Transcript Carbon Materials for Supercapacitor Application Chris Miller Electrolytic Capacitors Electric Double Layer Capacitor (EDLC) (aka Supercapacitor)

Carbon Materials for
Supercapacitor Application
Chris Miller
Electrolytic Capacitors
Electric Double Layer Capacitor (EDLC)
(aka Supercapacitor)
Batteries vs Supercaps
• Batteries
– Charge storage mechanism is chemical
– high energy
• discharge over hours, i.e. phone or computer batteries
– Low power
• Hybrid cars switch to gasoline when accelerating
• Supercapacitors
– Charge storage mechanism is purely physical
• Charges stored electrostatically on surface
• Porous materials provide extremely high surface area ~2000
m2/g
• Very fast charge / discharge ~seconds
• High power, low energy density
Ragone Plot
Specific power against
specific energy, also called a
Ragone plot, for various
electrical energy storage
devices. If a supercapacitor
is used in an electric vehicle,
the specific power shows
how fast one can go, and
the specific energy shows
how far one can go on a
single charge.
P. Simon, Y. Gogotsi. Nature Materials 7, 845 - 854 (2008)
Carbon Onions
• Annealed nanodiamond 1300 °C – 1800 °C in
high vacuum ~10-6 torr
• Extremely fast charge / discharge rates ~10 ms
Carbon Onions
Moderate surface area ~500 m2/g
Moderate capacitance ~50 m2/g
High conductivity ~4 S/cm
Transmission Electron Microscopy (TEM)
Carbon Black
Low surface area ~80 m2/g
Low specific capacitance ~2 F/g
High conductivity ~10 S/cm
Activated Carbon
Looks like Swiss cheese
Surface area ~2000 m2/g
Low conductivity ~0.5 S/cm
High capacitance ~150 m2/g
VERY high surface area due
to porous structure gives it
high capacitance
Cyclic Voltammetry
0.8
0.6
0.5
0.4
0.3
0.2
0.1
0
0
1
2
3
4
5
6
Time ( s )
7
8
9
10
6
4
I ( µA )
Voltage ( V )
0.7
2
0
-2
-4
-6
0
0.2
0.4
Voltage ( V )
0.6
0.8
Comparing Materials
Carbon Onions 1300 C
Carbon Onions 1800 C
Carbon Black
Activated Carbon
25
20
Current ( µA )
15
10
5
0
-5
-10
-15
-20
0
0.1
0.2
0.3
0.4
Voltage ( V )
Peak Current
Capacitanc e 
Scan Rate
0.5
0.6
0.7
0.8
Research Project
• Supercapacitors are currently being produced
commercially from Activated Carbon that is
doped with 5-15% Carbon Black.
• The Carbon Black increases the conductivity of
the electrodes, which decreases the charging
time.
• Carbon Onions could potentially replace
Carbon Black as an additive to Activated
Carbon in supercapacitors.
Glove Box
• Testing was
performed in a
glovebox.
• Environment was
free of water and
oxygen which can
react with the
electrolyte.
• Lack of dexterity
and required
processes make
progress very slow!
Research Project (continued)
• Electrodes were made from Activated Carbon
that were doped with Carbon Black (5, 10 and
15%) as well as Carbon Onions (5, 10, and
15%).
• Tests are still being conducted, but the data
appears to show that the carbon onion doped
electrodes outperform their carbon black
counterparts.
Lesson Plan- Experiment 1
• Materials:
– Several capacitors with a variety of capacitances
– LED Light Bulbs
– “D” Batteries
– Resistor
– Wires
• Students will build circuits containing a
capacitor, an LED, and a battery to determine
how capacitors function.
Lesson Plan- Experiment 1 (cont)
• When the circuit is connected the bulb will
initially be on, but as the capacitor becomes fully
charged, the light will go out.
• At this point the students will remove the battery
from the circuit and allow the capacitor to
discharge its electrical energy through the LED
light.
• Again, the bulb will initially be on, but when the
capacitor becomes fully discharged, it will go out.
Lesson Plan- Experiment 1 (cont)
• The students will time how long it takes for
the capacitor to charge and discharge.
• This experiment will be repeated with a
number of different capacitors.
• The students will then be able to plot a graph
of “charging time vs. capacitance” and explain
how the capacitance affected the amount of
energy stored.
Lesson Plan- Experiment 2
• Materials:
– Aluminum Foil
– Paper
– Multimeter
• The students will build very simple “parallel
plate” capacitors by placing a piece of paper
between two sheets of aluminum foil.
Lesson Plan- Experiment 2 (cont)
• The students will cut out 5 pairs of aluminum
foil squares, varying in size.
• The students will place a sheet of paper
between a pair of aluminum foil squares, thus
creating a capacitor.
• A multimeter will then be used to measure
the capacitance of each simple capacitor.
Lesson Plan- Experiment 2 (cont)
• Students will plot a graph to show the
relationship between surface area and
capacitance.
• Students will then discuss why nanomaterials
that are porous could be used to create better
capacitors.
Lesson Plan- Experiment 3
• Students will make supercapacitors in the lab
using ground charcoal, salt water, aluminum
sheets, and tissue paper.
• Students will hook these capacitors up to an
LED to see the energy that has been stored in
the device.
• Students will also test their aluminum a
aluminum foil capacitor with a LED for
comparison.
Outreach Plan
• I hope to incorporate research into the robotics
club at my school through a partnership with
faculty at Drexel University.
• This will allow students to conduct research on
robotic components. I believe giving students an
authentic research opportunity will help them
understand the nature of science and encourage
them to pursue STEM fields in the future.
• Currently the club only truly meets during three
months in the winter, so there is a great deal of
room to grow the program.