Journal
ACS NANO
Volume 8, Issue 12, Pages 12483-12493Publisher
AMER CHEMICAL SOC
DOI: 10.1021/nn505337p
Keywords
lithium oxygen batteries; lithium peroxide; cathodes; electrodes; surface passivation; electron transfer
Categories
Funding
- NSERC
- Waterloo Institute of Technology
- CNPq
- Joint Center for Energy Storage Research (JCESR), an Energy Innovation Hub - U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences
- DOE's Office of Biological and Environmental Research
- Department of Energy [DE-AC05-76RLO1830]
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Recently, there has been a transition from fully carbonaceous positive electrodes for the aprotic lithium oxygen battery to alternative materials and the use of redox mediator additives, in an attempt to lower the large electrochemical overpotentials associated with the charge reaction. However, the stabilizing or catalytic effect of these materials can become complicated due to the presence of major side-reactions observed during dis(charge). Here, we isolate the charge reaction from the discharge by utilizing electrodes prefilled with commercial lithium peroxide with a crystallite size of about 200-800 nm. Using a combination of S/TEM, online mass spectrometry, XPS, and electrochemical methods to probe the nature of surface films on carbon and conductive Ti-based nanoparticles, we show that oxygen evolution from lithium peroxide is strongly dependent on their surface properties. Insulating TiO2 surface layers on TiC and TiN - even as thin as 3 nmcan completely inhibit the charge reaction under these conditions. On the other hand, TiC, which lacks this oxide film, readily facilitates oxidation of the bulk Li2O2 crystallites, at a much lower overpotential relative to carbon. Since oxidation of lithium oxygen battery cathodes is inevitable in these systems, precise control of the surface chemistry at the nanoscale becomes of upmost importance.
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