An electrochromic smart dimming film and its roll-to-roll preparation method

Abstract

This invention discloses an electrochromic smart dimming film and its roll-to-roll preparation method. The dimming film employs an innovative four-layer structure, consisting of a first transparent conductive substrate, an electrochromic composite layer, a composite electrolyte layer with both ion conduction and storage functions, and a second transparent conductive substrate. By integrating the ion storage function into the electrolyte layer, the ion migration path is significantly shortened, thereby achieving an ultrafast response of less than or equal to 0.5 seconds and an ultra-long cycle life of ≥100,000 cycles. Its preparation utilizes a fully wet roll-to-roll coating process, including steps such as electrochromic layer coating and curing, electrolyte layer slot coating, roll lamination, and low-temperature curing. The product of this invention features a simplified structure, superior performance, low cost, and suitability for mass production, and can be widely applied in the automotive, consumer electronics, and building energy conservation fields.

Description

Technical Field

[0001] This invention belongs to the fields of electrochromic materials, smart dimming glass, and consumer electronics technology, specifically relating to an ultrafast response, long lifespan, low cost, and scalable electrochromic smart dimming film and its roll-to-roll continuous preparation method. Background Technology

[0002] Electrochromic materials can reversibly change their optical properties under low-voltage driving, showing broad application prospects in fields such as smart windows, automotive sunroofs, and displays. Traditional electrochromic devices typically employ a five-layer structure: a first transparent conductive layer, an electrochromic layer, an electrolyte layer, an ion storage layer, and a second transparent conductive layer, stacked sequentially. This type of structure and the corresponding fabrication processes, such as vacuum magnetron sputtering, suffer from problems including complex structure, high production energy consumption, slow response speed (typically tens of seconds to several minutes), limited cycle life, and difficulty in large-area continuous production.

[0003] To overcome the above-mentioned defects, there is an urgent need for an electrochromic smart dimming film with a simple structure, extremely fast response, long life, and the ability to be mass-produced using a low-cost roll-to-roll process, as well as its preparation method. Summary of the Invention

[0004] The technical problem to be solved by this invention is to address the fundamental defects of traditional five-layer electrochromic devices, which inevitably result in long ion migration paths and high interface impedance due to the physical separation of the "ion storage layer" and the "electrochromic layer". This invention provides an electrochromic smart dimming film and its low-cost roll-to-roll preparation method that fundamentally shortens the ion migration path through structural innovation, thereby achieving sub-second ultrafast response and ensuring ultra-long cycle life.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: In a first aspect, the present invention provides an electrochromic smart dimming film, characterized in that it comprises, from bottom to top, the following layers: • First transparent conductive substrate; • Electrochromic composite layer; • A composite electrolyte layer that combines ion conduction and storage functions; • Second transparent conductive substrate.

[0006] The core innovation of this invention lies in abandoning the traditional independent ion storage layer and simplifying the device structure to the aforementioned four layers. The key is to integrate the ion storage function into the composite electrolyte layer through material and interface design. This composite electrolyte layer possesses high ionic conductivity while providing sufficient ion capacity to support rapid, deep, and reversible redox reactions in adjacent electrochromic layers.

[0007] The aforementioned "four-layer simplified structure" and "functional integrated design" fundamentally change the physical mechanism of ion migration. In traditional five-layer devices, working ions (such as Li⁺ and H⁺) need to migrate long distances between the spatially separated ion storage layer and electrochromic layer, resulting in high diffusion resistance. In this invention, however, working ions only undergo short-range, high-speed reciprocating insertion / extraction at the interface region between the closely contacting electrochromic composite layer and the composite electrolyte layer. This extreme shortening of the ion migration path is the core physical mechanism by which the dimming film of this invention achieves an ultrafast response of ≤0.5 seconds.

[0008] Furthermore, by optimizing the composite electrolyte material system and its compatibility with the electrochromic layer interface, while achieving high-speed ion migration, the interfacial side reactions and structural fatigue of the material are effectively suppressed, thereby achieving an ultra-long cycle life of ≥100,000 cycles in a synergistic manner. This breaks through the technical bottleneck of the traditional electrochromic technology where "response speed" and "cycle life" are difficult to achieve simultaneously.

