Cellulose composite vanadium oxide sol, its preparation method and application

Abstract

The present application relates to a kind of cellulose composite vanadium oxide sol and its preparation method and application, preparation method includes the following steps: V2O5, water and hydrogen peroxide are mixed uniformly, and A glue is obtained by standing aging;Cellulose is added to water and dispersed uniformly, after freezing, B glue is obtained by thawing;B glue is added to A glue and mixed uniformly, and cellulose composite vanadium oxide sol is obtained;In the cellulose composite vanadium oxide sol, the concentration of vanadium pentoxide is 0.025-0.05mol / L;Cellulose accounts for 5.2% to 52.3% of the total mass of cellulose and vanadium pentoxide.The present application combines cellulose and vanadium oxide, both are uniformly mixed, and two phases stably coexist, and the prepared electrochromic material has high cycle stability.

Description

Technical Field

[0001] This invention relates to the field of electrochromic materials, specifically to a cellulose composite vanadium oxide sol, its preparation method, and its application. Background Technology

[0002] With societal development, people's demand for energy is increasing daily, making energy conservation, emission reduction, and improved energy efficiency inevitable trends. Among natural energy sources, solar energy, as a renewable energy source, is inexhaustible. Since 50% of solar energy comes from near-infrared light, paying attention to the near-infrared reflectivity of windows and making full use of solar energy is essential for buildings that require heating and cooling. In recent years, research on electrochromic materials for use in smart windows to improve optical transmittance and achieve intelligent energy saving has gained increasing favor. This green design concept can meet indoor lighting needs without increasing additional air conditioning load.

[0003] Vanadium oxide is widely used in electrochromic materials, and sol-gel synthesis techniques for vanadium oxide have been researched and developed over the past two decades. However, the unstable layered structure of vanadium oxide, while providing ion channels, also commonly suffers from structural collapse due to ion insertion and extraction, resulting in poor cycling stability. Furthermore, vanadium pentoxide is toxic and is listed as a Group 2B carcinogen by the WHO, with its hazard to humans related to the concentration of vanadium oxide. Summary of the Invention

[0004] The purpose of this invention is to overcome the above-mentioned technical deficiencies and provide a cellulose composite vanadium oxide sol, its preparation method and application, which solves the technical problem of poor cycle stability caused by the unstable structure of vanadium oxide as an electrochromic material in the prior art, while relatively reducing the vanadium pentoxide content and reducing harm.

[0005] To achieve the above-mentioned technical objectives, the present invention provides a method for preparing cellulose composite vanadium oxide sol:

[0006] Includes the following steps:

[0007] S1. Mix V2O5, water and hydrogen peroxide evenly and let stand to age to obtain glue A;

[0008] S2. Add cellulose to water and disperse evenly. After freezing and thawing, obtain gel B.

[0009] S3. Add glue B to glue A and mix well to obtain cellulose composite vanadium oxide sol;

[0010] In the cellulose-vanadium oxide composite sol, the concentration of vanadium pentoxide is 0.025–0.05 mol / L; cellulose accounts for 5.2%–52.3% of the total mass of cellulose and vanadium pentoxide.

[0011] Furthermore, in step S1, V2O5 is first added to deionized water to form a vanadium pentoxide solution, and then hydrogen peroxide is added.

[0012] Furthermore, in step S1, the mass fraction of hydrogen peroxide is 30%; the molar ratio between V2O5 and H2O2 is 1:8.

[0013] Furthermore, in step S1, the mixing is achieved by first magnetically stirring for 20-30 minutes, then ultrasonically oscillating for 15-25 minutes, and repeating this process 3-5 times.

[0014] Furthermore, in step S1, the settling and aging time is 5 to 8 days.

[0015] Furthermore, in step S2, the cellulose is methylcellulose or carboxymethylcellulose.

[0016] The cellulose composite vanadium oxide sol prepared by the above method has a viscosity of 4.3–153.6 mPa·s. -1 .

[0017] The application of the above-mentioned cellulose composite vanadium oxide sol in the preparation of electrochromic thin films includes the following steps:

[0018] The cellulose composite vanadium oxide sol was vertically dropped onto a clean conductive substrate, and the excess sol was removed by centrifugation and dried to obtain a uniform electrochromic film.

