Zinc-type smart electrochromic cathode material and preparation method thereof

Abstract

The application provides a preparation method of lanthanum and sodium co-doped vanadium oxide (LaSVO) film, which comprises the following steps: adding vanadium pentoxide into a sodium chloride solution, adding lanthanum nitrate hexahydrate to mix uniformly to form a brown suspension, purifying the brown suspension to prepare a precursor solution, and adding a film forming aid to uniformly coat on ITO glass to form the LaSVO film. The application also provides a lanthanum and sodium double metal co-doped vanadium oxide inorganic zinc-based electrochromic cathode material, wherein the cathode material is a composite structure, namely, ITO glass coated with a LaSVO film on the surface. The LaSVO cathode material of the application shows very high electrochemical activity, bright color contrast during bleaching and coloring, extremely fast color switching and excellent cycle stability by comparison with electrodes without lanthanum doping and electrodes with a small amount of lanthanum doping.

Description

Technical Field

[0001] This invention belongs to the field of electrochromic materials, and more specifically, relates to a zinc-type smart electrochromic cathode material and its preparation method. Background Technology

[0002] Electrochromic (EC) materials are characterized by reversible and durable changes in their optical properties when driven by an external voltage, which manifests as changes in color and transparency.

[0003] Electrochromic glass (smart windows) is a new type of energy-saving building material. Its structure generally consists of glass, a transparent conductive layer, an electrochromic layer, an electrolyte layer, an ion storage layer, and another transparent conductive layer. V₂O₅ is the only oxide material with bipolar electrochromic properties that can function as both a color-changing material and an ion storage material. Its typical layered structure facilitates the insertion and extraction of metal ions during redox processes. V₂O₅ is the most widely studied oxide among electrochromic materials, exhibiting a variety of color changes—yellow, green, blue, and intermediate states—in response to voltage variations, thus possessing high color contrast and a rich variety of color changes. However, as an electrode material, V₂O₅ also suffers from many problems, such as poor cycle performance, long response time, and low transmittance. To improve the electrochemical performance of electrode materials, many scholars have studied four typical methods in the past few years: (1) preparing nanostructured vanadium pentoxide electrode materials, which can significantly shorten the diffusion distance of lithium ions and increase the contact area between the electrode and the electrolyte; (2) improving the conductivity of vanadium pentoxide by adding carbon materials; (3) improving the electrochemical stability of vanadium pentoxide through surface coatings; and (4) doping with metal cations. Studies have shown that doping with metal cations is a very effective and promising method to improve the electrochemical performance of materials.

[0004] Currently, many researchers are improving the electrochemical performance of V₂O₅ materials by doping them with other metal ions. Studies by Chen et al. have shown that doping V₂O₅ with rare earth elements samarium (Sm) and dysprosium (Dy) increases its visible light transmittance modulation range; Jaya et al. improved the visible light transmittance of V₂O₅ films by doping with manganese (Mn) and bismuth (Bi). However, doping with these metal elements causes the film to have color in the reduced state, affecting the transmittance in the faded state of the device. To address the issue of optical transmittance, titanium (Ti) doping can be chosen. Ozer et al. and Lee et al. observed that appropriate amounts of titanium doping can improve the cycle stability and charge capacity of V₂O₅. Titanium not only reduces the cathode coloring effect of V₂O₅ but also enhances the adhesion between the film and the substrate. Furthermore, Jinjun He et al., in order to enhance the zinc ion storage capacity in aqueous zinc-ion batteries and improve the cycle stability of vanadium pentoxide (VO) cathodes, doped lanthanum (La) into VO to promote the formation of LaVO4, which exhibited larger interplanar spacing, higher conductivity, excellent zinc ion diffusion efficiency, and good cycle stability (no decay after 2000 cycles). However, the above-mentioned methods mainly focus on improving the electrochemical performance of V2O5 materials, with relatively little research on the electrochromic properties of V2O5. Summary of the Invention

[0005] Based on the problems of existing technologies, this invention provides a lanthanum and sodium co-doped vanadium oxide (LaSVO) thin film, which improves some of the electrochemical, optical and electrochromic properties of the film to varying degrees, such as electrochemical activity, light modulation range, response time or cycle stability, thereby obtaining a zinc-type smart electrochromic device with better performance.

