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Dan Steingart Printing & Electrochemical Engineering Laboratory Department of Chemical Engineering, CCNY

Page 1
Batteries!
Dan Steingart Printing & Electrochemical Engineering Laboratory Department of Chemical Engineering, CCNY
April 21st 2010

Page 2
What is a Battery?

Page 3
A ��Battery�� Is
• A pair of electrochemical reactions in
which electrons are passed through an external circuit
• The external circuit is your device • A cell is one pair • A battery is a series of cell

Page 4
Series vs. Parallel
• In series, potential adds, capacity is
constant
• In parallel, capacity adds, potential is
constant
• Either way the energy is the same • The efficiency/accessibility depends on
your device

Page 5
Electrochemical Reactions
• Are just like any other reaction, but
mediated by an electron transfer
• Just like fuel + oxygen leads is required
for combustion, a battery, internally, undergoes the same process
• only much more controlled

Page 6
Electrochemical Reactions
• Are critical beyond batteries
• Metal Plating • Corrosion • Sensors

Page 7
Batteries vs. Devices
computer, a radio transmitter, and a portable radio. Figure 1) Size of device vs. time
Figure 2) Common battery sizes vs. time

Page 8
Batteries vs. Devices

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Battery Basics

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Battery Ideals
• Chemistry
• Potential • Energy Density • Power Density
• Electrode Volume
• Absolute Energy
• Area of Electrodes
exposed to Electrolyte
• Absolute Power
No reaction No reaction No reaction L ~ 1/Conductivty Storage (volume) + Reaction (surface) A + ne <-> B Storage (volume) + Reaction (surface) C <-> D + ne
Anode (Reductant) Storage)
Current Collector Electrolyte (Ion Transport) Cathode (Oxidant Storage) Current Collector Load (Electron Transport)
Packaging
"+" "-"
- + Charge Discharge Charge Discharge

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Battery Ideals
• The potential of a reaction is determined
by the Gibbs Free Energy of a reaction:
• What determines the Gibbs free energy
is well beyond me
∆G = - nF∆E
n = # of electrons transferred per molecule E = Potential (V) F = Faraday��s Constant (C/mol of electrons) G = Free Energy of Reaction (J)

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Battery Ideals
• The capacity of the anode and cathode
should be balanced to optimize the energy and power density
• However, there are tradeoffs
• The effective capacity of the device can
be modeled using Faraday��s law and the active mass of the limiting electrode

Page 13
Battery Ideals
• The power density is determined by how
fast the slowest reaction involved can occur. The faster the reaction, the faster energy can be spent, the higher the power
• The rate of reaction is determined by the
elements in play
P = E/s
P = Power (W) E = Energy (J) s = Time (s)

Page 14
Battery Ideals
• For any given reaction, having larger
electrodes will increase capacity, and having more area exposed for reaction will improve power delivery
• (Just add batteries in parallel*)
Your Thing
* not quite that easy

Page 15
Battery Realities
Corrosion Corrosion Side Reactions Joule Heating Shape Change Side Reactions Fatigue Shape Change Side Reactions Fatigue Environmental Interactions
Anode (Reductant) Storage)
Current Collector Electrolyte (Ion Transport) Cathode (Oxidant Storage) Current Collector Load (Electron Transport)
Packaging
"+" "-"
- + Charge Discharge Charge Discharge

Page 16
Battery Realities
• The faster a battery can provide its
power, the less time it can sit of a shelf
• Not a hard a fast rule, but generally true for cheaper
cells

Page 17
Battery Realities
• Primary vs. Secondary
• Primary batteries cannot be recharged
• Why do we even bother?
• Cost (your duracell) • Energy Density (your watch battery)
• Why can��t they be recharged?
• All sorts of reasons

Page 18
The ��C�� Myth
• As rates increase over C/5, cheap and
small batteries demonstrate less capacity
• C may mean 50 minutes • 10 C may mean 1 minute
• Dependent on a host of factors
• Internal heating • Diffusion rates • Electrolyte ohmic drops

