China plans to upgrade its conventional submarines with lithium-ion batteries, which could significantly increase the combat and survivability of its fleet.
This month, the South China Morning Post reported that China’s conventional submarine fleet may soon be powered by lithium-ion batteries, capitalizing on technological advances in the country’s electric vehicle (EV) industry, currently the world’s largest.
The report notes that China produces three-quarters of the world’s electric vehicle batteries, giving it a leading position in battery technology.
Lithium-ion batteries can more than double a submarine’s underwater endurance and greatly improve its acceleration at high speeds, according to researchers at the Qingdao Naval Submarine Academy in the peer-reviewed Chinese journal Marine Electric and Electronic Engineering.
The South China Morning Post notes that the People’s Liberation Army Navy has been trying to replace traditional lead-acid batteries with lithium-ion batteries for more than a decade, but hesitated because of the danger. China is believed to have the largest fleet of conventional submarines in the world, with an estimated 60-70 boats.
Lead-acid batteries have been used in submarines since World War II. However, they suffer from low energy storage capacity, slow charging, low power, short life and generation of toxic fumes. In contrast, lithium-ion batteries have superior energy density, faster charging, higher discharge rates, and longer battery life.
However, lithium-ion batteries suffer from heat escape and fire, which is particularly acute in submarines, GlobalData Thematic Research notes. A single overheating cell can cause a chain reaction of heat-hardened faults throughout the battery bank, leading to catastrophic fires, it said.
Lead researcher Wang Fang said safety solutions to lithium-ion technology from the extensive development of China’s electric vehicle industry have been found, mitigating some of the earlier risks, the South China Morning Post said.
“Once these issues are resolved, the replacement of lead-acid batteries with lithium batteries in traditional submarines is just around the corner,” Feng states.
The research team said the use of cheap, readily available iron and phosphate could replace the conventional but dangerous combination of nickel and cobalt in lithium-ion batteries, improving safety without compromising performance.
According to industry data cited by the South China Morning Post, the Chinese market has more electric vehicles using iron phosphate battery technology than nickel cobalt batteries.
The research group’s other safety innovations regarding submarine lithium-ion batteries include hard carbon and ceramic coating in battery packs, which could improve their safety in submarines.
This development may also be enabled by China’s military-civilian fusion strategy, which has removed previous barriers between civilian research, commercial entities, and military and defense industries. The aim of the strategy is to take advantage of the dual use of technologies with civil and military applications, such as lithium ion batteries.
The South China Morning Post notes that Japan and South Korea are using lithium-ion batteries in their submarines, the former in 2018 and the latter in 2021. However, the article notes that Japan is using manganese metal in its lithium-ion batteries for increased safety, but at the expense of performance. Instead, South Korea uses nickel and cobalt, but has more safety features.
The source mentions that Germany and France have also developed prototype lithium-ion batteries for the submarine, which are planning for future military service.
Lithium-ion batteries have many advantages over air-independent propulsion (AIP) systems such as the Stirling engine and closed-cycle steam turbines. Fleets can combine them with hydrogen fuel cells to offset the limitations of the former.
In a 2020 article for The Warzone, Tyler Rogoway points out that Stirling AIP submarines, such as Sweden’s Gotland class, must carry liquid oxygen aboard, which poses inherent hazards, takes up a lot of interior space, and contains many moving parts that require additional soundproofing. Stirling engines are also limited by their low power output, possibly limiting them to short-range littoral combat operations.
Similarly, Rogoway points out that closed-loop steam turbines, such as France’s Autonomous Submarine Energy Module (MESMA), have the same limitations as a Stirling engine because it needs a shipboard supply of ethanol and liquid oxygen.
Additionally, Rogoway says that while the MESMA system can produce plenty of power for high-speed operations, it has many moving parts that also require expensive soundproofing.
Although fuel cells are a high-tech AIP solution, their biggest drawbacks come from their different ways of storing hydrogen fuel. These disadvantages range from poor gravimetric density, high oxygen consumption, CO2 and other emissions, and untested technology.
Nevertheless, Rogoway mentions that although fuel cells are a high-tech AIP solution, they cannot increase the power level as quickly as the MESMA system.
Rogoway points out that combining lithium-ion with fuel cells in submarines can deliver extreme durability, incredibly quiet operation, rapid acceleration and high cruising speeds, but cost and complexity remain significant issues.
Lithium-ion submarines also have the advantage of being quieter than nuclear-powered submarines. Although nuclear submarines have essentially unlimited range and endurance, their nuclear reactors produce noticeable heat and therefore must keep the cooling pumps running at all times, which may cause noticeable noise.
In addition, nuclear submarines emit small radiation traces in their wake, which can be detected by specialized trace sensors, such as the Soviet/Russian SOKS system.
The technical advantages of lithium-ion batteries can turn into functional advantages. Anand Datla and Paul Giarra note in an October 2021 Proceedings article that their faster discharge times correspond to faster dive times and faster dive speeds.
At the same time, their rapid loading has significant operational implications, including operations in the surface and underwater features of the strategic First Island Chain, which runs from Japan, Taiwan and the Philippines.
The lithium-ion battery upgrade to China’s conventional submarines will significantly improve their ability to enforce the blockade of Taiwan. The Asia Times has previously reported that advanced conventional submarines such as the Type 39 C/D would be the workhorses if China moves to blockade Taiwan in the event of a conflict.
Such an upgrade would improve the ability of Chinese submarines to remain on stealth patrol off Taiwan’s coast, thwarting moves by Taiwan and possibly the US Navy to break the blockade of the self-ruled island.
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