Page 240 - Lindens Handbook of Batteries

9.34 PRIMARY BATTERIES

FIGURE 9.33 Exploded view of a single cell from Polaroid P-80
battery pack.

Battery Construction The P-80 battery uses chemistry quite similar to Leclanché round cells,
although the shape is unique. Figure 9.33 details one cell (1.5 V). The electrode area is approxi-
mately 5.1 cm × 5.1 cm. The anode of zinc dust and binder (without mercury) is coated on a con-
ductive vinyl web.
The manganese dioxide is mixed in a thick paste that contains the electrolyte salts. The electro-
lyte is mainly zinc chloride with some ammonium chloride. The anode and the cathode are separated
by a thin film of cellophane. The complete 6 V battery has four cells. The four identical cells are
connected by vinyl frames to each other and the aluminum collector plates. A special conductive
coating allows the aluminum to bond to the plastic materials.

Battery Parameters The key battery parameters of the flat battery are similar to those of the
cylindrical one. The flat configuration provides low resistance by virtue of the geometry. The thin
layers need to stay in intimate contact to maintain the low resistance, and gassing effects have to be
minimized.
• Open-circuit (no-load) voltage: The open-circuit voltage in this battery is dependent on the
manganese dioxide activity and the system pH. The cathode slurry is adjusted to a constant pH
to minimize battery-to-battery voltage variation. For example, the P-80 battery is adjusted so the
voltage is 6.40 V at 56 days and 6.30 V after 12 months of shelf storage. The on-load voltage is
sensitive to the synthetic manganese dioxide used.
• Closed-circuit (on-load) voltage: The closed-circuit voltage is used as an indicator of the bat-
tery’s capability to deliver energy at high currents. In the case of the P-80 battery, a 1.63 A load
is used since that is one of the operating requirements for the camera. The closed-circuit voltage
is measured at 55 ms to minimize polarization effects. The normal closed-circuit voltage is 5.58 V
at 56 days and 5.35 V after 12 months of shelf storage. The on-load voltage is sensitive to the
synthetic MnO used.
2
• Internal resistance and voltage drop (delta V): The battery’s internal resistance is measured
by using the voltage drop or delta V at a given load for a specified pulse period. A major