Supercapacitors based on Partial pyrolysis of Polyacrylonitrile
1
Pyrolysis temperature / o C 400 500 600 700 800 900 Surface area /m 2 g -1 0 200 400 600 800 1000 1200 PAN swelled in DMF and mixed with Na 2 CO 3 (immediate cooling) PAN swelled in DMF and mixed with Na 2 CO 3 (pyrolysed for 2 hours) PAN swelled in DMF and mixed with milled Na 2 CO 3 (pyrolysed for 2 hours) PAN swelled in DMF and mixed with Na 2 CO 3 (pyrolysed for 4 hours) PAN swelled in DMF (pyrolysed for 2 hours) PAN only (immediate cooling) Surface area /m 2 g -1 0 500 1000 1500 2000 Capacitance /F g -1 0 100 200 300 400 500 600 Undoped Doped Supercapacitors based on Partial pyrolysis of Polyacrylonitrile M.Brittin,(1), F.J. Davis,(1), E. Eweka(2) (the late) A. Gilmour,(3), C.O. Giwa(3) G.R. Mitchell (2) and A.G. Ritchie(3) (1) Polymer Science Centre, University of Reading, RG6 6AD, (2) QinetiQ Limited, Haslar, Gosport, Hampshire, PO12 2AU, (3) Lexcel Technology Limited, Henley-on-Thames, Oxon., RG9 1LU 1. Introduction 6. Acknowledgements 5. Devices Conducting polymers are versatile materials that offer promise in a range of applications[1]. Previously we have been interested in the electro-chemical production of such materials since the properties may be controlled by control of electrochemical parameters (voltage, charge passed etc.)[2], or in some cases by simply the appropriate choice of counter-ion [3]; more complex properties may be introduced by chemical substitution [4]. Recently, as part of the UK vehicle foresight programme we have been involved in turning our experiences to the development of electrochemical capacitors or super-capacitors These are novel power devices with long cycle life (typically > 100,000 cycles) and energy storage capabilities, which are higher than those of conventional double layer capacitors. Super-capacitors are of particular application in electric vehicles, where they can be used to supply peak loads or to absorb electrical charge, e.g. during regenerative braking. Most super-capacitors use a high surface area carbon with a sulphuric acid electrolyte. Though materials such as polypyrrole-based composites [5] offer some advantages, from a commercial point of view a particularly attractive route to provide high capacitance materials is to use a system based on complexation between nitrogen atoms in nitrogen - containing polymers with sulphur trioxide [6]. [1] D. Kumar and R. C. Sharma European Polymer J., 1998, 34(8), 105. [2] F.J. Davis, H. Block, and R.G. Compton, J. Chem. Soc. Chem. Commun., [3] A. Kassim, H. Block, F.J. Davis, and G.R. Mitchell, J. Mater. Chem.., 1992, 2, 987. [4] P.J. Langley, F.J. Davis, and G.R. Mitchell, J.Chem. Soc, Perkin Transactions, 1997, 2229. [5] J.H. Kim, A.K. Sharma, and Y.S. Lee, Materials Letters, 2006, 60, 1697. [6] R. A. A. Gilmour , Non-aqueous electrochemical cell containing conjugated polyimine functionality coupled to sulphur trioxide, Patent no GB2335073, 8th September 1999. 2.Thermal Restructuring of Polyacrylonitrile We thank the EPSRC and the DTI for funding this programme (GR/M86613b) . We should also like to acknowledge additional contributions from Hawker Batteries and HILTech Developments Limited. 