I don't have practical experience with this flash, but lithium-ion batteries are not usually recommended for device with high wattage peaking loads such as in flashguns. This leads the batteries to deteriorate due to high heat generation. There are even risks of fire and battery explosion.
Lithium batteries offer large energy density so they are nice for mobile application, but they are usually meant for steady power draw, low wattage devices like cell phones, tablets, laptop or radios. May be an oversized battery would be safe, but that kind of kills the benefit of usign li-ion batteries.
Moreover, I like the idea of having easily available replacement batteries for my flash if my batt set dies unexpectedly.
Edit: I have a Sigma ef610dg super flash and I recall that the manual advised against using lithium batteries.