CN111176046B

CN111176046B - A kind of lithium cobalt oxide film and its preparation method and application

Info

Publication number: CN111176046B
Application number: CN201811339880.XA
Authority: CN
Inventors: 包山虎; 金平实; 谢玲玲; 朱莹; 张启轩; 黄爱彬
Original assignee: Shanghai Institute of Ceramics of CAS
Current assignee: Jiangsu Institute Of Advanced Inorganic Materials
Priority date: 2018-11-12
Filing date: 2018-11-12
Publication date: 2021-04-16
Anticipated expiration: 2038-11-12
Also published as: CN111176046A

Abstract

The invention relates to a lithium cobalt oxide film, a preparation method and application thereof. The valence states of cobalt ions in the lithium cobalt ^oxide film include Co ²⁺ and Co ³⁺ . The molar content of ⁺ is less than 45%; the molar content ratio of cobalt ions to lithium ions in the lithium cobalt oxide film is 1-3.5, preferably 1.5-3.

Description

Lithium cobaltate film and preparation method and application thereof

Technical Field

The invention relates to a method for preparing an inorganic ion storage layer passivity of an all-solid-state electrochromic device, in particular to a lithium cobaltate film and a preparation method and application thereof, belonging to the technical field of materials.

Background

The electrochromic is a reversible color change phenomenon of the optical properties of the material, such as transmittance and reflectivity, under the drive of low voltage, and the appearance of the material is represented by reversible change between a blue state and a transparent state. Electrochromism is a hotspot of research nowadays and has a wide application range. The electrochromic device and the technology are mainly applied to the fields of automobile anti-dazzle rearview mirrors, energy-saving building glass, windows of other moving bodies, display screens, electronic paper, camouflage and the like.

In a conventional all-solid-state electrochromic device, a first transparent conductive layer, an ion storage layer, an ion conductive layer, a second electrochromic layer, a second transparent conductive layer, and a protective layer are deposited on a substrate by magnetron sputtering in sequence. The ion storage layer assists the electrochromic layer to apply low voltage to the first transparent conducting layer and the second transparent conducting layer to realize electrochromic reaction. The ion conducting layer is used for providing a lithium ion and diffusion film layer and ensuring ion conductivity under the action of an electric field, and the structure and the preparation process of the ion conducting layer are one of the most important technologies for ensuring the electrochromic performance of the device.

The ion storage layer in the solid electrochromic device is inorganic transition metal oxide, most extensive oxides NiO and CoO₂、V₂O₅. The ion conductive layer is usually an inorganic lithium salt, and usually lithium tantalate (LiTaO) is used₃) Lithium niobate (LiNbO)₃)，LiAlF₄And the like. The nickel oxide is taken as a typical ion storage layer of an electrochromic device, but because nickel elements +2 and +3 in the nickel oxide are mixed, the nickel oxide containing the nickel element in a valence state of +3 is brown, and the thin film cannot be self-lithiated in the device to form a transparent nickel oxide thin film, and the colored transmittance of the thin film is about 10-60%. Therefore, the preparation of inorganic ion storage layers becomes a research hotspot in the industrial production nowadays. The preparation method of the transparent nickel oxide comprises the following steps: 1) the traditional preparation method is a heating method, the heating temperature is 300-600 ℃, and the nickel oxide film is deposited by magnetron sputtering. The nickel oxide film with the transmittance higher than 50 percent can be obtained. 2) Chinese patent "an inorganic metal oxide ion storage layer, its low-temperature solution processing method and use" (chinese application No. 201810102948.6) adopts specific polar solvent to realize the synergistic effect of the precursor and ligand of inorganic metal oxide, and obtains a variety of high-efficiency electrochromic device ion storage layers through simple solution coating film formation and low-temperature heat treatment. Thereby greatly reducing the production cost of the ion storage layer of the electrochromic device on the premise of ensuring the product quality.

In addition, more recently, lithium cobaltate (LiCoO)₂) The reports on the use of thin films as ion storage layers of electrochromic devices are described in the Chinese patent "all-solid-state thin film electrochromic glass and its preparation method" (application No. 201210400683.0), which uses a radio frequency power ceramic lithium cobaltate target to prepare lithium cobaltate (LiCoO)₂) And the thin film is an ion storage layer of the electrochromic device. The radio frequency power supply cannot be used comprehensively due to the reasons of large radiation, high production cost and the like.

