Intercell connections

The dispersion of a band is determined by the magnitude of the coefficients of the atoms that form intercell connections in the polymer. 

Welding of conductive tabs between cells is the preferred method of intercell connection for most of the other battery systems. The tab materials for most applications are either pure nickel or nickel-plated steel. The corrosion resistance of the nickel and its ease of welding result in reliable permanent connections. The resistance of the tab material must be matched to the application to minimize voltage loss. The resistance can be calculated from the resistivity of the material, which is normally expressed in ohm-centimeters. 

Intercell and battery connections need to be carefully made to withstand the severity of the equipment environment. Intercell connections shall be welded rather than soldered to avoid heat conduction to the interior of the cell. 

Cathode (Positive Plate). The cathode consists of a depolarizer and a current collector. These depolarizers are powders and are nonconductive. In order for the depolarizer to function, a form of carbon is added to impart conductivity a binder is added for cohesion, and a metal grid is used as a current collector, a base for the cathode, to facilitate intercel connections and battery terminations. Possible cathode formulations are shown in Table 17.3... 

Cast-on battery elements are either continuously connected or made in discrete one-cell modules. The first method requires that long intercell connections be used, which travel over the intercell partition and are seated in a slot in this partition this is known as the loop-over-partition design. In the second cast-on method, tabs on the ends of the plate straps are positioned over holes that have been prepunched into the intercell partitions of a battery case. These tabs are welded together manually with a very small torch or automatically by a resistance welding machine. The latter also squeezes the tabs and the intercell partition to provide a leak-proof seal. 

Traction batteries are physically sized to fit a myriad of different forklift trucks, and so the final assembly for a traction battery consists of inserting preformed and pretested cells into a sturdy metal box (tray), making intercell connections, making cable connections, and sometimes adding a tar or plastic (urethane) material in the spaces between cell covers. 

Electrical Networking. During the lifetime of a battery, individual cells may fail. Such an occurrence will result only in the reduction of the open circuit voltage by 2.58 V per cell failure because the failure mode of ZEBRA cells is an internal short (due to the reaction of the secondary liquid electrolyte with sodium forming a solid aluminum shunt). Because of this characteristic, long series chains with 216 cells and 557 V can be built. Intercell connections or voltage taps are not necessary. 

One such configuration is shown in Figure 27.4. The two-layer pellet consists of an electrolyte layer (lithium chloride-potassium chloride) with a binder such as kaolin or micro-size silica, and a second layer composed of calcium chromate, plus some electrolyte. Calcium metal is used as the anode and zirconium-barium chromate heat paper is again the heat source, with dumb-bell shaped parts serving as intercell connections. 

The pyrotechnic paper or heat paper supplies the thermal energy to elevate the thermal battery cell to operating temperatures. The pad consists of a ceramic fibre paper, which acts as a binder/carrier for a slurry of zirconium metal fuel and barium chromate oxidant. The paper is extremely fast burning, making it ideal for a fast activation cell. Because the remaining ash of the heat pad is electrically non-conductive, it is necessary to provide a means for series intercell connection. 

The intercell connection is provided, along with the calcium anode, by a dumb-bell shaped piece of steel... 

Table 60.1 shows current-life parameters for a wide variety of general-purpose thermal batteries produced by Catalyst Research Corporation. The height of the batteries is determined by the power required of the battery. The same power output can be achieved in a number of case diameters, by using different intercell connections (series, parallel or series-parallel) to provide the desired voltage-current parameters. A thermal battery is a low-impedance device much higher currents than indicated may be drawn for shorter periods of time. 

---