By starting with liquid electrolytes and then transforming them into solid polymers inside the electrochemical cell, the researchers take advantage of both liquid and solid properties to overcome key limitations in current battery designs.
"Imagine a glass full of ice cubes: Some of the ice will contact the glass, but there are gaps," said Qing Zhao, a postdoctoral researcher and lead author on the study. "But if you fill the glass with water and freeze it, the interfaces will be fully coated, and you establish a strong connection between the solid surface of the glass and its liquid contents. This same general concept in a battery facilitates high rates of ion transfer across the solid surfaces of a battery electrode to an electrolyte without needing a combustible liquid to operate."
The key insight is the introduction of special molecules capable of initiating polymerisation inside the electrochemical cell, without compromising other functions of the cell. If the electrolyte is a cyclic ether, the initiator can be designed to rip open the ring, producing reactive monomer strands that bond together to create long chain-like molecules with essentially the same chemistry as the ether. This now-solid polymer retains the tight connections at the metal interfaces, much like the ice inside a glass.
Beyond their relevance for improving battery safety, solid-state electrolytes are also beneficial for enabling next-generation batteries that utilise metals, including lithium and aluminum, as anodes for achieving far more energy storage than is possible in today's state-of-the-art battery technology. In this context, the solid-state electrolyte prevents the metal from forming dendrites, a phenomenon that can short circuit a battery and lead to overheating and failure.
Despite the perceived advantages of solid-state batteries, industry attempts to produce them at a large scale have encountered setbacks. Manufacturing costs are high, and the poor interfacial properties of previous designs present significant technical hurdles. A solid-state system also circumvents the need for battery cooling by providing stability to thermal changes.
This new in-situ strategy for creating solid polymer electrolytes is particularly exciting, according to senior author Professor Lynden Archer, because it shows promise for extending cycle life and recharging capabilities of high-energy-density rechargeable metal batteries.
