阅读说明：本技术 一种制备钛酸锂电致变色薄膜的方法 (Method for preparing lithium titanate electrochromic film ) 是由 刘凡 宋云龙 李明亚 王晓强 房林洋 于 2019-09-30 设计创作，主要内容包括：本发明的一种制备钛酸锂电致变色薄膜的方法,步骤如下：取锂盐溶液和有机钛盐溶液,将二者溶质按物质的量比,锂盐：有机钛盐＝(1-1.5):1混合均匀,获得A溶液；按溶质物质的量比,草酸：(锂盐+有机钛盐)＝(1-1.5):1,将草酸溶液加入A溶液中,混合均匀形成钛酸锂溶胶前驱体；取含有透明导电层的衬底,将钛酸锂溶胶前驱体涂膜于衬底的透明导电层表面,干燥,制得钛酸锂溶胶前驱体薄膜；将钛酸锂溶胶前驱体薄膜进行煅烧,煅烧温度为350-700□,保温时间为1h-6h,降温制得钛酸锂电致变色薄膜。该方法操作简单,制备的电致变色薄膜与传统变色层材料相比,应用钛酸锂材料使得变色层材料的循环性能和使用寿命等性能均得到大幅提高。(The invention relates to a method for preparing a lithium titanate electrochromic film, which comprises the following steps: taking a lithium salt solution and an organic titanium salt solution, and mixing the solutes of the lithium salt solution and the organic titanium salt solution according to the mass ratio of the lithium salt solution to the organic titanium salt solution: uniformly mixing organic titanium salt (1-1.5) and 1 to obtain solution A; according to the quantity ratio of solute substances, oxalic acid: adding oxalic acid solution into the solution A, and uniformly mixing to form a lithium titanate sol precursor; taking a substrate containing a transparent conductive layer, coating a lithium titanate sol precursor on the surface of the transparent conductive layer of the substrate, and drying to prepare a lithium titanate sol precursor film; calcining the lithium titanate sol precursor film at the calcining temperature of 350-700 □ for 1-6 h, and cooling to obtain the lithium titanate electrochromic film. The method is simple to operate, and compared with the traditional color-changing layer material, the prepared electrochromic film has the advantages that the cycle performance, the service life and other performances of the color-changing layer material are greatly improved by applying the lithium titanate material.)

1. A method for preparing a lithium titanate electrochromic film is characterized by comprising the following steps:

step 1, preparing a lithium titanate sol precursor:

(1) taking a lithium salt solution and an organic titanium salt solution, and mixing the solutes of the lithium salt solution and the organic titanium salt solution according to the mass ratio of the lithium salt solution to the organic titanium salt solution: uniformly mixing organic titanium salt (1-1.5) and 1 to obtain solution A;

(2) according to the quantity ratio of solute substances, oxalic acid: adding oxalic acid solution into the solution A, and uniformly mixing to form a lithium titanate sol precursor;

step 2, preparing a lithium titanate sol precursor film:

taking a substrate containing a transparent conductive layer, coating a lithium titanate sol precursor on the surface of the transparent conductive layer of the substrate, and drying to prepare a lithium titanate sol precursor film;

step 3, preparing the lithium titanate electrochromic film:

and calcining the lithium titanate sol precursor film at the calcining temperature of 350-700 ℃, keeping the temperature for 1-6 h, and cooling to obtain the lithium titanate electrochromic film.

2. The method for preparing lithium titanate electrochromic film according to claim 1, wherein in step 1(1), the lithium salt solution is prepared by: dissolving lithium salt in a solvent, and magnetically stirring to obtain a clear solution, wherein the mass concentration of the lithium salt is 0.1-1.5 mol/L; the preparation process of the organic titanium salt solution comprises the following steps: dissolving organic titanium salt in a solvent, and magnetically stirring to obtain a clear solution, wherein the mass concentration of the organic titanium salt is 0.1-2 mol/L; mixing the two solutions, and then fully and magnetically stirring to form a clear mixed solution; wherein, the solvent adopted in the preparation process of the lithium salt solution and the organic titanium salt solution is absolute ethyl alcohol.

3. The method for preparing the lithium titanate electrochromic film according to claim 1, wherein in the step 1 (1): the lithium salt is lithium acetate, and the organic titanium salt is one of tetrabutyl titanate, titanium isopropoxide and isopropyl titanate.