[0009] Preferably, the electrochromic smart dimming film has the following properties: • Visible light transmittance adjustment range: 5%–75%; • Full-frame color-changing response time: ≤ 0.5 seconds; • Cycle life: ≥ 100,000 cycles; • Infrared blocking rate: ≥ 70%; • Haze: <2%; Operating voltage: ±1.5V ~ ±2.5V.

[0010] The first and second transparent conductive substrates can be selected from one of PET / ITO film, glass / ITO, or flexible metal mesh transparent electrode.

[0011] The electrochromic composite layer comprises an electrochromic active material, a conductive agent, and a binder.

[0012] The composite electrolyte layer, which combines ion conduction and storage functions, is a gel or solid electrolyte membrane containing lithium salt, polymer matrix, and functional additives.

[0013] Secondly, the present invention provides a method for preparing the electrochromic smart dimming film, characterized by employing a roll-to-roll wet coating and low-temperature curing process, the specific steps of which include: • S1. Unwind and perform surface cleaning and activation treatment on the first transparent conductive substrate; • S2. On the surface of the activated first transparent conductive substrate, an electrochromic composite paste is coated by microgravure coating or slit coating to form a wet film, which is then dried and cured at 60-100℃ for 2-10 minutes to form an electrochromic composite layer with a dry film thickness of 100-500 nm. • S3. A composite electrolyte slurry is coated onto the surface of the electrochromic composite layer by a slot coating method to form a coating with a wet film thickness of 20-50 μm; • S4. Pre-dry the membrane material coated with composite electrolyte at 50-80℃ for 1-3 minutes, and then perform alignment roll pressing composite with the second transparent conductive substrate under a pressure of 0.1-0.5 MPa; • S5. The composite membrane material is cured at ≤60℃ for 24-48 hours to fully solidify the composite electrolyte layer, and then finally wound up and slit to obtain the finished product. Detailed Implementation

[0014] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be described in detail below with reference to embodiments and comparative examples. Example 1

[0015] This embodiment provides a method for preparing an electrochromic smart dimming film, the specific steps of which are as follows: 1. Substrate preparation: Take a PET / ITO transparent conductive film (sheet resistance <10Ω / □, visible light transmittance ≥88%) as the first transparent conductive substrate, and perform online plasma cleaning after unwinding to improve its surface energy.

[0016] 2. Coating the Electrochromic Layer: An electrochromic composite slurry was coated onto the cleaned substrate surface using a microgravure coating machine. This slurry was prepared by dispersing nano-tungsten oxide (WO3) particles, conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) binder in N-methylpyrrolidone (NMP) at a mass ratio of 85:10:5. The wet film thickness was controlled at 10 μm, and the coating line speed was 3 m / min. Subsequently, the coated film was placed in an 80°C hot air drying tunnel and dried and cured for 5 minutes to form a dense electrochromic composite layer with a dry film thickness of approximately 300 nm.

[0017] 3. Coating the composite electrolyte layer: A slit coater is used to coat the electrochromic layer with a composite electrolyte slurry. This slurry is prepared by dissolving lithium perchlorate (LiClO4), polyethylene oxide (PEO), and pre-lithium-intercalated titanium dioxide (Li0.5TiO2) nanoparticles (as ion storage functional components) in acetonitrile in a specific ratio. The wet film thickness of the slit coating is controlled to be 30 μm.

[0018] 4. Pre-drying and lamination: The film coated with the electrolyte layer is pre-dried at 70°C for 2 minutes, and then precisely aligned and rolled together with the second transparent conductive substrate (PET / ITO film of the same specification) under a rolling pressure of 0.3 MPa.

[0019] 5. Curing and Post-treatment: The roll-pressed film is placed in a constant temperature environment of 50℃ for 36 hours to cure the composite electrolyte layer completely. Finally, it is wound up and cut to obtain the finished electrochromic smart dimming film.

[0020] Performance Testing: The prepared dimming film sample was tested by applying a square wave voltage of ±2.0V. The results showed that its visible light transmittance could be reversibly adjusted between 7% and 75%, the response time for full-range color change (from transparent to colored state) was 0.4 seconds, and the fading response time was 0.3 seconds. After 100,000 cycles of continuous charge-discharge cycling at 1 Hz, the decay rate of both maximum and minimum transmittance was less than 5%. The infrared blocking rate reached 72%, and the haze was 1.8%.