In conclusion, in the current technology for preparing the transparent inorganic ion storage layer film, the advantages of the chemical method are obvious, the magnetron sputtering method is difficult to realize comprehensively, and although the optical performance of the transparent inorganic ion storage layer film prepared by the chemical method can be optimized preliminarily, the adhesion and weather resistance of the obtained film are poor, and the actual industrial production cannot be met.

Disclosure of Invention

In view of the above problems, the present invention aims to provide a loose and transparent lithium cobaltate thin film, and a preparation method and an application thereof.

In one aspect, the present invention provides a lithium cobaltate film, wherein the valence state of cobalt ions in the lithium cobaltate film comprises Co²⁺And Co³⁺Co in an amount of 100% based on the total molar amount of cobalt ions³⁺Less than 45% by mole; the molar content ratio of cobalt ions to lithium ions in the lithium cobaltate film is 1-3.5, and preferably 1.5-3.

The valence of cobalt ion in the lithium cobaltate film (brown state) of the present invention includes Co²⁺And Co³⁺And Co³⁺Is less than 45%. At room temperature, in the electrifying process of the lithium cobaltate film, the components in the film contain +2, and the +3 valence state can be subjected to auto-lithiation to generate reversible color change, so that the film has good dimming performance, and is uniform and stable. The lithium cobaltate thin film is self-lithiated and has the following essence: when voltage is applied to two ends of the device, lithium ions and electrons are transferred into the lithium cobaltate film under the drive of current, so that cobalt divalent ions and cobalt trivalent ions are promoted to generate redox reaction, and the color transparence of the lithium cobaltate film can be further completed.

Preferably, the lithium cobaltate film is further doped with at least one of Al, Ti, Zr, V, Mo, Ta, Nb, and Si in an amount of not more than 50%. Wherein, the doping element replaces Co element. Lithium cobaltate thin films (e.g., LiCo) that can also be doped with small amounts of metals_1-aM_aO₂) At least one of Al, Ti, Zr, V, Mo, Ta, Nb and Si, and the doping amount is not more than 50%. The doping can improve the stability of the lithium cobaltate thin film, for example, can inhibit the physical phase change process of the lithium cobaltate thin film and can also inhibit the diffusion of metal cobalt ions to the dielectric layer.

Preferably, the lithium cobaltate thin film has a visible light transmittance of less than or equal to 60% and a visible light transmittance of more than 75% after self-lithiation. For example, the lithium cobaltate thin film has an auto-lithiation transmittance value increased from 60% to 80%.

Preferably, the thickness of the lithium cobaltate thin film is 20 to 600nm, preferably 50 to 200 nm.

On the other hand, the invention also provides a preparation method of the lithium cobaltate film, which selects a cobalt-lithium alloy target material or/and a lithium cobaltate ceramic target material, and adopts a direct-current power supply to perform magnetron sputtering to deposit the lithium cobaltate film on the surface of the substrate, wherein the parameters of the direct-current power supply magnetron sputtering comprise: DC power density of 0.3W/cm²～2W/cm²Vacuum degree of less than 5X 10^-4Pa, and the deposition time is 5-100 minutes; the sputtering atmosphere is oxygen-argon mixture, and the oxygen content (oxygen partial pressure ratio) is 5-20 percent; the total working pressure is 0.5-5 Pa.

Preferably, the purity of the cobalt-lithium alloy target or/and the lithium cobaltate ceramic target is higher than 99.9%, the grain size is less than 100 micrometers, and the resistivity is 1-200 omega-cm; preferably, the molar content ratio of lithium to cobalt in the cobalt-lithium alloy target and the lithium cobaltate ceramic target is 0.8-3.

Preferably, the deposition rate of the DC power supply is 1-10 nm/min. The deposition rate of the lithium cobaltate film by a direct current power supply is 3 nm/min (or 4nm/min), which is nearly twice higher than that of the nickel oxide prepared by the direct current power supply.

In still another aspect, the present invention further provides a solid electrochromic device, including a first transparent conductive layer, the lithium cobaltate thin film as an ion storage layer, an electrochromic layer, and a second transparent conductive layer, which are sequentially formed on a surface of a substrate.

