In‐situ Polymerized Gel Polymer Electrolytes with High Room‐Temperature Ionic Conductivity and Regulated Na⁺ Solvation Structure for Sodium Metal Batteries

Abstract

Sodium metal batteries (SMBs) are promising candidates for low‐cost but high‐energy energy storage applications. Both long‐term stability and safety of SMBs can be largely enhanced when liquid electrolytes (LEs) are replaced by gel polymer electrolytes (GPEs). However, the low room‐temperature (RT) ionic conductivity and inferior interfacial compatibility of GPEs severely restrain their practical use. Herein, a poly(butyl acrylate)‐based GPE with a high RT ionic conductivity of 1.6 mS cm−1 is developed by in‐situ polymerization. Symmetrical cells assembled with this GPE show ultralong cyclability over 900 h at 0.2 mA cm−2, and ultralow overpotential of 233 mV at 1 mA cm−2. Full cells based on Na3V2(PO4)3(NVP) cathodes (NVP||GPE||Na) display significantly improved rate capability than that of LEs, benefiting from the solvation structure of Na+ in the GPE with much lower desolvation energy. Furthermore, the NVP||GPE||Na pouch cells exhibit a stable capacity of ≈92 mA h g−1 for 50 cycles at 1 C and excellent flexibility. The work not only provides a reliable GPE to develop RT SMBs but also offers new insight into the role of polymer frameworks in the rate performance of SMBs.

Regulating Na Electrodeposition by Sodiophilic Grafting onto Porosity-Gradient Gel Polymer Electrolytes for Dendrite-Free Sodium Metal Batteries

“…The PVH membrane was treated with a basic KOH solution to generate C�C and C�O groups by dehydrofluorination (see FT-IR and XPS spectra in Figures S3 and S4), 25,26 where the unsaturated C�C moieties act as anchoring sites of PEG methyl ether thiol by the photoinitiated thiol-ene click reaction. The resulting PVH−PEG membrane contains 1.1 mol % of PEG, which was quantitatively determined by 1 H and 19 F NMR spectroscopy methods (Figure S5). It was found that the porous PVH structure is preserved well after the postmodification as shown in the SEM image of PVH−PEG in Figure S6, demonstrating that PEG grafting has not altered the membrane structure including pore size and morphologies.…”

“…Optical photographs; FT-IR spectra; XPS spectra; 1 H and 19 F NMR spectra; ionic conductivities and electrolyte uptakes; SEM images and EDS mapping results; galvanostatic cycling profiles; and EIS spectra (PDF)…”

“…However, comprehensive studies on polymer materials for Na metal batteries, particularly concerning dendrite-suppressing capabilities, are still at a primitive stage. Among various polymeric components, polymer electrolytes play critical roles in all aspects of dendrite evolution because they essentially guide Na + flux by regulating ion transport at the Na metal interface. , Although extensive investigations associated with developing Li dendrite-suppressing polymer electrolytes could aid in devising Na dendrite-suppressing counterparts, , prior expertise collected from developing Li dendrite-suppressing polymer materials is not directly transferable to Na metal battery systems, primarily due to intrinsic differences in Li and Na, particularly regarding ion interactions either with a polymer matrix or electrolyte solvents. , Recently, several strategies have been proposed to alleviate Na dendrite growth by exploiting nanomaterials, − single-ion conducting polymers, , and sodiophilic polymers. − However, relatively little attention has been paid to the ion-regulating capability of polymer electrolytes achieved by surface engineering, and the underlying dendrite-suppressing mechanisms have not been explored.…”

“…The time-dependent relative humidity was measured using a printing humidity/temperature meter (TES−1362, TES Electrical Electronic Corp.). The molar compositions of the membranes were determined by 1 H and 19 F nuclear magnetic resonance (NMR) spectroscopy methods. All spectra were recorded on a Bruker Avance III HD (400 MHz), and acetone−d 6 (Sigma-Aldrich) was used as a solvent.…”

Interface chemistry for sodium metal anodes/batteries: a review

“…Therefore, the design and fabrication of advanced gel electrolytes are of the utmost importance for the realization of safe SMBs with excellent performance [117,118] . Wen et al designed a new photopolymerized gel electrolyte of ETPTA-NaClO 4 -QSSE, which exhibited unprecedented room-temperature ionic conductivity of 1.2 mS cm -1 , a wide electrochemical window up to 4.7 V (vs. Na + /Na), and outstanding compatibility with Na metal anode [119] . Due to its enhanced interfacial stability, Na symmetric cells based on this electrolyte showed superior long-term cycling performance and morphology of dendrite-inhibited SMAs.…”