A new electric car battery material could dramatically boost charging times

While high charging times make the shift to electric vehicles unattractive, as the crucial component, the battery must also be cheap enough to encourage EV adoption. Although progress has been made in developing lithium-ion batteries, solid-state batteries (SSBs) have also gained traction as an alternative.

The problem with solid-state batteries

Unlike a conventional lithium-ion battery, SSBs do not have a liquid electrolyte and are made from entirely solid materials, hence the name. The major advantage of this technology is safety since an SSB doesn't leak out toxic chemicals even when punctured. However, their adoption had been slow due to problems of durability.

During the charging and discharging process, when lithium ions are inserted or extracted from the electrodes of an SSB, the crystalline structure of the material undergoes a change and ends up expanding and shrinking, depending on the charge cycle. The changes in the volume damage the interface between the electrode and solid electrolyte and cause irreversible changes in the crystal chemistry, the press release said.

How the researchers resolved it

Naoaki Yabuuchi, a professor at the Yokohoma National University in Japan, led a team of researchers who explored a new material for the positive electrode of an SSB. The team zeroed their focus on Li_8/7Ti_2/7V_4/7O_2, a binary system composed of portions of lithium titanate (Li₂TiO₃) and lithium vanadium dioxide (LiVO₂).

When ball-milled to nanometer particle size, the material offered high capacity thanks to the large number of lithium ions that can be reversibly inserted and extracted during the charge and discharge process.

Unlike materials that have been previously used for the positive electrodes, the newly researched material occupies the same volume when fully charged or discharged. Researchers found that this unique property is due to a fine balance of two independent phenomena that occur during the charging and discharging process.

When lithium ions are removed from the electrode, the free volume of the crystalline structure increases, which causes it to shrink; however, some vanadium ions move into these newly vacated spaces and acquire a higher oxidation state. The repulsive interaction with oxygen after this causes the crystal lattice structure to expand, retaining the size of the electrode.

The researchers trialed their new material in an SSB with a capacity of 300mAh/g. Over 400 charge and discharge cycles were carried out, but the electrode showed no signs of degradation. By further refining the electrode materials, the researchers hope to manufacture batteries that are good for EVs.

"The development of long-life and high-performance solid-state batteries would solve some of the problems of EVs," said Yabuuchi in the press release. "In the future, it may be possible to fully charge an EV in as little as five minutes."

The research was published today in the journal Nature Materials.