[0019] Furthermore, the rotary centrifugation includes variable speed motion, starting at a low speed and then increasing to a high speed. The low speed is 2000–2200 RPM for 8–12 seconds, and the high speed is 3400–3600 RPM for 50–70 seconds.

[0020] Furthermore, the drying temperature is 45–60℃, and the time is 1–24 hours.

[0021] Compared with the prior art, the beneficial effects of the present invention include:

[0022] 1. This invention utilizes sol-gel technology to perfectly composite cellulose and vanadium oxide. Using vanadium pentoxide as the main material, a vanadium oxide sol was successfully prepared by dispersion with hydrogen peroxide; simultaneously, cellulose was dissolved in deionized water, and a stable cellulose gel was obtained through a one-step freeze-thaw process. After mixing the two, spin coating successfully yielded an electrochromic material suitable for high optical contrast and cycling stability, retaining over 80% of its charge capacity after 1000 cycles; at the same time, it effectively reduces the amount of pure vanadium pentoxide used in electrochromic materials, reducing potential hazards. The stable state of the cellulose-vanadium oxide composite sol and the simple coating technique provide a convenient solution for the selection of electrochromic materials.

[0023] 2. This invention provides a novel method for combining cellulose and vanadium pentoxide, enabling uniform mixing and stable coexistence of the two phases, allowing for stable storage for at least three months. Because methylcellulose and carboxymethylcellulose are powdery, direct addition to sol is difficult to achieve uniform mixing, and cellulose tends to agglomerate and generate bubbles. While cell disruptors can be used, the process is time-consuming, complex, and prone to imbalances in cellulose incorporation. This invention employs a sol-gel combined with one-step freeze-thaw process, solving the problems of poor cellulose dispersion and material waste, while ensuring the uniformity and stability of the composite.

[0024] 3. The vanadium oxide sol composed of cellulose increases the adhesiveness of the sol itself, giving it good film-forming properties and flexibility. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the formation process of methylcellulose composite vanadium oxide sol;

[0026] Figure 2 The SEM image of the thin film prepared by the methylcellulose composite vanadium oxide sol in Example 1 of this invention;

[0027] Figure 3 The CV curve of the thin film prepared by the methylcellulose composite vanadium oxide sol in Example 1 of this invention;

[0028] Figure 4 The CV curve of the V2O5 electrochromic thin film prepared in Comparative Example 1;

[0029] Figure 5 The absorbance and response time of the device assembled in Example 1 were measured. Detailed Implementation

[0030] 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.

[0031] This invention uses sol-gel technology to synthesize cellulose composite vanadium oxide sol, which can be used as an electrochromic material. It reduces the vanadium pentoxide content, reduces the harm of vanadium oxide to humans, improves the cycle stability of vanadium oxide electrochromic materials, and broadens the selection range of electrochromic materials, and is expected to be widely used.

[0032] I. The method for synthesizing cellulose composite vanadium oxide sol using the sol-gel method of the present invention includes the following steps:

[0033] (1) Clean the conductive substrate, dry it in an oven, and then store it for later use.

[0034] (2) Vanadium pentoxide (V2O5) is dispersed in 30% hydrogen peroxide (an aqueous solution of H2O2) with deionized water as solvent, magnetically stirred and ultrasonically vibrated, and allowed to stand and age fully. This is called glue A.

[0035] (3) Add cellulose to deionized water, stir magnetically, freeze in a freezer and thaw naturally, and record as B glue;

[0036] (4) Slowly add glue B to glue A and stir evenly to obtain cellulose composite vanadium oxide sol.

[0037] In the above method, the cleaning procedure in step (1) is as follows: sodium hydroxide solution, anhydrous ethanol and deionized water are used for cleaning, and the preferred cleaning times are 20 min, 15 min and 10 min, respectively. The drying temperature is 60℃.

[0038] In the above method, the molar ratio between V2O5 and H2O2 in step (2) is 1:8.

[0039] In the above method, the magnetic stirring time in step (2) is 20-30 min, the ultrasonic oscillation time is 15-25 min, and the number of cycles is 3-5. Within this range, uniform mixing and sufficient reaction can be guaranteed. The standing and aging time is 5-8 days, preferably seven days.

