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

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

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

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What is a Battery?

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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

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

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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

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

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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

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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)
"+" "-"
- + 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

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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)

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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

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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)
"+" "-"
- + Charge Discharge Charge Discharge

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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

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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

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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

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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

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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?)

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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

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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

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Battery Types

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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
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
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

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• 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

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• 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

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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!

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Lead Acid
• Overall 140 years old • The most common, lowest cost secondary
• Excellent power delivery • Heavy • Poor deep discharge performance
• ~500 cycles
• Nominally ~2 V per cell, dropping to ~1.5
over useful discharge life

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• 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)

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

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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
Host 1) Negative (Li
Host 2) Li+ Li+ a b V
+ -
V Non-aqueous liquid electrolyte Positive (Li
Host 1) Negative (Lithium) Li+ Li+
+ -
After 100 cycles
Nature 2001 Tarascon

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

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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

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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

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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

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

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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

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What battery should you use?

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Lithium Ion Polymer
(99% of the time)

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• Charge retention • Energy Density • Power Density • Loves Shallow Discharge
• No memory effect

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Overspec the battery
• For long term applications • At 80% Depth of Discharge (DoD) 500
• 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

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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

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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

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• 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

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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

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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

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• 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

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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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