Rock salt phase lithium vanadium oxide transparent thin film and preparation method and application thereof

Abstract

The application discloses a rock salt phase lithium vanadium oxide transparent film and a preparation method and application thereof, and relates to the technical field of electrochromic materials, and particularly relates to a rock salt phase lithium vanadium oxide transparent film and a preparation method and application thereof. The preparation method of the rock salt phase lithium vanadium oxide transparent film comprises the following steps: providing a V2O5 crystal film; using a lithium salt solution as a lithium source; and reacting the lithium source with the V2O5 crystal film through an electrochemical lithiation method to obtain a rock salt phase Li3V2O5 transparent film. The lithium salt solution is used as the lithium source, the lithium source is reacted with the V2O5 crystal film through the electrochemical lithiation method, and the rock salt phase Li3V2O5 transparent film is prepared. When a voltage load is applied to the rock salt phase Li3V2O5 transparent film, two states of light transmission and light absorption exist simultaneously, a great change in transmittance in the visible light region is generated, the transmittance in the infrared light region is always kept high, and thus the wavelength band can be independently controlled, which provides a possibility for realizing multi-wavelength band independent control in the field of electrochromic materials.

Description

Technical Field

[0001] This invention relates to the field of functional materials technology, and in particular to a rock salt phase lithium vanadium oxide transparent thin film, its preparation method and application. Background Technology

[0002] Electrochromic technology provides an effective way to controllably adjust the optical properties of materials. Under the action of an electric field, the redox reactions inside electrochromic materials change their valence state or composition, resulting in stable and reversible changes in the material's optical properties (absorption, transmittance, and reflectance, etc.) in the visible, infrared, and even microwave regions.

[0003] Currently, organic electrochromic materials based on organic molecules, polymers, and metal-organic frameworks offer fast response and a rich variety of colors. However, in practical applications, compared to inorganic electrochromic materials, organic electrochromic materials exhibit poorer thermal stability, light stability, chemical stability, and radiation resistance. Therefore, the high stability and durability of inorganic electrochromic materials give them a greater advantage over organic electrochromic materials in various application scenarios.

[0004] However, currently widely used inorganic electrochromic materials such as WO3, TiO2, and NiO suffer from a limited operating voltage range and limited controllability. Specifically, their ability to control different wavelengths of light—visible, near-infrared, and mid-far-infrared—is relatively limited; they can only synchronously switch between transmission and absorption states across multiple wavelengths, failing to achieve individual band-specific control, which significantly restricts their applications.

[0005] Therefore, existing technologies still need to be improved and developed. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the purpose of this invention is to provide a transparent thin film of rock salt phase lithium vanadium oxide (Li3V2O5) and its preparation method and application, aiming to solve the problem that the existing inorganic electrochromic materials have a single ability to control light of different wavelengths, and can only switch between multiple wavelengths synchronously between the two states of transmission and absorption, and cannot achieve individual control of different wavelengths.

[0007] The technical solution of the present invention is as follows:

[0008] In a first aspect, the present invention provides an application of a rock salt phase Li3V2O5 transparent thin film in the field of electrochromism.

[0009] Optionally, the rock salt phase Li3V2O5 transparent film is used as an electrochromic material to prepare electrochromic devices.

[0010] A second aspect of the present invention provides a method for preparing a rock salt phase Li3V2O5 transparent thin film, comprising the steps of:

[0011] Provide V2O5 crystalline thin films;

[0012] Using a lithium salt solution as a lithium source, the lithium source is reacted with the V2O5 crystal film through an electrochemical lithiation method to obtain the rock salt phase Li3V2O5 transparent film.

[0013] Optionally, the electrochemical lithiation method includes one of cyclic voltammetry and constant current charging.

[0014] Optionally, the process parameters used in the cyclic voltammetry method are as follows:

[0015] The cycling voltage range is 1–4.5V, the number of cycles is greater than or equal to 5, the scan rate is 0.1–20mV / s, and the lithium salt concentration is 0.5–2mol / L.

[0016] Optionally, the process parameters used in the constant current charging method are as follows:

[0017] Current density is 10–30 μA / cm 2 The cutoff voltage is 0.5–1V, and the lithium salt concentration is 0.5–2mol / L.

