Not sure this is right. Coal plants are at best 40% efficient, combined-cycle natural gas 60%. Then you have transmission losses (2-13%), and then inefficiency in EV chargers. Atkinson-cycle engines (often used in hybrids like the Prius) can reach 40% efficiency. Seems like a wash to me in terms of efficiency. On the other hand, if using solar or wind, efficiency becomes a little less interesting because the fuel is "free".
I meant in terms of emissions, rather than simple mechanical efficiency. Power stations at scale can have complex emissions management. Car engine's don't.
