lead-acid battery

The lead-acid battery may be any of the following kinds:

Image from MSN Encarta

The lead-acid battery, invented in 1859 by French physicist Gaston Planté, is the oldest type of rechargeable battery. Despite having the second lowest energy-to-weight ratio (next to the nickel-iron battery) and a correspondingly low energy-to-volume ratio, its ability to supply high surge currents means that the cells maintain a relatively large power-to-weight ratio.

These features, along with its low cost, makes the lead-acid battery ideal for use as car battery, as it can provide the high current required by automobile starter motors. The lead-acid battery also used in vehicles such as forklifts, in which the low energy-to-weight ratio may in fact be considered a benefit since the battery can be used as a counterweight. Large arrays of lead-acid battery cells are used as standby power sources for telecommunications facilities, generating stations, and computer data centers. The lead-acid battery is also used to power the electric motors in diesel-electric (conventional) submarines.

The principle of the lead-acid battery cell can be demonstrated with simple sheet lead plates for the two electrodes. However such a construction would only produce around an amp for roughly postcard sized plates, and it would not produce such a current for more than a few minutes.

A plate consists of a rectangular lead plate alloyed with a little antimony to improve the mechanical characteristics. The plate is in fact a grid with rectangular holes in it, the lead forming thin walls to the holes. The holes are filled with a mixture of red lead and 33% dilute sulphuric acid (different manufacturers have modified the mixture). The paste is pressed into the holes in the plates which are slightly tapered on both sides to assist in retention of the paste. This paste remains porous and allows the acid to react with the lead inside the plate increasing the surface area many fold. At this stage the positive and negative plates are identical. Once dry the plates are then stacked together with suitable separators and inserted in the battery container. An odd number of plates is always used, with one more negative plate than positive. Each alternate plate is connected together. After the acid has been added to the cell, the cell is given its first forming charge. The positive plates gradually turn the chocolate brown colour of lead dioxide, and the negative turn the slate gray of 'spongy' lead. Such a cell is ready to be used.

Source: WikiPedia

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