Manufacturing solid-state batteries with isostatic pressing

Battery researchers at the Department of Energy’s Oak Ridge National Laboratory are recommending that the solid-state battery industry focus on a technique known as isostatic pressing as it looks to commercialise next-generation batteries. Commercial-scale production of solid-state batteries is a goal for electric vehicle manufacturers because these batteries have the potential to charge faster, last longer and operate more safely than the lithium-ion batteries currently on the market.

In a focus review paper for ACS Energy Letters, ORNL researchers recommended attention be given to the isostatic pressing approach. This process uses fluids and gases like water, oil or argon inside a machine to apply consistent pressure across a battery component, creating a highly uniform material. With the help of an industry partner that produces this pressing equipment, ORNL researchers found that isostatic pressing could make battery production easier and faster while creating better conditions for energy flow.

When a battery charges or discharges, ions move through an electrolyte between its positive and negative poles, which are made of thin layers of metal. In Li-ion batteries, the electrolyte is a liquid through which ions travel easily. Unfortunately, this liquid can also spill or ignite if the separation between battery layers is compromised. ORNL’s Marm Dixit and colleagues found that isostatic pressing can create thin layers of solid, uniform electrolyte, maintaining a high level of contact between the layers for a smooth ion movement. The method works with a variety of battery compositions at different temperatures and pressures.

Isostatic pressing was also found to be successful at low temperatures and with soft electrolyte materials, which are easier to process and which have favourable crystal structures for ion movement. Previously isostatic pressing of batteries had been done mostly at extremes: very high temperatures or at room temperature, but not in between. Dixit said that all these materials have their unique advantages that researchers would like to exploit. “That’s why it’s important that you can do isostatic pressing at anywhere from room temperature to several thousand degrees Fahrenheit: it means you can use anything from polymers to oxides, the whole range of materials,” Dixit said.

Image caption: Isostatic pressing applies consistent heat and pressure from all directions across a battery component within a chamber. Image credit: Andy Sproles/ORNL, U.S. Dept. of Energy.

This versatility is key to a consistent manufacturing process for the variety of solid-state battery designs and materials being developed. Isostatic pressing could also be relatively easy to scale up commercially — a finding that has garnered attention as companies race to supply solid-state batteries to car manufacturers. Ilias Belharouak, a corporate fellow at ORNL, said solid-state battery technology needs to be perfected for large-scale manufacturing. “Make no mistake, all solid-state batteries are on a journey for the long haul. But the isostatic pressing technology, if scalable, would provide a way to assemble the battery layers without impractical external pressures,” Belharouak said.

Isostatic pressing has been used for decades in fusion bonding and joining materials. Recently it has been a tool for eliminating voids and anomalies in 3D-printed parts. However, its testing for battery applications has been limited. ORNL researchers believe isostatic pressing may also allow the manufacturing of the three battery layers as a single, dense system rather than creating them separately before joining them.

In the ACS Energy Letters paper, the researchers stressed the importance of pursuing solid-state batteries that can be scaled up for manufacturing, as it could “leapfrog present-day technology into the next decades by enabling energy-dense solid-state batteries to meet the burgeoning demands of portable electronics, grid storage and electric vehicles. “Isostatic pressing can alter texture — the question is whether it can actively control it. The ability to manipulate crystal texture would have significant benefits for solid-state batteries,” Dixit said.

Top image credit: iStock.com/PhonlamaiPhoto