22.–23.05.2024 #polismobility

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Relevance of projected cruising range of electric cars

Is range the new horsepower?

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The motorised individual mobility of the future will create a shift to a new refuelling mindset – on occasion instead of on demand.

Relevance of projected cruising range of electric cars

Relevance of projected cruising range of electric cars

Electric cars are apparently still suffering from the reputation of being short-winded. Data obtained from model-based test procedures, which indicated that the potential ranges of these vehicles were not very practical for everyday use, triggered disappointment among customers.

At a time of direct competition shortly after the arrival of these new electric cars on the market, this bipolar comparison mindset was still unsurprising as the refuelling mentality from the era of the internal combustion engine was still deep-rooted in customers’ minds. With the mobility transition, consumer ideologies now also need to change, moving away from comparisons of maximum values and towards workable solutions.

Newly developed test procedures currently offer a more clear-cut view of the capabilities of vehicles, their drive systems and energy sources. The assessment indicators thus follow more informed models and constitute an intermediate step en route to practical energy management in motorised private transport and sustainable fleet management.

The cruising range dilemma

In metropolitan areas with a widespread charging infrastructure, e-mobility is undoubtedly competitive, but the issue of range still plays a decisive role in purchasing decisions – particularly when thoughts turn to longer journeys.

As far as customer perception is concerned, those performance indicators that have a critical impact on opinion are key figures.

However, a smart plan for when to charge on long journeys can give relatively long-distance travel a certain road movie charm, if the stopovers calculated in advance are used as opportunities to explore a location or take a break. A shorter cruising range thus does not necessarily limit how far you can go, but instead merely influences how you plan your journey. At the same time, statements about cruising range are always subject to a certain lack of clarity and call for a closer look at the test procedures and the technologies on which they are based.

WLTP – imitating reality in the lab

In the Worldwide Harmonised Light Vehicle Test Procedure (WLTP), vehicles are subjected to precise load cycles on a test bench, thereby determining comparable values for exhaust emissions and fuel consumption under ideal conditions.

The New European Driving Cycle (NEDC) persisted as the standard test procedure and contributed to range specifications in the technical guidelines for almost 27 years. Since 2017, it has gradually been replaced in order to be able to offer more precise values that are more representative of real life.

Significant adjustments in terms of test modalities were made to the now-established WLTP standard. For example, the cycle time has been increased from 20 to 30 minutes and the idling time has been reduced to 13 per cent (previously 25 per cent). The vehicle is now driven at a higher average speed (29 mph – maximum 81 mph, compared to 21 mph – maximum 75 mph) and the drive power has also been increased (7 kW average – maximum 47 kW, up from 4 kW average – maximum 34 kW).

It is also worth mentioning, in particular, that optional extras, weight, aerodynamics and quiescent current are now taken into account – factors that were not yet included in the NEDC procedure. The maximum measured ranges therefore fall by approximately 20 per cent using the WLTP compared with the NEDC and are still higher than in normal operation. The procedure has thus been refined with a view to representing more realistic scenarios, but it still remains an idealised procedure, since the simulations are run on the test bench and real-life influencing variables only reveal their impact in actual use.

Solid-state batteries: a game changer

A key technical factor affecting cruising range in standard driving cycles on the one hand and in actual operation on the other are the kind of batteries that are installed. Lithium-ion technology, which has so far dominated the market, can be considered a pioneer in e-mobility thanks to innovative advancements and is expected to pave the way for more efficient and more powerful technologies in the foreseeable future.

The solid-state batteries that are currently emerging will bring about a decisive technological leap forward in this regard, as they not only have a volumetric energy density that is 50 to 100 per cent higher than conventional batteries, but they can also be charged even more quickly. In this new solid-state battery technology, it will be possible to deposit pure lithium at the battery anode. Until now, this has been solved by means of lithium deposits in a graphite layer, as lithium reacts adversely as a liquid electrolyte due to the formation of dendrites, which can cause batteries to develop defects or to self-discharge during operation.

With the ceramic layer of a solid-state electrolyte, the formation of dendrites can be more or less prevented and, because it is not flammable, the material would be even safer to use. However, these are still laboratory values obtained from prototypes. Nevertheless, since large sums of money are currently being invested in research and development in the solid-state battery segment, manufacturers are predicting that they will be ready for series production in 2025. This technology is expected to double the forecast cruising range and make it possible to achieve values as high as over 621 miles per charging cycle, with charging times being reduced to approximately 15 minutes (from 0–80 per cent). In addition, the solid-state batteries are reported to have longer life cycles – still delivering 80 per cent of their original power after 800 charging cycles.

But even this technology is facing nascent competition, or being blessed with possible new combination processes, before it is ready to launch on the mass market.

Artificial solid-electrolyte interphase (A-SEI) is the name given to the process – which has already been patented – in which an ultra-thin layer the thickness of an atom is applied to the cathode materials, enabling further increases in energy density and further reductions in charging times. As a result, it is expected that vehicles would still have a residual charge of 20 to 30 per cent after 621 miles of everyday use, even with dynamic driving and the use of air conditioning. This would make smaller batteries with a range of 621 miles conceivable, or larger variants with ranges of up to 1,243 miles.

On demand becomes on occasion

Technical parameters and laboratory values are still relevant and useful when it comes to comparing technologies and products. However, the true mobility transition will involve a change in attitude towards charging behaviour, shifting from “on demand” to “on occasion”.

Competitors will still use maximum cruising ranges to fuel outdated ways of thinking about individual mobility and to serve as a contrast to conventional refuelling. It’s only by breaking away from these antagonistic comparisons that we will become fully aware of the opportunities the new technologies present. Smaller batteries are more resource-efficient and cost-effective, which means that, if those vehicles that spend their daily downtimes parked up are charged on occasion, a denser charging infrastructure will be needed, but no more record values in terms of maximum range will be produced. In the case of journeys over 310 miles, vehicles can also make the most of coffee breaks to recharge their batteries. This new mindset will help shape the individual mobility of tomorrow.