Transcript 12_3_MAA - OpenWetWare

Brief history of the battery
Battery University online:
First battery
-0.76V vs SHE
0.34V vs SHE
Total voltage: 1.1 V
Energy Storage: Lithium ion
battery
e-
e-
Discharged
state
Discharging
Charged state
Cathode
Anode
= Li+
= LiPF6
C (graphite
anode)
LiC
6 (graphite anode)
FePO4 cathode
LiFePO
4 cathode
o (cobalt
Co
oxide
anode)
Li
oxide
anode)
3O4 (cobalt
2O/Co
CoO2 cathode
LiCoO
2 cathode
Common to all Li ion batteries
•
•
•
•
•
Conducting
current
collectors
Anode
Cathode
Electrolyte
Seperator
Tarascon, J.M. & Armand, M., Nature, 414, (2001)
Conducting current collectors
• Lightweight, typically
metallic
• Chemically resistant
• Stable at cell voltages
Stainless steel anode current collector
Courtesy: Lt. Col. F. John Burpo
Seperators: permeability and
stability
• Must be an
electronic insulator
• Must be ionic
conductor
• Chemically
resistant
• Stable in electrolyte
Read: Arora, P., and Ahengming, Z., Chemical Reviews, 2004, 4419-4462
Electrolyte
• The electrolyte must be a
good ionic conductor, and
an electronic insulator
• Must be stable at
necessary potentials and
temperatures
• Performs minimal side
reactions with electrodes
• Much of battery failure
and degradation is caused
by electrolyte side
reactions
Xu, K., Chemical Reviews, 2004 4303-4417
Safety concerns with current Li ion
batteries drive to higher potential anodes
•
•
•
Safety
improvements
Electrolyte
stabilization
Li dendrite
formation…
Lithium plating and dendrites
Tarascon, J.M. & Armand, M., Nature, 414, (2001)
Xu, K., Chemical Reviews, 2004 4303-4417
Cathode SEI and internal
resistance
• Cathodes can be fouled
by degradation of
electrolyte on the
surface of the material
• For instance Ethyl
carbonate can form
polymeric olefins on the
surface of the electrode
• Typically the SEI is a
poor ion conductor and
will increase the internal
resistance of the battery
Internal resistance
• The internal resistance
increases in the battery
over time
• The actual voltage output
is never exactly the same
when current is being
drawn from the battery as
when there is no current
being drawn
• The higher the internal
resistance is, the lower
the observed voltage will
be when
Internal resistance measurement
3.0
Potential (V)
2.5
2.0
1.5
DV=1.22 V
1.0
0.5
0.0
10
20
30
40
50
I
U
Ri  R
• Measured by intentionally
shorting the battery using a
defined resistor
• Once the internal resistance is
known, the maximum cell
output can be calculated
• Internal resistance is a function
of SEI, electrode conductivity,
and surface area
Time (sec)
DU
I
Ri
U
I sc 
Ri

2.978V
Chemical energy storage
• Cell potential is determined by the difference in Gibbs
free energy of the Lithium in the anode and cathode
• The electrodes must allow ions to flow through them
– This is helped by using layered structures
– Making nanoscale materials
– Coating or percolating the system with conducting material
• How do we measure battery materials?
–
–
–
–
Specific Capacity
Energy
Power
Ragone plot
• Galvanostatic measurement
Chemistries of electrodes
• Most common electrode
system is that of LiCoO2 and
graphite
0.1 V vs. Li
3.8-3.9 V vs. Li
3.7 V total
Characterization
• The cell voltage is
the average voltage
of the discharge
cycle
• LiCoO2 has an
average discharge
voltage of 3.7 V
From Nokia
Other Cathode Materials
LiFePO4
Li2MnSiO4
1. Ohzuku, T.; Brodd, R. J., J.Power Sources 2007, 174, (2), 449-456; 2. Amatucci, G. G.; Pereira, N., J. Fluorine
Chemistry 2007, 128, (4), 243-262; 3. Howard, W. F.; Spotnitz, R. M., J. Power Sources 2007, 165, (2), 887-891.
Capacity calculation on a typical
anode
0


