2024-02-21 01:02:45
Atomic memory: The ions of a solid-state battery do not flow evenly from one electrode to another when charging and discharging, but instead jump around in the atomic lattice of the electrolyte in ways that are difficult to predict. However, the ions apparently remember where they were before and jump back to these positions under certain circumstances, as researchers report in “Nature”. This discovery is a great help for the development of robust batteries and new materials.
Solid-state or solid-state batteries store and release electrical charge by moving ions back and forth between two electrodes. The ions appear to flow through the battery’s solid electrolyte like a gentle current. However, viewed at the atomic level, the individual ions hop irregularly from one free space to another within the electrolyte atomic lattice, as previous studies have shown. These jumps are difficult to predict.
Until now, researchers assumed that the ions move towards their target at random: they stumble along like a drunk, but eventually reach their destination. “Several strange and unusual things happen during the ion hopping process, such as sudden jumps and long pauses,” explains Aaron Lindenberg from SLAC National Accelerator Laboratory in California. “There is an element of randomness in this process that makes experiments difficult.”
Measurements at the atomic level
A research team led by Lindenberg and first author Andrey Poletayev from SLAC has now examined these ion movements in more detail. To do this, the scientists used differently thin, transparent crystals of a solid electrolyte from the beta aluminum oxide family of materials. These materials have tiny channels in which hopping ions can move quickly and therefore have very high conductivity.
In addition, these electrolytes are considered safer and more durable than liquid alternatives such as those found in lithium-ion batteries. The beta aluminum oxides are therefore used in common solid-state batteries, sodium-sulfur batteries and electrochemical cells.
Experimental setup: A laser device shocked the ions traveling through the electrolyte of a solid-state battery with a voltage surge. © Andrey D. Poletayev/Oxford University
To find out how the jumping ions move within this material, the scientists gave them a voltage shock with an extremely short laser pulse of about one picosecond. They then detected the light that was refracted from the electrolyte and sent back after different time intervals. From this they drew conclusions about the speed and direction of movement of the ions.
Ions have short-term memory
Surprisingly, most of the ions briefly changed direction and returned to their previous positions before continuing on their usual, more random journey, the analyzes showed. This is an indication that the ions somehow “remembered” where they had just been, report Poletayev and his colleagues.
“The ions in a battery resist a hard shock from a burst of laser light by moving backwards,” says Poletayev. They temporarily take their previous positions in the atomic lattice. However, this “memory” of the ions is fuzzy and extremely short: it only lasts a few picoseconds, the scientists report.
Common assumption refuted
The researchers conclude that, contrary to what was previously assumed, the ions do not move completely randomly in the electrolyte of a solid-state battery. Their analysis using finer measuring devices now refutes this interpretation of earlier studies that were carried out using coarser methods and therefore inevitably could not produce such fine observations.
The realization that ions have a kind of short-term memory could help predict for the first time what migrating ions will do next. This is an important consideration in the development of new materials and devices such as rechargeable solid-state batteries. “Our discoveries will help close the gap between the atomic motions we can model in a computer and the macroscopic performance of a material,” says Poletayev. (Nature, 2024; two: 10.1038/s41586-023-06827-6)
Quelle: DOE/SLAC National Accelerator Laboratory
February 21, 2024 – Claudia Krapp
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