Electrochromic device with symmetrical structure as well as preparation method and application of electrochromic device

Abstract

The invention relates to the technical field of functional materials and devices, in particular to a symmetric structure electrochromic device and a preparation method and application thereof. The symmetrical structure electrochromic device comprises a first transparent conductive substrate, a first bipolar electrochromic layer, an electrolyte layer, a second bipolar electrochromic layer and a second transparent conductive substrate which are sequentially stacked, and the first bipolar electrochromic layer and the second bipolar electrochromic layer comprise the same bipolar electrochromic material. The bipolar electrochromic material is an electrochromic material which can be colored in an oxidation state and a reduction state. The same bipolar electrochromic material is adopted in the two electrochromic layers, so that the device has large optical modulation amplitude, good stability and low driving voltage, the comprehensive performance of the electrochromic device is remarkably improved, and the electrochromic device has wide application prospects in the electrochromic field.

Description

Technical Field

[0001] The present invention relates to the technical field of functional materials and devices, and particularly relates to a symmetric structure electrochromic device, a preparation method thereof, and an application thereof. Background Art

[0002] At present, nearly half of the population is concentrated in cities, and the "island effect" of cities further exacerbates the impact of global warming on human life. Building energy consumption accounts for 30-40% of the global total energy, mainly used for indoor heating, cooling, ventilation, lighting, etc. With the development of future building technologies, there is great potential for building energy conservation. The main energy exchange between buildings and the environment is carried out through windows, and radiation is the main form of energy exchange. By adopting intelligent windows that can selectively adjust the transmittance of each wavelength band to achieve a balance between indoor lighting and appropriate transmittance is a very promising strategy for building energy conservation.

[0003] The core of an electrochromic intelligent window is an electrochromic device. A typical electrochromic device is generally composed of five layers of films stacked: between two transparent conductive layers, there are an electrochromic layer, an electrolyte layer, and an ion storage layer (another electrochromic layer) in sequence. Among them, the function of the transparent conductive layer is to transfer electrons from the external circuit to the electrochromic material. The function of the electrochromic layer is to conduct both ions and electrons simultaneously, and it is the film layer where redox reactions occur; its working principle is that under the action of an external electric field, ions and electrons are injected or extracted in the electrochromic layer, and redox reactions occur, causing changes in the optical constants (refractive index, extinction coefficient) of the material, resulting in changes in the transmittance and reflectivity of the material. According to the coloring properties, electrochromic materials can be divided into cathode electrochromic materials and anode electrochromic materials; cathode electrochromic materials are colored when electrons and ions are injected and fade when they are extracted, and representative materials include tungsten oxide (WO 3 )、titanium oxide (TiO 2 )、molybdenum oxide (MoO 3 )、niobium oxide (Nb 2 O 5 ) etc.; anode electrochromic materials are the opposite, fading when electrons and ions are injected and coloring when they are extracted, and typical materials include nickel oxide (NiO), iridium oxide (IrO 2 )、manganese dioxide (MnO 2 ) and cobalt oxide (Co 3 O 4 ) etc. In addition, there is a special amphoteric electrochromic material in transition metal oxides that can be colored in both the oxidized state and the reduced state, such as vanadium pentoxide (V 2 O5 )。The electrolyte layer is mainly used to conduct ions. It separates an electrochromic thin film from another ion storage thin film and is required to be a pure ion conductor and a good electronic insulator. The ion storage layer is mainly used to store ions and needs to match the properties of the electrochromic layer material. The ion storage layer materials can be divided into two categories: one is that there is basically no color change during the ion / electron insertion or extraction process, and its main function is to store ions; the other is a second electrochromic layer with coloring properties opposite to those of the electrochromic layer, that is, a cathode electrochromic material - an anode electrochromic material. Under voltage stimulation, these two thin films, the electrochromic layer and the second electrochromic layer, will be colored and faded synchronously, and compared with single-layer materials, a more significant color change effect can be achieved. The key to constructing an electrochromic device with good performance lies in finding suitable cathode electrochromic materials and anode electrochromic materials. According to the current material system, the cathode electrochromic materials already have a system with a large modulation amplitude, good stability, and rapid response; the anode electrochromic material system has relatively large deficiencies. The anode materials more or less have problems such as poor stability, low capacity, and unsatisfactory color, which is a major obstacle restricting the development of electrochromic devices.

[0004] In order to achieve a better modulation amplitude, traditional electrochromic devices use cathode electrochromic materials and anode electrochromic materials as counter electrodes to each other. However, due to the generally poor stability, low capacity, and small modulation amplitude of anode electrochromic materials, and more importantly, the inability to achieve a matching charge capacity and electrochemical window with the cathode electrochromic layer, generally a relatively large driving voltage is required, but this will damage the performance and lifespan of the electrochromic layer and the electrolyte, greatly limiting its application. The advantage of traditional symmetric structure electrochromic devices is that there is no electrochemical matching problem and the driving voltage is relatively low. However, since the two electrodes have the same material (such as both being Li x WO 3 ), and the coloring properties are the same. Therefore, the initial state of the device is a dark state. During operation, one electrode is colored and the other is faded, making the electrochromism of the device in a dark state and the modulation amplitude very weak. Therefore, there is an urgent need to construct an electrochromic device with excellent electrochromic performance, large modulation amplitude, good stability, and low driving voltage. Summary of the Invention

[0005] In view of the above deficiencies of the prior art, the purpose of the present invention is to provide a symmetric structure electrochromic device, its preparation method and application, aiming to solve the problems of low modulation amplitude, poor stability, and high driving voltage of existing electrochromic devices.

[0006] The technical solution of the present invention is as follows:

[0007] In the first aspect of the present invention, a symmetric electrochromic device is provided, which includes a first transparent conductive substrate, a first amphoteric electrochromic layer, an electrolyte layer, a second amphoteric electrochromic layer, and a second transparent conductive substrate that are sequentially stacked. The first amphoteric electrochromic layer and the second amphoteric electrochromic layer include the same amphoteric electrochromic material, and the amphoteric electrochromic material is an electrochromic material that can be colored in both the oxidized state and the reduced state.

[0008] Optionally, the thickness of the first amphoteric electrochromic layer is 30 - 700 nm, and the thickness of the second amphoteric electrochromic layer is 30 - 700 nm.

[0009] Optionally, the first amphoteric electrochromic layer includes a first amphoteric electrochromic material, and the first amphoteric electrochromic material is α-V 2 O 5 , ζ-Li a V 2 O 5 , ζ-Na a V 2 O 5 or ζ-K a V 2 O 5 , where 0 ≤ a ≤ 3; the second amphoteric electrochromic layer includes a second amphoteric electrochromic material, and the second amphoteric electrochromic material is α-V 2 O 5 , ζ-Li b V 2 O 5 , ζ-Na b V 2 O 5 or ζ-K b V 2 O 5 , where 0 ≤ b ≤ 3; a and b are the same or different.

