Japan successfully constructed the world's first lithium-ion batteries submarine "Oryu" (meaning: phoenix dragon) with the hull number SS-511. On October 4, Oryu was launched into the water in a naming ceremony.

Previously the Soryu-class submarines were equipped with lead-acid batteries. However, Oryu is the first one in the class to use lithium-ion batteries in place of lead-acid batteries for two advantages. First, the new li-ion batteries can store double the power as previous lead-acid batteries can. Next, the sub's submerged endurance is increased in the length of time. The boat's stealth and operational capabilities are enhanced.

Oryu is the 11th submarine of the Soryu class in the Japan Maritime Self-Defense Force (JMSDF). Soryu means blue dragon. The series of submarine is typically about 84 meters long. Oryu's displacement is 4,100 tons when underwater. Its top speed is 20 knots when submerged and it can dive into a depth of 700 meters.

Oryu's build cost is about 66 billion JPY (around 18 billion NTD). Its biggest upgrade in the Soryu class is to replace lead-acid batteries and the air-independent propulsion (AIP) system with lithium-ion ones that are supplied by Japan's GS Yuasa Technology. Oryu will enter service with JMSDF in March 2020.

Oryu is mainly supported by diesel generator and lithium-ion batteries. For a diesel engine to operate, it needs fresh air. Once the sub submerges, diesel generator cannot function. Therefore, inside the sub, there must be lots of batteries installed. When the sub is surfaced, these batteries must be fully charged. When submerged, the boat is on battery power.

Lead-acid batteries are the primary batteries for global attack submarines. However, when compared with li-ion batteries, lead-acid ones are huge in size and too heavy. Their performance is hard to continuously improve.

In order to increase the time of submerge, all countries' submarines initially use AIP systems because AIP allows a sub to stay underwater for more than three weeks during slow speeds without accessing to external oxygen. However, now Oryu uses li-ion batteries to replace AIP because most of AIP systems' fuels must be stored in low temperature and high pressure. This causes higher risk of safety during battles.

Many countries begin to look forward to li-ion batteries' applications in attack submarines for 2 reasons below. Firstly, li-ion batteries have been manufactured massively and commercialized. Its performance/cost ratio has improved year by year. Secondly, for li-ion batteries' performance, there is still huge room for improvement.

According to plans of Japan's Ministry of Defense, the subs that are built after 2015 are expected use li-ion batteries to replace lead-acid batteries. This move will increase Soryu-class sub's submerging time by 45%. Li-ion batteries will allow the sub to travel at higher speeds when underwater, and their weights are one-fifth of that of lead-acid ones.

Li-ion batteries boost the acoustic edge during sensitive operation for the new sub. Simply put, improvement of submarine stealth mainly depends on significantly quieter power source, to be harder to detect. When underwater, operators can shut off the primary diesel generator and rely on li-ion batteries for longer range of power endurance.

Li-ion batteries are gaining ground in the defense industry. For example, recently Donald Trump, the president of the US, expressed his hopes to enhance researches of lithium sea-water batteries, in order to strengthen the US defense industry's capability. In particular, there is lots of lithium in sea water. Thus, the cost of lithium sea-water batteries is lower than non-sea-water lithium batteries. What's more, sea-water batteries can reduce the risk of battery fire. If this sea water batteries technology can be massively developed, submarine safety can be hugely improved.

(Photo credit: Japan Maritime Self-Defense Force (JMSDF) Facebook; Article by Daisy Chuang)

Note: 20 knots are equal to 37.04000 km/hour