Researchers from the Department of Energy’s SLAC National Accelerator Laboratory, and Stanford University believe that they have found a way to revive rechargeable lithium battery cells. This could increase electric car range and battery life for next-generation electronic devices.
Small islands of inactive lithium build up between the electrodes as lithium batteries cycle. This reduces the battery’s capacity to hold charge. Researchers discovered that this “dead” lithium could be made to creep toward an electrode until it connects. This partially reversed the undesirable process.
Lost connection
Research is ongoing to find ways to create rechargeable batteries that are lighter, safer, faster, and more efficient than current lithium-ion technology used in smartphones, laptops, electric cars, and other electronic devices. The development of lithium-metal batteries is a particular focus. These batteries could store more energy per unit weight or volume. These next-generation batteries can be used in electric cars to increase mileage and take up less space.
Both types of batteries use positively charged lithiumions, which shuttle between the electrodes. Some of the metallic lithium can become electrochemically inactive over time, creating isolated lithium islands that don’t connect to the electrodes. This causes a loss in capacity, which is particularly problematic for lithium-metal technology as well as fast charging lithium-ion batteries.
The researchers showed that they were able to mobilize and recover lithium from the battery to prolong its life.
Yi Cui, a Stanford professor and SLAC investigator, led the research. “But, we have found a way to electrically connect this ‘dead” lithium with the negative electrode to activate it again.”
Creeping, not dead
Cui’s idea of applying voltage to an anode or cathode of a battery could cause an isolated lithium island to physically move between electrodes. This Cui team confirmed in their experiments.
The scientists fabricated an optical cell with a lithium-nickel-manganese-cobalt-oxide (NMC) cathode, a lithium anode and an isolated lithium island in between. They were able to monitor in real-time what happens in a battery during its use using this test device.
The team discovered that the isolated lithium island was not “dead”. It responded to battery operations. The island moved slowly towards the cathode when it was being charged; but when it was discharged, it moved in the opposite direction.
Cui described it as “a very slow worm that inches forward and pulls its tail back to move nanometers by nanometers.” It transports by destroying one end of the worm and depositing material on the other. If the lithium worm can be kept moving, it will touch the anode eventually and reestablish electrical connection.
Enhance your life expectancy
These results were validated by scientists using other test batteries as well as computer simulations. They also show how isolated lithium can be recovered in real batteries by changing the charging protocol.
Liu said that the discharging of the lithium detached can be used to move it toward the anode. These motions are also faster when the current is higher. We added a high-current, fast discharging step immediately after the battery charges. This moved the isolated lithium far enough that it could be reconnected with the anode. This activates the lithium to allow it to participate in the battery’s life.
She said, “Our findings also hold wide implications for design and development more robust lithium-metal battery designs.”
