World premiere: the fully electric Mercedes-Benz eCitaro G articulated bus with solid-state batteries – a milestone in automotive construction

• Consistent further development of electromobility for city buses
• New: solid-state batteries – a pioneering achievement in automotive construction
• New: the second generation of powerful NMC batteries
• New: eCitaro G – the first fully electric articulated bus with the three-pointed star
• New: maximum traction – two-axle drive on request
• New: modular eService contracts for plannable costs
• Next stop for the eCitaro: range extender with fuel cell

The curtain is raised on a double world premiere: Mercedes-Benz is launching the all-electric eCitaro G. It is optionally equipped with innovative solid-state batteries. With this battery concept, Mercedes-Benz takes the technological lead not just in the bus segment but in automotive construction worldwide. As an alternative, the eCitaro and eCitaro G are also being launched with a new generation of the lithium-ion batteries currently used, which will once again be much more powerful than the previous one. The Mercedes-Benz eCitaro and eCitaro G thus represent another milestone on the path to emission-free local public transport in towns and cities and therefore also to improved quality of life in urban areas. The first vehicles are already due to be supplied shortly.

Consistent further development of electromobility for city buses

City buses are used to adhering to strict timetables, and the Mercedes-Benz eCitaro has also remained reliably on schedule throughout the stages of its rapid development. In 2018, Mercedes-Benz opened a new chapter in electric mobility for city buses with the introduction of the all-electric eCitaro as an innovative solo bus. In just a short time, the eCitaro has become an established and trusted contributor to improved quality of life in urban areas, operating as a locally emission-free and low-noise city bus.

Now the next page is turned with the world premiere of the eCitaro G articulated bus as announced in 2018. Mercedes-Benz is simultaneously launching the eCitaro with solid-state batteries for both the solo and articulated versions of the bus, a pioneering achievement in the world of automotive construction. In tandem with this, Mercedes-Benz is also switching to the latest generation of the lithium-ion batteries (also called NMC batteries, after their chemical composition). The new battery generation once again represents an increase in power over its predecessor.

Over a very short period, the eCitaro has evolved from a one-off into a complete model series. It comprises the eCitaro solo bus and the new eCitaro G articulated bus and incorporates an extremely wide range of charging and battery technologies. The eCitaro is thus positioned as an all-electric city bus which can be tailored to match any application profile for regular service city buses, while Mercedes-Benz underscores its leadership position in the field of technology for electric mobility. The transport companies enjoy support from the in-house experts at eConsulting with regard to the choice of suitable technology and required infrastructure, from power supply and installations at the operating company through to operational planning.

New: solid-state batteries – a pioneering achievement in automotive construction

The new eCitaro G is the first city bus in its category anywhere in the world to be equipped with solid-state batteries. These lithium-polymer batteries are also part of the lithium-ion group of batteries. Because they contain electrolyte in its solid form as a polymer instead of the usual liquid, they are known as solid-state batteries. The battery anode is made of graphite with pure lithium, and the cathode of lithium iron phosphate.

Solid-state batteries are characterised by their extremely high energy density, which is around 25 percent greater than in the coming generation of traditional lithium-ion batteries with liquid electrolyte. Each battery assembly in the eCitaro and eCitaro G has an energy content of 63 kWh. With seven assemblies on board this amounts to an impressive total of 441 kWh. This gives the eCitaro G a range of up to 220 kilometres in favourable conditions with average demands on speed, topography and load along with straightforward climatic conditions. In the winter with the heating in operation, the eCitaro G covers an impressive 170 kilometres.

The characteristics of solid-state batteries differ significantly from NMC batteries: overall they have a greater volume and they cannot be swapped for NMC batteries.

As solid-state batteries operate at a temperature of around 80 degrees Celsius, there is no need for a complex cooling system as is the case with NMC batteries. Solid-state batteries reach their operating temperature solely through energy metabolism during use. During extended breaks, heating elements maintain the batteries at an ideal temperature. This occurs automatically in the eCitaro G with no need for the driver to take action.

