evco ev-conversion course advanced batteries (inside & outside) a tour of the possible
TRANSCRIPT
EVCO EV-Conversion Course
Advanced Batteries (inside & outside)
A tour of the possible
Advanced Batteries: The Inside• What is a battery?
• What’s going on inside?
• Second law of thermodynamics
• Maxwell's demon
• What are the properties of a battery?
• Typical battery chemistries and there relative properties
• 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
• E.g. 18650 4.2 volts & 3.0
• 3.6 volts nominal
Rate vs Capacity
• 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
• Number of charge/discharge cycles to 80% DOD (Depth of Discharge)
Typical battery chemistries and there relative properties Lead Acid
Positives: Economical Negatives: Heavy weight; poor service life; high internal resistance
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
NiMh Positives: Higher energy density then NiCad Negatives: Sensitive to over charging
Lithium Positives: Light weight; high energy density; readily available; reasonable cost
Negatives: *MUST* be managed!
The future of Electrochemistry
1834: Michael Faraday’s laws of electrolysis published
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)
Material Science Nanotechnology and silicon batteries
Engineering Requirements analysis
Questions?
Advanced Batteries: The Outside
Mechanical considerations
Electrical considerations
Safety considerations
Performance metrics: COP; SOC; SOH; Terminus of charge & discharge
Management considerations including manual VS automated battery management systems
Thermal considerations
Mechanical Considerations
Types of cells
Cylindrical 18650 VS 26650
Prismatic (Plastic/Steel/Aluminum)
Pouch (Kokam)
Assembly methods
Welding
Soldering
Terminal Lugs
Packaging and Configuration Parallel-Series VS Series-Parallel
E.g.: 10P50S VS 50S10P
Bulk-Charging
Electrical Considerations
Connectors
Less is more
Wiring
Large signal vs small signal
Charging methods
Constant Voltage: Voltage steady, Current varies
Constant Current: Current steady, Voltage varies
Trickle: compensates for self discharge
Pulsed: sulfides
Discharging
Balancing
Fusing
Safety considerations
Battery fires
What to do to avoid them
Out-gassing
Hydrogen
Fluorine
Electric Shock
Insulating materials
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!
Performance metrics
COP (Coefficient of Performance)
Current Based SOC Estimation (Coulomb Counting) Current sensing methods:
Current Shunt Hall Effect
SOH (State of Health) Subjective aggregate of: Charge acceptance Internal resistance Voltage Self-discharge
Thermal considerations Internal Resistance & "perket effect"
Heat is bad
Coefficient of Performance
Management considerations: including manual VS automated battery management systems
Manual Low cost Prone to error neglect
Automated Extends service life Lowers TCO
Questions?
