A broken vessel-The vessel used to collect the spilled wine:[1]

The wine is to be spilled into a broken vessel [such as a chipped plate or bowl], representing the Kelipos which is called cursed. [One may not break the dish on Yom Tov for this purpose, and it hence must be done before Yom Tov.]

The definition of a broken vessel:

In the most literal sense, this refers to a vessel that is slightly chipped on its rim and the like. However, some argue that so long as the vessel is made of cheap material, such as a plastic disposable vessel, it suffices.[2] Likewise, some ponder that perhaps so long as the vessel will not be used throughout Pesach then it suffices. Practically, it is best to use an actual broken vessel, and if necessary to chip the rim of a plastic disposable vessel before the start of the festival.

The Rebbes custom:[3]

It is attested that in the earlier years the Rebbe did not use an actual broken vessel, although in later years he did.

[1] Siddur Admur; Mishnas Chassidim 11:2; Nehora Hashaleim; Kaf Hachaim 473:164; Nitei Gavriel 87:14

[2] See Nitei Gavriel 87:14 footnote 24

[3] See Bakodesh Penima [in earlier years it was not broken while in later years it was]; Pesach Chasidi 138 [it was broken but was difficult to tell]; Maaseh Melech p. 203 [in earlier years it was not broken while in later years it was broken. The break in the vessel was made by Rav Chaim Halbershtam, on his own accord and not as the result of a directive of the Rebbe.]; Otzer Minahgei Chabad ibid [No apparent break in vessel]