4. The method for preparing the lithium titanate electrochromic film according to claim 1, wherein in the step 1 (2): the preparation process of the oxalic acid solution is as follows: dissolving oxalic acid in a solvent and stirring to obtain a clear oxalic acid solution, wherein the concentration of the oxalic acid solution is 1-4 mol/L.

5. The method for preparing the lithium titanate electrochromic film according to claim 1, wherein in the step 2, the substrate is conductive glass, and the conductive glass is ITO conductive glass, FTO conductive glass or AZO conductive glass.

6. The method for preparing the lithium titanate electrochromic film according to claim 1, wherein in the step 3, the transmittance of the lithium titanate electrochromic film in a lithiated state in an infrared wavelength range is 7-31% under a voltage of-3V to-1.5V.

7. The method for preparing the lithium titanate electrochromic film according to claim 1, wherein in the step 3, the prepared lithium titanate electrochromic film has an emissivity adjustability of 0.50-0.68 in a visible light wavelength range and an emissivity adjustability of 0.30-0.55 and an emissivity of 0.08-0.27 in a middle and far infrared wavelength range under a voltage of-3V-1.5V.

8. The method for preparing the lithium titanate electrochromic film according to claim 1, wherein in the step 3, the highest light modulation range of the prepared lithium titanate electrochromic film in a visible light wavelength range is 40.51-50.63% under a voltage of-3V-1.5V.

9. The method for preparing the lithium titanate electrochromic film according to claim 1, wherein in the step 3, after the prepared lithium titanate electrochromic film is subjected to an external electric field cycling test at a voltage of-3V to-1.5V for 5000-6000 times, the adjustment amplitude of the material in the visible light and infrared wavelength ranges is 83-90% of that of the initial test.

10. The method for preparing the lithium titanate electrochromic film as claimed in claim 1, wherein in the step 3, the prepared lithium titanate electrochromic film can store electric energy after being lithiated, and has electric quantity visualization.

The technical field is as follows:

the invention belongs to the technical field of electrochromic devices, and particularly relates to a method for preparing a lithium titanate electrochromic film.

Background art:

electrochromism is a phenomenon that the optical properties (reflectivity, transmittance, absorptivity and the like) of a material generate stable and reversible color change under the action of an external electric field, and the electrochromism is represented as reversible change of color and transparency in appearance. The electrochromic intelligent glass has the adjustability of light absorption and transmission under the action of an electric field, can selectively absorb or reflect external heat radiation and internal heat diffusion, can greatly reduce the power consumption of heat supply or cold supply when applied to high-rise buildings, and can also solve the problem of continuously intensified light pollution in modern cities. Besides buildings, the electrochromic technology has wide application prospects in the fields of intelligent electronics and devices, automobiles, low-energy-consumption display, aerospace and the like.

Lithium titanate (Li)₄Ti₅O₁₂) The crystal has a spinel structure, and the lattice constant and the volume change of the crystal are small and less than 1 percent when the crystal is inserted into or extracted from lithium ions, so that the crystal is a material with zero strain. Theoretically, under the circulating action of an external electric field, the characteristic of zero strain property can avoid the damage of the structure caused by the continuous insertion and extraction of lithium ions, thereby greatly improving the circulating performance and prolonging the service life of the material.

At present, most of research on lithium titanate is focused on the aspect of lithium ion battery cathode materials, and a few of application research on electrochromic materials is mainly focused on preparing an electrochromic material ion storage layer by using a magnetron sputtering method. The lithium titanate material is innovatively adopted as the electrochromic layer material, and the electrochromic layer material is Li₄Ti₅O₁₂Under the action of an external electric field, Li₄Ti₅O₁₂From Delithiated (DL) state (Li)₄Ti₅O₁₂) Conversion to lithiated (L) state (Li)₇Ti₅O₁₂) The appearance is then manifested by a thin film transition from a transparent colourless (delithiated) to a (lithiated) dark blue color, whose optical transmission in the visible wavelength range is greatly reduced, and, unlike conventional electrochromic layer materials, Li in the lithiated state₇Ti₅O₁₂The transmittance in the near-middle far-infrared wavelength range is low, and the diffusion of thermal radiation is adjustable to a certain extent. Second Li₄Ti₅O₁₂Material lithiation before and after visibleThe high emissivity adjustability is shown in the middle and far infrared wavelength range in the light range, so that the thermal camouflage paint can be applied to the field of thermal camouflage. Thus Li₄Ti₅O₁₂The broadband electrochromic property of (LTO) has good application prospect in the fields of infrared camouflage and temperature regulation.