3. Nitrogen content N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N < 3 0 0 °C 3 0 0 - 5 0 0 °C 5 0 0 - 6 0 0 °C 6 0 0 - 8 0 0 °C Polyacrylonitrile (PAN) is a low cost, readily available commercial material When heated to high temperature, a chemical reaction takes place which causes a structural rearrangement in the polymer. As a result, the polymer becomes conducting: Nitrogen in Exhaust gasesout Tubular furnace Porcelain boat containing polym er Sealed glasstube Pyridinic nitrogen atoms in the polymer can be used as sites for chemical doping (e.g. using lithium sulphite, Li2SO3): N N N N N N + Li 2 SO 3 SO 3 SO 3 SO 3 Before pyrolysis, samples are white discs After pyrolysis at 200 o C, samples have turned yellow After pyrolysis at 300 o C, samples have turned black and undergone a small decrease in volume After pyrolysis at temperatures of 400 o C and above, samples become gradually smaller and increasingly misshapen 4. Surface Area 0 100 200 300 400 500 600 700 800 900 0 10 20 30 40 50 60 70 80 N C H Pyrolysistem perature / o C Proportion ofelem entpresent w ith respectto each sam ple /w t% Relative proportions of carbon, nitrogen and hydrogen determined by combustion of samples at high temperatures. As the temperature increases, gradually more nitrogen and hydrogen are lost, with the proportion of carbon present increasing as a result SO3 DOPING Tested small sample (~2 g): immersed in liquid SO 3 for 1 day. Combustion analysis carried out on doped and undoped samples Undoped Doped % C 71.80 54.98 % H 1.50 2.12 % N 18.05 16.34 % S 0.00 3.75 CHN ANALYSIS XPS DATA During restructuring, nitrogen is lost from the polymer Nitrogen can exist in various forms; however, only pyridinic nitrogen is suitable for chemical doping XPS has been used to determine how much is present Binding energy /eV 390 392 394 396 398 400 Counts 2000 2500 3000 3500 4000 4500 5000 5500 "N -6" "N -5" "N -Q" Pyrolysi s temperat ure / o C N in unreact ed CN groups / % Pyridin ic-N / % Pyrroli c-N / % Quatern ary-N / % - 100 0 0 0 400 7.1 60.1 32.8 0.0 500 0.0 52.4 46.3 0.6 600 0.0 47.1 31.8 20.3 700 0.0 40.9 35.7 22.5 Pyrolysistem perature / o C 0 200 400 600 800 Am ountofnitrogen present/w t% 0 5 10 15 20 25 30 Am ountofpyridinic-N present/w t% 0 5 10 15 20 25 30 TotalN Pyridinic-N N N N “N-6” “N-5” “N-Q” Additive PAN: Pyrolysis Surface Additive temperature/ o C area /m 2 g -1 Carbazole 1:2 500 1.2 TMAI 1:2 500 1.3 PEG 1:3 750 72 C black 1:1 750 480 Na 2 CO 3 1:3 750 930 To increase the surface area, PAN was pyrolysed in the presence of a series of compounds. These included sodium chloride, sodium carbonate oxalic acid, polyethylene glycol, polyethylene oxide, carbazole, and tetra- methylammonium iodide SUPER C PRODUCTION PAN, binder, carbon, lithium sulphite Binder dissolved in solvent slurry coated by doctor blade process in inert atmosphere Propylene carbonate / LiBF4 electrolyte, tin / copper oxide negative electrode Under suitable pyrolysis conditions and doping with sulphite, we observed a specific capacitance of > 300 F/g pyrolysed PAN and an energy density > 50 Wh/kg. The cycle life of the PAN electrodes was evaluated using conventional cycling techniques. High surface area and high nitrogen content have been identified as being necessary to achieve high capacitance A high surface area material has been produced This shows high levels of capacitance, particularly when doped with Li 2 SO 3 . CONCLUSION
description
Supercapacitors based on Partial pyrolysis of Polyacrylonitrile M.Brittin,(1), F.J. Davis,(1), E. Eweka(2) (the late) A. Gilmour,(3), C.O. Giwa(3) G.R. Mitchell (2) and A.G. Ritchie(3) - PowerPoint PPT Presentation
