Greg Stewart / SLAC National Accelerator Laboratory

Researchers at the Department of Energy's SLAC National Accelerator Laboratory and Stanford University may have found a way to revitalize rechargeable lithium batteries, potentially increasing the range of electric vehicles and battery life in devices. new generation electronics.

As lithium batteries cycle, they accumulate small islands of inactive lithium which are cut off from the electrodes, decreasing the battery's ability to store charge. But the research team found they could crawl that "dead" lithium like a worm to one of the electrodes until it reconnects, partially reversing the unwanted process.

When an island of inactivated lithium metal travels to a battery's anode or negative electrode and reconnects, it comes back to life, bringing electrons to the battery's current flow and lithium ions to store charge until needed. The island moves by adding metallic lithium at one end (blue) and dissolving it at the other end (red). Researchers at SLAC and Stanford found they could stimulate island growth in the direction of the anode by adding a brief high-current discharge step just after the battery is charged. Reconnecting the island to the anode has increased the lifespan of their lithium-ion test cell by almost 30 percent.

Adding this extra step slowed down the degradation of their test battery and increased its life by almost 30 percent. A study on the work is published in Nature.

Fang Liu, Stanford Postdoctoral Fellow, Senior Author said We are now exploring the potential recovery of lost capacity in lithium-ion batteries using an extremely fast discharge step"

Much research is looking for ways to make lighter rechargeable batteries, with longer life, improved safety, and faster-charging speeds than lithium-ion technology currently used in cellphones, laptops, and electric vehicles. Emphasis is placed on the development of lithium-metal batteries, which could store more energy by volume or by weight. For example, in electric cars, these next-generation batteries could increase mileage per charge and possibly take up less trunk space.

Both types of batteries use positively charged lithium ions which shuttle between the electrodes. Over time, some of the metallic lithium becomes electrochemically inactive, forming isolated islands of lithium that no longer connect to the electrodes. This results in a loss of capacity and is a particular problem for lithium-metal technology and the rapid charging of lithium-ion batteries.

However, in the new study, researchers have shown that they can mobilize and recover isolated lithium to extend battery life.

Yi Cui, professor at Stanford and SLAC and researcher at the Stanford Institute for Materials and Energy Research (SIMES) who led the research stated "I've always thought that isolated lithium was bad because it causes batteries to degrade and even burn them down. But we have discovered how to electrically reconnect this "dead" lithium with the negative electrode to reactivate it."

The idea for the study arose when Cui hypothesized that applying a voltage to a battery's cathode and anode could physically move an isolated island of lithium between the electrodes – a process that his team has now confirmed with their experiences.

Scientists made an optical cell with a lithium-nickel-manganese-cobalt oxide (NMC) cathode, a lithium anode, and an isolated lithium island in between. This test device allowed them to follow in real-time what happens inside a battery during its use.

They discovered that the isolated lithium island was not "dead" at all, but was responding to battery operations. While charging the cell, the islet slowly moved towards the cathode; when discharging, he crawled in the opposite direction.

It is like a very slow worm that advances its head forward and pulls its tail to move nanometer by nanometer. In this case, it transports by dissolving at one end and depositing material at the other end. If we can keep the lithium worm moving, it will eventually hit the anode and reestablish the electrical connection, Yi Cui added.

The results, which the scientists validated with other test batteries and through computer simulations, also demonstrate how the isolated lithium could be recovered in a real battery by changing the charging protocol.

We have found that we can move the loose lithium towards the anode during discharge, and these movements are faster under higher currents. So we added a high current fast discharge step just after charging the battery, which moved the isolated lithium far enough to reconnect it to the anode. This reactivates the lithium so that it can participate in battery life. Our findings also have broad implications for the design and development of more robust lithium metal batteries, Fang Liu added.

This work was funded by the DOE Office of Energy Efficiency and Renewable Energy, Office of Vehicle Technologies under the Battery Materials Research (BMR), Battery 500 Consortium, and eXtreme Fast Charge Cell Evaluation of Li-ion Batteries (XCEL) programs.