Improving NASICON Sinterability through Crystallization under High-Frequency Electrical Fields

Abstract

The effect of high-frequency (HF) electric fields on the crystallization and sintering rates of a lithium aluminum germanium phosphate (LAGP) ion conducting ceramic was investigated. LAGP with the nominal composition Li1.5Al0.5Ge1.5(PO4)3 was crystallized and sintered, both conventionally and under effect of electrical field. Electrical field application, of 300 V/cm at 1 MHz, produced up to a 40% improvement in sintering rate of LAGP that was crystallized and sintered under the HF field. Heat sink effect of the electrodes appears to arrest thermal runaway and subsequent flash behavior. Sintered pellets were characterized using X-ray diffraction, scanning electron microscope, TEM, and electrochemical impedance spectroscopy to compare conventionally and field-sintered processes. The as-sintered structure appears largely unaffected by the field as the sintering curves tend to converge beyond initial stages of sintering. Differences in densities and microstructure after 1 h of sintering were minor with measured sintering strains of 31 vs. 26% with and without field, respectively. Ionic conductivity of the sintered pellets was evaluated, and no deterioration due to the use of HF field was noted, though capacitance of grain boundaries due to secondary phases was significantly increased.

Correlating Transport and Structural Properties in Li1+xAlxGe2–x(PO4)3 (LAGP) Prepared from Aqueous Solution

“…Among the numerous types of solid lithium-ion conductorsLISICONs, NASICONs, garnets, (anti-)­perovskites, and sulfide-based systems − NASICON materials are widely investigated. − Na Super Ionic CONductor (NASICON) describes a family of ionic conductors with the structure of NaZr 2 (PO 4 ) 3 , which crystallizes in the R 3̅ c space group (International tables #167). , Apart from different sodium-containing compounds, − there exist also stable lithium-ion conductors within this structure type. − The general formula of lithium-conducting NASICON materials is based on Li M (PO 4 ) 3 with M being a tetravalent metal ion. The basic structure consists of LiO 6 units in a trigonal antiprismatic coordination, M O 6 octahedra, and PO 4 tetrahedra.…”

Structural elucidation of NASICON (Na3Al2P3O12) based glass electrolyte materials: effective influence of boron and gallium

“…Many studies have already been carried out to develop a suitable RT solid electrolyte material. [13][14][15][16] In this regard nonoxide chalcogenide glasses (Na 2 (Ga 0.1 Ge 0.9 ) 2 14 In general, NASICON and the relevant solid electrolytes are produced using a conventional solid state reaction process, which includes sintering and calcination over 1100 C. 22 The sintering process usually leads to the formation of voids and may disturb the development of new structured materials to gain high conductivity.…”

“… 14 In general, NASICON and the relevant solid electrolytes are produced using a conventional solid state reaction process, which includes sintering and calcination over 1100 °C. 22 The sintering process usually leads to the formation of voids and may disturb the development of new structured materials to gain high conductivity.…”

AC electric field‐induced softening of alkali silicate glasses

“…Very recently Yu et al reported the reduction in furnace temperature for sintering of ceramics as a function of AC frequency. From a limited number of such studies it appears that AC fields have a similar effect on sintering rate of ceramic green bodies as DC flash sintering . A review of the current state of flash sintering compares the current density and volumetric power density of various test conditions and ceramics samples .…”

“…From a limited number of such studies it appears that AC fields have a similar effect on sintering rate of ceramic green bodies as DC flash sintering. 6,7 A review of the current state of flash sintering compares the current density and volumetric power density of various test conditions and ceramics samples. 5 Here, the power density between both DC and AC tests is similar, ranging from 10 to 100 mW/mm 2 .…”