Here is the proof:
Note: I will denote the successor of a natural number $n$ by $(n++)$
If one assumes the Peano axioms then they may define addition as follows:
$0+m:=m$
$(n++)+m=(n+m)(++)$
$\forall n,m\in\mathbb{N}$
Using these definitions, here is a simple proof of $1+1=2$
$1+1$
$=(0++)+1$
$=(0+1)(++)$
$=(1++)$
$=2$
$\therefore{1+1=2}$
$Q.E.D$
Yes, the proof is correct. I think the only way to sort of "improve" it would be to include right away in the definitions that $1$ is the successor of $0$ and $2$ is the successor of $1$.