Rechargeable and disposable batteries are a crucial element for electronic appliances, future electromobiles and stationary energy consumers. Work at the Institute concentrates on understanding internal processes in batteries during charge, discharge and failure using the instrumental suite available at the institute, namely neutron and X-ray imaging, diffraction methods and positron annihilation spectroscopy.
Besides cell chemistry, the quality of a lithium ion battery concerning their capacity, power, cycling stability and lifetime depends critically on the employed three-dimensional structural properties of the particles and the electrode. The performance of current and future electrode materials can essentially be improved by optimized 3D structures due to their effect on transport mechanisms.
Synchrotron X-ray tomography is an excellent method for in-situ/in-operando investigation of structure and processes in batteries. The example given in figure 1 shows investigations on rechargeable Zn-MnO2 batteries. The high spatial resolution of synchrotron tomography allows for analysis of the oxidation of individual zinc particles and the swelling and breaking of the MnO2 at the cathode (see Fig. 1).
Another example shows X-ray tomographic investigations on the electrolyte distribution in a lithium-ion capacitor (LIC) during cycling. This comparable new type of capacitors consists of parts of lithium ion batteries, e.g. lithiated carbon, and typical supercapacitor components, e.g. electrolytes and porous graphite electrodes. The electrolyte distribution strongly affects capacity and therfore lifetime of the LIC.
Fig. 2: Overview of the interior structure of the Li-ion capacitor. (a) Side view of the metal container with the current collectors on top; (b) side view after virtual removal of a part of the volume; (c) enlargement of the bottom section where a large electrolyte agglomeration is visible; (d) horizontal cross section; (e) enlargement of the part of (d) where a delamination is visible.