Supporting Information
Superstructure in the Metastable Intermediate-Phase Li2/3FePO4
Accelerating the Lithium Battery Cathode Reaction**
Shin-ichi Nishimura, Ryuichi Natsui, and Atsuo Yamada*
anie_201501165_sm_miscellaneous_information.pdf
Experimental
Sample Preparation
Li2/3FePO4 was prepared by quenching a stoichiometric mixture of triphylite, LiFePO4 and
heterosite, FePO4, from 623 K to room temperature. LiFePO4 was prepared using the
solid-state reaction method. Because a Li-deficient composition suppresses the nucleation of the
Li-rich phase, the molar ratio of LiFePO4 : FePO4 was set at 3 : 2 to prevent spontaneous phase
separation. Lithium carbonate (Wako, > 99%), iron(II) oxalate dihydrates (FeC2O4·2H2O)
(JUNSEI, > 99%), and diammonium hydrogen phosphate ((NH4)2HPO4) (Wako, > 99%) were
stoichiometrically weighed and thoroughly mixed using high-energy ball milling for 6 h with
acetone. This mixture was heated at 973 K for 6 h under the flow of argon gas. FePO4 was
prepared by chemical oxidation of LiFePO4 with nitronium tetrafluoroborate (NO2BF4)
(Aldrich, > 95%) as an oxidizing agent. A two-fold excess of NO2BF4 was dissolved in
acetonitrile before adding the LiFePO4 powder, and stirred for 24 h with Ar gas bubbling. The
mixture was filtered and washed several times with acetonitrile before drying the oxidized
powder under vacuum. LiFePO4 and FePO4 were thoroughly mixed with agate mortar and
pestle, and were subsequently sealed in a quartz glass tube under vacuum. The sealed sample
was heated to 623 K overnight and subsequently quenched by dropping in cold water.
X-ray and Neutron Diffraction
The neutron diffraction data were collected at ambient temperature using a high- throughput
neutron powder diffractometer (iMATERIA) at J-PARC. The quenched sample was ground and
loaded into a cylindrical vanadium sample container. Data from the backscattering detector
bank were summed and corrected for the incident neutron spectrum and detector efficiency. A
time-of-flight range of 1000-38000 µs was used for analysis.
Synchrotron X-ray diffraction experiments were conducted under an ambient atmosphere with a
high-resolution powder diffractometer, which was installed at beam-line 4B2 of Photon Factory,
High Energy Accelerator Research Organization (KEK), in Tsukuba, Japan. The incident beam
from the bending magnet source was monochromated by a double-crystal Si (111)
monochromator, and the diffraction data were collected using a multiple-detector system with
six scintillation counters. Ge(111) analyzing crystals were used to determine the angular and
energy resolutions. The wavelength was calibrated to 1.197142 Å using powder diffraction data
from NIST SRM640c.
The collected data were analyzed using the Rietveld method with the TOPAS - Academic
computer program, Ver. 4.1. The coherent scattering length adopted for Rietveld refinements
were −1.90 fm for Li, 9.45 fm for Fe, 5.13 fm for P, and 5.803 fm for O. The lithium positions
were constrained to the original special position (4a) of the Pnma setting.
No unusual weightings were used for the X- ray-neutron simultaneous refinement. The crystal
structures were visualized using the VESTA software.[27]
Electron diffraction
The powdered sample was dispersed in acetone by ultrasonication. The dispersed liquid was
dropped onto a holly micro-grid that was supported on a copper mesh. The SAED patterns were
recorded using a JEOL JEM-2100 that was operated at 200 kV. A Gatan ORIUS SC200D was
used for imaging.
Table S1 Crystallographic information of the metasbale intermediate phase Li0.6FePO4.
Chemical formula
Li0.67(4)FePO4
Mr
155.54 (15)
Crystal system, space group
Monoclinic, P21/n (c-unique)
Temperature (K)
298
a, b, c (Å)
11.8389 (1), 17.80634 (13), 4.73673 (3)
α, β, γ (°)
90, 90, 120.4908 (10)
V (Å3)
860.45 (1)
Z
12
Radiation type
Synchrotron, λ = 1.197142 Å
Rwp
0.0813 (x-ray), 0.0458 (neutron)
Rp
0.0662 (x-ray), 0.0351 (neutron)
GoF
2.13 (x-ray), 2.68 (neutron)
RBragg
0.0438 (x-ray), 0.0184 (neutron)
Table S2 Fractional coordinates parameters of the metastable intermediate phase
Li0.6FePO4.
