Al(iii)-doped lithium-ion-based self-supporting solid gel electrolyte and method of making same

Abstract

The present invention relates to a novel, transparent, self-supporting Al(III)-doped lithium-ion-based solid gel electrolyte for enhancing optical contrast of electrochromic devices. More specifically, the present invention relates to an Al(III)-doped lithium-ion-based self-supporting solid gel electrolyte for enhancing optical contrast, which comprises a unique transparent, flexible, self-supporting solid gel polymer electrolyte, and to the composition of the electrolyte and a method for preparing the same. This unique Al(III)-doped lithium-ion-based self-supporting solid gel electrolyte has a higher optical contrast and faster switching kinetics from bleached to colored state (or vice versa) upon external voltage change. With faster switching kinetics, the optical contrast is significantly improved from 50% to 82%.

Description

[0001] Invention Field This invention relates to an Al(III)-doped lithium-ion-based self-supporting solid gel electrolyte for enhancing the optical contrast of electrochromic devices. More specifically, this invention relates to an Al(III)-doped lithium-ion-based self-supporting solid gel electrolyte for enhancing optical contrast, the electrolyte comprising a unique transparent, flexible, self-supporting solid gel polymer electrolyte, and discloses its composition and preparation method. This unique Al(III)-doped lithium-ion-based self-supporting solid gel electrolyte exhibits high optical contrast and faster switching kinetics from a fading state to a colored state (and vice versa) upon changes in external voltage. Background of the Invention Recent research reports indicate that buildings worldwide contribute approximately 20% to total energy consumption and carbon dioxide emissions. With global warming becoming an increasingly serious problem, there is an urgent need to develop smart windows. These windows can not only reduce energy consumption but also minimize heat loss to the outside in winter and block outdoor heat from entering the building in summer, thereby reducing air conditioning costs and protecting buildings from ultraviolet and infrared radiation from sunlight.

[0003] Currently, the development of smart windows is mainly based on providing different types of glass coatings for window glass, including photochromic glass windows, thermochromic glass windows, and polymer-dispersed liquid crystal (PDLC) devices. However, these types of window systems all have their own limitations.

[0004] As is well known, photochromic glass has a long response time, which is further prolonged in colder seasons, and it cannot work in the absence of light (i.e., at night).

[0005] However, thermochromic materials only work in the presence of heat, so thermochromic devices cannot function effectively in winter.

[0006] PDLC (polymer-dispersed liquid crystal) glass films, which are originally opaque, cannot be observed through without applying sufficient voltage. They require a continuous voltage supply to remain transparent and not block infrared light.

[0007] Due to inherent defects in the aforementioned glass coatings, electrochromic (EC) devices, with their disruptive characteristics such as low voltage, high contrast, and long-term memory effect, are now leading the development of modern research. The first electrochromic material based on WO3 was invented long ago and has gradually expanded to other metal oxides in the smart field, such as V₂O₅, TiO₂, and Nb₂O₅. To date, many improvements have been made in the regulation of the performance of electrochromic thin films. However, challenges remain in optical contrast and rapid switching. In terms of design, electrochromic devices typically employ a five-layer structure: ITO (indium tin oxide) coated glass / electrochromic thin film / electrolyte / ion storage layer / ITO. High optical contrast allows the color of a smart window to change from near-transparent to a deeper opaque state, which not only protects privacy but also protects the interior from harmful ultraviolet and infrared radiation. From the perspective of electrochromic device manufacturing, a novel electrolyte composition may be a simple solution that is compatible with existing electrochromic films without replacing the entire electrochromic device. Therefore, this invention focuses on developing an electrolyte product for voltage-adjustable electrochromic devices in smart window applications.

[0008] See Chinese patent application CN103531840A, which relates to an electrolyte for lithium-sulfur batteries, comprising a lithium salt (LiClO4), an aluminum salt, a plasticizer (PMMA), and a THF / propylene carbonate solvent. The limitation of this patent is that it does not disclose the process of incorporating aluminum ions into lithium ions; furthermore, the application described herein is limited to battery systems, not electrochromic (EC) devices.

[0009] See Chinese patent application CN109721042A, which describes the concept of a Li-Al electrolyte combination. However, its drawback is that the sources of Li and Al, as well as the synthesis method of the electrolyte, differ from the information disclosed in this invention, and the patent does not reveal its application in EC systems.

[0010] Refer to Chinese patent application CN111584932A, in which the electrolyte uses a Li-Al composite salt as a filler, with LiClO4 and PC as the main components. Its drawback is that the preparation method involves various complex layer-by-layer deposition techniques, and its application is limited to solid-state lithium-ion batteries, without exploring its application in electrolytes (ECs).

[0011] See the article by PC Barbosa et al. published in *Polym. Adv. Technol* 22(2011) 1753-1759, which describes the preparation of a solid polymer electrolyte for electrochromic applications, comprising a poly(ethylene oxide-copolymer-propylene oxide) and poly(methyl methacrylate) matrix. The drawback is that the electrochromic (EC) system assembled with the prepared electrolyte exhibits moderate optical modulation performance; however, in the long term, the poly(ethylene oxide-copolymer-propylene oxide) may impair electrochemical performance due to its oxygen-trapping tendency.

