Coated magnetite nanoparticles with a 6−8 nm average diameter were prepared. The surfactants used to stabilize the nanoparticles and disperse them in organic solvents were oleic acid (OA), lauric acid , dodecyl phosphonate, hexadecyl phosphonate, and dihexadecyl phosphate. Transmission electron microscopy analyses of the aggregation of the coated particles suggest that carboxylate surfactants provide the particles with better isolation and dispersibility as compared with phosphonate surfactants. However, Fourier transform infrared spectra of the phosphonate and phosphate coated particles suggest that these surfactants cover the surface of the nanoparticles in islands of high packing density. The thermogravimetric and differential scanning calorimetry measurements suggest that there is a quasi-bilayer of these surfactants covering the surface of the nanoparticles, with varying amounts of surfactant in the outer layer and with the second layer weakly bound to the primary layer through hydrophobic interactions between the alkyl chains. The desorption temperatures of the alkyl phosphonates and phosphate are higher than those of the carboxylate coated particles. The enthalpy of binding of the ligands suggests strong P−O−Fe bonding on the surface. Nevertheless, regardless of binding strength, the OA coated particles are better dispersed in organic solvents. Their higher hydrophobicity is likely due to different interactions among the oleyl chains and/or a smaller tendency to form bilayer structures.

The mechanisms of oxidation of the basal plane and of the cross‐sectional face of highly oriented pyrolytic graphite (HOPG) and the formation of a solid electrolyte interphase (SEI) on HOPG samples that were cycled in ethylene carbonate:diethyl carbonate (EC:DEC 1:2) solutions containing 1 M LiAsF6 were studied. X‐ray photoelectron spectroscopy, energy dispersive spectrometry, and scanning electron microscope techniques were used for the analysis of the surface layer formed on the basal plane and cross section of HOPG. The analysis indicates that the oxidation mechanisms of the basal plane and the cross section are entirely different. The SEI formed in the LiAsF6 solution is thinner on the basal plane than on the cross section and its composition is different. The SEI formed on the cross section is rich in inorganic compounds whereas the SEI formed on the basal plane is rich in organic compounds. Thus it can be concluded that on the basal plane, the greatest contribution to SEI formation is solvent reduction (EC and DEC), whereas on the cross‐sectional face, it is electrolyte salt false(LiAsF6false) reduction. © 1999 The Electrochemical Society. All rights reserved.

One of the major hurdles of Ni‐rich cathode materials Li1+x(NixCozMnz)wO2, y > 0.5 for lithium‐ion batteries is their low cycling stability especially for compositions with Ni ≥ 60%, which suffer from severe capacity fading and impedance increase during cycling at elevated temperatures (e.g., 45 °C). Two promising surface and structural modifications of these materials to alleviate the above drawback are (1) coatings by electrochemically inert inorganic compounds (e.g., ZrO2) or (2) lattice doping by cations like Zr4+, Al3+, Mg2+, etc. This paper demonstrates the enhanced electrochemical behavior of Ni‐rich material LiNi0.8Co0.1Mn0.1O2 (NCM811) coated with a thin ZrO2 layer. The coating is produced by an easy and scalable wet chemical approach followed by annealing the material at ≥700 °C under oxygen that results in Zr doping. It is established that some ZrO2 remains even after annealing at ≥800 °C as a surface layer on NCM811. The main finding of this work is the enhanced cycling stability and lower impedance of the coated/doped NCM811 that can be attributed to a synergetic effect of the ZrO2 coating in combination with a zirconium doping.