Argonne scientists discover how to boost solid-state battery energy density and longevity

Imagine a battery that stores more power, lasts longer, and remains safe even under stress. Researchers at the U.S. Department of Energy’s (DOE) Argonne National Laboratory and the University of Chicago have discovered how to boost the energy density and cycle life of the power cells that form the core of all-solid-state batteries. This next-generation battery technology holds promise for transforming transportation.

The team’s approach added hundreds of charge-discharge cycles to the total life of the batteries while also significantly increasing the energy density — two essential steps on the road to commercial applications.

As the name implies, all-solid-state batteries consist of solid components. Unlike traditional lithium-ion batteries, they don’t contain liquid or gel materials. But, like all batteries, they contain a cathode (positive electrode) and an anode (negative electrode), which are separated by an electrolyte (the material through which ions flow).

“It’s a very simple process but with big science happening inside.” — Guiliang Xu, Argonne chemist

All-solid-state batteries offer several advantages over traditional batteries. These include improved safety, lighter weight, longer lifespans and higher energy density, which is the amount of energy a battery can store and provide relative to its mass.

However, developing all-solid-state batteries has been challenging due to poor connections between the solid electrolyte and the cathode material. This poor connection — called the interface — can hold back the flow of ions and reduce their performance.

“Addressing interfaces in solid-state batteries is the key to enabling this promising system,” said Khalil Amine, an Argonne Distinguished Fellow and professor at the University of Chicago.

Amine and Argonne chemist Guiliang Xu led a team focused on improving the performance of all-solid-state lithium-sulfur batteries and batteries with similar chemistries. They found that by rapidly mixing the solid electrolyte, cathode and other battery materials, they could trigger a process known as ​“halide segregation.” During halide segregation, lithium atoms that are bound to chlorine, bromine or a similar element move to the interface.

The researchers discovered that halide-segregated batteries performed substantially better and lasted longer than untreated batteries. They also outperformed all-solid-state batteries treated with other types of performance-boosting strategies, such as adding catalysts, dopants or surface coatings.

“This work represents a big advancement for this type of battery system, in particular for how we’ve markedly improved energy density, cycle life and cost by using earth-abundant sulfur,” Xu said.

In some cases, the energy density of halide-segregated batteries even surpassed the theoretical limits for this type of battery. Additionally, the batteries maintained full performance even after 100 charge-discharge cycles. After 450 cycles, performance stayed above 80%.

“This is a remarkable extension of performance in all-solid-state lithium-sulfur batteries,” Xu said.

The researchers observed this improved performance at room temperature, with no additional heating needed, which could make this approach easier to adopt for commercial applications.

The team believes they achieved halide segregation in their battery experiments because the high-speed mixing method they used — 2,000 revolutions per minute for five hours — generated heat and shear forces within the battery components. This induced a ​“mechanochemical reaction” that triggered halide segregation and improved lithium-ion movement during battery use.

“It’s a very simple process but with big science happening inside,” Xu said.

The scientists found the process also boosts the performance of other types of all-solid-state batteries. The team originally focused on all-solid-state lithium-sulfur batteries because their cathodes contain sulfur, a relatively abundant material. But they also tested batteries with cathodes made from selenium and tellurium, which are rarer elements that react similarly to sulfur, and saw similar halide segregation and better performance after high-speed mixing.

This suggests that high-speed mixing could solve interface problems in other all-solid-state batteries, elevating multiple battery chemistries on the journey to commercial use.

To observe halide segregation at the atomic level, the team used multiple advanced techniques, including cryogenic transmission electron microscopy at the Center for Nanoscale Materials and X-ray absorption spectra mapping at the Advanced Photon Source, two DOE Office of Science user facilities at Argonne.

Additional experiments were performed at the National Synchrotron Light Source II at Brookhaven National Laboratory and the Advanced Light Source at Lawrence Berkeley National Laboratory, also DOE Office of Science user facilities.

The team published its findings in Science. Co-lead authors on the paper are former Argonne postdoctoral researcher Jieun Lee, now at the Korea Institute of Science and Technology, and Argonne visiting graduate researcher Shiyuan Zhou. Additional authors are Victoria Ferrari, Chen Zhao, Angela Sun, Yuzi Liu, Chengjun Sun and Wenqian Xu at Argonne; Sarah Nicholas, Dominik Wierzbicki, Jianming Bai and Yonghua Du at Brookhaven; and Dilworth Parkinson of Berkeley Lab.

The research was funded by the DOE’s Transportation Technologies Office.