Supporting Information
A High Energy Density Li-ion Battery Cathode
Using Only Industrial Elements
Eshaan S. Patheria,
†
Pedro Guzman,
‡
Leah S. Soldner,
†
Michelle D.
Qian,
†
Colin T. Morrell,
†
Seong Shik Kim,
†
Kyle Hunady,
‡
Elena R. Priesen
Reis,
‡
Nicholas V. Dulock,
†
James R. Neilson,
¶
Johanna Nelson Weker,
§
Brent Fultz,
‡
and Kimberly A. See
∗
,
†
†
Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena,
California 91125, United States
‡
Department of Applied Physics and Materials Science, California Institute of Technology,
Pasadena, California 91125, United States
¶
Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523-1872,
United States
§
Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo
Park, California 94025, United States
E-mail: ksee@caltech.edu
1
Contents
Supplementary Note S1: Previous Work on Li
2
FeS
2
. . . . . . . . . . . . . . . . . . . . . .
4
Supplementary Note S2: Unfit Reflections and Superstructure in Li
2
FeS
2
and Li
2.2
Al
0.2
Fe
0.6
S
2
5
Table S1: Elemental Analysis of Li
2
FeS
2
and Li
2.2
Al
0.2
Fe
0.6
S
2
. . . . . . . . . . . . . . . .
6
Table S2: Impurities Ruled Out in sXRD Patterns . . . . . . . . . . . . . . . . . . . . . . .
6
Table S3: First Cycle Charge Fe, S, and Total Oxidation Capacities . . . . . . . . . . . . . .
6
Figure S1: Comparison of Anion Frameworks . . . . . . . . . . . . . . . . . . . . . . . . .
7
Figure S2: First Cycle Replicates of Li
2
FeS
2
, Li
2.2
Al
0.2
Fe
0.6
S
2
, and Li
2.4
Al
0.4
Fe
0.2
S
2
. . . . .
7
Figure S3: GITT of Li
2
FeS
2
, Li
2.2
Al
0.2
Fe
0.6
S
2
, and Li
2.4
Al
0.4
Fe
0.2
S
2
. . . . . . . . . . . . . .
8
Table S4: First Cycle Performance Metrics of Li
2
FeS
2
and Li
2.2
Al
0.2
Fe
0.6
S
2
. . . . . . . . .
8
Figure S4:
C
/10 Cycling Data of Individual Cells . . . . . . . . . . . . . . . . . . . . . . .
9
Figure S5: Representative
C
/10 Galvanostatic Cycles . . . . . . . . . . . . . . . . . . . . .
9
Figure S6: Rate Capability Data of Individual Cells . . . . . . . . . . . . . . . . . . . . . . 10
Figure S7: Representative Galvanostatic Cycles of Rate Capability Tests . . . . . . . . . . . 11
Supplementary Note S3: Additional Fe K-edge XAS Data and Its Limitations . . . . . . . . 12
Figure S8: Additional Fe K-edge XAS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Supplementary Note S4: Long-range Structural Changes in Li
2
FeS
2
and Li
2.2
Al
0.2
Fe
0.6
S
2
. . 14
Figure S9:
Ex-situ
XRD of (0 0 1) Reflection of Li
2
FeS
2
and Li
2.2
Al
0.2
Fe
0.6
S
2
. . . . . . . . 15
Figure S10: Full
Ex-situ
XRD Patterns of Li
2
FeS
2
and Li
2.2
Al
0.2
Fe
0.6
S
2
. . . . . . . . . . . . 16
Supplementary Note S5: Cation Inventory and Capacity Limits of Li
2
FeS
2
and Li
2.2
Al
0.2
Fe
0.6
S
2
17
Figure S11: XRD of ‘Al
0.2
Fe
0.6
S
2
’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Table S5: S Content Before and After Annealing . . . . . . . . . . . . . . . . . . . . . . . 18
Figure S12: Comparison of Crystal Structures of Li
2.2
Al
0.2
Fe
0.6
S
2
and Al
2
FeS
4
. . . . . . . . 19
Figure S13: XRD and Rietveld Analysis Before and After Annealing . . . . . . . . . . . . . 20
Figure S14: Weighted Averages and Weighted Standard Deviations of Isomer Shifts and
Quadrupole Splittings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Figure S15: Mössbauer Data and Fits of Li
