A team of scientists from the US Department of Energy’s Argonne National Laboratory has discovered valuable insights into early battery failure symptoms. While studying a phenomenon called soft-shorts, the scientists provided the research community with important methods for designing better batteries for electric vehicles (EVs).
The Argonne team’s research focused on solid-state batteries with lithium metal anodes. The use of this metal is considered a kind of “holy grail” for batteries due to its high energy capacity in a small space. This enables much greater electric vehicle ranges compared to traditional lithium-ion batteries with graphite anodes.
However, lithium metal poses challenges due to its reactivity in conventional batteries. Electrolytes, the conductive substances that transport charged particles called ions between two battery electrodes, can cause a chemical reaction and a phenomenon called low short circuiting.
While working on a new solid electrolyte for EV batteries, the Argonne scientists noticed something unusual.
“We observed very small, momentary voltage fluctuations while operating the batteries in the lab,” said Michael Counihan, a research associate at Argonne. “We decided to take a closer look.”
Through repeated cycles of charge and discharge for several hundred hours, the team determined that the batteries experienced a short circuit called a soft-short. This is a type of transient, momentary short circuit.
The team of scientists developed models that predict the flow of ions and electrons during short circuits. These models take into account factors such as the size of lithium fibers and electrolyte properties.
Short circuits can last for hours, days, or even weeks. But as the Argonne team discovered, the growth of lithium fibers over time eventually leads to battery failure.
“Soft-shorts are the first step toward permanent battery failure,” said Counihan.
Further studies by the team revealed that these momentary short circuits exhibit very dynamic behavior. They often occur, disappear, and reoccur within microseconds or milliseconds.
“This is a significant discovery for battery researchers,” stated Counihan. “During typical laboratory experiments, researchers measure voltage every minute. In that time, thousands of soft-short events could have occurred and disappeared. They are like tiny ghosts that destroy your battery, and you wouldn’t even know it.”
The Argonne scientists have developed and presented numerous new methods for detecting and analyzing this phenomenon. For example, one method allows for assessing the impact of short circuits on current flow resistance within the battery. Since various battery components contribute to this resistance, isolating the influence of soft-shorts can help researchers better evaluate battery health.
The study published in the journal Joule includes a list of nearly 20 short circuit detection and analysis techniques. About one-third of these methods come from recent research by the Argonne team, while the remaining methods are derived from unpublished knowledge within the research community.
“Let’s not forget that there is no literature work that utilizes more than two of these techniques,” said Counihan. “To make the list more useful for researchers, we added information about the advantages and disadvantages of each method. Because soft-shorts are so dynamic, it’s good for researchers to have multiple tools to better understand their impact on batteries.”
The team aimed to provide researchers worldwide with insights into soft-short circuits to support their work. For example, the techniques described in the article can aid in the development of solid electrolytes that inhibit the growth of lithium fibers.
“When researchers understand the dynamics of soft-short circuits in their batteries, they will be able to develop more efficient and safer solutions,” added Counihan.
Related links:
Argonne National Laboratory website
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