[0012] See the article by M. Solis et al. published in *Journal of Materials Science: Materials in Electronics* 3(2016)28, which developed a solid-like gel electrolyte composed of LiClO4, PMMA, and PC for SiO2 / PANI-based electrochromic systems. This electrolyte exhibits highly efficient electrochromic (EC) performance. However, the drawback of this electrolyte is that it is made solely from lithium perchlorate, thus suffering from all the potential problems of lithium-ion batteries; furthermore, the prepared electrolyte was tested on polymer electrochromic (EC) films, so it is unclear whether it is equally suitable for inorganic transition metal oxide-based electrochromic (EC) systems.

[0013] See the article by P. Pal et al. published in Electrochimica Acta 260(2018)157-167, which describes the preparation of a polymer based on LiClO4 and PMMA and a detailed study of its charge transfer properties, showing that the polymer has good electrical conductivity. However, this study did not explore its optical properties, especially transmittance (an important parameter for evaluating electrochromic (EC) devices), which is a shortcoming.

[0014] See the article by Chung-Wen Kuo et al. published in the Journal of Chinese Chemical Society, 61(2014)563-570, which applied a solid gel electrolyte made of LiClO4, PMMA, and PC to a polymer-based electrochromic (EC) system, achieving excellent coloring efficiency. However, a drawback of this system is its very poor optical contrast, which is a major concern for electrochromic smart windows.

[0015] See AV Kadam's article published in *Materials Today Proceedings* 23(2020) 352-358, which developed an electrolyte based on lithium perchlorate-propylene carbonate-polymethyl methacrylate-acetonitrile for WO3-based electrochromic (EC) devices. Its drawback is that while faster switching kinetics were achieved, optical modulation performance was reduced by approximately 52%, resulting in poorer coloring and limiting the use of this electrochromic device in smart window applications.

[0016] The foregoing discussion reviews existing literature on electrochromic electrolyte technology, outlining prior art references in this field. These references demonstrate the extensive research conducted in this area and provide valuable insights into the techniques and methods employed in production processes. The above information is intended only to enhance understanding of the background of this invention.

[0017] Therefore, given the shortcomings of existing technologies reported to date and at least the aforementioned problems, developing cost-effective methods for preparing self-supporting solid-state gel electrolytes remains a key challenge for commercial applications. On the other hand, some synthetic methods involving electrolytes exhibit moderate optical modulation properties; however, in the long run, the use of poly(ethylene oxide-copolymer-propylene oxide) can impair electrochemical performance due to its oxygen-trapping tendency. Developing more environmentally friendly and sustainable synthetic methods is a key focus for achieving such self-supporting solid-state gel electrolytes with good conductivity and optical properties.

[0018] In view of the above and to overcome the deficiencies of the prior art, the present invention relates to an Al(III)-doped lithium-ion-based self-supporting solid gel electrolyte for enhancing the optical contrast of electrochromic devices / assemblies. More specifically, the present invention relates to an Al(III)-doped lithium-ion-based self-supporting solid gel electrolyte for enhancing optical contrast, the electrolyte being composed of a unique transparent, flexible, self-supporting solid gel polymer electrolyte, and relates to the composition of the electrolyte and its preparation method. This unique Al(III)-doped lithium-ion-based self-supporting solid gel electrolyte exhibits high optical contrast and faster switching kinetics from a fading state to a colored state (and vice versa) upon changes in external voltage.

[0019] Purpose of the invention The primary objective of this invention is to provide an aluminum (III)-doped lithium-ion-based self-supporting solid gel electrolyte to enhance the optical contrast of electrochromic devices / assemblies. Another objective of this invention is to provide a fabrication process for a transparent aluminum-doped lithium-ion-based self-supporting solid gel electrolyte to enhance the optical contrast of electrochromic (EC) devices / assemblies. This process includes modifying the composition of lithium perchlorate (LiClO4) and aluminum sec-butoxide (C12H4O4).27 The concentration of O3Al was such that its weight ratio was in the range of 0–4 wt%.

[0020] Another object of the present invention is to provide a transparent aluminum (Al) 3+ A lithium-ion-based self-supporting solid gel electrolyte process was used to enhance the optical contrast of electrochromic window glass.

[0021] Another object of the present invention is to provide a lithium-aluminum based self-supporting solid gel electrolyte that helps reduce structural degradation, is associated with electrochemical cycling stability, and can be used under ambient temperature and pressure conditions.

[0022] Another object of the present invention is to provide an electrochromic (EC) device / assembly comprising a five-layer sandwich structure, which allows for adjustment of the optical contrast between a colored state and a faded state by applying a small voltage.

[0023] Another objective of this invention is to adjust the optical contrast between a colored state and a faded state by applying a small amount of external voltage through a five-layer electrochromic device / assembly, comprising an indium tin oxide (ITO) coated glass, an electrochromic (EC) thin film, a prepared electrolyte, an ion storage layer, and an ITO coated glass, and vice versa.

[0024] These and other related objects of the invention will become apparent after careful reading of the description and reference to the accompanying drawings. Other objects, advantages, and novel features of the invention will become apparent as the description unfolds, and some of these will become obvious to those skilled in the art upon reading the following.

[0025] Invention Summary Other features and embodiments of this disclosure will be better understood through the technology and other aspects thereof. Further embodiments of the invention are described in detail herein and are considered part of the claimed disclosure.