[0040] In the above method, the state change of the B gel in step (3) is from gel state to all-solid state and then back to gel state.

[0041] In the above method, step (3) involves freezing followed by thawing, which ensures that the cellulose molecular chains are arranged parallel to each other and tightly packed along the direction of the external force, resulting in a highly stable cellulose gel.

[0042] In the above method, the concentration of vanadium pentoxide in the cellulose composite vanadium oxide sol is 0.025–0.05 mol / L; cellulose accounts for 5.2%–52.3% of the total mass of cellulose and vanadium pentoxide, which will be referred to as the mass fraction of cellulose below to avoid redundancy.

[0043] II. The cellulose composite vanadium oxide sol prepared by the above method has a viscosity of 4.3–153.6 mPa·s. -1 .

[0044] III. The method for preparing electrochromic materials using cellulose composite vanadium oxide sol of the present invention includes the following steps:

[0045] (1) Take an appropriate amount of cellulose composite vanadium oxide sol and drop it vertically onto the surface of the conductive substrate material;

[0046] (2) Rotate and centrifuge to remove excess sol, obtain a uniform film, and use a hair dryer to dry the surface of the film;

[0047] (3) Repeat steps (1) and (2);

[0048] (4) Transfer to a forced-air drying oven and dry to obtain an electrochromic film;

[0049] (5) Use one electrochromic film as the counter electrode and the other as the working electrode, sandwich a diaphragm in the middle, and encapsulate the surrounding area with 3M VHB double-sided adhesive to assemble the device.

[0050] (6) The optical properties of the material are measured using an ultraviolet-visible-near-infrared spectrophotometer, and the electrochemical properties of the material are measured using an electrochemical workstation.

[0051] In the above method, the conductive substrate material in step (1) is firmly adsorbed onto the spin coater; the conductive substrate material includes ITO conductive glass, FTO conductive glass, PEN-ITO flexible conductive film, or PET-ITO flexible conductive film. The dimensions of different conductive substrate materials are consistent.

[0052] In the above method, the centrifugal rotation in step (2) is a variable speed motion, with a low speed of 2000-2200 RPM and a time of 8-12 s, and a high speed of 3400-3600 RPM and a time of 50-70 s. Preferably, the low speed is 2100 RPM and the time is 10 s, and the high speed is 3500 RPM and the time is 60 s.

[0053] In the above method, the number of repetitions in step (3) is 1 to 3 times.

[0054] In the above method, the drying temperature in step (4) is 45℃~60℃ and the drying time is 1h~24h.

[0055] In the above method, the counter electrode in step (5) is an electrochromic thin film pre-embedded with lithium ions, and the diaphragm (filter paper) is pre-wetted with electrolyte. These are all conventional technologies and will not be elaborated here.

[0056] In the above method, the optical system of the photometer described in step (6) all uses reflective optical elements coated with SiO2 protective layer, and the holographic grating has the highest line density. These are all conventional technologies and will not be elaborated here.

[0057] The reaction mechanism and application mechanism of this invention are as follows: Vanadium pentoxide reacts with hydrogen peroxide in an aqueous solution to produce peroxyvanadate, which is then aged in water for about a week to obtain a deep red V₂O₅·nH₂O sol. Methylcellulose and carboxymethylcellulose are soluble in water. After a one-step freeze-thaw cycle, the temperature gradient causes the cellulose molecular chains to align parallel to the direction of the external force and pack tightly together. Figure 1 This is a schematic diagram illustrating the formation process of the cellulose composite V₂O₅ sol in this invention, where linear cellulose fibers are interspersed within the V₂O₅ sol. After film formation, under an applied voltage, ions and electrons undergo directional movement between the working electrode and the counter electrode, and the electrochromic properties mainly depend on V₂O₅. 4+ and V 5+ The reversible reaction between them. The linear binding of cellulose reduces the volume expansion caused by ion intercalation, ensuring good cycling stability.

[0058] This invention provides specific examples of the content of each component and their electrochromic properties in different applications.

