Electrochemical energy storage for renewable sources and grid balancing

Electricity from renewable sources of energy is plagued by fluctuations (due to variations in wind strength or the intensity of insolation) resulting in a lack of stability if the energy supplied from such sources is used in 'real time'. An important solution to this problem is to store the energy electrochemically (in a secondary battery or in hydrogen and its derivatives) and to make use of it in a controlled fashion at some time after it has been initially gathered and stored. Electrochemical battery storage systems are the major technologies for decentralized storage systems and hydroge

X-ray Line Profile Analysis of Nanoparticles in Proton Exchange Membrane Fuel Cell Electrodes

We present a method to extract X-ray diffraction patterns from a multiphase system and analyze the particle size distribution of each phase. The method is demonstrated for crystalline nanoparticles in the electrodes of proton exchange membrane fuel cells (PEMFCs), where it is particularly useful to determine particle size distributions without destroying the device. The structure of the electrodes has a considerable influence on the power and durability of a fuel cell and can be further optimized, for example with respect to the durability of the cell. Since the membrane electrode assembly (MEA) contains multiple and partially X-ray transparent layers, the individual catalyst signals from the anode (platinum-ruthenium alloy) and the cathode (platinum) can be extracted from the diffraction patterns recorded of either side of the MEA using the technique presented in this article. By analysis of the platinum (220) reflection by fitting a pseudo-Voigt function, the individual particle size distributions are determined for the anode and the cathode. The catalyst surface area loss due to particle growth is studied in long-term experiments during the operation of a single model cell for 2100 h and, for comparison, during the storage in different gas atmospheres (Ar, H2, and O2) for 6500 h. With respect to the single cell operation, approximately one-third of the surface is lost in the storage experiment with a slight influence from the gas atmosphere and the catalyst type. The comparison with transmission electron micrographs shows that the size distributions have a similar shape and width but differ in absolute sizes

Fast and accurate measurement of entropy profiles of commercial lithium-ion cells

We report on an effective approach to speed up the measurement of thermodynamic characterization curves (entropy of reaction ΔrS(x)) of rechargeable batteries, in particular commercial 18,650 lithium ion cells. We propose and demonstrate a measurement and data processing protocol that reduces the time required to record entropy profiles from time scales of weeks to time scales of hours - without loss in accuracy. For time consuming studies such as investigations on ageing of battery cells, entropy profile measurements thus become as feasible as conventional electrochemical characterisation techniques like dV/dQ or cyclic voltammetry. We demonstrate this at the examples of two ageing protocols applied to a commercial high power and a commercial high energy cell, respectively: (i) accelerated calendric aging by storing cells at 100% state of charge at 60 °C and (ii) continuous cycling with a 1 C current at 25 °C