Yes, you can. I take 1500 mg of lithium and 60 mg of vyvanse a day. Although lithium may reduce the effectiveness of the vyvanse, which I'm not sure I've noticed it or not, the drug interaction...
From: http://www.drugs.com/drug_interactions.php
Interactions between your selected drugs
Lithium and Morphine (Moderate Drug-Drug)
MONITOR: Central nervous system- and/or respiratory-depressant...