The lithium titanate as a novel cathode electrochromic material has less related research, how to prepare large-area Li with good performance by simple equipment and relatively loose environmental conditions is simple and convenient₄Ti₅O₁₂The thin film is a problem to be solved urgently in the aspect of application of the thin film in electrochromic materials. Therefore, the invention provides a simple and cheap process and can prepare a large-area lithium titanate electrochromic film with good performance, which is very important.

The invention content is as follows:

the invention aims to overcome the defects in the prior art and provide a method for preparing a lithium titanate electrochromic film, which can realize the preparation of the lithium titanate electrochromic film with good performance; the method is simple and easy to realize, has low cost, and has the possibility of application and popularization in the electrochromic glass industry, the infrared camouflage field, intelligent electronics and devices and other aspects.

In order to achieve the purpose, the invention adopts the following technical scheme:

a method for preparing a lithium titanate electrochromic film comprises the following steps:

step 1, preparing a lithium titanate sol precursor:

(1) taking a lithium salt solution and an organic titanium salt solution, and mixing the solutes of the lithium salt solution and the organic titanium salt solution according to the mass ratio of the lithium salt solution to the organic titanium salt solution: uniformly mixing organic titanium salt (1-1.5) and 1 to obtain solution A;

(2) according to the quantity ratio of solute substances, oxalic acid: adding oxalic acid solution into the solution A, and uniformly mixing to form a lithium titanate sol precursor;

step 2, preparing a lithium titanate sol precursor film:

taking a substrate containing a transparent conductive layer, coating a lithium titanate sol precursor on the surface of the transparent conductive layer of the substrate, and drying to prepare a lithium titanate sol precursor film;

step 3, preparing the lithium titanate electrochromic film:

and calcining the lithium titanate sol precursor film at the calcining temperature of 350-700 ℃, keeping the temperature for 1-6 h, and naturally cooling to obtain the lithium titanate electrochromic film.

In the step 1 (1):

the preparation process of the lithium salt solution comprises the following steps: dissolving lithium salt in a solvent, and magnetically stirring to obtain a clear solution, wherein the mass concentration of the lithium salt is 0.1-1.5 mol/L; the preparation process of the organic titanium salt solution comprises the following steps: dissolving organic titanium salt in a solvent, and magnetically stirring to obtain a clear solution, wherein the mass concentration of the organic titanium salt is 0.1-2 mol/L;

mixing the two solutions, and then fully and magnetically stirring to form a clear mixed solution; wherein, the solvent adopted in the preparation process of the lithium salt solution and the organic titanium salt solution is absolute ethyl alcohol.

In the step 1 (1): the lithium salt is lithium acetate.

In the step 1 (1): the organic titanium salt is one of tetrabutyl titanate, titanium isopropoxide and isopropyl titanate.

In the step 1 (2):

the preparation process of the oxalic acid solution is as follows: dissolving oxalic acid in a solvent, and magnetically stirring to obtain a clear oxalic acid solution, wherein the concentration of the oxalic acid solution is 1-4 mol/L;

dripping the prepared oxalic acid solution into the clear mixed solution A in the step (1) at a slow speed, and fully and uniformly mixing to form a clear and transparent lithium titanate sol precursor;

in the step 2, the substrate is conductive glass, and the conductive glass is ITO conductive glass, FTO conductive glass or AZO conductive glass.

In the step 2, after the substrate is pretreated, coating is carried out, wherein the substrate pretreatment step is as follows:

ultrasonic cleaning treatment: sequentially cleaning the substrate with a detergent, deionized water, acetone and ethanol in an ultrasonic device, taking out, and drying with a drying device;

surface active treatment: performing surface active treatment on the substrate subjected to ultrasonic cleaning treatment for later use;

in the step 2, the coating process is a blade coating method, a spraying method, a wire rod coating method, a dip-coating method, a spin coating method or a slit extrusion coating method.

In the step 3, the lithium titanate electrochromic film prepared under the voltage of-3V to-1.5V obtains the transmittance of the lithiated film in the infrared wavelength range of 7-31%.

In the step 3, the prepared lithium titanate electrochromic film has the adjustability of emissivity of 0.50-0.68 in the visible light wavelength range and the adjustability of emissivity of 0.30-0.55 and 0.08-0.27 in the middle and far infrared wavelength range under the voltage of-3V to-1.5V.

