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  • Writer's pictureAddionics

Accessible Capacity

N.B. in this piece I quote capacity and range interchangeably as the physical parameter of battery electronics that is capacity translates in the range of an EV

Tesla model S selection page (as accessed on 11.12.18)

While we were attending the Paris Motor Show earlier in October we got the opportunity to chat with the Tesla team on their stand presenting the model 3 for the first time in Europe. I introduced myself as a potential buyer and was curious to what the various options were on offer and in particular with regards to the battery.

When choosing an EV, you are often prompted to decide between a variety of batteries and to do so various ranges are presented and often quoted with NEDC (New European Driving Cycle or MVEG) standards. Here the Tesla host pointed at two types of battery a standard one, good for urban application, and an extended range which he called the "500km one but actually you'll reach 400 to 450km max". Where does this difference yield from? Why do manufacturers quote a theoretical range but remain honest about the real life range?

There are multiple levels to answer this question. The first is that manufacturers are quoting the real capacity of the battery and as these are to be validated by standard certification, they are in legal obligation to quote such values. It appears in their interest to be honest about the actual possible ranges as well so to avoid customer complaints and cars coming back for battery checks more often than necessary.

The second level to this answer is that the mileage quoted is not only theoretically but will correspond to the real capacity measured in labs and on test tracks in ideal conditions. It is specifically the later point, the so-called "ideal conditions" that yield such a variance. To achieve the fully quoted mileage the recipe is very straightforward you need to have be alone in the car, weigh approx. 75kg, be in sunny yet not to hot weather, dry and flat roads with no traffic somewhere around 40mph and ideally no traffic lights either. Not your average ride.

Superman can see across walls, our CSO, Farid can see through batteries

Addionics brings a third and deeper level to answer this question. Superman can see across walls, our CSO, Farid can see through batteries and understand all the chemical and physical behaviours in-situ, i.e. while in charge and discharge. By doing so, we are able to understand what is going wrong and offer solutions to improve any recorded flaw.

Schematic of the internal structure of a standard battery. The internal resistance is shown only one the anode side for aesthetic purposes but occurs at every interface.

At the core of the battery lies the two electrodes and separator where the fundamental electrochemical reaction occurs. Depending on whether you charge or discharge, electrons are generated one way or the other within the battery. To travel to and power the motor these electrons cross the interface between the electrode where they are generated towards and a thin 2D layer called a current collector. This latter layer is very similar to the Aluminium foil we all have in our kitchens. When driving at high-speed, one asks for high current from the battery and a high number of electrons are generated at a given instant. So high is that number that we have noticed a high build up of resistance at this interface. Electrons pile-up and create "traffic-jam" at the source of this gap between theoretical and accessible capacity. In turn, the battery heats up and creates high internal stresses thus preventing the use of the full theoretical capacity.

In fact, the damage to the battery is not only short-term but this internal heating is also source of long term damage to the battery. High thermal stress cycling causes physical repeated physical expansion and contraction to the various metallic layers that compose a battery. In the long run, these stress will lead to delamination leading to potential catastrophic failure of batteries. Delamination is the physical separation of two layers allowing potential for air, or foreign species to penetrate in the battery and potentially short circuit the system internally.

Addionics Solution

To overcome this internal resistance build up, Addionics has created a novel way of fabricating complex 3D metallic structures. Our proprietary smart 3D current collectors allow us to embed the corresponding electrode (both anode and cathode). As such, we maximise the surface area for the same volume and increase the points of contact, or points where electrons can migrate from the electrode to the current collector. The resistance is considerably lowered and this translate in a reduction of charging time by 50% and increase in accessible capacity by 100%. In addition, by embedding two layer closely packed together, the long term delamination risk is also reduced thus increasing the safety of batteries equipped with Addionics technology.


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