[0006] To achieve the objectives of this invention, the following technical solution is adopted:

[0007] A method for preparing a lanthanum-sodium co-doped vanadium oxide (LaSVO) thin film includes the following steps:

[0008] (1) Add vanadium pentoxide to sodium chloride solution and mix well, then add lanthanum nitrate hexahydrate to it and mix well to form a brown suspension;

[0009] (2) The brown suspension was purified by adding deionized water, then centrifuged, and then sonicated. Deionized water was added to prepare a precursor solution.

[0010] (3) Add film-forming aid to the precursor solution and mix well to form LaSVO paste;

[0011] (4) The film was uniformly coated onto the ITO glass using a rod coating method, and then annealed to form a LaSVO film on the ITO glass.

[0012] Further, in step (1), the sodium chloride solution is 2 mol / L; the mass-to-volume ratio of vanadium pentoxide to sodium chloride solution is 1 g: 15 mL; the mixing time of vanadium pentoxide and sodium chloride solution is more than 96 h; the mass ratio of lanthanum nitrate hexahydrate to vanadium pentoxide is 1 to 2: 1; and the mixing time after adding lanthanum nitrate hexahydrate is more than 24 h.

[0013] In step (2), the centrifuge speed is 10000 r / min and the single centrifugation time is 8-10 min; the ultrasonic treatment time is 0.5-1 h; and the precursor solution concentration is 8-15 mg / mL.

[0014] In step (3), the film-forming aid is hydroxymethyl cellulose (HMC), hydroxyethyl cellulose (HEC), carboxymethyl cellulose (CMC), etc.

[0015] In step (3), the mass-to-volume ratio of the film-forming aid to the precursor solution is 0.6-0.8 g: 30 mL; and the film-forming aid is stirred and mixed for at least 6 hours after addition.

[0016] The ITO glass in step (4) is 5cm×5cm in size; the annealing temperature is 180℃ and the annealing time is 20h.

[0017] The present invention also provides a lanthanum and sodium co-doped vanadium oxide (LaSVO) thin film for use in electrochromic materials, obtained by the preparation method described in the present invention.

[0018] The present invention also provides a zinc-type smart electrochromic cathode material, the cathode material comprising ITO glass and a lanthanum and sodium co-doped vanadium oxide (LaSVO) thin film of the present invention for electrochromic materials coated on the ITO glass.

[0019] Furthermore, the cathode material, the zinc anode material, and the ZnCl2 solution electrolyte can achieve an electrochromic process.

[0020] The present invention also provides a method for testing the electrochromic properties of the LaSVO thin film, wherein the cathode material is a LaSVO thin film, the anode material is metallic zinc, and the electrolyte is a 1M ZnCl2 solution (pH≈5). A constant voltage of 2.2V is applied to the LaSVO thin film cathode material of the present invention using an electrochemical workstation to realize the fading process of the electrochromic device; a constant voltage of 0.1V is applied to realize the coloring process of the device.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] 1. This invention provides for the first time a lanthanum and sodium bimetallic co-doped vanadium oxide (LaSVO) thin film material, which improves some electrochemical, optical or electrochromic properties to varying degrees compared to vanadium oxide thin films or vanadium oxide thin films doped with only sodium, such as electrochemical activity, light modulation range (color contrast), response time (color change speed) or cycle stability (lifetime).

[0023] 2. The preparation method of the lanthanum and sodium co-doped vanadium oxide (LaSVO) thin film of the present invention is simple and convenient for industrial production. Attached Figure Description

[0024] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0025] Figure 1 A digital photograph of the LaSVO (Example 1) film attached to the ITO glass after annealing.

[0026] Figure 2 The LaSVO (Example 1) displays digital photos of different colors at different voltages, from left to right: 0.1V, 1.2V, and 2.2V.

[0027] Figure 3 Scanning electron microscope images of the cross sections of LaSVO (Example 1) and ITO / LaSVO (Example 1).

[0028] Figure 4 Transmission electron microscope images and elemental distribution images of LaSVO (Example 1).

[0029] Figure 5 The images show the cyclic voltammetry (CV) curves of LaSVO (Example 1), SVO (Comparative Example 1), and LaSVO (Comparative Example 2) in 1M ZnCl2 solution (pH≈5).