[0010] In the second aspect of the present invention, a method for preparing the symmetric electrochromic device described in the present invention is provided, which includes the steps:

[0011] Provide a first transparent conductive substrate, and form a first amphoteric electrochromic layer on the first transparent conductive substrate; provide a second transparent conductive substrate, and form a second amphoteric electrochromic layer on the second transparent conductive substrate; the first amphoteric electrochromic layer and the second amphoteric electrochromic layer include the same amphoteric electrochromic material, and the amphoteric electrochromic material is an electrochromic material that can be colored in both the oxidized state and the reduced state;

[0012] An electrolyte layer is formed between a first transparent conductive substrate having a first amphoteric electrochromic layer and a second transparent conductive substrate having a second amphoteric electrochromic layer. At this time, the electrolyte layer is adhered to the first amphoteric electrochromic layer and the second amphoteric electrochromic layer, and the symmetric structure electrochromic device is obtained through encapsulation;

[0013] Or,

[0014] Provide a first transparent conductive substrate, and sequentially deposit a first amphoteric electrochromic layer, an electrolyte layer, a second amphoteric electrochromic layer, and a second transparent conductive substrate on the first transparent conductive substrate to obtain the symmetric structure electrochromic device;

[0015] The first amphoteric electrochromic layer and the second amphoteric electrochromic layer include the same amphoteric electrochromic material, and the amphoteric electrochromic material is an electrochromic material that can be colored in both the oxidized state and the reduced state.

[0016] Optionally, the first amphoteric electrochromic layer includes a first amphoteric electrochromic material, and the first amphoteric electrochromic material is ζ-Li a V 2 O 5 , where 0 ≤ a ≤ 3;

[0017] When the first amphoteric electrochromic material is ζ-Li 0.3 V 2 O 5 At this time, the first amphoteric electrochromic layer is prepared according to the following steps:

[0018] Provide a first transparent conductive substrate, and form a Li 0.3 V 2 O 5 amorphous thin film on the first transparent conductive substrate by magnetron sputtering, and anneal the Li 0.3 V 2 O 5 amorphous thin film to obtain ζ-Li 0.3 V 2 O 5 thin film to obtain the first amphoteric electrochromic layer;

[0019] Or, when the first amphoteric electrochromic material is ζ-Li a V 2 O 5 and a is not 0.3, the first amphoteric electrochromic layer is prepared according to the following steps:

[0020] Provide a first transparent conductive substrate, and form a Li 0.3 V 2 O 5 amorphous thin film on the first transparent conductive substrate by magnetron sputtering, and for the Li0.3 V 2 O 5 The amorphous thin film is annealed to obtain ζ-Li 0.3 V 2 O 5 thin film;

[0021] Using a lithium salt solution as the lithium source, through an electrochemical lithiation method, the ζ-Li 0.3 V 2 O 5 thin film is converted into ζ-Li a V 2 O 5 thin film to obtain the first ambipolar electrochromic layer.

[0022] Optionally, the second ambipolar electrochromic layer includes a second ambipolar electrochromic material, and the second ambipolar electrochromic material is ζ-Li b V 2 O 5 , where 0 ≤ b ≤ 3;

[0023] When the second ambipolar electrochromic material is ζ-Li 0.3 V 2 O 5 , the second ambipolar electrochromic layer is prepared according to the following steps:

[0024] Provide a second transparent conductive substrate, and form a Li 0.3 V 2 O 5 amorphous thin film on the second transparent conductive substrate, and anneal the Li 0.3 V 2 O 5 amorphous thin film to obtain ζ-Li 0.3 V 2 O 5 thin film to obtain the second ambipolar electrochromic layer;

[0025] Or, when the second ambipolar electrochromic material is ζ-Li b V 2 O 5 and b is not 0.3, the second ambipolar electrochromic layer is prepared according to the following steps:

[0026] Provide a second transparent conductive substrate, and form a Li 0.3 V 2 O 5 amorphous thin film on the second transparent conductive substrate, and anneal the Li 0.3 V 2 O 5 amorphous thin film to obtain ζ-Li0.3 V 2 O 5 thin film;

[0027] Using a lithium salt solution as the lithium source, through an electrochemical lithiation method, converting the ζ-Li 0.3 V 2 O 5 thin film into ζ-Li b V 2 O 5 thin film to obtain a second amphoteric electrochromic layer.

[0028] Optionally, the conditions of the magnetron sputtering method include: using V and Li 2 O as the target, in an oxygen and argon environment, the sputtering gas pressure is 0.5 - 4 Pa, the V sputtering power is 70 - 300 W, and the Li 2 O sputtering power is 10 - 200 W, and the sputtering time is 0.3 - 10 h.

[0029] Optionally, the conditions of the annealing treatment include: the annealing temperature is 200 - 500 °C, and the annealing time is 0.5 - 10 h.

[0030] Optionally, the electrochemical lithiation method is a constant voltage charging method, and the conditions of the constant voltage charging method include: the cut-off voltage is 2.0 - 4.0 V, the time is 100 - 600 s, and the lithium salt concentration is 0.5 - 2 mol / L.

[0031] In the third aspect of the present invention, there is provided an application of the electrochromic device described in the present invention in the field of electrochromics.

[0032] Beneficial effects: By constructing a symmetric structure electrochromic device using the same amphoteric electrochromic material in two electrochromic layers, when the device undergoes an electrochemical cycle, one pole exhibits cathodic coloring characteristics while the other pole exhibits anodic coloring characteristics, enabling the two poles to color and fade synergistically. The matching of such a structure with electrochromic performance enables the device to have both a large optical modulation amplitude (the infrared modulation amplitude reaches 60%) and good stability (2000 cycles) and a low driving voltage, achieving a significant improvement in the comprehensive performance of the electrochromic device and having broad application prospects in the field of electrochromics. Description of the Drawings

[0033] Figure 1 is a schematic structural diagram of a symmetric structure electrochromic device provided by the present invention.

[0034] Figure 2 is the in-situ spectral transmittance change curve of the symmetric structure electrochromic device prepared in Example 1 in the colored state and the faded state.

[0035] Figure 3 It is the current-voltage change curve of the symmetric electrochromic device prepared in Example 1 during the electrochemical cycling process.

[0036] Figure 4 It is the spectral transmittance change diagram at 633 nm of the symmetric electrochromic device prepared in Example 1 during the electrochemical cycling process.

[0037] Figure 5 It is the spectral transmittance change diagram at 700 nm of the symmetric electrochromic device prepared in Example 1 during the electrochemical cycling process.

