A New Quasi-Solid Polymer Electrolyte for Next-Generation Na-O₂ Batteries: Unveiling the Potential of a Polyamide-Polyether System

AbstractA novel quasi‐solid polymer electrolyte (QSPE) composed of polyamide (PA) and polyethylene oxide (PEO), commercially known as Pebax1657, and combined with 1 M sodium bis(trifluoromethanesulfonyl)imide (NaTFSI) in diethylene glycol dimethyl ether (diglyme, DEGDME), has been investigated for sodium–oxygen (Na–O2) batteries. Pebax1657 QSPE exhibits high ionic conductivity (6.57 × 10−4 S cm−1 at room temprerature ‐ RT), an oxidation onset potential of 4.69 V versus Na/Na⁺, and an enhanced Na⁺ transference number (tNa⁺ ≈ 0.40). Structural analysis (Raman spectroscopy, differential scanning calorimetry, X‐ray diffraction, small‐angle X‐ray scattering) confirms reduced PEO crystallinity and formation of orderly nanodomains, facilitating Na⁺ transport. Long‐term galvanostatic cycling in Na|Na symmetrical cells demonstrates stable overpotentials (≈80 mV) at 75 µA cm⁻2 for 210 h, outperforming conventional liquid electrolytes (≈110 h). Pebax1657 QSPE enables higher discharge capacities (2.60 mAh cm⁻2 at 75 µA cm⁻2; 2.11 mAh cm⁻2 at 150 µA cm⁻2) with lower overpotentials (≈0.2 V). It sustains 25 cycles at 75 µA cm⁻2 and 35 cycles at 150 µA cm⁻2 at 0.25 mAh cm⁻2, with a Coulombic Efficiency (CE) of 80–90%. Compared to the state of the art, Pebax1657 QSPE offers improved electrochemical stability, lower overpotentials, and better capacity retention. Its sustainability and versatility make it a strong candidate for Na–O2 batteries and other energy storage applications

Chemical Instability of Dimethyl Sulfoxide in Lithium–Air Batteries

Although dimethyl sulfoxide (DMSO) has emerged as a promising solvent for Li–air batteries, enabling reversible oxygen reduction and evolution (2Li + O₂ ⇔ Li₂O₂), DMSO is well known to react with superoxide-like species, which are intermediates in the Li–O₂ reaction, and LiOH has been detected upon discharge in addition to Li₂O₂. Here we show that toroidal Li₂O₂ particles formed upon discharge gradually convert into flake-like LiOH particles upon prolonged exposure to a DMSO-based electrolyte, and the amount of LiOH detectable increases with increasing rest time in the electrolyte. Such time-dependent electrode changes upon and after discharge are not typically monitored and can explain vastly different amounts of Li₂O₂ and LiOH reported in oxygen cathodes discharged in DMSO-based electrolytes. The formation of LiOH is attributable to the chemical reactivity of DMSO with Li₂O₂ and superoxide-like species, which is supported by our findings that commercial Li₂O₂ powder can decompose DMSO to DMSO₂, and that the presence of KO₂ accelerates both DMSO decomposition and conversion of Li₂O₂ into LiOH

Elucidating the Impact of Sodium Salt Concentration on the Cathode–Electrolyte Interface of Na–Air Batteries

A promising approach to improve the specific capacity and cyclability in a Na–O2 cell using a pyrrolidinium-based ionic liquid electrolyte in a half-cell has been explored in this work. Increasing the concentration of sodium salt in an ionic liquid electrolyte produces a significant enhancement in the discharge capacity of up to 10 times, a reduction in the overpotential and an increase in the long-term cyclability. Additionally, a distinct discharge morphology is also observed, which is demonstrated to be result of a different oxygen reduction reaction mechanisms. These improvements are likely due to the solvation of Na+ in the electrolyte mixtures containing different Na+ concentrations; the coordination of Na+ by the anion of the ionic liquid dictates the discharge product morphology. At low concentrations, Na+ is strongly coordinated to the anion of the ionic liquid, and this also can have an effect on its mobility; however, at high Na+ concentration, this interaction is weakened and favors mass transport before product deposition. It therefore appears that the concentrated electrolyte strategy is a useful route to enhance the performance of Na–O2 batteries. Interestingly, when using a pressurized Swagelok-type cell, the discharge product presents a cubic morphology, which is typical of NaO2. This is the first work where this characteristic morphology appears when using an ionic liquid, opening new venues for future research

Rate-Dependent Nucleation and Growth of NaO₂ in Na–O₂ Batteries

Understanding the oxygen reduction reaction kinetics in the presence of Na ions and the formation mechanism of discharge product(s) is key to enhancing Na–O₂ battery performance. Here we show NaO₂ as the only discharge product from Na–O₂ cells with carbon nanotubes in 1,2-dimethoxyethane from X-ray diffraction and Raman spectroscopy. Sodium peroxide dihydrate was not detected in the discharged electrode with up to 6000 ppm of H₂O added to the electrolyte, but it was detected with ambient air exposure. In addition, we show that the sizes and distributions of NaO₂ can be highly dependent on the discharge rate, and we discuss the formation mechanisms responsible for this rate dependence. Micron-sized (∼500 nm) and nanometer-scale (∼50 nm) cubes were found on the top and bottom of a carbon nanotube (CNT) carpet electrode and along CNT sidewalls at 10 mA/g, while only micron-scale cubes (∼2 μm) were found on the top and bottom of the CNT carpet at 1000 mA/g, respectively

Bio-based ether solvent and ionic liquid electrolyte for sustainable sodium-air batteries.

