Because of their high theoretical energy density, lithium oxygen batteries (LOB) are the focus of much research for future generations of energy storage, particularly for pervasive electric vehicles. However, problems such as low round-trip efficiency, poor reversibility and inferior electrolyte stability have hindered practical applications.
A typical non-aqueous Li-oxygen battery is based on a reversible electrochemical reaction between Li+ and O2. During this process, oxidizing intermediates such as LiO2, O22-, OOH- or 1O2 may attack the organic electrolyte and cause performance decay. Finding an electrolyte with higher stability is one of the key issues in LOB development.
Ether-based electrolytes are widely used in lithium-oxygen batteries because of their relatively high ionic conductivity, O2 solubility, and electrochemical stability.
However, conventional ethers have weak points, and are prone to be attacked by superoxides or singlet oxygen via hydrogen abstract reactions, leading to performance decay during long-term operation.
Now, a team from Huazhong University of Science and Technology in China reports developing a fully methylated cyclic ether, 2,2,4,4,5,5-hexamethyl-1,3-dioxolane (HMD), that shows excellent stability in the presence of O2– or 1O2.
In a paper in the journal Angewandte Chemie, they report that the cycle life of a cell with an HMD-based electrolyte was 157 cycles—four times longer than for a cell with conventional 1,3‐dioxolane (DOL) or 1,2‐dimethoxyethane (DME) based electrolytes.
The researchers attributed HMD’s excellent stability in presence of superoxide or singlet oxygen because all the active α-H atoms are substituted with methyl groups.
According to the researchers, the findings could lead to the development of high-performance rechargeable lithium-oxygen batteries.
Zhimei Huang, Haipeng Zeng, Meilan Xie, Xing Lin, Zhaoming Huang, Yue Shen, Yunhui Huang (2018) “A stable lithium-oxygen battery electrolyte based on fully methylated cyclic ether” Angew. Chem. Int. Ed. doi: 10.1002/anie.201812983