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Electronics Engineering QUESTION #11715
Question 1
A Li-ion cell is charged using CC-CV (constant current / constant voltage) method. At what voltage does the charger switch from CC to CV phase?
  • 3.0 V (end of discharge)
  • 3.7 V (nominal voltage)
  • 4.2 V (full charge voltage)✔️
  • 4.5 V (overcharge threshold)
Correct Answer Explanation
Li-ion cells are charged in two phases: Constant Current (CC) from depleted state up to 4.2 V, then Constant Voltage (CV) at 4.2 V until current tapers to ~C/10 or C/20 (typically 50–100 mA), indicating full charge. Exceeding 4.2 V causes electrolyte decomposition, lithium plating, and severe safety hazards including thermal runaway.