Photo of Prof. Thomas H. Epps.
At UD, Prof. Thomas H. Epps, III and his team have patented an idea to improve lithium battery performance.

Imagine a world where cell phones and laptops can be charged in a matter of minutes instead of hours, rolled up and stored in your pocket, or dropped without sustaining any damage. It is possible, but the materials are not there yet. It would take more conductive, flexible and lighter-weight batteries and they would need to be more impact-resistant and safer. In May, an e-cigarette exploded in Florida and killed a man. Evidence reportedly suggests that this accident may have been due to battery-related issues, according to the U.S. Food and Drug Administration. Similar problems have plagued devices like the Samsung Galaxy Note 7 and auxiliary power units of the Boeing Dreamliner.

One way to overcome the challenge of improving both performance and safety in lithium-ion batteries is to improve the battery membranes and the associated electrolytes that are designed to shuttle the lithium ions, which offset the electrical charge associated with charging and discharging the battery.

University of Delaware (Newark, DE) researchers have patented an idea to improve battery performance by introducing tapers into the polymer membrane electrolytes, which allow the lithium ions inside the battery to travel back and forth faster. By chemically connecting two or more polymer chains with different properties, engineers can create block polymers that capitalize on the salient features from both materials. For example, polystyrene in a Styrofoam cup is relatively hard and brittle, while polyisoprene (tapped from a rubber tree) is viscous and molasses-like. When those two polymers are linked chemically, engineers can create materials for everyday items like car tires and rubber bands — materials that hold their shape but are impact resistant and stretchable. The research team realized they could tune the nanoscale structure of these polymers to imbue materials with certain mechanical, thermal and conductivity properties.

One of the benefits of block polymers is that they allow scientists to combine two or more components that are typically chemically incompatible. This same benefit, however, can present challenges for processing the materials. The group determined that tapering the region where the two distinct polymer chains connect can promote mixing between highly incompatible materials in a way that makes processing and fabrication faster and cheaper by requiring either less energy or less solvent in the manufacturing process. Manipulating the taper also allowed the researchers to control the nanoscale structures that can be formed by the block polymers. They created nanoscale networks that make the battery materials more conductive, allowing ions to move at higher speeds, thereby making the polymer more efficient.

In laboratory experiments, the team has shown that introducing a tapered region between polymer electrolyte chains increased the overall ionic conductivity over a range of temperatures. At room temperature, for example, the tapered materials are twice as conductive as their non-tapered counterparts. The taper also improves the material’s ability to be processed. Previous methods for increasing conductivity have either made the polymer harder to process or used greater amounts of chemical solvent, which makes the material more flammable and less environmentally friendly.

These polymers are also applicable to other rechargeable systems, such as sodium-ion and potassium-ion batteries. As technology advances, the team expects the next five to 10 years will usher in a plethora of devices that can flex and roll, such as cell phones and computers. The only way this works is if all of the components are flexible, including the battery and power units, not just the case, screen, or buttons. This aspect is where block polymers become really ideal because — like a rubber band that remembers its shape despite stretching, bending and other manipulation — with these “designer polymers”, you can make the internal components more impact resistant and shock absorbing, which will improve the phone’s lifespan.

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