[0018] Optionally, the lithium salt in the lithium salt solution includes at least one of lithium perchlorate, lithium hexafluorophosphate, lithium bis(oxaloyl)borate, lithium tetrafluoroborate, lithium difluorooxaloylborate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, and lithium tetrafluorooxaloyl phosphate, and the solvent in the lithium salt solution includes at least one of propylene carbonate, ethylene carbonate, dimethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl carbonate, and diethyl carbonate.

[0019] Optionally, the method for preparing the V2O5 crystalline thin film includes the following steps:

[0020] Provide a base;

[0021] A V2O5 amorphous thin film was formed on the substrate by magnetron sputtering, and after annealing, a V2O5 crystalline thin film was prepared on the substrate.

[0022] Optionally, the annealing temperature is 300–450°C, and the annealing time is 1–5 hours.

[0023] In a third aspect, the present invention provides a rock salt phase Li3V2O5 transparent thin film, wherein the film is prepared by the preparation method of the present invention as described above.

[0024] Beneficial Effects: This invention is the first to discover that when a voltage load is applied to a rock-salt phase Li3V2O5 transparent thin film, both light transmission and absorption states exist simultaneously. While the transmittance in the visible light region changes significantly, the transmittance in the infrared region remains consistently high, enabling individual control across different wavelength bands. Therefore, applying the rock-salt phase Li3V2O5 transparent thin film to the field of electrochromism solves the problem that existing inorganic electrochromic materials have limited control over different wavelength bands, only allowing for simultaneous switching between transmission and absorption states and lacking individual control across different wavelength bands. This provides a possibility for achieving independent multi-band control in the field of electrochromism. Attached Figure Description

[0025] Figure 1 This is a SEM image of the rock salt phase Li3V2O5 transparent film prepared in Example 1 of the present invention.

[0026] Figure 2 This is a SEM image of the rock salt phase Li3V2O5 transparent film prepared in Example 2 of the present invention.

[0027] Figure 3 The images show the XRD patterns of the rock salt phase Li3V2O5 transparent films prepared in Examples 1-3 of this invention.

[0028] Figure 4 The image shows the XRD pattern of the rock salt phase Li3V2O5 transparent film prepared in Example 4 of this invention.

[0029] Figure 5 The in-situ spectral transmittance curves of the colored and faded states of the transparent Li3V2O5 rock salt phase film prepared in Example 4 of this invention are shown.

[0030] Figure 6 The cyclic voltammetry curves are for the rock salt phase Li3V2O5 transparent thin film prepared in Example 4 of this invention.

[0031] Figure 7 The graph shows the change in spectral transmittance at 550 nm of the rock salt phase Li3V2O5 transparent film prepared in Example 4 of this invention during electrochemical cycling. Detailed Implementation

[0032] This invention provides a rock salt phase Li3V2O5 transparent thin film, its preparation method, and its application. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention.

[0033] 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 in the description of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0034] Currently used inorganic electrochromic materials such as WO3, TiO2, and NiO suffer from limitations in their operating voltage range and limited control capabilities. Specifically, their ability to control different wavelengths of light—visible, near-infrared, and mid-far-infrared—is relatively limited. They can only synchronously switch between transmission and absorption states across multiple wavelengths, failing to achieve individual control across different wavelength bands, which significantly restricts their applications.

[0035] Therefore, developing electrochromic materials capable of independently controlling light in different wavelength bands is of great significance for broadening the applications of electrochromic materials in energy, construction, information, and defense. Li3V2O5 is known as an electrode material in capacitors or lithium-ion batteries, but currently prepared Li3V2O5 electrode materials are black powders, making their application in the electrochromic field difficult. Based on this, this invention provides an application of a rock-salt phase Li3V2O5 transparent thin film in the field of electrochromism. This invention is the first to discover that a rock-salt phase Li3V2O5 transparent thin film possesses electrochromic properties. When a voltage load is applied to the rock-salt phase Li3V2O5 transparent thin film, both light transmission and light absorption exist simultaneously. While the transmittance in the visible light region changes significantly, the transmittance in the infrared region remains consistently high, exhibiting independent controllability in the visible and infrared light bands, enabling separate control in different wavelength bands. Therefore, applying rock salt phase Li3V2O5 transparent thin film to the field of electrochromism solves the problem that existing inorganic electrochromic materials have a single ability to control light of different wavelengths, and can only switch between multiple wavelengths synchronously between transmission and absorption states, and cannot achieve individual control of different wavelengths. This provides the possibility of achieving independent control of multiple wavelengths in the field of electrochromism.

