Hideon, I must say that I am somewhat confused by your post. On the one hand you say you don't really want to have anything more to do with him and, considering what he's done, I'd say that's a very wise decision. He sounds truly dangerous. But then you ask if you can be "just friends" with him. Why the desire to still try to maintain a friendship with someone who brings such chaos and drama into your life?
For what it's worth, I'm not friends with my AXGF. I find the less contact I have with her, the better and calmer my life is. Anyway, the people I regard as my friends don't treat me the way she's treated me. That being said, I have to have some dealings with her as we have children together so I do work at being polite but business-like when interacting with her. If it wasn't for the kids, I doubt I'd ever speak to her again.
There's no reason why it has to be impossible to be "just friends" with an alcoholic ex. But I would say that such a situation would require both people to want it. Whatever your ex might say, his actions suggest that he would want more than just polite friendship.
I'll be honest; if I was faced with someone like your ex and his violent outbursts, I'd be considering restraining orders rather than friendship.
Take care,
Mr B.