[0038] Figure 6 It is the spectral transmittance change diagram at 1100 nm of the symmetric electrochromic device prepared in Example 1 during the electrochemical cycling process.

[0039] Figure 7 It is the transmittance change diagram of the 1100 nm band and 550 nm band of the electrochromic device prepared in Comparative Example 1 during 30 cycles. Detailed implementation manners

[0040] The present invention provides a symmetric electrochromic device and its preparation method and application. To make the purpose, technical solution and effect of the present invention clearer and more definite, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0041] Unless otherwise defined, all technical terms and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the specification of the present invention herein are only for the purpose of describing specific implementation manners and are not intended to limit the present invention.

[0042] As Figure 1 shown, an embodiment of the present invention provides a symmetric electrochromic device, which includes a first transparent conductive substrate, a first amphoteric electrochromic layer, an electrolyte layer, a second amphoteric electrochromic layer and a second transparent conductive substrate stacked in sequence, wherein the first amphoteric electrochromic layer and the second amphoteric electrochromic layer include the same amphoteric electrochromic material, and the amphoteric electrochromic material is an electrochromic material that can be colored in both the oxidized state and the reduced state.

[0043] In the embodiments of the present invention, a symmetric electrochromic device is constructed by using the same amphoteric electrochromic material in two electrochromic layers. When the device undergoes an electrochemical cycle, one pole exhibits cathodic coloring characteristics while the other pole exhibits anodic coloring characteristics, enabling the two poles to color and fade synergistically. The matching of such a structure with electrochromic performance endows the device with both a large optical modulation amplitude (the infrared modulation amplitude reaches 60%) and good stability (2000 cycles) and a low driving voltage, achieving a significant improvement in the comprehensive performance of the electrochromic device and having broad application prospects in the field of electrochromics and great significance in applications in the fields of energy, construction, information, and national defense.

[0044] For the symmetric electrochromic device of the embodiments of the present invention, when a voltage load is applied, there are infrared transmission or infrared blocking states, and it can stably and reversibly greatly adjust the transmittance in the near-infrared band at a relatively small driving voltage. The infrared modulation amplitude reaches 60%, and it has good stability, effectively solving the problems of the relatively small modulation amplitude of traditional symmetric electrochromic devices (when the thickness of the electrochromic layer is the same, the modulation amplitude is basically only 20 - 30%) and the poor stability and large driving voltage of traditional asymmetric electrochromic devices (generally requiring a bias voltage of more than 4V). Moreover, the relatively small driving voltage results in fewer electrochemical side reactions generated inside the device during operation, which helps to improve the stability of the device; the lower driving voltage also means lower energy consumption and a simpler circuit system, enabling the device to adapt to a wider range of working scenarios. In addition, using the same amphoteric electrochromic material in the two electrochromic layers also simplifies the types of materials and reduces the preparation difficulty.

[0045] In this article, "the first amphoteric electrochromic layer and the second amphoteric electrochromic layer include the same amphoteric electrochromic material" includes the following situations: (1) The first amphoteric electrochromic layer and the second amphoteric electrochromic layer include amphoteric electrochromic materials with exactly the same chemical formula, belonging to the symmetric electrochromic device claimed in the present invention; for example, the first amphoteric electrochromic layer includes ζ-Li a V 2 O 5 (0 ≤ a ≤ 3) amphoteric electrochromic material, and the second amphoteric electrochromic layer includes ζ-Li b V 2 O 5(0 ≤ b ≤ 3) amphoteric electrochromic material, where a and b are the same; (2) The first amphoteric electrochromic layer and the second amphoteric electrochromic layer respectively include different ionic solid solution states of an amphoteric electrochromic material. Different ionic solid solution states of an amphoteric electrochromic material mean that the injection and extraction of ions in the material system hardly affect the crystal structure of the material, and the process is reversible, and different ionic content states can be converted into each other. Therefore, different ionic solid solution states of an amphoteric electrochromic material essentially belong to the same amphoteric electrochromic material and belong to the symmetric structure electrochromic device claimed in the present invention. For example, the first amphoteric electrochromic layer includes ζ-Li a V 2 O 5 (0 ≤ a ≤ 3) amphoteric electrochromic material, and the second amphoteric electrochromic layer includes ζ-Li b V 2 O 5 (0 ≤ b ≤ 3) amphoteric electrochromic material, where a and b are different.

[0046] In some embodiments, the thickness of the first amphoteric electrochromic layer is 30 - 700 nm, and the thickness of the second amphoteric electrochromic layer is 30 - 700 nm. In a symmetric structure electrochromic device, the thicker the electrochromic layer, the stronger the optical modulation generated, the lower the maximum transmittance of the thin film, and generally the larger the electrochemical capacity of the thin film. In the construction of the device, it is necessary to balance the maximum transmittance and the optical modulation amplitude to ensure that the electrochemical capacities of the two electrochromic layers are as equal as possible. Therefore, it is more appropriate to set the thicknesses of the first and second amphoteric electrochromic layers to 30 - 700 nm.

[0047] In some embodiments, the thickness of the electrolyte layer can be set according to actual needs, as long as it has good transparency and can serve as a good ion transport layer and a good electron blocking layer.

[0048] In a preferred embodiment, the thickness of the first amphoteric electrochromic layer is 280 nm, the thickness of the second amphoteric electrochromic layer is 280 nm, and the thickness of the electrolyte layer is 3 mm.

[0049] In some embodiments, the transparent conductive substrate has a transparent conductive layer on a transparent substrate. The first transparent conductive substrate and the second transparent conductive substrate can be selected from ITO transparent conductive glass or FTO transparent conductive glass, but are not limited thereto.

[0050] In some embodiments, the electrolyte layer can be formed from commonly used electrolyte solutions or solid electrolytes in the art.

[0051] In some embodiments, the first amphoteric electrochromic layer comprises a first amphoteric electrochromic material, and the first amphoteric electrochromic material is α-V 2 O 5 , ζ-Li a V 2 O 5 , ζ-Na a V 2 O 5 or ζ-K a V 2 O 5 , where 0 ≤ a ≤ 3; the second amphoteric electrochromic layer comprises a second amphoteric electrochromic material, and the second amphoteric electrochromic material is α-V 2 O 5 , ζ-Li b V 2 O 5 , ζ-Na b V 2 O 5 or ζ-K b V 2 O 5 , where 0 ≤ b ≤ 3; a and b are the same or different.

