Transport Properties Of Na Research Articles

Intermediate-Temperature Operation of Sodium Secondary Batteries with High Rate Capability and Cyclability Using Ionic Liquid Electrolyte

Ionic liquid electrolytes are widely studied to construct safe electrochemical devices owing to their unique properties such as low volatility, low flammability, and wide liquid-phase temperature range.Ionic liquids based on sulfonylamide anions (bis(fluorosulfonyl)amide anion (FSA-) have low melting point, low viscosity, and high ionic conductivitysome and are attractive as electrolytes in secondary batteries. The present study reports physical and electrochemical properties of FSA-based ionic liquid electrolytes for secondary betteries operating from room temperature to intermediate temperature. Intermediate operation of secondary batteries in is available in some circumstances such as an engine compartment of automobiles and is preferable to enhance both the ion transport and electrode reactions. The Na[FSA]-[C3C1pyrr][FSA] (C3C1pyrr+ = N-methyl-N-propylpyrrolidinium) and Na[FSA]-[C2C1im][FSA] (C2C1im+ = 1-ethyl-3-methylimidazolium) ionic liquid systems have wide liquid phase temperature ranges around room temperature and high ionic conductivities [1,2]. Immersion of Na metal in FSA- and TFSA-based ionic liquids clearly showed that FSA-based ionic liquids form stable film on Na metal to prevent futher reduction. Dendrite formation during Na metal electrodeposition is suppressed by increasing temperature. Excellent rate capability and cycle property were observed for the Na2FeP2O7 positive electrode in FSA-based ionic liquids at 363 K.[3] The origin of this performance will be discussed based on transport properties of Na+ by considering transport number and Na+fraction in these ionic liquids. Acknowledgements: This study was partly supported by Advanced Low Carbon Technology Research and Development Program (ALCA) of Japan Science and Technology Agency (JST) and Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT) program “Elements Strategy Initiataive to Form Core Research Center”.

First-principles molecular dynamics investigation on Na3AlF6 molten salt

Abstract Local structure and transport properties of Na 3 AlF 6 molten salt were investigated by First-principles molecular dynamics (FPMD) simulation. For Na 3 AlF 6 molten salt, the local ionic structure is governed by five-coordinated [AlF 5 ] 2− and six-coordinated [AlF 6 ] 3− . Coulomb force dominates the interionic interactions for Na 3 AlF 6 molten salt. The first-shell average coordination number (CN) of Na-F, Al-F in the Na 3 AlF 6 molten salt is 6.03, 5.45, respectively and the F-Al-F bond angles are mainly located at 87°, 124° and 171°. The percentage of bridging F b is small about 1–2%, while the free F f is up to 26%, suggesting the polymerization degree of local structure is lower. Al-F bonds of the [AlF x ] 3−x groups in Na 3 AlF 6 molten salt have ionic characters as well as partial covalent characters due to the hybridization of F-2p and Al-3s (3p) orbitals, while the Na-F and F-F bonds are mainly ionic. The order of ion diffusion ability was found as Na + > F − > Al 3+ . Calculated results of viscosity and ionic conductivity are in good agreement with the experimental results, generally within 7%.

Thermal and Transport Properties of Na[N(SO2F)2]–[N-Methyl-N-propylpyrrolidinium][N(SO2F)2] Ionic Liquids for Na Secondary Batteries

Understanding ion transport in electrolytes is crucial for fabricating high-performance batteries. Although several ionic liquids have been explored for use as electrolytes in Na secondary batteries, little is known about the transport properties of Na+ ions. In this study, the thermal and transport properties of Na[FSA]-[C3C1pyrr][FSA] (FSA–: bis(fluorosulfonyl)amide and C3C1pyrr+: N-methyl-N-propylpyrrolidinium) ionic liquids were investigated in order to determine their suitability for use as electrolytes in Na secondary batteries. In the x(Na[FSA]) range of 0.0–0.5 (x(Na[FSA]) = molar fraction of Na[FSA]), a wide liquid-phase temperature range was observed at close to room temperature. The viscosity and ionic conductivity of this system, which obey the Vogel–Tamman–Fulcher equation, increases and decreases, respectively, with an increase in x(Na[FSA]). Further, its viscosity and molar ionic conductivity satisfy the fractional Walden rule. The apparent transport number of Na+ in the investigated ionic liquids, as determined by the potential step method at 353 K, increases monotonously with an increase in x(Na[FSA]), going from 0.08 for x(Na[FSA]) = 0.1 to 0.59 for x(Na[FSA]) = 0.7. The Na+ ion conductivity, determined by multiplying the ionic conductivity with the apparent transport number, is an indicator of Na+ ion transport in Na secondary batteries and is high when x(Na[FSA]) is in the 0.2–0.4 range.

Test of the interaction potential energy for Na⁺-H₂ by gaseous ion transport data.

Transport properties of Na(+) ions in gaseous hydrogen are calculated using the recently developed "beyond Monchick-Mason" (BMM) approximation and an ab initio Na(+)-H2 potential energy surface. Good agreement with the experimental data on the reduced mobility and longitudinal diffusion coefficient proves the accuracy of the surface and the adequacy of the BMM method, allowing for its optimal parameterization.

The interaction potential and transport properties of Na+ ions in He gas

Symmetry-adapted perturbation theory is used to calculate the interaction potential between Na+ ions and He atoms with high accuracy over a wide range of ion-atom separations. This potential is used to compute the transport coefficients of Na+ ions in He gas. A comparison of the calculated results with the most recent transport data validates the claimed accuracy of the potential.

Interatomic potential and transport properties of Na+ ions in He/el

Hitherto unavailable experimental values of the ratio, DT/K, of the transverse diffusion coefficient to mobility for Na+ ions drifting in helium gas are reported. Results were obtained with estimated accuracies of better than 3% at temperatures between 302 and 304 K, and at electric field to neutral gas density ratios, E/N, ranging from 5 to 400 Td. By an independent approach, the three transport parameters are also computed by Monte Carlo simulation using the modified Tang-Toennies potential and the Koutselos, Mason and Viehland potential as input, separately. Comparison between the simulated results and available experimental data suggests that the latter potential represents fairly well the true interaction in the long and intermediate ranges, but its short-range repulsive region is too soft.