x
y
z
Biso / Å
Occ. (<1)
Li1
2a
0
0
0
1
0.40 (6)
Li2
2d
0
1/2
0
1
0.63 (6)
Li3
4e
0
1/3
0
1
0.82 (3)
Li4
4e
0
1/6
0
1
0.68 (3)
Fe1
4e
0.2829 (4)
0.8452 (2)
0.0317 (7)
0.2829 (4)
Fe2
4e
0.2839 (3)
0.5089 (2)
0.0191 (5)
0.2839 (3)
Fe3
4e
0.2761 (3)
0.1761 (2)
0.0351 (7)
0.2761 (3)
P1
4e
0.0912 (7)
0.7794 (4)
0.5787 (11)
0.0912 (7)
P2
4e
0.1006 (6)
0.4522 (4)
0.5798 (11)
0.1006 (6)
P3
4e
0.0970 (7)
0.1157 (4)
0.5857 (11)
0.0970 (7)
O11
4e
0.1001 (7)
0.7798 (4)
0.2639 (15)
0.1001 (7)
O12
4e
0.1220 (6)
0.4559 (4)
0.2616 (13)
0.1220 (6)
O13
4e
0.9039 (6)
0.8793 (4)
0.7374 (13)
0.9039 (6)
O21
4e
0.5399 (7)
0.0951 (4)
0.1748 (13)
0.5399 (7)
O22
4e
0.5434 (8)
0.7627 (5)
0.1985 (13)
0.5434 (8)
O23
4e
0.5538 (7)
0.4397 (4)
0.1912 (13)
0.5538 (7)
O31
4e
0.1594 (7)
0.8765 (4)
0.7140 (13)
0.1594 (7)
O32
4e
0.1838 (6)
0.5432 (4)
0.7186 (13)
0.1838 (6)
O33
4e
0.1633 (7)
0.2046 (4)
0.7352 (13)
0.1633 (7)
O34
4e
0.8318 (7)
0.2592 (4)
0.2621 (16)
0.8318 (7)
O35
4e
0.8278 (7)
0.9289 (4)
0.3052 (10)
0.8278 (7)
O36
4e
0.8352 (7)
0.5963 (4)
0.2602 (15)
0.8352 (7)
Figure S1 Schematic illustration unit cell of LiFePO4 (left) and Li0.6FePO4 (right). The
superstructure is superposed to the fundamental unit cell.
Relative Transmission / -
1.0
0.9
0.8
Observed
Calculated
Fe(II)
Fe(III)
0.7
-4
0
2
4
6
Velocity / mm s-1
0
Figure S2
-2
57
Fe Mössbauer spectrum of the Li0.6FePO4 at room temperature. Valence
state of Fe are fluctuated to Fe(II) and Fe(III). Large χ2 and residual
difference suggest existence of charge relaxation effects, whereas such
effects were neglected for clarity.
Table S3 Refined parameters used for Mössbauer spectrum of Li0.6FePO4.
Isomershift
Quadrupole splitting
Line Width
δ / mm·s-1
ΔEQ / mm·s-1
/ mm s–1
Fraction
Fe(II)
1.1758(5)
3.0474(11)
0.3047(15)
0.588(3)
Fe(III)
0.4972(8)
1.3872(16)
0.3047(15)
0.412(2)
(Normalized χ2 = 8.35)
Table S4 Fe—O bond length and bond valence sum (BVS) values. The BVS parameters
r0 = 1.734 for Fe2+ and 1.759 for Fe3+ respectively.
Fe1—O32
2.022 (6) Å
Fe1—O21
2.055 (7)
Fe1—O34
2.129 (7)
Fe1—O34
2.163 (8)
Fe1—O11
2.166 (8)
Fe1—O31
2.354 (6)
<Fe1—O>
2.148
BVS
2.035 (Fe2+)
Fe2—O23
1.934 (7)
Fe2—O35
1.935 (6)
Fe2—O12
2.011 (7)
Fe2—O31
2.019 (6)
Fe2—O32
2.130 (6)
Fe2—O36
2.137 (8)
<Fe2—O>
2.028
BVS
2.779 (Fe2+)
Fe3—O33
2.093 (7)
Fe3—O36
2.111 (7)
Fe3—O13
2.131 (6)
Fe3—O22
2.149 (8)
Fe3—O33
2.179 (7)
Fe3—O35
2.296 (6)
<Fe3—O>
2.160
BVS
1.927 (Fe2+)
2.177 (Fe3+)
2.973 (Fe3+)
2.062 (Fe3+)