Daimler now offers its electrically powered bus optionally with a solid fuel battery. The first series application of the new battery technology offers more range and less weight.
The solid fuel battery does not make its secret debut, but it is comparatively quiet and quiet with the articulated bus version of the eCitaro. The eCitaro G starts with the lithium-ion battery from the eCitaro solo bus. In 2020 Mercedes wants to bring a new generation of this NMC battery (nickel-manganese-cobalt), with which the capacity increases from 292 kWh to 396 kWh. The range of the articulated bus is correspondingly higher. In the year-round use it should travel 200, at best even 270 kilometers. For this, the electricity storage (consisting of 12 modules with 33 kWh each) weighs a total of 3.4 tons.
Solid state battery from the supplier
Even more remarkable: Despite the increased capacity of normal lithium-ion batteries with liquid electrolyte, the Citaro G will alternatively be equipped with solid-state batteries, “as a second technology path,” as Daimler says. The advantages of the solid-state battery from a Mercedes perspective: high energy density and particularly long service life. Mercedes buys the battery from Blue Solutions, a subsidiary of the French Bolloré group.
Chemically, they are lithium polymer batteries. The solid instead of liquid electrolyte – hence the name – also makes it less fire-prone than the liquid conventional lithium-ion battery. In addition, the battery type does not need raw materials such as cobalt, nickel or manganese. With seven battery packs, the solid-state battery in the eCitaro G consists of 7 modules with 63 kWh each and a total capacity of 441 kWh. One module weighs about 450 kg, the total battery comes to 3.2 tons. More capacity, less weight – the solid-state battery has a higher energy density than the alternative with liquid electrolyte – 0.14 kWh / kg instead of 0.11 kWh / kg. Because its comfortable temperature is around 80 degrees (compared to 25 degrees with conventional batteries), it must be well insulated. That’s why he needs a little more space, which is not a problem on the bus.
More range, slower charging
The range of around 230 kilometers in all-year use and around 320 kilometers is sufficient for typical use in city buses. The average value for year-round use for the LiNMC battery is approx. 200 km, at best 270 km. Why doesn’t the higher energy density bring more range plus? “The range of buses is heavily dependent on the air conditioning and heating, which is further reinforced by the low average speeds (sometimes only around 15 km / h). Against this background, efficient thermal energy management is of particular importance,” says Daniel Vorgerd, Overall project manager eCitaro at Mercedes.
The manageable quick-charging capacity makes the eCitaro G with solid-state battery a typical so-called depot charger, because charging with a maximum of 80 kW makes charging little useful during use – an 80-percent charge took just over four hours to charge after half an hour the range would have increased by a mere 25 kilometers – charging all night in the depot with less power fits the solid-state battery better.
Charge faster with liquid electrolyte
If the infrastructure on the bus routes fits and the waiting times in the depot are shorter, the conventional lithium NMC battery with liquid electrolyte is more suitable. It can charge at around 150 kW on the plug and even at around 300 kW on charging rails or overhead lines.
In the eCitaro G there are both technologies for the different deployment strategies of the transport companies. In addition to the driving profile, factors such as the depot situation, infrastructure and connected load are decisive. Because this is not so easy to assess, Mercedes also offers the appropriate advice on technology (e-mobility consulting) for transport companies. It is also about the cheaper solution. Surprisingly, the solid-state battery, which is more expensive to purchase, is cheaper for the customer over the life of the vehicle because it keeps the higher cycle stability considerably longer.
30 percent more energy density for the solid-state battery – that doesn’t sound like a quantum leap, but after a giant step. And even if the Mercedes bus department does not want to say anything about the transferability of the technologies in the eCitaro to trucks or even in the more space-critical cars: a solid-state battery in series is just as prickly as a fuel cell range extender. Given the government’s nine billion euros in investments in hydrogen technologies, one could well imagine that public transport will soon have more and more access to “green” hydrogen and buses will also be able to do without fossil fuels.