Batteries discharge

As a battery discharges the concentration of 2incate in the electrolyte increases. Eventually, the concentration exceeds the solubiUty of 2inc oxide [1314-13-2] ZnO, which can precipitate from the solution... 

As a lead-acid battery discharges, lead sulfate builds up at both terminals, and water builds up in the electrolyte. The reactions in a lead-acid battery, however, are reversible. When electrical power is applied to the battery, the flow of electrons is reversed. They now flow from the positive terminal to the negative terminal. 

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

Worked Example 7.7 The temperature voltage coefficient for a simple alkaline torch battery is —6.0 x 10 4 VK-1. What is the entropy change associated with battery discharge The number of electrons transferred in the cell reaction n = 2. 

Direct errors can occur in simple positive-displacement pumps as the result of battery discharge and other effects. 

Figure 1 shows the battery discharge effect on flow rate(3). 

The initial flow rate decrease is caused by the NiCd battery discharge characteristic. Direct error can also result from the effect of inlet pressure changes on flow as shown in Figure 2(3). Since the pump is working on a compressable fluid, air, any increase in the pressure drop reduces the flow rate. 

It follows from this brief outline that if maximum useful power is to be extracted from the cell then the electrolyte resistance must be kept to a minimum. This is dependent not only on the material but also on the geometry of the membrane which must be as thin as is practicable. As in the case of the fuel cell, the e.m.f can be calculated from thermodynamic principles. In fact the chemical reactions occurring when the sodium ions react with the sulphur are rather complex and the sodium sulphur ratios change as the battery discharges. The first product as the cell discharges is the compound Na2S5. 

V > 0.75 U. (For a 12 V nominal battery, discharge is not allowed to proceed under 9 V.) Conversely, if the current I is kept below 0.1 x U/p° during the application, it means that the generator is oversized for the application. 

The real situation is less stark than that indicated. For one thing, the material on the plates may not be uniform and that which electrochemically converts to another substance at first may do so more easily than the material at deeper layers on the electrodes. One of the properties by which the value of a battery is judged is the length of the almost flat plateau, i.e., a good battery discharges for many hours with only a... 

Battery Discharge reactions Electrolyte Electrode materials E M /V Applications... 

The mechanism of the reaction is very complex and not completely understood [368-370], These reactions take place both at the interface between FeS and the electrolyte and in the interior of the FeS granules. During battery discharge, the following reactions take place [371] ... 

Theoretical capacity — A calculated amount of electricity (-> charge) involved in a specific electrochemical reaction (expressed for -> battery -> discharge), and usually expressed in terms of -> ampere-hours per kg or -> coulombs per kg. The theoretical capacity for one gram-equivalent weight of material amounts to 96,487 C (see -> Faraday constant) or 26.8 Ah. The general expression for the calculation of the theoretical capacity (in Ah kg-1) for a given -> anode material and - cathode material and their combination as full cell is given by... 

What happens to l8CC as a battery discharges Is a battery a system at equilibrium Explain. What is clce when a battery reaches equilibrium ... 

During battery discharge, as shown in Figure 1 with the Daniell cell as an example, the electrode (a zinc rod immersed in a zinc sulfate solution) at which the oxidation reaction takes place is called the anode, and is the negative electrode. The other electrode (a copper rod immersed in a copper sulfate solution) at which the reduction reaction takes place is called the cathode and is the positive electrode. The electron flow in the external circuit is from anode to cathode (the current, /, conventionally flows in the opposite direction to that of the electrons), and in the electrolyte phase the ionic flow closes the circuit. The net result of the charge flow round the circuit is the cell reaetion, which is made up of the two half-reactions of charge transfer that describe the chemical changes at the two electrodes. 

Fig. 5.13 Typical lead-acid battery discharge voltage as a function of time...

Capacity. The capacity of a battery depends on how much of the active materials at each electrode are consumed during battery discharge. The theoretical capacity of each electrode, with units of ampere hours, is calculated from Faraday s law, with the weight (w) and molecular weight MW) of active (reactant) material and the number of electrons involved in the electrode reaction (n) ... 

FIGURE 26.38 Voltage vs. time curve during battery discharge at a constant current. 

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