The invention provides a lithium cobaltate film with double functions to replace an ion storage layer and an ion conduction layer, such as: CoO₂And an ion-conducting layer inorganic lithium salt; in the lithium-doped cobalt oxide system, the lithium ion state is transferred to the electrochromic layer under the application of a voltage to cause an electrochromic reaction, and a lithium cobaltate thin film (e.g., LiCoO)₂) The whole system is not only an ion storage layer of the traditional electrochromic device, but also assists the reaction of the electrochromic layer.

Preferably, the electrochromic layer is WO₃(ii) a Preferably, the first transparent layerThe conducting layer is an ITO conducting film or an FTO conducting film, and the second transparent conducting layer is an ITO conducting film or an FTO conducting film.

Preferably, a dielectric layer or an ion conducting layer is further included between the electrochromic layer and the lithium cobaltate thin film, or/and a protective layer is further included on the surface of the second transparent conducting layer away from the electrochromic layer; preferably, the ion conducting layer is lithium tantalate, the dielectric layer is at least one of a silicon oxide layer, an aluminum oxide layer, a silicon nitride layer, a silicon oxide layer containing hydrogen, lithium and sodium, and an aluminum oxide layer containing hydrogen, lithium and sodium, and the protective layer is at least one of a silicon nitride layer, an aluminum oxide layer and a silicon oxynitride layer.

In the invention, all the film deposition processes are carried out by adopting a direct current power supply at room temperature, thereby being beneficial to reducing the heat energy consumption and the preparation cost. Meanwhile, the lithium cobaltate film obtained by deposition does not need a heat treatment process, can be finished by one-step magnetron sputtering deposition, simplifies the film preparation steps and improves the feasibility of industrial production. The film has the characteristics of uniform distribution, uniform surface appearance, high visible light transmittance, excellent light modulation performance and the like.

The invention adopts room temperature magnetron sputtering to obtain brown lithium cobaltate film, and the film is automatically lithiated in an electrochromic device to complete transparentization, and can be used in the technical fields of electrochromic intelligent glass, automobile and other vehicle glass, automobile rearview anti-dazzle glasses and the like.

Drawings

FIG. 1 is an optical transmittance spectrum of a single-layer lithium cobaltate film with cation injection/extraction;

FIG. 2 is a schematic structural view of an all-solid electrochromic device in example 2;

FIG. 3 is an optical transmittance spectrum of the all-solid electrochromic device in example 2;

FIG. 4 is a spectrum of the coloring efficiency of the all-solid electrochromic device in example 2;

FIG. 5 is a schematic structural view of an all-solid electrochromic device in example 3;

FIG. 6 is an optical transmittance spectrum of a dual all-solid electrochromic device in example 3;

FIG. 7 is a spectrum of the coloring efficiency of the all-solid electrochromic device in example 3;

FIG. 8 is a photoelectron spectroscopy analysis spectrum of a lithium cobaltate thin film in example 1;

fig. 9 is an optical transmittance spectrum of the all-solid electrochromic device in example 5;

fig. 10 is a spectrum of the coloring efficiency of the all-solid electrochromic device in example 5.

Detailed Description

The present invention is further illustrated by the following examples, which are to be understood as merely illustrative and not restrictive.

In the disclosure, a direct-current power magnetron sputtering physical vapor deposition technology is adopted to deposit a sputtered lithium cobaltate thin film material on the surface of a substrate, and at room temperature, the direct-current power magnetron sputtering deposition is adopted to obtain a brown lithium cobaltate thin film. The target selected may be a specific alloy target sputtering or/ceramic target of lithium cobaltate (e.g., cobalt lithium alloy target or/lithium cobaltate ceramic target). Wherein the substrate is a transparent substrate, such as quartz glass, common glass or conductive glass.

In the disclosure, the film under specific parameters is obtained, and the components of the film are quantitatively analyzed, so that the ratio of two ions can be obtained, that is, the molar content ratio of lithium ions to cobalt ions in the lithium cobaltate film can be 1-3.5, and preferably 1.5-3. Wherein, the lithium cobaltate film is in brown state, the cobalt ions are in mixed valence state, which are +2 +3, and the mol content of trivalent cobalt ions is less than 45%. In an alternative embodiment, the lithium cobaltate thin film has a visible light transmittance of 60% or less and can achieve a visible light transmittance of more than 75% after being self-lithiated in the device.

In an alternative embodiment, the parameters of the dc power magnetron sputtering include: power density 0.3W/cm²～2W/cm²(ii) a Substrate vacuum degree less than 5X 10^-4Pa, and the deposition time is 5-100 min; the total working pressure is 0.5-5 Pa; the atmosphere is oxygen and argon mixture, and the oxygen content is preferably 5 to 20 percent.

