Depth-of-discharge

One hour charge/one hour discharge at 100% depth of discharge. 

Another important parameter for describing a secondary electrochemical cell is the achievable number of cycles or the lifetime. For economic and ecological reasons, systems with a high cycle life are preferred. The number of cycles indicates how often a secondary battery can be charged and discharged repeatedly before a lower limit (defined as a failure) of the capacity is reached. This value is often set at 80 percent of the nominal capacity. To compare different battery systems, besides the number of cycles, the depth of discharge must be quoted. 

An Li-Al Alloy was investigated for use as a negative electrode material for lithium secondary batteries. Figure 41 shows the cycle performance of a Li-Al electrode at 6% depth of discharge (DOD). The Li-Al alloy was prepared by an electrochemical method. The life of this electrode was only 250 cycles, and the Li-Al alloy was not adequate as a negative material for a practical lithium battery. 

Cycle life will depend strongly oil factors such as rate of discharge, end-point (cut-off) voltage, and depth of discharge... 

Figure 5. Performance of RAM AA cells as a function of the depth of discharge (DOD) recharging is done after each discharge. For an explanation of these example, see the text.

B-type cell, + Assumed cell volume=7.5 cm, 100 percent depth of discharge cycle life depends on cycling current. 

The power of the ZEBRA cell depends on the resistance of the cell during discharge. The resistance of the ZEBRA cell rises with increasing depth of discharge (DOD). There is a contribution to the resistance from the fixed values of the solid metal components and of the/ "-alumina solid electrolyte. The variable parts of the resistance arc the sodium electrode and the positive electrode. The increase in internal resistance during discharge is almost entirely due to the positive electrode, as can be seen from Fig. 4. 

As far as cycle life of the ECs is concerned, with the above conductive additives, and the active mass, consisting of activated carbon, for all groups of EC we built for this work, it exceeded 10,000,000 cycles (at depth of discharge of 30%) that is quite sufficient for the main spheres of application. 

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. 

Substituted nickel oxides, such as LiNii j /3ojAl/l2, are prime candidates for the cathode of advanced lithium batteries for use in large-scale systems as required for hybrid electric vehicles. On charging these mixed oxides the nickel is oxidized first to Ni + then the cobalt to Co +. SAFT has constructed cells with these substituted nickel oxides that have been cycled 1000 times at 80% depth of discharge with an energy density of 120—130 Wh/kg. ... 

Conventional and Advanced Aqueous Electrolyte Systems Improvements are expected in all the factors that count energy density (ED), cost/kWh, safety, reliability, as well as turnaround efficiency and cycle life at deeper depths of discharge (dod). 

Terms. TED - theoretical energy density (free energy of reaction/sum of molar wts of reactants) ED practical or realized Wh/kg SB - secondary or storage battery (rechargeable) dod - depth of discharge (% recharge removed before recharge) ... 

The rated capacity is 0.75 Ah. Typical discharge curves and charge-discharge cycle behaviour of these 3 V batteries are shown in Figs 7.27 and 7.28, respectively. Energy density of 130 Wh/kg and 280 Wh/dm3 and 300 complete cycles at 100% depth of discharge have been reported. The electrolyte solution is stable at low to medium temperatures, but polymerizes when the temperature exceeds 125°C to form polydioxolane with a consequent rapid rise in the internal resistance of the cell. This provides an internal shut-off safety mechanism which, combined with a built-in vent,... 

Iron-air cells have been developed by Matsushita Battery Industrial Co. and by the Swedish National Development Co., which have given an energy density of 80 Wh/kg at C/5 and a cycle life of 200 cycles to 60% depth of discharge. The latter company have produced 15-30 kWh batteries for EV testing. One limitation of the iron-air system for this application is the low power density achieved - a maximum value of 30-40 W/kg is reported. Similar cells are also being developed by Westinghouse (USA) and Siemens (Germany). 

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