High Na⁺ conducting Na₃Zr₂Si₂PO₁₂/Na₂Si₂O₅ composites as solid electrolytes for Na⁺ batteries

Abstract

Sodium superionic conductor Na3Zr2Si2PO12 (NZSP) is a promising material as a solid electrolyte for sodium‐ion batteries. The highest conductivity of ∼1.0 mS/cm at room temperature (RT) was reported for the compound with a Na content of approximately 3.3 per formula unit (f. u.) and when the material is synthesized with a final sintering temperature ≥1220°C. Herein, we propose a new synthesis method to enhance the conductivity of the NZSP by liquid‐phase sintering with the optimum amount of additive of amorphous‐Na2Si2O5. In this regard, a series of composite materials were prepared by mixing Na3Zr2Si2PO12 with amorphous‐Na2Si2O5 (NZSP/NS‐x wt.%; with x = 0.0, 2.5, 5.0, 7.5, 10.0) and sintering at a lower temperature of 1150°C. Enhanced conductivity of 1.7 mS/cm at RT has been achieved for the Na3Zr2Si2PO12/Na2Si2O5‐5.0 wt.% (NZSP/NS‐5.0) composite. The effects of additives on the NZSP phase formation, microstructure, and ion conductivity have been investigated by XRD, MAS NMR, SEM, and impedance spectroscopy. Our study demonstrates that the higher conductivity of the NZSP/NS‐5.0 composite is caused by the combined effect of increased Na content in the NZSP phase (by diffusion of Na+ ions from the liquid phase of NS to bare NZSP phase), higher density, and microstructures with lesser pores.

Li-Ion Conduction Mechanism and Relaxation Dynamics in Sorosilicate Compound Li2Cu5(Si2O7)2

“…Impedance spectroscopy is a well-established technique to determine the conductivity of a material as a function of temperature and frequency. − It allows differentiating between the real and imaginary parts of the various electrical parameters, such as impedance, ac conductivity, dielectric constant, electric modulus, and polarizability, which are useful for understanding the electric behavior of a material. This technique provides separate information for grain and grain boundary contributions to ionic conduction.…”

Role of Crystal Structure on the Ionic Conduction and Electrical Properties of Germanate Compounds A2Cu3Ge4O12 (A = Na, K)

“…In addition to the bottlenecks, the higher intersite distances for Na ions lead to higher activation energy and lower ionic conductivity in NCGO as compared to that for KCGO. Such bottlenecks are responsible for the low ionic conductivity as found to be ∼1.6 × 10 –5 S m –1 and 4.6 × 10 –7 S m –1 for KCGO and NCGO, respectively, at 573 K. These values are substantially lower than that of the NASICON compounds. − For the NASICON compounds, ionic conduction occurs in 3D without having any bottleneck along the conduction pathways as compared to 2D and 1D in KCGO and NCGO, respectively. Moreover, the partially occupied Na-ion sites are favorable for ionic conductions.…”

“…In the recent past, various sodium and potassium-based compounds were synthesized and characterized for ionic conduction investigations. For example, compounds such as A 6 [Rh 4 Zn 4 O­( l -cysteinate) 12 ]· n H 2 O with high conductivity values of ∼5.0 × 10 –2 and ∼1.3 S m –1 at 300 K for A = Na + and K + , respectively; Na 2 Ni 2 TeO 6 with ∼10.1 S m –1 at 573 K, Na 2 Zn 2 TeO 6 with ∼5.1 S m –1 at 573 K, Na 2 Co 2 TeO 6 with ∼3.1 S m –1 at 573 K, and sodium superionic conductor (NASICON) Na 10.8 Sn 1.9 PS 11.8 with 0.67 S m –1 at 298 K − were reported recently. These studies revealed that Na + and K + ion based inorganic compounds could be possible candidates for the development of the new ionic conductors.…”