Helping lithium–sulfur batteries reach their full potential

While lithium-ion batteries have come a long way since they were first introduced, they face some challenges, such as short lifetimes, overheating and supply chain issues for certain raw materials. Scientists at the U.S. Department of Energy’s (DOE) Argonne National Laboratory are researching solutions to these issues by testing new materials in battery construction. One such material is sulfur; sulfur is abundant and cost-effective and can hold more energy than traditional ion-based batteries. Researchers have now advanced sulfur-based battery research by creating a layer within the battery that adds energy storage capacity while nearly eliminating a traditional problem with sulfur batteries that caused corrosion.

Wenqian Xu, a beamline scientist at APS, said the research demonstrates that a redox-active interlayer could have a huge impact on Li-S battery development. A promising battery design pairs a sulfur-containing positive electrode (cathode) with a lithium metal negative electrode (anode). In between those components is the electrolyte, or the substance that allows ions to pass between the two ends of the battery. Early lithium–sulfur (Li-S) batteries did not perform well because sulfur species (polysulfides) dissolved into the electrolyte, causing its corrosion. This polysulfide shuttling effect negatively impacts battery life and reduces the number of times the battery can be recharged.

To prevent polysulfide shuttling, researchers tried placing a redox-inactive interlayer between the cathode and anode. ‘Redox-inactive’ means the material does not undergo reactions like those in an electrode. But this protective interlayer is heavy and dense, reducing energy storage capacity per unit weight for the battery. It also does not adequately reduce shuttling — this has proved a barrier to the commercialisation of Li-S batteries.

To address this, researchers developed and tested a porous sulfur-containing interlayer. Tests showed initial capacity about three times higher in Li-S cells with this active, as opposed to inactive, interlayer. The cells with the interlayer also maintained high capacity over 700 charge–discharge cycles.

Image shows microstructure and elemental mapping (silicon, oxygen and sulfur) of porous sulfur-containing interlayer after 500 charge–discharge cycles in lithium–sulfur cell. Image credit: Guiliang Xu/Argonne National Laboratory

“Previous experiments with cells having the redox-inactive layer only suppressed the shuttling, but in doing so, they sacrificed the energy for a given cell weight because the layer added extra weight. By contrast, our redox-active layer adds to energy storage capacity and suppresses the shuttle effect,” said Guiliang Xu, an Argonne chemist and co-author of the paper.

To further study the redox-active layer, the team conducted experiments at the 17-BM beamline of Argonne’s Advanced Photon Source (APS); the data gathered from exposing cells with this layer to X-ray beams allowed the team to ascertain the interlayer’s benefits. The data confirmed that a redox-active interlayer can reduce shuttling, reduce detrimental reactions within the battery and increase the battery’s capacity to hold more charge and last for more cycles.

The team plans to evaluate the growth potential of the redox-active interlayer technology, with the aim of making it thinner and lighter. A paper based on the research was published in Nature Communications.

Top image credit: iStock.com/jroballo