Additives keep lithium-ion batteries from catching fire

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Illustrations showing pancake formation from the additive compound(Credit: W. Li et al, Nature Communications)

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Processor chips may get all the glory, but if it wasn't for lithium-ion batteries, modern electronics would look like something out of the 1950s. Unfortunately, while they may be compact and long lasting, these batteries also suffer from overheating and can become fire hazards as they get old. Now a team led by Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory has come up with an additive that holds the promise of extending lithium battery life while improving safety and performance.

According to the team leader, Associate Professor Yi Cui, one of the big problems with lithium batteries is that over time the lithium metal starts to form dendrites as metal ions are deposited on the surface of the battery. That is, small, sharp fingers of lithium grow out of the metal that in time can pierce the barrier that separate the two sides of the battery. This can short out the battery, which can destroy it or worse, cause it to overheat and perhaps catch fire.

Building on previous research on how to get warnings of compromised batteries before they become dangerous, the team looked at how chemicals added to the battery's electrolyte could stop dendrites from forming. They discovered that when lithium nitrate, a chemical already studied as a performance enhancer, is mixed with lithium polysulfide, an unexpected reaction occurs. Lithium polysulfide is regarded as a contaminant that deposits sulfur on lithium electrodes and wrecks them. However, when combined with lithium nitrate, they form a solid and stable interface between the electrode and the electrolyte; preventing the formation of dendrites.

In tests, the team created button batteries similar to those used in watches and other small electronics. These used an ether electrolyte to which was added various concentrations and proportions of the new additive. After putting the batteries through numerous charge/discharge cycles, they were then dismantled and subjected to electron microscope and x-ray analysis.

The result? The team found that by balancing the ratio of the two additives, a pancake-like deposit formed on the lithium and prevented dendrite formations. In addition, the batteries ran with a 99 percent efficiency over 300 charging cycles, which the team says is a significant improvement over using lithium nitrate alone.

The researchers hope this new additive could lead to batteries that can store ten times more energy per weight that current consumer versions, with a huge potential for powering electronics and electric vehicles. Future research could involve scaling up the technology or looking at its application to other metals, such as magnesium, calcium, or aluminum.

"This is a really exciting observation," says Fiona (Weiyang) Li, a postdoctoral researcher. "We had been doing experiments all along with these two chemicals in there, but this was the first time we looked at the synergistic effect. This does not completely solve all the problems associated with lithium metal batteries, but it’s an important step."

The team's results were published in Nature Communications.

Source: SLAC

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