A Self‐Binding, Melt‐Castable, Crystalline Organic Electrolyte for Sodium Ion Conduction

Abstract

The preparation and characterization of the cocrystalline solid-organic sodium ion electrolyte NaClO (DMF) (DMF=dimethylformamide) is described. The crystal structure of NaClO (DMF) reveals parallel channels of Na and ClO ions. Pressed pellets of microcrystalline NaClO (DMF) exhibit a conductivity of 3×10 S cm at room temperature with a low activation barrier to conduction of 25 kJ mol . SEM revealed thin liquid interfacial contacts between crystalline grains, which promote conductivity. The material melts gradually between 55-65 °C, but does not decompose, and upon cooling, it resolidifies as solid NaClO (DMF) , permitting melt casting of the electrolyte into thin films and the fabrication of cells in the liquid state and ensuring penetration of the electrolyte between the electrode active particles.

Electrolytes, SEI Formation, and Binders: A Review of Nonelectrode Factors for Sodium‐Ion Battery Anodes

“…The first conclusion echoes what was reported in the paper by Sankaranarayanan and co‐workers while the latter conclusion is still unclear: it is possible that solvents affect long‐term cycling, but there is not enough data to support the claim, or at the very least, reject it. Furthermore, the promise of IL electrolytes, along with new work, such as water‐based electrolytes, gel‐electrolytes, and solid‐state electrolytes, and polymers, bear more consideration.…”

Solvate sponge crystals of (DMF)3NaClO4: reversible pressure/temperature controlled juicing in a melt/press-castable sodium-ion conductor

“… 18,19 The immediate goal behind the synthesis of such crystals was to enable a weak interaction between alkali metal ions and their solvent matrix and to isolate and restrict the movement of anions to enhance positive-ion conduction for practical battery electrolyte applications. However, in one of the cases—where N , N -dimethylformamide cocrystalizes with sodium perchlorate as (DMF) 3 NaClO 4 , 18 —its crystal structure and morphologies have been observed to exhibit novel molecular properties, such as liquid-like grain boundaries and stimuli-responsive, reversible stoichiometric conversion to a different cocrystalline solvate species, where the application of pressure and/or temperature expels the organic solvent reversibly (the latter being the subject of this report). These cocrystals present a rare combination of coupled structural and thermomechanical behaviour and combine useful properties of other individual materials in a single example.…”

“…In addition to the unique thermomechanical behavior, these cocrystals of DMF and NaClO 4 exhibit a low E a barrier for Na + ion hopping (25 kJ mol −1 , from impedance spectroscopy) and have ionic conductivity at room temperature in the range of 10 −4 S cm −1 to 10 −3 S cm −1 . 18 Scanning electron microscopy (SEM, Fig. 1a ) suggests the presence of an inherent liquid-like region at the surface/interface of the cocrystals of these electrolytes, which also results in self-binding grains with low boundary resistance and which do not require sintering.…”

“…This nanolayer results from the decreased lattice energy at the surface of the crystal, which aids in grain binding. 18,24,25 Unlike other solid electrolytes, this grain boundary facilitates—rather than impedes—the conduction of ions across or around grains, in addition to bulk-phase ion conduction. Unlike other adiponitrile or isoquinoline based cocrystalline electrolytes, 25,26 the DMF based electrolytes possess one-dimensional channels of closely spaced Na + or Li + ions, e.g.…”

“…, (DMF) 3 NaClO 4 (ref. 18 ) and DMF·LiCl. 19 As viewed from single-crystal XRD, the cocrystals of (DMF) 3 NaClO 4 have a one-dimensional channel of Na + ions where the distance of successive Na + ions is 3.23 Å, with 3 : 1 DMF : Na + .…”