Direct Observations of the Formation and Redox-Mediator-Assisted Decomposition of Li2 O2 in a Liquid-Cell Li-O2 Microbattery by Scanning Transmission Electron Microscopy

Chuchu Yang; Jiuhui Han; Pan Liu; Chen Hou; Gang Huang; Takeshi Fujita; Akihiko Hirata; Mingwei Chen

doi:10.1002/adma.201702752

Direct Observations of the Formation and Redox-Mediator-Assisted Decomposition of Li₂ O₂ in a Liquid-Cell Li-O₂ Microbattery by Scanning Transmission Electron Microscopy

Adv Mater. 2017 Nov;29(41). doi: 10.1002/adma.201702752. Epub 2017 Sep 11.

Authors

Chuchu Yang¹, Jiuhui Han¹, Pan Liu^{1

2}, Chen Hou², Gang Huang¹, Takeshi Fujita¹, Akihiko Hirata¹, Mingwei Chen^{1

2

3

4}

Affiliations

¹ WPI Advanced Institute for Materials Research, Tohoku University, Sendai, 980-8577, Japan.
² State Key Laboratory of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai, 200030, P. R. China.
³ CREST, JST, 4-1-8 Honcho Kawaguchi, Saitama, 332-0012, Japan.
⁴ Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, MD, 21214, USA.

PMID: 28892193
DOI: 10.1002/adma.201702752

Abstract

Operando scanning transmission electron microscopy observations of cathodic reactions in a liquid-cell Li-O₂ microbattery in the presence of the redox mediator tetrathiafulvalene (TTF) in 1.0 m LiClO₄ dissolved dimethyl sulfoxide electrolyte are reported. It is found that the TTF addition does not obviously affect the discharge reaction for the formation of a solid Li₂ O₂ phase. The coarsening of Li₂ O₂ nanoparticles occurs via both conventional Ostwald ripening and nonclassical crystallization by particle attachment. During charging, the oxidation reaction at significantly reduced charge potentials mainly takes place at Li₂ O₂ /electrolyte interfaces and has obvious correspondence with the oxidized TTF⁺ distributions in the electric fields of the charged electrode. This study provides direct evidence that TTF truly plays a role in promoting the decomposition of Li₂ O₂ as a soluble charge-transfer agent between the electrode and the Li₂ O₂ .

Keywords: Li-O2 batteries; liquid-cell TEM; operando scanning transmission electron microscopy; redox mediators; tetrathiafulvalene (TTF).