Rechargeable Na metal batteries have gained great recognition as a promising candidate for nextgeneration battery systems, largely on the basis of the high theoretical specific capacity (1165 mAh g −1 ) and low redox potential (−2.71 V versus the standard hydrogen electrode) of Na metal, as well as the natural abundance of Na and the similarities between these batteries and lithium batteries. Much effort has been dedicated to improving the electrochemical performance of rechargeable Na batteries through the development of high-performance cathodes, anodes, and electrolytes. Nevertheless, the practical application of Na metal batteries is quite challenging because the high chemical and electrochemical reactivity of Na metal electrodes with organic liquid electrolytes leads to low Coulombic efficiencies and limited cycling performance. Severe electrolyte decomposition at the Na metal electrode results in the formation of a resistive and non-uniform surface film, leading to dendritic Na metal growth. To control the Na metal electrode-electrolyte interface for high performance Na metal batteries, considerable efforts have been made to find electrolyte systems that are stable at the Na metal electrode. Using fluoroethylene carbonate (FEC) as an electrolyte additive for in situ formation of an artificial solid electrolyte interphase (SEI) layer could stabilize the anodeelectrolyte interface. However, the FEC-derived SEI acted as a resistive layer, impeding the sodiation-desodiation process and reducing the reversible capacity of the anodes. Finding new electrolyte systems that are stable at the Na metal electrode and possess high oxidation durability at high-voltage cathodes is necessary for the development of high-performance Na metal batteries.Very recently, there are some papers which introduced significant breakthroughs in lithium battery electrolytes. It is reported that improving the cycling efficiency of lithium plating/stripping and suppressing the formation of dendritic lithium metal is possible by using highly concentrated electrolytes, even at high current densities. And it is also reported that highly concentrated electroltyes can inhibit the dissolution of transition metals out of the 5 V-class LiNi0.5Mn1.5O4 (LNMO) electrode material and the corrosion of the Al current collector at high voltage conditions. After reading these papers, I thought that applying this highly concentrated electrolyte system to sodium metal batteries could be the solution for improvements in the electrochemical performance of Na metal anodes coupled with high-voltage cathodes.In this study, an ultraconcentrated electrolyte composed of 5 M sodium bis(fluorosulfonyl)imide in 1,2-dimethoxyethane will be introduced for Na metal anodes coupled with high-voltage cathodes.Using this electrolyte, a very high Coulombic efficiency of 99.3% at the 120 th cycle for Na plating/stripping is obtained in Na/stainless steel (SS) cells, with highly reduced corrosivity toward Na metal and high oxidation durability (over 4.9 V versus Na/Na ...

Sodium (Na) metal anodes with stable electrochemical cycling have attracted widespread attention because of their highest specific capacity and lowest potential among anode materials for Na batteries. The main challenges associated with Na metal anodes are dendritic formation and the low density of deposited Na during electrochemical plating. Here, we demonstrate a fluoroethylene carbonate (FEC)-based electrolyte with 1 M sodium bis­(fluorosulfonyl)­imide (NaFSI) salt for the stable and dense deposition of the Na metal during electrochemical cycling. The novel electrolyte combination developed here circumvents the dendritic Na deposition that is one of the primary concerns for battery safety and constructs the uniform ionic interlayer achieving highly reversible Na plating/stripping reactions. The FEC–NaFSI constructs the mechanically strong and ion-permeable interlayer containing NaF and ionic compounds such as Na2CO3 and sodium alkylcarbonates.

A thin, uniform, and highly stable protective layer tailored using tris(trimethylsilyl) phosphite (TMSP) with a high tendency to donate electrons is formed on the Li-rich layered cathode, Li1.17Ni0.17Mn0.5Co0.17O2. This approach inhibits severe electrolyte decomposition at high operating voltages during cycling and dramatically improves the interfacial stability of the cathode. The TMSP additive in the LiPF6-based electrolyte is found to preferentially eliminate HF, which promotes the dissolution of metal ions from the cathode. Our investigation revealed that the TMSP-derived surface layer can overcome the significant capacity fading of the Li-rich cathode by structural instability ascribed to an irreversible phase transformation from layered to spinel-like structures. Moreover, the superior rate capability of the Li-rich cathode is achieved because the TMSP-originated surface layer allows facile charge transport at high C rates for the lithiation process.

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Purpose: Micrometer spatial resolution dosimetry has become inevitable for advanced radiotherapy techniques. A new approach using radiochromic films was developed to measure a radiation dose at a micrometer spatial resolution by confocal Raman spectroscopy. Methods: The commercial radiochromic films (RCF), EBT3 and EBT-XD, were irradiated with known doses using 50, 100, 200, and 300 kVp, and 6-MV x rays. The dose levels ranged from 0.3 to 50 Gy. The Raman mapping technique developed in our early study was used to readout an area of 100 9 100 µm 2 on RCF with improved lateral and depth resolutions with confocal Raman spectrometry. The variation in Raman spectra of C-C-C deformation and CC stretching modes of diacetylene polymers around 676 and 2060 cm À1 , respectively, as a function of therapeutic x-ray doses, was measured. The single peak (SP) of CC and the peak ratio (PR) of CC band height to C-C-C band height with a spatial resolution of 10 µm on both types of RCF were evaluated, averaged, and plotted as a function of dose. An achievable spatial resolution, clinically useful dose range, dosimetric sensitivity, dose uniformity, and postirradiation stability as well as the orientation, energy, and dose rate dependence, of both types of RCFs, were characterized by the technique developed in this study. Results: A spatial resolution on RCF achieved by SP and PR methods was~4.5 and~2.9 µm, respectively. Raman spectroscopy data showed dose nonuniformity of~11% in SP method and <3% in PR method. The SP method provided dose ranges of up to~10 and~20 Gy for EBT3 and EBT-XD films, respectively while the PR method up to~30 and~50 Gy. The PR method diminished the orientation effect. The percent difference between landscape and portrait orientations for the EBT3 and the EBT-XD films at 4 Gy had an acceptable level of 1.2% and 2.4%, respectively. With both SP and PR methods, the EBT3 and the EBT-XD films showed weak energy (within~10% and~3% for SP and PR methods, respectively) and dose rate dependence (within~5% and~3% for SP and PR methods, respectively) and had a stable response after 24-h postirradiation. Conclusions: A technique for micrometer-resolution dosimetry was successfully developed by detecting radiation-induced Raman shift on EBT3 and EBT-XD. Both types of RCFs were suitable for micrometer-resolution dosimetry using CRS. With CRS both lateral and depth resolutions on RCF were improved. The PR method provided superior characteristics in dose uniformity, dose ranges, orientation dependence, and laser effect for both types of RCFs. The overall dosimetric characteristics of the RCFs determined by this technique were similar to those known by optical density 5238 scanning. The CRS with the PR method is advantageous over other the traditional scanning systems as a spatial resolution of <10 µm on RCF can be achieved with less deviations.