of 41
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