However, experts brush aside those concerns and instead say this type of technological leap increases power and performance, while reducing maintenance. It also could make Japanese subs more marketable overseas.
Yasushi Kojima, a spokesman for the Maritime Self-Defense Force (MSDF), said the change would affect the next four remaining Soryu-class submarines in Japan’s 10-boat class.
Senior officials from Australia, which struck a landmark technology agreement with Japan in June, told Defense News that they are aware of the switch to the Li-ion batteries and that they are still interested in pursuing Japanese sub-building technology, perhaps even purchasing Soryu-class subs outright.
The existing Soryu-class diesel-electric submarines (16SS) use AIP technology based on Kockums Stirling engines license-built by Kawasaki Heavy Industries, allowing them to stay submerged for long periods. The engines power Sweden’s smaller Gotland-class submarines for up to two weeks at 5 knots.
The current Soryu-class submarines are propelled by a large electric motor that has three power sources: diesel engines, the AIP engines and main storage batteries. Diesel engines, which require oxygen for combustion, power the boats on the surface or while snorkeling. The boats can snorkel for extended periods to limit their detectability while transiting submerged (only the snorkel mast is above the water) or for short periods to quickly recharge their batteries after operating underwater. The AIP engines — which burn small quantities of diesel fuel and liquid oxygen — are used for long-range underwater cruising at low speed, and to keep the batteries topped off. The batteries are used for ultra-quiet operation as well as high-speed underwater operations, which quickly depletes them.
By shifting to Lithium-ion batteries, the new Soryus would retain their main propulsion diesels, but be equipped with more powerful and far lower maintenance batteries than lead-acid types widely in use.
The Japanese submarines have become a major item of interest by the Royal Australian Navy, which has launched an AUS $35 billion (US $33 billion) program to replace its six aging, maintenance-heavy Collins-class diesel-electric submarines with a new fleet of larger boats better able to protect vital shipping routes in both the South and East China seas.
This June, following extensive talks between Japanese Defense Minister Itsunori Onodera, Foreign Minister Fumio Kishida and their Australian counterparts, Julie Bishop and David Johnston, Japan and Australia agreed to jointly develop a range of submarine technologies to these ends.
The Australian Defence Ministry had little to say when asked about the battery switch.
“No decision has yet been made on the design and build of the next generation of Australian submarines,” Defence Minister David Johnston said in a statement. “However, there will be more of them — with numbers to be determined through the white paper. As the prime minister has stated, defense acquisitions have to be made on the basis of defense logic, not industry policy nor regional policy.”
Six of 10 Soryu-class submarines — which take about four years to build — for Japan have been completed. Japan’s Defense Ministry has just requested 64.4 billion yen (US $589.5 million) to start building one new 2,900-ton Soryu submarine from April 2015, and this — and three other boats — will use Lithium-ion batteries.
The twist comes with the news that the Li-ion batteries for the Soryu subs are to be provided by GS Yuasa Battery, the same supplier of the problematical batteries used on Boeing’s 787 Dreamliners, which have experienced a series of alarming and difficult-to-solve safety issues. Fires and other concerns led both Japan Airlines and All Nippon Airlines to ground fleets in January 2013, causing — for the first time since 1979 — the US Federal Aviation Administration (FAA) to ground all 787s flying with US airlines.
Despite best efforts and ongoing investigations in the US and Japan led by the FAA, Japan Airlines this January reported further fires and meltdowns.
Discounting local media reports that Australia was close to committing itself to buying Soryu-class submarines with AIP technology, naval experts have downplayed concerns with the use of the new technology, saying, instead, it was more likely a deal-maker than a deal-breaker.
Alessio Patalano, an expert on Japan’s Navy at the Department of War Studies at Kings College in London, said the military had been looking at different options in terms of propulsion systems since the early 1990s and that AIP was first studied because fuel cells and Li-ion batteries were because the technology was not sufficiently mature.
“Given that submarines are the tip of the sword of Japan’s military posture … speed and endurance are central to submarine operations and a propulsion system that can offer increased performance in those areas is particularly attractive to the Japanese Navy,” he said.
For the Navy, Kojima said AIP technology, which reduces the speed of submerged submarines to just a few knots, is being increasingly seen as too slow for emerging strategic uses and that the Navy regards AIP as maintenance intensive. Improvements in batteries make this technology the better long-term bet.
Bob Nugent, a consultant at naval consulting firm AMI International, said it is “plausible” that going to Li-ion batteries will provide more speed and power.
The Soryu-class is about one-third larger than most European subs that use AIP technology, he said, adding the increased power and energy density of the batteries would allow for longer cruise and sprint bursts of speed.
“Li-ion-based chemistry could be made perfectly safe from the thermal runaway issues that have received heavy publicity,” Nugent said. “There are some other options such as fuel cells/AIP, and ultracapacitors, but those also bring with them some technical risk.”
Nugent said Australia also has challenging range and power requirements, so Australia could actually have a shared interest in alternative propulsion design options.
Guy Stitt, AMI International’s president, added that the Japanese Navy is highly capable and risk-averse and that the decision to use the technology would actually represent a “leap forward” in submarine power and that could introduce important operational improvements.
“They are giving up a secondary power generation device by removing the AIP. In exchange, they intend to enlarge and extend their current power storage devices by going from lead-acid batteries to Lithium-ion batteries,” Stitt said. “Lithium-ion batteries offer much greater energy density than current lead-acid batteries. They will have to develop some redundant safety electronics as well to monitor the stability of each battery cell.”
Stitt added that the Royal Australian Navy is “a long way from making procurement decisions” on its future submarine program, and if the Japanese Navy does well enough, many other navies would be looking at procuring the Japanese solution because of the extended range and longer operational time underwater that the new battery based system potentially offered.
Patalano added that “the Japanese are at the forefront of large conventional submarine development. This is a niche market but one with great potential for environmental and operational reasons.
“It is in Australian interests to be involved in this. In turn, the prospects of enhanced performance from a platform that features already excellent standards will make any submarine deal with Australia more interesting.”
The Sōryū-class submarines (16SS) are diesel-electric submarines that entered service with the Japan Maritime Self-Defense Force in 2009.