A primary battery contains chemical energy which can be released as
electrical energy on demand. Lithium batteries have been successful because
they contain more energy per unit mass than do conventional batteries. The
characteristics of lithium metal which makes this so are its high voltage,
reactivity, high capacity, and low equivalent weight. The same properties
which result in a lot of energy in a small package also contribute to
potential hazards if the energy is released at a fast uncontrolled rate.
Another hazard of lithium is its low melting temperature (180ºC). When
lithium melts it is no longer constrained by the anode configuration within
the electrode pack. Direct contact with the cathode can take place, leading to
violent chemical reactions.
Lithium batteries are relatively new and safety has been paramount in their
development. In recognition of the hazards of these high energy density
systems, safety has been incorporated into the design, specification, and
manufacture of lithium cells and batteries. The user is entitled to assume
that the batteries are safe when handled and used in a proper manner.
Not all hazards can be designed out of the batteries, nor can safety
devices take care of all situations. Warning labels should be provided with
all batteries. The warnings must be taken seriously. Batteries must not be
abused or used in situations for which they have not be designed. The user is
the last line of defense.
Any end item containing a lithium battery, and the battery itself if it is
handled outside the end item, must be marked with an external label warning
users of the hazards associated with lithium batteries. Marking in accordance
with the requirements of Title 49 Code of Federal Regulations (CFR) 1910.1200
is also required.
A Halon fire extinguisher should not be used on burning lithium. A graphite
based Class D extinguisher is useful for small fires involving lithium. The
burning lithium must be covered completely and allowed to cool.
Lithium in the presence of water will generate hydrogen gas. If the gas is
not dissipated quickly, an explosive mixture of hydrogen and oxygen may form.
Water is useful for small fires in an open, well ventilated area where the
hydrogen will be dissipated and the cooling effect of the water will
extinguish the fire. Residual water will be caustic.
Lithium battery fires are handled differently from burning lithium since
little, if any, lithium metal is exposed. These fires are due to the burning
of such materials as the plastic components, other battery parts, electrolyte
(that is released during venting or rupture), or chemicals produced as the
result of electrochemical reactions, in addition to lithium. Such fires will
also give off toxic gases and fumes.
Most recent recommendations suggest the use of copious amounts of water to
control a lithium battery fire. Water will cool the fire and reduce the
overall hazard. Graphite or Lith-X, used to control a lithium fire, are
conductive. They can short out a battery if they come in contact with the
terminals of a live battery. Alternatively, if feasible, it may be better to
evacuate all personnel and let the fire burn itself out.
If the fire can definitely be attributed to burning lithium, the fire
should be controlled with graphite or Lith-X and not with water.
Safety and Ancillary Features
Current and Thermal Protection System
Spiral-wound lithium cells are capable of delivering high current output
due to the high surface area of the wound electrodes. To ensure safe
operation, manufacturers of high rate cells normally require the use of
protective devices, such as electrical fuses to limit the amount of current
which can be drawn from the battery. Thermal switches can be used to cut off
the discharge if a battery reaches high temperatures during use. These devices
provide good protection against electrical abuse. However, such devices can
also be troublesome. Fuses must be replaced when blown. Protective devices can
create dimensional problems when battery size is critical. Protective devices
increase battery costs.
PTC (Positive Temperature Coefficient) devices eliminate the need for
electrical fuses or thermal devices to protect the battery against short
circuits or discharge at currents above design limits. Under normal operating
conditions, the PTC device does not impair cell performance. However, when a
cell is short-circuited or discharged above design limits, the PTC device
causes the cell's internal resistance to increase substantially. This limits
the amount of current which can be drawn from the cell and keeps the internal
temperature of the cell well within safe limits.
Solid cathode designs appear to be intrinsically safe for operation at
temperatures up to 70ºC. Provided that devices in which they are used do not
allow voltages over 3 V across a single cell, violent rupture is a remote
likelihood. For series connected cells, diode protection can be incorporated.
This practice will prevent one cell from becoming discharged before others and
being forced to carry a current which would drive its electrodes into a
reaction which would result in a violent rupture.
Soluble cathode designs are considerably less robust because these are
often large surface area, high rate designs. Thus, they must be protected
against short-circuiting, overdischarge, temperatures above 75º - 85ºC,
crushing, puncturing, and incineration.
Navy policy requires that safety qualification tests shall be conducted
according to Technical Manual (TM) S9310-AQ-SAF-010. The pass/fail criteria
specified in the TM are platform specific and must be applied to the overall
system. The safety review is dependent on the battery and the equipment as
well as their planned use. Therefore, this review is normally conducted by the
Navy activity (or by Navy personnel) and funded by the Navy Program
Mechanical Design - Safety
The mechanical design of any battery and its housing will be governed by
environmental, safety and reliability requirements. TM S9310-AQ-SAF-010
requires that, for safety, multi-cell batteries "be constructed so that they
are not interchangeable with commercial batteries used in consumer products
such as flashlights or radios."
Methods of mechanical connection should be appropriate for the stresses
which they will receive. Because errors in assembling a battery could
introduce safety risks, TM 9310-AQ-SAF-010 states, "in development programs,
assembly of batteries by user personnel should be avoided."
The use of lithium batteries poses several serious concerns. First, liquid
cathode systems such as thionyl chloride, sulfur dioxide, and sulfuryl
chloride pose serious health risks if onboard venting were to occur,
discharging toxic gases inside the submarine. In addition, these gases are
very corrosive and could cause serious damage to equipment. Use of other types
of lithium batteries (such as solid cathode systems) do not pose the same
level of health risk, but still introduce the problems associated with packing
a large amount of energy within a relatively small space. Therefore, the solid
cathode batteries are preferred for submarine use.
Specific concerns about the use of lithium batteries include cases where
cells malfunctioned or are electrically abused (by shorting, charging, or
over- discharging). These events can cause cells to vent with flame, thus
initiating shipboard fires. In addition, the combustion products of a lithium
battery fire can be quite toxic and corrosive. Table 9-4 lists some lithium
battery chemistries that have been approved for specific systems on specific