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The method, developed by researchers at the US Department of Energy’s SLAC National Accelerator Laboratory and Stanford University, could boost battery life in next-gen electronic devices and extend range in electric vehicles.
As lithium batteries cycle, they accumulate small ‘islands’ of inactive lithium that are cut off from the electrodes, decreasing the battery’s capacity to store charge. The research team discovered that they could make this ‘dead’ lithium creep towards one of the electrodes until it reconnected, partially reversing the process.
The step slowed the degradation of a test battery and increased its lifetime by nearly 30%.
“We are now exploring the potential recovery of lost capacity in lithium-ion batteries using an extremely fast discharging step,” said lead author Fang Liu from Stanford.
Lithium-ion and lithium-metal batteries both use positively charged lithium ions that shuttle back and forth between electrodes. Over time, some of the metallic lithium becomes electrochemically inactive, forming isolated islands of lithium that no longer connect with the electrodes. This is a particular problem for lithium-metal technology, and for the fast charging of lithium-ion batteries.
In the new study, the researchers demonstrated they could mobilise and recover the isolated lithium to extend battery life. The team fabricated an optical cell with a lithium-nickel-manganese-cobalt-oxide (NMC) cathode, a lithium anode and an isolated lithium island in between, allowing them to track what happens inside a battery in real time.
They discovered that the isolated lithium island wasn’t ‘dead’ at all, but responded to battery operation. When charging the cell, the island slowly moved towards the cathode – when discharging, it crept in the opposite direction.
“It’s like a very slow worm that inches its head forward and pulls its tail in, to move nanometre by nanometre,” said research leader Professor Yi Cui. “In this case, it transports by dissolving away on one end and depositing material to the other end. If we can keep the lithium worm moving, it will eventually touch the anode and re-establish the electrical connection.”
The research reveals how to reconnect the ‘dead’ lithium with the negative electrode to reactivate it, Cui said.
The results, which the team validated with other test batteries and computer simulations, also demonstrate how isolated lithium could be recovered in a real battery by modifying the charging protocol.
“We found that we can move the detached lithium toward the anode during discharging, and these motions are faster under higher currents,” said Liu. “So we added a fast, high-current discharging step right after the battery charges, which moved the isolated lithium far enough to reconnect it with the anode. This reactivates the lithium so it can participate in the life of the battery.”
She added: “Our findings also have wide implications for the design and development of more robust lithium-metal batteries.”
The research was published in Nature.
This piece was originally published in January 2022.
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