The discharge rate capability of rechargeable Li–O2 batteries

Abstract

The O₂electrode in Li–O₂cells was shown to exhibit gravimetric energy densities (considering the total weight of oxygen electrode in the discharged state) four times that of LiCoO₂ with comparable gravimetric power. The discharge rate capability of Au-catalyzed Vulcan carbon and pure Vulcan carbon (VC) as the O₂electrode was studied in the range of 100 to 2000 mA g_carbon ⁻¹. The discharge voltage and capacity of the Li−O₂ cells were shown to decrease with increasing rates. Unlike propylene carbonate based electrolytes, the rate capability of Li−O₂ cells tested with 1,2-dimethoxyethane was found not to be limited by oxygen transport in the electrolyte. X-Ray diffraction (XRD) showed lithium peroxide as the discharge product and no evidence of Li₂CO₃ and LiOH was found. It is hypothesized that higher discharge voltages of cells with Au/C than VC at low rates could have originated from higher oxygen reduction activity of Au/C. At high rates, higher discharge voltages with Au/C than VC could be attributed to faster lithium transport in nonstoichiometric and defective lithium peroxide formed upon discharge, which is supported by XRD and X-ray absorption near edge structure O and Li K edge data.