A321 Captain reported being notified by a Flight Attendant of a passenger's smoldering Lithium Ion battery pack during descent. The battery pack was placed in a Thermal Containment Bag while the flight crew was provided priority handling to the destination where a safe landing was executed.

Narrative

Descending out of FL180 on the Arrival into ZZZ1 we received a F/A (Flight Attendant) call from the cabin. I was flying and working on ATC instructions so Person A; my FO (First Officer); answered the call. He told me that the FAs had encountered a smoking lithium battery pack and had soaked it and it appeared to be no longer smoking. I looked at our position and saw ZZZ2 at my 11 o'clock and 20 miles; ZZZ3 at my 10 o'clock and 50 miles and ZZZ1 at my 12 o'clock and 50 miles. I told him to [request priority handling] and get direct to ZZZ1 and lower. We were given 10;000 ft and a heading of XXX. Passing 14;000 [ft.] I asked Person A to call in the back and check on the smoldering electronic device. The F/A said it had stopped smoking and it had been placed in the over head. We asked that it be put in the 'Fire Containment Bag' and secured for our landing in ZZZ1. 30 miles from ZZZ1 we were given pilots discretion to 2;000 ft. At about 18 miles from we asked for direct ZZZZZ (a fix X.X miles from the airport on the Runway XXL localizer). We called the airport 'insight' and as we were passing 3;000 feet we were told we were leaving class B airspace. We were cleared for the visual approach to Runway XXL. We were expediting our flight to ZZZ1 and slowing to 200 kts at this point was not in the best interest of the safety of flight so we maintained 250 knots until approximately 10 miles from the airport and configured for our flaps full landing. I asked Person A if he would contact rescue 1; after we land; to coordinate with them and how they wanted to take possession of the fire containment bag (at the gate before or after passengers deplaning or before). They said they wanted to come on the aircraft prior to passenger deplaning and take possession of the fire containment bag. I also asked Person A to ask the flight attendants about possible smoke in the cabin after landing. As long as we did not have smoke in the cabin we were going to taxi to the gate. We landed and we did not have smoke in the cabin and rescue 1 would follow us to the gate and collect our fire containment bag. I made an announcement similar to a medical emergency and asked that all passengers remain seated and allow some emergency personnel to enter the aircraft. I would make an announcement when the passengers could deplane. We were escorted to [the] Gate and parked. The firemen collected the fire containment bag and the passengers deplaned without incident. I spoke with the Fire Chief; Station Manager; Dispatch and then my Chief Pilot.