The batteries in your mobile phone and the ones powering electric vehicles (EVs) share a common feature: they use liquid electrolytes. These liquids, which contain lithium salt, act as highways, enabling lithium ions to flow between the battery’s positive and negative electrodes, thereby generating electricity.
But liquid electrolytes come with risks—they can leak or catch fire if overheated. Solid-state electrolytes (SSEs) are emerging as a safer, more efficient alternative, said Derrick Fam, Deputy Head of the Energy Materials Department at the A*STAR Institute of Materials Research and Engineering (A*STAR IMRE).
Polymer-based SSEs are easier to manufacture than oxide- and sulfide-based counterparts, but their low ionic conductivity, caused by crystal formation, limits their performance, explained Fam. Most polymer-based SSEs also need operating temperatures above 60°C to function effectively. These challenges prompted Fam and Ning DIng, a Senior Research Scientist in the department, to investigate ways to improve polymer-based SSEs, particularly for room-temperature use.
“If we can reduce the crystals being formed, it is then possible to increase the conductivity to practical levels and make low-cost polymer-based solid-state batteries (SSBs),” explained Fam.
Collaborating with researchers from Singapore Polytechnic; Dankook University, Korea; University of Chicago, US; and the A*STAR Institute of High Performance Computing (A*STAR IHPC), Fam’s team employed advanced tools such as inductively coupled plasma optical emission spectroscopy (ICP-OES) and Raman mapping to study the crystalline structure of PEO-LiTFSI, a solid-state electrolyte.
They observed that each lithium ion coordinates eight polymer coordinating functional groups, not six as widely reported. Once the Li-ion is coordinated or locked in an PEO(8)LiTFSI crystal, it renders the Li-ion unable to move, reducing the overall ion conductivity.
A PEO shell around growing crystals can slow the growth rate, enabling high ionic conductivity. “However, the main bottleneck towards the construction of a room-temperature solid-state battery is the need to slow down the speed of crystallisation of the solid polymer electrolyte, which is caused by the electrode particles,” commented Ding.
“Tackling the crystallisation in the cathode, the thickest battery layer, is key to achieving room-temperature performance,” said Fam. “Simply engineering the polymers for high ionic conductivity is not sufficient.”
Their findings could enable safer, more affordable batteries in EVs and portable devices. The team has already patented their innovative non-crystalline polymer electrolyte and is now in talks with HydroQuebec—a leader in solid electrolytes—to validate their findings.
The A*STAR-affiliated researchers contributing to this research are from the A*STAR Institute of Materials Research and Engineering (A*STAR IMRE) and the A*STAR Institute of High Performance Computing (A*STAR IHPC).
