China's Winston Battery company (aka "Everspring" and "Thunder Sky") might be developing Lithium-ion Batteries (LIBs) for submarines. Alternatively Winston might merely be marketing the idea (see) of LIBs for submarine, to attract foreign joint ventures. Russia may be a direct joint venturer. Swedish, French or German firms may be participating (through the European dual-use loophole) in joint ventures assisting China to develop LIBs for submarine.
Chinese marketing of LIBs at: "Winston Battery WB-LYP10000AHA in large submarines" states at