Densification of a Solid-State NASICON Sodium-Ion Electrolyte Below 400 °C by Cold Sintering With a Fused Hydroxide Solvent

Abstract

A modified cold sintering process is described, which permits the densification of the prototypical sodium-ion electrolyte, Na 3 Zr 2 Si 2 PO 12 , to greater than 90% relative density at a process temperature below 400 °C. The roomtemperature grain boundary ionic conductivity is greater than 2 × 10 −4 S/cm. Sintering of Na 3 Zr 2 Si 2 PO 12 to such densities and conductivities typically requires sintering near 1200 °C for many hours. We modify the cold sintering process by replacing the aqueous transient solvent with a fused hydroxide (NaOH, T m = 312 °C) to increase the reactivity of the solvent−particle interaction while also retaining the increased driving forces for densification characteristic of cold sintering, namely, the transient nature of the solvent and uniaxial pressure applied to an open system. We demonstrate the changes in phase purity, conductivity, and density by varying the process temperature, weight fraction hydroxide, and dwell time. The best results are obtained near 375 °C, 10 w/w NaOH, and 3 h of sintering.

Influence of R=Y, Gd, Sm on Crystallization and Sodium Ion Conductivity of Na5RSi4O12 Phase

“…These materials are grouped under the term “NASICON,” which stands for “Na superionic conductor.” The ionic conductivity of this class of solid electrolytes varies between 1 × 10 −4 and 1 × 10 −3 S/cm at 25 °C [ 12 ]. Although numerous compositions and stoichiometric variations of the basic NASICON has been synthesized and characterized, their sintering process remains challenging, and several attempts have been investigated to reduce the sintering temperatures by using field-assisted sintering (FAST), a cold sintering Process (CSP), or the additions of sintering additives for liquid phase sintering (LPS) [ 11 , 13 , 14 ]. For conventional sintering processes, temperatures above 1200 °C (up to 1300 °C) together with several hours of soaking time are necessary to achieve dense microstructures.…”

Microstructural Tuning of Solid Electrolyte Na3Zr2Si2PO12 by Polymer-Assisted Solution Synthesis Method and Its Effect on Ionic Conductivity and Dielectric Properties

“…One is monoclinic phase ( C 2/ c ), and another is rhombohedral ( R 3 C̅ ). On the basis of Na + distribution and its symmetry in the NASICON structure, the ionic conductivity of NZSP varies, significantly. − From the literature, it is noticed that the ionic conductivity of such a system can be improved by optimizing the sodium proportion in the final product density. Usually, microstructurally dense systems favor facile ionic movement, which leads to the improved electrolytic and storage performance of these system.…”

Compatibility assessment of solid ceramic electrolytes and active materials based on thermal dilatation for the development of solid-state batteries

“…However, the need of electronic additives such as carbon or metals and sintering aid (to favor the sintering [87][88][89] ) may change these conclusions. Additives used to decrease the sintering temperature 11,90,91 might act as a buffer regarding constrains with plastic deformation and allow minimal cracks during cooldown after sintering. For example use of plastic behavior sealant material in SOFC (metal or glass-ceramics) improves the resistance toward constraints as brittle fractures are more damaging than plastic deformation 92 .…”