Most of the work has been focused on developing new catalyst and cathode structures with limited work carried out on understanding the role of the electrolyte on cell performance.

...In this work, we have carried out a combined experimental/computational study of the stability during discharge of electrolytes based on propylene carbonate and a tri(ethylene glycol)-substituted trimethylsilane (1NM3) in lithium-air batteries. The experimental studies are based on X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) studies of charge and discharge products. Density functional studies have been carried out on several possible decomposition mechanisms for the two solvents. The results confirm the instability of propylene carbonate, while indicating that the oligoether substituted silane is stable during discharge.

—Zhang et al.

Li-air batteries combine a lithium anode in combination with an oxygen cathode; during discharge, the lithium anode is oxidized by releasing an electron to the external circuit to produce lithium ions in the electrolyte, whereas the oxygen is reduced at a cathode surface to form lithium peroxide or lithium oxide which then can be recharged internally.

The organic carbonate electrolytes commonly used in Li-ion batteries have been shown by some recent studies not to be stable against oxygen reduction products formed during discharge in Li-air batteries, the authors note.

In their study, they found evidence that the ethers are more stable toward oxygen reduction discharge species. Only lithium oxides and no carbonates are formed when the 1NM3 electrolyte is used. In contrast, propylene carbonate (PC) in the same cell configuration decomposes to form lithium carbonates during discharge.

• XPS and FTIR experiments show that only lithium oxides and no carbonates are formed when this oligoether silane-based electrolyte is used. In contrast, XPS shows that PC in the same cell configuration decomposes to form lithium carbonates during discharge.

• Density functional calculations of probable decomposition reaction pathways involving C—O cleavage and proton/hydrogen abstraction to potential oxygen reduction species confirm that the 1NM3 species should be more stable during discharge than PC. Results for other ethers give similar results in the calculations.

• There is a large initial reduction in the cell charge overpotential when only lithium oxides form on discharge with use of the 1NM3 electrolyte compared to PC electrolyte, which produces carbonates on discharge. This suggests that large overpotentials in Li-air batteries can be significantly lowered with sufficient control of the discharge products.

Resources

• Zhengcheng Zhang, Jun Lu, Rajeev S. Assary, Peng Du, Hsien-Hau Wang, Yang-Kook Sun, Yan Qin, Kah Chun Lau, Jeffrey Greeley, Paul C. Redfern, Hakim Iddir, Larry A. Curtiss, and Khalil Amine (2011) Increased Stability Toward Oxygen Reduction Products for Lithium-Air Batteries with Oligoether-Functionalized Silane Electrolytes. The Journal of Physical Chemistry C doi: 10.1021/jp208741