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Japan's Silent Submarines Extend Range With Lithium-Ion Batteries (nikkei.com)
AmiMoJo shares a report from Nikkei Asian Review: Japan's first submarine powered by lithium-ion batteries was launched on Thursday. The [Soryu-class diesel-electric] submarine can reach speeds of roughly 20 knots and displaces 2,950 tons. It will be delivered to the Japan Maritime Self-Defense Force in March 2020. Batteries are recharged by the energy generated by Oryu's diesel engines. The vessel switches to batteries during operations and actual combat in order to silence the engines and become harder to detect. The lithium-ion batteries radically extend the sub's range and time it can spend underwater.
Subs running on batteries still drive propellers that create noise. It's not the power source of a sub that is most important it is the advanced sensor suites capable of hearing a dolphin fart 100 miles away that makes it dangerous. There are no great technological secrets involved with building a modern day sub. Specs on everything from power sources to composite hull materials are available to anyone. The specs for the sensor suites and targeting systems are not so readily available. For a lot of countries costs determines what type of sub they build but countries such as the US have never shied away from developing cutting edge military technology regardless of how much it costs.