Page 169 - Battery Reference Book

Lithium-thionyl chloride primary batteries 9/9

Table 9.7 Comparison of lithium-sulphur dioxide and mercuric as great or greater energy densities, in particular the
oxide-zinc cells lithium-thionyl chloride systems (see below). How-
ever, the latter system may give rise to sponta-
Lithium-sulphur Mercuric neous decomposition of explosive violence in high-
dioxide oxide-zinc
rate batteries while the other lithium systems do not
have the high-rate capabilities of those using soluble
Volumetric energy depolarizers.
density (W h/dm3) 420 500 (at best) Lithium-sulphur dioxide cells are available in a
Normal working variety of cylindrical cell sizes from companies such
voltage (V) 2.75 1.25 as Honeywell and Duracell International. capacities
Volumetric capacii y available ranging from 0.45 to 21 Ah. Larger cells
(A wh) 153 400 are under development. A number of the cells are
Relative cell volume manufactured in standard ANSI (American National
(per A h) 2.6 1 .o Standards Institute) cell sizes in dimensions of popular
conventional zinc primary cells. While these single
cells may be physically interchangeable, they are not
oxide-zinc battery can occupy considerably more electrically interchangeable because of the high cell
space than the equivalent lithium-sulphur dioxide cell. voltage of the lithium cell.
The lithium-sulphur dioxide system is versatile and Standard and high-rate cells are available. The
relatively inexpensive. This battery has excellent stor- standard cell is optimized to deliver high-energy output
age characteristics. Honeywell claim that the batteries over a wide range of discharge loads and tempera-
should store for 12 years at 20°C. The battery can tures. The high-rate cell is designed with longer and
be supplied either as reserve batteries with capacities thinner electrodes than the standard cell and delivers
between 20 and lO0Ah or as active batteries in the more service at a high discharge rate (higher than the
0.7-20Ah range (see Table 56.2). 10 h rate) and at low temperatures. At lower discharge
The lithium-sulphur dioxide battery has a high rates, the service life of the high-rate cell is less than
power density and is capable of delivering its energy that delivered by the standard cell.
at high current or power levels, well beyond the In addition, Duracell manufacture a lithium limited
capability of conventional primary batteries. It also has (or balanced) cell (designated SX). The cell is designed
a flat discharge characteristic. with a stoichiometric ratio of lithium to sulphur diox-
Lithium-sulphur dioxide batteries are subject to ide in the order of 1: 1 rather than the excess of lithium
the phenomenon known as voltage delay, a char- used in the other designs. The lithium-limited feature
acteristic shared with lithium-vanadium pentoxide ensures the presence of sulphur dioxide throughout the
arid lithium-thionyl chloride batteries. After extended life of the cell to protect the lithium from chemically
long-term storage at elevated temperatures, the cell reacting with the other cell components. This design
may exhibit a delay in reaching its operating voltage has been found successfully to withstand extended
(above 2.0 V) when placed on discharge, especially at reverse discharge below 0 V at rated loads. In addition,
high current loads and at low temperatures. This start- these cells do not produce the toxic chemicals that form
up delay is basically caused by film formed on the when standard cells are fully discharged, thus simplify-
anode, the characteristic responsible for the excellent ing disposal procedures. The lithium-limited cell does,
shelf life of the cell. The voltage delay is minimal however, deliver lower capacity at low discharge rates,
for discharge temperatures above -30°C. No delay is compared with the standard cell (below the 5 h rate).
measurable for discharge at 21°C even after storage at Claimed advantages of lithium-sulphur dioxide
71°C for 1 year. On -30°C discharges, the delay (time cells are their high energy density (275Wh/kgg1),
to 2V) was less than 200ms after 8 weeks' storage three times that of carbon-zinc cells, their high power
at 71°C on discharges below the 40h rate. At higher density, a wide operating temperature range (-54 to
rates, the voltage delay increased with an increase in 71"C), high cell voltage (2.95V), flat discharge curve
storage temperature and time. However, even at the and long shelf life (99% capacity retention after 5 to
2 h discharge rate, the maximum start-up time is 80 s 10 years storage at 2l'C).
after 8 weeks' storage at 71°C. After 2 weeks' storage,
the sta-up time is only 7 s. The start-up voltage delay 9.3 Lithium-thionyl chloride primary
can be eliminated by preconditioning with a short dis- batteries
charge at a higher rate until the opening voltage is
reached, since tlhe delay will return only after another This system uses a lithium anode and a gaseous cath-
extended storage period. ode dissolved in an inorganic electrolyte. It has a
As mentioned above, the lithium-sulphur dioxide 3.63 V open-circuit voltage and a typical voltage under
system has emerged as the leading candidate among rated load of 3.2-3.4V. Like the lithium-sulphur
the high energy density batteries for high-rate applica- dioxide system, it has a very flat discharge profile
tions. Other lithiurn batteries are capable of delivering through 90% of its life. Cell construction is similar