[0026] A key aspect of this invention is the provision of a transparent aluminum-doped lithium-ion-based self-supporting solid gel electrolyte for enhancing the optical contrast of electrochromic devices / assemblies. This electrolyte comprises lithium perchlorate (LiClO4) and aluminum sec-butoxide (C4). 12 H 27 O3Al), with a weight ratio concentration ranging from 0 to 4%.

[0027] Another aspect of the present invention provides a lithium-aluminum based self-supporting solid gel electrolyte, wherein the weight ratio of aluminum sec-butoxide to lithium perchlorate is 1:1. This ratio optimizes the optical modulation effect, increasing it from 50% to 82%, with a coloring efficiency in the range of 600 cm² / C to 700 cm² / C, and a faster switching kinetics time of 2.5 seconds.

[0028] One embodiment of the present invention discloses a transparent aluminum (Al) 3+ A method for preparing a lithium-ion-based self-supporting solid gel electrolyte, comprising the following steps: (a) Using lithium perchlorate (LiClO4) and aluminum sec-butoxide (C 12 H 27 O3Al) was used as an electrolyte ion precursor to obtain a precursor mixture; (b) The precursor mixture obtained in step (a) was mixed with 0.25 mL of propylene carbonate (PC) and 1 g of polymethyl methacrylate and kept in a hot air oven at 110°C for 24 hours to obtain a polymer matrix; (c) Dissolve the polymer matrix obtained in step (b) in 20 mL of aprotic solvent and stir for 24 hours to obtain the prepared mixture; (d) Pour the prepared mixture obtained in step (c) onto a flat petri dish, then cover the petri dish with aluminum foil and let it stand for 48 hours to air dry to obtain a transparent solid; (e) Remove the transparent solid prepared in step (d) from the petri dish and cut it into transparent self-supporting solid-gel electrolyte sheets with a size of 10 cm × 10 cm.

[0029] In another embodiment of the invention, a polymer matrix is ​​disclosed containing an ion migrating agent selected from phthalates, phosphate esters, carboxylic acid esters, epoxidized fatty acid esters, polymeric polyesters, modified polymers; liquid rubbers and plastics, nitrile rubber (NBR), chlorinated polyethylene (PE), ethylene-vinyl acetate copolymer (EVA), polymethyl methacrylate, propylene carbonate, and mixtures thereof.

[0030] In another embodiment of the invention, the aprotic solvent medium used in step (c) is disclosed to be selected from acetone, dimethylformamide (DMF), tetrahydrofuran (THF), dichloromethane (CH2Cl2), acetonitrile (CH3CN), dimethyl sulfoxide (DMSO), dimethylmalonylurea, ethyl acetate, pyridine, sulfolane, hexamethylphosphoramide, and mixtures thereof.

[0031] In another embodiment of the invention, a solid-gel electrolyte is disclosed, comprising a lithium-aluminum solid-gel electrolyte having a polymer network structure, wherein the polymer network structure has circular channels and a porous matrix, enabling Li... + And Al 3+ To occupy the passageway.

[0032] In another embodiment of the present invention, an electrochromic device fabricated by sandwiching a five-layer structure is disclosed, wherein the electrochromic device comprises: (a) Counter electrode and working electrode; (b) Electrochromic thin film; (c) Transparent lithium-aluminum based self-supporting solid gel electrolyte sheet; (d) Ion storage layer.

[0033] In another embodiment of the present invention, a method for preparing an electrochromic device is disclosed, comprising the following steps: a. Coating an ion storage layer onto a transparent lithium-aluminum-based self-supporting solid gel electrolyte sheet to obtain the coated transparent electrolyte sheet; b. Place the coated transparent electrolyte sheet obtained in step (a) on the conductive surface of the counter electrode; c. Coat the working electrode with an rGO-WO3 electrochromic film; d. Clamp the transparent aluminum-lithium based solid gel electrolyte sheet from step (b) tightly with the working electrode from step (c) to ensure that there is no air gap between the two electrodes.

[0034] In another aspect of the invention, aluminum (Al) is provided. 3+ A lithium-ion-based self-supporting solid gel electrolyte doped with aluminum (Al) was tested using cyclic voltammetry. 3+ The lithium-ion-based self-supporting solid gel electrolyte doped with rGO-WO3 exhibits a broad integral curve, which is correlated with ion intercalation / deintercalation. This curve was obtained using a 3.24 cm⁻¹ rGO-WO3 / ITO working electrode. 2 Optical contrast ratio of 50%-82% is achieved within a potential range of -1 V to +1 V. In another aspect of the invention, a doped aluminum ion (Al) is provided. 3+ A lithium-ion-based self-supporting solid gel electrolyte, wherein aluminum ions are doped (Al... 3+ The lithium-ion-based self-supporting solid gel electrolyte exhibits extremely low charge transfer impedance and a small semicircle radius as measured by electrochemical impedance spectroscopy (Z' / -Z” in the range of 0-140 ohms), thus providing 50-82% optical contrast.

[0035] Another aspect of the present invention provides an aluminum ion (Al3+ A lithium-ion-based self-supporting solid gel electrolyte doped with aluminum ions (Al) 3+ The doped lithium-ion-based self-supporting solid gel electrolyte contains Al 3+ It helps reduce structural degradation, is associated with electrochemical cycle stability, and can be used under normal temperature and pressure conditions. Attached Figure Description

[0036] To complete the specification and aid in a better understanding of the invention, a set of accompanying drawings is provided. These drawings form part of the specification and illustrate one embodiment of the invention, but should not be construed as limiting the scope of the invention, but rather as examples of implementation methods.

