The EXP Share 2 is a key item that is obtained in the Phoenix Iota at the very end of the game. Whereas a standard Exp. Share is only capable of sharing experience between its holders and the Pokémon actively participating in the fight, EXP Share 2 treats each Pokémon as if they are holding an Exp. Share themselves and divides the experience among them evenly (relative to level of course). The exact amount of experience each Pokémon receives is not displayed.
Additionally, EXP Share 2 comes with a convenient feature that allows the player to disable/enable the item whenever they feel like using it. As it is a key item, it can be registered and quickly enabled/disabled for ease of access.
An EXP share that can be turned on and off, spreading EXP to your entire team instead of just one member.