Activated carbons increase energy density
Scientists develop new electrode materials for high-efficiency double layer capacitors within the project ActivCaps. In contrast to purely empirical investigations they will characterize the structur of the materials at the nanoscale and will adjust simulation algorithms to the materials. The developed simulation tools can then be used for development of materials.
|Project status||Project completed|
|Project duration||September 2013 until August 2016|
The complex challenges of future decentralized energy supply can only be met on the basis of novel hybrid electrical energy storage technologies. In this context, electrochemical double layer capacitors (EDLC) play a major role due to their excellent power density during rapid charge and discharge cycles. Conversely, current EDLC technologies suffer from lower energy densities compared to batteries or redox-flow systems. The molecular mechanisms of energy storage in EDLCs are characterized by complex interactions at the interface between activated carbon material and the electrolyte. The overall objective of the project is the development of advanced electrode materials for use in stationary energy storage devices based on a fundamental understanding of the mechanisms operating at the electrode/electrolyte interface.
The starting point of the AktivCaps project is the superior power density of electrochemical double layer capacitors (EDLC) combined with their high energy efficiency of up to 90% which is the highest energy efficiency of all electrical energy storage devices. The advantages of the EDLC such as the high efficiency and low maintenance costs are currently antagonized by a lower energy density compared to batteries or redox flow systems. The objective of the AktivCaps project is an increase of the energy density of EDLC compared to state-of-the-art systems.
Material properties and material understanding
AktivCaps is based on a fundamental understanding of the mechanisms of energy storage using molecular simulations to predict the properties of the electrochemically active materials. In contrast to purely empirical studies, simulations tools are implemented and validated in the project in order to facilitate the simulations. The algorithms are specifically based on Monte Carlo methods which are adapted to the materials studied. The required optimization of the synthesis protocols for the carbide derived carbons is based on the in-depth understanding of the electrochemical mechanisms leading to energy storage.
Starting point for the optimization is the mechanistic understanding of the energy storage mechanisms. The simulation tools developed in the AktivCaps project can furthermore be applied in other contexts such as the development of materials based on graphene.
Characterization, synthesis processes and simulation tools
The AktivCaps project is based on the nanostructural characterization of activated carbon materials obtained by the reaction of chlorine with metal carbides at high temperatures to form carbide derived carbons (CDC) and aims at an optimization of the synthesis procedures by employing advanced simulation technologies. Based on the implementation of simulation algorithms within a user-configurable framework, the electrochemical properties of active carbon materials can be predicted which allows for a more direct route of optimization. In the first phase of the project, a variety of different carbon materials have already been synthesized and thoroughly characterized both structurally and in terms of their electrochemical performance. The implementation of the core functionalities of the simulation tools have been completed.
In the next phases of the project, which extend at least over the next two years, an adaptation of the synthesis steps based on the predictions of the simulation will be attempted. A key factor will be the future understanding of the interaction of the electrolyte with the surfaces of the activated carbon materials. This includes the interplay between the electrolyte´s mobility and the largest possible electrochemically active surface to facilitate a higher energy density compared to present state-of-the-art materials while maintaining the highest possible power density.
Sub-project "Simulation Tools (Scienomics)"
In the sub-project "Development of software tools for the simulation of activated carbons", a novel Monte Carlo program is developed that employs user configurable and material specific moves. This approach ensures high efficiency of the Monte Carlo algorithm which is required in order to be able to screen a large variety of possible conformations. The Monte Carlo method can be used to build models for activated carbons using the experimental data as input, while the structures generated are checked by comparison with experimentally obtained values. The building of models will be supported by simulations.
Sub-project "Mechanisms of energy storage (Fraunhofer IFAM)"
The contribution to the project of Fraunhofer IFAM includes the physicochemical characterization of the amorphous electrode materials as well as simulations to predict the molecular processes at the activated carbon interface. The carbon/electrolyte interactions are investigated using molecular dynamics simulations of the ions’ mobilities within the complex pore system of the activated carbon. The aim is to derive structure/property correlations and to incorporate this information into the targeted synthesis of optimized carbon materials with higher energy densities compared to standard materials.
Sub-project "Development of activated carbons (FAU Erlangen-Nürnberg)"
The work of the University of Erlangen-Nuremberg focusses on the synthesis of porous carbon materials for high-efficiency EDLC electrodes with improved specific capacitance by 40%. The scientific challenge is to identify the best material for a given application and be able to produce the material specifically with a well-defined pore distribution and specific surface properties. Simultaneously, the surface chemistry of the materials is affected by suitable functionalizations as well as cleaning processes depending on the specific combination of solvent and ions within the electrolyte at hand.