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Energy Storage

New electrolyte improves Li-S batteries

Made from a lithium salt and diglyme, the electrolyte keeps troublesome sulfur reactions in check and thwarts formation of harmful lithium dendrites

by Mitch Jacoby
August 16, 2018 | APPEARED IN VOLUME 96, ISSUE 33

 

Lithium-sulfur batteries can pack up to five times as much energy by weight as some lithium-ion batteries, in principle. In practice, experimental versions of the batteries have fallen short of expectations because of unwanted chemical reactions between the electrodes and the electrolyte solution that alter the electrodes, thereby reducing energy storage and shortening battery life.

09633-scicon5-electrolyte.jpg
Credit: Quanquan Pang/U. Waterloo
By tuning the composition of a Li-S-battery electrolyte solution containing the solvent diglyme and a lithium salt, researchers have come up with an electrolyte that mediates the electrochemistry needed to run the battery but avoids unwanted reactions. Specifically, it barely dissolves harmful polysulfides (evidenced by a colorless electrolyte solution) and leads to smooth lithium deposition at the anode (left micrograph) as opposed to forming wispy dendrites (right). Micrographs measure 5 x 5 µm.

Rather than trying to solve these problems by modifying the electrodes, as many researchers have done, a team led by Quanquan Pang and Linda F. Nazar of the University of Waterloo have come up with a promising alternative approach. The team designed a customized electrolyte solution that limits these destructive reactions and suppresses battery degradation (Nat. Energy 2018 DOI: 10.1038/s41560-018-0214-0).

Lithium polysulfides are well-known bad actors in Li-S battery chemistry. The species, which dissolve in electrolyte solutions, shuttle between the cathode and anode, removing electrochemically active cathode material and corroding the anode. So the Waterloo team designed an electrolyte that barely dissolves polysulfides, and they used it sparingly in a Li-S battery. The electrolyte they arrived at contains the solvent diglyme and a lithium salt.

The team found that the electrolyte solution mediates the ionic reactions needed to drive the battery steadily for over 100 charge cycles but confines the sulfur chemistry to a quasi-solid state. The team also found that upon repeated charging, the electrolyte facilitates smooth deposition of lithium on the anode, avoiding formation of lithium dendrites, which can cause safety and battery degradation problems.

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