Antimony Doped Tin Oxide–Synthesis, Characterization and Application as Cathode Material in Li-O2 Cells: Implications on the Prospect of Carbon-Free Cathodes for Rechargeable Lithium-Air Batteries

H Beyer,X Wu,J Sicklinger,M Metzger,H A Gasteiger,K U Schwenke

doi:10.1149/2.0441706jes

Abstract

To develop reversible Li-O2 batteries, the need for novel carbon-free cathode materials is evident. In this study, we present the hydrothermal synthesis of highly conductive crystalline antimony doped tin oxide (ATO) nanoparticles, the fabrication of ATO electrodes with high surface area, and their application as cathodes in aprotic Li-O2 cells. We use a pressure transducer and an online electrochemical mass spectrometer to quantify consumed and evolved gases during discharge and charge of Li-O2 cells. Solid discharge products on the cathode are identified by infrared spectroscopy and quantified by acid-base titration and UV-vis spectroscopy. Thus we demonstrate an unprecedented cell chemistry: In contrast to carbon cathodes, ATO cathodes enable the formation of Li2O and prevent the formation of carbonates on the cathode surface. Formed Li2O can be recharged at high potentials, which leads to the evolution of oxygen. These new mechanistic insights provide implications for cathode design concepts that might enable the reversible cycling of Li-O2 cells.

Highlights

Since its introduction in 1996,1 the concept of an aprotic Li-air battery has attracted huge interest due to its outstanding theoretical energy density of ∼3400 Wh/kg on a material level.[2]
We apply a hydrothermal synthesis of antimony-doped tin oxide (ATO) nanoparticles from chlorine-free precursors using a modified procedure first reported by Zhang and Gao,[39] followed by additional calcination and milling steps
An Sb-doping level of 5 mol% is chosen on the basis of both theoretical and experimental data in the literature: Doping levels of 2–7 mol% Sb should lead to degenerate semiconductors with metallic properties

Summary

Introduction

Since its introduction in 1996,1 the concept of an aprotic Li-air battery has attracted huge interest due to its outstanding theoretical energy density of ∼3400 Wh/kg on a material level.[2]. The development of rechargeable Li-O2 cells is facing major challenges such as low rate capability, low round trip efficiency and poor cycle life, as discussed in several review articles.[4,5,6] The cycle life of aprotic Li-O2 cells with state of the art carbon cathodes fundamentally depends on the reversible formation/decomposition of lithium peroxide via the following 2 e− cathode reaction:[7]. Li2O by in-situ ambient pressure X-ray photoelectron spectroscopy (APXPS) on LixV2O5 at a very low cell voltage.[11,12] Apart from this work, Li2O has not been observed in Li-O2 cells to date, and its formation on carbon materials has been explicitly excluded by differential electrochemical mass spectrometry (DEMS)[13] and XPS.[14] Li2O has been found to be non-rechargeable even at the decomposition potential of a diglyme electrolyte when using carbon electrodes artificially prefilled with Li2O.15

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Conclusion