Ludwig Jörissen

Magnesocene-Based Electrolytes: A New Class of Electrolytes for Magnesium Batteries.

Unlike ferrocene, bis(η5 -cyclopentadienyl)magnesium (magnesocene, MgCp2 ) is slightly dissociated in solvents, such as ethers, resulting in electrolyte solutions with low conductivity. MgCp2 /tetrahydrofuran solutions make possible reversible magnesium plating and stripping with low over-potentials for many cycles. The Mg deposits appear with a cauliflower-like morphology. IR and NMR spectroscopy confirm that the electrolyte is stable and not decomposed during prolonged cycling. The anodic stability limit is in the range of 1.5u2005V (at platinum) and 1.8u2005V versus Mg/Mg2+ (at stainless steel), which may be sufficient for low-voltage cathode materials. MgCp2 is a first example of a completely new class of halide-free electrolytes, which may open up a new research direction for future magnesium metal and magnesium-ion batteries.

Electrochemical and electron microscopic characterization of Super-P based cathodes for Li-O2 batteries.

Summary Aprotic rechargeable Li–O2 batteries are currently receiving considerable interest because they can possibly offer significantly higher energy densities than conventional Li-ion batteries. The electrochemical behavior of Li–O2 batteries containing bis(trifluoromethane)sulfonimide lithium salt (LiTFSI)/tetraglyme electrolyte were investigated by galvanostatic cycling and electrochemical impedance spectroscopy measurements. Ex-situ X-ray diffraction and scanning electron microscopy were used to evaluate the formation/dissolution of Li2O2 particles at the cathode side during the operation of Li–O2 cells.

An in situ SEM-FIB-based method for contrast enhancement and tomographic reconstruction for structural quantification of porous carbon electrodes.

A new in situ Scanning Electron Microscope-Focused Ion Beam-based method to study porous carbon electrodes involving Pt filling of pores from gaseous precursors has been demonstrated to show drastically improved image contrast between the carbon and porous phases when compared with the Si-resin vacuum-impregnation method. Whereas, the latter method offered up to 20% contrast, the new method offers remarkably higher contrast (42%), which enabled fast semi-automated demarcation of carbon boundaries and subsequent binarization of the images with very high fidelity. Tomographic reconstruction of the porous carbon electrode was then obtained from which several morphological parameters were quantified. The porosity was found to be 72±2%. The axial and radial tortuosites were 1.45±0.04 and 1.43±0.04, respectively. Pore size, which is defined to be the distance from the medial axis of the pore to the nearest solid boundary, was quantified. Average pore size determined from the pore size distribution was 90 nm and the corresponding 1 sigma ranges from 45 to 134 nm. Surface-to-volume ratio of the carbon phase was 46.5 µm(-1). The ratio of total surface area to the total volume of electrode including pores (i.e., specific surface area) was 13 µm(-1).