Supercapacitors for Automotive Applications/file/PHall.pdf · Supercapacitors •Store energy...
Transcript of Supercapacitors for Automotive Applications/file/PHall.pdf · Supercapacitors •Store energy...
Supercapacitors for Automotive Applications Peter J Hall, Anthony J R Rennie, Vitor L Martins, Roberto M Torresi* Chemical Engineering, U Sheffield, UK * Chemistry, U Sao Paulo, Brazil
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Three Questions:
1. What are supercapacitors?
2. Why are they not routinely used in automotive power trains?
3. What are we doing about it?
WHAT ARE SUPERCAPACITORS?
1st Question
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Supercapacitors • Store energy
electrostatically through the separation of ions at a surface (~1nm)
• Colossal electrode surface area ~1000’s m2: ~kF devices are possible
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Supercaps can reduce the size of battery packs
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WHY ARE SUPERCAPS NOT USED MORE BROADLY?
2nd Question:
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Problems with Supercaps
• Typical Maxwell Unit (BCAP0350): • 350F, 9.5 kW kg-1 but 5.9 Wh kg-1 (ESR 3.2 mΩ)
• Acetonitrile electrolyte (metabolised to HCN), volatile
• Energy density is too low for many practical automotive applications
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WHAT ARE WE DOING ABOUT IT?
Question 3:
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Improvements:
• Use electrolytes with higher ESW • E = ½ C (Vmax – Vmin)2
• Vmax acetonitrile = 2.85 V
• Vmax ionic liquid = 3.9 V (240% increase in specific energy if Vmin = 0.9 V)
• Use controlled porosity polymer-derived carbons
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[Pyr14] [Tf2N]
N-n-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl) imide
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Operating voltage 3.6-3.9V Specific energy up to 30 Whkg-1
Typically operated at 60ºC
Sulfonium based cations
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Triethylsulfonium
[S222]
Diethylmethylsulfonium
[S221]
Diethylpropylsulfonium
[S223]
Physical characteristics
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Ionic Liquid Td [ºC]
Tm [ºC]
δ [g cm-3]
η [mPa s-1]
σ [mS cm-1]
[Pyr14][Tf2N] 445 -6.5 1.40 78 3.0
[S221][Tf2N] 295 -11.7 1.50 41 6.7
[S222][Tf2N] 290 -17.6 1.46 34 7.3
[S223][Tf2N] 280 -6.4 1.42 38 5.5
H2O < 10ppm
Performance
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J. Phys. Chem. C 2015, 119, 23865-23874
Conclusions
• Ionic liquids are ideal bases for supercapacitors for automotive applications
• Carbon porosity needs to be tailored to match electrolyte
• Latest research shows that poly ionic liquid binders can increase energy density
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