[0030] Figure 6 Visible light transmission spectrum images of LaSVO (Example 1), SVO (Comparative Example 1), and LaSVO (Comparative Example 2) under different colors.

[0031] Figure 7 The images show the response times of LaSVO (Example 1), SVO (Comparative Example 1), and LaSVO (Comparative Example 2) in 1M ZnCl2 solution (pH≈5).

[0032] Figure 8 The images show the cyclic stability of LaSVO (Example 1), SVO (Comparative Example 1), and LaSVO (Comparative Example 2) in 1M ZnCl2 solution (pH≈5). Detailed Implementation

[0033] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0034] Example 1

[0035] A lanthanum- and sodium-doped vanadium oxide (LaSVO) thin film is prepared by the following steps:

[0036] (1) Add 1g V2O5 to 15mL of 2mol / L NaCl solution, stir for 96h to form a brown suspension, then add 1g La(NO3)3·6H2O and continue stirring for 48h.

[0037] (2) Add the stirred liquid to deionized water for purification, and then centrifuge 6 times. Dilute with deionized water to a precursor solution of 10 mg / mL and sonicate for 1 h.

[0038] (3) Add hydroxyethyl cellulose (0.7 g / 30 mL) to the ultrasonicated precursor solution and stir for 24 h.

[0039] (4) The ITO glass was cleaned with ethanol and deionized water, then a film was formed by rod coating, and finally annealed at 180°C for 20 h to obtain a lanthanum and sodium co-doped vanadium oxide (LaSVO) thin film.

[0040] The LaSVO thin film of Example 1 was characterized as follows:

[0041] ① Figure 1 A digital photograph of the LaSVO (Example 1) film attached to the ITO glass after annealing, shown in a brownish-yellow color.

[0042] ② Figure 2 The LaSVO (Example 1) displays digital photos of different colors at different voltages, from left to right: 0.1V, 1.2V, and 2.2V, which are displayed as green, brownish-yellow, and orange, respectively.

[0043] ③ Scanning electron microscope (SEM) images, analyze microstructure, and measure the thickness of LaSVO films;

[0044] like Figure 3 As shown in figure a, LaSVO has a nanofiber (rod) structure; as Figure 3 As shown in b, the thickness of the LaSVO film coated on the ITO glass is approximately 970 nm.

[0045] ④ Transmission electron microscopy (TEM) and elemental analysis images are used to analyze the microstructure and whether the doping is uniform;

[0046] like Figure 4 As shown in figure a, a single rod-like structure of LaSVO was captured, consistent with the results obtained by scanning electron microscopy; as Figure 4 As shown in bf, the LaSVO nanorods contain four elements: La, Na, O, and V, which are uniformly distributed.

[0047] Example 2

[0048] A lanthanum- and sodium-doped vanadium oxide (LaSVO) thin film is prepared by the following steps:

[0049] (1) Add 1g V2O5 to 15mL of 2mol / L NaCl solution, stir for 96h to form a brown suspension, then add 1g La(NO3)3·6H2O and continue stirring for 36h.

[0050] (2) Add the stirred liquid to deionized water for purification, and then centrifuge 6 times. Dilute with deionized water to a precursor solution of 15 mg / mL and sonicate for 0.5 h.

[0051] (3) Add hydroxymethyl cellulose (0.6 g / 30 mL) to the ultrasonicated precursor solution and stir for 6 h.

[0052] (4) The ITO glass was cleaned with ethanol and deionized water, then a film was formed by rod coating, and finally annealed at 180°C for 20 h to obtain a lanthanum and sodium co-doped vanadium oxide (LaSVO) thin film.

[0053] Example 3

[0054] A lanthanum- and sodium-doped vanadium oxide (LaSVO) thin film is prepared by the following steps:

[0055] (1) Add 1g V2O5 to 15mL of 2mol / L NaCl solution, stir for 120h to form a brown suspension, then add 2g La(NO3)3·6H2O and continue stirring for 24h.

[0056] (2) Add the stirred liquid to deionized water for purification, and then centrifuge 6 times. Dilute with deionized water to a precursor solution of 10 mg / mL and sonicate for 1 h.

