Sodium, Silver and Lithium-Ion Conducting β″-Alumina + YSZ Composites, Ionic Conductivity and Stability

Liangzhu Zhu,Anil V Virkar

doi:10.3390/cryst11030293

Liangzhu Zhu, Anil V Virkar

Open Access

https://doi.org/10.3390/cryst11030293

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Abstract

Na-β″-alumina (Na2O.~6Al2O3) is known to be an excellent sodium ion conductor in battery and sensor applications. In this study we report fabrication of Na- β″-alumina + YSZ dual phase composite to mitigate moisture and CO2 corrosion that otherwise can lead to degradation in pure Na-β″-alumina conductor. Subsequently, we heat-treated the samples in molten AgNO3 and LiNO3 to respectively form Ag-β″-alumina + YSZ and Li-β″-alumina + YSZ to investigate their potential applications in silver- and lithium-ion solid state batteries. Ion exchange fronts were captured via SEM and EDS techniques. Their ionic conductivities were measured using electrochemical impedance spectroscopy. Both ion exchange rates and ionic conductivities of these composite ionic conductors were firstly reported here and measured as a function of ion exchange time and temperature.

Highlights

Na-β”-alumina (Na2O.~6Al2O3) solid electrolyte (BASE) is known to be an excellent sodium ion conductor with uses in sodium-sulfur batteries, sodium-nickel chloride (ZEBRA) batteries, alkali-metal thermoelectric convertors (AMTEC) and in sensors [1,2,3,4,5,6,7,8]
Due to the abundance of sodium compared to lithium resulting in lower cost [10,11,12] and high ionic conductivity of about 1 Scm−1 in single crystal Na-β”-alumina and 0.2–0.4 Scm−1 in polycrystalline β”alumina at 300 ◦C, Na-β”-alumina still sees an encouraging future in certain applications
Na-β”-alumina packing powder was made by mixing Na2CO3, LiNO3 and α-Al2O3 and calcined at 1250 ◦C for 2 h

Summary

Introduction

Na-β”-alumina (Na2O.~6Al2O3) solid electrolyte (BASE) is known to be an excellent sodium ion conductor with uses in sodium-sulfur batteries, sodium-nickel chloride (ZEBRA) batteries, alkali-metal thermoelectric convertors (AMTEC) and in sensors [1,2,3,4,5,6,7,8] Among these applications, sodium sulfur batteries, originally developed by Weber and Kummer at the Ford Motor Company in the 1960s [9] have demonstrated attractive applications in automobiles before lithium batteries became more popular. Conventional process for the fabrication of Na-β”-alumina involves first calcining a mixture of alumina (Al2O3), Na2CO3 and LiNO3 (or MgO) at 1250 ◦C for 2 h This leads to the formation of a mixture of Na-β”-alumina, Na-β-alumina (Na2O.~11Al2O3) and NaAlO2. The samples are placed in platinum containers or MgO containers and heated in air to ~1600 ◦C for a few minutes and rapidly cooled to ~1450 ◦C and heat-treated for an hour to convert Na-β-alumina into Na-β”-alumina by the reaction [13]: Na2O.~11Al2O3 + 2NaAlO2 → 2(Na2O.~6Al2O3)

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