Breaks make batteries last longer

Non-rechargeable lithium batteries are seen as a beacon of hope. They could give electrically powered vehicles a range of up to 1100 kilometres. However, they have a significant disadvantage: unlike the lithium-ion batteries currently in widespread use, lithium batteries quickly lose their storage capacity, which is why they are used, among other things, as single-use button cells in watches. However, researchers led by materials scientist Wenbo Zhang from Stanford University have now found a way to recharge lithium batteries several times: You just have to give them a little break. They describe their findings in a study published on 7 February 2024 in Nature. "We were looking for the simplest, cheapest and fastest way to improve the lifespan of lithium batteries," said Zhang in a press release.

In lithium batteries, not only the cathode contains lithium ions, but also the anode, which is made of carbon in lithium-ion batteries. This means that lithium batteries are lighter and can store around twice as much energy as lithium-ion batteries. However, lithium batteries wear out after a few charging cycles: Their ability to store energy dwindles quickly. The reason for this is that areas with metallic lithium are enclosed by decomposition products of the electrolyte. This cuts the particles off from their surroundings and they can no longer absorb energy. "For this reason, we consider isolated lithium to be dead," explains Zhang.

In previous experiments, however, the research group had noticed that the decay products of the electrolyte degrade in fully discharged batteries. They therefore decided to investigate what exactly happens in these cases. "We found that some of the decay products surrounding the dead lithium dissolve when the battery rests in a discharged state for just one hour," said chemist Philaphon Sayavong, who was also involved in the "Nature" study, in a press release. "So when you recharge the battery, the dead lithium reconnects to the anode."

This marks an important step forward in battery research. Until now, experts had assumed that the isolated lithium could no longer be recovered. In addition, resting a discharged battery was considered harmful - and now it turns out that this is exactly what could enable it to be used as a rechargeable battery. The authors of the study emphasise that their findings could easily be put into practice. Electric cars typically consist of thousands of individual battery cells, so the entire module would have to be programmed so that a fully discharged cell only receives power again after one hour.

However, there is still a long way to go before the technology is actually used, writes researcher Laura C. Merrill in an accompanying article in "Nature". Although the new study contributes to the understanding of lithium batteries, there are still many gaps in our knowledge. For example, it is too early to say whether the protocol proposed by Zhang and his team is transferable to consumer applications where the number of charge cycles and rest time vary.

Spectrum of Science

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