Na-based Materials Research Articles

Elucidation of Gas Evolution in Model Sodium Battery Cells By Online Electrochemical Mass Spectrometry

Na-ion batteries are regaining attention as the geopolitically independent option, especially for large-scale stationary energy storage. Numerous Na-based materials have been discovered, synthesized, and verified in the past decade as promising active material candidates. However, long-term cyclability of Na-based cells is still generally inferior to the Li-based ones, hindering their wide-spread commercialization. Moreover, cycling performance obtained in half-cells is not sufficiently accurate, which is largely attributed to the much higher reactivity of Na-metal, as compared to Li-metal, and the unstable solid electrolyte interface (SEI), inevitably leading to rapid performance degradation. The parasitic side-reactions between electrodes and electrolyte are most often associated with the release of gaseous products, such as H2, CO2, C2H4, O2, and so on. Their evolution rates, onsets, and amounts disclose vital information concerning the formation of SEI and stability of electrode materials. However, there are only limited studies focusing on gassing behaviors of individual Na-based systems.In this study, we embarked on a systematic investigation on the gassing of model sodium battery cells by means of online electrochemical mass spectrometry (OEMS). Gaseous species generated within the cell were quantitatively analyzed in real-time. We compared oxidative and reductive stability of common alky-carbonate-based solvents using Na3V2(PO4)2F3, Na3V2(PO4)3, and hard carbon as model electrodes. Results indicate that linear carbonates cannot form a stable SEI layer, as supported by continuous electrolyte reduction and formation of alkane and H2. On the other hand, cyclic carbonates form a more stable SEI layer with characteristic alkene formation, similarly to Li-ion case. In this presentation, we will discuss the SEI stability of sodium cells and the origin of gas formed upon cycling. In addition, we will compare gassing from polyanionic-type cathodes with layered oxides. The impact of electrolyte additives on SEI stability and related gas evolution will also be addressed. Presenting author present address: Department of Chemistry, Ångström Laboratory, Uppsala University, Box 538, SE-751 21, Uppsala, Sweden. Figure 1

Cucurbiturils in nucleic acids research.

During the past ten years, the importance of cucurbiturils (CB[n]) as macrocyclic hosts in supramolecular assemblies with various types of natural and synthetic nucleic acids (NAs) has increased explosively. As a component of such systems, CB[n] macrocycles can play a wide spectrum of roles from drug and gene delivery vehicles to catalysts/inhibitors of biochemical reactions and even building blocks for NA-based materials. The aim of this highlight article is to describe the development of the CB[n] applications in nucleic acids research and to outline the current situation and perspectives of this fascinating synergistic combination of supramolecular chemistry of CB[n] and NAs.

Probing the thermal effects of voltage hysteresis in anionic redox-based lithium-rich cathodes using isothermal calorimetry

Probing the thermal effects of voltage hysteresis in anionic redox-based lithium-rich cathodes using isothermal calorimetry

Carbon-Polytetrahydrofuran Double-Coated Na3V2(PO4)2F3 Submicron-Composite as High-Energy/Power Cathode Material for Sodium Metal Battery

A carbon-polytetrahydrofuran double-coated Na3V2(PO4)2F3 composite has been prepared by synthesis of carbon coated Na3V2(PO4)2F3 followed by in situ polymerization of tetrahydrofuran on its surface. Thermal gravimetry analysis, Fourier transform infrared spectrum and high-resolution transmission electron microscopy are used to confirm the encapsulation structure of the inner carbon layer and the outer polytetrahydrofuran layer on Na3V2(PO4)2F3. Electrochemical tests show that electrochemical performance and electronic conductivity of the composite are significantly improved due to the polytetrahydrofuran coating, and a reversible capacity of 123.6 mAh g−1 at a moderate 2 C rate is obtained with a high capacity retention of 98.5% after 250 cycles. Even at an extremely high rate of 10 C the discharge capacity is still as high as 115.8 mAh g−1 with a capacity retention of 80% over 400 cycles. Interestingly, sodium ion distribution in augmented triangular prismatic sites of Na3V2(PO4)2F3 is not unchanged, but shifts from the high energy Na(2)' site to the low energy Na(3)' site after a certain cycle, thus Na3V2(PO4)2F3 could obtain a higher energy density. The full cell coupled with the composite cathode and Na metal anode constructed with Na-Sn alloy substrate exhibits excellent rate discharge capability and good cycling stability. The nano-level carbon-PTHF double-coating developed in this work could provide a new way to improve Na+-storage and rate performance of Na-based materials.

Influence of sodium-based materials on the slagging characteristics of Zhundong coal

Zhundong coal from the Zhundong coalfield in in Xinjiang, China, is charactered by high content of Na. Na-related slagging of Zhundong coal is unclear. The aim of this study is to determine the influence of Na-based materials on the slagging characteristics of the coal. The raw coal was prepared by first removing Na by chemical extraction and subsequently impregnating it with the Na-based materials, such as NaCl, Na2SO4 and NaAc. Laboratory slagging experiments in a muffle furnace were conducted using the mixtures of prepared Zhundong coal and quartz sand. It was found that the Na-based materials affected the slagging behavior of the coal in the order NaAc/Na2SO4 > NaCl. For the mixtures with the NaCl additive, fusion was most noticeable at 900 °C. However, for the mixtures soaked with Na2SO4 and NaAc, a monotonically increasing relationship was indicated between the degree of slagging and the temperature. Adding the Na-based materials to the coal resulted in increased Na content in the residual ash, especially in the instances with Na2SO4 and NaAc additives. The formation of silicates, which were ascribed to the reactions between the Na-based materials and the SiO2, was the primary cause of slagging. Various mineral elements, especially Fe, were captured by Na2O, derived from the decomposition of Na2SO4 or the combustion of NaAc, to exist in the form of a low-melting temperature eutectic. Additionally, the presence of Fe, Ca, K, and Mg in the ash aggravated slagging under the influence of Na2O.