Development of a Mg/O ReaxFF Potential to describe the Passivation Processes in Magnesium‐Ion Batteries

One of the key challenges preventing the breakthrough of magnesium-ion batteries (MIB) is the formation of a passivating boundary layer at the Mg anode. To describe the initial steps of Mg anode degradation by O$_2$ impurities, a Mg/O ReaxFF (force field for reactive systems) parameter set was developed capable of accurately modeling the bulk, surface, adsorption, and diffusion properties of metallic Mg and the salt MgO. It is shown that O$_2$ immediately dissociates upon first contact with the Mg anode (modeled as Mg(0001), Mg(10$\bar1$0)A, and Mg(10$\bar1$1)), heating the surface to several 1000 K. The high temperature assists the further oxidation and forms a rock salt interphase intersected by several grain boundaries. Among the Mg surface terminations, Mg(10$\bar1$0)A is the most reactive, forming an MgO layer with a thickness of up to 25 Å. The trained force field can be used to model the ongoing reactions in Mg–air batteries but also to study the oxidation of magnesium metal in general

Development of a Mg/O ReaxFF Potential to describe the Passivation Processes in Magnesium-Ion Batteries

One of the key challenges preventing the breakthrough of magnesium-ion batteries (MIB) is the formation of a passivating boundary layer at the Mg anode. To describe the initial steps of Mg anode degradation by O2 impurities, we have developed a Mg/O ReaxFF reactive force field description capable of accurately modeling the bulk, surface, adsorption, and diffusion properties of both metallic Mg and the salt MgO. We show that O2 immediately dissociates upon first contact with the Mg anode (modeled as Mg(0001), Mg(10m10)A, and Mg(10m11)), heating the surface to several 1000 K. The high temperature assists the further oxidation and forms a rocksalt interphase intersected by several grain boundaries. Among the Mg surface terminations, Mg(10m10)A is the most reactive, forming an MgO layer with a thickness of up to 25 Å. We also demonstrate the recrystallization of an amorphous MgO particle, which is obtained performing grand-canonical Monte Carlo simulations, into the rocksalt structure by thermal annealing at elevated temperatures. Our force field can be used to model the ongoing reactions in Mg-air batteries and constitutes an important step towards modeling the solid--electrolyte interface formation at the Mg anode

Low-molecular-weight heparin in the treatment of patients with venous thromboembolism

Background Low-molecular-weight heparin is known to be safe and effective for the initial Treatment of patients with proximal deep-vein thrombosis. However, its application to patients with pulmonary embolism or previous episodes of thromboembolism has not been studied. Methods We randomly assigned 1021 patients with symptomatic venous thromboembolism to fixed-dose, subcutaneous low-molecular-weight heparin (reviparin sodium) or adjusted-dose, intravenous unfractionated heparin. Oral anticoagulant therapy with a coumarin derivative was started concomitantly and continued for 12 weeks, Approximately one third of the patients had associated pulmonary embolism, The outcome events studied over the 12 weeks were symptomatic recurrent venous thromboembolism, major bleeding, and death. We sought to determine whether low-molecular-weight heparin is at least equivalent to unfractionated heparin in patients with venous thromboembolism. Results Twenty-seven of the 510 patients assigned to low-molecular-weight heparin (5.3 percent) had recurrent thromboembolic events, as compared with 25 of the 511 patients assigned to unfractionated heparin (4.9 percent). The difference of 0.4 percentage point indicates that the two therapies have equivalent value according to our predetermined definition of equivalence. Sixteen patients assigned to low-molecular-weight heparin (3.1 percent) and 12 patients assigned to unfractionated heparin (2.3 percent) had episodes of major bleeding (P=0.63), and the mortality rates in the two groups were 7.1 percent and 7.6 percent, respectively (P=0.89). Conclusions Fixed-dose, subcutaneous low-molecular-weight heparin is as effective and safe as adjusted-dose, intravenous unfractionated heparin for the initial management of venous thromboembolism, regardless of whether the patient has pulmonary embolism or a history of venous thromboembolism. (C) 1997, Massachusetts Medical Society