[0037] The attached figures include the following: Figure 1 The synthesis of Al is shown 3+ Process flow diagram of doped lithium-ion-based self-supporting solid gel electrolyte and electrochromic (EC) devices / assemblies.

[0038] Figure 2 (ab) shows the field emission scanning electron microscope (FESEM) morphology of the transparent self-supporting solid gel electrolyte product (10 cm × 10 cm) and the lithium-aluminum based solid gel electrolyte.

[0039] Figure 3 Cyclic voltammetry curves of the electrochromic (EC) film of rGO-WO3 using Li-based solid gel electrolyte and Li-Al-based solid gel electrolyte are shown.

[0040] Figure 4 The improved optical modulation performance of the rGO-WO3 electrochromic device using a lithium aluminum-based self-supporting solid gel electrolyte (a) is shown compared to that of a conventional lithium electrolyte (b).

[0041] Figure 5 The electrochemical impedance spectroscopy of rGO-WO3 electrochromic (EC) films in lithium-based self-supporting solid gel electrolytes and lithium-aluminum-based self-supporting solid gel electrolytes is shown as a comparison.

[0042] Figure 6 A schematic diagram of the charge transfer mechanism of a typical electrochromic (EC) device is shown, where (a) uses a lithium-based self-supporting solid gel electrolyte and (b) uses a lithium-aluminum-based self-supporting solid gel electrolyte. Detailed description of the invention The following description should not be considered limiting, but only as an illustration of the broad principles of the invention. Embodiments of the invention will be described by way of example with reference to the accompanying drawings, which illustrate elements and results according to the invention.

[0043] The foregoing detailed description of this disclosure is intended to enable those skilled in the art to clearly understand it. Additional features, embodiments, and advantages of the invention will be described below, forming the subject matter of the claims of this disclosure. However, the disclosure set forth in the specification should be best understood in conjunction with the foregoing appended claims and the accompanying drawings. Those skilled in the art will understand that the disclosed concepts and specific embodiments can be readily used as the basis for modifying or designing other structures for achieving the same purpose as this disclosure. Those skilled in the art will also recognize that such equivalent processes do not depart from the spirit and scope of this disclosure as set forth in the appended claims. It is readily understood that the various aspects of this disclosure, as generally described herein and illustrated in the accompanying drawings, can be arranged, substituted, combined, and designed in various configurations, all of which are expressly considered and constitute a part of this disclosure.

[0044] While the present invention has been disclosed with reference to certain embodiments, those skilled in the art will understand that various modifications can be made and equivalents can be substituted without departing from the scope of the invention. Furthermore, various modifications can be made to adapt to specific situations or materials without departing from the scope of the invention, thereby conforming to the teachings of the invention.

[0045] Unless the context clearly indicates otherwise, throughout the specification and claims, the following terms shall have the meanings expressly given herein. “a,” “an,” and “the” include plural references. “in” includes both “in” and “on.” When referring to the accompanying drawings, the same numerals in each drawing denote the same parts. Furthermore, unless otherwise stated or inconsistent with the disclosure herein, references to the singular shall also include plural meanings.

[0046] This invention relates to a transparent aluminum-doped lithium-ion-based self-supporting solid gel electrolyte for enhancing the optical contrast of electrochromic devices / assemblies. The electrolyte comprises lithium perchlorate (LiClO4) and aluminum sec-butoxide (C4). 12 H 27 O3Al), with a weight ratio concentration ranging from 0 to 4 wt%.

[0047] In one embodiment of the present invention, a lithium-aluminum based self-supporting solid gel electrolyte is provided, wherein the weight ratio of aluminum sec-butoxide to lithium perchlorate is 1:1. This optimized ratio enables an optical modulation range of 50% to 82%, a coloring efficiency of 600 cm² / C to 700 cm² / C, and a faster switching kinetics time of 2.5 seconds.

[0048] In one embodiment of the invention, transparent aluminum (Al) is used to enhance the optical contrast of electrochromic devices / components. 3+ The preparation method of the doped lithium-ion-based self-supporting solid gel electrolyte includes the following steps: a. Using lithium perchlorate (LiClO4) and aluminum sec-butoxide (C 12 H 27 O3Al) serves as a precursor for electrolyte ions.

[0049] b. Mix the precursor mixture obtained in step a with 0.25 mL of propylene carbonate PC and 1 g of polymethyl methacrylate, and place in a hot air oven at 110°C for 24 hours.

[0050] c. Dissolve the mixture obtained in step b in 20 mL of the organic solvent tetrahydrofuran (THF) and stir for 24 hours to ensure a homogeneous mixture.

[0051] d. Pour the mixture prepared in step c into a flat-bottomed petri dish, cover the petri dish with aluminum foil, and let it air dry for 48 hours.

[0052] e. Peel the transparent solid prepared in step ad from the petri dish and cut it into transparent self-supporting solid-gel electrolyte sheets with a size of 10 cm × 10 cm.

