New electrolyte for lithium-ion batteries performs well in frigid regions and seasons — ScienceDaily

In present lithium-ion batteries, the principle downside lies within the liquid electrolyte. This key battery element transfers charge-carrying particles known as ions between the battery’s two electrodes, inflicting the battery to cost and discharge. However the liquid begins to freeze at sub-zero temperatures. This situation severely limits the effectiveness of charging electrical automobiles in chilly areas and seasons.

To deal with that downside, a group of scientists from the U.S. Division of Vitality’s (DOE) Argonne and Lawrence Berkeley nationwide laboratories developed a fluorine-containing electrolyte that performs effectively even in sub-zero temperatures.

“Our group not solely discovered an antifreeze electrolyte whose charging efficiency doesn’t decline at minus 4 levels Fahrenheit, however we additionally found, on the atomic degree, what makes it so efficient,” mentioned Zhengcheng “John” Zhang, a senior chemist and group chief in Argonne’s Chemical Sciences and Engineering division.

This low-temperature electrolyte reveals promise of working for batteries in electrical automobiles, in addition to in vitality storage for electrical grids and client electronics like computer systems and telephones.

In at present’s lithium-ion batteries, the electrolyte is a mix of a extensively out there salt (lithium hexafluorophosphate) and carbonate solvents comparable to ethylene carbonate. The solvents dissolve the salt to type a liquid.

When a battery is charged, the liquid electrolyte shuttles lithium ions from the cathode (a lithium-containing oxide) to the anode (graphite). These ions migrate out of the cathode, then move by means of the electrolyte on the best way into the anode. Whereas being transported by means of the electrolyte, they sit on the heart of clusters of 4 or 5 solvent molecules.

Throughout the preliminary few fees, these clusters strike the anode floor and type a protecting layer known as the solid-electrolyte interphase. As soon as shaped, this layer acts like a filter. It permits solely the lithium ions to move by means of the layer whereas blocking the solvent molecules. On this method, the anode is ready to retailer lithium atoms within the construction of the graphite on cost. Upon discharge, electrochemical reactions launch electrons from the lithium that generate electrical energy that may energy automobiles.

The issue is that in chilly temperatures, the electrolyte with carbonate solvents begins to freeze. In consequence, it loses the power to move lithium ions into the anode on cost. It is because the lithium ions are so tightly certain inside the solvent clusters. Therefore, these ions require a lot greater vitality to evacuate their clusters and penetrate the interface layer than at room temperature. For that cause, scientists have been trying to find a greater solvent.

The group investigated a number of fluorine-containing solvents. They had been in a position to determine the composition that had the bottom vitality barrier for releasing lithium ions from the clusters at sub-zero temperature. In addition they decided on the atomic scale why that exact composition labored so effectively. It relied on the place of the fluorine atoms inside every solvent molecule and their quantity.

In testing with laboratory cells, the group’s fluorinated electrolyte retained steady vitality storage capability for 400 charge-discharge cycles at minus 4 F. Even at that sub-zero temperature, the capability was equal to that of a cell with a traditional carbonate-based electrolyte at room temperature.

“Our analysis thus demonstrated the way to tailor the atomic construction of electrolyte solvents to design new electrolytes for sub-zero temperatures,” Zhang mentioned.

The antifreeze electrolyte has a bonus property. It’s a lot safer than the carbonate-based electrolytes which are at present used, because it is not going to catch hearth.

“We’re patenting our low-temperature and safer electrolyte and at the moment are trying to find an industrial accomplice to adapt it to one in every of their designs for lithium-ion batteries,” Zhang mentioned.

This analysis seems in Superior Vitality Supplies. Along with John Zhang, Argonne authors are Dong-Joo Yoo, Qian Liu and Minkyu Kim. Berkeley Lab authors are Orion Cohen and Kristin Persson.

This work was funded by the DOE Workplace of Vitality Effectivity and Renewable Vitality, Car Applied sciences Workplace.