Bio-based ether solvent and ionic liquid electrolyte for sustainable sodium-air batteries

Bio-based ether solvent and ionic liquid electrolyte for sustainable sodium-air batteries

Bio-based ether solvent and ionic liquid electrolyte for sustainable sodium-air batterie

Bio-based ether solvent and ionic liquid electrolyte for sustainable sodium-air batteries.

Sodium-air batteries (SABs) are receiving considerable attention for the development of next generation battery alternatives due to their high theoretical energy density (up to 1105 W h kg-1). However, most of the studies on this technology are still based on organic solvents; in particular, diglyme, which is highly flammable and toxic for the unborn child. To overcome these safety issues, this research investigates the first use of a branched ether solvent 1,2,3-trimethoxypropane (TMP) as an alternative electrolyte to diglyme for SABs. Through this work, the reactivity of the central tertiary carbon in TMP towards bare sodium metal was identified, while the addition of N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([C4mpyr][TFSI]) as a co-solvent proved to be an effective strategy to limit the reactivity. Moreover, a Na-β-alumina disk was employed for anode protection, to separate the TMP-based electrolyte from the sodium metal. The new cell design resulted in improved cell performance: discharge capacities of up to 1.92 and 2.31 mA h cm-2 were achieved for the 16.6 mol% NaTFSI in TMP and 16.6 mol% NaTFSI in TMP/[C4mpyr][TFSI] compositions, respectively. By means of SEM, Raman and 23Na NMR techniques, NaO2 cubes were identified to be the major discharge product for both electrolyte compositions. Moreover, the hybrid electrolyte was shown to hinder the formation of side-products during discharge - the ratio of NaO2 to side-products in the hybrid electrolyte was 2.4 compared with 0.8 for the TMP-based electrolyte - and a different charge mechanism for the dissolution of NaO2 cubes for each electrolyte was observed. The findings of this work demonstrate the high potential of TMP as a base solvent for SABs, and the importance of careful electrolyte composition design in order to step towards greener and less toxic batteries

Highly Homogeneous Sodium Superoxide Growth in Na–O₂ Batteries Enabled by a Hybrid Electrolyte

Energy storage is a major challenge for modern society, with batteries being the prevalent technology of choice. Within this area, sodium oxygen (Na–O2) batteries have the capability to make a step change, thanks to their high theoretical energy density. In order to facilitate their use, the development of electrolytes is critical to overcome certain limitations that arise because of the technology’s unique chemistry, particularly relating to the stability of superoxide species. In this study, we have demonstrated the importance of selecting a suitable electrolyte to facilitate both a highly homogeneous distribution of the discharge products and to minimize the formation of undesirable reaction products. The combination of pyrrolidinium-based ionic liquid and diglyme can dramatically change the cell performance. The effect of sodium salt concentration as well as the amount of diglyme and N-butyl-N-methylpyrrolidinium bis­(trifluoromethylsulfonyl)­imide, [C4mpyr]­[TFSI], in Na–O2 batteries has also been comprehensively studied by combination of experimental and simulation techniques

Unveiling the Impact of the Cations and Anions in Ionic Liquid/Glyme Hybrid Electrolytes for Na–O₂ Batteries

A series of hybrid electrolytes composed of diglyme and ionic liquids (ILs) have been investigated for Na–O2 batteries, as a strategy to control the growth and purity of the discharge products during battery operation. The dependence of chemical composition of the ILs on the size, purity, and distribution of the discharge products has been evaluated using a wide range of experimental and spectroscopic techniques. The morphology and composition of the discharge products found in the Na–O2 cells have a complex dependence on the physicochemical properties of the electrolyte as well as the speciation of the Na+ and superoxide radical anion. All of these factors control the nucleation and growth phenomena as well as electrolyte stability. Smaller discharge particle sizes and largely homogeneous (2.7 ± 0.5 μm) sodium superoxide (NaO2) crystals with only 9% of side products were found in the hybrid electrolyte containing the pyrrolidinium IL with a linear alkyl chain. The long-term cyclability of Na–O2 batteries with high Coulombic efficiency (>90%) was obtained for this electrolyte with fewer side products (20 cycles at 0.5 mA h cm–2). In contrast, rapid failure was observed with the use of the phosphonium-based electrolyte, which strongly stabilizes the superoxide anion. A high discharge capacity (4.46 mA h cm–2) was obtained for the hybrid electrolyte containing the pyrrolidinium-based IL bearing a linear alkyl chain with a slightly lower value (3.11 mA h cm–2) being obtained when the hybrid electrolyte contained similar pyrrolidinium-based IL bearing an alkoxy chain