[0052] In this embodiment, α and ζ before V 2 O 5 are a naming method, indicating different crystal structures of the V 2 O 5 material. ζ-Li a V 2 O 5 or ζ-Li b V 2 O 5 represents the material formed by Li + being embedded into the channel structure of ζ-V 2 O 5 , which is a different ionic solid solution state of ζ-V 2 O 5 . The subscripts a and b of Li represent the embedding amount of Li + in the channel structure of ζ-V 2 O 5 . For example, a: 2 or b: 2 means the atomic ratio or molar ratio of Li to V. For example, ζ-Li 0.3 V 2 O 5 represents that the atomic ratio of Li to V is 0.3: 2. Additionally, when a or b is 0, it means that no Li 2 O 5 is embedded in the channel structure of ζ-V + .

[0053] In some embodiments, a can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.66, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.33, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, etc.; b can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.66, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.33, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, etc.

[0054] An embodiment of the present invention provides a method for preparing the symmetric structure electrochromic device described in any one of the foregoing embodiments, which includes the steps of:

[0055] Providing a first transparent conductive substrate, and forming a first amphoteric electrochromic layer on the first transparent conductive substrate; providing a second transparent conductive substrate, and forming a second amphoteric electrochromic layer on the second transparent conductive substrate; the first amphoteric electrochromic layer and the second amphoteric electrochromic layer include the same amphoteric electrochromic material, and the amphoteric electrochromic material is an electrochromic material that can be colored in both the oxidized state and the reduced state;

[0056] Forming an electrolyte layer between the first transparent conductive substrate with the first amphoteric electrochromic layer and the second transparent conductive substrate with the second amphoteric electrochromic layer. At this time, the electrolyte layer is attached to the first amphoteric electrochromic layer and the second amphoteric electrochromic layer, and the symmetric structure electrochromic device is obtained through encapsulation.

[0057] In some embodiments, the first amphoteric electrochromic layer includes a first amphoteric electrochromic material, and the first amphoteric electrochromic material is ζ-Li a V 2 O 5 , where 0 ≤ a ≤ 3;

[0058] When the first amphoteric electrochromic material is ζ-Li 0.3 V 2 O 5 (i.e., a is 0.3), the first amphoteric electrochromic layer is prepared according to the following steps:

[0059] Step S1: Provide a first transparent conductive substrate, and form Li 0.3 V 2 O 5Amorphous thin film, for the Li 0.3 V 2 O 5 The amorphous thin film is annealed to obtain ζ-Li 0.3 V 2 O 5 thin film, obtaining the first amphoteric electrochromic layer;

[0060] Alternatively, when the first amphoteric electrochromic material is ζ-Li a V 2 O 5 and a is not 0.3, the first amphoteric electrochromic layer is prepared according to the following steps:

[0061] Step S11: Provide a first transparent conductive substrate, and form a Li 0.3 V 2 O 5 amorphous thin film on the first transparent conductive substrate, and anneal the Li 0.3 V 2 O 5 amorphous thin film to obtain ζ-Li 0.3 V 2 O 5 thin film;

[0062] Step S12: Using a lithium salt solution as a lithium source, through an electrochemical lithiation method, convert the ζ-Li 0.3 V 2 O 5 thin film into a ζ-Li a V 2 O 5 thin film, obtaining the first amphoteric electrochromic layer.

[0063] In some embodiments, the second amphoteric electrochromic layer includes a second amphoteric electrochromic material, and the second amphoteric electrochromic material is ζ-Li b V 2 O 5 , where 0 ≤ b ≤ 3;

[0064] When the second amphoteric electrochromic material is ζ-Li 0.3 V 2 O 5 the second amphoteric electrochromic layer is prepared according to the following steps:

[0065] Step S21: Provide a second transparent conductive substrate, and form a Li 0.3 V 2 O 5 amorphous thin film on the second transparent conductive substrate, and anneal the Li 0.3 V 2 O5 The amorphous thin film is annealed to obtain ζ-Li 0.3 V 2 O 5 thin film, and a second ambipolar electrochromic layer is obtained;

[0066] Alternatively, when the second ambipolar electrochromic material is ζ-Li b V 2 O 5 and b is not 0.3, the second ambipolar electrochromic layer is prepared according to the following steps:

[0067] Step S31: Provide a second transparent conductive substrate, and form a Li 0.3 V 2 O 5 amorphous thin film on the second transparent conductive substrate, and anneal the Li 0.3 V 2 O 5 amorphous thin film to obtain ζ-Li 0.3 V 2 O 5 thin film;

[0068] Step S32: Using a lithium salt solution as a lithium source, through an electrochemical lithiation method, convert the ζ-Li 0.3 V 2 O 5 thin film into a ζ-Li b V 2 O 5 thin film to obtain a second ambipolar electrochromic layer.

[0069] In some embodiments, in step S1, step S11, step S21, and step S31, the conditions of the magnetron sputtering method include: using V and Li 2 O as a target, in an oxygen and argon environment, the sputtering gas pressure is 0.5-4 Pa, the V sputtering power is 70-300 W, the Li 2 O sputtering power is 10-200 W, and the sputtering time is 0.3-10 h. Specifically, the sputtering atmosphere / sputtering gas pressure / sputtering power / sputtering time and other conditions used during magnetron sputtering can be set according to actual needs. Preferably, by controlling the ratio of oxygen and argon in the sputtering atmosphere to be 9:1, the sputtering gas pressure to be 1 Pa, the V sputtering power to be 160 W, the Li 2 O sputtering power to be 50 W, and the sputtering time to be 2.5 h, a Li 0.3 V 2 O 5 amorphous thin film is formed on the substrate.

[0070] In some embodiments, in steps S1, S11, S21 and S31, the conditions of the annealing treatment include: the annealing temperature is 200-500 °C, and the annealing time is 0.5-10 h. Preferably, the annealing temperature is 300 °C and the annealing time is 2 h. Through the annealing treatment, Li 0.3 V 2 O 5 can be converted into ζ-Li 0.3 V 2 O 5 , and ζ-Li 0.3 V 2 O 5 thin film is obtained.

[0071] In some embodiments, in steps S12 and S32, the lithium salt solution is composed of a lithium salt and a solvent. The lithium salt in the lithium salt solution includes at least one of lithium perchlorate, lithium hexafluorophosphate (LiPF 6 ), lithium bis(oxalato)borate (LiBOB), lithium tetrafluoroborate (LiBF 4 ), lithium difluoro(oxalato)borate (LiODFB), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium difluorophosphate (LiPO 2 F 2 ), and lithium tetrafluoro(oxalato)phosphate (LiFOP), but is not limited thereto. 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, but is not limited thereto.

