Batteries of the future

Fraunhofer is developing the next generation of batteries. The spectrum includes the whole range of energy storage: from the smallest applications such as button cells, to large stationary systems such as redox-flow batteries.

Battery research at Fraunhofer

What can the battery of the future offer?

The technology for energy storage systems is changing rapidly. Electric cars need high-performance batteries, and power from renewable energy sources such as solar or wind is dependent on stationary energy storage. The Fraunhofer-Gesellschaft is researching intensively into new concepts. What is the current status of the technology? Where do the greatest challenges lie?

Batteries have been our unseen companions for decades. They are hidden in portable radios, flashlights and smartphones. Only when we have to charge our smartphone every evening, it becomes obvious that there is room for technological improvement. Apart from that, up to now there has never been any particular reason to give batteries much thought.

All that has changed. Two important industries, the energy and automobile industries, are currently involved in intensive research in this area. As the energy revolution gathers pace, batteries will be needed, for example, for energy storage in order to equalize the fluctuating power production of photovoltaic solar systems or wind turbines. The trend for electromobility adds extra currency to the subject.

Globally, research labs, universities and manufacturers are working to drive battery technology forward. Strictly speaking, in this context it is incorrect to use the term battery. The correct term is accumulators, or rechargeable batteries. Even so, in common parlance most people just talk about batteries.

The Work of the Fraunhofer Institutes

Fraunhofer researchers have been working in this field for years. Their efforts are important because there are many unanswered questions. They are concerned with aspects such as energy density, range, charging time, weight and size, as well as suitability for everyday use. Electric cars, for example, are dependent on having a good range. That can only be achieved through higher energy density and improved efficiency, ideally with the battery being as small and lightweight as possible. Environmental issues also have to be considered. Rechargeable batteries are environmentally friendly when they are operational, but this is not necessarily true for their manufacture. And what about recycling spent rechargeable batteries?

The ongoing development of battery concepts also calls for expertise in matters of safety. Safety experts must ensure that the highly compacted, high-tech rechargeable batteries of the future are safe in all situations. As strange as it may seem, batteries are still in their infancy, at least when it comes to high-performance rechargeable batteries.

Fraunhofer Battery Alliance

Research and development for the battery of the future

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The Fraunhofer Battery Alliance develops next generation batteries. Research work at the Fraunhofer Network focuses on batteries and supercaps, including redox flow systems. The value chain extends from materials used in the smallest storage units, through to modular construction and battery management, quality assurance in production, and the simulation of materials and designs.

Electromobility: Safety first

Electric cars, in comparison with vehicles powered by combustion engines, are considered to be more expensive and are not widely accepted by people due to their short range and to their infrastructure and supply structures, which are currently unsatisfactory. The safety of the batteries also causes headaches for both consumers and manufacturers. Battery technology is complex and presents new and different challenges compared to combustion engines. Furthermore, the demands placed on batteries when they are used for electromobility are very high, and there are many outstanding issues to be dealt with. This is why a great many Fraunhofer institutes are working hard to ensure that the batteries of the future are even safer and more suited for everyday use.

This is especially true for highly compressed batteries, trimmed to energy density, which are used in car manufacturing. This is equally true for batteries used in stationary energy supplies or for mobile devices. Battery safety is a technically challenging topic. These days, electric cars are already very safe, but because technology is developing rapidly, it is important for safety experts to remain vigilant and thoroughly test new battery types, particularly for any weak points.

This is exactly why, the Fraunhofer Institutes in the Battery Alliance are researching a range of issues around the area of battery safety, and we are working to ensure that the electric cars of the future are a safe as is humanly possible – in every conceivable situation.

In the measurement chamber, the semi-cylindrical impactor strikes the battery. Here, displacement, power, voltage and temperature that act on the battery during the dynamic experiment are measured.
© Photo Fraunhofer EMI

In the measurement chamber, the semi-cylindrical impactor strikes the battery. Here, displacement, power, voltage and temperature that act on the battery during the dynamic experiment are measured.

On the battery test bench, batteries can be crushed with a force of up to 500 kilonewtons and speeds of up to ten meters per second.
© Photo Fraunhofer EMI

On the battery test bench, batteries can be crushed with a force of up to 500 kilonewtons and speeds of up to ten meters per second.

Crash tests with battery

The classic crash test is not the only area, but it is a very important one. The researchers at the Fraunhofer EMI are not content just to crash cars into cement walls to see if the batteries burn. They concentrate on the way the battery itself behaves. Batteries are tested under every conceivable stress scenario and under extreme conditions, the same as they would be exposed to during a high speed crash.

The batteries are ‘tortured’ in every possible way. They are exposed to extreme acceleration and extreme pressure and tensile stress, or are attacked with blades and blunt and pointed objects. Thus researchers can find out how the materials behave under stress and where the weak points lie.

Finally, the damage is assessed. Have the housing and the cells inside been deformed? Is the electrolyte fluid leaking? Have the internal elements shifted? Is the membrane separating the electrodes in the battery from each other damaged? Generally this results in a dangerous short circuit and the possibility of fire.

