Anonymous has kindly provided the comments (original words) and further translated by Pete below on November 8, 2018.
A full Lithium-ion Battery (LIB) system was adopted on the first Japanese Soryu Mark 2 submarine ("SS" sequence number 27SS– see red in Table below), which was launched on October 4, 2018. [Pete comment: A LIB system not only means 100s of tonnes of new type batteries but new or altered electrical wiring, connections, adjusted propulsion motor, adjusted consumer hotel load equipment (eg. computers), and many other weight conscious rearranegements = new buoyancy settings.]
LIBs replace the Stirling air independent propulsion (AIP) and lead-acid batteries (LABs) in previous Soryus (see Table below). The Japanese Ministry of Defense (MoD) and Navy adopted LIBs, because they perceived major problems in Japan's 13 years of using Stirling AIP.
More specifically in the older Soryu Mark 1 (AIP + LABs) submarines Stirling AIP’s drawbacks probably include/included:
i) major weight, balance-buoyancy changes as 10s of tonnes of liquid oxygen (LOx) is consumed in the heavy LOx tanks. See “Combat Technology of Submarine” 2015 by H. Yamaichi. Ex-captain of JS Setoshio (SS-575) which was a Yushio class submarine). He was is also ex-Professor in the National Defense Academy of Japan. He said “Weight of goods (water, food, etc) is strictly controlled in submarine.”
ii) low AIP energy output, which effects acceleration and speed,
iii) Stirling AIP can only operate at a diving depth down to 200m. See more below on this last diving depth point.
iv) [Pete comment: Time needed to warm up the AIP? AIP cannot be instantly accelerated or switched on to confront a crisis, like a Chinese torpedo.]
The relative high costs of LIBs and Stirling AIP is an uncertain issue. It is not known why Japan did not decide to retain Stirling AIP and then add LIBs in a new submarine.
[Pete comment - Note that Japan’s needs submarine stored energy (be it diesel, battery electricity or AIP chemicals) that is appropriate to Japan’s mission requirements. Requirements which may vary from short defensive missions to longer (4,000+ km) range missions in the western Pacific. AIP very well meets requirements in small enclosed seas but can have major overall drawbacks in open seas/oceans.]
Further to point iii) above - by recharging in gentle seas the LIBs Soryu Mark 2s can be operate for a far longer period than LABs-AIP Soryu Mark 1s (whose fully submerged operational period is controlled by the limited amount of LOx carried in Mark 1s).
According to Japan’s MoD, the replacement of Stirling AIP-LABs is because LIBs allow a longer time submerged. “In simple thinking, this statement seems to be false because energy from Stirling AIP is nearly 100 MWh larger than that from LIBs” (50 MWh). But, if a Stirling AIP-LABs Soryu needs to operate below a depth of 200m, it can no longer utilise AIP [due to AIP's no greater than 20 bars exhaust pressure limitations] and instead must rely on its LABs.
AIP’s diving depth limited down to 200m is a problem because Japanese submarines are operated in the Sea of Japan and West Pacific Ocean which are much deeper than 200m. In those standard situation a LIBs Soryu will yield a longer submerge period than AIP-LABs Soryu.
So Japan’s MoD has selected LIBs Soryus for full range-operation deeper diving efficiency.
AIP More Useful for Some Other Navies
In the case of the latest ChineseYuan class 039A/041 submarines which use [covertly acquired, indigenous and/or bought] Stirling AIP and LABs, the situation seems to be a bit different form Japanese submarines. These Chinese submarines are intended to be mainly operated in the East China Sea [and use this inter-active sea depth map] which is mostly very shallow (almost three-fourths of the sea is less than 200m). There, China’s Stirling AIP-LABs system is still effective.
For the same reason, Sweden’sSAAB Gotlands and future A26s are/will be effective in the mostly shallow Baltic Sea. [Pete Comment: Also missions in the Baltic can be very short so Swedish sub’s can completely use their AIP with no LABs needed. Singapore which is using Stirling and soon German AIP on the new Type 218s may also enjoy only-need-AIP operations.]
