Argonne National Laboratory is a U.S. federal research and development institution in Lamont, Illinois. It issued a press release on February 7, 2024 concerning what it lightly called ‘ghosts in batteries’. Although they were speaking of soft shorts in lithium-metal cells, and they were indeed making a ground-breaking announcement.
How Lithium-Metal Batteries Eventually Fail
The Argonne team were studying solid-state batteries using lithium-metal chemistry. This format intrigued them, because it could store large amounts of electricity in compact spaces. Lithium-metal batteries could therefore theoretically deliver longer electric-vehicle driving ranges, than lithium-ion with graphite anodes.
Ions flow in conventional batteries from anodes to cathodes through electrolytes, as they discharge. While electrons flow simultaneously in the same direction through an external device. This process reverses during recharging, and continues for the life of the battery.
However, lithium-metal disrupts this process as thin lithium filaments grow off the anode, and reach through the electrolyte to contact the cathode. Eventually, all the electrons travel through this shorter path in an internal short circuit. And as a result the battery can no longer power an external device.
Argonne Finds Soft Shorts in Lithium-Metal Batteries
“When we operated our batteries in the laboratory, we observed very small, very brief voltage fluctuations,” the Argonne researchers recall. “So we decided to take a deeper look.” They charged and recharged their batteries hundreds of times, while measuring electrical factors including voltage.
The team observed numerous tiny short circuits that affected battery output momentarily. They realized these soft shorts in lithium-metal batteries occurred as lithium filaments grew from the anode to the cathode. However, the filament growth was smaller than the dendrites that caused permanent short circuits.
The Argonne lithium-metal metal batteries continued to work for days, even weeks after the lithium filaments began to form. Meanwhile, the filaments continued to grow in numbers until all the electrons were able to flow through them. The team concluded that soft shorts in lithium-metal batteries “are the first step off the cliff to permanent battery failure,”
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