[0053] In one embodiment of the invention, for transparent aluminum (Al) 3+ In the preparation method of lithium-ion-based self-supporting solid gel electrolyte, the ion migrating agent used in the polymer matrix in step (b) is selected from phthalates, phosphates, carboxylic esters, epoxidized fatty acid esters, high molecular weight polyesters, modified polymers, liquid rubbers, plastics, nitrile rubber (NBR), chlorinated polyethylene (PE), ethylene-vinyl acetate copolymer (EVA), polymethyl methacrylate, propylene carbonate and mixtures thereof.

[0054] In one embodiment of the invention, for transparent aluminum (Al) 3+ In the preparation method of lithium-ion-based self-supporting solid gel electrolyte, the aprotic solvent medium used in step (d) is selected from acetone, dimethylformamide (DMF), tetrahydrofuran (THF), dichloromethane (CH2Cl2), acetonitrile (CH3CN), dimethyl sulfoxide (DMSO), dimethylmalonylurea, ethyl acetate, pyridine, sulfolane, hexamethylphosphoric triamine and mixtures thereof.

[0055] In another embodiment of the invention, aluminum (Al) is provided. 3+ A lithium-ion-based self-supporting solid gel electrolyte doped with aluminum (Al) was tested using cyclic voltammetry. 3+ The lithium-ion-based self-supporting solid gel electrolyte exhibits a broad integral curve, which is correlated with ion intercalation / deintercalation, using an rGO-WO3 / ITO working electrode (3.24 cm⁻¹). 2Optical contrast ratio of 50%-82% is achieved within a potential range of -1 V to +1 V. In another embodiment of the invention, aluminum (Al) is provided. 3+ A lithium-ion-based self-supporting solid gel electrolyte doped with aluminum (Al) 3+ The lithium-ion-based self-supporting solid gel electrolyte exhibits extremely low charge transfer impedance and small semicircular radius as measured by electrochemical impedance spectroscopy (Z' / -Z” in the range of 0-140 ohms), thus providing 50%-82% optical contrast.

[0056] In another embodiment of the invention, aluminum (Al) is provided. 3+ A lithium-ion-based self-supporting solid gel electrolyte doped with aluminum (Al) 3+ Doped lithium-ion-based self-supporting solid gel electrolytes include Al 3+ It helps reduce structural degradation, is related to electrochemical cycle stability, and can operate under normal temperature and pressure conditions.

[0057] In another embodiment of the invention, aluminum (Al) is provided. 3+ A lithium-ion-based self-supporting solid gel electrolyte doped with aluminum (Al) 3+ The lithium-ion-based self-supporting solid gel electrolyte is composed of a lithium-aluminum solid gel electrolyte with a polymer network structure, which includes circular channels and a porous matrix. Lithium ions (Li...) + ) and aluminum ions (Al 3+ Occupying the channel, and Al 3+ Compared to ions, Li + The smaller ionic radius of Al results in fewer ions being adsorbed within the same pore area. 3+ The number of tungsten bronze complexes is greater than that of Li. + This results in a bluer color, thereby improving the optical contrast of the electrochromic (EC) component.

[0058] In another embodiment of the invention, aluminum (Al) is provided. 3+ A lithium-ion-based self-supporting solid gel electrolyte doped with an electrochromic (EC) device / assembly includes a sandwich five-layer structure consisting of a lithium-aluminum-based transparent self-supporting solid gel electrolyte sheet, a counter electrode, and a working electrode, placed between indium tin oxide (ITO) glass on both sides, for modulating the optical contrast between a colored state and a faded state when a small voltage is applied.

[0059] In another embodiment of the present invention, a method for fabricating an electrochromic (EC) device / assembly is provided, the method comprising the following steps: a. Carefully place the coating of the transparent electrolyte sheet onto the conductive surface of the NiOx / ITO counter electrode.

[0060] b. Coat the ITO working electrode with electrochromic rGO-WO3.

[0061] c. The Al-Li based solid gel electrolyte sheet / NiOx / ITO counter electrode and the rGO-WO3 / ITO working electrode are clamped together with no air gap between the two electrodes.

[0062] In another embodiment of the invention, a self-supporting solid-gel electrolyte with tunable composition is provided, which is achieved by changing the composition of lithium perchlorate (LiClO4) and aluminum sec-butanol (C2000). 12 H 27 The concentration of (O3Al) was determined by the concentration of lithium perchlorate, which was pre-treated in a vacuum oven at 110°C for 24 hours. The lithium perchlorate (LiClO4) and aluminum sec-butanol (C 12 H 27 The weight ratios of O3Al were 1:0, 1:1, 2:1, and 1:2. 0.25 mL of propylene carbonate (PC) and 1 g of polymethyl methacrylate (PMMA, pre-treated in a hot air oven at 110°C for 24 hours) were added to the weighed precursor mixture. This mixture was then dissolved in 20 mL of tetrahydrofuran (THF) and stirred for 24 hours to achieve homogeneity. After 24 hours, the electrolyte solution became completely transparent and was poured into a flat-bottomed petri dish. The dish was covered with aluminum foil, with small holes left in the foil to allow the solvent (THF) to evaporate, and left to air dry for 48 hours. The process was then allowed to stand for 48 hours for natural drying.