In an optional embodiment, the purity of the selected target (wherein the content ratio of lithium to cobalt is 0.8-3) is higher than 99.9%, the grain size is less than 100 micrometers, and the resistivity is 1-200 Ω & cm.

Before the lithium cobaltate film is prepared by deposition, the substrate can be cleaned firstly, the target material is cleaned by pre-sputtering, and then the lithium cobaltate film is prepared by adjusting the preparation process parameters. As an example of the magnetron sputtering deposition substrate (quartz glass, ordinary glass or conductive glass) ultrasonic cleaning, there are: firstly, washing a substrate with deionized water for 10 minutes, then ultrasonically washing the substrate with absolute ethyl alcohol or isopropanol for 10 minutes, fixing the substrate on a substrate of the substrate, putting the substrate into a sample introduction chamber, and then moving the substrate to a vacuum degree (backing vacuum degree) of 5 multiplied by 10^-4Pa or above.

As an example of specific parameters for the preparation of lithium cobaltate thin films, the following are included: adopting cobalt-lithium alloy target material, the degree of vacuum pre-pumping of sputtering cavity is less than 5X 10^-4Pa. Argon gas with the flow rate of 50-300 sccm (standard cubic centimeter per minute) and oxygen with the flow rate of 1.0-20.0sccm are fully mixed and then are introduced into a sputtering chamber to ensure that the sputtering pressure is 0.5-5.0 Pa (preferably 0.5-2.5 Pa), wherein the oxygen content is 5-30%. The power density of sputtering deposition of each target in the back-and-forth movement of the sample stage can be 0.3W/cm²～2W/cm². The film forming time of the lithium cobaltate is 5-100 min.

Generally, lithium cobaltate (or a doped lithium cobaltate film) is deposited on a transparent conductive layer by using a lithium cobaltate ceramic target (or a lithium cobaltate ceramic target doped with a small amount of metal, or a cobalt-lithium alloy target and a cobalt-lithium alloy target doped with a third metal element), and using a direct current power supply and pulsed direct current. In addition, when the lithium cobaltate or the doped lithium cobaltate film is prepared, bias voltages such as 0-300V direct current voltage, pulse direct current voltage, radio frequency and the like can be applied, the ion concentration and energy near the substrate can be accurately controlled, and a uniform and defect-free film structure can be obtained. The lithium cobaltate film is obtained by an optimized preparation method and is characterized in that lithium ions or lithium atoms are doped in a cobalt oxide structure system, and the lithium ions can move and migrate to a color changing layer under the drive of voltage.

In the present disclosure, a brown lithium cobaltate film is combined with an ion conducting layer (e.g., lithium tantalate (LiTaO)₃) Electrochromic layer(for example, tungsten oxide (WO)₃) Etc. to complete reversible color change by applying voltage to lithium cobaltate film for lithiation. With electrochromic layer (WO)₃) The mutual complementation generates electrochromic reaction, and the color of the device in a colored state can reach 5 percent.

In one embodiment of the present invention, the solid electrochromic device including the brown lithium cobaltate thin film has a structure as shown in fig. 2. The solid electrochromic device is characterized by comprising the following components in part by weight: the method comprises the steps of selecting a transparent substrate (quartz glass, common glass or conductive glass), and sequentially forming a first transparent conductive layer (ITO conductive film, FTO conductive film), a lithium cobaltate film, an ion conductive layer (lithium tantalate)/a dielectric layer (silicon oxide, aluminum oxide, silicon nitride or the above oxides containing hydrogen, lithium and sodium), an electrochromic layer (tungsten oxide), a second transparent conductive layer (ITO conductive film, FTO conductive film) and a protective layer (such as silicon nitride, aluminum oxide, silicon oxynitride and the like) with certain thickness.

As an example of one provided electrochromic device, its main structure comprises ITO/LiCoO₂/WO₃ITO, optionally with a dielectric layer (on LiCoO)₂And WO₃In between) and protective layer (outer layer of ITO), improve device life-span and stability, its electrochromic reaction:

lithium cobaltate thin film layer: LiCoO₂→Li⁺+e^-+CoO₃ ^2-；

Electrochromic layer: WO₃(colorless) + Li⁺+e^-→LiWO₃(blue).