[0036] In one embodiment, the rock salt phase Li3V2O5 transparent thin film is used as an electrochromic material to prepare an electrochromic device. The electrochromic device can independently control light in different wavelength bands, achieving band-specific control, and can be applied in multiple fields such as energy, construction, information, and defense.

[0037] This invention also provides an electrochromic device, including an electrochromic material layer, wherein the material of the electrochromic material layer includes the rock salt phase Li3V2O5 transparent film as described in this invention embodiment.

[0038] This invention also provides a method for preparing a rock salt phase Li3V2O5 transparent thin film, wherein the method for preparing the rock salt phase Li3V2O5 transparent thin film includes the following steps:

[0039] S1. Provide V2O5 crystalline thin films;

[0040] S2. Using a lithium salt solution as a lithium source, the lithium source is reacted with the V2O5 crystal film by an electrochemical lithiation method to obtain the rock salt phase Li3V2O5 transparent film.

[0041] This invention uses a lithium salt solution as a lithium source and prepares a stable, disordered rock salt phase Li3V2O5 transparent film by reacting the lithium source with a V2O5 crystal film through an electrochemical lithiation method.

[0042] Furthermore, when a voltage load is applied to the rock-salt phase Li3V2O5 transparent film, both light transmission and absorption exist simultaneously. This allows for significant changes in transmittance in the visible light region while maintaining high transmittance in the infrared region, enabling individual wavelength-band control. This overcomes the limitation of existing inorganic electrochromic materials, which only offer limited control over different wavelengths and can only switch synchronously between transmission and absorption states, thus failing to achieve individual wavelength-band control. This provides a possibility for multi-band independent control in the field of electrochromism. In addition, the large operating voltage window of the rock-salt phase Li3V2O5 transparent film allows for the compatibility with a wider range of counter electrode materials when used in the fabrication of electrochromic devices, further broadening the application scope of the rock-salt phase Li3V2O5 transparent film.

[0043] In step S1, in one embodiment, the method for preparing the V2O5 crystal thin film includes the following steps:

[0044] S11, Provide the substrate;

[0045] S12. An amorphous V2O5 thin film is formed on the substrate by magnetron sputtering, and after annealing, a crystalline V2O5 thin film is prepared on the substrate.

[0046] In this embodiment, an amorphous V2O5 thin film is formed on a substrate by magnetron sputtering, and then further annealed to transform the amorphous V2O5 thin film into a crystalline V2O5 thin film.

[0047] In step S1, the substrate is a conductive substrate, specifically, it can be indium tin oxide conductive glass (ITO) or fluorine-doped tin dioxide conductive glass (FTO), but is not limited to these.

[0048] In step S2, in one embodiment, forming a V2O5 amorphous thin film on the substrate by magnetron sputtering specifically includes the following steps:

[0049] Using vanadium as the target material, a V₂O₅ amorphous thin film is formed on the substrate by magnetron sputtering in an oxygen and argon atmosphere. Specifically, the sputtering power and sputtering pressure used during magnetron sputtering can be set according to actual needs.

[0050] In one embodiment, the annealing temperature is 300–450°C (e.g., 300°C, 350°C, 380°C, 400°C, 420°C, or 450°C), and the annealing time is 1–5 hours (e.g., 1, 2, 3, 4, or 5 hours). The annealing temperature of 300–450°C and the annealing time of 1–5 hours ensure that the amorphous V₂O₅ thin film is fully transformed into a crystalline V₂O₅ thin film, thereby facilitating the preparation of a rock-salt phase Li₃V₂O₅ transparent thin film.

[0051] This invention combines the magnetron sputtering method described in this embodiment with the aforementioned electrochemical method to prepare a stable, disordered rock salt phase Li3V2O5 transparent film.

[0052] In one embodiment, the electrochemical lithiation method includes at least one of cyclic voltammetry and constant current charging.

[0053] In one embodiment, the process parameters used in the cyclic voltammetry method are as follows:

[0054] The cycling voltage range is 1–4.5V, the number of cycles is greater than or equal to 5, the scan rate is 0.1–20mV / s, and the lithium salt concentration is 0.5–2mol / L.

