A superionic polymer developed by US scientists could potentially help overcome of the biggest hurdles in solid-state batteries and make them safer, more efficient and more practical.

The innovative solution, engineered by researchers at the Department of Energy’s Oak Ridge National Laboratory (ORNL), tackles slow ion movement, the restricted, sluggish transport of ions within the electrolyte.

For the project, the scientists carefully controlled the chemical composition of a lithium salt-based polymer and designed a novel material that enables superfast transport of ions in batteries ad other energy storage technologies.

Catalin Gainaru, an R&D scientist at ORNL, said polymer electrolytes offer clear advantages over liquids. “Achieving fast ion transport has always been a major challenge of polymer electrolytes, but our recent research demonstrates that this may no longer be the case,” Gainaru added.

Solving ion transport

Batteries consist of two electrodes, a cathode and an anode, which are separated by an electrolyte, where ions move back and forth during charge cycles. However, while traditional batteries use liquid or gel electrolytes rising demand is pushing solid-state batteries with solid electrolytes.

Some solid-state batteries use ceramic electrolytes known as superionic ceramics, as they transport ions very effectively. Yet, they are brittle, difficult to manufacture and often struggle to maintain good contact with battery electrodes.

Meanwhile, polymers are flexible and easier to process but struggle from poor ion transport. Now the team showed that a polymeric material can reach a superionic state, in which ions can move up to 10 billion times faster than their surroundings.

“The ORNL polymer electrolyte contains polar segments that favor the inclusion of lithium salts and strongly enhance the mobility of ions,” Tomonori Saito, PhD, a distinguished researcher at ORNL said.

The researchers tuned the structure of the polymer by adding precise amounts of molecular groups, zwitterions. This enabled the ions to form pockets. Zwitterions carry both positive and negative charges. This increases local polarity but leaves the molecule neutral.

Creating better batteries

Once incorporated into the polymer backbone in the right proportion, zwitterions encourage ions to cluster into small pockets. As more of these pockets form, they begin to connect into continuous, channel-like pathways. The result is a network that allows ions to hop efficiently through the material with minimal resistance.

The researchers identified an optimal configuration when roughly 80 percent of the polymer units were functionalized, thus enabling the formation of stable ion-conducting channels.

In this optimized state, ions can move orders of magnitude faster relative to their surroundings. This significantly improves the material’s conductivity.

The team is planning to expand the work by studying the mechanisms behind the polymer’s superionic behavior. They reportedly aim to watch and understand ion interactions at the molecular level with supercomputing, AI-driven autonomous chemistry and neutron scattering at the Spallation Neutron Source.

“It’s hard to predict all the technologies that could leverage this discovery,” Saito concluded in a press release. “Anything that needs an impermeable barrier layer, but let ions move freely across it, is a potential application.”

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