The characterization of an electrochemical workstation and a spectrophotometer shows that the visible light transmittance of the lithium cobaltate film obtained by the invention can reach 80 percent at most, the coloring state transmittance of a component device can be 5-80 percent (for example, 5 percent), and the requirement of an intelligent building window is met. In one embodiment of the invention, the ITO/LiCo all-solid-state electrochromic device prepared by magnetron sputtering of the direct-current power supply_2.55O_x(x is about 2 to 6)/LiTaO₃/WO₃ITO, photoelectron spectroscopy analysis thereofShown; compared with the existing all-solid-state electrochromic device ITO/NiO containing transparent nickel oxide film prepared by heat treatment at room temperature_y/LiTaO₃/WO₃ITO having a colored state transmittance of less than the same 10% to 20%.

The present invention will be described in detail by way of examples. It is also to be understood that the following examples are illustrative of the present invention and are not to be construed as limiting the scope of the invention, and that certain insubstantial modifications and adaptations of the invention by those skilled in the art may be made in light of the above teachings. The specific process parameters and the like of the following examples are also only one example of suitable ranges, i.e., those skilled in the art can select the appropriate ranges through the description herein, and are not limited to the specific values exemplified below. In the following embodiments, unless otherwise specified, the target material is a cobalt-lithium alloy target material, the purity of the cobalt-lithium alloy target material is higher than 99.9%, the grain size is less than 100 micrometers, and the resistivity is 1-200 Ω · cm; the molar content ratio of lithium to cobalt in the cobalt-lithium alloy target is 0.5-3.

Example 1

Sputtering deposition: introducing mixed gas of argon and oxygen into a sputtering deposition chamber, controlling the total gas pressure at 1Pa, the oxygen partial pressure ratio at about 10%, and the DC power supply power at 0.75W/cm²Depositing with cobalt-lithium alloy as target (deposition rate of 3 nm/min) for 30min to obtain brown lithium cobaltate film (including Co²⁺And Co³⁺，Co³⁺The molar content of the cobalt ions in the lithium cobaltate thin film is 40% (shown in figure 8), the molar content ratio of the cobalt ions to the lithium ions in the lithium cobaltate thin film is 1-3.5, and the thickness is 90 nm.

The films were characterized by electrochemical workstation and spectrophotometer at PC (propylene glycol carbonate) + LiClO₄The light transmittance of the solution and the standard sodium hydroxide solution is improved, the film has reversible light transmittance change along with the injection of anions/cations after being extracted, and the lithium cobaltate film is coated on PC + LiClO₄In the solution, positive and negative voltages were applied to make the cation-impregnated/extractable film as shown in FIG. 1, and from FIG. 1, it is understood that the permeability of the film accompanying cation impregnation/extractionFrom 60% to 80%.

Example 2

Upon completion of example 1, an ion conductive layer (LiTaO) was magnetron sputter deposited in sequence as described in example 1₃Thickness 40nm), an electrochromic layer (WO)₃And 400nm in thickness) of the electrochromic device, the structure of which is shown in fig. 2. Fig. 2 shows a substrate (200), a first transparent conductive layer (210), an ion storage layer (220), an ion conductive layer (230), an electrochromic layer (240), a second transparent conductive layer (250), and a protective layer (260) in this order. The substrate is glass, the first transparent conducting layer is ITO (thickness is 200nm), the second transparent conducting layer is ITO (thickness is 400nm), and the protective layer is silicon oxide (thickness is 200 nm).

The electrochromism performance and the light transmittance performance of the device are represented by an electrochemical workstation and a spectrophotometer, different voltages are applied to the device for 30s, the visible light transmittance value changes, as shown in fig. 3, the transmittance in a transparent state can be changed from 78% to 25%, the transmittance is different by 53% after the device is stabilized for 30s, and specific numerical values are shown in table 1. After the rated voltage is applied to the device, the light transmittance changes with time, as shown in fig. 4, it can be seen that the response time of the device is less than 5s, and the transmittance shifts with the duration of the applied voltage, and the transmittance can reach the minimum value of 5%, and the specific response time is shown in table 2.

