Sure, I can do the math on that.

Gasoline has about 45 MJ/kg[1]. 1 kg of lithium contains 868x10^23 atoms, or 13.9 megacoulombs if each atom donates a single electron. Since a joule is one volt-coulomb, every electron must average out (nominal) to 3.24 volts. Todays li-ion batteries have a nominal voltage of ~3.65 V, and the nominal voltage of li-air batteries are 2.91 V.

The actual voltage of li-air is ~90% lower than the required voltage to reach raw parity with gasoline, which makes sense given that the theoretical limit of li-air batteries is 40.1 MJ/kg (.9 * 45 = 40.5).

Reaching the same power density as gasoline in vehicle engines (=<9 MJ/kg) isn't too bad (very close to 10x best current consumer batteries, closer to weirder chemistries), but parity with the real power of gasoline is a very hard ask. Donating more than one electron per lithium would require some serious re-evaluation of what we know about chemistry. If you only have one electron per atom, you have almost no weight left over for other materials to use to develop a voltage difference with. A battery that exceeds gasoline's full heat energy would need some very exotic materials- either lighter atoms[2], different ways of storing electrons[3], or ways to store energy besides electrons[4].

[1] divide by 5 for a realistic engine efficiency. At that rate, a gallon of gas provides 9.4 kWh- enough to get a Tesla model S over 35 miles.

[2] there are none, besides hydrogen, which itself isn't really helpful. It's not very good for electrochemistry.

[3] preferably, in a different state than me. Electrons hate each other. A 3 Ah battery has 11,000 hateful coulombs in it, each electron within a less than a nanometer of the others around it. That's a 10^9 on top and a 10^-9 on the bottom. Not positive on the math on that but I'm reasonably sure it's in the thousands of megatons. It is rapidly trying to change chemical and then geographical state.

[4] preferably on another planet from me. If you're storing energy with a different force than the electromagnetic force, you're pretty much guaranteed to be doing some real fuckery to subatomic particles, and they are not going to be happy.

So, GP's comment of "develop the tech that seems impossible as the biggininng" (typo included) is the important part. It might be that in the future, because the motors and other moving parts become increasigly efficient (& are already much better than a combustion engine) then less energy is required for the same resulting work. Even more so, the ingenious ways that energy can be 'reharvested' to flow back into the system could in fact allow us to develop something that seems impossible...simply because we're harvesting energy and pouring it into our Lion dependant system better than Gas ever can.

The resulting work is more important than the efficiency. Teslas have exceptionally low air drag, which is great for driving range.

However when you go from 80 to 90% system efficiency, you only increase range by 12%. Once youre at 99%, you really cant improve any more. 99% to 99.5% means the motor outputs half as much heat but goes hardly any farther.