Technical issues and the Soryu - Lithium-ion batteries no AIP

A bank of lithium-ion batteries (LIBs) for marine use. LIBs are being developed and offered for future Japanese, German, French and probably Swedish submarines.

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The new batch of around 6 Soryus being built for the Japanese Navy (known as Japan Maritime Self-Defence Force (JMSDF)) over the next 8 years will be built around Lithium-ion batteries (LIBs). LIBs represent a very significant technical departure from the existing lead acid batteries. This influences the structure of the submarine's entire electrical system (wires etc) not just the batteries themselves.

Use of LIBs may allow a submarine to stay submerged for a longer time than lead acid batterries as long as the submarine is not driven too quickly for too long as this runs the batteries flat.

Air independent propulsion (AIP)

Some confusion has been created that LIBs are some separate component replacing  air independent propulsion (AIP). This is basically untrue. LIBs are replacing lead acid batteries in new submarines to be built from around 2015. LIBs cannot be retrofitted to replace lead acid batteries in individual submarines already operating. Any battery, LIB or lead acid, will almost always rely on regular recharging from a submarine's air dependent diesel engines. Some AIP technologies can charge batteries - but there are downsides-tradeoffs. The relatively few subs in the Asia-Pacific region that have AIP (none are Australian) might still use AIP even if they are in future built with LIBs. Those that use AIP might typically want their subs capable of a close to shore (closed shallow waters, littorals, straits and harbour mouths etc) near motionless, defensive missions of up to 3 weeks submerged.

AIP, unlike batteries, cannot be recharged during a mission.

AIP has been compared (by submarine sales teams and the mainstream media) to nuclear propulsion. This is not true. AIP might allow a submarine to move at 20+ knots for 5+ hours while a nuclear reactor can run at 30+ knots for 3 months or until a crew's food runs out.

Australia decided not to use AIP in the Collins class due to Australian submarine mission profiles which need much diesel for long range rapid transit. This is even though Australia bought its subs from Kockums who are AIP experts. I haven't heard of any Australian interest in AIP for the future submarine. It is unclear whether Singapore's two HDW 218SG's on order will use AIP (but likely) and LIBs (maybe). Some Chinese subs are believed to use AIP, most likely mainly in defensive mode, not far offshore.

AIP is basically a 200 ton plug in the submarine for inclusion of a small engine and storage of extra fuel, alcohol or hydrogen and an oxidiser. The first batch of 6 to 7 Soryus (up to SS-507?) do operate with Swedish designed Stirling engine AIP technology. The next 6 Soryu will most probably use LIBs.

The downsides of using AIP include: dangerous highly flamable oxidiser, heavy moving parts that need maintenance, less effective in warm seas, 3rd party contractual issues, technical advances including LIBs partly bypassing AIP, have persuaded the Japanese Navy that AIP is not worth including in their future Soryus. The 200 tons might be better used for more diesel or batteries. Australia, Malaysia and Indonesia have not used AIP in their submarines due to AIP's marginal worth.

More on LIBs

Returning to LIBs - LIBs are reputedly lighter (than the traditional lead acid batteries they are replacing). LIBs carry more charge (greater energy density) translating into more speed or a longer period the submarine can submerge. LIBs should take less time to recharge, so there is less "indiscretion" time when the submarine has to snorting-snorkel near the surface. The increased capability of anti-submarine sensors, including those mounted on satellites and UAVs, mean that  submarines in near surface snorting mode are becoming more vulnerable.

LIBs involve potential technical risks. LIBs may be more prone to catch fire (based on experience with the 787 aircraft LIBs). LIB use for submarines may be becoming safer than aircraft use due to heavier submarine LIBs with the extra mass more able to absorb heat. This should mean submarine LIBs do not get as hot as aircraft LIBs - hence submarine LIBs should be less prone to catching fire.
A second major difference is that aircraft LIBs have (or had) no dedicated fire suppressant systems while such systems should be built around submarine LIBs. Overall the experience of ironing out bugs on aircraft and car LIBs is valuable in the development of submarine LIBs.

New technology always involves some uncertainty. Lead acid batteries for submarine have a record of use since 1888 (hence their characteristics are more predictable) while LIBs probably have no operational use on submarines. The replacement cycle for submarine LIBs is also hard to predict.

Before Australia operates Soryus Japanese Navy Soryus will most probably have had several years experiece of using LIBs - hopefully ironing out all the bugs. Australia may be better placed if there is an option of deciding on LIBs or lead acid batteries before Soryus earmarked for Australia begin to be built.

Germany, and France are also developing and beginning to offer LIBs for submarine use. Presumably Sweden, South Korea and the US (for backup batteries) are also developing submarine LIBs.

Life Cyle Differences

One additional issue is that the Japanese Navy has been running its submarines with the assumption the service life is 15-20 years while Australia assumes submarines should be in service for at least 30 yours. This may or may not be a problem. After 15-20 years moving parts may or may not start to wear out. This may be most significant in the submarine's diesel engines and the very large electrical motor. Changing engines-motors is very heavy maintenance involving cutting into the submarine hull. This might only be possible in Japan for the Soryu? Maintenance realities may or may not be a problem.

If all these issues prove too hard over the next 5 years there are submarines operated by Germany,  France and Sweden (all of around 2,000+ tons surfaced) that may be adequate for what Australia needs. This is particularly under limitations in funds for purchase and crew availability problems.

Pete