Nanomaterial increases capacity
Supercapacitors are very important to the management of the power system
as a short-term storage and to improve the efficiency of a plurality of
different systems. They are essential in public transport. The research
group are researching the project nanoEES3D this technique now more
accurate and simultaneously improve the energy storage capacity.
|Project status||Near completion|
|Project duration||June 2012 until May 2017|
Electrical and electrochemical energy storage have emerged as bottleneck technologies for the implementation of renewable energy to the grid - but also for portable and stationary applications that require high efficiency and high reliability. Supercapacitors, encompassing both, pure electrical double layer capacitors and pseudocapacitors, are a highly promising technology to deliver high power handling while showing a life time and cylcling lifetime stability superior to common battery technologies. In our project, we investigate (i) basic features of energy storage in supercapacitors, (ii) ways to significantly improve the energy storage capacity as the main limiting factor of the current state of the art technology, and (iii) explore cheap, alternative raw materials for improved performance systems. All our supercapacitors are carbon based, but include beyond pure carbon (mostly carbide-derived) also pseudocapacitive metal oxides, polymers, and surface functional groups.
Main focus in energy storage has shifted from the narrow focus of high energy density or low costs to a broader context of a myriad of parameters: temperature behavior, safety, environmental friendliness, availabiliy of raw materials, and power handling. In particular fast charge and discharge technologies are a major concern for the implementation of renewable energy sources to the power grid - yet, peak shaving and load levelling are increasingly important not only from an economocial point of view, but also from a grid stability point of view. The latter is becoming an issue with the addition of a large number of highly fluctuating energy sources whereas conventional power sources such as coal power plants (that are partially used for regulation purposes, too) are shut down. For that reason, high power electrical and electrochemical energy storage systems - beyond the limitations of state-of-the-art battery systems - are the focus of our research project.
From synthesis to cells producing
The research project stretches from basic research, synthesis of novel materials, and in situ testing to small scale cells (with the capacitance of a few Farads). This range of activities, encompassing studying the molecular phenomena at the interface between charged surfaces and liquid electrolytes up to dynamic and equilibrium characterization of full cells, enables a comprehensive understanding of the energy storage mechanism(s). In particular, the goal is to explore (1) basic mechanisms, (2) limiting factors, (3) alternative (cost efficient) materials, and (4) to develop storage cells with a high energy density.
Starting point is porous carbon derived from ceramic and polymer precursors. Synthesis parameters are suitable tools to finely tune the porosity to enable high specific surface area and pore size distributions optimized for fast ion transport (which is imparative for high power density storage cells). Polymer and sol gel processes are used to enable a high degree of freedom of shape of the resulting electrode films – ranging from thin films, foams, and fibers up to spheres and hollow beads.
Synthesis of polymer and sol-gel derived electrospun fiber mats. Using polymer and sol-gel chemistry, nanofibers are derived which can be used as binder-free and free-standing electrodes for electrochemical capacitors. Of particular importance are 3D hierarchical porous fiber networks that are also used as a framework for the implementation of redox active materials, such as metal oxides and electroactive polymers.
In situ characterization of energy storage mechanisms dominated by ion electrosorption or Faradaic reactions. This part involves the utilization of methods such as electrochemical dilatometry to evaluate the volumetric changes of carbon electrodes during operation in supercapacitors and the use of electrochemical quartz crystal microbalance and -admittance to study possible ion insertion processes and kinetcs.