24.–26.05.2023 #polismobility

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The Future is solid

Focus on storage technologies

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Developments in the field of energy storage are proceeding rapidly. Energy surpluses could already be used effectively in the foreseeable future, and the role of the automobile is also about to change. In addition, the range discussion could soon be over.

© Firstsignal – iStockphoto.com

© Firstsignal – iStockphoto.com

Developments in the field of energy storage are proceeding rapidly. Energy surpluses could already be used effectively in the foreseeable future, and the role of the automobile is also about to change: as "prosumers", electric vehicles are now also capable of feeding electricity back into the cycle. In addition, the range discussion could soon be over - a not insignificant part of this is due to the progress of a Chinese start-up.

One of the loudest and most widespread arguments against large-scale electrification of the mobility sector is the high electricity consumption that such an undertaking would entail. However, experts estimate the increase in the total demand for renewable energies - after electrification and simultaneous stock reduction - at only ten percent. One of the reasons for this is that the prospects are good for increasingly developing storage options for electrical energy in the coming years - so far this is still one of the neuralgic points of electromobility.

The Technical University of Dresden, for example, is conducting research - funded by the German Federal Ministry of Economics and Technology - into the mechanisms of decentralised energy storage using integrated kinetic rotational mass storage systems, or demiks for short. These work with the help of a flywheel mass that is accelerated and thereby converts electricity into kinetic energy that can be used as electricity when needed. The higher energy density, the higher efficiency and the longer service life are cited as important advantages over conventional storage media. The currently largest rotational kinetic storage system, which achieves an output of 500 kW, stands as a prototype in Upper Lusatia. The goal: to store the surplus energy from wind turbines directly on site. With a steel flywheel weighing several tonnes that rotates in a vacuum at around 3,000 revolutions per minute, the prototype in the district of Görlitz is far larger than the rotational kinetic storage systems from the Aachen-based company Stornetic, which have already been in use since 2015.

Solid-state batteries take up far less space than conventional lithium-ion batteries. © NIO

Solid-state batteries take up far less space than conventional lithium-ion batteries. © NIO

But it is not only the storage of freshly generated energy that holds great potential. The electric car itself, which in the past was merely a consumer of electricity and did not contribute to the generation or transmission of electricity, will take on a new role in the future: that of temporary battery storage. The solution, known as vehicle-to-grid (V2G), will enable consumers to temporarily store energy available in the stationary vehicle and feed it back into the grid as soon as it is needed elsewhere.

For this sector coupling, the vehicle must be equipped with a battery that can be charged bidirectionally, i.e. in two directions, and the cable must also be able to transport large amounts of electricity quickly. Even though the idea itself is not new and is already practised in some countries - in Japan, the Mitsubishi i-MiEV even forwards car power to household appliances via vehicle-to-home (V2H) - there is still a lack of implementation in Germany. However, this is set to change soon, if the Munich-based company The Mobility House has its way. In addition, the vehicle manufacturer Sono Motors - also from the Bavarian capital - is still working on its Sion model, which is equipped with a bidirectionally chargeable battery. However, the vehicle is still waiting to be ready for the market.

The premise of V2G or V2H approaches is the fact that most vehicles are parked for more than 22 hours a day and the charging time is significantly less than the standing time. Accordingly, the battery charging time can be adapted to the grid requirements and the electric car can be used for load management.

According to experts, in the long term - with a high level of conversion activity in favour of electromobility - electricity quantities can be stored and made available that exceed the entire German peak load. An attractive side effect: the feed-in of one's own electricity into the grid is remunerated. The car is transformed from consumer to "prosumer".

All-rounder solid-state battery?

However, it is not only such smart grid approaches that will change the role of the electric car in the future; the battery itself is also about to undergo a radical change. One promising technology of the future is the solid-state battery, on which studies are being conducted worldwide. It differs from the conventional lithium-ion battery essentially in that both electrodes and electrolytes in the battery are not liquid, but are in a solid state. Solid electrolytes can consist of plastic polymers or glass, for example, and - just like liquid electrolytes - have the task of conducting ions between the cathode and anode. Solid electrolyte structures have several advantages: on the one hand, they are lighter and take up less space due to the reduced need for cooling and safety equipment; on the other hand, many times more electrical energy can be stored in the same space because the energy density is higher. As a result, they allow for a filigree design with low weight and take up less space in order to provide an energy volume customary in traffic. At the same time, the fire hazard often discussed in the media in the past, especially with electric cars, is supposed to be eliminated because the solid materials are more difficult to ignite. Solid-state batteries are therefore considered more reliable and safer than lithium-ion batteries with liquid electrolytes.

Replacing the battery in the system developed by NIO takes no more time than refuelling with liquid fuel - about five minutes. © NIO

Replacing the battery in the system developed by NIO takes no more time than refuelling with liquid fuel - about five minutes. © NIO

In addition to some European and East Asian industry representatives, including Volkswagen in cooperation with Quantum-Scape, the Chinese start-up NIO, which already produces five series-produced vehicles with battery-electric drive, is particularly noteworthy on the side of the solid-fuel pioneers.

With the ET7, which was announced last January for 2022, there is now an upper-class sedan (480 kW/653 hp) in the company's portfolio after a sports car and three crossover models - for the first time with a solid-state battery. The range of the ET7 is estimated at 1,000 kilometres according to the NEDC cycle. In addition, the model is expected to achieve the third stage of autonomous driving. In addition to the new technology, the charging solution of the NIO ET7 also sounds promising: to bring the "pit stop" closer to the speed of petrol refuelling, NIO has installed a battery swap system. Instead of charging at the charging station, a wash-street-like automated exchange station is used to swap the empty battery for a full one and continue the journey. The empty battery is charged on the spot and, as soon as it has reached its maximum level, can be picked up by the next person passing by. The whole process takes only a few minutes.

Although NIO is making an exciting advance with the ET7, it cannot be assumed that the solid-state battery will revolutionise the electric industry any time soon. There are still too many uncertainties and imponderables to make a quick market entry. Nevertheless, the technology has the potential to play an important role in the mobility sector in the long term; VW partner QuantumScape, for example, expects series production to start around 2024. The empirical values that the NIO ET7 will generate in operation will be of great relevance for further development. Developments in electricity storage, whether it is surplus wind energy or the excess production of the electric car parked in the garage, will also play a serious role in answering the question of how to provide the energy needed.

In combination with modern storage technologies, sustainable energy generation from renewable sources is essential. © Petamal - iStockphoto.comfabric. © NIO

In combination with modern storage technologies, sustainable energy generation from renewable sources is essential. © Petamal - iStockphoto.comfabric. © NIO

Author

David O´Neill