Sodium-ion batteries promise potential

The world's transition away from fossil fuels to sustainable green energy sources is rapidly increasing the demand for economical storage methods that has thus far centered on lithium-ion batteries. The limited availability in the West of lithium and other critical metals, such as cobalt and rare earth elements, raises significant concern about the sustainability of the lithium-ion technology.

One potential alternative may be the sodium-ion battery.

According to the European Commission's Critical Raw Materials Act, the demand for critical raw battery materials is expected to increase exponentially as European Union countries transition to renewable energy systems and electric vehicles. The green transition will also require more local production of batteries, other new fossil-free technologies, and a steady supply of raw materials needed to build this clean energy future. At the same time, such production carries a high risk of supply disruptions, due to the limited number of sources for raw materials.

Researchers around the world are racing to develop affordable options to replace the potentially costly lithium-based battery.

At Chalmers University of Technology in Gothenburg, Sweden, a research team has demonstrated that sodium-ion batteries have a climate impact that is equal to their lithium-ion counterparts without the risk of running out of raw materials, which are essentially table salt and forest biomass.

"The materials we use in the batteries of the future will be important in order to be able to switch to renewable energy and a fossil-free vehicle fleet," said Rickard Arvidsson, associate professor of environmental systems analysis at Chalmers.

Abundant sodium for batteries

The development of new battery technologies is moving fast in the quest for the next generation of sustainable energy storage – which should preferably have a long lifetime, have a high energy density and be easy to produce.

The research team at Chalmers chose to look at sodium-ion batteries, which contain sodium, an abundant mineral found in seawater.

In a recent study, the scientists carried out a life-cycle assessment of the batteries in which they examined their total environmental and resource impact during raw material extraction and manufacturing.

The article, "Prospective life-cycle assessment of sodium-ion batteries made from abundant elements," was published Nov. 13, 2023, in the Journal of Industrial Ecology.

"We came to the conclusion that sodium-ion batteries are much better than lithium-ion batteries in terms of impact on mineral resource scarcity, and equivalent in terms of climate impact. Depending on which scenario you look at, they end up at between 60 and just over 100 kilograms of carbon dioxide equivalents per kilowatt hour theoretical electricity storage capacity, which is lower than previously reported for this type of sodium-ion battery. It's clearly a promising technology," Arvidsson said.

The researchers also identified some measures with the potential to further reduce climate impact, such as developing an environmentally better electrolyte, as it accounted for a large part of the battery's total impact.

Today's sodium-ion batteries are already expected to be used for stationary energy storage in the electricity grid, and with continued development, they will probably also be used in future EVs.

"Energy storage is a prerequisite for the expansion of wind and solar power. Given that the storage is done predominantly with batteries, the question is what those batteries will be made from? Increased demand for lithium and cobalt could be an obstacle to this development," said Arvidsson.

The major advantage of the technology is that the materials in the sodium-ion batteries are abundant and can be found all over the world. One electrode in the batteries-the cathode-has sodium ions as a charge carrier, and the other electrode-the anode-consists of hard carbon, which in one of the examples the Chalmers researchers have investigated can be produced from biomass from the forest industry.

In terms of production processes and geopolitics, sodium-ion batteries are also an alternative that can accelerate the transition to a fossil-free society.

"Batteries based on abundant raw materials could reduce geopolitical risks and dependencies on specific regions, both for battery manufacturers and countries," said Arvidsson.

"Lithium-ion batteries are becoming a dominant technology in the world, and they are better for the climate than fossil-based technology is, especially when it comes to transport. But lithium poses a bottleneck. You can't produce lithium-based batteries at the same rate as you want to produce electric cars, and the deposits risk being depleted in the long term," the Chalmers professor added.

In addition, critical battery materials, such as lithium and cobalt, are largely mined in just a few places in the world, posing a risk to the supply.

Sodium-ion batteries offer promise

The study is a prospective life-cycle assessment of two different sodium-ion battery cells where the environmental and resource impact is calculated from cradle to gate, i.e., from raw material extraction to the manufacture of a battery cell. The functional unit of the study is 1 kWh theoretical electricity storage capacity at the cell level. Both types of battery cells are mainly based on abundant raw materials.

The anode is made up of hard carbon from either bio-based lignin or fossil raw materials, and the cathode is made up of so-called "Prussian white" (consisting of sodium, iron, carbon, and nitrogen). The electrolyte contains sodium salt. The production is modeled to correspond to a future, large-scale production. For example, the actual production of the battery cell is based on today's large-scale production of lithium-ion batteries in gigafactories.

Two different electricity mixes were tested, as well as two different types of so-called allocation methods-that is, allocation of resources and emissions. One where the climate and resource impact is distributed between co-products based on mass, and one method where all impact is allocated to the main product – the sodium-ion battery and its components and raw materials.

Most sodium-ion batteries today contain a liquid electrolyte, which has a fundamental flammability risk. In contrast, sodium super ionic conductor (NASICON) materials are non-flammable solid-state electrolytes with high ionic conductivity and superior chemical and electrochemical stability.

Researchers at the University of Maryland's A. James Clark School of Engineering, recently reported developing a NASICON-based solid-state sodium battery architecture that outperforms current sodium-ion batteries in their ability to use sodium metal as the anode for higher energy density, cycle it at record high rates, and all with a more stable ceramic electrolyte that is not flammable like current liquid electrolytes.

According to Eric Wachsman, distinguished university professor and director of the Maryland Energy Innovation Institute notes, "Sodium opens the opportunity for more sustainable and lower cost energy storage while solid-state sodium-metal technology provides the opportunity for higher energy density batteries. However, until now no one has been able to achieve the high room temperature solid-state sodium-metal cycling rates we have achieved here."

The unique 3D electrolyte architecture was published Dec. 13 in Energy & Environmental Science and provides the promise of high-energy density and commercially viable solid-state sodium batteries.

The successful demonstration of both stable sodium cycling at high current densities and full cell cycling with thin 3D structured ion-conducting NASICON solid-electrolytes are a significant advancement towards sustainable and more economical energy storage technology.