In the step 3, the highest light modulation range of the lithium titanate electrochromic film in the visible light wavelength range is 40.51-50.63% under the voltage of-3V to-1.5V.

In the step 3, after the prepared lithium titanate electrochromic film is subjected to a cyclic test of an external electric field with a voltage of-3V to-1.5V for 5000-6000 times, the adjustment amplitude of the material in the visible light and infrared wavelength ranges is 83-90% of that of the initial test.

In the step 3, the lithiation process of the prepared lithium titanate electrochromic film is carried out in a liquid electrolyte, and platinum is used as a counter electrode.

In the step 3, after the lithium titanate electrochromic film is lithiated, certain electric energy can be stored, and electric quantity visualization is achieved.

In the step 3, the prepared lithium titanate electrochromic film can realize electrochromic under the action of an external voltage, and simultaneously can store certain electric energy, so that a super capacitor film is formed, an electric appliance and the like are connected to supply energy to the film and realize fading to a certain degree, and the state of the contained electric quantity can be judged through the depth degree of the coloring appearance, so that certain visualization is realized. The prepared lithium titanate electrochromic film has low infrared region transmittance after lithiation, has the characteristic of emissivity adjustability, and has a certain infrared camouflage effect.

The invention has the beneficial effects that:

(1) the method for preparing the lithium titanate electrochromic film is simple to operate, simple in equipment, loose in preparation requirement environmental conditions, low in preparation process energy consumption, capable of greatly reducing the production cost, beneficial to industrial large-area production, and expected to be popularized in the industrial process of the electrochromic film.

(2) The lithium titanate used by the method is different from a traditional electrochromic device color-changing layer material, and the lithium titanate material is a zero-strain material. The crystal has small lattice constant and volume change when lithium ions are inserted or removed, and compared with the traditional color changing layer material, the lithium titanate material is applied to improve the cycle performance and the service life of the color changing layer material.

(3) The lithium titanate used by the method is different from a traditional electrochromic device color-changing layer material, and the lithium titanate material has low transmittance in an infrared region after being lithiated, so that the lithium titanate material has certain adjustability for the diffusion of heat radiation. The lithium titanate material shows the adjustability of emissivity in visible light wavelength and middle and far infrared wavelength ranges before and after lithiation, so that the lithium titanate material can be applied to the field of thermal camouflage.

(4) The film prepared by the method is lithiated, shows color change in appearance and stores certain electric energy, forms a super capacitor film at the moment, is connected with an electric appliance and the like to supply energy to the super capacitor film and realize fading to a certain degree, and can judge the state of the contained electric quantity through the depth of coloring in appearance, so that the super capacitor film has certain visualization.

Description of the drawings:

FIG. 1 is an XRD pattern of a lithium titanate film prepared in example 1 of the present invention;

FIG. 2 is an SEM photograph of the surface of the lithium titanate electrochromic film prepared in example 1 of the present invention;

FIG. 3 is an SEM photograph of a cross section of an electrochromic film of lithium titanate prepared in example 1 of the present invention;

FIG. 4 is a digital photograph of the assembled device of example 1 after coloring;

FIG. 5 is a digital photograph of the assembled device of example 1 after color fading;

FIG. 6 is a graph of UV-visible light transmittance before and after lithiation of the lithium titanate electrochromic film prepared in example 1 of the present invention;

FIG. 7 is a current-potential diagram of an electrochromic film of lithium titanate prepared in example 1 of the present invention;

fig. 8 is a cyclic voltammogram of the lithium titanate electrochromic film prepared in example 1 of the present invention.

The specific implementation mode is as follows:

the present invention will be described in further detail with reference to examples.

For better understanding of the present invention, the technical solutions and effects of the present invention will be described in detail by the following embodiments with reference to the accompanying drawings.

The following preferred examples further illustrate the present invention and it will be understood by those skilled in the art that the following examples are intended to illustrate the present invention and are not intended to limit the scope of the present invention.

In the following examples, the starting materials used are all commercially available.

