In search of safer lithium-ion batteries, a team of engineers at the University of Illinois (UI) has proposed a polymer-based solid electrolyte that not only repairs itself, but can also be recycled without the need for high temperatures. By using special cross-linked polymers, new electrolytes become harder under heating rather than breaking down.
Lithium-ion batteries are one of the best examples of the success 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-discharge cycle, they easily form needle-shaped or branch-shaped lithium figs and grow in the structure of the battery. This can lead to shorter service life or electrical short circuits. In extreme cases, it can also damage the battery itself, causing fires and explosions.
Part of the reason for these explosive failures is that lithium-ion batteries use liquid electrolytes – if the battery is severely damaged, it reacts with the electrodes. Brian Jing, a graduate student in materials science and engineering at the University of Illinois, says solid-state polymers or ceramic electrolytes are seen as alternatives, but they tend to melt at high temperatures inside the batteries. One way to solve this problem is to produce rubber-like lithium conductors using cross-linked polymer strands. It has a longer life than a harder solid electrolyte, but it cannot be self-healing and is difficult to recycle.
The UI team developed a way to make cross-linking keys so that they produce an exchange reaction and swap polymer chains between them. This means that the polymer hardens when heated and repairs itself, resulting in less growth of branch-like lithium figs. In addition, polymers can be decomposed without the need for strong acids or high temperatures. Instead, it dissolves in water at room temperature. However, the technology is not yet practical.
“I think it provides an interesting testing platform for others,” said Christopher Evans, the team leader. We use very special chemical properties and very special dynamic bonds in polymers, but we think the platform can be reconfigured to be used with many other chemical properties to regulate conductivity and mechanical properties. “
The study was published in the Journal of the American Chemical Society.