Batteries: Efficient Conversion of Chemical Energy

• Concept: electrons must pass through external circuit to complete the chemical reaction.
• Discussion of power delivered by and total energy available from batteries:
  • Electrical power in terms of cell potential and current
  • Cell potentials
  • Change in Gibbs free energy and electrical work
  • Discharge efficiency
  • Specific energy of batteries
  • Specific power of batteries
• Discharge efficiency depends upon the chemical reaction. Lead-acid batteries are about 80% efficient.
• Recharging: drive the system in reverse with the same cell potential but opposite current.
• Recharge efficiency varies during the recharge process. Initially, it can be 95%, but as the battery nears being completely charged the efficiency can drop to 50%. A reasonable value for the average charge efficiency is 85%.
• Do battery-powered vehicles use fossil fuels more efficiently than an internal combustion engine?