Direct Observations of the Formation and Redox-Mediator-Assisted Decomposition of Li2O2 in a Liquid-Cell Li–O2 Microbattery by Scanning Transmission Electron Microscopy

5 years ago

Direct Observations of the Formation and Redox-Mediator-Assisted Decomposition of Li2O2 in a Liquid-Cell Li–O2 Microbattery by Scanning Transmission Electron Microscopy

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

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 Li2O2 phase. The coarsening of Li2O2 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 Li2O2/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 Li2O2 as a soluble charge-transfer agent between the electrode and the Li2O2. Operando scanning transmission electron microscopy is used to investigate the cathodic reactions in a liquid-cell Li–O2 microbattery in the presence of redox mediators. The real-time and real-space observations provide experimental insights into the solution mechanisms of Li2O2 growth in a dimethyl-sulfoxide-based electrolyte and the working mechanisms of redox mediators as charge-transfer agents between the electrode surfaces and the solid Li2O2 phase.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/adma.201702752