Thermal batteries are preferred for their ruggedness,
safety, reliability, and deliver extremely long shelf life.
However, due to the use of squibs and the need to keep
the electrolyte continually molten at 400°C to 700°C for
optimum conductivity, thermal batteries are somewhat bulky to
incorporate a squib and layers of insulation that retain heat to
keep the electrolyte molten, while also protecting surrounding
components from heat-related damage.
Silver-zinc batteries are complex to manufacture since they
require a gas generator, tubular electrolyte reservoir, manifold,
battery block, vent, and heater system. As a result, silver-zinc
batteries tend to be expensive and require long production
lead times. Silver-zinc batteries also have performance
limitations due to their low energy density.
SPIN-ACTIVATED LEAD-ACID BATTERIES
Military fuses and certain marine applications are often
powered by spin-activated lead-acid batteries that store the
electrolyte (typically flouroboric acid) inside an ampoule or
bladder. When the projectile is fired, the bladder slices open
and the electrolyte is distributed throughout the cell stack
by centrifugal force. Spin-activated batteries manufactured
using lithium thionyl chloride (LiSOCL2) chemistry are used
to power minelets or communication jammers, which are
propelled by artillery shells and equipped with parachutes to
ensure a soft landing. The main advantage of a spin-activated
battery is its ability to deliver high rate power for extended
periods of time with no voltage delays. Spin-activated
batteries also have major drawbacks: relatively low capacity,
delayed activation, and the inability to be tested prior to use.
HIGH-POWER LITHIUM METAL-OXIDE BATTERIES
Lithium metal-oxide batteries are now available that use
commercial off-the-shelf (COTS) technology to deliver high
current pulses and high rate energy.
Constructed in a cylindrical shape with a carbon-based
anode, a multi metal-oxide cathode, organic electrolyte, and
a shut-down separator, lithium metal-oxide cells feature an
extremely high energy-to-size ratio, and are available in three
standard sizes: AA, CR- 2, and 20 mm length. For example,
an AA-size lithium metal-oxide cell can deliver up to 2 Wh of
energy with a nominal voltage of 4 V, a discharge capacity of
1,100 mAh, including the ability to generate 15 A pulses and
5 A continuous current.
Lithium metal-oxide batteries provide long-term reliability,
offering up to 20-year storage life due to a very low
annual self-discharge rate. These batteries feature a wide
temperature range (-40ºC to +85ºC), and permit instant
activation without the need for squibs or gas generators.
Once installed, they can remain “on” continuously while
drawing nominal amounts of daily current to permit periodic
testing for system readiness, thus reducing the number of
“duds” in missile guidance systems. These batteries also
comply with MIL-STD 810G specs for vibration, shock,
temperature, salt fog, altitude, acceleration (50,000 gn), and
spinning (30,000 rpm), and meet UN 60086 standards for
crush, impact, nail penetration, heat, over-charge and short
circuit. In addition, lithium metal oxide cells do not generate
high internal temperatures, so there is no need for the thermal
insulation layers common to reserve/thermal technologies.
Here are some real-life case histories involving lithium metal
BAE Systems/ODAM 60mm mortar guidance
systems: Under DARPA’s Optically Directed Attack Munitions
(ODAM) project, BAE Systems undertook a development and
integration initiative to demonstrate the feasibility of a laser-
guided, low cost 60-mm mortar round. BAE Systems selected
CR- 2 sized high power lithium batteries to power the system’s
laser-guided optical seekers. Lithium metal oxide batteries
were chosen over CR- 2 consumer type batteries because
their ability to operate in extremely cold environments (-40°C),
with up to four times longer shelf life ( 20 years vs. 5 years).
Unmanned aerial vehicles (UAVs): UAVs widely utilized
for unmanned air reconnaissance incorporate a battery-
powered back-up guidance system that allows an aircraft with
main power failure to glide to a safe landing. To power the
UAV’s emergency recovery system, a 32 V/480 W custom
battery pack was developed using 96 AA-size lithium metal
oxide batteries: resulting in a highly compact power supply that
weighed just 2 Kg including the metal enclosure (Figure 1).
Powering missile systems: Air-to-ground missile systems
previously powered by large silver zinc battery packs can be
converted to a pack half the size using high power lithium
batteries, enabling shorter design and production cycles
and major cost savings due to simplified manufacturing and
greater availability. This solution also led to reduced weight
and volume, and greater energy density (Figure 2).
Guided artillery shells: large reserve batteries are
currently utilized to deliver medium power, high capacity,
and low current pulses to power the artillery shell’s guidance
system. Converting to a lithium metal-oxide battery pack
would enable greater design flexibility, major size and weight
reductions, and significant cost savings.
The introduction of the lithium metal-oxide battery has
enabled single-use military systems to become more miniature,
cost effective, and reliable with the ability to perform periodic
system readiness tests. However, as with any new technology,
careful evaluation is required to ensure that the right battery is
being selected based on application-specific requirements.
Figure 2. Air-to-ground missile
systems can use high power lithium
batteries to replace large silver-zinc
battery packs, shortening design and
production cycles and reducing costs
due to simplified manufacturing and