[0059] The detection method of a specific embodiment of the present invention is as follows:

[0060] 1. Viscosity: The viscosity of the prepared cellulose composite vanadium oxide sol was measured using a capillary viscometer. The viscosity measurement was performed at room temperature, and the viscometer was kept stationary throughout the measurement process.

[0061] 2. The morphology of the prepared electrochromic material film surface was analyzed using scanning electron microscopy.

[0062] 3. A three-electrode system (calomel electrode as reference electrode, platinum sheet electrode as counter electrode, and electrochromic material as working electrode) was used to test the electrochromic properties of the prepared electrochromic material using an electrochemical workstation and a UV-Vis-NIR spectrophotometer. The electrochemical workstation applied a voltage range of -1V to 1V, and the tests were conducted in 1M LiClO4 / PC electrolyte. The CV scan rate was 50mV / s. The absorbance was measured using UV coupled with the electrochemical workstation, with a -1V application time of 20s followed by a 1V application time of 20s, without deducting for substrate material loss.

[0063] Examples 1-6

[0064] The synthetic cellulose composite vanadium oxide sol includes the following steps:

[0065] (1) The conductive substrate was ultrasonically cleaned with sodium hydroxide solution, anhydrous ethanol and deionized water for 20 min, 15 min and 10 min respectively. After absorbing the surface moisture with absorbent paper, it was dried in a drying oven at 60℃ and then sealed for later use.

[0066] (2) Add vanadium pentoxide to a beaker containing deionized water and a magnetic ball to form a vanadium pentoxide solution. Then add hydrogen peroxide. The molar ratio of vanadium pentoxide to hydrogen peroxide is 1:8. Stir magnetically first, then sonicate. After multiple cycles, let stand and age for 1 week. This is called glue A.

[0067] (3) Add cellulose to 5-15 ml of deionized water, stir magnetically for 20-24 h, freeze in a freezer until solid, and then thaw at room temperature (the state of cellulose hydrogel changes from gel state to solid state and then back to gel state. During the freezing process, ensure that it is completely frozen into a solid state before thawing). This is called gel B. Among them, methylcellulose (MC) is used.

[0068] (4) Slowly add glue B to glue A and stir evenly to obtain cellulose composite vanadium oxide sol; the concentration of vanadium pentoxide in cellulose composite vanadium oxide sol is 0.025-0.05 mol / L; the mass fraction of cellulose is 5.2%-52.3%.

[0069] Step (2) The magnetic stirring time is 20-30 min, the ultrasonic oscillation time is 15-25 min, and the number of cycles is 3-5.

[0070] The specific experimental conditions and test parameters are shown in Table 1 below.

[0071] Table 1 Experimental conditions and test parameters for Examples 1-6

[0072]

[0073]

[0074] Table 1 shows that, at the same concentration, the viscosity of the vanadium oxide sol increases with the increase of the cellulose mass fraction; the V2O5 concentration is positively correlated with the viscosity of the composite sol. Considering both the preparation conditions and the electrochromic properties, the preferred V2O5 concentration in this invention is 0.025–0.05 mol / L, and the cellulose mass fraction is 5.2%–52.3%.

[0075] The MC composite vanadium oxide sol prepared by this invention has a viscosity of 4.3–153.6 mPa·s. -1 .

[0076] Based on the CV curves of Examples 1-6 and the operability of spin-coated films at different viscosities (including film surface uniformity, smoothness, rheology, etc.), it is preferable to use 9.9 wt% cellulose composite 0.05 M vanadium pentoxide sol.

[0077] Application Example 1

[0078] Based on the CV test curves and the feasibility of spin coating at different viscosities, the sol obtained in Example 4 (9.9 wt% methylcellulose composite 0.05 M vanadium pentoxide sol) was used to prepare electrochromic materials, including the following steps:

[0079] (1) Measure an appropriate amount of sol and drop it vertically onto the surface of the conductive substrate adsorbed on the spin coater;

[0080] (2) Rotate and centrifuge to remove excess sol and obtain a uniform film. Use a hair dryer to dry the surface of the film.

[0081] (3) Repeat steps (1) and (2).

[0082] (4) Transfer the electrochromic film to a 45°C forced-air drying oven and dry for 24 hours to obtain the electrochromic film.

