A major challenge with solid-state batteries is increasing the diffusivity of Li-ions in the solid-state electrolyte, which is typically slower than in the liquid organic electrolytes now used in lithium-ion (Li-ion) batteries. Researchers have enhanced the mobility of Li-ions in solid-state batteries using the paddlewheel effect, which is the coordinated motion of atoms.
Solid-state batteries, using solid electrolytes in place of the usual liquid organic electrolytes, have emerged as promising replacements for today’s Li-ion batteries. They offer the potential of safer and longer-lasting batteries that can deliver higher energy density that is important to a variety of electrochemical energy storage applications such as vehicles, robots, and drones.
An unwanted chemical reaction called the thermal runaway reaction has led to fires and explosions involving today’s Li-ion batteries, which continue to burn until they run out of fuel. Because of these hazards, researchers seek to eliminate the internal liquid organic electrolyte by replacing it with a solid.
The researchers addressed a phenomenon that dramatically speeds up ion diffusion: the rotational motion of normally static negative ions (anions) in the solid-state electrolyte framework that help drive the motion of the Li+ positive ions (cations). The anion building blocks that comprise the solid framework are not rigid but undergo rotational motion. The anion dynamics can be turned on even at room temperature by tuning the framework and the anion dynamics are strongly coupled to cation diffusion by the paddlewheel effect. This is somewhat similar to the transport of people through a multi-person revolving door.
While new solid electrolytes are still in the developmental stage, the advances are encouraging. A solid-state electrolyte enabling fast Li+ cation motion could be a drop-in replacement for liquid organic electrolytes and immediately rid batteries of the thermal runaway reaction that causes fire in today’s Li-ion batteries.