Hydrogen is even more common than lithium, but good luck mining it.
It's just a matter of price. At a sufficiently high price for hydrogen there would be no problems in supplying very large quantities of it.
Not even all that high - water is pretty common...
Epic work, it's always fascinates me when author explores the topic so deep, that doesn't know where to begin, so finally starts with the whole history of the universe or the existence of human race.
http://waitbutwhy.com/2015/08/how-and-why-spacex-will-colonize-mars.html