Page 351 - Lindens Handbook of Batteries

14.16 PriMAry BATTerieS

be minimal and there will be no safety problems. Larger or high-rate cells can develop high inter-
nal temperatures if short-circuited or operated at excessively high rates. These cells are generally
equipped with safety vent mechanisms to avoid more serious hazards. Such cells or batteries should
be fuse-protected (to limit the discharge current). Thermal fuses or thermal switches should also be
used to limit the maximum temperature rise. Positive temperature coefficient (PTC) devices are used
in cells and batteries to provide this protection.

Forced Discharge or Voltage Reversal. Voltage reversal can occur in a multicell series-connected
battery when the better performing cells can drive the poorer cell below 0 V, into reversal, as the bat-
tery is discharged toward 0 V. in some types of lithium cells, this forced discharge can result in cell
venting or, in more extreme cases, cell rupture. Precautionary measures include the use of voltage
cutoff circuits to prevent a battery from reaching a low voltage, the use of low-voltage batteries (since
this phenomenon is unlikely to occur with a battery containing only a few cells in series), and limit-
ing the current drain, since the effect of forced discharge is more pronounced on high-rate discharges.
Special designs, such as the “balanced” Li/SO cell (see Sec. 14.5), also have been developed that are
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capable of withstanding this discharge condition. The use of a current collector in the anode maintains
lithium integrity and may provide an internal shorting mechanism to limit the voltage in reversal.
Charging. Lithium primary batteries, as well as the other primary batteries, are not designed to be
recharged. if they are, they may vent or explode. Batteries that are connected in parallel or that may
be exposed to a charging source (as in battery-backup CMOS memory circuits) should be diode-
protected to prevent charging (see chap. 5).

Overheating. As discussed, overheating should be avoided. This can be accomplished by limiting
the current drain, using safety devices such as fusing and thermal cutoffs, and designing the battery
to provide necessary heat dissipation.

Incineration. Lithium cells are either hermetically or mechanically sealed. They should not be
incinerated without proper protection because they may rupture or explode at high temperatures.
Currently special procedures govern the transportation and shipment of lithium batteries, and
procedures for the use, storage, and handling of lithium batteries have been recommended. 13–14
Disposal of some types of lithium cells also is regulated. The latest issue of these regulations should
be consulted for the most recent procedures (see Sec. 4.10 for details.) The U.S. Federal Aviation
Agency has adapted technical standard order TSO-C142-Lithium Batteries, governing the installa-
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tion and use of lithium primary batteries on commercial aircraft. U.S. DOT, iATA, iCAO, and other
governmental agencies issue regulations governing the shipment of lithium batteries.

14.5 LITHIUM/SULFUR DIOXIDE (Li/SO ) BATTERIES
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One of the more advanced lithium primary batteries, used mainly in military and in some industrial
and space applications, is the lithium/sulfur dioxide (Li/SO ) system. The battery has specific energy
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and energy density of up to 300 Wh/kg and 415 Wh/L, respectively, in large sizes. The Li/SO
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battery is particularly noted for its capability to handle high current and high power requirements,
excellent low-temperature performance, and long shelf life.
14.5.1 Chemistry

The Li/SO cell uses lithium as the anode and a porous carbon cathode electrode with sulfur dioxide
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as the active cathode material. The cell reaction mechanism is
2Li + 2SO → 2 Li SO ↓ (lithiumdithionite)
2 2
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