2
FeS
2
. . . . . . . . . . . . . . . . . . . . . . . 22
2
Figure S16: Mössbauer Data and Fits of Li
2.2
Al
0.2
Fe
0.6
S
2
. . . . . . . . . . . . . . . . . . . 23
Table S6: All Mössbauer Fit Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Figure S17: Fe K-edge EXAFS First and Second Shells . . . . . . . . . . . . . . . . . . . . 27
Figure S18: Li
2
FeS
2
EXAFS
k
3
χ
(
k
)
Data and Fits . . . . . . . . . . . . . . . . . . . . . . 28
Figure S19: Li
2.2
Al
0.2
Fe
0.6
S
2
EXAFS
k
3
χ
(
k
)
Data and Fits . . . . . . . . . . . . . . . . . . 29
Figure S20: Li
2
FeS
2
EXAFS
k
3
-weighted
|
χ
(
R
)
|
Data and Fits . . . . . . . . . . . . . . . . 30
Figure S21: Li
2.2
Al
0.2
Fe
0.6
S
2
EXAFS
k
3
-weighted
|
χ
(
R
)
|
Data and Fits . . . . . . . . . . . 31
Table S7: All EXAFS Fit Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Figure S22: Parameter-free Mössbauer Centroids of Li
2
FeS
2
and Li
2.2
Al
0.2
Fe
0.6
S
2
. . . . . . 34
Supplementary Note S6: Relative Covalency of (S
2
)
2 –
and S
2 –
with Fe . . . . . . . . . . . . 35
Figure S23: Volumetric vs. Gravimetric Energy Densities of Commercial and Emerging
Li-ion Battery Cathodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Table S8: Relevant Values and References for Energy Densities . . . . . . . . . . . . . . . . 37
3
Supplementary Note S1: Previous Work on Li
2
FeS
2
Li
2
FeS
2
has been studied for decades, first reported by Sharma in 1976
1
and then character-
ized as a cathode
2–7
and spectroscopically interrogated by Mössbauer,
6–9
infrared,
10
and X-ray
absorption
7
all in the 1980s. Later, in 2008, Kendrick and coworkers revisited Li
2
FeS
2
to de-
velop a synthesis using the industrial Li precursor Li
2
CO
3
rather than air-sensitive Li
2
S used for
traditional air-free solid state synthesis.
11
They then evaluated how Li
2
FeS
2
performs versus a
commercial graphite anode, showing an energy density of
≈
740 Wh
·
kg
−
1
with a capacity fade
of
≈
1% per cycle over 70 cycles at
C
/5,
12
and investigated the rate capability versus Li metal.
13
All prior mechanistic studies support distinct, sequential Fe
2+
oxidation to Fe
2+/3+
followed by S
2 –
oxidation during charge. The mechanism of S
2 –
oxidation was suggested to be formation of (S
2
)
2 –
using IR data as evidence.
10
Later, we showed S K-edge X-ray absorption spectroscopy (XAS)
data that definitively shows formation of (S
2
)
2 –
upon oxidation.
14
We refer to these processes
henceforth as ‘Fe oxidation’ and ‘S oxidation’. The electrochemical data suggests that the Fe and
S oxidation capacities are
≈
30 to 40% and
≈
70 to 60% of the total multielectron redox capacity,
respectively.
11–14
We also note that what we refer to as just ‘Fe oxidation’ actually involves remov-
ing electrons from covalent, mixed Fe-S electronic states, with clear involvement of S-based states
that we previously showed computationally and experimentally.
14
We also determined that the Fe
oxidation capacity is limited by an intrinsic stability limit of removing
≈
0.5 to 0.6e
–
per formula
unit from the mixed Fe-S states, after which anion redox proceeds from S-localized nonbonding
3
p
states, removing another
≈
1 to 1.1 e
–
per formula unit (i.e., only
≈
50% of the total S content
participates in anion redox).
14,15
4