No abstract

Graphite/LFP commercial cells are stored under 3 different conditions of temperature (30°C, 45°C, and 60°C) and SOC (30, 65, and 100%) during up to 8 months. Several non-destructive electrochemical tests are performed at different storage times in order to understand calendar aging phenomena. After storage, all the cells except those stored at 30°C exhibited capacity fade. The extent of capacity fade strongly increases with storage temperature and to a lesser extent with the state of charge. From in-depth data analysis, cyclable lithium loss was identified as the main source of capacity fade. This loss arises from side reactions taking place at the anode, e.g. solvent decomposition leading to the growth of the solid electrolyte interphase. However, the existence of reversible capacity loss also suggests the presence of side reactions occurring at the cathode, which are less prominent than those at the anode. The analyses do not show any evidence about active-material loss in the electrodes. The cells do not suffer substantial change in internal resistance. According to EIS analysis, the overall impedance increase is 70% or less.

Sorption of mercury(II) onto well-characterized samples of pyrite was studied between pH 2 and 12 using X-ray photoelectron spectroscopy for surface analysis and extended X-ray absorption fine structure for surface speciation. In the presence of Hg, the surface oxidation of pyrite was strongly decreased. Even if the sorption capacity of pyrite for Hg was high, the sorption reversibility was possible by adding some strong ligands, such as I-, S2O3 2-, and CN-, to the aqueous phase. Spectroscopic studies showed the absence of Hg(0) and S(−II) and evidenced the formation of a surface complex between S(−I) and Hg(II). At low pH, ternary surface complexes ⋮S-I−Hg−OH or ⋮S-I−Hg−Cl were formed with the following distances:  R ⋮ S - Hg = 2.40 Å, R Hg - OH = 2.25 Å, and R Hg - Cl = 2.33 Å if Cl- was present. At high pH, the spectroscopic signals of Hg, S, or Fe decreased, possibly because of the presence at the surface of a solid solution constituted of Fe (hydr)oxides and surface complexes between Hg and both oxides and pyritic sulfur.