Battery resistance

The weight of the electrolyte is a major contribution to that of the complete battery and hence must be minimized. In any case the electrode spacings should be small to minimize battery resistance. 

On the other hand, battery resistance reduction means higher power capability, as it means less resistance for a current to flow within battery. These considerations confirm that a lower internal resistance directly relates to and enhances the high-power performance, increases energy efficiency, and reduces battery heat generation (Figure 5.13). 

Lithium-ion batteries are electrochemical systems whose processes are related to temperature higher temperatures accelerate side reactions which cause a reduction of battery capacity or an increase in battery resistance. Long-term exposure to temperature values above 32 °C should be minimized to meet a 10-year durability target (see Figure 8.16). Each specific battery chemistry has a different sensitivity, but the general rule applies to all systems. 

FIGURE 10.294 Randles model of a lead acid battery. The overall battery resistance consists ofpure Ohmic resistance, inductance, and capacitance. There are many other models. 

In preparation for the CCA test, the battery is taken off charge and placed in a freezer at -19°C for 24 h to ensure uniformity of the core temperature. After this period, a fair amount of gas can be liberated from the battery. The gases that are attached to surfaces along the ionic flow path, such as plate and separator surfaces, are of concern. Because gas bubbles are infinitely resistant to ionic flow, the surface area occupied by the gas will essentially be blinded and cause an increase in overall battery resistance. To account for the influence of entrapped gas, it is therefore appropriate to think of the functional resistance instead of measured or calculated electrical resistance [8] ... 

Ohmic measurement is one of the oldest and most reliable methods to measure internal battery resistance. The battery is discharged for a few seconds or minutes, a voltmeter measures the voltage drop, and Ohm s law calculates the resistance value (voltage divided by current equals resistance). The discharge current on a smaller... 

The internal resistance of the battery component is expressed as rfV, and the polarization effect component is the voltage drop t/Fj- Since some energy was removed by the pulse, a more correct expression for the battery resistance is the voltage drop expressed by dV. ... 

FIGURE 15.13 Load voltage and battery resistance vs. Q for coated-anode Li/Ij battery discharged at 100 /xA, 37°C. (Courtesy of Medtronic, Inc.)... 

FIGURE 23.21 Comparison of lead-add battery designs. Effect of temperature on battery resistance. 

The battery voltage Edischarge current /jis delivered across a load is called the polarization curve. The voltage drop (Voc - E) = t I) of a typical curve (Fig. 1.7) is a measure of the battery resistance ... 

The battery performance can be accurately defined according to the two technical parameters and the applied current density. In general, the larger the value for these two parameters at a certain applied current density, the better the battery performance for a given cell stack. The increase in power output corresponds to the decrease in EE. Strategies such as reducing the battery resistance, improvement in the selectivity and conductivity of the membrane and optimisation of the electrolyte flow in the cell can be effective in improving the power output at the same EE. 

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