Page 19
Battery Realities
• Secondary batteries don��t last for ever • When they fail, they are failing because
they are breaking themselves apart to work for you (literally dying for you)
• All secondary batteries except NiCd last
longer when minimally discharged
• Really

Page 20
Battery Nonlinearity
• Batteries are rated for a given capacity
• A good NiMH provides 2500 mAh @ 1.2 V
• C rating is discharge rate, thus
• C/10 (250 mA) = 10 hours to full discharge • C/5 (500 mA) = 5 hours to full discharge • C (2.5 A) = 1 hour (or is it?) • 10 C (25 A) = 6 minute discharge (really?)

Page 21
Battery Non-linearity
• If you to spend X coulombs in Y
seconds, why does it matter if X is getting larger and Y is getting smaller?
• Batteries are non linear devices
• As current draw from a battery increases, the
capacity consumed is disproportionally higher

Page 22
What this means
• To preserve the life of a battery, design
at least 2 hours of battery life into the product
• More on this later

Page 23
Battery Types

Page 24
Battery Comparison
  Energy density [W-hr/kg] Cost [$/W-hr] Cycle life Temperature [K] Notes
Zn-MnO2 55-60 0.05 1-50 Ambient Cheap! Primary (non rechargeable) Lithium Metal 1000 1 1-10 Ambient Best energy density, Primary
Zn-NiOOH
55~80 0.15~ 0.25 ~500 Ambient Relatively high energy density, deep cycling, low cost, limited cycle life Li-ion 100~200 1 ~1200 Ambient High energy density, high cost, difficult to scale Na-S 180 ~0.6 500~2000 620K High Temperature, Molten Na Dangerous Zn-Br
2
30 0.3 2000 Ambient Complex reaction, Bromine Dangerous Lead-Acid 30~50 ~0.4 ~500 Ambient Low energy density, limited cycle life MH-NiOOH 60~75 ~0.4 1000 Ambient Consumer Electronics / Hybrid Vehicles

Page 25
Zn-MnO2
• The backbone of both alkaline and
acidic (zinc-carbon) batteries, though the reaction is different
• As cheap as batteries come • The complexities of various manganese
oxides and zinc morphologies make it hard to recharge
• 1.6 V to 1.1 V over a useful discharge

Page 26
Zn-Air
• By using ambient oxygen as the oxidant,
these batteries provide the best energy density of any system
• Air electrodes are complex beasts, a
��bifunctional�� air electrode does not yet exists
• we��re trying
• Once the battery is activated, reacts to
completion regardless of what you do
• energy vs. corrosion

Page 27
Lithium Metal
• Batteries with a pure lithium negative electrode • High energy density, long lasting
• watch batteries, pace makers
• Low power density by design to improve shelf life • Instability of lithium plating prevents cyclability
• explosive
• Lithium batteries have non-aqueous electrolytes,
cannot be exposed to air or oxygen
• explosive!

Page 28
Lead Acid
• Overall 140 years old • The most common, lowest cost secondary
battery
• Excellent power delivery • Heavy • Poor deep discharge performance
• ~500 cycles
• Nominally ~2 V per cell, dropping to ~1.5
over useful discharge life
http://en.wikipedia.org/wiki/Lead–acid_battery

Page 29
NiMH
• A very popular secondary battery,
second now to lithium ion in consumer electronics
• Essentially a ��closed�� fuel cell, hydrogen
is stored as a metal hydride, oxygen is stored in the nickel oxide
• Excellent cycle life, moderate cost • Low operating potential (~1.4 V to 1.2 V)

Page 30
NiCd
• Like NiMH, but a bit cheaper, much less
robust, and quite toxic internally
• Pro Tip: don��t use these!

