Spark Plasma Sintering of Lithium Aluminum Germanium Phosphate Solid Electrolyte and its Electrochemical Properties

Abstract

Sodium superionic conductor (NASICON)-type lithium aluminum germanium phosphate (LAGP) has attracted increasing attention as a solid electrolyte for all-solid-state lithium-ion batteries (ASSLIBs), due to the good ionic conductivity and highly stable interface with Li metal. However, it still remains challenging to achieve high density and good ionic conductivity in LAGP pellets by using conventional sintering methods, because they required high temperatures (>800 °C) and long sintering time (>6 h), which could cause the loss of lithium, the formation of impurity phases, and thus the reduction of ionic conductivity. Herein, we report the utilization of a spark plasma sintering (SPS) method to synthesize LAGP pellets with a density of 3.477 g cm−3, a relative high density up to 97.6%, and a good ionic conductivity of 3.29 × 10−4 S cm−1. In contrast to the dry-pressing process followed with high-temperature annealing, the optimized SPS process only required a low operating temperature of 650 °C and short sintering time of 10 min. Despite the least energy and short time consumption, the SPS approach could still achieve LAGP pellets with high density, little voids and cracks, intimate grain–grain boundary, and high ionic conductivity. These advantages suggest the great potential of SPS as a fabrication technique for preparing solid electrolytes and composite electrodes used in ASSLIBs.

Enhanced Li1+xAlxGe2–x(PO4)3 Anode-Protecting Membranes for Hybrid Lithium–Air Batteries by Spark Plasma Sintering

“…Recently, Zhu et al . 40 have investigated the effect of SPS temperature on the compactness and ionic conductivity of LAGP pellets. The highest ionic conductivity was achieved in their study for pellets sintered at 650 °C for 10 min with a relatively high density of 97.6%, while for higher sintering temperatures, they report a drastic decrease in density.…”

“…Recently, Zhu et al . have investigated the effect of SPS temperature on the compactness and ionic conductivity of LAGP pellets.…”

“…Moreover, heating to temperatures above 900 °C will inevitably lead to partial decomposition (sometimes confused in the early literature on LAGP with the surviving amorphous phase) and substantial dopant losses, which might explain the moderate conductivity observed by these authors. Recently, Zhu et al 40 have investigated the effect of SPS temperature on the compactness and ionic conductivity of LAGP pellets. The highest ionic conductivity was achieved in their study for pellets sintered at 650 °C for 10 min with a relatively high density of 97.6%, while for higher sintering temperatures, they report a drastic decrease in density.…”

Ultrafast Crystallization and Sintering of Li1.5Al0.5Ge1.5(PO4)3 Glass and Its Impact on Ion Conduction

“…Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 (LAGP), a widely used NASICON-type solid-state electrolyte, is typically produced on an industrial scale by a melt-quenching technique in glass form. Then, LAGP is crystallized with further heat treatment at T > 600 °C. ,, To achieve a solid electrolyte, crystalline LAGP powders are sintered at high temperatures (800–900 °C for 6 to 12 h). ,− However, crystallization and sintering are lengthy processes occurring at high temperatures, which may cause Li loss, leading to the precipitation of secondary phases. , Furthermore, the high energy requirements of sintering contribute to a significant portion of the solid-state battery preparation costs. , …”

“…For the first time, LAGP was sintered and crystallized by UHS directly from glass powders in a single step taking just 180 s. Further, the strategy represents a significant advance as LAGP pellets are typically produced from crystalline LAGP using either conventional methods or UHS. ,− , It should be noted that, thanks to the short processing time of UHS, Li mass loss and the related formation of unwanted secondary phases were suppressed . The influence of UHS annealing on the sintering and crystallization processes of LAGP was also investigated, as these are sensitive to the heating rate .…”