In contrast to NMC batteries, the suitability of solid-state batteries for rapid charging is very limited as they have a maximum charging output of around 80 kW. Their suitability for intermediate charging is therefore severely restricted, and they are only supplied by Mercedes-Benz in combination with charging via connector. The solid-state batteries have an impressively long service life of up to ten years.

Furthermore, this battery technology does not require the use of cobalt.

Due to their very contrasting characteristics, city buses with solid-state batteries cover a different range of applications from those powered by NMC batteries. Mercedes-Benz wants transport operators to have the choice: for this reason, the eCitaro will in future be offered with a choice of NMC or solid-state batteries. 

New: the second generation of powerful NMC batteries

Since its world premiere in 2018, the eCitaro has been powered by lithium-ion batteries. Mercedes-Benz uses lithium nickel manganese cobalt oxide cells, or NMC for short. The composition is specially selected to make them suitable for high charging currents during high-power charging and, thanks to their energy density, to give the vehicle an extensive range. The first eCitaro G buses to be supplied will also have this battery technology.

As already announced at the world premiere of the eCitaro in 2018, Mercedes-Benz will switch to the latest generation of NMC batteries at the beginning of the coming year. This comes against the background of rapid advances made in battery development and ensures transport operators always have the latest technology at their disposal.

The new generation of NMC batteries has a considerably greater capacity, meaning increased vehicle range. With a capacity of around 33 kWh instead of 24 kWh per battery assembly and the maximum number of assemblies fitted, the total capacity amounts to 396 kWh. A solo bus with this equipment would have a range of about 200 kilometres in winter operation or up to 270 kilometres in favourable conditions. That means average demands in terms of speed, topography and load as well as straightforward climatic conditions.

In terms of geometry, the new prism-shaped NMC batteries are identical to the batteries currently in use and they have the same connections. This means that transport operators using the current eCitaro will actually be able to increase the range of their vehicles by changing to the new batteries. Depending on the battery configuration and the charging system, there is potential accommodation for a maximum 146 seats in the eCitaro G.

Mercedes-Benz keeps the batteries at an ideal temperature of around 25 degrees Celsius by means of a liquid cooling system. This results in maximum charging capability, power and service life.

New: eCitaro G – the first all-electric articulated bus with the three-pointed star

Mercedes-Benz is continuing resolutely on its path towards the electrification of city buses: the new eCitaro G is the first all-electric articulated bus to bear the three-pointed star. It is ideal for operations in congested towns and cities on routes with large numbers of passengers and is an important factor for improving the quality of life in inner cities.

The new eCitaro G combines the advantages of the well-proven Citaro G articulated bus with the outstanding electric drive technology of the eCitaro. Therefore, like the conventionally powered Citaro G, it is 18.13 metres in length and available as a three- or four-door model and with a large number of seating and equipment variants. 

The eCitaro G adopts its characteristic design features from the eCitaro. These start with the electric bus’s distinctive independent face, with its arching windscreen with integral destination display. Visually, the windscreen smoothly transitions into the roof with dark bars on the left and right. The roof-mounted equipment on the eCitaro is concealed behind an elegant roof-edge ridge made of a multi-piece extruded aluminium section. The glossy black lower segment extends the generous side-window glazing of the city bus. The upper segment is painted in the vehicle colour. These design features lend the eCitaro G perfect proportions.

New: huge range of charging variants

The batteries in the eCitaro G and eCitaro are charged via a charging connector with a charging output of up to 150 kW. The connector is located as standard on the right-hand side above the wheel arch of the front axle. In addition to this, some more plug positions on the left-hand side and at the rear of the vehicle are due to be offered in the coming spring. This gives the eCitaro the flexibility to fit into the transport operator’s depot strategy and access charging points in a variety of positions. An on-board charger is not envisaged, charging is via DC current.

