New Polymer Materials Help Lithium Batteries Achieve Self-healing

- Jan 12, 2020-

Lithium-ion batteries are notorious for frequent internal short circuits. Internal short circuits can ignite the battery's liquid electrolyte, causing the battery to explode and cause a fire. Recently, engineers at the University of Illinois have developed a polymer-based solid electrolyte that can heal itself after damage, or it can be recovered without the use of harsh chemicals or high temperatures.

The new research can help manufacturers produce commercial batteries that are recyclable and self-healing. The study is published in the Journal of the American Chemical Society.

Researchers say that as lithium-ion batteries undergo multiple charge and discharge cycles, they form tiny dendritic solid lithium, called dendritic crystals. These structures shorten the battery life, cause hot spots and short circuits, and sometimes become large enough to pierce the internal components of the battery, resulting in an explosive chemical reaction between the electrode and the electrolyte.

Chemists and engineers have been pushing to replace liquid electrolytes in lithium-ion batteries with solid materials, such as ceramics or polymers. However, most of these materials are rigid and fragile, which can lead to poor contact between the electrolyte and the electrode and decrease in electrical conductivity.

BrianJing, co-author of the paper, said: "Solid ion-conducting polymers are an option for developing non-liquid electrolytes. However, the high temperature conditions inside the battery will melt most of the polymers, causing dendrites and failures again."

Past research has produced solid electrolytes using polymer chain networks that cross-link to form rubbery lithium conductors. Although this method delays the growth of dendritic crystals, these materials are complex and cannot be recovered or repaired after damage.

To solve this problem, researchers have developed a network polymer electrolyte in which the cross-linking points can undergo exchange reactions and exchange polymer chains. The researchers say that these networks actually harden when heated compared to linear polymers, minimizing dendrite problems. In addition, they are easily broken down and re-solidified into a mesh structure after damage, making them recyclable, and due to their self-healing properties, they can restore conductivity after damage.

"This new type of network polymer also shows excellent properties, that is, conductivity and stiffness increase with heating, which is not found in conventional polymer electrolytes," Jing said.

"Most polymers require strong acids and high temperatures to decompose. Our materials are soluble in water at room temperature and are very energy efficient and environmentally friendly," said Christopher Evans, professor of materials science and engineering and first author of the paper. Craft. "

The research team explored the electrical conductivity of this new material and discovered its potential as an effective battery electrolyte, but they acknowledged that it would take a certain amount of time to compete with batteries currently in use.

Evans said: "I think this work provides an interesting testing platform for others, we use a very special chemical substance and a very special dynamic bond in the polymer, but we think this platform Can be reconfigured for use with many other chemicals to adjust conductivity and mechanical properties. "