University of Illinois at Urbana-Champaign engineers have developed a solid polymer-based electrolyte that can self-heal after damage. Plus the material can also be recycled without the use of harsh chemicals or high temperatures.

Images demonstrating the breaking and healing of dynamic network r = 0.085 on a rheometer plate heated at 140 ̊ C. Image Credit: University of Illinois at Urbana-Champaign. Click image for the largest view.

The new study, which could help manufacturers produce recyclable, self-healing commercial batteries, is published in the Journal of the American Chemical Society.

Lithium-ion batteries are notorious for developing internal electrical shorts that can ignite a battery’s liquid electrolytes, leading to explosions and fires.

The researchers explain that as lithium-ion batteries go through multiple cycles of charge and discharge, they develop tiny, branchlike structures of solid lithium called dendrites. These structures reduce battery life, cause hotspots and electrical shorts, and sometimes grow large enough to puncture the internal parts of the battery, causing explosive chemical reactions between the electrodes and electrolyte liquids.

There has been a push by chemists and engineers to replace the liquid electrolytes in lithium-ion batteries with solid materials such as ceramics or polymers. However, many of these materials are rigid and brittle resulting in poor electrolyte-to-electrode contact and reduced conductivity.

Brian Jing, a materials science and engineering graduate student and study co-author said, “Solid ion-conducting polymers are one option for developing nonliquid electrolytes. But the high-temperature conditions inside a battery can melt most polymers, again resulting in dendrites and failure.”

Past studies have produced solid electrolytes by using a network of polymer strands that are cross-linked to form a rubbery lithium conductor. This method delays the growth of dendrites; however, these materials are complex and cannot be recovered or healed after damage, Jing noted.

To address this issue, the researchers developed a network polymer electrolyte in which the cross-link point can undergo exchange reactions and swap polymer strands. In contrast to linear polymers, these networks actually get stiffer upon heating, which can potentially minimize the dendrite problem, the researchers said. Additionally, they can be easily broken down and resolidified into a networked structure after damage, making them recyclable, and they restore conductivity after being damaged because they are self-healing.

Jing described the results with, “This new network polymer also shows the remarkable property that both conductivity and stiffness increase with heating, which is not seen in conventional polymer electrolytes.”

Lead author Christopher Evans added, “Most polymers require strong acids and high temperatures to break down. Our material dissolves in water at room temperature, making it a very energy-efficient and environmentally friendly process.”

The team probed the conductivity of the new material and found its potential as an effective battery electrolyte to be promising, the researchers said, but acknowledge that more work is required before it could be used in batteries that are comparable to what is in use today.

Evans wound up saying, “I think this work presents an interesting platform for others to test. We used a very specific chemistry and a very specific dynamic bond in our polymer, but we think this platform can be reconfigured to be used with many other chemistries to tweak the conductivity and mechanical properties.”

The coming years are going to see, at a minimum, tremendous improvements in lithium ion batteries. This technology may well be an important step. There is also likely to be major gains in competitive battery chemistries to watch and perhaps see in consumer products. Things are going to change, and managing that cell phone, laptop and tablet battery charge is going to get a lot easier.


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