[0083] (5) One electrochromic film is pre-embedded with ions as the counter electrode, and the other is used as the working electrode. A membrane wetted with electrolyte is sandwiched in the middle, and the device is encapsulated with 3M glue around the edges.

[0084] (6) The optical and electrochemical properties of the material were measured using an ultraviolet-visible-near-infrared spectrophotometer and an electrochemical workstation, respectively.

[0085] The conductive substrate material in step (1) is a PET-ITO flexible conductive film.

[0086] The motion program for centrifugation in step (2) is as follows: low speed 2100 RPM, time 10s, high speed 3500 RPM, time 60s.

[0087] The spin coating process in step (3) is repeated 3 times.

[0088] Comparative Example 1

[0089] The electrochromic material was prepared using only vanadium pentoxide sol, and the remaining preparation steps and parameters were the same as in Example 4 and Application Example 1.

[0090] Tests revealed poor stability within 1000 cycles, and the contrast of the film at 646 nm was lower than that of the cellulose-doped film.

[0091] To fully understand the structure and performance of the cellulose composite vanadium oxide electrochromic thin film and device of Application Example 1 of this invention, SEM, CV, and spectral tests were performed on them, and the results are as follows: Figure 2-5 As shown.

[0092] Figure 2 The image shows a SEM image of the cellulose composite vanadium oxide electrochromic film prepared in Example 1, indicating that cellulose and V2O5 are uniformly composited and the film surface is smooth.

[0093] Figure 3 The CV curve of the electrochromic thin film prepared in Example 1 is shown. Figure 4 The CV curves of the electrochromic thin film prepared in Comparative Example 1 are shown. From the redox peaks and the area of ​​the region covered by the curves, it is clear that after 1000 cycles, the application of Example 1 (…)… Figure 3 The peak currents of one set of redox peaks were 1.443V, -0.905V and 0.883V, -0.637V, respectively, with the charge capacity remaining at 80.6%; compared to Comparative Example 1 ( Figure 4 The V₂O₅ electrochromic film without cellulose doping exhibits more stable electrochromic properties after 1000 cycles, while the V₂O₅ electrochromic film in Comparative Example 1 only retains 47.6% of its charge capacity after 1000 cycles. Therefore, the electrochromic film prepared by the composite sol of this invention has higher stability, and cellulose acts as a "reinforcing agent".

[0094] The film states were observed under manual bending at 30°, 90° and 180°, and the results are shown in Table 2 below.

[0095] Table 2 Comparison of the bending states of the electrochromic films obtained in Application Example 1 and Comparative Example 1 of the present invention

[0096]

[0097] Furthermore, based on the sol viscosity of Examples 1-6 under different doping ratios and the results in Table 2, it can be seen that the present invention significantly improves the sol viscosity and the flexibility of the film by using cellulose with high strength, high transparency and low coefficient of thermal expansion, which has a nanowire structure interspersed in the vanadium oxide layered structure to improve stability.

[0098] Figure 5 The absorbance dynamic test of the electrochromic device prepared in Example 1 was conducted to demonstrate the rapid response of the thin film between different colors, with a total switching response time of 6.8 s.

[0099] Therefore, the electrochromic film prepared by the present invention can achieve reversible change from blue to green and then to yellow, and still retain more than 80% of its charge capacity after 1000 cycles.

[0100] Comparative Example 2

[0101] MC and CMC powders were directly added to vanadium pentoxide sol and pulverized using an ultrasonic cell disruptor. The remaining preparation steps were the same as in Examples 4 and 7.

[0102] The research process revealed the presence of agglomerates that were difficult to disperse, with some flocculent powder adhering to the beaker wall. The actual doping amount was too low, causing the actual results to deviate significantly from the theoretical values.

[0103] Comparative Example 3

[0104] The nanocellulose and polypyrrole were combined, and the remaining preparation steps and parameters were the same as in Example 4 and Application Example 1.

[0105] The preparation of nanocellulose by this method is relatively complex, while the preparation process of cellulose composite V2O5 electrochromic film is simple. Tests have shown that the cycling stability of cellulose composite polypyrrole is not as good as that of the latter.