[0021] Comparative Example 1 To verify the superiority of the simplified four-layer structure of this invention, a conventional five-layer electrochromic film was prepared as a comparative example. The specific steps are as follows: • Repeat steps 1 and 2 of Example 1 to prepare a first conductive substrate with an electrochromic layer.

[0022] • Coating a conventional electrolyte layer: Coat a conventional gel electrolyte containing only LiClO4 and PEO (without ion storage functional components) onto the electrochromic layer, with a wet film thickness of 20 μm, and pre-dry at 70°C for 2 minutes.

[0023] • Coating of ion storage layer: On the conventional electrolyte layer, an additional ion storage layer formed by nickel oxide (NiO) slurry is coated, with a wet film thickness of about 200 nm, and dried at 80°C.

[0024] • Composite: The membrane material with the ion storage layer is rolled and laminated with the second transparent conductive substrate under a pressure of 0.3 MPa and then cured at 50°C for 36 hours.

[0025] • Performance Testing: Under the same testing conditions, the full-width color-changing response time of this five-layer dimming film is 2.1 seconds, and the fading time is 1.8 seconds. After 30,000 cycles of testing, its transmittance adjustment range has decreased by more than 15%, showing significant performance degradation.

[0026] Comparison of effects between the examples and the comparative examples Comparative Example 1 (Four-layer structure of the present invention) vs. Comparative Example 1 (Traditional five-layer structure) Device structure: Four-layer (functional integration) Five-layer (functional separation) Full-frame color-changing response time: 0.3-0.4 seconds to 1.8-2.1 seconds Cycle life (attenuation <5%): Approximately 30,000 cycles (attenuation >15%) out of 100,000 cycles As can be seen from the above comparison, by adopting a composite electrolyte layer with ion storage function and a four-layer simplified structure, the present invention not only significantly improves the response speed (reaching the sub-second level) but also greatly extends the cycle life, while simplifying the device structure and fabrication process, achieving unexpected technical effects.

[0027] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An electrochromic smart dimming film, characterized in that, From bottom to top, they include: First transparent conductive substrate; Electrochromic composite layer; A composite electrolyte layer that combines ion conduction and storage functions; Second transparent conductive substrate.

2. The electrochromic smart dimming film according to claim 1, characterized in that, The full-width color-changing response time of the dimming film is less than or equal to 0.5 seconds, and the cycle life is ≥100,000 times.

3. The electrochromic smart dimming film according to claim 1, characterized in that, The composite electrolyte layer is a gel or solid electrolyte membrane containing lithium salt, polymer matrix and functional additives.

4. The electrochromic smart dimming film according to claim 1, characterized in that, The electrochromic composite layer comprises a metal oxide electrochromic material, a conductive agent, and a binder.

5. A method for preparing the electrochromic smart dimming film according to any one of claims 1 to 4, characterized in that, The roll-to-roll wet coating process includes the following steps: S1. An electrochromic composite paste is coated on a first transparent conductive substrate and dried and cured to form an electrochromic composite layer; S2. A composite electrolyte slurry is coated onto the electrochromic composite layer by a slot coating method to form a wet film; S3. The membrane material coated with the composite electrolyte slurry is pre-dried and then rolled and laminated with the second transparent conductive substrate; S4. The composite membrane material is subjected to low-temperature curing to solidify the composite electrolyte layer, thereby obtaining the dimming membrane.

6. The method according to claim 5, characterized in that, In step S2, the wet film thickness of the composite electrolyte slurry is controlled at 20-50 μm.

7. The method according to claim 5, characterized in that, In step S4, the temperature for low-temperature curing is ≤60℃, and the curing time is 24-48 hours.

8. The method according to claim 5, characterized in that, In step S3, the pressure of the roller pressing composite is 0.1-0.5 MPa.

9. A type of automotive sunroof, smart glasses, or energy-saving architectural glass, characterized in that, The electrochromic smart dimming film comprising any one of claims 1 to 4.