The lithium-ion battery packs that power modern electric cars are far less energy-dense than the liquid hydrocarbon fuels that power internal-combustion cars.

They can't hold nearly as much energy in a given volume or weight, a disadvantage that shows in the relatively short ranges of many electric cars despite their heavy battery packs.

However, the energy density of the the storage medium alone—be it a liquid fuel or a battery cell—may not be the best way to assess cars, a group of researchers claim.

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If the efficiency of the powertrain as a whole is considered, some electric cars will approach the energy density of gasoline by 2045, according to a report from Argonne National Laboratory (via Charged EVs).

The Argonne researchers argue that an accurate comparison between electric cars and gasoline cars requires factoring in the efficiency of the conversion of stored energy into mechanical energy to turn the wheels.

Under this metric, gasoline soon loses its advantage in energy density.

Volvo CMA modular compact car platform

Volvo CMA modular compact car platform

Researchers compared three mid-size passenger cars—a gasoline car with a 300-mile range, an electric car with a 100-mile range, and an electric car with a 300-mile range.

They then considered—in five-year increments—the effects of projected advances in weight reduction, battery technologies, powertrain components, and other technical aspects.

Results showed that current gasoline cars require on average 10 times the energy input per kilogram of powertrain weight compared to electric cars.

MORE: What Comes After Lithium-Ion Batteries To Power Electric Cars, And When? (Dec 2015)

Fuel consumption is expected to drop as carmakers work to meet stricter global emissions standards, researchers noted.

But by 2045, gasoline cars will still need about twice as much energy input per kilogram as the 300-mile battery-electric car, they said.

Because of their greater average mass, electric cars would still expend more energy at the wheel, though.

Volvo CMA modular compact car platform

Volvo CMA modular compact car platform

Powertrain efficiency gains and the potential development of lighter-weight battery packs could close that gap, too, according to the report.

Yet a battery pack and electric motor will likely always weigh more than an internal-combustion engine and its gas tank.

Of course, electric powertrains drive cars without any carbon emissions. That's one of their main advantages over internal combustion.

And after a certain point—some suggest it's a real-world range of 200 or 250 miles—buyers don't care about energy density, but about what a vehicle does for them, and at what cost.


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