As indicated at launch, the eCitaro can also be supplied with a current collector / pantograph as an optional alternative to plug-in charging. In a further variant, the eCitaro will become available with contact rails for charging from a fixed pantograph. The first models are scheduled for supply in the coming spring. These two variations double the already high charging output to up to 300 kW. The pantograph and charging rail equipment will only be offered in combination with NMC batteries due to the limited rapid-charging capability of solid-state batteries.

New: maximum traction – two-axle drive on request

Like the solo bus, the eCitaro G is powered by the tried-and-tested ZF AVE 130 electric axle, which is located in the rear section. For maximum traction and use in demanding topography, the new eCitaro G can even be supplied with two powered axles.

The additional powered centre axle is a significant advantage of the electric drive technology from Mercedes-Benz, with asynchronous motors located close to the wheel hubs. In the eCitaro G, as in the eCitaro, they deliver up to 2 x 125 kW of power per axle, generating 2 x 485 Nm of torque. With the transmission ratio used, this equates to 2 x 11,000 Nm at the axle and will be fully available from launch subject to technical considerations. This gives the articulated bus a commanding amount of drive power. 

Right down to the finest detail (I): weight distribution a case in point

As with the solo bus, Mercedes-Benz has factored in optimum weight distribution in the new eCitaro G in order to achieve maximum passenger capacity. The seven solid-state battery assemblies are distributed in the eCitaro G as follows: four battery assemblies on the roof in the installation space above the centre axle, one further forward on the roof over the rear coach, and finally two assemblies on the left in the rear in place of the combustion engine and gearbox.

With the full complement of NMC batteries there are eight assemblies mounted on the roof above the centre axle. Two assemblies are located on the roof at the front end of the rear coach. Another two assemblies are also housed on the left-hand side at the rear. Both variants use the well-proven front axle from the eCitaro with up to eight tonnes axle load.

Right down to the finest detail (II): highly efficient heating and climate control

The battery capacity of an all-electric city bus is not in itself a satisfactory indicator of its performance capability and range - the true measure is that of energy consumption. In the case of a city bus, this is impacted significantly by climatic conditions and the need to cool and, above all, to heat the interior. In the eCitaro G with three axles and an increase of over 50 percent in the permissible gross vehicle weight of 30 tonnes, this is a much more important factor than in the lighter two-axle solo bus.

Great emphasis has therefore been placed on thermal management. Compared with the current Citaro G with combustion engine, the energy requirement for heating, ventilation and climate control has been reduced by about 40 percent. This remarkable energy efficiency is the basis for the practicable range of the eCitaro G, even under the most unfavourable conditions.

First, the NMC batteries are brought up to the ideal temperature of 25 degrees Celsius. The result is maximum charging capability, performance and service life. The solid-state batteries reach their operating temperature of 80 degrees Celsius automatically during use.

The passenger compartment is heated by means of an energy-saving heat pump, supported if necessary – in the case of substantial temperature changes – by braking resistance. It is now connected to the water circuit in all eCitaro and eCitaro G models for the first time. This reduces energy consumption by the fan heaters, increasing vehicle range during winter operations. The heater at the front is equipped with a double heat exchanger. The components that give off heat are linked together, to keep the amount of energy required for their cooling to a minimum. The output of the heating and air conditioning system varies depending on the vehicle’s load and the outside temperature. 

The roof air conditioning is equipped with an additional heat pump function as standard. As a result, the passenger compartment is heated very efficiently even when the outside temperature is low. As a refrigerant, the system uses CO2, which is both highly efficient and environmentally friendly.

Another advantage: the interior can be preconditioned up to the desired temperature even while the batteries are still being charged at the depot. This means the energy required for air conditioning is not drawn from the battery at the start of a trip, which in turn increases range. It is even possible to condition the bus beyond the normal target temperature, so that in the winter it can set off from the depot with a higher temperature to counter cooling from outside. This reduces consumption when the bus is in operation. Accordingly, in summer the temperature can be reduced to lower levels. Another advantage: with an electric air-conditioning system the required power is always available at any time. By contrast, conventional systems depend on the current engine speed of the combustion engine and so need greater power.