[0063] After 48 hours, the liquid electrolyte transformed into a transparent solid, which could be easily peeled from a 12 cm diameter petri dish. A 10 cm × 10 cm transparent, self-supporting solid gel electrolyte was then cut from the gel. The product is stable for over one year under ambient temperature and humidity conditions. The morphology of the electrolyte film was analyzed using field emission scanning electron microscopy (FESEM), and its thermal properties were measured by thermogravimetric analysis (TGA).

[0064] In the fabrication of electrochromic (EC) devices, a transparent electrolyte sheet must be carefully placed on the conductive surface of the counter electrode, which is pre-coated with a NiOx ion storage layer. Finally, the working electrode coated with an rGO-WO3 electrochromic film is sandwiched together to ensure that there are no air gaps between the two electrode layers.

[0065] In a three-electrode system, cyclic voltammetry (CV) tests were performed on the rGO-WO3 thin film using the prepared Li-Al electrolyte and a conventional Li electrolyte. The optical properties of typical electrochromic (EC) devices were measured against the aforementioned solid-state electrolyte. For detailed procedures, please refer to [link to detailed procedures]. Figure 1 The flowchart shown.

[0066] The morphology of the Al(III)-doped lithium-ion electrolyte was characterized by field emission scanning electron microscopy (FESEM), and its thermal behavior was studied by thermogravimetric analysis (TGA). For the fabricated EC device composed of "ITO conductive glass / EC film / electrolyte / ion storage layer / ITO conductive glass", electrochemical and optical characterization was performed using Li electrolyte and Li-Al electrolyte to evaluate its electrochromic properties.

[0067] Figure 2 Image a shows the prepared 10cm × 10cm electrolyte. Figure 2 b shows a field emission scanning electron microscope (FESEM) micrograph of the Li-Al solid gel electrolyte, clearly revealing the polymer network structure containing circular channels. Figure 3 The electrochemical performance of Li electrolyte and Li-Al electrolyte under cyclic voltammetry (CV) was depicted. The larger area of ​​the CV integral curve indicates that Li-Al electrolyte has better ion intercalation / deintercalation performance. The electrochemical impedance spectroscopy (EIS) spectra are shown below. Figure 4 As shown. The electrolyte of this invention exhibits a significantly smaller semicircle radius in electrochemical impedance spectroscopy (EIS), which is correlated with lower charge transfer impedance. These results are consistent with... Figure 5 The excellent optical contrast shown is related to the lower charge transfer impedance, which is also related to the faster color switching response of the electrochromic (EC) system. Figure 6 a and Figure 6 b shows schematic diagrams illustrating the charge transfer mechanisms in typical rGO-WO3 electrochromic devices using Li electrolytes and Li-Al electrolytes, respectively. Solid gel electrolytes consist of a porous matrix, as shown in field emission scanning electron microscopy (FESEM) images. Figure 2 As shown in a), Li + And Al 3+ Contained in the channel, where Li + The ionic radius is relatively large, similar to Al. 3+ Compared to other ions, fewer ions are adsorbed within the same pore area. Therefore, Al 3+ The number of tungsten bronze complexes formed is greater than that of Li. + This results in a bluer color, thereby improving the optical contrast of the electrochromic component.

[0068] This invention discloses a unique freestanding solid-state gel electrolyte and its preparation method. This method is simple and easy to implement, and has excellent potential in improving the optical contrast of typical electrochromic devices. This invention describes a novel method for adjusting the composition of lithium-ion-based electrolytes by introducing trivalent cations [Al(III)] to prepare transparent, stable, and flexible freestanding electrolytes. Optimized aluminum ions (Al... 3+ The use of a lithium-ion-based electrolyte (mass ratio 1:1) increases the optical modulation range from 50% to 82% and provides faster switching dynamics of 2.5 seconds. Furthermore, this invention includes the first independently developed method for improving electrochromic (EC) performance through electrolyte composition modification.

[0069] The synthesis process of the novel solid-state gel electrolyte described in this invention includes several unique steps and involves simple precursor combinations. All precursor materials used in this invention can be synthesized under ambient temperature and pressure conditions.

[0070] For electrochromic devices / components, optical contrast, i.e., the difference in optical transmittance between the colored state and the faded state, is the most important characteristic to be achieved. In this invention, Li + And Al 3+ Ions can occupy the pores of the polymer matrix. However, compared to pure lithium-ion based electrolytes, Al... 3+ The ionic radius of Al is relatively small, therefore more ions are adsorbed within the same pore area. Therefore, for Al... 3+ The number of tungsten bronze complexes formed is greater than that of Li. + This produces a stronger blue color, thereby improving the optical contrast of the electrochromic (EC) component.

[0071] Lithium ions are the most widely used ion in the electrolyte system of electrochromic devices, but their reserves are the smallest, resulting in extremely high costs. Therefore, the need for alternative electrolytes is urgent. Aluminum ions (Al...) 3+ The precursors for aluminum ions are more abundant and more cost-effective for use in electrochromic devices. However, due to the significant electrostatic interaction between aluminum ions and the electrochromic layer, we optimized their concentration to no more than 1:1. This invention reduces the cost of the electrolyte system by approximately 50%.

[0072] During repeated ion insertion / extraction cycles, Li + The relatively large ionic radius of Al can sometimes cause deformation of the crystal structure of electrochromic (EC) materials. 3+ The smaller radius helps reduce structural degradation, thereby also improving electrochemical cycling stability.

