Technology Offers Energy Technology

Eco-friendly gel polymer electrolytes (GPEs) for energy storage systems with high ionic conductivities

Gel polymer electrolytes (GPEs) have advantageous properties in case of leakage or exposure to higher temperatures when compared to conventional fluid electrolytes. Unfortunately, in case such an energy storage system catches fire, the polymer matrix of the usual gel polymer electrolyte may decompose, resulting in a release of highly toxic hydrogen fluoride. Evan more important, the ionic conductivity of gel polymer electrolytes based on highly fluorinated polymers is in many cases significantly less than that of the underlying fluid electrolyte. Here we present novel freestanding gel polymer electrolytes based on a polyhydroxyurethane matrix which show even higher ionic conductivities compared to usual GPEs reported in the art. In addition, the novel gel polymer electrolytes are eco-friendly. They are free of fluorine and can be produced from bio-based starting materials or biological/renewable (re)sources such as carbohydrates and proteins. The internal resistance being composed of the reaction resistance and the electrical resistance of the GPE-based cell, was significant lower compared to the internal resistance of a reference cell. In particular, ionic conductivities of the novel gel polymer electrolytes, as measured by electrochemical impedance spectroscopy, were up to 20 times higher compared to conventional systems.



Battery electrodes made of silicon layers with optimized porosity and microstructure

The use of silicon as anode material promises high theoretical energy density in lithium-ion batteries. However, the volume of a silicon-based anode may increase substantially during lithiation. In order to solve this problem, scientists at the Institute of Photovoltaics (ipv), University of Stuttgart, now succeeded in developing a method for producing micro-stabilized and porous silicon anodes by means of laser irradiation. The battery electrodes related to this invention offer a high potential for lithiation and at the same time improved mechanical stability. Due to a large active surface they provide high energy density. They can be used for the production of mechanically flexible batteries.



Compact ammonia-water absorption chiller with increased coefficient of performance

Scientists at the University of Stuttgart have developed an absorption chiller that is extremely compact, lightweight and stable in terms of operation, even at low evaporator temperatures and high heat rejection temperatures. Because of its compactness the absorption chiller has lower production costs and requires less refrigerant than conventional absorption chillers.



Online measurement of deposits in high temperature furnaces/ power plant boilers

The Institute of Combustion and Power Plant Technology (IFK) of the University of Stuttgart has developed a measuring device for use in coal power plants. The device allows for permanent monitoring of the conditions inside the boiler, particularly of soot deposition.
Besides determining the deposition rate inside the boiler, growth characteristics, adhesion, ash qualities and waste disposal behavior with deposit as well as the extent to which these can be cleaned using soot blowers can be judged. Thus, the measuring device can indicate potential for optimization, e.g. of coal compositon in the fuel feed.
The prototype has been tested successfully.



Non-permanent contacting for the characterization and classification of busbarless solar cells

Scientists at the University of Konstanz have developed a measuring device for non-permanent contacting of busbarless solar cells that allows for precise and direct characterization of electrical properties. As each contact finger can be contacted repeatedly over reversibly releasable connections the device allows for accurate measurement of I-V characteristics without requiring subsequent adjustment with correction factors.



Macro-porous, nanocrystalline silicon layer for lithium-ion batteries

For the production of rechargeable batteries, it is desirable to use silicon as anode material in Li-ion batteries. The use of silicon anodes theoretically increases battery capacity tenfold compared to conventional graphite anodes. However, the attempt had previously failed, since the layers would expand by 300 to 400 % due to the storage of lithium ions in the Si bulk material. This induces a high residual strain and can destroy the bulk Si after only a few charge cycles. In addition, as a consequence of the irreversible reaction between the Si anode and electrolyte a layer of solid electrolyte interphase (SEI) can develop and lead to a low coulombic efficiency. 
Scientists of the University of Stuttgart now succeeded in developing a porous semiconductor layer, which displays a pore distribution from 50 to 3000 nm and eliminates the residual strain. It can be manufactured in a continuous process.



Novel cathode material for lithium-sulfur batteries and lithium-ion batteries

At Aalen University, a novel composite material and a production process thereof was developed which makes the structural and material separation of current collector and cathode material unnecessary. The cathode material can be manufactured and formed in a continuous single stage electroplating process without the need to add binding material and electrically conductive particles. The proportion of active material in the cathode can thus be increased. Moreover, the mechanical stability and the efficiency of Li-Ion cells and Li-Sulfur cells improve.



S3L-Inverter: Switching-loss-free 3-level pulse-controlled inverter with snubber circuit

The new Soft Switching Three Level Inverter (S3L – Inverter) is of striking simplicity and is therefore inexpensive. Because of the underlying principle, it works without losses and thus with maximum efficiency. The inverter is easily controlled, has EMC friendly inherent di/dt- and du/dt limitation, and can be built using low-cost standard semiconductors.

Field of use: electric drives, solar power inverter, wind power inverter, uninterruptible power supplies (UPS).