Is it possible to change the stirling engine with Lithium Ion battery by cutting the hull in half?They might have added a few more after 2017. PLAN went stealth mode plus tight control on the media with regards to submarines since then. Its not like years ago when there was plenty of pictures of submarines.
From what I think is that the entire Yuan class fleet went into a refit except for the newest ones which didn't need to. The older ones, the ones with the squarish sails, were refitted with new sails that have the curved and webbed corners. From this time on, the number of pictures of the square sailed Yuans dramatically dropped, and most of the pictures you see now are the ones with the curved sails. Upgrades might also include other things within the submarine.
It might be possible but it hardly fits with PLAN's modest approach to in-service upgrades. I expect the only reason they'd consider it is if the AIP system was a non-functional deadweight. Excluding that, it's just more efficient to build new boats.
PLAN AIP submarines does get their battaries replaced. Here's a video of that in action, starts at 1:35.Definitely.
Plus I am not sure if Lithium Ion is a smart idea for a sub even if the Japanese were trying it. You know how these batteries work in your smartphone or laptop. They got a life that will eventually expire. They get less efficient with age. How do you replace the batteries on a submarine? Not easily. Battery fires and accidents, although rare, they do occur. You know why the US bans mailing of items with Lithium Ion by air. What are you going to do if the batteries warp? Each cell would require its own diagnostic circuit.