Electrochromic cells change their light transmission characteristics based on the direction of an applied electric field. In short, they are comprised of an electrolyte sandwiched between two electrodes (a cathode and an anode), where each electrode will darken or bleach based on the flow of ions (and electrons) in or out of the electrode. For lithium-based electrochromic cells, the electrolyte contains mobile lithium which enables lithium ion transfer between the electrodes. The present technology provides both a cell structure and method for fabricating that structure yielding improved performance, cost and stability.
An example of the present invention is an electrochemical cell with a negative electrode containing a cathodic electrochromic material that darkens upon electrochemical reduction (gain of electrons); a positive electrode made of lithium nickel tungsten oxide nanocomposite material (LiNiWO) that darkens upon electrochemical oxidation (loss of electrons); and a lithium ion electrolyte between the two electrodes. The LiNiWO positive electrode can be produced by a variety of deposition techniques including RF sputtering, pulsed laser deposition, DC sputtering, and DC/RF reactive sputtering. Results have shown strong anodic electrochromic activity as well as high charge capacity for battery applications. These materials have also demonstrated rapid color change and excellent repeatability.
We have also demonstrated a novel deposition process which eliminates existing procedures that are both cumbersome and costly. The current state of the art requires that one or both of the electrochromic layers undergo lithiation in a separate and subsequent procedure in order to provide the lithium ions needed for proper device performance. Our method includes a one-step synthesis technique for directly creating lithiated electrochromic transition metal oxides. By using a lithiated electrochromic material as a source material, a lithiated thin film layers containing significant amount of lithium can be deposited without a post-deposition process. The lithium in this deposited film is in mobile ionic form and is available in useful quantities for intercalation to and from an adjacent electrolyte or ion conductor layer.
This process also creates advantageous nanocrystalline characteristics in the film that provide superior cycling stability compared with devices made of conventional amorphous materials.
For more information, contact Erin Beaumont at:
U.S. Patent # 8,643,930
Applications and Industries
- Smart windows & window glazing
- Switchable mirrors for automobiles
- Lighting and display
- Optical communication systems
- Architectural materials
- Analytical instruments
- Consumer goods
- Rapid bleaching and darkening with excellent repeatability
- Can be produced by a wide variety of deposition techniques
- Cost effective by eliminating second deposition step
- Superior cycling stability
- Charge capacity twice the state-of-the-art