Page 31
Lithium Ion
• Similar to
Lithium metal, but with an intercalation host for an anode
cou ture Li M com T seve trol invo 2b).
et al
earl prin Ni– than prin incr tion shif or th mor inse ��M– alm uted Li a mee
insight review articles
Non-aqueous liquid electrolyte Positive (Li
x
Host 1) Negative (Li
x
Host 2) Li+ Li+ a b V
+ -
V Non-aqueous liquid electrolyte Positive (Li
x
Host 1) Negative (Lithium) Li+ Li+
+ -
After 100 cycles
Nature 2001 Tarascon

Page 32
Lithium Ion Cells
• A feat of materials and packaging
engineering
• A completely engineered structure
containing less than 1 PPM H2O and O2 leads to unprecedented shelf life and cycle life

Page 33
Lithium Ion Cells
• Many intercalation hosts available, most
common are graphite as the anode and LiCoO2 as the cathode
• Charged potential of 4.2 V, down to ~2.5
V at full discharge (but you don��t want to pull past 3.5 V if you can help it)
• Since P = IV, there��s a bigger penalty the lower you
go

Page 34
Why Do Batteries Break?

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Mass transfer
• Basically related to the issues of
reacting and moving a significant fraction of mass quickly in a small space

Page 36
Uneven Surfaces over Cycles
Flow 2mm
Ito et. al. JOPS 2010

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Uneven Surfaces over Cycles
100 s
500 µm
Gallaway et. al. JECS 2010

Page 38
Microscopic Fracture
Zn on Printed Ag AgO
200 µm
Red = Zinc Loss Blue = AgO -> Ag + ?
200 µm Flow

Page 39
Nano & Atomic Scale Stress
Wang ECS 1999
Figure TEM b
diffraction peaks from the added graphite phase. Figure 7. Experimental SAD patterns of cycled LiCoO2 particles. (a) A par-–
Before Cycling After 50 Cycles

Page 40
What battery should you use?

Page 41
Lithium Ion Polymer
(99% of the time)

Page 42
Why?
• Charge retention • Energy Density • Power Density • Loves Shallow Discharge
• No memory effect

Page 43
Overspec the battery
• For long term applications • At 80% Depth of Discharge (DoD) 500
Cycles
• At 50% DoD, 1500 Cycles • At 10% DoD, > 10000 Cycles • So if you use 10% of the battery, you
ultimately get > 2.5 times the energy delivered

Page 44
Undercharge the battery
• For an LiCoO2 cell, charge to 4 V
instead of 4.2 V
100 0 10 20 30 40 50 60 70 80 90 5 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 Capacity (%) P o te n tia l (V )
Discharge Curve for a "Sony Cell"
Ideal Region

Page 45
Different Li Ion Cells
• Three years ago, there was just one type
of cell to buy, but now there are a few.
• An easy guide:
• If you want more capacity for a given size use
cells with a LiCoO2 cathode
• If you want more power for a given size use cells
with a LiFePO4 cathode
• If you want even more power, use the above
cathode with a Li4Ti5O12 anode

Page 46
But?
• Large Li-Polymer-Ion batteries generate
a lot of heat, and to handle them safely serious regard must be given to cooling
source: tesla motors

Page 47
Also , Money
• They��re quite expensive, roughly ~5 to
10 times more per unit energy than lead acid, and 2-3 times more than NiMH

Page 48
In fact
• If you want to ��set it and forget it��*, you
may want to think about using alkaline primaries
• Easier to implement, better energy density than any
secondary cell, and a fraction the cost of any secondary cell per unit energy
* please don��t forget it

Page 49
Overall

Page 50
Batteries...
• Combine controlled chemical reaction
and mass transfer within confined spaces
• Have benefited from materials
engineering, but not to the degree enjoyed by ICs
• Will provide more energy over their
lifetime if cycled shallow and gently

Page 51
Questions and Next Steps?
• Questions? • Would you be interested in a ��future of
batteries talk��?
• Or a workshop where you build and test
your own batteries?

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