[0055] Specifically, a three-electrode system was used, with metallic lithium as the reference and counter electrode, a V₂O₅ crystal thin film as the working electrode, and a lithium salt solution as the lithium source. Cyclic voltammetry was employed, performing several cycles within a voltage range of 1–4.5 V to prepare the aforementioned rock-salt phase Li₃V₂O₅ transparent thin film. Using these process parameters, higher quality rock-salt phase Li₃V₂O₅ transparent thin films can be prepared.

[0056] For example, the lithium salt concentration can be, but is not limited to, 0.5 mol / L, 0.8 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, or 2 mol / L. The scan rate can be, but is not limited to, 0.10 mV / s, 0.5 mV / s, 0.8 mV / s, 1 mV / s, 5 mV / s, 10 mV / s, 15 mV / s, or 20 mV / s.

[0057] In some implementations, the cyclic voltage range is 1.5 to 4.5 V.

[0058] In one embodiment, the process parameters used in the constant current charging method are as follows:

[0059] Current density is 10–30 μA / cm 2 The cutoff voltage is 0.1–1V, and the lithium salt concentration is 0.5–2 mol / L.

[0060] Specifically, a three-electrode system is adopted, using metallic lithium as the reference and counter electrode, a V₂O₅ crystalline thin film as the working electrode, and a lithium salt solution as the lithium source. A constant current charging method is used, with a current of 10–30 μA / cm². 2 A transparent Li3V2O5 film of the rock salt phase was prepared by using a current density of 0.1–1 V and a cutoff voltage of 0.1–1 V. Using these process parameters, a higher quality transparent Li3V2O5 film of the rock salt phase can be prepared.

[0061] For example, the current density may be 10 μA / cm. 2 15μA / cm 2 20μA / cm 2 25μA / cm 2 or 30μA / cm 2 The cutoff voltage can be 0.1V, 0.2V, 0.3V, 0.4V, 0.5V, 0.6V, 0.7V, 0.8V, 0.9V or 1V.

[0062] In one embodiment, the lithium salt in the lithium salt solution includes at least one of lithium perchlorate, lithium hexafluorophosphate (LiPF6), lithium bis(oxaloyl)borate (LiBOB), lithium tetrafluoroborate (LiBF4), lithium difluorooxaloylborate (LiODFB), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium difluorophosphate (LiPO2F2), and lithium tetrafluorooxaloyl phosphate (LiFOP), but is not limited thereto.

[0063] In one embodiment, the solvent in the lithium salt solution includes at least one of propylene carbonate, ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl carbonate, and diethyl carbonate.

[0064] The present invention does not limit the thickness of the rock salt phase Li3V2O5 transparent film prepared by the above preparation method, and can select it according to actual needs. For example, the thickness of the rock salt phase Li3V2O5 transparent film is 200-400 nm, specifically, it can be 200 nm, 250 nm, 300 nm, 350 nm or 400 nm, etc.

[0065] This invention also provides a rock salt phase Li3V2O5 transparent thin film, which is prepared using the preparation method described above. The rock salt phase Li3V2O5 transparent thin film provided in this embodiment has a large voltage window and independent controllability in the visible and infrared light bands, enabling individual band-specific control. Specifically, when a voltage load is applied to the rock salt phase Li3V2O5 transparent thin film, both light transmission and absorption exist simultaneously. While the transmittance in the visible light region changes significantly, the transmittance in the infrared region remains consistently high, thus achieving individual band-specific control. The discovery of this property of the rock salt phase Li3V2O5 transparent thin film provides more possibilities for achieving multi-band independent control in the field of electrochromism (existing inorganic electrochromic materials have relatively limited controllability over different light bands in the visible, near-infrared, and mid-far-infrared regions; they can only synchronously switch between multiple wavelengths between transmission and absorption states, and cannot achieve individual band-specific control). Furthermore, the large operating voltage window of the rock salt phase Li3V2O5 transparent film allows it to be matched with more counter electrode materials when used to fabricate electrochromic devices, further broadening the application range of the rock salt phase Li3V2O5 transparent film.

[0066] The following detailed description uses specific examples.

[0067] Example 1

[0068] This embodiment provides a method for preparing a rock salt phase Li3V2O5 transparent thin film, including the following steps:

[0069] (1) Provide commercial ITO, clean it, and use it as a substrate;

[0070] (2) Using magnetron sputtering, pure vanadium (99.99%) target material was sputtered on the substrate for 120 minutes under the conditions of oxygen-argon volume ratio of 1:9, sputtering pressure of 1 Pa and power of 150 W to obtain a V2O5 amorphous thin film with a thickness of 350 nm. Then, it was annealed at 350 °C for 2 h to obtain a V2O5 crystalline thin film.

