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EVCO EV-Conversion Course
Advanced Batteries
(inside & outside)
A tour of the possible
Introduction
Doug Yuill: EVCO Director
[email protected]
Go-One Owner
Advanced Batteries: The Inside
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What is a battery?
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What’s going on inside?
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Second law of thermodynamics
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Maxwell's demon
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What are the properties of a battery?
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Typical battery chemistries and there relative properties
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The future of Electrochemistry
What is a battery?
Batteries are devices that convert stored chemical energy into useful electrical energy.
A battery may be thought of as a clever variant of a standard exothermic chemical
reactor that yields chemical products with lower energy content than the chemical
reactants.
In such a chemical reactor, the overall chemical reaction proceeds spontaneously (possibly requiring a catalyst
and/or elevated temperature) when the reactants are brought into physical contact. In a battery, the overall
chemical reaction is divided into two physically and electrically separated processes: one is an oxidation process
at the battery negative electrode wherein the valence of at least one species becomes more positive, and the
other is a reduction process at the battery positive electrode wherein the valence of at least one species becomes
more negative.
The battery functions by providing separate pathways for electrons and ions to move between the site of oxidation
and the site of reduction. The electrons pass through the external circuit where they can provide useful work, for
example power a portable device such as a cellular phone or an electric vehicle.
The ions pass though the ionically conducting and electronically insulating electrolyte that lies between the two
electrodes inside the battery. Therefore, the ionic current is separated from the electronic current, which can be
easily controlled by a switch or a load in the external circuit.
When a battery is discharged, an electrochemical oxidation reaction proceeds at the negative electrode and
passes electrons into the external circuit, and a simultaneous electrochemical reduction reaction proceeds at the
positive electrode and accepts electrons from the external circuit, thereby completing the electrical circuit.
The change from electronic current to ionic current occurs at the electrode/electrolyte interface. Faraday’s Law,
which describes the quantitative proportional relationship between the equivalent quantities of chemical reactants
and electrical charge, governs this change. When one attempts to recharge a battery by reversing the direction of
electronic current flow, an electrochemical reduction reaction will proceed at the negative electrode, and an
electrochemical oxidation reaction will proceed at the positive electrode.
What’s going on inside a battery?
Second law of thermodynamics
The second law of thermodynamics is an expression of the universal principle of increasing entropy,
stating that the entropy of an isolated system which is not in equilibrium will tend to increase over
time, approaching a maximum value at equilibrium.
The origin of the second law can be traced to French physicist Sadi Carnot's 1824 paper
Reflections on the Motive Power of Fire, which presented the view that motive power (work) is due
to the flow of caloric (heat) from a hot to cold body (working substance).
In simple terms, the second law is an expression of the fact that over time, ignoring the effects of
self-gravity, differences in temperature, pressure, and density tend to even out in a physical system
that is isolated from the outside world.
Entropy is a measure of how much this evening-out process has progressed. There are many
versions of the second law, but they all have the same effect, which is to explain the phenomenon
of irreversibility in nature.
Another way of stating is: The second law of thermodynamics ensures (through statistical
improbability) that two bodies of different temperature, when brought into contact with each other
and isolated from the rest of the Universe, will evolve to a thermodynamic equilibrium in which both
bodies have approximately the same temperature. The second law is also expressed as the
assertion that in an isolated system, entropy never decreases.
Maxwell's demon
... if we conceive of a being whose faculties are so sharpened that
he can follow every molecule in its course, such a being, whose
attributes are as essentially finite as our own, would be able to do what is impossible to
us. For we have seen that molecules in a vessel full of air at uniform temperature are
moving with velocities by no means uniform, though the mean velocity of any great
number of them, arbitrarily selected, is almost exactly uniform. Now let us suppose that
such a vessel is divided into two portions, A and B, by a division in which there is a small
hole, and that a being, who can see the individual molecules, opens and closes this
hole, so as to allow only the swifter molecules to pass from A to B, and only the slower
molecules to pass from B to A. He will thus, without expenditure of work, raise the
temperature of B and lower that of A, in contradiction to the second law of
thermodynamics
What are the properties of a battery?
Charge & discharge terminus voltages
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E.g. 18650 4.2 volts & 3.0
3.6 volts nominal
Rate vs Capacity
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E.g. 18650 (18mm diameter x 65mm length) @ 2800 mAh
Capacity @ 1C rate
2.8 Ah x 3.6 v = 10.08 Wh
Times 240 cells = 2.4 kWh
Service life
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Number of charge/discharge cycles to 80% DOD (Depth of
Discharge)
Typical battery chemistries and there relative
properties
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Lead Acid
 Positives: Economical
 Negatives: Heavy weight; poor service life; high internal resistance
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NiCad
 Positives: Low internal resistance equals very high current capacity; long
service life; flat discharge profile.
 Negatives: Cell reversal if over discharged; “memory effect” if not fully
discharged
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NiMh
 Positives: Higher energy density then NiCad
 Negatives: Sensitive to over charging
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Lithium
 Positives: Light weight; high energy density; readily available; reasonable
cost
 Negatives: *MUST* be managed!
The future of Electrochemistry
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1834: Michael Faraday’s laws of electrolysis published
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155 years later: Pons & Fleishmann practice alchemy using electrolysis to
discover a new source of energy (course grade heat) by catalyzing hydrogen
into helium atoms using metal hydrides thus creating the study of LENR (Low
Energy Nuclear Reactions) and CMNS (Condensed Matter Nuclear Science)
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Material Science
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Nanotechnology and silicon batteries
Engineering
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Requirements analysis
Questions?
Advanced Batteries: The Outside
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Mechanical considerations
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Electrical considerations
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Safety considerations
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Performance metrics: COP; SOC; SOH; Terminus of charge & discharge
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Management considerations including manual VS automated battery
management systems
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Thermal considerations
Mechanical Considerations
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Types of cells
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Cylindrical 18650 VS 26650
Prismatic (Plastic/Steel/Aluminum)
Pouch (Kokam)
Assembly methods
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Welding
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Packaging and Configuration Parallel-Series VS SeriesParallel
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E.g.: 10P50S VS 50S10P
Soldering
Terminal Lugs
Bulk-Charging
Electrical Considerations
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Connectors
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Wiring
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Large signal vs small signal
Charging methods
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Less is more
Constant Voltage: Voltage steady, Current varies
Constant Current: Current steady, Voltage varies
Trickle: compensates for self discharge
Pulsed: sulfides
Discharging
Balancing
Fusing
Safety considerations
A bomb and a battery both have fuses, the difference is, a bomb,
you want to go off, a battery you don’t want to go off!
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Battery fires
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Out-gassing
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What to do to avoid them
Hydrogen
Fluorine
Electric Shock
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Insulating materials
Performance metrics
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COP (Coefficient of
Performance)
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Current Based SOC Estimation
(Coulomb Counting)
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Current sensing methods:
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Current Shunt
Hall Effect
SOH (State of Health)
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Subjective aggregate of:
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Charge acceptance
Internal resistance
Voltage
Self-discharge
Thermal considerations
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Internal Resistance & "perket effect"
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Heat is bad
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Coefficient of Performance
Management considerations: including manual VS
automated battery management systems
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Manual
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Low cost
Prone to error neglect
Automated
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Extends service life
Lowers TCO
Questions?
Your feedback is solicited;
Comments and questions to:
[email protected]