Final Statement

We started our blog, based on the assumption that batteries are an outdated technology without much further use in the relatively new trend of electric vehicles. This assumption was inspired by the many criticisms towards batteries that can be found and the alternatives such as hydrogen fuel cells. During the process of writing our blog, we did research on the current and emerging battery technologies and the use of batteries in current electric vehicles.

The energy density versus range of different types of fuel

The main drawback for current batteries to be used in electric vehicles is their limited operating range. Because of the low energy density of batteries compared to diesel and gasoline, they are not well suited for long distances. But this does not necessarily mean that batteries are useless for electric vehicles: Vehicles running on gasoline need a heavier engine and transmission, can’t profit from regenerative braking and have additional losses in their transmission. Thus these vehicles intrinsically consume more energy to travel the same distance as an electric vehicle. If we take all these factors into account, battery powered vehicles become increasingly interesting again.

For shorter ranges, batteries are even more interesting and efficient than traditional vehicles as can be seen in the above Figure. This is because for a greater range, an electric vehicle needs a bigger battery pack, which adds a lot of weight and a traditional vehicle only needs a bigger fuel tank with a relatively small weight.

HEV Cost Comparisons

Since weight is such an important factor in the determination of the range of an electric vehicle, lately most of the research has been focused on the improvement of lithium based batteries. It might be interesting to focus on lead acid batteries as well, their weight is a lot higher but their production costs are only a fraction of those of lithium batteries as shown in Figure \ref{fig:cost}. This means that for the same price, a lot more lead acid batteries can be incorporated in a vehicle, allowing for a comparable range. Probably both battery technologies will continue to coexist and allow for a wider variety of possible electric vehicles.

If research on battery technologies continues to increase performance and energy density like it did over the last decades, batteries certainly have a future in electric vehicles. While increasing energy density, the range of electric vehicles will increase as well; and if more focus is put on more aerodynamic vehicles, built from lighter composite materials, the range will increase even further.

What concerns us the most however, is not the limited energy density or operating range of batteries; it is the lack of a standard way to charge or swap these batteries. Currently every car manufacturer has its own standard for battery packs; and if you buy an electric vehicle now, the chance is slim that you will find a way to charge it, except for at your own charging point at home. Some companies are working on a standard way of charging, but it needs to be adopted by the majority of manufacturers for it to become really useful. It is likely that in the coming years, a lot of so-called standards will emerge, and only when one real standard is chosen, electric vehicles will be able to take over the market from traditional vehicles.

Service station by Better Place

Since charging of the batteries is not fast enough to compete with filling a fuel tank, battery swapping is a viable alternative. It can be done very fast if the design of the vehicle and battery pack are adapted to it. It is clear that this is not something that should be left to the customers, but some sort of service station, comparable to a petrol station. A render for such a service station by Better Place can be seen in Figure \ref{fig:service}. The investment required for this service stations, risks to turn this into a chicken and the egg story where no one is willing to invest in service stations until there are enough electric vehicles and only some electric vehicles will be sold until the possibility to swap batteries is offered. \nocite{bp}

If every car manufacturer keeps on using its own battery pack design, service stations are even less likely to be founded because this would mean that a service station can only swap battery packs for those car models of which it has the battery pack in stock and the required equipment. For the future of electric vehicles, it would be better if the car manufacturers agreed on some standards for their battery packs. Dimensioning and technology can still change, depending on the application of the vehicle, but a set of standards would allow for the different number of battery packs to be limited.

If we conclude, we see that a lot of work still needs to be done for batteries and electric vehicles in general to form an alternative to traditional vehicles. It is too easy to say that batteries have no future in electric vehicles and that they are holding back the advance of electric vehicles in general. We believe batteries certainly belong in the electric vehicles of the future, but there is a lot more work that needs to be done by manufacturers to prepare the market for electric vehicles. Standards for the battery pack, charging methods and swapping techniques are required to allow the adoption of electric vehicles by the majority of the people. It is only after more effort is put into battery technology and lightweight materials and that standards have been set for EV battery packs that electric vehicles will form a realistic alternative to traditional vehicles.

