Bi2O3-Assisted Sintering of Na3Zr2Si2PO12 Electrolyte for Solid-State Sodium Metal Batteries

Abstract

Solid-state sodium metal batteries using non-flammable solid-state electrolytes are recognized as next-generation energy storage technology in view of their merits of high safety and low cost. However, the lower ion conductivity (below the application requirements of 10−3 S cm−1) and interface issues that exist in electrolytes/electrodes for most solid-state electrolytes hinder their practical application. In this paper, NASICON-type Na3Zr2Si2PO12 (NZSP) electrolytes with enhanced ion conductivity are synthesized by the Bi2O3-assisted sintering method. The influence of the Bi2O3 sintering agent content on the crystalline phase, microstructure, density and ion conductivity as well as the electrochemical performances applied in batteries for the obtained NZSP electrolytes are investigated in detail. With the presence of Bi2O3, the formed Na3Bi(PO4)2 impurity increased the Si/P ratio in the NASICON structure with higher Na+ occupancy, then enhanced the ionic conductivity to a level of 1.27 × 10−3 S cm−1. Unfortunately, the Bi2O3-assisted sintered NZSP shows a degradation in the cycling stability when applied to solid-state sodium batteries because of the decreased interfacial stability with Na anodes. The formation of a Bi-Na alloy during cycling might be conducive to Na dendrite growth in electrolytes, degrading the cycling performance. This work presents a facial method to improve the ion conductivity of NASICON-type electrolytes and gives insight into the interface issues of solid-state sodium metal batteries.

Screening of Sintering Aids for Oxide Ceramics: A Case of NASICON Electrolyte

“…It is worth noting that the remaining sintering aids may also have a beneficial effect on the sintering process. [19][20][21][22][23][24] Certainly, this method is not limited to the NZSP material system, but also can be extended to the other kinds of oxides system, such as Li Figure 2a,b show the XRD patterns of NZSP-NBO sintered at 1100 °C (NZSP-NBO-1100 °C). The main diffraction peaks of samples coincide well with the monoclinic structure of Na 3 Zr 2 Si 2 PO 12 (PDF#: 84-1200).…”

“…[36] The E a of NZSP-7%NBO-1100 °C, NZSP-3%NaF-1150 °C, and NZSP-3%CuO-1100 °C is 0.24, 0.23, and 0.24 eV, respectively, which are pretty lower in comparison with these recently related reports (Table S2, Supporting Information). [5,24,29,37,38] Figure 7a shows the EIS plots of bare NZSP-1200 °C, NZSP-7%NBO-1100 °C, NZSP-3%NaF-1150 °C, and NZSP-3%CuO-1100 °C ceramic electrolytes-based symmetric sodium metal cells. In general, the sintering aids modified NZSP electrolytes-based symmetric cells show smaller impedance than that of the Na/NZSP/Na cell.…”

“…It is worth noting that the remaining sintering aids may also have a beneficial effect on the sintering process. [ 19–24 ] Certainly, this method is not limited to the NZSP material system, but also can be extended to the other kinds of oxides system, such as Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 (LATP) (Figure S2, Supporting Information), Li 7 La 3 Zr 2 O 12 (LLZO), and β‐Al 2 O 3 ceramic electrolyte systems.…”

“…[ 36 ] The E a of NZSP‐7%NBO‐1100 °C, NZSP‐3%NaF‐1150 °C, and NZSP‐3%CuO‐1100 °C is 0.24, 0.23, and 0.24 eV, respectively, which are pretty lower in comparison with these recently related reports (Table S2, Supporting Information). [ 5,24,29,37,38 ]…”

NaBr-Assisted Sintering of Na3Zr2Si2PO12 Ceramic Electrolyte Stabilizes a Rechargeable Solid-state Sodium Metal Battery

“…However, usually, related equipment is expensive and not suitable for large-scale production. In addition, the sintering aids, such as CuO, NaPO 3 , Na 2 SiO 3 , Bi 2 O 3 , Na 2 BO 3 , B 2 O 3 , and NaF, are employed to accelerate the uniform growth of grain and realize the densification sintering of ceramic electrolytes at a relatively low temperature. − Our previous research reported that the densification sintering of the Na 3 Zr 2 Si 2 PO 12 ceramic and the sodium ion transfer capability across the grain boundary were facilitated by using Na 2 B 4 O 7 as a sintering aid . In the meantime, the area-specific resistance of Na/Na 3 Zr 2 Si 2 PO 12 -10 wt %Na 2 B 4 O 7 (36 Ω cm 2 ) is observably lower than that of Na/Na 3 Zr 2 Si 2 PO 12 (90 Ω cm 2 ).…”