[0072] In some embodiments, in steps S12 and S32, the electrochemical lithiation method is a constant voltage charging method. The conditions of the constant voltage charging method include: the cut-off voltage is 2.0-4.0 V, the time is 100-600 s, and the lithium salt concentration is 0.5-2 mol / L. Specifically, by controlling the cut-off voltage, charging time, and lithium salt concentration, the amount of lithium intercalated or deintercalated in the ζ-Li 0.3 V 2 O 5 channels is controlled to ensure that the ζ-Li 0.3 V 2 O 5 thin film is converted into ζ-Li a V 2 O 5 thin film or ζ-Li b V 2 O 5 thin film.

[0073] In some specific embodiments, through the electrochemical lithiation method, the ζ-Li 0.3 V2 O 5 The thin film is converted into ζ-Li a V 2 O 5 The thin film or ζ-Li b V 2 O 5 The thin film, specifically using a three-electrode system: using metallic lithium as the reference electrode and the counter electrode, and using ζ-Li 0.3 V 2 O 5 The thin film as the working electrode, using a lithium salt solution as the lithium source, adopting a constant voltage charging method, using a cut-off voltage of 2.0 - 4.0 V, and performing constant voltage charging for 100 - 600 s to prepare the said ζ-Li a V 2 O 5 The thin film or ζ-Li b V 2 O 5 The thin film. By adopting these process parameters, ζ-Li with better quality can be prepared a V 2 O 5 The thin film or ζ-Li b V 2 O 5 The thin film.

[0074] For example, the cut-off voltage can be 2.0 V, 2.05 V, 2.1 V, 2.15 V, 2.2 V, 2.25 V, 2.3 V, 2.35 V, 2.4 V, 2.45 V, 2.5 V, 2.55 V, 2.6 V, 2.65 V, 2.7 V, 2.75 V, 2.8 V, 2.85 V, 2.9 V, 2.95 V, 3.0 V, 3.05 V, 3.1 V, 3.15 V, 3.2 V, 3.25 V, 3.3 V, 3.35 V, 3.4 V, 3.45 V, 3.5 V, 3.55 V, 3.6 V, 3.65 V, 3.7 V, 3.75 V, 3.8 V, 3.85 V, 3.9 V, 3.95 V, 4.0 V, etc. The time can be 100 s, 150 s, 200 s, 250 s, 300 s, 350 s, 400 s, 450 s, 500 s, 550 s, 600 s, etc. The lithium salt concentration can be 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L or 2 mol / L, etc.

[0075] In some embodiments, when the first ambipolar electrochromic layer comprises a first ambipolar electrochromic material, the first ambipolar electrochromic material is ζ-Li a V 2 O 5 (0 ≤ a ≤ 3), the second ambipolar electrochromic layer comprises a second ambipolar electrochromic material, the second ambipolar electrochromic material is ζ-Li b V 2 O 5 (where 0 ≤ b ≤ 3), the method for preparing the symmetric structure electrochromic device (semi-solid state electrochromic device) comprises the steps of:

[0076] Providing a first transparent conductive substrate, forming a Li 0.3 V 2 O 5 amorphous thin film on the first transparent conductive substrate, annealing the amorphous Li 0.3 V 2 O 5 thin film to obtain a ζ-Li 0.3 V 2 O 5 thin film; using a lithium salt solution as a lithium source, through an electrochemical lithiation method, converting the ζ-Li 0.3 V 2 O 5 thin film into a ζ-Li a V 2 O 5 (a not being 0.3) thin film, and forming a first ambipolar electrochromic layer on the first transparent conductive substrate;

[0077] Providing a second transparent conductive substrate, forming a Li 0.3 V 2 O 5 amorphous thin film on the second transparent conductive substrate, annealing the Li 0.3 V 2 O 5 amorphous thin film to obtain a ζ-Li 0.3 V 2 O 5 thin film; using a lithium salt solution as a lithium source, through an electrochemical lithiation method, converting the ζ-Li 0.3 V 2 O 5 thin film into a ζ-Li b V 2 O 5 (b not being 0.3) thin film to obtain a second ambipolar electrochromic layer;

[0078] An electrolyte layer is formed between a first transparent conductive substrate having a first amphoteric electrochromic layer and a second transparent conductive substrate having a second amphoteric electrochromic layer. At this time, the electrolyte layer is adhered to the first amphoteric electrochromic layer and the second amphoteric electrochromic layer, and the symmetric structure electrochromic device is obtained through encapsulation.

[0079] In some embodiments, the preparation method of the symmetric structure electrochromic device includes the steps of:

[0080] Providing a first transparent conductive substrate, and sequentially depositing a first amphoteric electrochromic layer, an electrolyte layer, a second amphoteric electrochromic layer, and a second transparent conductive substrate on the first transparent conductive substrate to obtain the symmetric structure electrochromic device;

[0081] The first amphoteric electrochromic layer and the second amphoteric electrochromic layer include the same amphoteric electrochromic material, and the amphoteric electrochromic material is an electrochromic material that can be colored in both the oxidized state and the reduced state.

[0082] In some embodiments, when the first amphoteric electrochromic layer includes a first amphoteric electrochromic material, and the first amphoteric electrochromic material is ζ-Li a V 2 O 5 (0 ≤ a ≤ 3), the second amphoteric electrochromic layer includes a second amphoteric electrochromic material, and the second amphoteric electrochromic material is ζ-Li b V 2 O 5 (where 0 ≤ b ≤ 3), the preparation method of the symmetric structure electrochromic device (all-solid-state electrochromic device) includes the steps of:

[0083] Providing a first transparent conductive substrate, forming a Li 0.3 V 2 O 5 amorphous thin film on the first transparent conductive substrate by magnetron sputtering, annealing the Li 0.3 V 2 O 5 amorphous thin film to obtain a ζ-Li 0.3 V 2 O 5 thin film; using a lithium salt solution as a lithium source, and converting the ζ-Li 0.3 V 2 O 5 thin film into a ζ-Li a V 2 O 5 (a is not 0.3) thin film, and forming a first amphoteric electrochromic layer on the first transparent conductive substrate;

[0084] Deposit an electrolyte layer, Li b V 2 O 5 amorphous thin film, and a second transparent conductive substrate on the first amphoteric electrochromic layer in sequence to obtain a raw device;

[0085] Anneal the raw device to obtain the symmetric structure electrochromic device.

[0086] An embodiment of the present invention provides an application of the symmetric structure electrochromic device described in any one of the foregoing embodiments in the field of electrochromics.

[0087] In some embodiments, the symmetric structure electrochromic device is applied in the fields of electrochromic smart windows, electrochromic smart displays, electrochromic optical camouflage, etc.

[0088] The present invention will be further described below through specific embodiments.

