Aluminium catalyst helps Chinese researchers improve sodium-sulphur battery performance

Researchers at the Chinese Academy of Sciences (CAS) have developed an aluminium-based catalyst that could help make sodium–sulphur batteries last longer. The catalyst addresses a problem that has limited the technology: Sodium polysulphides can dissolve and move away from the cathode, reducing battery life.

The research team, led by Professors Wang Hui and Zheng Fangcai at CAS's High Magnetic Field Laboratory in Hefei, changed the atomic structure of aluminium by replacing one oxygen atom with nitrogen. The team wrote in the press release, “This created an asymmetric structure with three oxygen atoms and one nitrogen atom around each Al atom.” It is an Al–O3N structure (three oxygen atoms and one nitrogen atom surrounding each aluminium atom).

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Researchers have traditionally relied on costly metals such as platinum, cobalt and nickel for battery catalysts, while cheaper metals such as aluminium have shown lower catalytic activity. 

The change improved the interaction between aluminium and sulphur species, helping to control the movement of polysulphides and speed up the battery's internal reactions. The team added, “The batteries also maintained stable performance over thousands of charge-discharge cycles, showing good potential for long-lasting sodium–sulfur batteries.”

Replacing one oxygen atom with nitrogen changed the electron distribution around the aluminium atom, creating a local electric charge. This strengthened the interaction between aluminium and sulphur species, helping to prevent polysulphides from moving away from the cathode and improving the battery's reaction speed and stability. 

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During laboratory tests, the aluminium-based cathode recorded a capacity of 1,196 mAh g⁻¹ after 100 cycles. It also completed 2,500 charge-discharge cycles, with performance declining by just 0.017 per cent per cycle.

The researchers said the findings show that changing the local atomic structure of a catalyst can improve its performance. The work also points to the potential of aluminium, a relatively abundant and inexpensive metal, in developing catalysts for sodium–sulphur batteries.

The study was published in Angewandte Chemie.