Supporting Information: Multielectron, Cation
and Anion Redox in Lithium-Rich Iron Sulfide
Cathodes
Charles J. Hansen,
†
Joshua J. Zak,
†
Andrew J. Martinolich,
†
Jesse S. Ko,
‡
Nicholas H. Bashian,
¶
Farnaz Kaboudvand,
§
Anton Van der Ven,
§
Brent C. Melot,
¶
Johanna Nelson Weker,
‡
and Kimberly A. See
∗
,
†
†
Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena,
California 91125, United States
‡
Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo
Park, California 94025, United States
¶
Department of Chemistry, University of Southern California, Los Angeles, California 90089,
United States
§
Materials Department, University of California, Santa Barbara, California 93106, United States
E-mail: ksee@caltech.edu
Experimental Details
Na
2
S was prepared from stoichiometric Na (Acros Organics, rod, 99.8%, mechanically cleaned
prior to use) and S (see main text) in separate alumina crucibles (Almath) in an evacuated silica
ampoule. The reactants were heated at 1 °C min
−
1
to 300 °C for 48 h and cooled ambiently to
room temperature. The ground product was a fine powder of a slightly tan-color. The product was
determined to be phase pure by XRD.
S1
The
operando
electrochemical cell comprised of a 1.2" (I.D.) stainless steel Swagelok union
with a thin sheet of plastic wrapped around the interior of the cell to prevent the electrodes from
shorting. The stack inside the cell included the Be window and current collector, the free-standing
electrode (cathode), a glass-fiber separator (Whatman, GF/D), a Li foil anode, a spacer, a spring,
and a stainless steel plunger that served as the other current collector. The cell was flooded with
LP100 electrolyte and sealed around the plunger with PTFE ferrules. The cell was placed on the
diffractometer stage such that the X-rays would directly access the cathode after penetrating the Be
window. A VMP3 mutli-channel potentiostat (Bio-Logic) was used to perform the electrochemical
experiments.
Supplemental Tables and Figures
Tables S1-S2 include potential impurities that appear absent from the high-resolution powder X-
ray diffraction (XRD) data for Li
2
FeS
2
and LiNaFeS
2
, respectively. Note that in the tables the
variables x, y, z, and
n
may take on any value corresponding to reported phases in the Inorganic
Crystal Structure Database including 0 (e.g. LiOH is a valid compound under "LiOH
·
n
H
2
O").
Table S1: List of potential impurities not found in Li
2
FeS
2
based on the 11-BM XRD data.
precursors
other sulfides
reaction with tube
air exposure
Fe
FeS
graphite
LiOH
·
n
H
2
O
pyrite-FeS
2
Fe
7
S
8
LiC
6
Li
x
Fe
y
O
z
·
n
H
2
O
Fe
3
S
4
Fe
x
Si
y
O
z
Li
x
Fe
y
(SO
4
)
z
·
n
H
2
O
marcasite-FeS
2
computed Li
2
FeS
2
polymorphs
Table S2: List of potential impurities not found in LiNaFeS
2
based on the 11-BM XRD data.
precursors
other sulfides
reaction with tube
air exposure
Fe
FeS
Fe
x
Si
y
O
z
Fe
x
O
y
S
8
Fe
7
S
8
Li
x
Fe
y
O
z
Li
x
Fe
y
(SO
4
)
z
Li
2
S
Fe
3
S
4
Na
x
Fe
y
O
z
LiOH
·
n
H
2
O
Na
2
S
marcasite-FeS
2
NaOH
·
n
H
2
O
Na
pyrite-FeS
2
Li
x
Fe
y
(SO
4
)
z
·
n
H
2
O
Na
x
Fe
y
S
z
Na
x
Fe
y
(SO
4
)
z
·
n
H
2
O
S2