Reaction Mechanisms for the Limited Reversibility of Li-O2 Chemistry in Organic Carbonate Electrolytes

Journal Article · Tue Nov 15 04:00:00 EST 2011 · Journal of Power Sources

DOI:https://doi.org/10.1016/j.jpowsour.2011.06.099· OSTI ID:1027690

Xu, Wu; Xu, Kang; Viswanathan, Vilayanur V; Towne, Silas A; Hardy, John S; Xiao, Jie; Nie, Zimin; Hu, Dehong; Wang, Deyu; Zhang, Jiguang

The Li-O2 chemistry in nonaqueous carbonate electrolytes and the underneath reason of its limited reversibility was exhaustively investigated. The discharge products collected from the air cathode in a Li-O2 battery at different depth of discharge (DOD) were systematically analyzed with X-ray diffraction. It is revealed that, independent of the discharge depth, lithium alkylcarbonate (either lithium propylenedicarbonate - LPDC, or lithium ethylenedicarbonate - LEDC, with other related derivatives) and lithium carbonate (Li2CO3) are always the main products, obviously originated from the electrolyte solvents propylene carbonate (PC) and ethylene carbonate (EC). These lithium alkylcarbonates are obviously generated from the single-electron reductive decomposition of the corresponding carbonate solvents initiated by the attack of superoxide radical anions. On the other hand, neither lithium peroxide (Li2O2) nor lithium oxide (Li2O) is detected. More significantly, from in situ gas chromatography/mass spectroscopy it is found that Li2CO3 and Li2O cannot be oxidized even when charged up to 4.6 V vs. Li/Li+, while LPDC, LEDC and Li2O2 are readily able to, with CO2 and CO released with the re-oxidation of LPDC and LEDC. It is therefore concluded that the quasi-reversibility of Li-O2 chemistry observed hitherto in an organic carbonate-based electrolyte is actually reliant on the formation of lithium alkylcarbonates through the reductive decomposition of carbonate solvents during discharge process and the subsequent oxidation of these same alkylcarbonates during charge process. It is the poor oxidizability of these alkylcarbonate species that constitutes the obstruction to an ideal rechargeable Li-O2 battery.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1027690
• Report Number(s): PNNL-SA-78429
• Journal Information: Journal of Power Sources, Journal Name: Journal of Power Sources Journal Issue: 22 Vol. 196; ISSN JPSODZ; ISSN 0378-7753
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
AIR
ANIONS
CARBONATES
CARBONIC ACID ESTERS
CATHODES
CHEMISTRY
Carbonate electrolyte
Cycleability
ELECTROLYTES
ETHYLENE
Gas chromatography/mass spectroscopy
LITHIUM
LITHIUM CARBONATES
LITHIUM OXIDES
Li-O2 battery chemistry
Lithium alkylcarbonate
OXIDATION
PEROXIDES
REACTION KINETICS
Reversibility
SOLVENTS
SPECTROSCOPY
SUPEROXIDE RADICALS
X-RAY DIFFRACTION