Table 1 shows the transmission in the different colored states of the electrochromic device prepared in example 2:

table 2 shows the specific response times of the electrochromic devices prepared in example 2:

electrochromic device	Difference in transmittance (T%)	Time to change color(s)
			3×4cm	65	3-5

。

Example 3

Upon completion of example 1, a dielectric layer (lithium-containing alumina, 50nm thick), an electrochromic layer (WO) were magnetron sputter deposited as described in example 1₃And 450nm in thickness) of the electrochromic device, the structure of which is shown in fig. 5. Fig. 5 shows a substrate (500), a first transparent conductive layer (510), an ion storage layer (520), a dielectric layer (530), an electrochromic layer (540), a second transparent conductive layer (550), and a protective layer (560) in that order. The substrate is glass, the first transparent conducting layer is ITO (thickness is 200nm), the second transparent conducting layer is ITO (thickness is 400nm), and the protective layer is silicon oxide (thickness is 200 nm).

The electrochromism performance and the light transmittance performance of the device are represented by an electrochemical workstation and a spectrophotometer, the device applies different voltages for 30s, the visible light transmittance value changes, as shown in fig. 6, the transmittance in a transparent state can be changed from 75% to 28%, the transmittance is different by 47% after the stabilization of 30s, and the specific numerical values are shown in table 3. After the device is applied with a rated voltage, the light transmittance changes with time, as shown in fig. 7, it is known that lithium ions contained in the lithium cobaltate thin film can migrate, the lithium ions migrate slowly, the lithium ion migration rate increases with time, the transmittance can reach the minimum value of 10%, and the response time is shown in table 4.

Table 3 shows the transmittance in different colored states of the electrochromic device prepared in example 3

State of electrochromic device	Applied voltage/(V)	T％
			Transparent state 1 (marked with "1" in FIG. 6)	-2.0	76
Transparent state 2 (labeled "2" in FIG. 6)	0	75
			Colored state 1 (labeled "3" in FIG. 6)	+1	72
Colored state 2 (labeled "4" in FIG. 6)	+1.5	45
			Colored state 3 (labeled "5" in FIG. 6)	+2.0	28

。

Table 4 shows the specific response times of the electrochromic device prepared in example 3:

electrochromic device	Difference in transmittance (T%)	Time to change color(s)
			3×4cm	47	20

。

Example 4

Sputtering deposition: introducing mixed gas of argon and oxygen into a sputtering deposition chamber, controlling the total gas pressure at 1Pa, the oxygen partial pressure ratio at about 20%, and the DC power supply power at 0.75W/cm²Depositing with cobalt-lithium alloy as target (deposition rate of 4nm/min) for 25min to obtain brown lithium cobaltate film (including Co²⁺And Co³⁺，Co³⁺The molar content of the lithium cobaltate film is 30%, the molar content ratio of lithium ions to cobalt ions in the lithium cobaltate film is 1-3.5, and the thickness is 90 nm.

Example 5

Upon completion of example 4, an ion conductive layer (LiTaO) was magnetron sputter deposited in sequence as described in example 4₃Thickness 40nm), an electrochromic layer (WO)₃And 400nm in thickness) of the electrochromic device, the structure of which is consistent as shown in fig. 2. Fig. 2 shows a substrate (200), a first transparent conductive layer (210), an ion storage layer (220), an ion conductive layer (230), an electrochromic layer (240), a second transparent conductive layer (250), and a protective layer (260) in this order. The substrate is glass, the first transparent conducting layer is ITO (thickness is 200nm), the second transparent conducting layer is ITO (thickness is 400nm), and the protective layer is silicon oxide (thickness is 200 nm).

The electrochromism performance and the light transmittance performance of the device are represented by an electrochemical workstation and a spectrophotometer, different voltages are applied to the device for 30s, the visible light transmittance value changes, as shown in figure 9, the transmittance in a transparent state can be changed from 73% to 23%, and the transmittance is different by 50% after the device is stabilized for 30 s. After the rated voltage is applied to the device, the light transmittance changes with time, as shown in fig. 10, it is known that the response time of the device is long, and the transmittance value shifts with the time length of the applied voltage, and the transmittance value increases, and finally reaches 15%.

