A319 Captain reported the aircraft began to slide towards another aircraft during pushback from the gate. As the brakes were ineffective; reverse thrust was needed to stop the uncontrolled slide. Reverse thrust was maintained until the tug was reconnected and the aircraft was towed back to the gate until conditions improved.

Narrative

Prior to push; the taxiways were reported as slippery conditions." On pushback the tug had issues getting enough traction to push us back further than we requested. They disconnected and we started engines. After engine start; I elected to finish the Before Takeoff Checklist to the line; so I could utilize the assistance of the FO (First Officer) during taxi. Upon brake release to taxi; the aircraft immediately started sliding and we had no tiller or brake control. There was Aircraft Y that had just pushed next to us and we started sliding in their direction. To prevent us from colliding with Aircraft Y; we had to use reverse thrust to bring us to a stop. Once I set the parking brake; stowed the reverse thrust; and went back into forward idle; the aircraft again started sliding towards Aircraft Y. We put the thrust back into reverse and had to use idle; up to max reverse in some occasions; to stop the uncontrolled slide. When we had the aircraft stopped; we contacted ZZZZ Operations to tow us back to the gate. We kept idle reverse until the tow was hooked up and then shut down the engines. Operations then towed us back to the gate. We delayed until the conditions improved and departed four hours late without further issue.[The cause was] cold weather with ice on airport surfaces [and] lack of PIREPs on ramp area conditions. I didn't wait to depart until conditions improved and could have asked for reports from previous aircraft before pushing back.[I suggest] better reporting on ramp area conditions - it was only reported slippery. I should have visually looked more carefully on ramp conditions before beginning the pushback. Airport Operations could be better equipped to improve surface conditions; especially in northern destinations."