Potassium is helpful, but the problem is that too much potassium can cause heart arrhythmias. Lithium also displaces sodium since it is also higher on the electromotive series of chemicals, which is why they use it instead of potassium. They figure killing the liver is still better than killing the heart.
Magnesium also appears to help with bipolar. The form though is important. You do not want the caustic magnesium oxide/hydroxide. Look for magnesium malate. Both the magnesium and the malic acid (malate) help produce adenosine triphosphate (ATP). ATP is the fuel that allows our cells to operate, and helps them to operate properly.