[0089] Example 1

[0090] A symmetric structure electrochromic device is prepared in this example, including the following steps:

[0091] (1) Provide ITO transparent conductive glass. Using magnetron sputtering method, with V and Li 2 O as the target materials, in an environment where the volume ratio of oxygen to argon is 9:1, the sputtering pressure is 1 Pa, the V sputtering power is 160 W, and the Li 2 O sputtering power is 50 W, and the sputtering time is 9000 s. Form a Li 0.3 V 2 O 5 amorphous thin film on the ITO transparent conductive glass; Anneal the Li 0.3 V 2 O 5 amorphous thin film at 300 °C for 2 h, with a heating rate of 5 °C / min to obtain a ζ-Li 0.3 V 2 O 5 thin film;

[0092] (2) Adopt a three-electrode system, use metallic lithium as the reference electrode and the counter electrode, use the ζ-Li 0.3 V 2 O 5 thin film obtained in step (1) as the working electrode, use a 1 mol / L propylene carbonate solution of lithium perchlorate as the lithium source, and adopt a constant voltage charging method to apply a constant voltage of 2.65 V to the ζ-Li 0.3 V 2 O 5 thin film and charge for 150 s. The ζ-Li 0.3 V 2O 5 The thin film is converted into ζ-Li 0.66 V 2 O 5 thin film, that is, ζ-Li is formed on the ITO transparent conductive glass (the first transparent conductive substrate) 0.66 V 2 O 5 thin film layer (the first amphoteric electrochromic layer, with a thickness of 280 nm);

[0093] (3) Using the same method as in steps (1) and (2) above, ζ-Li is formed on another ITO transparent conductive glass (the second transparent conductive substrate) 0.66 V 2 O 5 thin film layer (the second amphoteric electrochromic layer, with a thickness of 280 nm);

[0094] (4) Add a propylene carbonate solution of 1 mol / L lithium perchlorate between two ITO transparent conductive glasses with ζ-Li 0.66 V 2 O 5 thin film layers to form an electrolyte layer (with a thickness of 3 mm). At this time, the electrolyte layer is adhered to the two ζ-Li 0.66 V 2 O 5 thin film layers, and use a 3-mm-thick encapsulation tape for encapsulation to obtain a semi-solid-state symmetric structure electrochromic device.

[0095] Example 2

[0096] A symmetric structure electrochromic device is prepared in this example, including the following steps:

[0097] (1) Provide ITO transparent conductive glass, and use the magnetron sputtering method. Using V and Li 2 O as the target, in an environment where the volume ratio of oxygen to argon is 9:1, the sputtering pressure is 1 Pa, the V sputtering power is 160 W, and the Li 2 O sputtering power is 50 W, and the sputtering time is 9000 s. Form Li 0.3 V 2 O 5 amorphous thin film on the ITO transparent conductive glass; Anneal the Li 0.3 V 2 O 5 amorphous thin film at 300 °C for 2 h, with a heating rate of 5 °C / min, to obtain ζ-Li 0.3 V 2 O 5 thin film;

[0098] (2) A three - electrode system is adopted, with metallic lithium as the reference electrode and the counter electrode, and the ζ - Li 0.3 V 2 O 5 thin film obtained in step (1) as the working electrode, 1 mol / L propylene carbonate solution of lithium perchlorate as the lithium source, and the constant - voltage charging method is used to apply a constant voltage of 2.25 V to the ζ - Li 0.3 V 2 O 5 thin film and charge for 150 s, converting the ζ - Li 0.3 V 2 O 5 thin film into a ζ - Li 1.33 V 2 O 5 thin film, that is, forming a ζ - Li 1.33 V 2 O 5 thin - film layer (the first amphoteric electrochromic layer with a thickness of 280 nm) on the ITO transparent conductive glass (the first transparent conductive substrate);

[0099] (3) Using the same method as steps (1) and (2) above, form a ζ - V 2 O 5 thin - film layer (the second amphoteric electrochromic layer with a thickness of 280 nm) on another ITO transparent conductive glass (the second transparent conductive substrate), with the difference that the constant voltage of 2.25 V in the constant - voltage charging method in step (2) is adjusted to 4.0 V;

[0100] (4) Add 1 mol / L propylene carbonate solution of lithium perchlorate between the ITO transparent conductive glass with the ζ - Li 1.33 V 2 O 5 thin - film layer and another ITO transparent conductive glass with the ζ - V 2 O 5 thin - film layer to form an electrolyte layer (with a thickness of 3 mm). At this time, the electrolyte layer is bonded to the ζ - Li 1.33 V 2 O 5 thin - film layer and the ζ - V 2 O 5 thin - film layer, and use a 3 - mm - thick encapsulation tape for encapsulation to obtain a semi - solid - type symmetric - structure electrochromic device.

[0101] Example 3

[0102] A symmetric - structure electrochromic device is prepared in this example, including the following steps:

[0103] (1) Provide ITO transparent conductive glass, and use the magnetron sputtering method with V and Li 2Using O as the target, in an environment where the volume ratio of oxygen to argon is 9:1, the sputtering pressure is 1 Pa, the sputtering power of V is 160 W, and the sputtering power of Li 2 O is 50 W, and the sputtering time is 9000 s to form Li 0.3 V 2 O 5 amorphous film on the ITO transparent conductive glass; annealing the Li 0.3 V 2 O 5 amorphous film at 300 °C for 2 h with a heating rate of 5 °C / min to obtain ζ-Li 0.3 V 2 O 5 film, that is, forming a ζ-Li 0.3 V 2 O 5 film layer (the first amphoteric electrochromic layer with a thickness of 280 nm);

[0104] (2) Using the same method as in step (1) above, forming a ζ-Li 0.3 V 2 O 5 film layer (the second amphoteric electrochromic layer with a thickness of 280 nm) on another ITO transparent conductive glass (the second transparent conductive substrate);

[0105] (3) Adding a propylene carbonate solution of 1 mol / L lithium perchlorate to form an electrolyte layer (with a thickness of 3 mm) between two ITO transparent conductive glasses with ζ-Li 0.3 V 2 O 5 film layers. At this time, the electrolyte layer is bonded to the two ζ-Li 0.3 V 2 O 5 film layers and using a 3-mm-thick encapsulation tape for encapsulation to obtain a semi-solid-state symmetric structure electrochromic device.

