Gasoline, electricity, and the energy to move transportation systems

By David Herron
A key difference between electric and gasoline cars is the amount of energy each carries.  A typical (mid-2015) electric car like the Nissan Leaf has battery pack capacity that's equivalent to about 2/3rds a gallon of gasoline.  With that much energy it can travel 85 miles at highway speed, while a gasoline car would barely get 20 miles range on 2/3rds a gallon of gas.  The key measurement is energy density or the amount of energy carried within a given size or weight.

EV battery pack energy density increases will usher in affordable 200+ mile range electric cars.  Gasoline's big advantage is its extremely high energy density, but electric vehicles big advantage is their low fuel cost.

Gasoline and diesel, the dominant fuels of the last 100 years, have a very high energy density. Easily transported and dispensed, both fuels are easily piped into the innards of internal combustion engines for the explosions that make cars run. The fossil fuel industry made sure to deliver an excellent refueling experience with wide-spread refueling stations. That, and the reliable electric starter motor, are what enabled widespread gasoline vehicle adoption, and to kill off the electric car the first time.

Electricity storage systems, on the other hand, have a relatively low energy density. The 80 mile range of 24 kiloWatt-hour electric cars requires a fairly large and heavy battery pack. And while you might read that as a condemnation, it's a huge improvement over older battery technologies like lead-acid or nickel-metal-hydride. Roughly speaking Li-Ion batteries have 4x the energy density of lead acid batteries, 2x the energy density of the NiMH batteries used in the previous wave of electric cars, but a fraction the energy density of gasoline. That 4x improvement is what made lithium-ion powered electric cars practical enough for every-day use by anyone.

In 2017 we're at the starting point for a new wave of electric vehicle advancement. What made affordable 200+ mile range EV's possible? The automakers lowered battery costs and increased energy density.


Accurate terminology is important if we are to properly communicate with each other. Fortunately, Wikipedia has some nice pages to help us understand the terminology.

( Energy Density is the amount of energy stored by volume. There's a general definition, like the energy in a given region of space, and it can apply to all kinds of things like magnetic fields. But, for electric vehicles we need to focus on the extractable energy stored in the battery pack.

( Specific Energy, similarly, is the amount of energy stored by mass (weight). Like for Energy Density, there's a generalized usage of Specific Energy to cover all kinds of things, but we need to focus on the extractable energy stored in the battery pack.

The units of measurement are: Energy Density: kiloWatt-hours/liter, Specific Energy: kiloWatt-hours/kilogram

Another piece of similar terminology is ( Power Density. In electric motors and electric drive train components the correct phrase is volume power density. This measures the amount of energy (power) the system can handle measured against either size or weight. The unit of measure is Watts/cubic meter, Watts/liter, or Watts/kilogram. A similar phrase is "power to weight ratio".

That's cool, but why is it important to electric vehicles?

It's a matter of physics that performing a function like carrying you and your family over the hills and through the woods to grandmothers house takes a certain quantity of energy.

In a vehicle potential energy is stored as electricity in a battery pack or gasoline in a fuel tank. That energy is converted to kinetic energy in the drive system. That's either a combustion causing a crankshaft to turn, or the meshing of electromagnetic fields causing the electric motor shaft to turn. The resulting kinetic energy is what carries you to grandma's house.

Your vehicle must have enough potential energy to cause all that to happen. The more potential energy carried by your vehicle the more it can do. But, vehicles have size (liters in volume) and weight (mass) limits within which the energy storage unit must fit. If the size or weight of the energy storage unit becomes too big or too heavy, the vehicle will be inefficient, or maybe even be unable to move.

If grandma's house is 2000 miles away, an electric car would require an 800 kiloWatt-hour battery pack to make the trip. That big of a pack can't (with today's technology) be made small enough to fit in a car, and would be so heavy the car wouldn't be able to move. If battery packs are ever able to store 10x the energy per kilogram, and per liter, than current battery packs, it would then be possible to build an electric car with 2000 mile range.

Even a gasoline car is unable to make a 2000 mile trip. Gasoline car owners have to stop 7-8 times for refueling during the trip. An electric car owner could also make the trip, if there's sufficient charging infrastructure. That's the advantage gasoline car owners have, a more useful refueling infrastructure.

Tesla Motors has proved it's possible to build a highly desirable electric car supporting the Road Trip experience. The Tesla Model S, with a 260-335 mile electric driving range, can recharge in about an hour, and Tesla Motors has built continent-spanning recharging networks in North America and Europe, and are partway to the goal in other places like China and Australia. But that car comes at the twin costs of weight, Understanding kiloWatt-hours in electric cars and other gizmos, and price, about $100,000 a car. Later in 2017, Tesla is promising the Tesla Model 3 at a base $35,000 price, which will change things considerably.

Two of the big hurdles to electric vehicle adoption is the driving range, and the relatively high cost compared to equivalent gasoline powered cars. It's promised that energy density, uh .. specific energy, improvements will allow electric cars to carry the 60-80 kiloWatt-hours of energy, for a 200 mile range, at an affordable vehicle cost.

Existing battery technology, energy density, specific energy

The following chart is derived from the Wikipedia pages linked on each row, so take it with a grain of salt. For each battery type, a range is given for each rating, because each row discusses all batteries from all manufacturers of the given type. Of course each row covers a range of products each with their own specific characteristics. In other words, don't take these numbers with a great deal of precision, but instead notice that, generally speaking, while NiMH batteries have a higher energy density than lead-acid, Lithium-ION has a higher density than both.

