Factors Affecting Internal Resistance of a Cell | govind goyal - salonjardin.info
When no current is drawn from the cell, the potential difference between the two For a new cell, the value of internal resistance is very low but as the cell is put the distance between the electrodes; the nature of the electrolyte; the nature of . two electrodes of the cell when no current is drawn from the cell. Comparison of EMF and P.D: P.D is the difference of potentials between any two i) Larger the separation between the electrodes of the cell, more the length i.e. internal resistance depends on the nature of the electrolyte. iii) The internal. Affecting Internal Resistance of a Cell Distance between Electrodes Area . of the cell is decreased we can increase the potential difference.
In nickel metal hydride batteries the negative electrode consists of a layer of metal particles bound to a nickel foil. The metal particles absorb hydrogen during charging and desorb during discharging.
The electrolyte slowly corrodes the metal particles, increasing the dead layer at the surface of the grain, which makes it harder for the hydrogen ions to get to and from the metal, increasing the resistance.
Why does internal resistance of a battery increase over time? Impedance?
In lead acid batteries large, non-conductive, less soluble crystals of lead sulfate grow when the battery is left uncharged or partly charged, which increases the resistance of the battery. In lithium ion batteries the ion receptor channels in both the positive and negative electrodes can collapse or get clogged with lithium metal or corrosion products Concentration polarization Liquid electrolyte batteries rely on diffusion to get fresh reactants to the electrode surfaces.
- Battery impedance and resistance
Diffusion is typically a slow process, so the reactants are typically depleted near the electrode surface. The difference in concentration existing between the electrode surface and the bulk electrolyte creates a potential difference which looks like an increase in resistance.
Activation polarization Activation polarization comes from the speed of the chemical reaction at the electrode surface. The factors that influence this are the thermodynamics of the reaction and the surface area. Porous electrodes are often used to increase the surface area, but as the battery ages the pores can get plugged by reaction products, spalling of the electrode material, or corrosion products.
Temperature effects A fundamental law of nature is that chemical processes slow down with lower temperature. This is because diffusion slows down, and the average kinetic energy of the molecules is reduced.
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So as the temperature goes down you can expect higher impedance of the chemicals. The resistance of the metals in the battery is lowered as the temperature goes down, but this is very small effect compared with the chemical effects.
Total current through the combination is the sum of individual currents through the various branches. The potential difference across all the resistances is the same.
The current through each branch is inversely proportional to the resistance of that branch. The reciprocal of the total resistance of the combination is equal to the sum of the reciprocals of the individual resistances.
Grouping of cells There are generally three types of groupings of the cells: Circuit diagram of cells in series Here, the external resistor is connected to the free terminals of the first and the last cells. Let n identical cells be connected in series; each of emf E and internal resistance r. Let R be the resistance of external resistor.
Therefore, current in the external resistance R is given by In this case, nr can be neglected as compared to R. Then, equation i becomes In this case, R can be neglected as compared to nr. From the above equations we can conclude that the maximum current can be drawn from the series combination of cells if the external resistance is very high as compared to the internal resistance of the cells.
Circuit diagram of cells in parallel Again let us consider n identical cells are connected in parallel, each of emf E and internal resistance r.
Since the internal resistances of all the cells are connected in parallel, their total internal resistance rp is given by up to n terms Therefore, total resistance in the circuit Current in the resistance R is given by