Presentation on theme: "EVCO EV-Conversion Course Advanced Batteries (inside & outside) A tour of the possible."— Presentation transcript:
EVCO EV-Conversion Course Advanced Batteries (inside & outside) A tour of the possible
Introduction Doug Yuill: EVCO Director Go-One Owner
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 volts & volts nominal Rate vs Capacity E.g (18mm diameter x 65mm 2800 mAh 1C rate 2.8 Ah x 3.6 v = 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
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 VS 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
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