Diesel electric submarines may be on the verge of returning to their simpler roots with the help of lithium-ion batteries.
High-tech diesel-electric submarines may begin to return to their simpler roots as Japan is pioneering a concept today that aims to eliminate AIP altogether. Their next generation Soryu class diesel-electric attack submarines will be equipped with lithium-ion batteries, and just like submarines dating back before World War I, they will run undersea on battery power alone.
The Soryu class is already a very modern submarine, having been introduced into service just over a decade ago. As an outgrowth of the previous Oyashioclass, these are not tiny boats, displacing 4,200 tons submerged and measuring 275 feet long, They are the largest submarines Japan has constructed since the end of World War II. They also feature an “X” tailplane configuration for extreme maneuverability in tight littoral environments.
Today seven boats are operational, all of which leverage Stirling Engine AIP technology licensed directly from Kockums—the same Swedish company that produces the Gotland class. Japan, an island nation with long and complex coastlines, uses its submarines to patrol its territorial holdings and to protect its shores. As such, the proven and affordable Stirling Engine-based AIP technology, paired with the class’s large size and ample fuel reservoirs, was a good, balanced fit for their needs. But now Japan wants to eliminate AIP technology altogether without losing its benefits, and in doing so free up room for other capabilities while also simplifying design, construction and sustainment of their future submarines. Above all else, this new configuration should result in quieter operation than most existing AIP capable submarines.
The idea is to install thousands of lithium-ion batteries along with powerful diesel engines and generators, as well as large exhaust and intakes stacks to accommodate them, into a tweaked Soryu design. A new power handling system that can deal with high power loads and optimize efficiency is also included in the concept. Basically, the configuration is similar to a standard diesel-electric submarine, that uses diesel engines and batteries alone for propulsion, but infused with new technology.
Lithium-ion batteries have a ton of advantages over their old-school lead-acid cousins. They keep up their output even when their charge runs low, they are lighter than lead-acid batteries, they can be charged exceptionally fast (hence the more powerful diesel engine and generators), and they can store much more energy. Compared to the AIP system they aim to replace, endurance should be similar, while the overall boat’s propulsion system design will be less complex and bulky. Not just that, but lithium-ion batteries can provide large output on demand, allowing the boat to dash mush faster while dived compared to one running on an AIP system.
The main downside to lithium-ion batteries is very well publicized: they are known to “runaway” and combust—exactly what you don’t want on a submarine. When they do so they produce very high heat, give off toxic fumes and expel conductive dust. They are also hard to extinguish using traditional means. But because weight is not as much of an issue on a large sea-going vessel, new methods of abatement can be put in place to lower the risk of a fire and its potentially catastrophic results.