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Printed, Flexible, Rechargeable Battery Powers Wearable Sensors

Pat Waurzyniak
By Patrick Waurzyniak Contributing Editor, SME Media

Nanoengineers at the University of California San Diego have developed the first printed battery that is flexible, stretchable and rechargeable. These zinc batteries could be used to power everything from wearable sensors to solar cells and other kinds of electronics.

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Rajan Kumar is the co-first author of the Advanced Energy Materials paper and leads a team to commercialize the technology.

The researchers made the printed batteries flexible and stretchable by incorporating a hyper-elastic polymer material made from isoprene, one of the main ingredients in rubber, and polystyrene, a resin-like component. The substance, known as SIS, allows the batteries to stretch to twice their size, in any direction, without suffering damage. The work appears in the April 19, 2017 issue of Advanced Energy Materials. An abstract of the paper is available at http://onlinelibrary.wiley.com/doi/10.1002/aenm.201602096/full.

The ink used to print the batteries is made of zinc silver oxide mixed with SIS, the scientists reported. While zinc batteries have been in use for a long time, they are typically non-rechargeable. The researchers added bismuth oxide to the batteries to make them rechargeable.
 

“This is a significant step toward self-powered stretchable electronics,” said Joseph Wang, one of the paper’s senior authors and a nanoengineering professor at the Jacobs School of Engineering at UC San Diego, where he directs the school’s Center for Wearable Sensors. “We expect this technology to pave the way to enhance other forms of energy storage and printable, stretchable electronics, not just for zinc-based batteries but also for Lithium-ion (Li-ion) batteries as well as supercapacitors and photovoltaic cells.”

The prototype battery the researchers developed has about 1/5 the capacity of a rechargeable hearing aid battery, the researchers said, but it is 1/10 as thick, cheaper and uses commercially available materials. It takes two of these batteries to power a 3-V LED. The researchers are still working to improve the battery’s performance. Next steps include expanding the use of the technology to different applications, such as solar and fuel cells, and using the battery to power different kinds of electronic devices.

The researchers used standard screen printing techniques to make the batteries—a method that dramatically drives down the technology’s costs. Typical materials for one battery cost only $0.50. A comparable commercially available rechargeable battery costs $5.00. Batteries can be printed directly on fabric or on materials that allow wearables to adhere to the skin. They also can be printed as a strip to power a device that needs more energy. They are stable and can be worn for a long period of time.

The key ingredient that makes the batteries rechargeable is a molecule called bismuth oxide which, when mixed into the batteries’ zinc electrodes, prolongs the life of devices and allows them to recharge. Adding bismuth oxide to zinc batteries is standard practice in industry to improve performance, but until recently there hasn’t been a thorough scientific explanation as to why.

Last year, UC San Diego nanoengineers led by Professor Y. Shirley Meng published a detailed molecular study addressing this question. When zinc batteries discharge, their electrodes react with the liquid electrolyte inside the battery, producing zinc salts that dissolve into a solution. This eventually short circuits the battery. Adding bismuth oxide keeps the electrode from losing zinc to the electrolyte. This ensures that the batteries continue to work and can be recharged.

The work shows that it is possible to use small amounts of additives, such as bismuth oxide, to change the properties of materials.

“Understanding the scientific mechanism to do this will allow us to turn nonrechargeable batteries into rechargeable batteries—not just zinc batteries but also for other electro-chemistries, such as Lithium-oxygen,” said Meng, who directs the Sustainable Power and Energy Center at the UC San Diego Jacobs School of Engineering.

Rajan Kumar, a co-first author on this Advanced Energy Materials paper, is a nanoengineering Ph.D. student at the Jacobs School of Engineering. Kumar and nanoengineering professor Wang are leading a team focused on commercializing aspects of this work. The team is one of five to be selected to join a new technology accelerator at UC San Diego. The technology accelerator is run by the UC San Diego Institute for the Global Entrepreneur, which is a collaboration between the Jacobs School of Engineering and Rady School of Management.

The research was sponsored by the Advanced Research Projects Agency-Energy (DE-AR0000535) and the National Science Foundation Graduate Research Fellowship. The work was performed in part at the San Diego Nanotechnology Infrastructure (SDNI), a member of the National Nanotechnology Coordinated Infrastructure, which is supported by the National Science Foundation.