[0106] Example 4

[0107] A symmetric structure electrochromic device is prepared in this example, including the following steps:

[0108] (1) Provide ITO transparent conductive glass. Using the magnetron sputtering method, with V and Li 2 O as the target, in an environment where the volume ratio of oxygen to argon is 9:1, the sputtering pressure is 1 Pa, the sputtering power of V is 160 W, and the sputtering power of Li 2 O is 50 W, and the sputtering time is 9000 s to form Li 0.3 V 2 O5 Amorphous thin film; the Li 0.3 V 2 O 5 The amorphous thin film is annealed at 300 °C for 2 h with a heating rate of 5 °C / min to obtain ζ-Li 0.3 V 2 O 5 thin film;

[0109] (2) A three-electrode system is adopted, with metallic lithium as the reference electrode and the counter electrode, and the ζ-Li 0.3 V 2 O 5 thin film obtained in step (1) as the working electrode, a propylene carbonate solution of 1 mol / L lithium perchlorate as the lithium source, and a constant voltage charging method is used to apply a constant voltage of 4.0 V to the ζ-Li 0.3 V 2 O 5 thin film and charge for 150 s, converting the ζ-Li 0.3 V 2 O 5 thin film into a ζ-V 2 O 5 thin film, that is, a ζ-V 2 O 5 thin film layer (the first amphoteric electrochromic layer, with a thickness of 280 nm) is formed on the ITO transparent conductive glass (the first transparent conductive substrate);

[0110] (3) Using the same method as in step (1) above, a ζ-Li 0.3 V 2 O 5 thin film layer (the second amphoteric electrochromic layer, with a thickness of 280 nm) is formed on another ITO transparent conductive glass (the second transparent conductive substrate);

[0111] (4) Add a propylene carbonate solution of 1 mol / L lithium perchlorate between the ITO transparent conductive glass with the ζ-V 2 O 5 thin film layer and another ITO transparent conductive glass with the ζ-Li 0.3 V 2 O 5 thin film layer to form an electrolyte layer (with a thickness of 3 mm). At this time, the electrolyte layer is adhered to the ζ-V 2 O 5 thin film layer and the ζ-Li 0.3 V 2 O 5 thin film layer, and is encapsulated with a 3-mm-thick encapsulation tape to obtain a semi-solid-state symmetric structure electrochromic device.

[0112] The electrochromic performance of the symmetric electrochromic devices prepared in Examples 1-4 was tested:

[0113] (1) For the symmetric electrochromic device prepared in Example 1, the constant voltage method was used for testing. The electrochromic device was scanned with the scanning parameters of 2.0 V for 180 s and 0 V for 200 s. The experimental results showed that the color of the electrochromic device changed with the applied voltage, proving that the prepared device was an electrochromic device.

[0114] (2) For the symmetric electrochromic device prepared in Example 1, the constant voltage method was used for testing with the scanning parameters of 2.0 V for 180 s and 0 V for 200 s. The in-situ spectral transmittance change curves in the colored state and the bleached state were captured. Figure 2 Figure is the in-situ spectral transmittance change curve of the symmetric electrochromic device prepared in Example 1 in the colored state and the bleached state. According to this figure, when a voltage load was applied to this electrochromic device, there were infrared transmission or infrared blocking states.

[0115] (3) For the symmetric electrochromic device prepared in Example 1, the constant voltage method was used for testing. The electrochromic device was scanned with the scanning parameters of -2.0 V for 180 s, 0 V for 200 s, and 2000 cycles were carried out. Figure 3 Figure is the current-voltage change curve of the symmetric electrochromic device prepared in Example 1 during the electrochemical cycling process. Figure 4 Figure is the spectral transmittance change diagram of the symmetric electrochromic device prepared in Example 1 at 633 nm during the electrochemical cycling process. Figure 5 Figure is the spectral transmittance change diagram of the symmetric electrochromic device prepared in Example 1 at 700 nm during the electrochemical cycling process. Figure 6 Figure is the spectral transmittance change diagram of the symmetric electrochromic device prepared in Example 1 at 1100 nm during the electrochemical cycling process. According to Figure 4 、 Figure 5 and Figure 6 it can be seen that this symmetric electrochromic device switched between different transmittances and had good stability. For 1 cycle, the maximum modulation amplitude was 60%, and for 2000 cycles, the maximum modulation amplitude was 59%.

[0116] (4) The electrochromic performances of the symmetric electrochromic devices prepared in Examples 2-5 were similar to those of the device in Example 1, having both large optical modulation, good stability, and a small driving voltage.

[0117] Comparative Example 1

[0118] A comparative example prepared an electrochromic device, including the following steps:

[0119] (1) Provide ITO transparent conductive glass. Using magnetron sputtering method, with V as the target, in an environment where the volume ratio of oxygen to argon is 9:1, the sputtering pressure is 1 Pa, the V sputtering power is 160 W, and the sputtering time is 9000 s, to form V 2 O 5 amorphous film on the ITO transparent conductive glass; Anneal the V 2 O 5 amorphous film at 300 °C for 2 h, with a heating rate of 5 °C / min, to obtain α-V 2 O 5 film;

[0120] (2) Adopt a three-electrode system, with metallic lithium as the reference electrode and the counter electrode, using the α-V 2 O 5 film obtained in step (1) as the working electrode, using a 1 mol / L propylene carbonate solution of lithium perchlorate as the lithium source, adopting a constant voltage charging method, applying a constant voltage of 2.3 V to the α-V 2 O 5 film and charging for 150 s, to convert the α-V 2 O 5 film into δ-Li 1.0 V 2 O 5 film, that is, to form a δ-Li 1.0 V 2 O 5 film layer (the first amphoteric electrochromic layer, with a thickness of 280 nm) on the ITO transparent conductive glass (the first transparent conductive substrate);

[0121] (3) Using the same method as in steps (1) and (2) above, form a δ-Li 1.0 V 2 O 5 film layer (the second amphoteric electrochromic layer, with a thickness of 280 nm) on another ITO transparent conductive glass (the second transparent conductive substrate);

[0122] (4) Add a 1 mol / L propylene carbonate solution of lithium perchlorate between two ITO transparent conductive glasses with δ-Li 1.0 V 2 O 5 film layers to form an electrolyte layer (with a thickness of 3 mm). At this time, the electrolyte layer is bonded to the two δ-Li 1.0 V 2 O 5 film layers, and use a 3 mm thick encapsulation tape for encapsulation to obtain the electrochromic device.

[0123] For the electrochromic device prepared in Comparative Example 1, the constant voltage method was used for testing, and the scanning parameters were 2.0 V, 180 s; 0 V, 200 s. The in-situ spectral transmittance change curves in the colored state and the bleached state were captured. Figure 7 The transmittance change diagrams in the 1100 nm band and the 550 nm band for 30 cycles of the electrochromic device prepared in Comparative Example 1 were obtained. According to this diagram, Comparative Example 1 does not have the modulation amplitude and stability of Examples 1-5.

[0124] In summary, the core of the symmetric structure electrochromic device provided by the present invention lies in using the same amphoteric electrochromic material in two electrochromic layers (for example, ζ-Li a V 2 O 5 and ζ-Li b V 2 O 5 ), so that when the device undergoes an electrochemical cycle, one pole exhibits cathodic coloring characteristics while the other pole exhibits anodic coloring characteristics, enabling the two poles to color and fade synergistically. The matching of such a structure with electrochromic performance enables the device to have both large optical modulation, good stability, and a small driving voltage, achieving a significant improvement in the comprehensive performance of the electrochromic device and having broad application prospects in the field of electrochromics.

