Chemistry team develops gel electrolyte that shows promise for safer, higher-density batteries

Researchers in Virginia Tech’s College of Science have developed a prototype polymer-ion gel that could solve two of the battery industry’s most difficult problems: risk of fire and limited charge storage capacity.

Two years ago, Department of Chemistry doctoral students Ying Wang, from Anhui province, China, and Ying Chen, now of Richland, Washington, working with Associate Professor Lou Madsen, created a gel material that incorporates the toughness of a Kevlar-like polymer – similar to that used in bulletproof vests ‒ with an ionic liquid, a conductive liquid salt.

Early work on the new gel –which conducts ions quickly and safely while remaining thermally stable – recently was published in the high impact journal Advanced Materials.

Essentially, the prototype gel is an efficient ion conductor without compromising stability under high heat or mechanical stress, a compromise that has an abiding presence in today’s commercial batteries. This gel should allow for the use of electrodes such as lithium metal, which can boost battery energy density two to three times higher than the best commercial batteries now available, said Madsen.

“All of the properties that experts say are needed to build such high capacity and safe batteries appear to exist in this new material,” added Madsen, who joined the Department of Chemistry in 2006.

While rigorous testing is still needed, if brought to market, batteries using this new gel material could revolutionize the estimated $48 billion industry, touching scores of everyday technologies – from cell phones, cars, and computers, to hearing aids and remote medical devices.

For years researchers around the globe have been trying to build compact, light, powerful batteries that can withstand the heat of charging and discharging, but not burn up or short out as seen in recent news reports involving so-called Hoverboards that are powered by lithium batteries. Tesla, LG, 3M, BASF, GM, Apple, and Toyota are all working to build batteries that hold more charge and will not hinder users with excess weight or size, or more seriously, dangerous failure.

Electric cars ‒ seen as the future of transportation to reduce oil reliance – have thus far been hampered by limitations involving batteries, including size, weight, and mileage range. Even top of the line models are restricted to under 200-mile trips before requiring a recharge.

With the look and feel of clear licorice, the pliable gel was created inside a small, thin test tube by Wang and Chen as part of an experiment to create a new gel by mixing two materials in Madsen’s lab. The first sample quickly hardened, requiring the students to break the glass tube to extract the material. An electrical test of the substance showed low resistance – which translates to quick charging capability.

“This kind of ion gel, with the complementary features of high ion mobility, excellent thermal stability, and mechanical integrity, has potential to become a next-generation electrolyte and replace the batteries we have currently,” said Chen, who graduated with her Ph.D. in chemistry in December 2015 and is now a researcher at Pacific Northwest National Laboratory. “It may have a great impact on the battery industry and all of our lives.”

Madsen said batteries are now built with what amounts to governors. Batteries can now only charge/discharge to a ceiling of 120 degrees Fahrenheit, lest they become overheated, creating a fire hazard. The gel developed by Wang, Chen, and Madsen has withstood tests of more than 570 degrees Fahrenheit.

“It takes a huge volume of new ideas in different fields to make a breakthrough,” said Madsen. “We feel we have made such a breakthrough by doing interdisciplinary research that combines high performance polymers, ionic liquids, and detailed analysis of the ion motions. This area involves chemistry, polymer science, physics, engineering, and materials science. Our lab incorporates ideas from all these areas.”

“However, building a long-lasting and safe lithium battery is challenging because the desired material parameters for the best performing battery must all be balanced with cost and durability,” added Madsen. Several years of testing are ahead as the gel properties are understood and perfected, and then packaged into lab-testable batteries. To do this, Madsen is working globally with Delft University of Technology in The Netherlands on the polymer chemistry side, and Deakin University in Australia on the battery engineering side, as well as working with faculty from Virginia Tech’s College of Engineering.

Madsen is also making inquiries to battery development and start-up companies to accelerate adoption of the gels into commercial batteries. 

“From working on the gel, I feel really excited about exploring the formation process of the gel electrolyte as well as developing the comprehensive properties required for next-generation batteries, such as lithium metal batteries. I am very enthusiastic to continue discovering advanced electrolyte materials in the future,” said Wang, who is set to graduate this summer with a doctoral degree in macromolecular science and engineering.

Conventional lithium battery power is not the only potential use for the gel, according to the team. Other types of futuristic batteries – lithium-sulfur, lithium-air, sodium, zinc, magnesium – should also work with this electrolyte gel. The team also envisions this same gel material being tailored for many purposes, including water desalination, fuel cells, as well as photo/optical sensors. Another potential use: the gel could be adapted as an artificial muscle actuator in robotics, machinery, or human prosthetics.

Project work has been funded by a $400,000 National Science Foundation grant Madsen received in 2014 focusing on ionic polymer membranes. Assistance also has come from Virginia Tech’s Macromolecules and Interfaces Institute, part of the university’s Institute for Critical Technology and Applied Sciences.