[0073] Li +The large radius of the ions limits the application of this electrolyte to bulk materials and leads to the degradation of the electrochromic (EC) properties of materials with dimensions of a few nanometers. In this regard, Al 3+ It is a recognized candidate for resonance with nanocrystals of such materials. Therefore, due to the quantum confinement effect brought about by the nanoscale, the electrolyte composition of the present invention can be well applied to materials with quantum confinement properties.

[0074] Example The following embodiments (including preferred embodiments) are used to illustrate the implementation of the present invention. However, it should be understood that the details shown are for illustrative purposes only and are used to illustrate the preferred embodiments of the invention. Therefore, they should not be construed as limiting the scope of the invention.

[0075] Example 1 Add 0.1 g of lithium perchlorate (LiClO4) and 0.1 g of aluminum sec-butoxide (C 12 H 27 Add 1 g of O3Al, 1 g of polymethyl methacrylate (PMMA), 0.25 mL of propylene carbonate (PC), and 20 mL of tetrahydrofuran (THF) to a 100 mL beaker. Stir the mixture for 24 hours to achieve homogeneity and form a uniform, clear solution. After 24 hours, pour the electrolyte solution into a 12 cm diameter flat-bottomed petri dish and cover it with a layer of perforated aluminum foil. Let it stand for 48 hours to allow sufficient time for it to dry and form a clear, self-supporting solid gel electrolyte, then carefully peel it off from the petri dish.

[0076] Electrochemical performance The redox properties of the EC films using the electrolyte composition of this invention were evaluated by cyclic voltammetry using a three-electrode system on an electrochemical workstation (Pine Instruments, Wave Driver 100, USA). All experiments used films with an area of ​​3.24 cm². 2 An EC thin film was used as the working electrode, a saturated calomel electrode as the reference electrode, and platinum as the counter electrode. The redox reaction was monitored by varying the potential from -1 V to +1 V. The obtained data were then analyzed by comparing the area under the integral hysteresis curves of the rGO-WO3 samples under Li electrolyte and Li-A electrolyte conditions.

[0077] Optical properties During the cyclic voltammetry experiment, an in-situ spectrophotometer from Shimadzu Corporation, coupled with a PineWave Driver, was used to simultaneously measure the optical transmission spectra of the samples. The changes in transmittance over time during the coloring and fading cycles revealed the changes in optical transmittance, i.e., optical contrast, of the rGO-WO3 film under both conventional and the electrolyte conditions of this invention.

[0078] Example 2 0.133 g of lithium perchlorate (LiClO4) and 0.067 g of aluminum sec-butoxide (C 12 H 27 Add 1 g of O3Al, 1 g of polymethyl methacrylate (PMMA), 0.25 mL of propylene carbonate (PC), and 20 mL of tetrahydrofuran (THF) to a 100 mL beaker. Stir the mixture for 24 hours to allow it to mix evenly and form a homogeneous, transparent solution. After 24 hours, pour the electrolyte solution onto a 12 cm diameter flat-bottomed petri dish and cover it with a layer of perforated aluminum foil. Let it stand for 48 hours to allow sufficient time for it to dry and form a transparent, self-supporting solid gel electrolyte, then carefully peel it off from the petri dish.

[0079] Electrochemical performance The redox properties of the EC films using the electrolyte composition of this invention were evaluated by cyclic voltammetry in a three-electrode system on an electrochemical workstation (Pine Instruments, Wave Driver 100, USA). All experiments used films with an area of ​​3.24 cm². 2 An EC thin film was used as the working electrode, a saturated calomel electrode as the reference electrode, and platinum as the counter electrode. The redox reaction was monitored by varying the potential from -1 V to +1 V. The obtained data were then analyzed by comparing the area under the integral hysteresis curves of the rGO-WO3 samples under Li electrolyte and Li-A electrolyte conditions.

[0080] Optical properties During the cyclic voltammetry experiment, an in-situ spectrophotometer from Shimadzu Corporation, coupled with a PineWave Driver, was used to simultaneously measure the optical transmission spectra of the samples. The changes in transmittance over time during the coloring and fading cycles revealed the changes in optical transmittance, i.e., optical contrast, of the rGO-WO3 film under both conventional and the electrolyte conditions of this invention.

[0081] Example 3 0.067 g of lithium perchlorate (LiClO4) and 0.133 g of aluminum sec-butoxide (C 12 H 27Add 1 g of O3Al, 1 g of polymethyl methacrylate (PMMA), 0.25 mL of propylene carbonate (PC), and 20 mL of tetrahydrofuran (THF) to a 100 mL beaker. Stir the mixture for 24 hours to allow it to mix evenly and form a homogeneous, transparent solution. After 24 hours, pour the electrolyte solution onto a 12 cm diameter flat-bottomed petri dish and cover it with a layer of perforated aluminum foil. Let it stand for 48 hours to allow sufficient time for it to dry and form a transparent, self-supporting solid gel electrolyte, then carefully peel it off from the petri dish.

[0082] Electrochemical performance The redox properties of the EC films using the electrolyte composition of this invention were evaluated by cyclic voltammetry in a three-electrode system on an electrochemical workstation (Pine Instruments, Wave Driver 100, USA). All experiments used films with an area of ​​3.24 cm². 2 An EC thin film was used as the working electrode, a saturated calomel electrode as the reference electrode, and platinum as the counter electrode. The redox reaction was monitored by varying the potential from -1 V to +1 V. The obtained data were then analyzed by comparing the area under the integral hysteresis curves of the rGO-WO3 samples under Li electrolyte and Li-A electrolyte conditions.