Battery type Specific Energy Energy Density Specific Power Cycle Durability Notes
( Lead Acid Battery 33–42 Wh/kg 60–110 Wh/l 180 W/kg 500–800 cycles The oldest form of electrical battery, originally developed in the 1850's. It's the low cost that keeps this technology alive.
( Nickel Cadmium 40–60 W·h/kg 50–150 W·h/L 150 W/kg 2,000 cycles These nickel-based batteries have a history dating back to the 1890's, and have at times been in wide use. Their higher energy density than lead-acid batteries is what made them attractive. However, because Cadmium is carcinogenic, the market share for Ni-Cd batteries is falling rapidly and in some areas you simply cannot buy them.
( Nickel Metal-Hydride 60–120 Wh/kg 140–300 Wh/L 250–1,000 W/kg 500–2000 cycles These nickel-based batteries have negative electrodes made of a hydrogen-absorbing metal alloy. The workable form of this battery chemistry was developed by Ovonic Battery Company (Energy Conversion Devices), but has become caught up in a patent encumbrance situation causing some to scream about oil companies trying to undermine electric vehicles. Whether or not that's true, NiMH batteries are of less interest to EV's because lithium-ion batteries have a higher energy density.
( Nickel Zinc 100 W·h/kg 280 W·h/L > 3000 W/kg 400–1000 cycles Originally developed in 1901 in Edison's laboratories. A few current manufacturers, including PowerGenix.
( Lithium-Ion 100–265 W·h/kg (0.36–0.95 MJ/kg) 250–620 W·h/L (0.90–2.23 MJ/L) ~250-~340 W/kg 400–1200 cycles These are batteries using lithium, not in a metallic form but ionically bound to other materials. There are several types of lithium-ion batteries distinguished by specific chemistries.
( Lithium Polymer 100–265 W·h/kg (0.36–0.95 MJ/kg) 250–730 W·h/L (0.90–2.23 MJ/L) There are two meanings to Li-Poly cells. The name can refer to a "polymer electrode", or in other cases to cells packaged in small pouches.
( Lithium Iron Phosphate 90–110 Wh/kg (320–400 J/g) 220 Wh/L (790 kJ/L) around 2400 W/kg 2,000 cycles This chemistry is a type of lithium-ion battery, and while its energy density figures are more modest than other types, they offer a better lifetime and are inherently safer.
( Lithium Sulfur 500 W·h/kg demonstrated 350 W·h/l disputed This chemistry is a hoped-for successor to the Lithium-Ion type of battery, because of its very high energy density. The main problem is volumetric distortion, that is the battery swells up considerably. That causes major mechnical stress and battery components degrade rapidly.
( Lithium Air 11,140 (theoretical) W·h/kg ??? ??? ??? First proposed in 1970, this battery type is very difficult to develop. "Air" forms part of the circuit, but lithium metal oxidizes rapidly in the air.

Upcoming battery technology, energy density, specific energy

Feb 4, 2015 Bosch CEO Denner “ ( Electric cars are good, but connected electric cars are better” Bosch CEO Dr. Volkmar Denner spoke at the CAR Symposium about future technology trends. His company supplies parts to several vehicle manufacturers, and they've made a big foray into electric bicycles. Among the predictions is that hybrid vehicles will be ubiquitous by 2015, and that by 2020 batteries will deliver 2x the energy density at 1/2 the cost.

Jan 31, 2015 ( SolidEnergy targeting rechargeable Li-metal smartphone battery in 2016, EV battery with 2x range in 2017 The company says that in 2017 their battery manufacturing partners will be delivering a 20 amp-hour automotive grade battery cell offering twice the energy density of current designs. They've shown volumetric energy density of 1200 Wh/L and 1337 Wh/L in 2 amp-hour pouch cells. Their technology uses a Solid Polymer Ionic Liquid (SPIL) electrolyte, originally developed at and licensed from MIT.

Nov 4, 2014  ( OXIS Energy is leading the World with its latest cell Energy Density and Capacity The company is working on lithium-sulfur batteries, and had announced having achieved a 25 amp-hour cell with 300 Wh/kg energy density. It's a work in progress, that they say is a 12-fold improvement in 18 months. By mid-2015 they expect to build a 33 amp-hour cell, and achieve 400 Wh/kg energy density by the end of 2016 and 500 Wh/kg by the end of 2018. Oxis Lithium-sulfur cells comprise a Lithium metal anode; sulfur-based cathode; a ceramic lithium sulfide passivation layer; and a non-flammable electrolyte protecting the lithium metal. OXIS cells have a 100% available Depth-of-Discharge and cannot be damaged by over-discharge.

Nov 6, 2014  ( Prof. Dr. Martin Winterkorn Science Award for Electrochemistry Speaking to an awards ceremony at Stanford University, Dr. Winterkorn discussed potential for improved battery characteristics. Specifically, he said there is "great potential in this new technology, possibly boosting the range to as much as 700 kilometers (1,000 Wh/l)" signalling upcoming battery designs with this high an energy density. He also spoke of decreasing the cost, to as low as 100 euros per kiloWatt-hour.

Sept 4, 2014  ( Nevada Selected As Official Site for Tesla Battery Gigafactory July 30, 2014  ( Panasonic and Tesla Sign Agreement for the Gigafactory Tesla Motors is building a gigantic factory to make battery cells. With a 50 gigaWatt-hour per year capacity, this one factory will be supplying cells to Model 3 manufacturing as well as grid energy storage systems. They expect battery costs to drop significantly due to this factory, and to make technology improvements by working closely with manufacturing partners.

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