Electric Vehicle - Battery (r)Evolutions

If you have watched the electric vehicle industry over the past year and tracked the developments in the battery department, you will have noticed that Lithium is hot stuff.  

A battery is a battery, right? - [IMG SRC]

 

Lithium is now used a lot and is by far the most well known battery in the electric vehicle application. It is used in cars, scooters and airplanes. So what is happening now with battery development? Any new material, the next lithium for example, that is popping up? With an estimated $96.000.000.000 being invested in battery technology, what are the results and promises on the horizon.

 

Lithium, the new oil? - [IMG SRC]

 

Lithium is widely used in the electric vehicle batteries, often with different additions like iron phosphate (LiFePO4) for example. The basis remains lithium, the addition of such materials add specific properties such as a more stable/robust battery, better heat resistance, higher allowed powers, etc. Lithium was initially implemented in the consumer electronics industry, where compact and light weight devices prefer the light, compact and high power and energy density properties that lithium batteries allow for. Back then, they provided a significant boost compared to the traditional batteries that were used in consumer devices back then.

 

Current research on batteries focusses on a few key areas; safety/reliability and power- and energy density/weight reduction. Batteries still are rather heavy components in the EV, if you can reduce the battery weight, the result is a lighter vehicle, which in turn uses less kWh to travel the same distance. The energy density [kWh/kg] is about how much energy is stored in the battery, the higher the amount of kWh per kg of battery, the better. This is closely related to the weight reduction efforts. The safety and reliability research focusses on creating safer and more reliable batteries; batteries that can be charged at higher powers, at higher c-rates (quicker charging) and allow for more charge cycles to be performed without degradation of the battery performance.

 

A few technologies which are aiming at these goals, which in my opinion are very promising, are Zinc-Air, super-capacitors and graphene (either as a base material, or as an addition to for example lithium).

 

The idea behind the Zinc-Air is relatively simple; any battery has an anode and cathode side (a positive and a negative), where each side consists of a different material. If one of those materials is a metal like Zinc, while the other is Air, you have potentially reduced the battery weight by half! It does not work out exactly that way, but you get the idea. Air is lighter than the metal and you can use the outside air, though probably it would be conditioned to meet a few technical requirements before allowing it into the battery. One company who is betting big on the Zinc-Air technology is Toyota, but others have also started to look into other combinations with Air, which are equally promising.

 

Super-capacitors are similar to batteries in the sense that they can store energy, though the method at which this happens is completely different. Super-capacitors allow for a light weight construction which can handle significantly higher discharge (or charge) powers. The only downside of this technology is the limited energy density that is possible; it is less suited to power an electric vehicle for a long duration. It is ideal to be used for quick storage and release, for example to store recovered braking energy in, or boosting power to accelerate.  At the moment super-capacitors under development will be able to achieve a higher energy density, but also companies are looking at a hybrid storage with a battery paired with a super-capacitor. This would theoretically allow the best of both worlds.

 

Graphene, the next step? - [IMG SRC]

 

Last but not least, graphene is my last top pick of a promising battery technology. The material is pure carbon, a structure which resembles a sheet of paper, only with the thickness of one single atom. Not only does this material have great mechanical properties, it is also a great electric conductor. In some cases graphene is applied to existing lithium batteries, allowing the batteries to be charged a lot quicker than currently is possible. Another graphene approach is with a gel-like battery, where graphene is sandwiched with a layer of water. The unique properties of graphene exist for as long as it remains the perfect sheet of paper. As soon as the structure is altered (for example multiple sheets touching each other), the beneficial properties go down. By isolating the sheets with a layer of water, one can maintain the sheet structures of graphene and have a super cheap bill of materials; plain water and carbon is all that is required.

 

For the next few years I expect the most of these three battery technologies, though I'm curious to find out that is developed next and if these promising technologies will be superseded by the next big battery technology.