Table 5 shows the transmission in the different colored states of the electrochromic device prepared in example 5:

electrochromic device states	Applied voltage/(V)	T％
			Transparent state 1 (marked with "1" in FIG. 9)	0	73
Colored state 1 (labeled "2" in FIG. 9)	+1	63
			Colored state 2 (labeled "3" in FIG. 9)	+1.5	57
Colored state 3 (marked with "4" in FIG. 9)	+2.0	41
			Colored state 4 (labeled "5" in FIG. 9)	+2.5	32
Colored state 5 (labeled "6" in FIG. 9)	+3.0	23

。

Table 6 shows the specific response times of the electrochromic devices prepared in example 5:

electrochromic device	Difference in transmittance (T%)	Time to change color(s)
			3×4cm	37	20

。

Claims

1. A lithium cobaltate thin film, wherein a valence state of a cobalt ion in the lithium cobaltate thin film comprises Co²⁺And Co³⁺Co in an amount of 100% based on the total molar amount of cobalt ions³⁺Less than 45% by mole; the molar content ratio of cobalt ions to lithium ions in the lithium cobaltate film is 1-3.5;

the preparation method of the lithium cobaltate film comprises the following steps: selecting cobalt-lithium alloy target material or/and lithium cobaltate ceramic target materialDepositing a lithium cobaltate film on the surface of the substrate by adopting direct-current power supply magnetron sputtering, wherein the parameters of the direct-current power supply magnetron sputtering comprise: DC power density of 0.3W/cm²～2W/cm²(ii) a Vacuum degree less than 5X 10^-4Pa, deposition time is 5-100 minutes; the sputtering atmosphere is oxygen-argon mixture, and the oxygen content is 5-20 percent; the total working pressure is 0.5 Pa-5 Pa;

the visible light transmittance of the lithium cobaltate thin film is less than or equal to 60 percent, and the visible light transmittance after self-lithiation is more than 75 percent;

wherein, the process of self-lithiation is as follows: when voltage is applied to two ends of the lithium cobaltate film, lithium ions in the lithium cobaltate film migrate under the drive of current, so that cobalt divalent ions and cobalt trivalent ions are promoted to perform redox reaction, and the color transparentization of the lithium cobaltate film can be further completed.

2. The lithium cobaltate thin film according to claim 1, wherein a molar content ratio of cobalt ions to lithium ions in the lithium cobaltate thin film is 1.5 to 3.

3. The lithium cobaltate film according to claim 1, wherein the lithium cobaltate film is further doped with at least one of Al, Ti, Zr, V, Mo, Ta, Nb, and Si in an amount of not more than 50%.

4. The lithium cobaltate thin film according to any one of claims 1 to 3, wherein the lithium cobaltate thin film has a thickness of 20 nm to 600 nm.

5. The lithium cobaltate thin film according to claim 4, wherein the thickness of the lithium cobaltate thin film is 50nm to 200 nm.

6. The lithium cobaltate thin film according to claim 1, wherein the purity of the cobalt lithium alloy target or/and the lithium cobaltate ceramic target is higher than 99.9%, the grain size is less than 100 microns, and the resistivity is 1 Ω -cm to 200 Ω -cm.

7. The lithium cobaltate thin film according to claim 6, wherein the molar content ratio of lithium to cobalt in the cobalt-lithium alloy target and the lithium cobaltate ceramic target is 0.8-3.

8. The lithium cobaltate thin film according to claim 1, wherein the direct current power source deposition rate is 1 nm/min to 10 nm/min.

9. A solid state electrochromic device comprising a first transparent conductive layer, the lithium cobaltate thin film according to any one of claims 1 to 8 as an ion storage layer, an electrochromic layer and a second transparent conductive layer, which are formed in this order on a surface of a substrate.

10. The solid state electrochromic device of claim 9, wherein the electrochromic layer is WO₃。

11. The solid state electrochromic device according to claim 10, wherein the first transparent conductive layer is an ITO conductive film or an FTO conductive film, and the second transparent conductive layer is an ITO conductive film or an FTO conductive film.

12. The solid state electrochromic device according to claim 9, further comprising a dielectric layer or an ion conducting layer between the electrochromic layer and the lithium cobaltate thin film, or/and further comprising a protective layer on a surface of the second transparent conducting layer away from the electrochromic layer.

13. The solid state electrochromic device according to claim 12, wherein the ion conducting layer is lithium tantalate, the dielectric layer is at least one of a silicon oxide layer, an aluminum oxide layer, a silicon nitride layer, a silicon oxide layer containing hydrogen/lithium/sodium, and an aluminum oxide layer containing hydrogen/lithium/sodium, and the protective layer is at least one of a silicon nitride layer, an aluminum oxide layer, and a silicon oxynitride layer.