A vital component to the viability of clean transportation, whether it be via air, land or water, is the form of energy storage used. The reason fuels such as gasoline continue to be the most commonly used energy source in transportation is their extremely high energy density. Energy density refers to the amount of energy that can be stored in a given volume. When referring to a given mass, the term ‘specific energy’ is used, measured in mega joules per kilogram (MJ/kg).

Although uranium has one of the highest energy densities (in the magnitude of millions of MJ/kg – far greater than that of coal) its practical uses aren’t quite so feasible to every day applications. Given the complexities, it remains in the realm of high end applications such as power plants.

Jet fuel, diesel and gasoline, however, have specific energies in the range of 40-50 MJ/kg.

In the battery realm, rechargeable lithium ion batteries have been receiving a lot of attention due to their high energy storage relative to other battery types. Their specific energies currently range from 0.3 to 0.9 MJ/kg.

So, not quite on par with conventional fuels.

But that’s still a big jump from your typical car battery – these are ‘lead acid’ batteries, which typically have a specific energy of 0.17 MJ/kg.

In the early days of electric cars, hobbyists were converting gasoline cars to electric by loading enormous numbers of lead acid batteries into the car, adding colossal amounts of weight to the car while having very little range (less than 50 miles). The onset of lithium-ion batteries and gradual reduction in costs has led to a dramatic reduction in the weight and volume taken up by on-board batteries, whilst allowing a great increase in driveable range. This has made commercial production electric cars such as those of Tesla Motors much more feasible, with 200 mile plus ranges now common.

But there is still a long way to go to match the energy storage capabilities of conventional fuels. However, with battery storage technologies reaching into sectors ranging from computing and automobile to telecommunications and the military, there is a huge focus being placed on battery research.

Three companies making significant strides in this field are:

Amprius (www.amprius.com)

Prieto Battery (www.prietobattery.com)

Xerion (www.xerionbattery.com)

Each are undertaking research on ways to dramatically reduce charging times, as well as increase energy density and battery safety (lithium batteries are renowned their penchant for catching fire- just take a look on Youtube). Batteries involve chemical reactions between two components- an anode and a cathode, and the movement of ions between the two. The structure of batteries means these ions traditionally move relatively slowly (which is why charging your phone battery takes as long as it does).

One of the ways these companies are improving battery performance is by using three-dimensional lattice structures or porous materials within the battery. These configurations introduce a far greater surface area for chemical reactions to take place than traditional battery structures, and result in much faster movement of ions through the system. Prieto’s, for example, introduces a 60 times greater surface area. The result? Dramatically reduced charge times, and far greater amounts of power available for a given battery size and weight.

However, the technologies remain in the lab environment and are still a long way from commercial production. But such developments mean a promising future for clean transport, with far greater ranges at reduced weight and volume. Battery science is a critically important area of research, and whoever can bring significant advances to market first is going to be very, very popular.