Ballistic Ion Transport Discovery Paves the Way for Better All-Solid-State-Batteries
A team of researchers from the Lawrence Berkeley National Laboratory (LBNL) have laid the foundations in a study published in Energy & Environmental Science for safer, more energy-dense solid-state battery designs by identifying a class of glassy polymers with high ion-conductivity at room temperature.
Led by senior scientist and leader of the Applied Energy Materials Group Gao Liu, the LBNL team and collaborators from the University of California Berkeley and the University of Kentucky reported success with a unique electrode material called a mixed ionic-electronic conducting (MIEC) polymer. Unlike many polymers, MIEC allows the conduction of both ions and electrons that is necessary for battery charging.
Researchers have faced one key drawback to MIEC materials — lithium ion transport through these polymers remains sluggish except at high temperatures.
Liu’s team has now given MIEC polymer materials the engineering boost needed to overcome this obstacle via ballistic ion transport, which significantly improves ion movement through the electrode at room temperature.
“We have successfully demonstrated, for the first time, fast and long-range ion transport in a glassy polymer in this work. In this case, the ionic conductivity is decoupled with polymer segmental motion,” said Liu. “These new materials could be a game changer for solid state battery manufacturing.”
Ballistic ion transport allows ions to move quickly through a polymer with minimal resistance and scattering. The team achieved 10-100 times better conductivity with ballistic transport at room temperature than has been possible with a commonly used state-of-the-art polymeric ion conductor battery material, polyethylene oxide (PEO).
Since the 1970s, scientists have been searching for a workaround to low conductivity at room temperature. This is driven by the physical properties of polymers and the inefficient way that ions often move through them — frequently colliding with other molecules and being slowed by rigid polymer chain segments. As its name implies, ballistic transport instead sends ions through in a clear, straight path.
“Polymeric ion conductors can be easily processed for scalable battery production, however, they traditionally have low ionic conductivity at room temperature, preventing their commercial applications,” said Liu.
The LBNL team used several state-of-the-art tools to make their discovery, including soft X-ray absorption spectroscopy (sXAS) at the LBNL Advanced Light Source and four-dimensional scanning transmission electron microscopy (4D STEM).
Their work has major implications for the future of all-solid-state-batteries (ASSBs), which offer benefits like better safety, energy density, and lifespan.