[0125] It should be understood that the application of the present invention is not limited to the above examples. For those of ordinary skill in the art, improvements or transformations can be made according to the above description, and all such improvements and transformations should fall within the protection scope of the appended claims of the present invention.

Claims

1. A symmetrical electrochromic device, characterized in that: The invention comprises a first transparent conductive substrate, a first amphoteric electrochromic layer, an electrolyte layer, a second amphoteric electrochromic layer and a second transparent conductive substrate which are stacked in sequence, wherein the first amphoteric electrochromic layer and the second amphoteric electrochromic layer comprise the same amphoteric electrochromic material, and the amphoteric electrochromic material is an electrochromic material which can be colored in both an oxidized state and a reduced state.

2. The symmetrically structured electrochromic device according to claim 1, characterized in that: The thickness of the first amphiphilic electrochromic layer is 30-700 nm, and the thickness of the second amphiphilic electrochromic layer is 30-700 nm.

3. The symmetrically structured electrochromic device according to claim 1, characterized in that: The first bisexual electrochromic layer includes a first bisexual electrochromic material, wherein the first bisexual electrochromic material is α-V2O5, ζ-Li a V2O5, ζ-Na a V2O5 or ζ-K a V2O5, wherein 0≤a≤3; the second bisexual electrochromic layer comprises a second bisexual electrochromic material, and the second bisexual electrochromic material is α-V2O5, ζ-Li b V2O5, ζ-Na b V2O5 or ζ-K b V2O5, wherein 0≤b≤3; said a and b are the same or different.

4. A method for preparing a symmetrically structured electrochromic device according to claim 1, characterized in that: Includes steps: A first transparent conductive substrate is provided, and a first amphoteric electrochromic layer is formed on the first transparent conductive substrate; a second transparent conductive substrate is provided, and a second amphoteric electrochromic layer is formed on the second transparent conductive substrate; the first amphoteric electrochromic layer and the second amphoteric electrochromic layer comprise the same amphoteric electrochromic material, and the amphoteric electrochromic material is an electrochromic material that can be colored in both an oxidized state and a reduced state; An electrolyte layer is formed between a first transparent conductive substrate having a first amphoteric electrochromic layer and a second transparent conductive substrate having a second amphoteric electrochromic layer, wherein the electrolyte layer is bonded to the first amphoteric electrochromic layer and the second amphoteric electrochromic layer, and the symmetrical structure electrochromic device is obtained by encapsulation; or, Providing a first transparent conductive substrate, and sequentially depositing a first amphoteric electrochromic layer, an electrolyte layer, a second amphoteric electrochromic layer, and a second transparent conductive substrate on the first transparent conductive substrate to obtain the electrochromic device with a symmetrical structure; The first and second amphoteric electrochromic layers include the same amphoteric electrochromic material, which is an electrochromic material capable of being colored in both an oxidized state and a reduced state.

5. The method for preparing a symmetrically structured electrochromic device according to claim 4, characterized in that: The first bisexual electrochromic layer includes a first bisexual electrochromic material, and the first bisexual electrochromic material is ζ-Li a V2O5, where 0≤a≤3; When the first bisexual electrochromic material is ζ-Li 0.3 When V2O5 is used, the first bisexual electrochromic layer is prepared according to the following steps: Providing a first transparent conductive substrate, forming a Li on the first transparent conductive substrate by magnetron sputtering 0.3 V2O5 amorphous film, for the Li 0.3 Annealing of V2O5 amorphous film to obtain ζ-Li 0.3 V2O5 thin film, to obtain the first bipolar electrochromic layer; Alternatively, when the first bisexual electrochromic material is ζ-Li a When V2O5 and a is not 0.3, the first bisexual electrochromic layer is prepared according to the following steps: Providing a first transparent conductive substrate, forming a Li on the first transparent conductive substrate by magnetron sputtering 0.3 V2O5 amorphous film, for the Li 0.3 Annealing of V2O5 amorphous film to obtain ζ-Li 0.3 V2O5 thin film; Using a lithium salt solution as a lithium source, the ζ-Li 0.3 Conversion of V2O5 thin films into ζ-Li a V2O5 thin film to obtain the first bipolar electrochromic layer.

6. The method for preparing a symmetrically structured electrochromic device according to claim 4, characterized in that: The second bisexual electrochromic layer includes a second bisexual electrochromic material, and the second bisexual electrochromic material is ζ-Li b V2O5, where 0≤b≤3; When the second bisexual electrochromic material is ζ-Li 0.3 When V2O5 is used, the second bisexual electrochromic layer is prepared according to the following steps: Providing a second transparent conductive substrate, forming a Li on the second transparent conductive substrate by magnetron sputtering 0.3 V2O5 amorphous film, for the Li 0.3 Annealing of V2O5 amorphous film to obtain ζ-Li 0.3 V2O5 thin film, to obtain the second bipolar electrochromic layer; Alternatively, when the second bisexual electrochromic material is ζ-Li b When V2O5 and b is not 0.3, the second bisexual electrochromic layer is prepared according to the following steps: Providing a second transparent conductive substrate, forming a Li on the second transparent conductive substrate by magnetron sputtering 0.3 V2O5 amorphous film, for the Li 0.3 Annealing of V2O5 amorphous film to obtain ζ-Li 0.3 V2O5 thin film; Using a lithium salt solution as a lithium source, the ζ-Li 0.3 Conversion of V2O5 thin films into ζ-Li b V2O5 thin film to obtain a second bipolar electrochromic layer.

7. The method for preparing a symmetrically structured electrochromic device according to claim 5 or 6, characterized in that: The conditions of the magnetron sputtering method include: using V and Li2O as target materials, in an oxygen and argon environment, the sputtering pressure is 0.5-4Pa, the V sputtering power is 70-300W, the Li2O sputtering power is 10-200W, and the sputtering time is 0.3-10h.

8. The method for preparing a symmetrically structured electrochromic device according to claim 5 or 6, characterized in that: The annealing conditions include: an annealing temperature of 200 to 500° C. and an annealing time of 0.5 to 10 hours.

9. The method for preparing a symmetrically structured electrochromic device according to claim 5 or 6, characterized in that: The electrochemical lithiation method is a constant voltage charging method, and the conditions of the constant voltage charging method include: a cut-off voltage of 2.0 to 4.0 V, a time of 100 to 600 s, and a lithium salt concentration of 0.5 to 2 mol / L.

10. Use of the electrochromic device according to claim 1 in the field of electrochromism.

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