I'm guessing it'll have something to do with his Haxx Vollstandig, which seems to oneshot Cang Du.
Also I'm pretty sure Aizen doesn't have a Zanpaktou anymore, when he merged with the Hogyoku it kinda... merged with his hand. Then when he got broken out of his super form he lost the blade, so now he only has Kido... Not that that's MUCH of a problem for Aizen