We hope we have made a small step forward in the safe and efficient use of lithium-based batteries in EVs. Our battery management system has at least proven to do so in the Umicar Inspire solar car.

References

Michael Fischera, P. V. S., Mathew Werbera.  (2009, July). Batteries: Higher energy density than gasoline? Energy Policy, 37 (7).

Better Place. (2010). Charging electric vehicles. France. Available from http://www.betterplace.com/solution/charging/

Battery cost is as important as their energy

When different battery technologies are compared, one often falls back on a comparison of either energy, power or cycle life. While these are certainly important factors, it may not be enough to choose the battery type of the future. In this comparison, we will use the required power/energy as a constant and explore the other factors. This allows to evaluate different battery types in the same application.

The first factors that should be taken into account are volume and weight. This is a factor that is mostly described in terms of energy density, volumetric and/or gravimetric. The importance of the volume is fairly obvious since space in a (hybrid) electric vehicle is limited, certainly if you focus on an aerodynamic design. As stated in our previous blog-post, the weight is a factor that has a big effect on the range of an electric vehicle. Batteries with a high weight, and thus a high gravimetric energy density, can get a higher range for the same energy stored in the batteries. With these factors in mind, Lithium-Ion and Lithium-Polymer batteries have a huge advantage over traditional battery types such as Lead-Acid and Nickel-Metal Hydride.

While volume and weight are logical factors to consider and are often referred to in studies, the battery cost is often neglected. The Lithium-Ion battery technology was first released by Sony in 1991, over the last two decades huge increases in performance, safety and cycle-life have been achieved. While this are very important improvements, they all came with an increase of production cost. The result of these two decades of research is a very broad spectrum of possible combinations of energy density, cycle life and capacity. No one doubts that these batteries are improved since their first design, but the total improvement is only 8% to 10%. If you want to take the most advantage of these technologies however there is a serious price tag coming with it. The standard Lithium Ion batteries have a cost of $0,45 to $0,55 per Wh, high-end types have prices up to $1,50 per Wh. Lithium Polymer batteries are the cheapest alternative available with still a decent performance at $0,35 per Wh.

Lead Acid batteries exist for many years (their first appearance was around 250BC!), but until the late 1960’s, no significant improvements have been made. During the last three decades, a lot of research has been done by Axion in America and CSiro in Australia. The results of these studies are high-end Lead Acid batteries. Axion has developed a PbC-battery that claims an increase of 400% in power at a double of the cost of standard Lead Acid batteries: $0,20 to $0,30 per Wh. The CSiro research resulted in a so-called “ultrabattery”, which is a hybrid of a Lead Acid battery and a super capacitor. In a 100 000-mile test, the ultrabattery got a decrease in gas mileage of 2,8% over the original Nickel Metal Hydride battery pack, but this while saving $2000 in cost.

If we use this data to make a comparison between (hybrid) electric vehicles based on their battery choice and capacity, we see that the advantage of Lithium-batteries is smaller than thought. In table 1, an overview of the cost estimates for different battery packs has been made, and it is clear that for the same energy, Lead Acid batteries are a lot cheaper than their Lithium Ion counterparts.

Table 1: Cost of battery packs

Battery Capacity (kWh)	Li-Ion Cost	Advanced PbA Cost	PbA Cost Advantage
0,50	$667	$250	$417
1.00	$1,333	$500	$833
1.50	$2,000	$750	$1,250
5.00	$6,665	$2,500	$4,165
16.00	$21,328	$8,000	$13,328

This difference in price plays an important role in the price of the electric vehicle; electronics and the power train are roughly the same for both designs, and thus the cost of the vehicle is largely related to cost of the battery pack. This difference can be seen in the following graph, depicting the cost of the different components of a vehicle and the total cost using either Lithium Ion or advanced Lead Acid batteries.

HEV Cost Comparisons

The conclusion of this blog post is that despite it might be too early to draw a final decision, the focus everyone seems to place on Lithium Ion batteries for the future seems to be a little bit hasty. The costs of the total should be taken into account when comparing the different technologies. Every technology will probably have its use, but for high power applications, Lead Acid shouldn’t be written of despite their higher weight/lower energy density.