A novel sodium-sulphur battery has 4 times the capacity of lithium-ion batteries

The new sodium-sulfur batteries are also environmentally friendly, driving the clean energy mission forward at a low cost.
Jijo Malayil
Lithium ion electric charge graphic
Lithium ion electric battery charge

iStock / Black_Kira 

To realize the universal goal of net-zero emissions by 2050, the world is keenly looking at advancements in battery technology. Lower costs, higher capacity, and optimal utilization of scarce natural resources are expected to play a major role in taking the mission forward.

Helping to realize the goal, a group of researchers at the University of Sydney has come up with a sodium-sulfur battery with a significantly higher capacity than lithium-ion cells. The battery also costs considerably less to manufacture.

Their findings were published in Advanced Materials.

The need for alternatives

The team led by Dr. Shenlong Zhao from the University’s School of Chemical and Biomolecular Engineering made use of a molten salt mixture of the constituent materials processed from seawater, which considerably reduces the cost.

After a series of downward revisions in the average price of lithium-ion batteries over the decade, rising raw material costs and inflation resulted in a seven percent increase in 2022 to reach $151/kWh.

“Our sodium battery has the potential to dramatically reduce costs while providing four times as much storage capacity. This is a significant breakthrough for renewable energy development which, although reduces costs in the long term, has had several financial barriers to entry,” said Dr. Zhao in a release.

How scientists achieved the result

The concept of sodium-sulfur (Na-S) cells has existed for over 50 years but primarily remained impractical due to their low energy capacity and short life cycles. The researchers have now used a "simple pyrolysis process and carbon-based electrodes to improve the reactivity of sulfur and the reversibility of reactions between sulfur and sodium." This led to a dramatically increased capacity and longevity at room temperature.

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Na-S cells are also less toxic and more energy intense, making them easier to recycle and more economical to produce when compared to lithium-ion batteries, which are widely used in electronic devices and for energy storage.

The team has kept in mind the various use-case scenarios during the battery's development, with priority given to providing a viable alternative for "large renewable energy storage systems, such as electrical grids, while significantly reducing operational costs."

Such technology has the "potential to guarantee greater energy security more broadly and allow more countries to join the shift towards decarbonization.”

The team fabricated and tested the technology with lab-scale batteries at the University's chemical engineering facility. The next step involves scaling the technology used in the Ah-level pouch cells to commercialize it on a large scale.

Study Abstract:

Room-temperature sodium–sulfur (RT-Na/S) batteries possess high potential for grid-scale stationary energy storage due to their low cost and high energy density. However, the issues arising from the low S mass loading and poor cycling stability caused by the shuttle effect of polysulfides seriously limit their operating capacity and cycling capability. Herein, sulfur-doped graphene frameworks supporting atomically dispersed 2H-MoS2 and Mo1 ([email protected]/SGF) with a record high sulfur mass loading of 80.9 wt.% are synthesized as an integrated dual active sites cathode for RT-Na/S batteries. Impressively, the as-prepared [email protected]/SGF display unprecedented cyclic stability with a high initial capacity of 1017 mAh g−1 at 0.1 A g−1 and a low-capacity fading rate of 0.05% per cycle over 1000 cycles. Experimental and computational results including X-ray absorption spectroscopy, in situ synchrotron X-ray diffraction and density-functional theory calculations reveal that atomic-level Mo in this integrated dual-active-site forms a delocalized electron system, which could improve the reactivity of sulfur and reaction reversibility of S and Na, greatly alleviating the shuttle effect. The findings not only provide an effective strategy to fabricate high-performance dual-site cathodes, but also deepen the understanding of their enhancement mechanisms at an atomic level.