodiments herein need not be performed in any particular order. In addition, although the elements disclosed in the embodiments of the present invention may be described or claimed in individual form, they may also be understood as plural unless explicitly limited to the singular.

[0060] Those of ordinary skill in the art should understand that the discussion of any above embodiment is only exemplary and is not intended to imply that the scope of disclosure of the embodiments of the present invention (including the claims) is limited to these examples; under the concept of the embodiments of the present invention, the technical features between the above embodiments or different embodiments can also be combined, and there are many other variations in different aspects of the embodiments of the present invention as described above, and they are not provided in detail for the sake of brevity. Therefore, any omission, modification, equivalent replacement, improvement, etc. made within the spirit and principle of the embodiments of the present invention shall be included within the protection scope of the embodiments of the present invention.

Claims

1. A method for the low-temperature preparation of M-phase vanadium dioxide and reducing its phase transition temperature, characterized in that It includes the following steps: Prepare M-phase vanadium dioxide by using the method of adding an oxidant in a certain proportion; Reduce the phase transition temperature of the M-phase vanadium dioxide by using an acid etching method.

2. The method for low-temperature preparation of M-phase vanadium dioxide and reducing its phase transition temperature according to claim 1, characterized in that, The preparation of M-phase vanadium dioxide by using the method of adding an oxidant in a certain proportion includes: After uniformly mixing and grinding a solid of vanadium with a high valence containing ammonia and vanadium pentoxide to obtain a mixed powder, sinter the mixed powder under vacuum conditions to obtain an M-phase vanadium dioxide powder.

3. The method for preparing M-phase vanadium dioxide at low temperature and reducing its phase transition temperature according to claim 2, characterized in that, Reducing the phase transition temperature of the M-phase vanadium dioxide by using an acid etching method includes: Place the M-phase vanadium dioxide powder in an acid solution at a predetermined ratio, perform ultrasonic dispersion and then stir and soak, wash and dry the soaked M-phase vanadium dioxide powder to obtain an M-phase vanadium dioxide powder with a low phase transition temperature.

4. The method for low-temperature preparation of M-phase vanadium dioxide and reducing its phase transition temperature according to claim 2, characterized in that, The solid of vanadium with a high valence containing ammonia includes one or more of ammonium metavanadate and ammonium polyvanadate.

5. The method for low-temperature preparation of M-phase vanadium dioxide and reducing its phase transition temperature according to claim 2, wherein The molar ratio of the solid of vanadium with a high valence containing ammonia to vanadium pentoxide is (1-2):

1.

6. The method for low-temperature preparation of M-phase vanadium dioxide and reducing its phase transition temperature according to claim 2, wherein The vacuum conditions include a vacuum degree ≤ -0.09 MPa, a sintering heating rate of 2-10 °C / min, a reaction temperature of 300-500 °C, and a heat preservation time of 15-120 min.

7. The method for low-temperature preparation of M-phase vanadium dioxide and reducing its phase transition temperature according to claim 3, characterized in that, The acid solution includes a sulfuric acid solution.

8. The method for low-temperature preparation of M-phase vanadium dioxide and reducing its phase transition temperature according to claim 7, characterized in that, The ratio of the M-phase vanadium dioxide powder to the sulfuric acid solution ≤ 50 g / L.

9. The method for low-temperature preparation of M-phase vanadium dioxide and reducing its phase transition temperature according to claim 7, characterized in that, The concentration of the sulfuric acid solution is 0.1-0.5 mol / L, and the stirring and soaking time is 0.5-2 h.

10. The method for low-temperature preparation of M-phase vanadium dioxide and reducing its phase transition temperature according to claim 3, characterized in that, The stirring is carried out by a magnetic stirrer.

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