We're part of an international team of scientists behind the creation of a new family of organic materials that can conduct ions - atoms or molecules with a net electrical charge - in solids.
The discovery could lead to new classes of flexible and safe solid electrolytes - salt or minerals that carry an electrical charge.
The resulting solid electrolytes have potential applications in batteries, sensors, and electrochromic devices like smart windows, low power displays, and reflective blinds.
Organic solids are generally advantageous over inorganic materials because of their lightweight and flexible physical properties, and the potential to source them renewably.
Ionic conductivity
The scientific team involved Professor Chris Groves, in our Department of Engineering.
The research was led by Professor Paul McGonigal, now at the University of Oxford, while working in our Department of Chemistry with former Durham PhD students Juliet Barclay and Jack Williamson.
Normally, when liquids solidify, their molecules become locked in place, making it much harder for ions to move and leading to a steep decrease in ionic conductivity.
The team synthesised a new class of materials, called state-independent electrolytes (SIEs), that break that rule.
They achieved this by designing a new class of organic molecular ions with special physical and electronic properties.
Flat, disc-shaped centre
Each molecule has a flat, disc-shaped centre surrounded by long flexible side chains - like a wheel with soft bristles.
Positive charge is spread out evenly across the molecule by the movement of electrons, preventing it from tightly binding with its negatively charged partner.
This allows the negative ions to move freely, flowing through the side chains.
Then, in the solid state, these organic ions naturally stack on top of each other, forming long rigid columns surrounded by many flexible arms: much like static rollers in a car wash.
Despite forming an ordered structure, the flexible side chains still create enough space for the negative ions to continue moving as freely as they would in a liquid.
The result is a dynamic ordered structure allowing negatively charged ions to move through just as easily in the solid state as in liquid form, with no sharp decrease in ionic conductivity.