New Nanodiamond Coatings Offer Improved Abrasive Wear Properties

Nanodiamond material specialist Carbodeon (Vantaa, Finland) has worked with metal finishing specialist CCT Plating of Germany to develop a new electroless nickel, PTFE and nanodiamond composite coating.

Electroless nickel-PTFE (EN-PTFE) coatings provide excellent anti-adhesive and low friction properties but are traditionally soft and wear quickly in abrasive conditions. PTFE is polytetrafluoroethylene, or Teflon. By adding nanodiamond particles to the EN-PTFE coating, Carbodeon has been able to improve the abrasive wear resistance of these coatings without compromising the sliding or release properties.

Nanodiamond material consists of small, spherical diamond nanoparticles that are specially treated to make them disperse in coating liquids and carry a positive electrical charge on their surfaces. In the plating process, the diamond particles behave similarly to positively charged metal ions and, together with the nickel and the PTFE material, co-deposit onto the component.

Key performance characteristics are:

  • Excellent resistance to adhesive and abrasive wear with a Taber Wear Index 30% better than the equivalent EN-PTFE coatings.
  • Coatings can also be heat treated, bringing the Taber Wear Index down to 14 or lower.
  • Coefficient of friction matches existing EN-PTFE systems – less than 0.2 when measured against steel counterparts.
  • No increase in wear of the counterpart.
  • The process contains no hexavalent chromium and so is environmentally friendly.
  • Low diamond content makes these coatings affordable and easy to apply.
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New generation Carbodeon nanodiamond coatings can reduce sliding parts wear by as much as 85%.

Target applications include automotive components, including engine parts, chassis parts and body mechanisms; plastics forming molds, including complex structures, moving cores and slides; military applications requiring hard wearing and lubricant-free operations; and printing and textile production equipment and machinery.

“Customer applications have multiple requirements that are a challenge for existing coatings,” Carbodeon CTO Vesa Myllymaki said in prepared remarks. “Through a combination of these three materials – nickel, nanodiamond and PTFE – we produce coatings that are resistant to the multiple modes of wear and failure components and systems are subject to, while keeping the low friction and release properties of the NE-PTFE surface.”

The nanomaterial for the process can be obtained from Carbodeon for addition to existing electroless nickel-PTFE systems. Alternatively, job plating or turnkey solutions can be carried out by CCT Plating in Stuttgart, Germany.

Carbodeon has patented the nanodiamond material and the plating application.

Tobii Pro Expands Eye-Tracking Research into Virtual Reality

Tobii Pro (Stockholm, Sweden), developer of eye-tracking research solutions, announced its new Tobii Pro VR Integration for conducting eye-tracking research within immersive virtual reality (VR) environments. The research tool, based on the HTC Vive headset integrated with Tobii eye-tracking technology, comes with the Tobii Pro software development kit (SDK) for research applications. Researchers can accurately collect and record eye tracking data from a VR environment and gain deeper insights on human behavior.

Eye tracking research in immersive VR is transforming how studies can be conducted and opens up new possibilities in psychology, consumer behavior, and human performance, according to Tobii Pro. Through VR, researchers have complete control over a study environment, which allows them to run scenarios that previously would have been too costly, risky or difficult to conduct in real life.

“Combining eye tracking with VR is growing as a research methodology and our customers have started to demand this technology to be part of their toolkit for behavioral studies,” Tom Englund, Tobii Pro president, said in prepared remarks. “The Tobii Pro VR Integration is our first step in making eye tracking in immersive VR a reliable and effective research tool for a range of fields. It marks our first major expansion of VR-based research tools.”

Tobii Pro VR Integration is a retrofit of the HTC Vive business edition headset with integrated Tobii eye-tracking technology. It is capable of eye tracking all types of eyes, collecting binocular eye-tracking data at 120 Hz (images per second). The solution allows study participants to move naturally while wearing the headset without compromising the user experience or the output of the eye tracking data.

The solution comes with Tobii Pro’s SDK, which enables eye-tracking data collection for both live interactions and analysis. The Pro SDK supports millisecond synchronization and gives researchers the freedom to build analysis applications customized to their research on either Matlab, Python, C, or .Net compatible with Unity programming software tools. For more information or to receive updates, please see http://bit.ly/2rwjC1m.

Tech Front is edited by Senior Editor Patrick Waurzyniak.

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