ORNL’s thin film boosts battery safety, could provide 2x energy density for EVs

Researchers are accelerating the development of next-generation solid-state batteries by using a polymer to create a robust yet flexible thin film.

The work done by a team at Oak Ridge National Laboratory (ORNL), part of the Department of Energy, claims to advance the development of electric vehicle power enabled by flexible, durable sheets of solid-state electrolytes.

Thanks to the sheets, future solid-state batteries with electrodes with a higher energy density could be produced more massively.

According to researchers, keeping positive and negative electrodes apart would offer high-conduction pathways for ion flow and avert hazardous electrical shorts.

“The major motivation to develop solid-state electrolyte membranes that are 30 micrometers or thinner was to pack more energy into lithium-ion batteries so your electric vehicles, laptops and cell phones can run much longer before needing to recharge,” said Guang Yang, research and development associate at ORNL, in a statement .

Polymer Chain Strength

The new development enhanced an earlier ORNL innovation by modifying the polymer binder to work better with solid-state sulfide electrolytes. It is a component of continuing initiatives to create guidelines for choosing and handling materials.

This investigation aimed to find the “Goldilocks” spot—a film thickness ideal for sustaining both ion conduction and structural strength.

The conductivity of the plastic polymer used in current solid-state electrolytes, which conduct ions, is substantially lower compared to liquid electrolytes. Liquid electrolytes are occasionally added to polymer electrolytes to enhance performance.

Comparable to the liquid electrolyte now used in lithium-ion batteries, sulfide solid-state electrolyte possesses ionic conductivity. “It’s very appealing. The sulfide compounds create a conducting path that allows lithium to move back and forth during the charge/discharge process,” said Yang.

Researchers found that the molecular weight of polymer binders plays a key role in the durability of solid-state-electrolyte films. Films with low-molecular-weight binders featuring shorter polymer chains struggle to maintain contact with the electrolytic material due to insufficient strength.

Conversely, high-molecular-weight binders with longer polymer chains provide greater structural stability. Moreover, films with long-chain binders require less material to achieve effective ion conductivity.

Enhanced battery durability

The team aimed to reduce the amount of polymer binder used, as it does not conduct ions. The binder’s primary role is to hold the electrolyte particles within the film. While increasing the binder quantity can improve the film’s quality, it also reduces ion conduction. On the other hand, using less binder enhances ion conduction but negatively impacts film quality.

Scanning electron microscopy, energy-dispersive X-ray spectroscopy, and nanoindentation were used for detailed analysis, and synchrotron radiation measurements revealed particle morphology.

Advanced characterization techniques were essential for examining the intricate details of the sulfide solid-state electrolyte sheet, enabling the researchers to enhance the electrolyte’s ion conduction and stability.

According to researchers, the detailed analysis is crucial for developing more reliable and efficient solid-state batteries. The scientists are expanding their 7,000 square feet of ORNL lab space by establishing low-humidity areas dedicated to sulfide research, as these materials can contaminate others.

To address this challenge, the team requires specialized equipment, such as dedicated glove boxes, which ORNL provides eight of specifically for this work.

Next, the team plans to build a device capable of integrating the thin film into next-generation negative and positive electrodes, allowing them to test its performance under practical battery conditions. They will then collaborate with researchers from industry, academia, and government to further develop and test the thin film in various devices.

The details of the team’s research were published in the journal ACS Energy Letters .