Active materials utilization

Figure 8. The experimental data and computed curve of the active material utilization factor...

Figure 8 provides a comparison of theoretically computed vs experimental dependences of the active material utilization factor for the investigated electrode. Analytical equations (24) and (25) were used to calculate polarization as a function of the oxidation state, and to calculate the limiting value of the oxidation state as the function of the discharge current (see Figures 7 and 8). 

The expression for the active material utilization factor shows that in the process considered, it is impossible to achieve full utilization of the active reagents in the galvanostatic mode. 

Table 5.3. Range of mean active-material utilization (mAhg ) of negative plates with varying amounts of additive. ...

Table 7.5 Specific capacities, specific energies and positive active-material utilizations for cells with and without 2 wt% loadings of conductive additives [63,51].

In this section, the author describes only the functional electrolytes for corrosion inhibition of the aluminum current collector for use in high-power, large-size batteries. The functional electrolytes not only is improving the active material utilization, but also all other materials, which improves the overall cell performance. If we compare the cells to our human body, the electrolyte can be considered to be... 

Depending on the type of battery used, the specific expander as well as its content in NAM should be selected. For example, VRLA batteries normally use a higher expander concentration than conventional flooded batteries. Expanders such as Indulin AT and Kraftplex (both lignins) increase the active material utilization when increasing their concentration in the range of 0.25 to 0.75 wt%. The Lignotech D-1380 expander can improve the battery s capacity as its concentration is increased, as shown in Figure 2.6. 

The primary disadvantage of sintered nickel electrodes is that they contain a relatively low ratio of active materials to inaetive materials compared to some types of non-sintered electrodes. Sintered electrodes typieaUy eontain as much as 60% inactive material, in the form of the porous electrode substrate and/or current collector. Practical sintered nickel electrodes yield about 100 to 120 mAh/g, depending on the method of preparation and the active material utilization. This is only about 40% of the theoretical specific energy of the active material. Also, the sintering proeess itself is relatively expensive and must be done at high temperatures under a redueing atmosphere. 

The average zinc electrode active material utilization was found to be about 60% of the theoretical capacity. The reason for this relatively low electrochemical utilization has not been reported in the literature but may be related to the solubility and complex chemistry of zinc in alkaline solution. The utilization obtained will be a function of the electrode design and composition and will be affected by the use of any additives either to the electrode or the electrolyte. The utilization of the zinc electrode may also vary for a specific cell design and must be taken into account in the electrochemical design and active material balance of the cell. 

Electrochemical Design. The electrochemical design of the cell consists primarily of balancing the active materials present in the electrodes. This previously has been discussed for each of the two electrodes separately, the nickel positive electrode and the zinc negative electrode. When combined in the cell, the two active materials must be present in some ratio with respect to each other. As with most other alkaline nickel batteries, the nickel-zinc system is typically positive (nickel electrode) limited. This means that the cell contains more zinc active material, on an Ampere-hour basis, than nickel active material. This must take into account the active materials present in the cell in addition to the active material utilization of each. 

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