[0057] (3) Add carboxymethyl cellulose (0.8 g / 30 mL) to the ultrasonicated precursor solution and stir for 12 h.

[0058] (4) The ITO glass was cleaned with ethanol and deionized water, then a film was formed by rod coating, and finally annealed at 180°C for 20 h to obtain a lanthanum and sodium co-doped vanadium oxide (LaSVO) thin film.

[0059] Comparative Example 1

[0060] Preparation method of sodium-doped vanadium oxide thin films:

[0061] A sodium-doped vanadium oxide (SVO) thin film, the preparation method of which includes the following steps:

[0062] (1) Add 1g of V2O5 to 15mL of 2mol / L NaCl solution and stir for 96h to form a brown suspension.

[0063] (2) Add the stirred liquid to deionized water for purification, and then centrifuge 6 times. Dilute with deionized water to a precursor solution of 10 mg / mL and sonicate for 1 h.

[0064] (3) Add hydroxyethyl cellulose (0.7 g / 30 mL) to the ultrasonicated precursor solution and stir for 24 h.

[0065] (4) The ITO glass was cleaned with ethanol and deionized water, then a film was formed by rod coating, and finally annealed at 180°C for 20 h to obtain sodium-doped vanadium oxide (SVO) thin film.

[0066] Comparative Example 2

[0067] Preparation method of lanthanum and sodium co-doped vanadium oxide thin films:

[0068] A lanthanum- and sodium-doped vanadium oxide (LaSVO) thin film is prepared by the following steps:

[0069] (1) Add 1g V2O5 to 15mL of 2mol / L NaCl solution, stir for 96h to form a brown suspension, then add 0.5g La(NO3)3·6H2O and continue stirring for 48h.

[0070] (2) Add the stirred liquid to deionized water for purification, and then centrifuge 6 times. Dilute with deionized water to a precursor solution of 10 mg / mL and sonicate for 1 h.

[0071] (3) Add hydroxyethyl cellulose (0.7 g / 30 mL) to the ultrasonicated precursor solution and stir for 24 h.

[0072] (4) The ITO glass was cleaned with ethanol and deionized water, then a film was formed by rod coating, and finally annealed at 180°C for 20 h to obtain a lanthanum and sodium co-doped vanadium oxide (LaSVO) thin film.

[0073] Electrochemical and optical tests (Example 1, Comparative Example 1, and Comparative Example 2)

[0074] ① Cyclic voltammetry (CV) measurements of LaSVO (Example 1), SVO (Comparative Example 1), and LaSVO (Comparative Example 2) were performed using an electrochemical workstation in a 1M ZnCl2 solution (pH≈5), with a scan rate of 50 mV / s for each measurement.

[0075] like Figure 5 As shown, compared with SVO (Comparative Example 1), the La-doped film (Example 1) exhibits a higher current density in its CV curve, indicating that LaSVO (Example 1) has higher electrochemical activity. Compared with LaSVO (Comparative Example 2), the different La doping amounts result in different voltages corresponding to the redox peaks. Specifically, the higher the La doping amount, the more the oxidation peak shifts to the right, corresponding to a higher voltage; conversely, the more the reduction peak shifts to the left, corresponding to a lower voltage.

[0076] ② The visible light transmission spectra of LaSVO films under constant voltages (different colors) of 0.2V, 1.2V, and 2.2V were measured using a visible light spectrophotometer;

[0077] like Figure 6 As shown, LaSVO (Example 1), SVO (Comparative Example 1), and LaSVO (Comparative Example 2) exhibit the same color at constant voltages of 0.2V, 1.2V, and 2.2V: green, brownish-yellow, and orange, respectively. The results indicate that the lower the La doping content, the higher the transmittance of the thin film.

[0078] Among them, LaSVO (Example 1) had the largest optical modulation range in the 532-537 nm range, approximately 28.4%; SVO (Comparative Example 1) had the largest optical modulation range in the 524 nm range, approximately 33.2%; and LaSVO (Comparative Example 2) had the largest optical modulation range in the 534-535 nm range, approximately 27.2%. These measurement results indicate that the maximum optical modulation ranges of the La-doped films are similar, corresponding to almost identical wavelengths, while the maximum optical modulation range of the undoped films is significantly larger, with a blue shift in the corresponding wavelength, indicating a significantly smaller range.

