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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. Intercalation Hosts. Ion exchange: (fixed charge density) - PowerPoint PPT Presentation
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Graphite Intercalation with Large Fluoroanions
Dept. of Chemistry and Center for Advanced Materials, Oregon State University
Oregon State University 2
Intercalation
http://www.cem.msu.edu/~pinnweb/research-na.htm
Oregon State University 3
Intercalation HostsIon exchange: (fixed charge density)
smectite clay Nax+y[Al2-yMgySi4-xAlxO10(OH)2]
layered double hydroxide [Mg3Al(OH)8]Clmetal phosphorous sulfide K0.4[Mn0.80.2PS3]
Redox reaction: (variable charge density)
metal dichalocogenide Lix[MoS2]
layered oxides Lix[CoO2], Nax[MoO3]
graphite K[C8], [C24]HF2
Oregon State University 4
EnergeticsFor 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
Oregon State University 5
Graphite structure C-C in-plane = 1.42 Å Usually (AB)n hexgonal
stacking Interlayer distance
= 3.354 Å
Source: http://www.ccs.uky.edu/~ernst/
A
B
A
Graphite is a semi-metal, chemically stable, light, strong
Oregon State University 6
Graphite Intercalation
-+
-+
-+
oxidant
This is an acceptor-type GICDonor-type reduces layers and intercalates cations
Oregon State University 7
GIC typesReduction M+Cx
-
Group 1 except Na Oxidation Cx
+An-
F, Br3-, O (OH)
BF4-, P BiF6
- , GeF62- to PbF6
2-, MoF6-, NiF6
2-, TaF6-, Re PtF6
-
SO4-, NO3
-, ClO4-, IO3
-, VO43-, CrO4
2-
AlCl4-, GaCl4-,FeCl4-, ZrCl6-,TaCl6-
Oregon State University 8
Staging and dimensions
Ic = di + (n - 1) (3.354 Å)
For fluoro, oxometallates di ≈ 8 A, for chlorometallates di ≈ 9-10 A
Oregon State University 9
Graphite oxidation potentials
H2O oxidation potential vs Hammett acidity
Colored regions show the electrochemical potential for GIC stages.
0.9
1.1
1.3
1.5
1.7
-7 -5 -3 -1 1 3 5
H0
E /
V
stage 1 GIC
stage 2
stage 3
high stage
no intercalation
49% hydrofluoric acidAll GICs are
unstable in ambient atmosphere , they oxidize H2O
Oregon State University 10
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
Oregon State University 11
CxPFOS - preparationCx+ K2Mn(IV)F6 + KSO3C8F17
CxSO3C8F17 + K3Mn(III)F6
(CxPFOS)
Solvent = aqueous HF3.35 A
Oregon State University 12
CxPFOS intercalate structure
Anions self-assemble as bilayers within graphite galleries
Oregon State University 13
PFOS twist angle Chain twist
defined by FC-CF tortion
angle
Oregon State University 14
CxPFOS thermal stability
0
20
40
60
80
100
0 200 400 600
temp / °C
mas
s pe
rcen
t
-2.0
-1.0
0.0
1.0
2.0
pow
er /
mW
0
20
40
60
80
100
0 200 400 600
temp / °C
-1.0
2.0
5.0
8.0
11.0
14.0
KPFOSCxPFOS
New syntheses: chemical method
N SO
OCF3S
O
OF3C ..
Cx + K2MnF6 + LiN(SO2CF3)2 CxN(SO2CF3)2 + K2LiMnF6oxidant anion source GIC
1,2
1. 48% hydrofluoric acid, ambient conditions2. hexane, air dry
Oxidant and anion source are separate and changeable. Surprising stability in 50% aqueous acid.
Oregon State University 16
CxN(SO2CF3)2 chem prepn
5 15 25 35 45 55
2 / deg
Inte
n / a
rb u
nits
15 sec
1 min
2 min
4 min
8 min
12 min
15 min
4 wks
graphite
0
20
40
60
80
100
120
0.1 1 10 100 1000 10000reaction time (h)
x
New syntheses: N(SO2CF3)2 orientation
F
F
F
F
Oregon State University 18
CxN(SO2CF3)2 echem prepn
2.0
3.0
4.0
5.0
6.0
0 100 200 300 400 500 600
Capacity (mAh/g)
V v
s Li
+ /Li
charge discharge
ab c
d e
100
4.30 4.70 5.10V vs Li+/Li
dQ/d
V
2 13 2
Oregon State University 19
CxN(SO2CF3)2 - echem prepn
4.0
4.5
5.0
5.5
6.0
0 100 200 300 400
Charge (mAh/g)
V vs
Li+ /L
i
(a)(b)
a
b c
d eb
dCxPFOS
CxN(SO2CF3)2
Oregon State University 20
CxN(SO2CF3)2 anion orientation
Oregon State University 21
CxN(SO2CF3)2 thermal stability
0
20
40
60
80
100
0 200 400 600 800
t / °C
Mas
s lo
ss /
pct (a)(b)
(d)
(e)
(c)
LiN(SO2CF3)2
Oregon State University 22
Imide (NR2-) intercalates
Anion MW di / Å
N(SO2CF3)2 280 8.1
N(SO2C2F5)2 380 8.2
N(SO2CF3) 430 8.3
(SO2C4F9)
Oregon State University 23
Other intercalated anionsAnion MW di / Å
C(SO2CF3)3 411 12.3
SO3C8F17 499 29.5
SO3C10F21 599 33.7
SO3C6F10(C2F5) 461 24.4
1.12
0.78 nm
CxB(O2C2O(CF3)2)2
Stage 2
1.13
0.85 nm
Stage 1
CxB(O2C2(CF3)4)2
Borate chelate GIC’s
Blue: obsPink: calc
Unexpected anion orientation - long axis to sheets
T
Oregon State University 25
Intercalation rates Intercalate Temp / °C Reaction Anion half-life / h
SO3C8F17 20 10N(SO2CF3)2 20 0.01N(SO2CF3)(SO2C4F9) 70 100N(SO2CF2CF3)2 70 500C(SO2CF3)3 70 > 1000 SO3C6F5 20, 70 no reaction
Oregon State University 26
GIC ambient stabilities
0.0
0.1
0.2
0.3
0.4
0.5
0.01 1 100 10000time / h
1 / n
'
TFMI
PFOS
PFEI
nitrate (HF)
sulfate (HF)
bifluoride
stage2
345610
Oregon State University 27
Application - IRP strategy
1. Intercalation2. Removal3. Optional cycle
Targets1. increase internal volume and disorder not surface
area2. low residual content
Parameters: intercalate anion, reduction method (thermolysis, hydrolysis, hydrogenation)
Oregon State University 28
IRP charge-discharge
• GIC is CxPFOS stage 2
• removal is by
heating under N2 for 3 h
• rate = C / 20
irrev reversible
Oregon State University 29
IRP for Li ion battery anodes
0
100
200
300
400
500
600
0 200 400 600 800 1000
temp / °C
capa
city
, mA
h/g
NG, rev
NG, irrev
rev. after IRP
irrev. after IRP
e- + Cx + Li+ = CxLi