Underwater combat has a new power system and entered the past lives of lithium-ion submarines.

  Science and Technology Daily reporter Zhang Qiang

  In the past few days, many people’s circle of friends has been screened by Japan’s latest lithium-ion polymer battery submarine. Recently, the 11th Japanese black dragon-class "Huanglong" conventional power submarine was launched, which is also the first submarine in the world to use lithium-ion batteries as power.

  As early as 2014, Japan Maritime Self-Defense Force announced that the Canglong class submarine, which will be started in 2015, will revolutionize the use of lithium-ion batteries. At that time, foreign media reported that the Japanese Canglong class submarine would cancel the original AIP system while replacing the lithium-ion battery, that is, only the power combination of lithium battery pack and diesel engine would be retained. For this revolutionary idea, the views at that time were not very unified, and many people had doubts about this rather radical design. The launch of the "Phoenix Dragon" made this radical design a reality.

  Yi Fang, a special researcher at Outlook Think Tank, pointed out: "Lithium-ion submarine is a way to improve the electric propulsion subsystem of AIP submarine when lithium-ion polymer batteries are mature, but it is by no means the only advanced way."

  Battery performance constraints gave birth to AIP submarines.

  Since the submarine came out, with its unpredictable concealment and strong assault, it has become a weapon for naval warfare actively developed by various countries. However, the early submarines were far from people’s imagination. In people’s imagination, the submarine should be able to sail in the depths of the ocean for a long time, just like the Nautilus in the science fiction Two Wan Li under the Sea. However, technology has limited people’s imagination. Until World War II, the military of various countries still used diesel-electric submarines invented by scientists in the late 19th century, that is, internal combustion engines were used when sailing on the water, and batteries and motors were used when sailing underwater. And this kind of design still has a wide market until today.

  Due to the limitation of battery technology, diesel-electric submarines can only sail underwater for 10-mdash; After 100 hours, it must be recharged. The operation of diesel engine is inseparable from oxygen, so it must float to the surface of water or use a snorkel. In this way, its concealment is greatly reduced. To this end, people have been looking for various ways to break through this restriction, and nuclear energy is one of the choices. The name Nautilus was used in the world’s first nuclear submarine designed by Americans. However, due to various constraints, nuclear submarines have always been the patents of a few countries.

  Is there a better solution for conventional power submarines with a wider range of applications?

  For hundreds of years, due to the slow progress of battery technology, conventional power submarines have been mainly using lead-acid batteries. Lead-acid battery has stable and reliable performance, easily available and cheap raw materials, simple structure and easy maintenance. However, with the development of battery technology, the shortcomings of lead-acid batteries have also begun to be amplified — — Its volume and weight are too large, but the specific energy storage is very low, and it takes time to fully charge, which means that its energy density is lower than that of lithium batteries and other latecomers.

  Therefore, it is very important to increase the persistence and concealment of underwater navigation of diesel-electric submarines and improve the storage capacity and efficiency of batteries. However, the progress of battery technology obviously cannot meet the military needs, so people have developed an air-independent power propulsion system — — AIP system

  Yi Fang introduced: "Early AIP submarines, such as ‘ Sterling ’ The engine AIP power nuclear submarine mainly adopts the way of heat engine and lead-acid battery as the electric propulsion subsystem. Although it improves the underwater safety performance, it reduces the underwater speed and increases the system complexity. Therefore, later, closed-cycle diesel engine power system, closed-cycle steam turbine power system and fuel cell power system appeared. "

  Lead-acid batteries will be replaced by new batteries.

  AIP submarine has reduced the submarine’s requirements for batteries to some extent, but this does not mean that submarines do not need better batteries. After all, compared with diesel-electric submarines, the system of AIP submarines is more complicated.

  "Huanglong" replaced the AIP power system and lead-acid battery of the whole Stirling engine with lithium-ion batteries while maintaining the specifications and speed unchanged.

  This design adopted by "Huanglong" makes the most popular AIP submarine have a new alternative, and from the technical principle, it has changed back to a diesel-electric submarine.

  "Lead-acid batteries have a series of problems, and the room for improvement according to their working principles is very limited. Moreover, additional engines are needed to supply power, which takes up too much space in submarines. Therefore, once more mature battery technologies, such as lithium-ion polymer batteries, appear, they will inevitably be replaced." Yi Fang said.

  In fact, lithium batteries have long been used in weapon systems, covering many arms, such as military communication equipment, underwater robots, unmanned reconnaissance aircraft and so on. The energy density, battery life, volume and weight of military equipment power supply are important factors affecting combat capability, and lithium batteries have the advantages of high energy density, small size, light weight and long cycle life, and become the first choice for military equipment power supply.

  Yi Fang pointed out, "Because the submarine has high requirements for the power system when diving, a battery technology is not dare to be used rashly if it is not mature, because once the power supply is interrupted, it will inevitably lead to submarine safety accidents. Therefore, the previous conventional submarines mainly used mature lead-acid batteries, and new alternatives were not adopted until battery technologies such as lithium-ion polymer batteries gradually matured. "

  The emergence of lithium-ion submarines is a matter of course

  Because of the unique advantages of conventional power submarines, technicians from all over the world have been making continuous design improvements, including constantly trying various new battery technologies.

  Besides lithium batteries, technicians have also used silver-zinc batteries. In 1950s, the United States used the "Big Bluefish" conventional power high-speed test submarine to test the silver-zinc battery. It has been pointed out that a submarine with a displacement of 1,500 tons uses 220 tons of batteries, which can allow the submarine with a displacement of 1,500 tons to move for 1.5 hours at a speed of 33 knots. This is the first time that a conventional submarine has reached the sports capability of a nuclear submarine. However, the price of silver-zinc batteries is too expensive, and the silver ingots for making these batteries are still borrowed from the US Treasury.

  At present, there is also a fuel cell AIP submarine in the AIP submarine family, but there are essential differences between the fuel cell submarine and the Japanese lithium-ion submarine. Fuel cell belongs to primary battery, which can directly convert the chemical energy of fuel into electric energy, also called electrochemical generator. The battery belongs to the secondary battery, which needs to be charged and discharged, and the electric energy is stored and discharged.

  "Fuel cell is a self-powered battery technology. This submarine can work underwater for a long time as long as it has enough fuel and scientific waste discharge, which can be considered as a kind of ‘ Sub-nuclear submarine ’ 。” Yi Fang said, "The lithium-ion battery is a kind of storage battery and needs to be charged. In other words, after a period of snorkeling, the lithium-ion submarine also needs to float to the surface of the water and be charged by the diesel generator system. After the charging is completed, it can continue to dive. "

  Many people are concerned that lithium batteries have been used in submarines and many weapons, so will it be widely used in the battlefield in the future, or just a substitute for the transitional stage? Will lithium-ion submarines become the first choice for conventional submarines in the future, just as electric vehicles replace fuel vehicles now?

  In this regard, Yi Fang believes that "the application of lithium batteries in conventional submarines is only one of the mature schemes, which appears with the emergence of mature technologies in relevant countries, mainly because of its advantages such as high specific capacity, high output voltage of single battery, low self-discharge rate, long service life and good safety performance, etc., and it has become a choice of electric propulsion subsystem, and it is not a substitute in the transitional stage, but an inevitable choice. In fact, sodium — New high-energy thermal batteries such as nickel chloride are also an alternative. At present, the fuel cell AIP submarine has a good prospect and is the main direction of future research. Combining fuel cell technology with battery technology can ensure the better safety of conventional AIP submarines. "