A method for preparing a lithium titanate electrochromic film comprises the following steps:

step 1, preparing a lithium titanate sol precursor:

(1) taking a lithium salt solution and an organic titanium salt solution, and mixing the solutes of the lithium salt solution and the organic titanium salt solution according to the mass ratio of the lithium salt solution to the organic titanium salt solution: uniformly mixing organic titanium salt (1-1.5) and 1 to obtain solution A;

(2) according to the quantity ratio of solute substances, oxalic acid: adding oxalic acid solution into the solution A, and uniformly mixing to form a lithium titanate sol precursor;

step 2, preparing a lithium titanate sol precursor film:

taking a substrate containing a transparent conductive layer, coating a lithium titanate sol precursor on the surface of the transparent conductive layer of the substrate, and drying to prepare a lithium titanate sol precursor film;

step 3, preparing the lithium titanate electrochromic film:

and calcining the lithium titanate sol precursor film at the calcining temperature of 350-700 ℃, keeping the temperature for 1-6 h, and naturally cooling to obtain the lithium titanate electrochromic film.

In the step 1 (1):

the preparation process of the lithium salt solution comprises the following steps: dissolving lithium salt in a solvent, and magnetically stirring to obtain a clear solution, wherein the mass concentration of the lithium salt is 0.1-1.5 mol/L; the preparation process of the organic titanium salt solution comprises the following steps: dissolving organic titanium salt in a solvent, and magnetically stirring to obtain a clear solution, wherein the mass concentration of the organic titanium salt is 0.1-2 mol/L;

mixing the two solutions, and then fully and magnetically stirring to form a clear mixed solution; wherein, the solvent adopted in the preparation process of the lithium salt solution and the organic titanium salt solution is absolute ethyl alcohol.

In the step 1 (1): the lithium salt is lithium acetate.

In the step 1 (1): the organic titanium salt is one of tetrabutyl titanate, titanium isopropoxide and isopropyl titanate.

In the step 1 (2):

the preparation process of the oxalic acid solution is as follows: dissolving oxalic acid in a solvent, and magnetically stirring to obtain a clear oxalic acid solution, wherein the concentration of the oxalic acid solution is 1-4 mol/L;

dripping the prepared oxalic acid solution into the clear mixed solution A in the step (1) at a slow speed, and fully and uniformly mixing to form a clear and transparent lithium titanate sol precursor;

in the step 2, the substrate is conductive glass, and the conductive glass is ITO conductive glass, FTO conductive glass and AZO conductive glass.

In the step 2, after the substrate is pretreated, coating is carried out, wherein the substrate pretreatment step is as follows:

ultrasonic cleaning treatment: sequentially cleaning the substrate with a detergent, deionized water, acetone and ethanol in an ultrasonic device, taking out, and drying with a drying device;

surface active treatment: performing surface active treatment on the substrate subjected to ultrasonic cleaning treatment for later use;

in the step 2, the coating process is a blade coating method, a spraying method, a wire rod coating method, a dip-coating method, a spin coating method or a slit extrusion coating method.

In the step 3, the lithium titanate electrochromic film prepared under the voltage of-3V to-1.5V obtains the transmittance of the lithiated film in the infrared wavelength range of 7-31%.

In the step 3, the prepared lithium titanate electrochromic film has the emissivity adjustability of 0.50-0.68 in the visible light wavelength range, the emissivity adjustability of 0.30-0.55 and the emissivity adjustability of 0.08-0.27 in the middle and far infrared wavelength range under the voltage of-3V to-1.5V, namely the emissivity adjustability of 0.30-0.55 in the middle and far infrared wavelength range and the emissivity adjustability of 0.08-0.27 in the far infrared wavelength range.

In the step 3, the highest light modulation range of the lithium titanate electrochromic film in the visible light wavelength range is 40.51-50.63% under the voltage of-3V to-1.5V.

In the step 3, after the prepared lithium titanate electrochromic film is subjected to a cyclic test of an external electric field with a voltage of-3V to-1.5V for 5000-6000 times, the adjustment amplitude of the material in the visible light and infrared wavelength range (namely the whole wavelength range from visible light to infrared) is 83-90% of that of the initial test.

In the step 3, the lithiation process of the prepared lithium titanate electrochromic film is carried out in a liquid electrolyte, and platinum is used as a counter electrode.

In the step 3, after the lithium titanate electrochromic film is lithiated, certain electric energy can be stored, and electric quantity visualization is achieved.

In the step 3, the prepared lithium titanate electrochromic film can realize electrochromic under the action of an external voltage, and simultaneously can store certain electric energy, so that a super capacitor film is formed, an electric appliance and the like are connected to supply energy to the film and realize fading to a certain degree, and the state of the contained electric quantity can be judged through the depth degree of the coloring appearance, so that certain visualization is realized. The prepared lithium titanate electrochromic film has low infrared region transmittance after lithiation, and has a certain infrared camouflage effect.