Transcript of Supercapacitors based on Partial pyrolysis of Polyacrylonitrile
Pyrolysis temperature / oC
400 500 600 700 800 900
Sur
face
are
a / m
2 g-1
0
200
400
600
800
1000
1200
PAN swelled in DMF and mixed with Na2CO3 (immediate cooling)
PAN swelled in DMF and mixed with Na2CO3 (pyrolysed for 2 hours)
PAN swelled in DMF and mixed with milled Na2CO3 (pyrolysed for 2 hours)
PAN swelled in DMF and mixed with Na2CO3 (pyrolysed for 4 hours)
PAN swelled in DMF (pyrolysed for 2 hours) PAN only (immediate cooling)
Surface area / m2 g-1
0 500 1000 1500 2000
Cap
acit
ance
/ F
g-1
0
100
200
300
400
500
600
UndopedDoped
Supercapacitors based on Partial pyrolysis of Polyacrylonitrile
M.Brittin,(1), F.J. Davis,(1), E. Eweka(2) (the late) A. Gilmour,(3), C.O. Giwa(3) G.R. Mitchell (2) and A.G. Ritchie(3) (1) Polymer Science Centre, University of Reading, RG6 6AD, (2) QinetiQ Limited, Haslar, Gosport, Hampshire, PO12 2AU,
(3) Lexcel Technology Limited, Henley-on-Thames, Oxon., RG9 1LU
1. Introduction1. Introduction
6. Acknowledgements6. Acknowledgements
5. Devices5. Devices
Conducting polymers are versatile materials that offer promise in a range of applications[1]. Previously we have been interested in the electro-chemical production of such materials since the properties may be controlled by control of electrochemical parameters (voltage, charge passed etc.)[2], or in some cases by simply the appropriate choice of counter-ion [3]; more complex properties may be introduced by chemical substitution [4]. Recently, as part of the UK vehicle foresight programme we have been involved in turning our experiences to the development of electrochemical capacitors or super-capacitors These are novel power devices with long cycle life (typically > 100,000 cycles) and energy storage capabilities, which are higher than those of conventional double layer capacitors. Super-capacitors are of particular application in electric vehicles, where they can be used to supply peak loads or to absorb electrical charge, e.g. during regenerative braking. Most super-capacitors use a high surface area carbon with a sulphuric acid electrolyte. Though materials such as polypyrrole-based composites [5] offer some advantages, from a commercial point of view a particularly attractive route to provide high capacitance materials is to use a system based on complexation between nitrogen atoms in nitrogen - containing polymers with sulphur trioxide [6].
[1] D. Kumar and R. C. Sharma European Polymer J., 1998, 34(8), 105.[2] F.J. Davis, H. Block, and R.G. Compton, J. Chem. Soc. Chem. Commun., 1984, 890.[3] A. Kassim, H. Block, F.J. Davis, and G.R. Mitchell, J. Mater. Chem.., 1992, 2, 987.[4] P.J. Langley, F.J. Davis, and G.R. Mitchell, J.Chem. Soc, Perkin Transactions, 1997, 2229.[5] J.H. Kim, A.K. Sharma, and Y.S. Lee, Materials Letters, 2006, 60, 1697.[6] R. A. A. Gilmour , Non-aqueous electrochemical cell containing conjugated polyimine functionality coupled to sulphur trioxide, Patent no GB2335073, 8th September 1999.
2.Thermal Restructuring of Polyacrylonitrile 2.Thermal Restructuring of Polyacrylonitrile
We thank the EPSRC and the DTI for funding this programme (GR/M86613b) . We should also like to acknowledge additional contributions from Hawker Batteries and HILTech Developments Limited.
