The dissolution of transition-metal (TM) cations into a liquid electrolyte from cathode material, such as Mn ion dissolution from LiMn2O4 (LMO), is detrimental to the cycling performance of Li-ion batteries (LIBs). Though much attention has been paid to this issue, the behavior of Mn dissolution has not been clearly revealed. In this work, by using a refined in situ ultraviolet–visible (UV–vis) spectroscopy technique, we monitored the concentration changes of dissolved Mn ions in liquid electrolyte from LMO at different state of charge (SOC), confirming the maximum dissolution concentration and rate at 4.3 V charged state and Mn2+ as the main species in the electrolyte. Through ab initio molecular dynamics (AIMD) simulations, we revealed that the Mn dissolution process is highly related to surface structure evolution, solvent decomposition, and lithium salt. These results will contribute to understanding TM dissolution mechanisms at working conditions as well as the design of stable cathodes.

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The issue of antibiotic residue and contamination has attracted significant attention. Most of the existing degradation methods are inefficient and costly. Photocatalytic technology is an up-and-coming method. Titanium dioxide (TiO 2 ) is a photocatalyst widely used to degrade the residual antibiotics in water under ultraviolet (UV) irradiation. However, its application efficiency under visible light is poor, owing to its wide bandgap. This paper reports the successful synthesis of Ag 2 S/TiO 2 composite nanofiber membranes through electrospinning and hydrothermal processes, and adsorption and photocatalytic removal of tetracycline (TC) under visible light irradiation. Ag 2 S/TiO 2 showed excellent photocatalytic property for TC degradation compared with Ag 2 S and TiO 2 , and the efficiency was up to 70.54%. It kept high photocatalytic performance after five cycles. The detailed mechanism of TC degradation by Ag 2 S/ TiO 2 was also proposed based on the radical trapping experiment and the analysis of degradation intermediates. Benefiting from the large surface area, effective photocatalysis under visible light irradiation, and excellent recyclability, Ag 2 S/TiO 2 composite fiber membranes are promising in the treatment of antibiotic wastewater.

The effects of tungsten W doping and coating on the electrochemical performance of LiCoO 2 cathode are comparatively studied in this work. The amount of modification component is as low as 0.1 wt% and 0.3 wt% respectively. After 100 cycles between 3.0 V-4.6 V, 0.1 wt% W doping provides an optimized capacity retention of 72.3%. However, W coating deteriorates battery performance with capacity retention of 47.8%, even lower than bare LiCoO 2 of 55.7%. These different electrochemical performances can be attributed to the surface aggregation of W between doping and coating methods. W substitution is proved to be a promising method to develop high voltage cathodes. Practical performance relies on detailed synthesis method.