Suppression of Aluminum Current Collector Dissolution by Protective Ceramic Coatings for Better High-Voltage Battery Performance.

Batteries based on cathode materials that operate at high cathode potentials, such as LiNi0.5 Mn1.5 O4 (LNMO), in lithium-ion batteries or graphitic carbons in dual-ion batteries suffer from anodic dissolution of the aluminum (Al) current collector in organic solvent-based electrolytes based on imide salts, such as lithium bis(trifluoromethanesulfonyl) imide (LiTFSI). In this work, we developed a protective surface modification for the Al current collector by applying ceramic coatings of chromium nitride (Crx N) and studied the anodic Al dissolution behavior. By magnetron sputter deposition, two different coating types, which differ in their composition according to the CrN and Cr2 N phases, were prepared and characterized by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and their electronic conductivity. Furthermore, the anodic dissolution behavior was studied by cyclic voltammetry and chronocoulometry measurements in two different electrolyte mixtures, that is, LiTFSI in ethyl methyl sulfone and LiTFSI in ethylene carbonate/dimethyl carbonate 1:1 (by weight). These measurements showed a remarkably reduced current density or cumulative charge during the charge process, indicating an improved anodic stability of the protected Al current collector. The coating surfaces after electrochemical treatment were characterized by means of SEM and XPS, and the presence or lack of pit formation, as well as electrolyte degradation products could be well correlated to the electrochemical results.

Synthesis, crystal-structure determination and magnetic properties of two new transition-metal carbodiimides: CoNCN and NiNCN.

Synthesis, structure determination, and magnetic properties are reported for the metastable and crystal-chemically isotypic phases cobalt carbodiimide, CoNCN, and nickel carbodiimide, NiNCN, adopting the hexagonal system and space group P63/mmc (NiAs type) with interatomic distances of Co-N = 2.17 Angstrom and Ni-N = 2.12 Angstrom and an octahedral coordination of the transition-metal ions; the NCN(2-) units reveal the carbodiimide shape with two C=N double bonds. The low-susceptibility data go back to strong antiferromagnetic spin-spin coupling, similar to the behavior of the electronically related oxides CoO and NiO.

Synthesis, crystal structure, and properties of MnNCN, the first carbodiimide of a magnetic transition metal.

Synthesis, single-crystal structure determination, and magnetic properties are reported for manganese carbodiimide, MnNCN. The presumably unstable but inert phase adopts the trigonal system (R3m) with a = 3.3583(4) A, c = 14.347(2) A, V = 140.13(3) A3, and Z = 3. Divalent manganese is octahedrally coordinated by nitrogen atoms at 2.26 A, and the NCN(2-) unit adopts the linear [N=C=N](2-) carbodiimide shape with two C=N double bonds of 1.23 A. MnNCN contains high-spin Mn(II) with five unpaired electrons and behaves like an antiferromagnet with an ordering temperature below 30 K.