Fuel cell technology and rechargeable batteries

1. Fuel cell technology and rechargeable batteries Dr. Jonathan C.Y. Chung Jonathan.chung@cityu.edu.hk http://personal.cityu.edu.hk/~appchung/Teaching.htm Dept. of Physics and Materials Science http://www.ap.cityu.edu.hk/ City University of Hong Kong http://www.cityu.edu.hk/

2. Public Interest • Subject matters: • What are fuel cells, batteries and rechargeable batteries? • Why some rechargeable batteries explode? • Accidents in the past. • A dream: thin Film batteries. • Another dream: fuel cells that drink beer!!

3. High-Technology Electronics Equipments Mobile Phone Laptop Computer PDA MP3 Player Digital Camera PMP

4. Agenda • The construction of a battery • The electrochemical reaction • A fuel cell • The rechargeable batteries • Ni-Cd, Ni-MH • Li-ion rechargeable batteries: • What type of batteries will explode? • Thin film rechargeable batteries

5. History of batteries 1800 Voltaic pile: silver zinc 1836 Daniell cell: copper zinc 1859 Planté: rechargeable lead-acid cell 1868 Leclanché: carbon zinc wet cell 1888 Gassner: carbon zinc dry cell 1898 Commercial flashlight, D cell 1899 Junger: nickel cadmium cell 1946 Neumann: sealed NiCd 1960s Alkaline, rechargeable NiCd 1970s Lithium, sealed lead acid 1990 Nickel metal hydride (NiMH) 1991 Lithium ion 1999 Lithium ion polymer

6. Electrodes Electrochemical cell • Cathode is the electrode where reduction takes place. • Anode is the electrode where oxidation takes place. Battery • Positive electrode: (+) of the cell • Discharging: cathode (reduction) • Negative electrode: (-) of the cell • Discharging: anode (oxidation)

7. Good vs. bad batteries • Voltage (materials, thermodynamics) • Spontaneous Chemical reaction (unwanted side reaction) • Oxidation of the electrodes (surface and bulk: affect the kindetics of the electro-chemical reaction) • Degradation of the electrolyte (decompose?) • Effects of environmental contaminants (poisoning?) • High energy per unit weight • Safety (to human and equipment)

8. Primary (Disposable) Batteries • Zinc carbon (flashlights, toys) • Heavy duty zinc chloride (radios, recorders) • Alkaline (all of the above) • Lithium (photoflash) • Silver, mercury oxide (hearing aid, watches) • Zinc air

9. Battery Characteristics • Size • Physical: button, AAA, AA, C, D, ... • Energy density (watts per kg or cm3) • Longevity • Capacity (Ah, for drain of C/10 at 20°C) • Number of recharge cycles • Discharge characteristics (voltage drop) • Cost • Behavioral factors • Temperature range (storage, operation) • Self discharge • Memory effect • Environmental factors • Leakage, gassing, toxicity • Shock resistance

10. Standard Zinc Carbon Batteries • Chemistry Zinc (-), manganese dioxide (+) ammonium chloride aqueous electrolyte • Features • Inexpensive, widely available • Inefficient at high current drain • Poor discharge curve (sloping) • Poor performance at low temperatures

11. Alkaline Battery Discharge

12. Heavy Duty Zinc Chloride Batteries • Chemistry Zinc (-), manganese dioxide (+) Zinc chloride aqueous electrolyte • Features (compared to zinc carbon) • Better resistance to leakage • Better at high current drain • Better performance at low temperature

13. Standard Alkaline Batteries • Chemistry Zinc (-), manganese dioxide (+) Potassium hydroxide aqueous electrolyte • Features • 50-100% more energy than carbon zinc • Low self-discharge (10 year shelf life) • Good for low current (< 400mA), long-life use • Poor discharge curve

14. Alkaline-Manganese Batteries

15. Lithium Manganese Dioxide • Chemistry Lithium (-), manganese dioxide (+) Alkali metal salt in organic solvent electrolyte • Features • High energy density • Long shelf life (20 years at 70°C) • Capable of high rate discharge • Expensive

16. Choice of Anode Materials

17. Battery or Pack Two or more electrochemical cells electrically interconnected in an appropriate series/parallel arrangement to provide the required operating voltage and current levels. Under common usage, the term "battery" is often also applied to a single cell.

18. Projected Production Yield of battery in pack from cells

19. Applications • Lead acid starter: vehicles • Industrial lead acid: power backup systems, traction applications • Primary batteries

20. Agenda • The construction of a battery • The electrochemical reaction • A fuel cell • The rechargeable batteries • Ni-Cd, Ni-MH • Li-ion rechargeable batteries: • What type of batteries will explode? • Thin film rechargeable batteries

21. Definition of battery • “A battery is a device that converts the chemical energy contained in its active materials directly into electrical energy by means of an electrochemical oxidation- reduction (redox) reaction” M(s) → Mn+(dis) + ne- or mM(s) + nXm-(dis) → MmXn(s) + (n·m)e- • The active material at the anode of a battery is the “fuel” that undergoes oxidation. • When this anode material or fuel is a metal, the oxidation process consists of corrosion. • This is sometime called “constructive corrosion”.

22. Constructive vs. Destructive corrosion Electro-chemical reaction vs. chemical reaction

23. A typical battery - e load salt bridge (allows ions to migrate) Reduction at Cathode (e.g. Cu) Oxidation at Anode (e.g. Zn) ZnSO CuSO 4 4 Half Cell I Half Cell II

24. Electrochemical Cell • Salt bridge only allows negative ions to migrate through. This also limits the current flow. (kinetics) • Need to find a low-resistance bridge.

