Home' Asia Pacific Defence Reporter : APDR October 2015 Contents 48 Asia Pacific Defence Reporter OCT 2015
charging and discharging, as well as preventing the
cell from exposure to excessive heat.
As yet, no operational submarine has been
commissioned with rechargeable lithium ion batteries
(LiB) in place of conventional lead acid accumulators.
Despite the great promise of increased energy density
and the smaller form factor, so more can be fitted
into the same space occupied by classic lead acid
accumulators, submarine developers are proceeding
APDR met and discussed LiB developments with
R&D personnel at HDW in Kiel. They have been
involved in careful design and testing as they scale up
from small numbers of cells to large scale assemblies.
APDR had the opportunity to observe some of this
testing and discovered the precautions being taken
when recharging against overcharge which can cause
thermal runaway, resulting in cell rupture and the
possibility of a fire or explosion.
Effective control systems and the LiB’s chosen
chemistry remove this risk. A comprehensive risk/
safety analysis has to be performed, taking into
account all aspects of risks and how risks can be
mitigated, this includes and is not limited to the cell
level, the system level, the overarching control as well
as the spatial/mechanical integration, cooling and
It is the electrolyte which is the problem.
A common source of lithium ions used is lithium
hexafluorophosphate, a white crystalline compound
LiPF6, which is dissolved in organic solvents like
propylene carbonate and dimethoxyethane. The latter,
being an ether, is highly flammable.
The chemical compounds being tested for submarine
LiBs are a closely held secret by the various designers
with no unclassified sources of information available.
LiBs are low maintenance, with no memory issues
and no scheduled charging/discharging cycles
required to prolong their lives. Each cell is fragile and
requires protection circuits to maintain safe operation
by restricting the peak voltage while charging, and
from dropping the cell voltage too low on discharge.
As well, the temperature needs to be monitored, with
the ideal ambient temperature maintained to around
room temperature, which is also comfortable for crew
working near them. Some manufacturers recommend
maintaining a 40% charge if the cell is to be out of use
for any period of time.
New battery chemistries are being tested all the
time and it is quite possible that future LiBs found on
submarines will have quite different chemistry from
present batteries, with much improved long-term aging
LiB CONTROL TECHNOLOGY
Charging and discharging control technologies for
LiBs are different from traditional battery charging. The
polar electrolyte requires monitoring of polarisation
voltage to control charging, rather than the simpler
techniques of constant current or constant voltage
charging methods usually encountered with other
types of batteries. What can be measured in an
LiB-system is current, voltage and temperature, with
the voltage giving a strong indicating whether you are
about to overcharge, deep discharge.
This means that the monitoring system needs to
monitor time, and through sensors, an intelligent/
adaptive cell model and corresponding algorithms for
each LiB cell’s state of charge and state of health,
since no two cells will ever be identical in terms of their
characteristics. As mentioned previously, there must
be fail-safe mechanisms triggered if there is a risk of
over-charge or over-discharge. The trigger has to be
set for ‘comfort’ rather than at the point where safety
dictates absolutely immediate action.
WILL AUSTRALIA’S FUTURE
SUBMARINES HAVE LITHIUM
Almost certainly. The Japanese may already be there,
and if so the French and Germans will not be far
behind. No Navy is going to commit conventional
submarines to the oceans without absolute confidence
that all elements of their ‘system of systems’ are safe
and working as they should.
With increasing range and accuracy of anti-shipping
missiles, there is now considerable debate about the
utility of destroyers and frigates in combat unless they
are comprehensively, and expensively, fitted out with a
wide range of defensive systems which can detect and
defeat multiple missile strikes coming in their direction
Submarines have great utility in confrontational
situations or even declared hostilities. Even the threat
they may be about, but not detected, will cause
surface vessels to be very cautious and constrained in
their freedom of action.
Australia’s Future Submarines will have the range
and underwater endurance required if LiB technology,
with fail-safe charging and control systems, is
coupled with highly efficient and quiet air independent
propulsion units. The risks of problems arising through
installed LiBs should be very slight indeed. ¢
" A common source of lithium ions used is lithium
hexafluorophosphate, a white crystalline compound LiPF6,
which is dissolved in organic solvents like propylene carbonate
and dimethoxyethane "
Action in the Control Room as HMAS Dechaineux surfaces. (CoA)
17/09/2015 5:21 pm
Links Archive APDR Sept 2015 APDR November 2015 Navigation Previous Page Next Page