Grids, lead-acid cells

Fig. 5.13 Motive power lead-acid cell with tubular positive plates in which the active material is contained in pre-formed terylene tubes, and negative pasted grid plates surrounded by microporous polyvinyl chloride separator envelopes. The case and lid are formed of heat-sealed polypropylene. (By courtesy of Chloride Industrial Batteries.)...

The plates (electrodes) of the lead—acid cell comprise grids (current collectors) and active mass. The active mass is huilt of two functional structures ... 

Figure 17.2 Antimony influence in the grid alloy on charge characteristic of vented lead acid cells.

Figure 1.19 represents the theoretical maximum amount of energy that a lead-acid cell can deliver. For 1 kWh to be delivered by a theoretical lead-acid battery cell, 6.15 kg of active materials are needed for the reaction. To transform this theoretical cell into a practical power source, however, a number of technical components are necessary such as grids, separators, battery container, valve, H2SO4 diluted with water in excess amount, etc. 

The reactants in a lead-acid cell are spongy lead packed into a lead grid at the anode, red-brown lead(lV) oxide packed into a lead grid at the cathode, and an electrolyte solution consisting of dilute sulfuric acid (about 35% H2SO4, by mass). In this strongly acidic medium, the ionization of H2SO4... 

As the name suggests, the materials used in a lead-acid battery include lead and an acid. Figure 11.19 shows that the electrodes in each cell are constructed using lead grids. One electrode consists of powdered lead packed into one grid. The other electrode consists of powdered lead(IV) oxide packed into the other grid. The electrolyte solution is fairly concentrated sulfuric acid, at about 4.5 mol/L. 

The lead/acid battery used in conventional gasoline-fueled automobiles consists of six 2.05 V cells connected in series (for a 12 V electrical system). The current collectors are lead grids filled, when in the charged condition, with powdered lead (anode) and a lead/lead(IV) oxide mixture (cathode), and the electrolyte is aqueous sulfuric acid. During discharge, the following reactions occur ... 

Active mass — The portions of a -> battery or -> accumulator which are participating in electrode reactions, i.e., in the transformation of chemical into electrical -> energy or vice versa. In a -> lead-acid battery active masses are lead dioxide and lead, with the lead or lead alloy grid serving as -> current collector and mechanical holder and all other components are not active masses. For maximum -> energy density the fraction of active mass in the overall cell weight should be as large as possible. 

Current collector — In the battery discipline, a good electron conductor support designed to transfer electrons from the external circuit to the active materials of the cell. Current collectors are usually metal foils or nets that are inert under the operational chemical and electrochemical conditions. In some cases carbon cloth is also used. In secondary - lead-acid batteries the chemical nature of the current collectors (plates, grids) is particularly imperative, as it influences the self-discharge and the performance under overcharge and discharge conditions. Frequently, current collectors have also the important role of imparting mechanical stability to the electrodes. 

Another common storage battery is the lead-acid battery. The standard automobile battery is an example of a lead-acid battery. Most auto batteries of this type contain six cells that generate about 2 V each for a total output of 12 V. The anode of each cell consists of two or more grids of porous lead, and the cathode consists of lead grids filled with lead(IV) oxide. This type of battery probably should be called a lead-lead(IV) oxide battery, but the term lead-acid is commonly used because the battery s electrolyte is a solution of sulfuric acid. 

The value of backup power is as much as three to four times the value of primary power on a kilowatt basis. For example, the lifecycle cost of the backup power systems found at the base of a cell tower, which now consists of a bank of lead acid batteries and a diesel or natural gas fired combustion engine, is between 3000 and 4000 per kW. Critical power facilities for data processing centers and the like are also in this cost range. The simple fact is that customers need electricity and will pay a considerable insurance premium to obtain assurance of uninterruptible power. In the case of cellular phone service providers, their federal FCC license may be at risk if they are unable to demonstrate adequate operating capability in the event of grid outages. 

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