The number of submarines patrolling the world’s oceans is constantly growing. To protect their territorial waters as well as their interests in different regions of the world, submarine operating nations are therefore facing two significant challenges: range – and therefore autonomy – and discretion. Propulsion plays a significant role in this context, but existing technologies have a number of limitations, including the production of hydrogen-like Lead-Acid Batteries (LAB) – which presents a significant safety risk.
Lithium-Ion Batteries (LIB) hold great promises on a number of aspects. They provide greater energy than LABs, therefore giving submarines greater submerged autonomy while reducing indiscretion rate. They are also far more efficient in relation to charging. Where in order to reach 100% charge for LAB, the charging needs to happen onshore (the final charging phase releases hydrogen), LIB does not present the same risk. In fact, LIB batteries reach 98% charge by phase two, therefore making it possible to charge them while at sea. Finally, because the amount of power they produce is the same, regardless of the battery’s state of charge, they offer more tactical mobility.
Recognising LIB’ significant potential, Naval Group launched preliminary studies on the topic in 2006. The company subsequently concluded the system design phase, which included the selection of the battery supplier.
When designing the LIB for integration onto a submarine, Naval Group had to take a number of factors into account. First and foremost, from a safety point of view, it had to ensure the battery’s chemical intrinsic stability and perform safety analyses on physical, electrical and thermal safety barriers. Second, from a design standpoint Naval Group had to consider how to use industrial cells and how to organise the architecture of the batteries. In fact, while the risk of hydrogen is eliminated with LIB, the risk of fire remains. As such, Naval Group has applied a layered, Russian dolls approach: a string design, which includes mechanical barriers, encases packs that contain modules that contain the cells.
In 2020 Naval Group qualified the LIB in an on-shore facility, but trials have yet to take place on a submarine. In the meantime, the company has already been thinking about how to implement the technology on submarines. This includes considering the submarine electrical network’s architecture and charging systems, which will have to be different from those designed for LABs. Ventilation and cooling will also need to be taken into consideration.
Finally, Naval Group highlights the fact that future submarine designs will have to include room for evolutions.
“LIBs are in constant evolution, so it is important that such potential is taken into consideration from the start.”
Anthony Covarrubias, Operational Marketing Manager