Supporting Materials
“The Influence of CO2 Poisoning on Overvoltages and
Discharge Capacity in Non-aqueous Li-Air Batteries”
Yedilfana S. Mekonnen1,2, Kristian B. Knudsen1, Jon S. G. Mýrdal1,2, Reza Younesi1, Jonathan
Højberg1, Johan Hjelm1, Poul Norby1, Tejs Vegge1,2,a
1
Department of Energy Conversion and Storage, Technical University of Denmark,
Frederiksborgvej 399, DK-4000 Roskilde, Denmark.
2
Center for Atomic-scale Materials Design and Department of Physics, Technical University of
Denmark, DK-2800 Lyngby, Denmark
a
Corresponding Author E-mail: teve@dtu.dk
1
Density functional theory (DFT)21-23 as implemented in the GPAW code24 is used to perform the presented
calculations through the atomic simulation environment (ASE).25 GPAW is built on real space grids and nonvalence electrons are described by the projector-augmented wave method (PAW).26,27 Electron exchange and
correlation is approximated by the RPBE functional.28 The stepped (11̅00) Li2O2 surface with a super cell
consisting of a 56-64 atoms slab with a 18 Å vacuum layer between periodic images along the z-axis is used
in this study, as shown below. The k-points are sampled with a (4,4,1) Monkhorst-Pack mesh and 0.15 grid
points. Atomic energy optimization calculations are performed until all forces are less than 0.01 eV/Å.
Energy barriers are calculated by the climbing image nudged elastic band (CINEB) method.29-31
The computational lithium electrode approach is used in the free energy calculations.6,32 Defined as, U = 0,
when bulk Li anode and Li ions in solution (Li+ + e-) are at equilibrium. The free energy change of the
reaction is shifted by −𝑛𝑒𝑈 at an applied bias, where 𝑛 is the number of electrons. The ground state energy
of O2 is calculated from the water reference (𝐸(𝑂2 ) = 2𝐸𝐷𝐹𝑇 (𝐻2 𝑂) − 2𝐸𝐷𝐹𝑇 (𝐻2 ) − 2𝐸𝑒𝑥𝑝 (𝐻2 𝑂)), since
DFT does not describe the triplet ground state of O2 correctly.32 The entropy at STP for O2 and CO2 in the
gas phase are -0.63 and -0.64 eV, respectively. While the entropy for solid phases (Li bulk and Li 2O2) are
assumed to be zero when the free energy is estimated in Fig.2.
FIG S1: The stepped (11̅00) Li2O2 surface with 3x3x2 super cell consisting of a 56-64 atoms slab with a 18
Å vacuum layer between periodic images along the z-axis.
2
Energy barrier for CO2 diffusion: CO2 binds preferentially at the step valley site and weakly binds at the step
ridge site. The CINEB calculations in Figure S2 below shows that once CO2 is adsorbed at step valley site, it
is bound by barriers higher than 3 eV since the CO2 molecule is required to desorb from the surface prior to
re-adsorbing at the step site.
FIG S2. Climbing image Nudged elastic band calculations for CO2 migration from less favorable terrace
site (left) to more favorable step valley site (right) on stepped (11̅00) Li2O2 surface with energy barrier
above 3 eV.
3
a)
b)
FIG S3: The average discharge and charge curves of each of the three atmospheric conditions (0, 1 and 50 %
CO2) are taken from the three cells measurements at 127.3 µA/cm2.
4
FIG S4: A Complete Galvanostatic charge profiles at 127.3 µA/cm2 (solid) and 63.6 (dotted) µA/cm2
(dotted) at three different atmospheres: 50 % CO2, 1 % CO2 and 0 % CO2.
FIG S5. Evolution of O2 and CO2 as a function of time during a constant current charge following a constant
current discharge to 2 V. The current of both charge and discharge was 100 µA/cm2. The tested cell is
Li|DME+1M LiTFSI|P50 carbon paper. The measurement is performed with a differential electrochemical
mass spectrometer.
5