For the same reason, Sweden’sSAAB Gotlands and future A26s are/will be effective in the mostly shallow Baltic Sea. [Pete Comment: Also missions in the Baltic can be very short so Swedish sub’s can completely use their AIP with no LABs needed. Singapore which is using Stirling and soon German AIP on the new Type 218s may also enjoy only-need-AIP operations.]
Also the recovered heat from the combustion gases of Stirling engines can be used for heating of LIBs to avoid thermal runaway at low temperatures. Cold sea (eg. North Sea and Baltic) users benefit most from the recovery-heat differential nature of AIP. Potential users include the Netherlands' Walrus Replacement, German, Norwegian Type 212A/CD and, of course SwedishA26s.
Though France’s Naval Group and German TKMS have already reported interest and some development of LIBs for submarine (probably most in collaboration with SAFT) Sweden’s SAAB, has not said much about adopting LIBs.
TABLE for SORYU & Oyashio Program as at November 9, 2018
SS No. Diesel Type Motor | Build No Name | Pennant No. | MoF approved amount ¥ Billions FY | LABs, LIBs, AIP | Laid Down | Laun -ched | Commi ssioned | Built By |
8105 Oyashio | SS-590/ TS3608 | ¥52.2B FY1993 | LABs only | Jan 1994 | Oct 1996 | Mar 1998 | KHI | |
6SS-15SS | 8106 -8115 various | SS-591-600 | ¥52.2B per sub FY1994-FY2003 | LABs only | 15SS Feb 2004 | 15SS Nov 2006 | 15SS Mar 2008 | MHI & KHI |
16SS | 8116 Sōryū | SS-501 | ¥60B FY2004 | LABs + AIP | Mar 2005 | Dec 2007 | Mar 2009 | MHI |
17SS | 8117 Unryū | SS-502 | ¥58.7B FY2005 | LABs + AIP | Mar 2006 | Oct 2008 | Mar 2010 | KHI |
18SS | 8118 Hakuryū | SS-503 | ¥56.2 FY2006 | LABs + AIP | Feb 2007 | Oct 2009 | Mar 2011 | MHI |
19SS | 8119 Kenryū | SS-504 | ¥53B FY2007 | LABs + AIP | Mar 2008 | Nov 2010 | Mar 2012 | KHI |
20SS | 8120 Zuiryū | SS-505 | ¥51B FY2008 | LABs + AIP | Mar 2009 | Oct 2011 | Mar 2013 | MHI |
No 21SS | No 21SS built | |||||||
22SS | 8121 Kokuryū | SS-506 | ¥52.8B FY2010 | LABs + AIP | Jan 2011 | Oct 2013 | Mar 2015 | KHI |
23SS | 8122 Jinryu | SS-507 | ¥54.6B FY2011 | LABs + AIP | Feb 2012 | Oct 2014 | 7 Mar 2016 | MHI |
24SS | 8123 Sekiryū | SS-508 | ¥54.7B FY2012 | LABs + AIP | KHI | |||
25SS | 8124 | SS-509 | ¥53.1B FY2013 | LABs + AIP | 22 Oct 2013 | 12 Oct 2016 | MHI | |
26SS end of SMC-8s | SS-510 | LABs + AIP | 2014 | 6 Nov 2017 | Mar 2019? | KHI | ||
27SS First | SS-511 | LIBs only | 2015 | 4 Oct 2018 | Mar 2020? | MHI | ||
28SS Second | 8127 | SS-512 | ¥63.6B FY2016 | LIBs only | 2016? | Oct 2019? | Mar 2021? | KHI |
29SS First Soryu Mark 3 SMC-9? | 8128 | ? | ¥76B FY2017 | LIBs only? | ? | ? | 2023? | MHI? |
8029? | ? | ¥71.5B FY2018 | LIBs only? | ? | ? | 2024? | KHI? |
Table from information exclusively provided to Submarine Matters. LABs = lead-acid batteries, AIP = air independent propulsion, LIBs = Lithium-ion Batteries. ¥***B = Billion Yen. MHI = Mitsubishi Heavy Industries, KHI = Kawasaki Shipbuilding Corporation of Kawasaki Heavy Industries.
---Thankyou Anonymous (with further translation and some [bracketed] comments by Pete).