How can I increase the knockback of a slime in minecraft?

I’m using command blocks to make a custom slime, I’ve tried using the command: /summon slime ~ ~ ~ {Size:3b,Attributes:[{Name:"generic.attack_knockback", Base:8.0,}]}

but it doesn’t work. Replacing "slime" with "zombie" does work however. I’ve tried giving the slime a knockback sword, but they can’t make use of items. Is there any way to increase their knockback?