Samsung is apparently hedging its bets and trying to attract battery-making talent than is not the two infamous suppliers it used for the Note 7. When Samsung's battery subsidiary SDI struggled with the high density requirements of the Note 7 units, and used unorthodox electrodes that didn't survive real life usage, Samsung ramped up production at Amperex, the other supplier which in its turn couldn't produce those millions of batteries with satisfactory quality that Samsung was demanding in the span of two short weeks.
We all know what happened, but apart from the fresh round of quality assurance testing that Samsung has implemented for his battery suppliers going forward, like x-ray exams for each piece, it also sought and, apparently found, a third supplier. The rumors that this is a Japanese company have now been rehashed once more by Wall Street Journal sources. Previously it was said that Murata will be Samsung's supplier, after its acquisition of Sony's battery subsidiary.
Sony sold its losing battery business to Murata not long ago, but the deal is now unlikely to go through before July, so it will be still Sony supplying the batteries. Samsung has apparently been very impressed with the quality of the Li-ion packs that the Japanese company is able to churn out, so it has co-opted it as a third-party supplier. It's hard to blame them, given that Sony pioneered the Li-ion battery chemistry, and a big order from Samsung might be just the jumpstart its battery operations need.
source: WSJ (paywall)