Graphite Intercalation with
Large Fluoroanions
Dept. of Chemistry and Center for Advanced Materials,
Oregon State University
Intercalation
http://www.cem.msu.edu/~pinnweb/research-na.htm
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Intercalation Hosts
Ion exchange: (fixed charge density)
smectite clay
Nax+y[Al2-yMgySi4-xAlxO10(OH)2]
layered double hydroxide
[Mg3Al(OH)8]Cl
metal phosphorous sulfide
K0.4[Mn0.80.2PS3]
Redox reaction: (variable charge density)
metal dichalocogenide
Lix[MoS2]
layered oxides
Lix[CoO2], Nax[MoO3]
graphite
K[C8], [C24]HF2
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Energetics
For clays – reaction is ion-exchange:
Na+ Mont- + N(R)4+ Cl- (aqu) -> N(R)4+ Mont- + NaCl (aqu)
For graphite – reaction is redox:
Cx + A -> Cx+ A-
ΔHrxn = I (Cx) - Ea (A) - ΔHL
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Graphite structure



Graphite is a
semi-metal,
chemically stable,
light, strong
A
B
A
C-C in-plane = 1.42 Å
Usually (AB)n hexgonal
stacking
Interlayer distance
= 3.354 Å
Source:
http://www.ccs.uky.edu/~ernst/
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Graphite Intercalation
oxidant
+
+
+
-
This is an acceptor-type GIC
Donor-type reduces layers
and intercalates cations
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GIC types
Reduction
M+Cx-
Group 1 except Na
Oxidation
Cx+An-
F, Br3-, O (OH)
BF4-, P  BiF6- , GeF62- to PbF62-, MoF6-, NiF62-, TaF6-, Re  PtF6SO4-, NO3-, ClO4-, IO3-, VO43-, CrO42AlCl4-, GaCl4-,FeCl4-, ZrCl6-,TaCl6Oregon State University
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Staging and dimensions
Ic
=
di + (n - 1) (3.354 Å)
For fluoro, oxometallates di ≈ 8 A,
for chlorometallates di ≈ 9-10 A
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Graphite oxidation potentials
H2O oxidation potential
vs Hammett acidity
Colored regions show
the electrochemical
potential for GIC
stages.
All GICs are
unstable in
ambient
atmosphere , they
oxidize H2O
49%
hydrofluoric
acid
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GIC special issues



Anions must be oxidatively stable
Larger anions could give larger
galleries, wider range of chemistry
GICs that rapidly decompose in air or
aqueous acid are hard to process
further
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CxPFOS - preparation
Cx+ K2Mn(IV)F6 + KSO3C8F17
 CxSO3C8F17 + K3Mn(III)F6
(CxPFOS)
Solvent = aqueous HF
3.35 A
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CxPFOS intercalate structure
Anions selfassemble as
bilayers within
graphite galleries
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PFOS twist angle
Chain twist
defined by
FC-CF tortion
angle
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CxPFOS thermal stability
CxPFOS
80
1.0
60
0.0
40
-1.0
20
0
0
200
400
100
2.0
-2.0
600
power / mW
mass percent
100
14.0
80
11.0
KPFOS
60
8.0
40
5.0
20
2.0
0
-1.0
0
200
400
600
temp / °C
temp / °C
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New syntheses: chemical
method
Cx + K2MnF6 + LiN(SO2CF3)2 1,2 CxN(SO2CF3)2 + K2LiMnF6
oxidant
anion source
1. 48% hydrofluoric
acid, ambient conditions
2. hexane, air dry
GIC
O
O
CF3
S
F3C S N
..
O
O
Oxidant and anion source are separate and changeable.
Surprising stability in 50% aqueous acid.
CxN(SO2CF3)2 chem prepn
4 wks
120
15 min
Inten / arb units
100
12 min
80
x
8 min
60
4 min
2 min
40
1 min
20
0
15 sec
0.1
15
25
35
2 / deg
45
10
100
reaction time
graphite
5
1
1000 1000
0
(h)
55
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New syntheses: N(SO2CF3)2 orientation
F
F
F
F
CxN(SO2CF3)2 echem prepn
6.0
charge
discharge
e
5.0
b
c
a 32
+
V vs Li /Li
d
dQ/dV
4.0
21
3.0
4.30
4.70
V vs Li+/Li
5.10
2.0
0
100
200
300
400
500 100
600
Capacity (mAh/g)
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CxN(SO2CF3)2 - echem prepn
6.0
d
CxPFOS
(b)
V vs Li+/Li
5.5
(a)
b
e
d
5.0
b
c
a
4.5
CxN(SO2CF3)2
4.0
0
100
200
300
400
Charge (mAh/g)
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CxN(SO2CF3)2 anion orientation
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CxN(SO2CF3)2 thermal stability
100
Mass loss / pct
(b)
(a)
80
(c)
LiN(SO2CF3)2
(d)
60
(e)
40
20
0
0
200 400 600 800
t / °C
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Imide (NR2-) intercalates
Anion
MW
di / Å
N(SO2CF3)2
280
8.1
N(SO2C2F5)2
380
8.2
N(SO2CF3)
(SO2C4F9)
430
8.3
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Other intercalated anions
Anion
MW
di / Å
C(SO2CF3)3
411
12.3
SO3C8F17
499
29.5
SO3C10F21
599
33.7
SO3C6F10(C2F5) 461
24.4
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Borate chelate GIC’s
1.13
CxB(O2C2(CF3)4)2
Stage 1
1.12
0.85 nm
CxB(O2C2O(CF3)2)2
Blue: obs
Pink: calc
Stage 2
0.78 nm
T
Unexpected anion orientation - long axis
to sheets
Intercalation rates
Intercalate
Anion
Temp / °C
SO3C8F17
N(SO2CF3)2
N(SO2CF3)(SO2C4F9)
N(SO2CF2CF3)2
C(SO2CF3)3
SO3C6F5
20
20
70
70
70
20, 70
Reaction
half-life / h
10
0.01
100
500
> 1000
no reaction
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GIC ambient stabilities
stage
2
0.5
TFMI
1 / n'
0.4
3
4
5
6
10
0.3
0.2
PFOS
PFEI
nitrate (HF)
0.1
sulfate (HF)
0.0
0.01
bifluoride
1
100
10000
time / h
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Application - IRP strategy
1. Intercalation
2. Removal
3. Optional cycle
Targets
1. increase internal volume and disorder not surface area
2. low residual content
Parameters: intercalate anion, reduction method
(thermolysis, hydrolysis, hydrogenation)
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IRP charge-discharge
irrev
reversible
• GIC is CxPFOS
stage 2
• removal is by
heating under N2
for 3 h
• rate = C / 20
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IRP for Li ion battery anodes
600
capacity, mAh/g
e- + Cx + Li+ = CxLi
rev. after IRP
500
400
NG, rev
300
irrev. after IRP
200
100
NG, irrev
0
0
200
400
600
temp / °C
800 1000
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