But that is still not enough. In the climatic chamber, cold and heat as well as temperature fluctuations can be recreated to simulate realistic operating conditions for a battery in use in a vehicle. 

The classic crash test with the complete vehicle is also one of the required tests. Of course, a car with a typical gas tank behaves differently than an electric car. Generally speaking, the large, heavy batteries as part of the overall build have an influence on the overall rigidity of the vehicle which may, under certain circumstances, increase the crash-safe zone. Modern vehicles, however, rely more on flexible structures which are able to absorb as much energy as possible during a crash. The size, weight and positioning of the battery in the vehicle also play a considerable role here.

Individual tests for vehicle manufacturers

The X-CC (X-Ray Car Crash) is also a helpful technology which combines X-rays and high-speed photos. Compared to typical X-ray processes, the exposure time is shorter by a factor of 1000. This way, researchers at the Fraunhofer EMI are able to recognize dynamic deformations within materials. For example, they can see how extreme acceleration or an impact changes the structures and elements inside the battery.

The X-CC tests help to identify and alleviate the short-comings of modern batteries before they are used by making tiny, intermittent events within the battery visible, for example when a cell buckles or an electrical contact is not working anymore. Then the battery could ignite or even explode.

Release of gases

At the Fraunhofer ICT, battery experts are conducting various abuse tests on batteries in a specially-constructed test building, in order to test the inner workings of the batteries. This is because in the course of mechanical, electrical and thermal safety tests, harmful gases can be released, and these are then examined for their chemical composition. Experts can identify highly reactive components and products that are relevant for the evaluation of battery safety. This special gas analysis can also accompany electric vehicle crash tests.

Additionally, researchers at the Fraunhofer ICT are conducting post-mortem examinations of damage to batteries or damage caused by batteries. This also aids in assessing scenarios where batteries are used, and in answering safety questions.

The Fraunhofer Institutes are capable of conducting individual tests which are customer-specific. Each manufacturer uses batteries according to its own specifications and relies on individual designs of structure, material and chemical composition. Where the battery is located in the vehicle also varies from manufacturer to manufacturer. At this early stage of development, it is not currently sensible to introduce standardization. This would rob the manufacturers of the possibility to optimize their technology on an individual basis.

FAQs

Frequently Asked Questions

  • A battery is based on the principle of electrochemical conversion and is comprised of multiple galvanized elements or cells which are brought together in a functional unit. A cell is comprised of two electrodes (anode and cathode) which are electrically separated by a thin, finely porous membrane and connected by an ionically conductive electrolyte fluid. The electrodes generally consist of an active material, are electrically conductive and are the energy source of the cell. During an energy delivery process, the discharge, electrochemical energy is converted into electrical energy as electrodes move from the anode to the cathode. This allows electrical devices to be run.

  • Batteries are generally divided into primary and secondary batteries. Primary batteries are intended for one-time use. That means that they can only be discharged once. Secondary batteries, on the other hand, so-called accumulators, can be charged and discharged multiple times. When energy is delivered upon discharge, the chemically stored energy is converted to usable electrical energy.

  • The charge of the battery, often also called “capacity”, is given in ampere hours (Ah) and expresses the length of time the battery can deliver electricity. Another important number is the voltage, given in volts (V). This is derived from the potential difference between the two electrodes and the interconnection of the cells. The energy density describes the amount of energy stored in a cell, and either refers to the weight (gravimetric, also called specific energy) of the battery or the volume (volumetric), and it is given in watt hours per kilogram or liter (Wh/kg or Wh/L).

  • The most common batteries at the moment are lithium-ion batteries. This technology has virtually no memory effect, that is, they lose virtually no capacity no matter how they are charged.

    Completely discharging the battery shortens its lifespan in the same way as longer-term storage while fully-charged. The long-term optimal condition is a charge level of between 40 and 60 percent as well as a storage temperature of between 0 and 15 degrees Celsius.

    A new battery will reach its full capacity the first time it is charged. It is not necessary to fully charge or discharge it prior to its first use in order to “calibrate it to its full performance”.

    The speed of the charging process slows down markedly from a charge level of 80 percent.

    As they age, batteries increasingly lose capacity. This loss is irreversible and is known as the aging of the battery. This aging can be reduced through storage at low temperatures and a mid-range charge level.

  • This is due to side effects of the electrochemically active materials. They lead to slow self-discharging.

  • During charging, an electrochemical process is initiated where the electricity introduced by the charging device is converted to chemical energy. The inherent chemical reactions cannot be arbitrarily sped up.

  • For lithium-ion batteries, the electrolyte fluid uses an organic solvent which contains what is called a lithium conducting salt. If the cell is broken or the temperature is too high, the electrolytes react with the electrode material and generate reaction products. These can be corrosive, and so the cell housing can become porous or may even be destroyed, causing the cell to leak. The reaction can also lead to a build-up of gas, causing the battery cells to expand. In the worst case scenario, these defects can mean that the cell starts to burn.