Sodium Diffusion and Dynamics in Na2Ti3O7: Neutron Scattering and Ab-initio Simulations

We have performed quasielastic and inelastic neutron scattering (QENS and INS) measurements from 300 K to 1173 K to investigate the Na-diffusion and underlying host dynamics in Na2Ti3O7. The QENS...

Sodium Dialysate Prescription in a New Dialysis Facility

As the Medical Director of this new dialysis facility, I recommend a fixed sodium dialysate (Nadial) concentration at 138 mEq/L. This relates to my former experience in the Tassin unit in France and the fear of sodium as a powerful uremic toxin. I realize that, according to the Na+ set-point theory, a fixed value of the Nadial may create a plasma–dialysate (P–D) gradient and may favor intradialytic plasma Na+ changes. In cases where this is associated with signs of negative Na+ balance (bad session tolerance/quality of life) or positive Na+ balance (high interdialytic weight gain or high blood pressure), individualization of the Nadial to reduce the P–D gradient and change in plasma Na+ concentration may be useful, even though evidence remains scarce. I look forward to the possibility of using new dialysis machines that allow for the evaluation of sodium balance and tailoring of the sodium diffusion process.

Capacity losses due to solid electrolyte interphase formation and sodium diffusion in sodium-ion batteries

Knowledge about capacity losses due to the formation and dissolution of the solid electrolyte interphase (SEI) layer in sodium-ion batteries (SIBs) is still limited. One major challenge in SIBs is the fact that the SEI generally contains more soluble species than the corresponding SEI layers formed in Li-ion batteries. By cycling carbon black electrodes against Na-metal electrodes, to mimic the SEI formation on negative SIB electrodes, this study studies the associated capacity losses in different carbonate electrolyte systems. Using electrochemical testing and synchrotron-based X-ray photoelectron (XPS) experiments, the capacity losses due to changes in the SEI layer and diffusion of sodium in the carbon black electrodes during open circuit pauses of 50 h, 30 h, 15 h and 5 h are investigated in nine different electrolyte systems. The different contributions to the open circuit capacity loss were determined using a new approach involving different galvanostatic cycling protocols. It is shown that the capacity loss depends on the interplay between the electrolyte chemistry and the thickness and stability of the SEI layer. The results show, that the Na-diffusion into the bulk electrode gives rise to a larger capacity loss than the SEI dissolution. Hence, Na-trapping effect is one of the major contribution in the observed capacity losses. Furthermore, the SEI formed in NaPF6-EC:DEC was found to become slightly thicker during 50 h pause, due to self-diffused deintercalation of Na from the carbon black structure coupled by further electrolyte reduction. On the other hand, the SEI in NaTFSI with the same solvent goes into dissolution during pause. The highest SEI dissolution rate and capacity loss was observed in NaPF6-EC:DEC (0.57 μAh/hpause) and the lowest in NaTFSI-EC:DME (0.15 μAh/hpause).

Theoretical Analysis of Experimental Data of Sodium Diffusion in Oxidized Molybdenum Thin Films

In this work, the diffusion process of sodium (Na) in molybdenum (Mo) thin films while it was deposited on soda lime glass (SLG) was studied. A small amount of oxygen was present in the chamber while the direct-current (DC) magnetron sputtering was used for the deposition. The substrate temperatures were varied to observe its effect. Such molybdenum films, with or without oxidations, are often used in thin film solar cells, either as back contact or as hole transport layers. Secondary ion mass spectrometry (SIMS) was used to quantify the concentration of the species. A grain diffusion mechanistic model incorporating the effect of grain and grain boundary geometrical shape and size was developed. The model was used to provide an in-depth theoretical analysis of the sodium diffusion in molybdenum thin films that lead to the measured SIMS data. It was observed that not only diffusion coefficients should be considered when analyzing diffusion processes in thin films but also the ratio of grain boundary size to grain size. Both depend on substrate temperature and directly affect the amount of diffused species in the film. The data were analyzed under the light of the film growth speed versus diffusion front speed, the effect of oxygen content, and the effect of substrate temperature on the overall diffusion process. The temperature inversely affects the ratio of grain boundary size and grain size and directly affects the diffusion coefficient, which leads to a preferable temperature at which the highest amount of alkali can be found in the film.

Электронная структура и диффузия натрия в Na-=SUB=-4-x-=/SUB=-K-=SUB=-x-=/SUB=-Mg(MoO_4)-=SUB=-3-=/SUB=-

The electronic structure and sodium diffusion in Na4-xKxMg(MoO4)3 with an alluadite structure have been investigated by ab initio methods. It was found that this molybdate is an insulator with a band gap of 3.5 eV for x = 0.25. The most probable positions of potassium in the sodium sublattice have been determined, and the preferred pathways for sodium migration have been established. It has been shown that the barriers to sodium diffusion in Na4-xKxMg(MoO4)3 significantly depend on the composition, position of potassium, and migration path. The introduction of potassium leads to a significant decrease in the barriers to both one-dimensional (1D) and two-dimensional (2D) sodium diffusion. However, the presence of potassium in 1D channels can hinder the rapid migration of sodium, and a sharp increase in conductivity occurs only at high temperatures due to the order-disorder transition.