3. Nitrogen content 3. Nitrogen content
N N N N N N N N N N N
N
N N N N NN
N N N
N
N
N
N N N N NN N
N
N NN
N
< 3 0 0 ° C 3 0 0 - 5 0 0 ° C
5 0 0 - 6 0 0 ° C
6 0 0 - 8 0 0 ° C
Polyacrylonitrile (PAN) is a low cost, readily available commercial material
When heated to high temperature, a chemical reaction takes place which causes a structural rearrangement in the polymer. As a result, the polymer becomes conducting:
Nitrogenin
Exhaustgases out
TubularfurnacePorcelain boat
containing polymer
Sealedglass tube
Pyridinic nitrogen atoms in the polymer can be used as sites for chemical doping (e.g. using lithium sulphite, Li2SO3):
N N NN N N
+ Li2SO3 SO3 SO3 SO3 Before pyrolysis, samples are white discs
After pyrolysis at 200 oC, samples have turned yellow
After pyrolysis at 300 oC, samples have turned black and undergone a small decrease in volume
After pyrolysis at temperatures of 400 oC and above, samples become gradually smaller and increasingly misshapen
4. Surface Area4. Surface Area
0 100 200 300 400 500 600 700 800 900
0
10
20
30
40
50
60
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80
NCH
Pyrolysis temperature / oC
Pro
port
ion
of e
lem
ent p
rese
ntw
ith
resp
ect t
o ea
ch s
ampl
e / w
t%
Relative proportions of carbon, nitrogen and hydrogen determined by combustion of samples at high temperatures.
As the temperature increases, gradually more nitrogen and hydrogen are lost, with the proportion of carbon present increasing as a result
SO3 DOPING
Tested small sample (~2 g): immersed in liquid SO3 for 1 day. Combustion analysis carried out on doped and undoped samples Undoped Doped% C 71.80 54.98% H 1.50 2.12% N 18.05 16.34% S 0.00 3.75
CHN ANALYSIS
XPS DATA
During restructuring, nitrogen is lost from the polymer Nitrogen can exist in various forms; however, only pyridinic nitrogen is suitable for chemical doping XPS has been used to determine how much is present
Binding energy / eV
390 392 394 396 398 400
Cou
nts
2000
2500
3000
3500
4000
4500
5000
5500"N-6" "N-5"
"N-Q"
Pyrolysis temperature
/ oC
N in unreacted CN groups
/ %
Pyridinic-N/ %
Pyrrolic-N/ %
Quaternary-N/ %
- 100 0 0 0
400 7.1 60.1 32.8 0.0
500 0.0 52.4 46.3 0.6
600 0.0 47.1 31.8 20.3
700 0.0 40.9 35.7 22.5
Pyrolysis temperature / oC
0 200 400 600 800
Am
ount
of
nitr
ogen
pre
sent
/ w
t %
0
5
10
15
20
25
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Am
ount
of
pyri
dini
c-N
pre
sent
/ w
t %
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5
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15
20
25
30
Total N Pyridinic-N
N NN“N-6” “N-5” “N-Q”
Additive PAN: Pyrolysis Surface
Additive temperature/ oC area /m2 g-1
Carbazole 1:2 500 1.2
TMAI 1:2 500 1.3
PEG 1:3 750 72
C black 1:1 750 480
Na2CO3 1:3 750 930
To increase the surface area, PAN was pyrolysed in the presence of a series of compounds. These included sodium chloride, sodium carbonate oxalic acid, polyethylene glycol, polyethylene oxide, carbazole, and tetra-methylammonium iodide
SUPER C PRODUCTION
PAN, binder, carbon, lithium sulphite
Binder dissolved in solvent slurry coated by doctor blade process in inert atmosphere
Propylene carbonate / LiBF4 electrolyte, tin / copper oxide negative electrode
Under suitable pyrolysis conditions and doping with sulphite, we observed a specific capacitance of > 300 F/g pyrolysed PAN and an energy density > 50 Wh/kg. The cycle life of the PAN electrodes was evaluated using conventional cycling techniques.High surface area and high nitrogen content have been
identified as being necessary to achieve high capacitance
A high surface area material has been produced
This shows high levels of capacitance, particularly when doped with Li2SO3.
CONCLUSION
