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Examoogle • User • info@examoogle.com • EE-2024-8821
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As compared to a lead-acid cell, the efficiency of a nickel-iron cell is less due to its
compactness
lower e.m.f
small quantity of electrolyte used
higher internal resistance
higher internal resistance
Quick Summary: The efficiency of a nickel-iron (Edison) cell is lower (approximately 60% to 70%) compared to a lead-acid cell (approximately 80% to 90%) primarily due to its significantly higher internal resistance. The high internal resistance leads to higher $I^2R$ power losses during both charging and discharging cycles.
The efficiency of a nickel-iron (Edison) cell is lower (approximately 60% to 70%) compared to a lead-acid cell (approximately 80% to 90%) primarily due to its significantly higher internal resistance. The high internal resistance leads to higher I2R power losses during both charging and discharging cycles.
η=EinEout×100% — General efficiency formula for batteries
Ploss=I2Rint — Power dissipation due to internal resistance
The internal resistance in a nickel-iron cell is higher because the electrolyte (potassium hydroxide) has lower conductivity than the sulfuric acid used in lead-acid cells, and the active material structure contributes to ohmic drops. Since efficiency is defined as the ratio of output energy to input energy, the energy dissipated as heat (which is proportional to resistance R) reduces the total energy recovery, resulting in lower overall cycle efficiency.
Nickel-iron cells are robust and have long cycle lives but lower energy efficiency.
The electrolyte in nickel-iron cells is an alkaline solution (KOH with lithium hydroxide).
High internal resistance is the dominant factor limiting the charging/discharging efficiency.
Lead-acid cells use a liquid acid electrolyte which provides better ionic mobility.
Extremely long service life
Mechanically robust and resistant to overcharging/short-circuiting
Lower energy efficiency
High self-discharge rate
Railway signaling
Heavy-duty industrial standby power
| Feature | Nickel-Iron | Lead-Acid |
|---|---|---|
Efficiency | 60% - 70% | 80% - 90% |
Internal Resistance | High | Low |
The higher internal resistance also leads to a more significant voltage drop under heavy load conditions in nickel-iron cells.
Option B is incorrect because while nickel-iron cells have a lower nominal voltage (~1.2V) than lead-acid (~2.0V), voltage magnitude does not directly dictate thermodynamic efficiency in this context.
D is correct — The higher internal resistance of the nickel-iron cell causes greater energy dissipation as heat, thereby reducing its overall efficiency.
Always remember that internal resistance is a key parameter for efficiency; higher internal resistance always results in lower efficiency due to increased I2R heating losses.