25. CathodeHigh Electron Affinity (reduction: gain electrons) Gold Mercury Silver Copper Lead Nickel Cadmium Iron Zinc Aluminum Magnesium Sodium Potassium Lithium AnodeLow Electron Affinity (oxidation: lose electrons) Electrochemical Activity • What are the differences between a chemical reaction and an electrochemical reaction? • We want to have electrochemical reaction for battery. • Thermodynamics

26. Schematic of Battery • Properties of electrode • Properties of electrolyte • Properties of the electrolyte-electrolyte interface • Properties of the separator • Properties of package

27. Reaction Energy & Activation energy Thermodynamics: E Kinetics: E1, and E2 A + BC + E1 A--B--C  AB +C + E2

28. Thermodynamics • A comparison of energy before and after a reaction Etotal= Echemical + Esurface +Edefects +Eelastic +Einterface +Ekinetic +…… EAB= Etotal (B-A) • E can be determined by experimental methods • We can thus determine whether a transformation is exothermic (favourable) or endothermic • The thermodynamic analysis only let us know that the reaction (or transformation) is favorable, it do not tell us “how” can and “when” will the reaction take place

29. The importance of kinetics • The “ultimate equilibrium” may be not practically achievable when EA (activation energy) required is too large slow reaction • Small EA  fast reaction ( fast spontaneous discharge) E EA(AB) A B

30. Agenda • The construction of a battery • The electrochemical reaction • A fuel cell • The rechargeable batteries • Ni-Cd, Ni-MH • Li-ion rechargeable batteries: • What type of batteries will explode? • Thin film rechargeable batteries

31. Fuel Cell • Vs. Nuclear bomb • Vs. Explosives • A fuel cell is a device that uses hydrogen and oxygen to create electrochemical process • Electrolyte sandwiched between a porous anode and a cathode

32. Fuel cell construction • Hydrogen rich fuel • Anode: a catalyst separates protons and electrons • Cathode: oxygen combines with e-, protons, or water, resulting in water or hydroxide ions • Polymer electrolyte membrane (PEM) and phosphoric acid fuel cells: protons move through the electrolyte to cathode producing water and heat • Alkaline, molten carbonate, and solid oxide fuel cells: negative ions travel through the electrolyte to the anode generating water and electrons • The electrons from the anode cannot pass through the membrane to the cathode: they must travel via a circuit

33. Fuel cell system • A fuel processor • An energy conversion device • A current converter • Heat recovery system • Others: (optional) • Cell humidity control • Temperature control • Gas pressure control • Wastewater control

34. Fuel Processor • Pure Hydrogen fuel cell: only require a filter to control purity • H-rich fuel cell: • a reformer to convert hydrocarbons into a gas mixture of hydrogen and carbon compound (reformate) • Remove impurity from reformate (prevent poisoning of the catalysts) What is the meaning of poisoning?

35. Fuel • Pure Hydrogen • Hydrogen-rich fuels: • Methanol • Gasoline • Diesel • Gasified coal • Magnesium-Air Fuel Cell (http://www.magpowersystems.com/)

36. Fuel Cell vs. Primary battery • What are the differences and similarity between fuel cell and primary battery? • What are the differences and similarity between fuel cell and rechargeable battery?

37. Agenda • The construction of a battery • The electrochemical reaction • A fuel cell • The rechargeable batteries • Ni-Cd, Ni-MH • Li-ion rechargeable batteries: • What type of batteries will explode? • Thin film rechargeable batteries

38. Secondary (Rechargeable) Batteries • Lead acid • Nickel cadmium (NiCd) • Nickel metal hydride (NiMH) • Alkaline • Lithium ion • Lithium ion polymer Why they are rechargeable?

39. Reversible reaction

40. Volumetric Energy and Specific Energy

41. Battery Materials • Importance of battery materials • Portable electronic and electric appliances, e.g. cellular telephones, video cameras, lap-top computers and hand tools • Market increase by 2 digit (%) p.a. • Electric vehicles • Require higher capacities and better performances relative to Ni/Cd batteries. • Ni/MH (metal hydride) is one promising candidate • Li-ion is even lighter but more expensive

42. Battery Capacity

43. Performance Characteristics

44. Discharge Rates Voltage: application dependent Current: higher is better

45. Other performance indicators (2004)

46. Lead-acid Battery cathode: PbO2 anode: Pb Eelctrolyte: H2SO4 Reactions: Cathode: PbO2+4H++SO42-+2e- ↔ PbSO4+2H2O Anode: Pb+SO42- ↔ PbSO4+2e- Overall: Pb + PbO2 + H2SO4 2 PbSO4 + 2 H2O

47. Degradation • Oxide formation (kinetics) • Precipitation (electrolyte) • Contamination (electrolyte)

48. Agenda • The construction of a battery • The electrochemical reaction • A fuel cell • The rechargeable batteries • Ni-Cd, Ni-MH • Li-ion rechargeable batteries: • What type of batteries will explode? • Thin film rechargeable batteries

49. Ni-Cd Battery cathode: Ni(OH)2 anode: Cd Electrolyte: KOH(aq) Reaction at cathode: -Ni(OH)2 + OH--NiOOH + H2O + e- Reaction at anode: O2 + 2H2O + 4e- 4OH- 4OH- + 2Cd  2Cd(OH)2 +4e-

50. Cross-section of a classic NiCd cell While charging, the cell pressure of a NiCd can reach 1379kilopascals (kPa) or 200pounds per square inch (psi). A venting system is added on one end of the cylinder. Venting occurs if the cell pressure reaches between 150 and 200psi. The negative and positive plates are rolled together in a metal cylinder. The positive plate is sintered and filled with nickel hydroxide. The negative plate is coated with cadmium active material. A separator moistened with electrolyte isolates the two plates. [Panasonic Battery]