Efficiency

When you charge and then discharge a battery cell you lose energy, the ratio of the amount of discharge to charge energy is the efficiency.

If we put 11 Wh into a battery cell when charging and recover 10 Wh when discharging the energy efficiency = 10 / 11 = 90.9%

Typical energy efficiencies:

  • Lead acid ~70%

Coulombic Efficiency

Also known as Faradaic Efficiency, this is the charge efficiency by which electrons are transferred in a battery. It is the ratio of the total charge extracted from the battery to the total charge input to the battery over a full cycle.

Coulombic efficiency values:

  • Lead acid ~85%
  • Lithium ion >99%

High coulombic efficiency usually indicates a long battery cycle life.

Voltaic Efficiency

This is the ratio of the average discharge voltage to the average charge voltage over a cycle. The charging voltage is always higher than the rated voltage to activate the chemical reaction within the battery and hence losses.

References

  1. Vedran Bobanac, Hrvoje Basic, Hrvoje Pandzic, Determining Lithium-ion Battery One-way Energy Efficiencies: Influence of C-rate and Coulombic Losses, IEEE EUROCON-2021