8Li  Co3O4  8e 
4
Li
O

3
Co

2
Ch arg e


Disch arg e
8e  X 95484 A  sec
1hour
1000mA
1mole
X
X
X
1mole
3600sec
1Amp
240.8 g
Capacity calculated for cobalt oxide to be 881 mAh/g
Volume changes in battery
electrodes
•
•
•
•
•
Metallic anodes behave
entirely different from
typical oxide anodes
Typically a metal will form
an alloy with lithium by
formally reducing the
lithium
Failures in metallic
anodes are usually due
to volume changes
Volume changes literally
cause for the electrode to
be destroyed
Most alloying electrodes
are not stable for more
than a couple
charge/discharge cycles
Tirado, J.L., Materials Science and Engineering R 40, 2003, 103-136
Gold or metallic anodes
• Au anode can alloy with lithium (this is not the
same as graphite being plated with lithium
• Phases of gold/lithium alloys
• Ag and Au can have several alloy phases (AgLi9
or Au4Li15)
• There are many systems that can form alloys
with lithium (tin or silicon) but the volumetric
expansion is so great that the electrode is
unstable
• These electrodes are special in that they actually
catalyze the reduction of Li+ to Lio
• This catalysis has various potentials vs. Li metal,
typically around 0.7 V
Alloy forming anodes for Lithium ion batteries
•
Au or Ag : capable of alloying with Li
up to AgLi9 and Au4Li15 at very
negative potential
•
Advantages in minimizing cell voltage
reduction
•
http://www.asminternational.org/
High theoretical capacity
Taillades, 2002, Sold State Ionics
Pure Au viral nanowires
• Plateaus:
– 0.2 and 0.1 V/discharge
– 0.2 and 0.45V/charge
Diameter: ~40 nm, free surface
• Capacity from 2nd cycle
– 501 mAh/g [AuLi3.69]
Discharge/charge curves from the
first two cycles
Au0.9Ag0.1
Au0.5Ag0.5
Au0.67Ag0.33
Gradual changes in potential during
discharge
Capacity at 2nd cycle : 499 for Au0.5Ag0.5
459 for Au0.67Ag0.33
Au0.9Ag0.1
Curve shape
similar with Au
Capacity at 2nd
cycle : 439
Calculating capacity for Gold Anode
Capacity is measured in mAh/g and is a measure of the amount of
current you can get out of your electrode with respect to mass
This will yield an overall capacity of 445.9 mAh/g
Calculating capacity for Gold Anode
Use the theoretical capacity to determine the charge rate
First find the active mass, not everything in the electrode is active
Example: a 2 mg electrode with 20% inactive material (super P and PTFE
binder)
2 mg X 0.8  1.12 mg active material
In order to discharge this electrode over one hour, apply a -0.499 mA current
Coin cell assembly
• Used Mortar and
Pestle to prepare
electrodes
• Added binder to roll
out electrode
• Assemble into coin
cell
Stainless steel anode current collector
Courtesy: Lt. Col. F. John Burpo
Testing battery on Solartron
16 channels for
testing batteries
8 coin cell
testers
Celltest program for
measurement and
analysis
Preparing test schedule
Battery measurements are done on the Solartron using the program Celltest:
In order to test the battery, place in coin cell holder:
Celltest works in a simple order, first make a test schedule, then an experiment, then
run.
Each test schedule will
consist of:
Initial rest that lasts one
minute (this is just to
make sure that the coin
cell is being tested
correctly)
A discharge step
A charge step
Preparing test schedule
Do a 1C charge and discharge
Change to
current control
Constant
for 60
hours
Type in calculated
charge/discharge
current (negative for
discharge)
Preparing test schedule
Measure on change
On “termination” tab jump
to next step based on
voltage:
0.1V for discharge, 2.5V for
charge
Preparing a Celltest experiment
Save data file as
your group name
Select your test schedule to
run on the correct channel
You must set safety limits of 5 V and 4 A, in
case something got connected incorrectly
Calculating actual capacity for Gold Anode
After running the electrode the data that will be available will be: the
negative applied current, the time of the measurement and the
mass of active material
Use the current (in milliAmps), time (in hours) and the mass (in
grams) to determine the actual capacity for your anode
The Ragone chart
Necessary for comparing different energy types
For comparison Gasoline has an energy density of 12 kWh/kg and nuclear fission
can yield 25 billion Wh/kg
The chart plots the total amount of energy stored vs how quickly the energy if made
available
Rate Capability of a-FePO4 nanowire/SWCNTs
conjugate templated on different phages.
Ragone plot showing
improvement in high
power performance
with higher binding
affinity towards SWCNTs
Well-dispersed SWCNTs even with smaller amount alone make better electric wiring to
active materials due to better percolation networks than super p carbon powders.
Y. J. Lee et al., Science 324, 1051 (May, 2009).
Tested 2 V and 4.3 V
Amount of material to provide electricity for
one hour, one day, one week and one month
with no external energy production
Daily short term:
•For short term daily energy
storage, ~50 kg of Li-ion
batteries, will provide all
electrical needs of the average
household
Long term:
•Insolation never drops below
50% of the average throughout
the year (even on the cloudiest
day!), so with >50% energy
production by solar, two 2000
gallon tanks will provide all
electricity required for the three
months of winter if they can be
adequately charged during the
summer months
Helpful websites
• http://www.sandia.gov/ess/About/projects.ht
ml
• http://www.eia.doe.gov/fuelelectric.html
(Nearly all information on energy production
and consumption in the US)
• http://rredc.nrel.gov/solar/old_data/nsrdb/re
dbook/atlas/ (information on solar energy)
• http://www.electricitystorage.org