Unraveling the Dynamic Interfacial Behavior of LiCoO2 at Various Voltages with Lithium Bis(oxalato)borate for Lithium-Ion Batteries.

The electrochemical dynamic behavior of the solid electrolyte interface (SEI) formed on LiCoO2 (LCO) by lithium bis(oxalato)borate (LiBOB) is investigated at various cutoff voltages. Particularly, for layered cathode active materials, various cutoff voltages are used to control the delithiation states; however, systematic investigations of the voltage and SEI are lacking. To increase the practical energy density of the LCO, a high cutoff voltage is pursued to utilize a state of high delithiation. However, this high cutoff voltage causes the electrolyte to undergo side reactions and the crystalline structure changes irreversibly, limiting the cycle life. In a low-voltage environment (<4.7 V), LiBOB improves the initial Coulombic efficiency and cycling performance by forming an effective SEI, which suppresses side reactions. At higher voltage levels (4.7-4.9 V), LiBOB no longer effectively protects the surface, causing the electrochemical performance to decrease rapidly. The main cause of this phenomenon is the decomposition of LiBOB-SEI at a high voltage, as shown by systematic surface and electrochemical analyses comprising linear sweep voltammetry, cyclic voltammetry, and electrochemical impedance spectroscopy. In conclusion, LiBOB can suppress side reactions of the electrolyte by SEI formation, but the SEI decomposes at voltage levels higher than 4.7 V.

Acid-Modified Hierarchical Porous Rare-Earth-Containing Y Zeolite as a Highly Active and Stable Catalyst for Olefin Removal.

Rare-earth-containing ultrastable Y zeolite (ReUSY) was modified by oxalic acid solution leaching treatment and applied in industrial units for catalytic olefin removal from aromatic hydrocarbons. The porous structure and amount of acidity of the modified ReUSY (denoted as ReUSY-x, where x indicated the amount of oxalic acid in solution) could be tuned by different concentrations of oxalic acid solution, and the ReUSY-x samples exhibited different catalytic performances. Based on the best catalytic performance of ReUSY-25, an industrial catalyst was prepared and applied in industrial units for catalytic olefin removal. The industrial catalyst exhibited excellent activity and regeneration stability with a long lifetime of about 2 years, which was about 13 times longer than that of activated clay.