Charge-discharge coefficient

As sulfuric acid is an active material, its stratification will affect cell capacity. Figure 3.18 shows this relationship. It can be seen that the capacity decreases by 1% per 0.01 sp gr. (rel.dens.) unit of stratification. This capacity loss also depends on the DOD and the charge/ discharge coefficient. 

Capacity loss vs the extent of stratification for charge/discharge coefficients 1.02, 1.05... 

Charge/discharge coefficient This is given by the expression... 

This coefficient is very convenient for expressing the degree of overcharge. Thus, a value of 1.05 means 5% ever charge. In practice, the charge/ discharge coefficient is 1.05 to 1.15. 

A reaction has been characterised as a tempered hybrid system and it has been determined that the system will relieve single-phase gas/, vapour. Relief sizes for both a safety valve and a bursting disc system are required. The reactor contains a charge of 3000 kg. Data for relief sizing have been compiled in Table A6.2. -The type of safety valve selected has a de-rated discharge coefficient under BS 6759131 of 0.87. 

As explained before, the open-circuit potential of the battery depends on concentration, temperature, and transport limitations. The real voltage delivered by a battery in a closed circuit is affected by ohmic limitations (ohmic potential), concentration limitations (concentration overpotential), and surface limitations (surface overpotential). The close circuit potential of the cell is given by the open-circuit potential of the cell minus the drop in potential due to ohmic potential, concentration overpotential, and surface overpotential. The ohmic potential is due to the ohmic potential drop in the solution. It is mostly affected by the applied charge/discharge current of the battery. The concentration overpotential is associated with the concentration variations in the solution near the electrodes. It is strongly affected by transport properties such as electrolyte conductivity, transference number, and diffusion coefficients. Finally, the surface overpotential is due to the limited rates of the electrode reactions. 

However, a precise reproduction of the impedance spectrum without low frequency data is possible, when the coefficient for heat exchange with environment is determined by a separate measurement. This can be achieved by heating up the cell with an alternating, rectangular charge/discharge profile, which is illustrated in Figure 11. 

This measurement method is partieularly advantageous with lithium technologies whose capacity depends very little on the charge/discharge current (see section 6.2.11.). For other technologies, we can apply coefficients on the basis of the amplitude and sign of the current. 

A coefficient voltage efficiency (f/ ) was introduced to characterize the charge/ discharge voltage ratio ... 

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