A Redox-Flow-Battery

Energy Storage

A Redox-Flow-Battery
Image: Jan-Peter Kasper (University of Jena)
production of a pouch cell production of a pouch cell

The next generation of
storage systems

We work on the development of various storage technologies, from small, flexible battery systems to supercapacitors and large stationary batteries. The particular challenge is the combination of high power densities, maximum flexibility, minimized losses and long life cycles of the systems with an optimal environmental compatibility, dependable availability of resources and a minimized risk potential. We refrain from raw materials that are critical regarding mining or their environmental compatibility, such as aggressive acids, rare-earth elements, vanadium, cobalt, lead or other heavy metals. Instead, environmentally friendly alternatives, like ceramics, plastics (polymers), glasses or carbons, which are available in Germany and Europe, are used.

(Printable) film batteries Show content

In organic radical batteries (ORBs) organic polymers are used on active electrode material. These are based on so-called stable organic radicals – molecules with at least one unpaired electron – and replace critical heavy metal compounds such as the cobalt-containing cathode material in lithium-ion batteries. Therefore, ORBs are of low risk and sustainable. In addition, they are characterized by a high power density, fast charging processes (within a few minutes) and long lifetimes. In principle, these thin batteries can be produced by means of printing techniques.

New active materials as well as optimized electrolytes for ORBs are being developed at the CEEC Jena.

Solar batteries Show content

Solar batteries are hybrid systems that combine a solar cell for energy production with a battery for storage of the produced energy. In such systems, the power generated by the solar cell can both supply consumers and be stored directly by the integrated battery. If there is no sunlight, the battery takes over the power supply. The development of these systems is still at a fundamental level.

At the CEEC Jena, we are researching the development of organic solar batteries, i.e., the combination of organic solar cells with organic film batteries.

Sodium-ion batteries Show content

Sodium-ion batteries are considered as a pioneering technology in the area of stationary battery storage technology. The basic idea is to replace the undesired resource lithium with sodium – a resource that is a thousand times more abundant on earth than lithium. Next to the better availability of the element, another advantage of using sodium-based batteries is the opportunity for simplified recycling at the end of their service life. The key challenge of the technology is to control thermal processes and corrosion, thereby ensuring cycle stability and system safety. In addition, efforts are being made on an international level to make this system ready for mass-implementation and to compensate for disadvantages like size, weight and lower operating voltage. Potential applications for the various types of sodium ion batteries are stationary storage applications, for example, as storage tanks for wind turbines and solar systems.

Both high-temperature and room temperature systems are being investigated at the CEEC Jena.

Polymer-based redox flow batteries Show content

Redox flow batteries (RFBs) are electrochemically reversible cells based on active materials that are dissolved in liquid solvents. The two so-called electrolytes (catholyte and anolyte) are stored in separate tanks and pumped for charging and discharging in an electrochemical cell where the redox reactions are taking place. The big advantage of RFBs is the independent scalability of capacity and power. The key challenge is to develop RFBs which do not rely on rare and therefore expensive substances (e.g., vanadium compounds) or corrosive solvents (e.g., sulfuric acid). At the same time, the systems have to be stable, cost-effective and scalable in the long term.

At the CEEC Jena, materials and concepts for significantly improved RFBs are investigated with the aim of developing easily manageable, safe and at the same time economical energy storage systems. One approach is the use of polymeric active materials, which allow the use of inexpensive dialysis membranes instead of expensive ion-selective membranes. Additionally, vanadium compounds and sulfuric acid can be replaced by polymers and aqueous saline solution, respectively.

Supercapacitors Show content

Electrochemical double layer capacitors (EDLCs, or supercapacitors) are mainly used in high power applications like e.g., for defibrillators. In EDLCs the energy is stored through a physical process, the double-layer formation, which occurs between the electrodes and the ions of the electrolyte. Since the double layer formation is a very fast process – it can take place in the millisecond time frame – EDLCs can be charge and discharge in very short time (seconds or less) and display extremely high power (10 kW kg-1). Moreover, since this physical storage process does not imply (theoretically) any structural change and it can take place with very high efficiency, EDLCs also display extremely high cycle life (lifetime >500000 cycles). The energy of these devices is in order of 5 Wh kg-1.

At the CEEC Jena both novel and innovative electrolytes and nanostructured and carbon-based electrode materials for supercapacitors are developed.

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