| AVS 61st International Symposium & Exhibition | |
| Energy Frontiers Focus Topic | Tuesday Sessions |
| Session EN+EM+NS-TuA |
| Session: | Charge Storage Materials and Devices |
| Presenter: | Malakhi Noked, University of Maryland, College Park |
| Authors: | M. Noked, University of Maryland, College Park M.A. Schroeder, University of Maryland, College Park A.J. Pearse, University of Maryland, College Park C. Liu, University of Maryland, College Park A.C. Kozen, University of Maryland, College Park S.B. Lee, University of Maryland, College Park G.W. Rubloff, University of Maryland, College Park |
| Correspondent: | Click to Email |
Electrochemical power sources based on metal anodes have specific energy density much higher than conventional Li ion batteries, due to the high energy density of the metal anode (3842mAh/g1 for Li). Rechargeable Li-O2 batteries consume oxygen from the surrounding environment during discharge to form Li oxides on the cathode scaffold, using reactions
(1) [anode] Li(s) ↔ Li+ + e−
(2) [cathode] Li+ + ½ O2 (g)+ e− ↔ ½ Li2O2 (s), ~2.959 V vs Li/Li+
(3) [cathode] Li+ + e− + ¼ O2 (g) ↔ ½ Li2O (s), ~ 2.913 V vs Li/Li+
The cathode reaction requires large over-potentials for charging due to the mass transfer resistance of reagents to the active sites on its surface, decreasing the round trip efficiency, making recharge of the Li-O2 cell difficult. To overcome these problems, the cathode needs good electrical conductivity and a porous structure that enables facile diffusion of oxygen and can accommodate the reduced oxygen species in the pores.
Two significant challenges exist in the use of the traditional activated carbon material as the cathode of the Li-O2 system. First, in the presence of Li2O2 the carbon electrode becomes relatively unstable even at low voltages (~3V). Second, cathode structures must be porous to accommodate a substantial amount of Li–peroxide (Li2O2) without blocking ion transport channels in the cathode. While a few studies have been reported on the effect of catalyst on the onset potentials for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in the Li-O2 cell, the results were inconclusive due to the lack of systematic study in a single system and conditions.
We report here results from a model cathode system which enable determination of the effects of various catalysts on the OER/ORR reactions in the non-aqueous Li-O2 cell. Mesoporous CNT sponge is used as the model cathode material, decorated with catalyst nanoparticles by nucleation-controlled atomic layer deposition (ALD) of Ru, RuO2, MnO2, and Pt catalyst components whose loading and composition are controlled by manipulating the ALD conditions. Using a custom Li-O2 battery cell, we have studied the effect of different catalysts on the voltage of the OER and ORR, and on the cycling performances of the cell. We demonstrate a Li-O2 cell that sustains >3000 mAhgc-1 over more than 15 cycles at current density of 200 mAgc-1. To our knowledge, this is the first comparison of a variety of catalysts with a well-defined morphology (controlled by ALD and monitored by TEM), and under the same electrochemical conditions.