Lithium oxide sublimation opens doors for cheaper and quicker battery manufacturing

A common lithium salt has revealed new possibilities for manufacturing cheaper, longer-lasting battery materials.

The discovery centers on sublimation, a commonly known process whereby under the right conditions, a solid turns directly into a vapor. Sublimation is what creates the tail of a comet as it flies by the sun. As the comet’s icy shell heats up, the ice instantly becomes vapor, instead of first melting into liquid water.

Now, scientists at the U.S. Department of Energy’s Pacific Northwest National Laboratory have taken a page out of nature’s playbook. In a new finding published in Nature Energy, the PNNL-led team showed that vapor from lithium oxide (Li₂O) sublimation accelerates a chemical reaction that forms single crystals when mixed with nickel-rich precursors. Moreover, the sublimation happens at just one atmosphere of pressure, the everyday pressure felt at sea level. Single-crystal battery materials are thought to help batteries last longer.

“The discovery offers a potentially faster, more efficient, and cheaper way to scale up the manufacturing of nickel-rich lithium-ion batteries,” said Jie Xiao, co-author on the paper and a Battelle Fellow who holds a joint appointment with PNNL and the University of Washington. At UW, Xiao is the university’s Boeing Martin Professor in the Mechanical Engineering Department.

“The research shows us how materials science can be applied to simplify the manufacturing process,” Xiao continued.

The promise of nickel

Creating materials for batteries is a little like baking: Combine the right ingredients, apply heat, and produce something new. For batteries, researchers hunt for materials to make positive and negative electrodes of a battery (sometimes referred to as cathodes and anodes, respectively). Positive electrodes work by accepting ions and electrons, which creates the flow of electricity that powers devices like flashlights, laptops, cell phones, or even cars and data centers.

As demand for devices with rechargeable batteries grows, scientists are constantly looking for materials that can store more energy and last longer. Conventional lithium-ion batteries are limited by cost and how much energy they can hold, Xiao said. To reduce the cost, cheaper nickel and manganese are often mixed with cobalt into the battery material.

Recently, researchers including Xiao’s PNNL team have been studying how to cost-effectively incorporate even more nickel into battery cathodes. Nickel can store more energy than cobalt, so increasing the amount of nickel in a lithium-ion battery makes the materials more cost-effective. Nickel may also help reduce the cost of scaling up cathode manufacturing.

But despite its benefits, working with nickel still presents a challenge, Xiao said. Nickel-rich lithium cathode material tends to form as agglomerations known as “polycrystals,” like a cookie packed with chocolate chips. Boundaries between the crystals—like the boundary between the cookie and the chocolate chips—become weaker as the battery discharges and charges. Over time, these weaknesses lead to cracking, which degrades the battery and shortens its lifetime.

“You can imagine all those tiny particles are agglomerated together, and they get pushed and pulled as the battery charges and discharges,” Xiao said. “The movement can create cracks, which weakens the battery.”

In the past five years, Xiao and her colleagues have been searching for materials that form single-crystal structures, like a plain chocolate cookie. The chocolate is still there, but it’s evenly distributed through the cookie rather than packed in clumps.

“Single-crystal cathodes don’t have the vulnerabilities that arise from polycrystal structures,” Xiao said. “So, we hope single crystals will mitigate and eventually eliminate all the big challenges in nickel-rich cathode materials.”

The mystery of sublimation

Over the last few years, Xiao’s team has been exploring different lithium salts supplied by industry partner Albemarle Corporation. Mixing these salt ingredients, or precursors, with nickel-rich precursors produces cathode material. One of the most common production methods is to melt the lithium salt, which then reacts with the nickel-rich precursor. For this process, researchers have preferred lithium hydroxide (LiOH) because it has a low melting point.

In contrast, Li₂O has a high melting point at 1,438 degrees Celsius, so it’s rarely used for cathode material synthesis. But when experimenting with Li₂O in Xiao’s materials synthesis lab at PNNL, something surprising happened: when combining the nickel-rich precursor with Li₂O at temperatures around 900 degrees Celsius, single-crystal cathode material readily formed.

Xiao and her colleagues replicated the reaction over and over, trying to find the mechanism. Eventually, they turned to their industry partner Thermo Fisher Scientific, who studied the reaction under an instrument called a MicroReactor. With those observations and a newly designed experiment, the team was able to successfully reveal the sublimation phenomenon.

“We are excited to record the reaction between Li₂O and the precursor in the microscope,” said Libor Novák, the inventor of the MicroReactor at Thermo Fisher Scientific.

The new research confirms the mechanism is driven by Li₂O sublimation. In the baking scenario, it would be like combining the cookie dough with vaporized chocolate. When you cut the cookie in half, there are no chunks of chocolate, just a chocolate cookie with no distinct boundaries.

“The vapor can penetrate everywhere, right into the other precursors’ pores or surface and immediately react,” Xiao said. “Single crystals form much faster in the presence of those vapors.”

The team further applied the Li₂O sublimation phenomenon to directly convert spent polycrystals into single crystals simply through a mixing-and-heating process. The successful formation of new single crystals shows that Li₂O salt considerably simplifies the recycling process of spent or waste polycrystals. Especially for those scraps from the production line, they can be quickly “remade” into high-performance single crystals by this salt ingredient, Xiao said.

What’s more, the new single crystals, either from fresh precursors or from spent polycrystals, withstood 1,000 charge/discharge cycles—meaning they can remain stable for long periods of time.

Potential boon to manufacturing

With the time and energy savings, plus the high performance of Li₂O-derived single crystals, the discovery provides a new way to manufacture single crystals. However, the team has more work to do before any batteries can be produced, Xiao said. Because Li₂O is not broadly used for materials synthesis, the cost to use it commercially is currently too high. However, Xiao noted that Li₂O is easily produced by processing other lithium salts, such as LiOH.

With industry partners, Xiao and her team are now working to scale up the process with lower manufacturing costs. The team hopes to provide single crystals to their strategic partners in 2026.