[0071] (3) The V2O5 crystal film obtained in step (2) was placed in a glove box and subjected to electrochemical lithiation using an electrochemical workstation with a three-electrode system. The V2O5 crystal film was used as the working electrode, and a lithium metal sheet was used as the reference and counter electrode. A 1 mol / L lithium perchlorate propylene carbonate solution was used as the lithium source. A constant current charging method was used with a current density of 30 μA / cm². 2 A cutoff voltage of 0.5V was used to obtain the target product, a transparent rock-salt phase Li3V2O5 film (attached to ITO). The film was then rinsed with dimethyl carbonate and dried using a nitrogen gun. The surface morphology of the rock-salt phase Li3V2O5 transparent film is shown below. Figure 1 As shown.

[0072] Example 2

[0073] This embodiment provides a method for preparing a transparent Li3V2O5 film with a rock salt phase. The only difference from Example 1 is that the cutoff voltage is 0.1V. The surface morphology of the transparent Li3V2O5 film with a rock salt phase is as follows: Figure 2 As shown.

[0074] Example 3

[0075] This embodiment provides a method for preparing a transparent thin film of rock salt phase Li3V2O5, which differs from Embodiment 1 only in that the cutoff voltage is 1V.

[0076] The XRD results of the rock salt phase Li3V2O5 transparent films in Examples 1-3 are as follows: Figure 3 As shown, Figure 3 The two diffraction peaks at 44.3° and 63.9° correspond to the (200) and (220) crystal planes of Li3V2O5, respectively, which fully demonstrates that rock salt phase Li3V2O5 was prepared by the preparation method provided in this embodiment.

[0077] Example 4

[0078] This embodiment provides a method for preparing a rock salt phase Li3V2O5 transparent thin film, including the following steps:

[0079] (1) Same as step (1) in Example 1;

[0080] (2) Same as step (2) in Example 1;

[0081] (3) The V2O5 crystal film obtained in step (2) was placed in a glove box and subjected to electrochemical lithiation using a three-electrode system on an electrochemical workstation. The V2O5 crystal film was used as the working electrode, lithium metal sheets as the reference and counter electrodes, and a 1 mol / L lithium perchlorate propylene carbonate solution as the lithium source. Cyclic voltammetry was used, with a cycle range of 1.0 V to 4.5 V and a scan rate of 5 mV / s, for 10 cycles to obtain the target product, a rock salt phase Li3V2O5 transparent film. The XRD results at different voltages during the cycling process are shown below. Figure 4 As shown, Figure 4 The two diffraction peaks at 44.3° and 63.9° correspond to the (200) and (220) crystal planes of Li3V2O5, respectively, which fully demonstrates that rock salt phase Li3V2O5 was prepared by the preparation method provided in this embodiment.

[0082] Electrochromic properties of the rock salt phase Li3V2O5 transparent film prepared in Example 4 were tested:

[0083] 1) The in-situ spectral transmittance change curves in the colored and faded states were captured using the galvanostatic method, and the results are as follows: Figure 5 As shown, when a voltage load is applied to the rock-salt phase Li3V2O5 transparent film, both light transmission and light absorption exist simultaneously. While the transmittance in the visible light region changes significantly, the transmittance in the infrared region remains consistently high, allowing for individual control across different wavelengths. This discovery of this property of the rock-salt phase Li3V2O5 transparent film in this invention provides more possibilities for achieving multi-band independent control in the field of electrochromism. Furthermore, the large operating voltage window of Li3V2O5 allows it to be matched with a wider range of counter electrode materials when used in the fabrication of electrochromic devices, further broadening the application scope of Li3V2O5.

[0084] 2) Cyclic voltammetry was used, with a cycle range of 1.0–4.5 V and a scan rate of 20 mV / s, for 50 cycles. The changes in the electrochemical cyclic voltammetry curves were recorded, and the results are as follows: Figure 6 As shown, the variation of spectral transmittance at 550 nm during the electrochemical cycling process was recorded in situ, and the results are as follows. Figure 7 As shown, the rock salt phase Li3V2O5 transparent film can switch between different light transmittances and has good stability.

