ENVIRONMENTALLY COMPATIBLE APPLICATIONS OF NANOTECHNOLOGY
2 Nano-structured cell components for reversible energy stores with improved service life (supercapacitors)
Field of work:Energy Storage Devices
The development of markets for the short-term storage of excess energy production poses new challenges to efficient energy storage systems for mobile and stationary applications. So-called supercapacitors or double-layer capacitors are currently the only technology that allows a nearly unlimited number of fast charging and discharging cycles.
The project deploys technical solutions for the development of novel materials offering high energy density and cyclical stability, through understanding the underlying electrochemical and technological mechanisms that lead to gradual ageing by capacitance loss and increase of resistance. On the basis of the work programme, relevant material defects were discovered in supercapacitors based on carbon materials which provide an impetus for the development of improved materials:
1. Long-term experiments on supercapacitors and model systems under thermal stress and voltage overload: The failure criteria identified for technical components were the degradation of the polymer-bonded composite of porous carbon particles on the metallic current collector, the decomposition of the electrolyte system on account of elevated temperature and overvoltage, as well as the electrochemical oxidation of the anode material.
2. Development of new measuring methods for estimating cycle and service life and electrode state in long-term experiments: Voltammetric and impedance spectroscopic methods have been established in order to reliably determine the actual usable capacitance and the parasitic residual charges arising from the ageing processes.
3. Instrumental analysis of residues in failed components: In the course of ageing, decomposition and polymerisation reactions occur in the electrolyte system and at the electrodes, which have been analysed by gas chromatography in detail for the first time.
This work has resulted in suggestions for practical improvements:
1. Development of nano-porous electrode materials with a high specific capacitance, e.g. deploying carbon nanoparticles derived from carbides or colloidal metal oxides.
2. Development of modified electrolyte systems for more effective deployment of the fractal electrode structure, e.g. novel solvents and additives.
3. Identification of the chemical-technological processes in the production and operation of real supercapacitors which lead to the gradual ageing. For example, an anodic formation on the electrodes during the component manufacture is not helpful.
This project is carried out in cooperation with material and component manufacturers and also covers existing industrial storage applications.