In the mid-1990s, K.M. Abraham and co-workers demonstrated the first non-aqueous Li–air battery with the use of a Li negative electrode (anode), a porous carbon positive electrode (cathode), and a gel polymer electrolyte membrane that served both as the separator and ion-transporting medium.Oxygen from the atmosphere enters the pores of the carbon cathode to serve as the active material. Under discharge, this oxygen was reduced and the products stored in the pores of the carbon electrode. The Li+ conducting gel polymer electrolytes were based on polyacrylonitrile (PAN) and polyvinyllidene fluoride (PVdF). In such an aprotic electrolyte, the half reactions which occur are:
At anode:
Li--------- Li+ +e].2.
At cahoode:
Li+ + e- +O2 → LiO2* (unstable intermediate).
Li+ + e- +LiO2* →Li 2O2.
------------------------------------------
2Li+ +O2------- (-Reversible reaction) ---- --- Li2O2.
This reaction representing the overall reaction has cell voltage (E^0) equal to 3.10 V. The forward reaction represents discharging (O2 consumed) and the backward represents charging (O2 evolution).In a way, Li2O2 is produced during discharging while it is consumed during charging .As Li2O2 is insoluble in aprotic electrolytes, it leads to cathode clogging which delays discharging, i.e.it takes more time wrt the charging .
Thank you for your answer. But, for my cases, the charging curve shorter than discharging curve.
May I humbly add?
Sorry; I used an improper word (delayed) while concluding the answer:
What I wanted to convey was that the time taken for discharging was more than than charging because of clogging , Li2O2 it liberates O2 at a slower rate than the rate at which Li metal has reacted with the O2.
Please look in two graphs given on page 34 of the paper (click):
Prof. Dr. Petr Novák .... A. Débart, M. Holzapfel, P. Novák, and P. G. Bruce, J. Am. Chem. Soc. 2006 (128), p. 1390.
and then read as:
If we plot graphs between voltage and time both for charging (electrode withLi2O2) and discharging(electrode without Li2O2) ,time taken for discharging is more(1375m) than taken for charging(1250m) for the same volts loss(4.7-3.0=1.3V).
- Badges
- Science topic
- Similar topics
- Electrochemistry
- Battery