Coating processes – Electrical product produced – Metallic compound coating
Reexamination Certificate
1998-03-02
2001-01-23
Beck, Shrive (Department: 1762)
Coating processes
Electrical product produced
Metallic compound coating
C427S108000, C427S126200, C427S165000, C427S376200
Reexamination Certificate
active
06177130
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to preparing lithiated vanadium oxide coatings of optical quality useful, e.g., as ion-storage counterelectrodes for electrochromic devices.
Electrochromic materials undergo a color change upon oxidation or reduction. In an ion-intercalation electrochromic device, an electrochromic material and an ion-storage counterelectrode material are separated by an ion-conducting electrolyte. The optical properties of the electrochromic material change when ions (e.g., hydrogen ions or metal ions such as lithium ions) intercalated within the structure of the ion-storage material are removed and intercalated within the structure of the electrochromic material in response to an applied electric potential. The ions are removed and returned to the ion-storage material by reversing the polarity of the applied potential, thereby returning the electrochromic material to its original optical state.
A preferred ion-storage material is lithiated vanadium oxide. These materials have been prepared in a number of different ways. According to one process, a solution phase precursor is coated onto an electronically conductive substrate (e.g., an FTO-coated glass substrate) and then heated to generate a vanadium oxide layer. This layer is then charged in a separate step by negatively biasing the vanadium oxide-coated substrate while it is submerged in a lithium ion-containing electrolyte solution to electrochemically insert lithium ions into the oxide layer.
Other processes for preparing lithiated vanadium oxide include physical vapor deposition processes such as sputtering, laser ablation, pulsed laser deposition, and evaporation. These processes, which are typically performed in a vacuum chamber, can be adjusted to yield lithiated material directly, in which case it is not necessary to insert lithium ions in a separate charging step. However, unlike the solution phase processes, many physical vapor deposition processes are not well-suited to producing uniform large-area oxide coatings. They are also relatively expensive.
SUMMARY OF THE INVENTION
In a first aspect, the invention features a method for producing a lithiated vanadium oxide-coated substrate that includes: (a) preparing a solution that includes (i) a solvent, (ii) a soluble lithium source, and (iii) a soluble vanadium source; (b) applying the solution to a substrate to form a coated substrate; and (c) heating the coated substrate to form an optical quality coating that includes lithiated vanadium oxide.
An “optical quality coating” is a coating that is substantially non-light scattering such that when interposed between a viewer and an object such as an emissive display, it does not disrupt the viewability of the object.
“Lithiated vanadium oxide” refers to vanadium oxide containing intercalated lithium ions that is capable of discharging at least some of the lithium ions in response to an applied electric potential. At least some of the vanadium ions in this material exist as V
4+
ions. Upon application of an electric potential, the V
4+
ions are oxidized to form V
5+
ions, which is coincident with the discharge of lithium ions.
A “soluble” lithium or vanadium source means that the source dissolves in the solvent at room temperature or upon heating.
The method yields lithiated vanadium oxide coatings that may be used “as is.” If desired, however, the lithiated vanadium oxide coating may be charged in a separate step with additional lithium ions. In the case of electrochromic devices, where the lithiated vanadium oxide coating acts as a supply of lithium ions for a material such as tungsten trioxide that exhibits the primary electrochromic behavior, including additional lithium ions results in devices with greater reversible optical dynamic range.
The lithiated vanadium oxide coating preferably is substantially amorphous, as evidenced by an x-ray diffraction pattern that lacks sharp diffraction peaks characteristic of crystalline material. The solvent is preferably an organic solvent, particularly where the solution is applied to a glass substrate. Examples of preferred organic solvents include methanol, ethanol, and combinations thereof. The coating solution may be prepared in a variety of ways. In one embodiment, the solution is prepared by combining lithium hydroxide, lithium hydroxide monohydrate, or a combination thereof and vanadium pentoxide with an organic solvent. In another embodiment, the solution is prepared by combining lithium hydroxide, lithium hydroxide monohydrate, or a combination thereof and vanadium pentoxide or vanadic acid (prepared, e.g., by acidifying a metavanadate salt such as sodium or ammonium metavanadate) in the presence of water to form an aqueous solution, drying the aqueous solution to remove water and form an intermediate that includes lithium and vanadium, and combining the intermediate with an organic solvent.
The solution is preferably applied to the substrate by dip coating. The coated substrate is preferably heated at a temperature of greater than or equal to about 150° C., but no greater than about 350° C., to form the optical quality, lithiated vanadium oxide coating.
In a second aspect, the invention features a method for preparing an electrochromic device that includes coating a substrate bearing an electronic conductor according to the above-described process to form a substrate bearing an optical quality, lithiated vanadium oxide coating on the electronic conductor, and combining that coated substrate with (i) a second substrate that includes an electronic conductor and an electrochromic material deposited on the conductor and (ii) an electrolyte, to form the electrochromic device. The electrochromic material preferably includes tungsten trioxide. The electrolyte preferably includes a solid, lithium ion-conducting, polymeric electrolyte.
The invention provides a solution phase process for preparing optical quality, lithiated vanadium oxide coatings. The process is particularly useful for preparing uniform, optical quality, large scale coatings on relatively flat, smooth surfaces. Because the coatings are in lithiated form following the heating step, it is not necessary to charge the coatings in a separate operation, thereby simplifying manufacture. In addition, the process does not require complex vacuum equipment of the type used in physical vapor deposition processes such as sputtering.
Other features and advantages of the invention will be apparent from the following description of the preferred embodiments thereof, and from the claims.
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Goldner et al.,
Barr Michael
Beck Shrive
Fish & Richardson
Minnesota Mining and Manufacturing Company
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