[0085] In summary, this invention provides a rock-salt phase Li3V2O5 transparent thin film, its preparation method, and its applications. Using a lithium salt solution as the lithium source, the invention employs an electrochemical lithiation method to react the lithium source with a V2O5 crystal thin film, thereby preparing a stable, disordered rock-salt phase Li3V2O5 transparent thin film. When a voltage load is applied to the rock-salt phase Li3V2O5 transparent thin film, both light transmission and absorption states exist simultaneously. While the transmittance in the visible light region can vary significantly, the transmittance in the infrared region remains consistently high, enabling individual control across different wavelength bands. This solves the problem of existing inorganic electrochromic materials having limited control over different wavelength bands, only allowing for simultaneous switching between transmission and absorption states, and thus lacking the ability to achieve individual control across different wavelength bands. This provides a possibility for multi-band independent control in the field of electrochromism. Furthermore, the large operating voltage window of the rock-salt phase Li3V2O5 transparent thin film allows for the matching of more counter electrode materials when used in the fabrication of electrochromic devices, further broadening the application range of the rock-salt phase Li3V2O5 transparent thin film.

[0086] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing a transparent thin film of rock salt phase Li3V2O5, characterized in that, The rock salt phase Li3V2O5 transparent film is an electrochromic material used in the field of electrochromism. The preparation method of the rock salt phase Li3V2O5 transparent film includes the following steps: Provide V2O5 crystalline thin films; Using a lithium salt solution as a lithium source, the lithium source is reacted with the V2O5 crystal film by an electrochemical lithiation method to obtain the rock salt phase Li3V2O5 transparent film. The electrochemical lithiation method includes one of cyclic voltammetry and constant current charging. The process parameters used in the cyclic voltammetry method are as follows: The cycling voltage range is 1–4.5V, the number of cycles is greater than or equal to 5, the scan rate is 0.1–20mV / s, and the lithium salt concentration is 0.5–2mol / L. The process parameters used in the constant current charging method are as follows: Current density is 10–30 μA / cm 2 The cutoff voltage is 0.1–1V, and the lithium salt concentration is 0.5–2 mol / L; The method for preparing the V2O5 crystalline thin film includes the following steps: Provide a base; A V2O5 amorphous thin film was formed on the substrate by magnetron sputtering, and after annealing, a V2O5 crystalline thin film was prepared on the substrate. The annealing temperature is 300–450°C, and the annealing time is 1–5 hours.

2. The preparation method according to claim 1, characterized in that, The lithium salt in the lithium salt solution includes at least one of lithium perchlorate, lithium hexafluorophosphate, lithium bis(oxaloyl)borate, lithium tetrafluoroborate, lithium difluorooxaloylborate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, and lithium tetrafluorooxaloyl phosphate. The solvent in the lithium salt solution includes at least one of propylene carbonate, ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl carbonate, and diethyl carbonate.

3. A transparent thin film of rock salt phase Li3V2O5, characterized in that, It is prepared by the preparation method described in any one of claims 1-2.

4. The application of a rock-salt phase Li3V2O5 transparent thin film as an electrochromic material in the field of electrochromism, wherein the preparation method of the rock-salt phase Li3V2O5 transparent thin film includes the following steps: Provide V2O5 crystalline thin films; Using a lithium salt solution as a lithium source, the lithium source is reacted with the V2O5 crystal film by an electrochemical lithiation method to obtain the rock salt phase Li3V2O5 transparent film. The electrochemical lithiation method includes one of cyclic voltammetry and constant current charging. The process parameters used in the cyclic voltammetry method are as follows: The cycling voltage range is 1–4.5V, the number of cycles is greater than or equal to 5, the scan rate is 0.1–20mV / s, and the lithium salt concentration is 0.5–2mol / L. The process parameters used in the constant current charging method are as follows: Current density is 10–30 μA / cm 2 The cutoff voltage is 0.1–1V, and the lithium salt concentration is 0.5–2 mol / L; The method for preparing the V2O5 crystalline thin film includes the following steps: Provide a base; A V2O5 amorphous thin film was formed on the substrate by magnetron sputtering, and after annealing, a V2O5 crystalline thin film was prepared on the substrate. The annealing temperature is 300–450°C, and the annealing time is 1–5 hours.

Images