[0083] Optical properties During the cyclic voltammetry experiments, an in-situ spectrophotometer from Shimadzu Corporation, coupled with a PineWave Driver, was used to simultaneously measure the optical transmission spectra of the samples. The changes in transmittance over time during the coloring and fading cycles revealed the changes in optical transmittance, i.e., optical contrast, of the rGO-WO3 film under both conventional and the electrolyte conditions of this invention, as listed in Table 1.

[0084]

[0085] Advantages of the present invention a. This invention uses Li + And Al 3+ Ions that can occupy the pores of the polymer matrix produce a richer blue color, thus improving the optical contrast of the electrochemical component.

[0086] b. The preparation process of the novel solid-gel electrolyte in this invention is unique and simple, and can be operated under normal temperature and pressure conditions.

[0087] c. The preparation process of the novel lithium-ion-based self-supporting solid gel electrolyte in this invention is cost-effective and industrially feasible.

[0088] d. Smaller Al3+ The radius helps reduce structural degradation in novel lithium-ion-based self-supporting solid gel electrolytes, thereby also improving electrochemical cycling stability.

[0089] e. The novel lithium-ion-based self-supporting solid gel electrolyte composition of the present invention, due to its nanoscale size, can be applied to materials with quantum confinement effects.

Claims

1. A transparent aluminum-doped lithium-ion-based self-supporting solid gel electrolyte for enhancing the optical contrast of electrochromic devices, comprising lithium perchlorate (LiClO4) and aluminum sec-butoxide (C). 12 H 27 O3Al, with a weight ratio concentration ranging from 0 to 4 wt%.

2. The lithium-aluminum based self-supporting solid gel electrolyte as described in claim 1, wherein, The weight ratio of aluminum sec-butoxide to lithium perchlorate is 1:1, the optical modulation range is 50% to 82%, the coloring efficiency range is 600 cm² / C to 700 cm² / C, and the switching kinetics time is 2.5 seconds.

3. The transparent aluminum Al as described in claim 1 3+ A method for preparing a lithium-ion-doped self-supporting solid gel electrolyte includes the following steps: a. Using lithium perchlorate (LiClO4) and aluminum sec-butoxide (C) 12 H 27 O3Al was used as an electrolyte ion precursor to obtain a precursor mixture; b. The precursor mixture obtained in step a is mixed with 0.25 mL of propylene carbonate PC and 1 g of polymethyl methacrylate and kept in a hot air oven at 110°C for 24 hours to obtain a polymer matrix; c. Dissolve the polymer matrix obtained in step b in 20 mL of aprotic solvent and stir for 24 hours to obtain the prepared mixture; d. Pour the prepared mixture obtained in step c into a flat-bottomed petri dish, then cover the petri dish with aluminum foil and let it stand for 48 hours to air dry to obtain a transparent solid; e. Peel the transparent solid prepared in step d from the petri dish and cut it into transparent self-supporting solid-gel electrolyte sheets with a size of 10 cm × 10 cm.

4. The method of claim 3, wherein the polymer matrix contains an ion migrating agent selected from phthalates, phosphate esters, carboxylic acid esters, epoxidized fatty acid esters, high molecular weight polyesters, modified polymers, liquid rubbers, plastics, nitrile rubber (NBR), chlorinated polyethylene (PE), ethylene-vinyl acetate copolymer (EVA), polymethyl methacrylate (PMMA), propylene carbonate, and mixtures thereof.

5. The method according to claim 3, wherein the aprotic solvent medium used in step (c) is selected from acetone, dimethylformamide (DMF), tetrahydrofuran (THF), dichloromethane (CH2Cl2), acetonitrile (CH3CN), dimethyl sulfoxide (DMSO), dimethylpropionamide, ethyl acetate, pyridine, sulfolane, hexamethylphosphoric triamine, and mixtures thereof.

6. The lithium-aluminum based self-supporting solid gel electrolyte of claim 1, wherein the solid gel electrolyte comprises a lithium-aluminum solid gel electrolyte having a polymer network structure, the polymer network structure having circular channels and a porous matrix, so that Li + And Al 3+ Occupying the channel.

7. An electrochromic device, fabricated by sandwiching a five-layer structure, wherein the electrochromic device comprises: a: Counter electrode and working electrode; b: Electrochromic film; c: The sheet of the transparent lithium-aluminum-based self-supporting solid gel electrolyte as described in claim 1; d: Ion storage layer.

8. The method for preparing the electrochromic device according to claim 7, comprising the following steps: a. Coating an ion storage layer onto the transparent lithium-aluminum-based self-supporting solid gel electrolyte sheet as described in claim 1 to obtain the coated transparent electrolyte sheet; b. Place the coated transparent electrolyte sheet obtained in step a on the conductive surface of the counter electrode; c. Coat the working electrode with an rGO-WO3 electrochromic film; d. The transparent lithium-aluminum based solid gel electrolyte sheet prepared in step b is tightly clamped with the working electrode in step c, so that there is no air gap between the two electrodes.

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