Electric Vehicles

The Volkswagen XL-1 was a plugin hybrid diesel car, and without using energy from the battery it had 120 MPG.

It was a limited run / concept car though, with a very aggressive aero design. I don't know of any comparable electric cars off the top of my head (besides the Aptera prototypes, which are even more aggressive), but I reckon an electric car with a similar body shape would have even higher thermal efficiency.

Not that it makes that much sense to compare the thermal efficiency of an EV and ICE, unless you're considering the combined efficiency of a fossil fuel power plant and EV. The reason being that you can't practically turn electricity into hydrocarbon fuel (without losing a ton of energy anyway), so if your EV was less efficient than an ICE its not like you'd be going "dang, I'd be better off using these solar panels to make gasoline instead". The important part about electric vehicles from a societal standpoint is that its vastly more practical to decarbonize electricity production than it is to produce carbon neutral motor fuel. From a personal standpoint its that it works out to more miles per dollar.