In search of safer lithium-ion batteries, a team of engineers at the University of Illinois (UI) proposed a polymer-based solid electrolyte that is not only self-healing but also recyclable without the need for high temperatures. By using special cross-linked polymers, the new electrolyte becomes harder when heated, rather than breaking down.
Lithium-ion batteries are one of the successful examples of modern electrical technology. Without them, devices from smartphones to electric cars would be impractical-but they are far from perfect. When they go through a regular charge and discharge cycle, it is easy to form needle-like or dendritic lithium dendrites and grow in the structure of the battery. This can lead to shortened service life or electrical shorts. In extreme cases, it can also damage the battery itself, causing fire and explosion.
Part of the reason for these explosive failures is that the lithium-ion battery uses a liquid electrolyte—if the battery is severely damaged, it can chemically react with the electrodes. Brian Jing, a graduate student in materials science and engineering at the University of Illinois, said that solid polymers or ceramic electrolytes have been seen as alternatives, but they tend to melt at the high temperatures generated inside the battery. One way to solve this problem is to produce rubber-like lithium conductors using cross-linked polymer strands. It has a longer service life than the harder solid electrolyte, but it cannot repair itself and is difficult to recycle.
The UI team developed a way to make cross-linking bonds so that they produce an exchange reaction and exchange polymer chains between them. This means that the polymer will harden when heated and will heal itself, resulting in reduced dendritic lithium dendrite growth. In addition, no strong acid or high temperature is required to decompose the polymer. Instead, it dissolves in water at room temperature. However, this technology is not yet practical.
Team leader Christopher Evans said: “I think this work provides an interesting testing platform for others. We use very special chemistry and very special dynamic bonds in polymers, but we think we can use this platform Reconfigured for use with many other chemistry to adjust conductivity and mechanical properties.