Discharge capacity batteries

Eig. 14. Retention of discharge capacity of miniature 2inc—mercuric oxide batteries after storage at temperatures of A, 40°C B, 20°C and C, 0°C (21). 

Fig. 21. Retention of discharge capacity of miniature zinc—air battery having an unopened sealed cell after storage at 20°C (-) projected data (21).

The limit for the application of an accumulator battery is a protection current of about 20 mA. This is calculated to be supplied by a 100-A h capacity battery over a period of about 7 months. It is sufficient to change the discharged battery for a fully charged one every 6 months. 

The discharge curve (Fig. 8) is another important feature of battery systems therefore the terminal voltage is plotted against the discharge capacity. For an ideal battery the terminal voltage drops to zero in a single step when the stored energy is completely consumed. 

Charge-discharge capacity/mAh Figure 20. Charge-discharge characteristics of an Ni—MH battery (cell type AA). 

Polyacene is classified as a material which does not belong to either soft or hard carbons [84], It is also made by heat-treatment of phenol resin. As the heat-treatment temperature is lower than about 1000 °C, polyacene contains hydrogen and oxygen atoms. It has a conjugated plane into which lithium ions are doped. It was reported that the discharge capacity of polyacene is more than 1000 mAhg. However, there are no practical lithium-ion batteries using polyacene. 

The first cell has the maximum capacity of 108 A h kg" and the energy density of 111 W h kg" The coulombic efficiency was close to 100% over at least 2000 complete cycles when cycled between 1.35 V and 0.5 V at a constant current density of 1 mA cm". The second cell also showed excellent recyclability (4000 cycles with 95% coulombic efficiency), on the other hand the discharge capacity decreased steadily from 40 to 25 A h kg" after 4000 cycles. In PANI batteries with aprotic... 

Figure 6. Prismatic 7 Ah battery discharge capacity vs. cycle number plot.

Figure 7. Prismatic 7Ah battery. Typical charge-discharge capacities vs. cycle number. Battery was cycled at different temperatures at C/4.

Cycle life is another important factor because it determines the longevity of the battery in practical use. The number of lifetime cycles depends strongly on the so-called depth of discharge if only some 10-20% of the full discharge capacity is used (as in the Toyota Prius for instance) the batteries can handle millions of shallow cycles . However, for PHEVs or BEVs the number of deep cycles (typically 80% discharge) is a relevant characteristic. 

Cheng et al. carried out the impedance study on a foam-type NiMH battery with nonwoven PP separator to determine the main causes of early cycle deterioration. Their data indicated that the decrease in the voltage characteristic of the battery was due to drying out of the separator that increases the ohmic resistance of the battery and that decay of the total discharge capacity is due to an inactive surface that increases the charge-transfer of the battery. 

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