Functional cockpit, easy operation, maximum safety

The cockpit of the eCitaro G is not significantly different from the already familiar driver’s workspace – for the most part, the operating concept is the same as that of the conventional Citaro G. The direction of travel is selected using the usual D-N-R push buttons, but there have been changes to the instruments. Instead of the rev counter there is a power meter with a display of current power requirement or recuperation. The charge status of the battery is also shown. The driver can view the range, available power and charging levels on the central display.

To save energy, the eCitaro G and the solo bus have an acceleration control system: whether empty or fully occupied, the eCitaro G always accelerates under full load away from the bus stop or the traffic light always with the same dynamics. This prevents unnecessary energy consumption and is also conducive to a passenger-friendly driving style.

In addition, the eCitaro G gains energy through recuperation, where kinetic energy is converted into electrical energy when the vehicle is braking or in overrun mode. In this situation, the electric motors function as generators. The driver can use a multi-stage e-brake lever on the steering wheel to set the braking torque of the articulated bus and thus the recuperation rate. In the basic setting, the bus coasts in an energy-efficient manner, when the driver takes their foot off the accelerator pedal, it "glides".

The eCitaro G is more than clean, it is safe as well. Like the conventional-drive Citaro G it also comes with the kink inhibiting Articulation Turntable Controller (ATC) as standard. ATC is similar to ESP in the way it works. As an option, Mercedes-Benz will supply the eCitaro G with the turning assistance system Sideguard Assist with pedestrian detection and Preventive Brake Assist, the first active braking assistance system for city buses. 

New: modular eService contracts for plannable costs

E-mobility requires specific services that keep pace with the constantly evolving vehicles. For this reason, Omniplus is now adopting a modular concept for its offering of tailored eService contracts with the introduction of the new battery technologies.

An important element of this is the standard basic warranty for the high-voltage battery when purchasing an eCitaro with solid-state batteries. This is valid for up to ten years or 280 MWh of energy throughput per battery pack. There is also a warranty for the high-voltage components themselves (up to 200,000 km). The basic warranty for the NMC 2 battery of a Mercedes-Benz eCitaro in the solo or articulated bus variant (without pantograph) applies for a duration of up to five years, or at the longest to an energy throughput of 60 to 80 MWh per battery assembly, dependent in each case on the number of battery assemblies installed in the vehicle.

If transport operators require a longer term or a higher energy throughput, an extended battery warranty for plannable costs can be concluded on the basis of a customer-specific feasibility study.

In addition to this, the well-known eBasic and ePremium service contracts are also optionally available to transport operators. These offer package solutions for repair and maintenance work on high-voltage components and the vehicle itself. The new guarantee supersedes the existing cover for the high-voltage battery. In this way, the optimum service for the electric bus fleet can be compiled from the basic guarantee module, the extended battery guarantee and service contract to meet the wishes and requirements of individual customers.

Next stop for the eCitaro: range extender with fuel cell

The first eCitaro G with solid-state batteries or NMC batteries will be supplied to customers this year. Immediately after that, the eCitaro G with the new more powerful generation of NMC batteries will follow in the coming year.

This is by no means the end of the schedule for the Mercedes-Benz eCitaro. In 2022, the range of the eCitaro and eCitaro G will be increased yet again by a range extender in the form of a fuel cell that generates electricity. In terms of performance and energy supply, its design will allow the the buses to fulfil nearly 100 percent of all requirements of city buses regarding range. This technology will eliminate the need for intermediate charging and the complex infrastructure required for it in almost all cases. By then at the latest, all-electric and locally emission-free city buses will be able to completely replace vehicles with conventional drive systems.