The Japanese Navy has added a new submarine, "Toryu" (Fighting Dragon), built by Kawasaki Heavy Industries. The submarine differs from others in the power plant - its role is performed by lithium-ion batteries. Exactly the same as in most smartphones and other gadgets, only in large quantities. This provides the submarine with an unprecedented supply of energy, but significantly increases the risks of accident and death.
Most submarines without a nuclear power plant are diesel-electric, they need to float to the surface from time to time in order to turn on generators and store energy. In the last century, bulky but reliable lead-acid batteries were used for these purposes, in the 90s they were massively replaced by nickel-metal hydride batteries. Now the time has come for lithium-ion - they have the highest energy density per unit volume, and the weight is much less than that of their predecessors.
However, lithium-ion batteries are extremely dangerous because lithium is highly flammable when in contact with water. The temperature during its combustion reaches 1500 ℃, in addition, hydrogen gas is released. In the confined space of a submarine, this is fraught with an explosion or an unprecedented fire, so the maintenance of lithium-ion batteries will have to be carried out with great precautions. However, the leadership of the Japanese fleet decided that the submariners had enough professional skills to solve this problem.