Big Boi from 'Outkast' -- Wife Files for Divorce ... Custody War Brewing

Big Boi from Outkast could be going to war with his estranged wife -- 'cause she just filed divorce papers against the rapper in which she demands SOLE CUSTODY of their 12-year-old kid.

Big Boi's estranged wife Sherlita Patton filed the docs yesterday ... stating her 11-year marriage to Antwan Patton is "irretrievably broken."

The two were married in Feb. 2002 and have 2 kids together -- a 18-year-old and a 12-year-old.

According to the docs, obtained by TMZ, Sherlita is demanding sole custody of the minor ... plus child support.

She's also seeking spousal support, a split of the marital assets and attorney's fees.

We reached out to Big Boi for comment -- so far, no word back.