[0079] ③ The response time and cycle stability of LaSVO (Example 1), SVO (Comparative Example 1) and LaSVO (Comparative Example 2) were measured using an electrochemical workstation coupled with a visible light spectrophotometer in 1M ZnCl2 solution (pH≈5).

[0080] like Figure 7 As shown, the response times of LaSVO (Example 1), SVO (Comparative Example 1), and LaSVO (Comparative Example 2) were measured over multiple cycles in a 1M ZnCl2 solution (pH≈5). Each cycle was 120 seconds, i.e., a constant voltage of 0.1V was applied for 60 seconds and a constant voltage of 2.2V was applied for 60 seconds. The response time was defined as the time required to reach a final transmittance of 90%. Among them, the LaSVO film (Example 1) had the fastest coloring time at 531 nm (4.8 s) and fading time (12.5 s); the SVO film (Comparative Example 1) had a coloring time of 8.6 s and a fading time of 17.9 s at 524 nm; and the LaSVO film (Comparative Example 2) had a coloring time of 6 s and a fading time of 18.6 s at 531 nm.

[0081] like Figure 8 As shown, LaSVO (Example 1), SVO (Comparative Example 1), and LaSVO (Comparative Example 2) were subjected to 100 CV cycles in 1M ZnCl2 solution (pH≈5), with a scan rate of 100 mV / s for each cycle. The ratio of the areas enclosed by the CV curves represents the ratio of the electrode capacities. The measurement results show that LaSVO (Example 1) exhibited the least capacity decay and the highest capacity retention after 100 CV cycles; while SVO (Comparative Example 1) and LaSVO (Comparative Example 2) showed significantly greater capacity decay and lower capacity retention.

[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a lanthanum and sodium co-doped vanadium oxide thin film, characterized in that, Includes the following steps: (1) Add vanadium pentoxide to sodium chloride solution and mix well, then add lanthanum nitrate hexahydrate and mix well to form a brown suspension; (2) The brown suspension was purified by adding deionized water, then centrifuged, and then sonicated. Deionized water was added to prepare a precursor solution. (3) Add film-forming aid to the precursor solution and mix evenly to form a lanthanum and sodium co-doped vanadium oxide paste; (4) The vanadium oxide film co-doped with sodium was uniformly coated onto the ITO glass by rod coating and then annealed to form a lanthanum and sodium co-doped vanadium oxide film on the ITO glass. Wherein, the sodium chloride solution is 2 mol / L; the mass-to-volume ratio of vanadium pentoxide to sodium chloride solution is 1 g: 15 mL; the mixing time of vanadium pentoxide and sodium chloride solution is 96–120 h; the mass ratio of lanthanum nitrate hexahydrate to vanadium pentoxide is 1–2:1; and the mixing time after adding lanthanum nitrate hexahydrate is 24–36 h. The film-forming aid is hydroxymethyl cellulose, hydroxyethyl cellulose, or carboxymethyl cellulose; the mass-to-volume ratio of the film-forming aid to the precursor solution is 0.6–0.8 g: 30 mL; the film-forming aid is added and then stirred for 6–24 h.

2. The preparation method according to claim 1, characterized in that, In step (2), the centrifuge speed is 10000 r / min and the single centrifugation time is 8-10 min; the ultrasonic treatment process takes 0.5-1 h; and the precursor solution concentration is 8-15 mg / mL.

3. The preparation method according to claim 1, characterized in that, In step (4), the ITO glass is 5cm×5cm in size; the annealing temperature is 180℃ and the annealing time is 20h.

4. A lanthanum and sodium co-doped vanadium oxide thin film for use in electrochromic materials, characterized in that, The thin film is prepared by the preparation method according to any one of claims 1-3.

5. A zinc-type intelligent electrochromic cathode material, characterized in that, The cathode material includes ITO glass and a thin film coated on the ITO glass as described in claim 4.

6. The zinc-type intelligent electrochromic cathode material according to claim 5, characterized in that, The cathode material, together with the zinc anode material and the ZnCl2 solution electrolyte, can achieve an electrochromic process.

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