Flat rectangular batteries

Lithium iodine batteries are available mostly in the pacemaker shape, i.e. in that flat nearly semicircle geometry of, e.g. 5 x 30 x 40 mm, with 1 to 3 Ah capacity at a weight of 10 to 30 g. For industrial applications flat rectangular formats are made with contact pins that make them mountable onto electronic boards. Button cells are also realizable. All cells have glass-to-metal seals for both polarities or for the negative one only. A button cell s cross-section is shown in Figure 18.26... 

The slim or flat rectangular batteries are designed to meet the needs of lightweight and compact equipments. The rectangular shape permits more efficient battery assembly, eliminating the voids that occur with the assembly or cylindrical batteries. The volumetric energy density of batteries can be increased by a factor of about 20%. 

Batteries are built in many different shapes and configurations—button, flat, prismatic (rectangular), and cylindrical (AA, AAA, C, D, 18650, etc.). The cell components (including separators) are designed to... 

Flat cell designs increase the available space for the cathode mix because the package and electrical contacts are minimized, thereby increasing the energy density. In addition, a rectangular construction reduces wasted space in multi-cell assemblies, (which is, in fact, the only application for the flat cell). The volumetric energy density of an assembled battery using flat cells is nearly twice that of cylindrical cell assemblies. 

The Li/Mn02 cells are manufactured and commercially available in a number of flat and cylindrical batteries ranging in capacity from about 30 to 1400 mAh. Larger-size batteries have been developed in cylindrical and rectangular configurations. The physical and electrical characteristics of some of these are summarized in Tables 14.19, 14.20 and 14.21. In some instances interchangeability with other battery systems is provided by doubling the size of the battery to accommodate the 3-V output of the Li/MnOj cell compared with 1.5 V of the conventional primary batteries, for example battery type CR-V3. 

The Li/(CF) system is adaptable to a variety of sizes and configurations. Batteries are available in flat coin or button, cylindrical, and rectangular shapes, ranging in capacity from 0.020 to 25 Ah larger-sized batteries have been developed for specialized applications. 

Li/l2 medical batteries are produced in a variety of sizes and shapes to meet specific applications. Their profiles range from rectangular to semicircular, or a combination. All of them are made quite thin and have flat sides because their primary application is in cardiac pacemakers. Cell thickness is typically 5 to 10 mm. The area of the lithium anodes ranges between 10 and 20 cm in current batteries. Some cells use a ribbed anode (see Fig. 15.9) to increase the amount of active anode surface area in the battery. 

This type of battery has a spiral-wound electrode pack, made from rectangular foil electrodes. Lithium foil is rolled on to an expanded metal mesh current collector as the negative electrode, and is separated from the similarly supported cathode by a polypropylene separator. Two types of cell construction are used jelly-roll electrodes in crimp-sealed or hermetically sealed cylindrical cells, and large 20-100Ah 12V flat-plate electrodes in large reserve batteries. It is a relatively high-pressure system and cells must have salety vents to avoid explosion in the event of accidental incineration (see Part 2 for further details of construction). 

In flat cells a zinc plate is coated with carbon to form a duplex electrode - a combination of the zinc of one cell and the carbon of the adjacent one. The Union Carbide Mini-Max cell contains no expansion chamber or carbon rod as does the round cell. This increases the amount of depolarizing mix available per unit cell volume and therefore increases the energy content. In addition, the flat cell, because of its rectangular form, reduces waste space in assembled batteries. 

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