Originally Posted by
cyccommute
I agree with most everything you quoted except the sustainability part. Super capacitors are, essentially batteries and use the similar components to perform the electrochemical actions that make them work. Both use materials that cause environmental damages through extraction. Cobalt, nickel, iron, aluminum and steel are used in both.
LiFePo4 doesn't use nickel or cobalt, and while it has lower energy density (60%?) than other lithium ion cells that do use those metals, it loses less capacity over more cycles, so coulombs delivered over their useful lifetimes may be similar? (I just thought of that, didn't check it.)