[0106] In this invention, if the vanadium pentoxide content is too high, the layered structure is prone to collapse. For example, Comparative Example 1 has a vanadium pentoxide content of 100%, which results in poor cycle stability. On the other hand, if the cellulose content is too high, the film has poor conductivity because cellulose itself is non-conductive. The ion channels are filled with too much linear cellulose, which hinders the insertion of ions. This not only fails to improve the electrochromic properties of the material, but also causes the color change range to be narrow and indistinct.

[0107] Compared with existing technologies:

[0108] This invention provides a method for preparing a cellulose composite vanadium oxide stable sol and its application based on electrochromic materials. The cellulose composite vanadium oxide stable sol is used in electrochromic materials. The preparation method includes the following steps: (1) Vanadium pentoxide is dispersed in hydrogen peroxide solution, magnetically stirred and ultrasonically treated to obtain a uniform solution. After the solution is allowed to stand and age, vanadium oxide sol is obtained; (2) Cellulose is weighed and added to deionized water, and stirred at room temperature to reach a transparent state; (3) The transparent solution obtained in step (2) is frozen to a solid state, and then thawed at room temperature to reach a transparent gel state; (4) The vanadium oxide sol obtained in step (1) and the cellulose gel obtained in step (3) are thoroughly mixed to obtain a stable cellulose composite vanadium oxide sol; (5) The final product is spin-coated on conductive glass and a flexible conductive substrate to form a film and successfully assembled an electrochromic device. This invention employs an improved sol-gel technique and a one-step freeze-thaw method to fully utilize the temperature gradient characteristics of cellulose, successfully developing a cellulose-reinforced electrochromic material suitable for high stability and rich color. The preparation process is simple, providing a pathway for the practical application of electrochromic materials in various environments.

[0109] 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 preparing an electrochromic thin film, characterized in that, Includes the following steps: S1. Mix V2O5, water and hydrogen peroxide evenly and let stand to age to obtain glue A; S2. Add cellulose to water and disperse it evenly. After freezing and thawing, use the temperature gradient to make the cellulose molecular chains align parallel to the direction of the external force and pack tightly to obtain B glue. S3. Add glue B to glue A and mix evenly to obtain cellulose composite vanadium oxide sol; cellulose has a nanowire structure that is interspersed in the vanadium oxide layered structure; In the cellulose-vanadium oxide composite sol, the concentration of vanadium pentoxide is 0.025~0.05 mol / L; cellulose accounts for 5.2%~52.3% of the total mass of cellulose and vanadium pentoxide. S4. The cellulose composite vanadium oxide sol is vertically dropped onto a clean conductive substrate, and the excess sol is removed by centrifugation and dried to obtain a uniform electrochromic film.

2. The method for preparing the electrochromic thin film according to claim 1, characterized in that, In step S1, V2O5 is first added to water to form a vanadium pentoxide solution, and then hydrogen peroxide is added.

3. The method for preparing the electrochromic thin film according to claim 1, characterized in that, In step S1, the mass fraction of hydrogen peroxide is 30%; the molar ratio between V2O5 and H2O2 is 1:

8.

4. The method for preparing the electrochromic thin film according to claim 1, characterized in that, In step S1, the mixing is achieved by first magnetic stirring for 20-30 minutes, followed by ultrasonic oscillation for 15-25 minutes, and repeating this process 3-5 times.

5. The method for preparing the electrochromic thin film according to claim 1, characterized in that, In step S1, the aging period is 5 to 8 days.

6. The method for preparing the electrochromic thin film according to claim 1, characterized in that, In step S2, the cellulose is methylcellulose or carboxymethylcellulose.

7. The method for preparing the electrochromic thin film according to claim 1, characterized in that, The viscosity of the cellulose composite vanadium oxide sol is 4.3~153.6 mPa·s. -1 .

8. The method for preparing the electrochromic thin film according to claim 1, characterized in that, Rotary centrifugation involves variable speed motion, starting at low speed and then increasing to high speed. The low speed is 2000–2200 RPM for 8–12 s, and the high speed is 3400–3600 RPM for 50–70 s.

9. The method for preparing the electrochromic thin film according to claim 1, characterized in that, The drying temperature is 45~60℃, and the time is 1~24 h.

10. An electrochromic thin film prepared by the preparation method according to any one of claims 1-9.

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