Elsevier

Electrochimica Acta

Volume 191, 10 February 2016, Pages 1-7
Electrochimica Acta

Na ion- Conducting Ceramic as Solid Electrolyte for Rechargeable Seawater Batteries

https://doi.org/10.1016/j.electacta.2016.01.054Get rights and content

Highlights

  • Rechargeable seawater batteries are assembled using two Na+ conducting ceramics.

  • The battery with β″-Al2O3 electrolyte is irreversible even at 1 cycle.

  • The battery with NASICON shows a coulombic efficiency of 91% after 20 cycles.

  • NASICON is much more stable in seawater than β″-Al2O3.

Abstract

This study describes the assembly of a rechargeable seawater battery using hard carbon as the anode, seawater as the cathode, and a fast Na ion-conducting ceramic as the solid electrolyte. Two different Na ion-conducting ceramics, β″-Al2O3 and Na3Zr2Si2PO12 (NASICON), are used as the solid electrolytes in this study. The discharge capacity of the seawater battery with the NASICON solid electrolyte is 120 mAh g−1 after the first cycle and over 91% coulombic efficiency after twenty cycles. However, under the same experimental conditions, the discharge capacity of the seawater battery with a β"-Al2O3 electrolyte significantly drops to 10 mAh g−1 after one cycle. It is observed that the stability of NASICON in seawater is superior to that of β"-Al2O3 and impedance results of NASICON are not changed significantly compared to that of β"-Al2O3 after cycling tests. The stability of Na ion-conducting ceramics in seawater and their effects on the electrochemical performance of seawater batteries are presented and discussed.

Introduction

Environmental concerns over the use of fossil fuels and their resource constraints have motivated the development of electric and renewable energy systems for portable electronic devices, electric vehicles (EVs), and energy storage system (ESS). Rechargeable lithium-ion batteries (LIBs) have been successfully commercialized for mobile electronic devices and EVs, but have found limited use in ESSs due to their high cost. Moreover, the increasing demand for LIBs combined with possible lithium resource restrictions might lead to a prohibitive price for these batteries [1], [2], [3]. Thus, many scientists are exploring alternative battery technologies in which lithium is replaced by sodium because sodium is naturally abundant, easily accessible, and low cost [4], [5], [6].

Rechargeable seawater batteries have been recently introduced as a result of requests for new ESSs that use sodium [7], [8], [9]. These batteries are built using a fast Na ion-conducting ceramic as the solid electrolyte. A solid ceramic electrolyte is one of the key components in a seawater battery system because the sodium metal electrode can be protected from direct exposure to seawater. The feasibility of a rechargeable battery system using seawater as an electrode material has been demonstrated [9]. However, it is expected that the capacity, reliability, and coulombic efficiency of seawater batteries will depend on the stability of the solid electrolyte in seawater. Two Na ion-conducting ceramics, β″-Al2O3 and Na3Zr2Si2PO12 (NASICON), have been considered as solid electrolyte materials. β″-Al2O3 possesses a two-dimensional(2D) structure, and exhibits Na ion conductivity up to ∼2.0 × 10−3 Scm−1 at room temperature [10]. NASICON has demonstrated an ionic conductivity of 2.5 × 10−3 Scm−1 [11] in a three-dimensional(3D) structure [12], [13], [14]. β″-Al2O3 is known to be moisture-sensitive. Will [15] reported that there is a rapid exothermic occlusion of water in the surface micropores of β″-Al2O3, which caused saturation of these pores in less than 1 h. This was followed by slow diffusion of H3O+ ions into the β″-Al2O3 lattice leading to ion exchange with sodium. Flor et al. [16] substantiated that β″-Al2O3 is unstable to moisture using thermogravimetric and X-ray techniques. Flor et al. reported that rapid penetration takes place in the first few microns near the conduction plane boundaries. Water absorption caused changes in lattice parameters a and c of β"-Al2O3 [16]. In contrast, NASICON-type materials are known to be stable in a moist environment. However, it was later found that the formation of hydronium NASICON [17] occurred on the surface of NASICON by ion exchange between H3O+ and Na+ [18] during the reaction of NASICON in hot water. It was also reported that NASICON's instability in water could be due to the dissolution of a secondary amorphous phase, Na3PO4, in NASICON [19]. However, most of these studies were conducted using NASICON powders at a high temperature of 80 °C to accelerate its reaction with water so that comparative results could be collected in a short time. For seawater batteries operating at room temperature, dense ceramic plates are required for the electrolyte and separator, but their stability in contact with seawater and its effect on seawater battery performance have not been reported.

In this study, we used two different solid electrolytes, β″-Al2O3 and NASICON, in seawater batteries at room temperature. The ceramic electrolytes exposed to seawater during cycling were collected after testing, and their stability in seawater and its related seawater battery performance were compared to understand their influence on the seawater battery system.

Section snippets

Sample preparation

A Sodium-ion conductive ceramic with nominal composition Na3Zr2Si2PO12 (NASICON) was prepared by solid state reaction of Na3PO4·12H2O (Daejung, 99%), ZrO2 (Kanto, 99.9%) and SiO2 (Daejung, 99%). The powders were mixed and first-calcined under air at 400 °C for 5 h. The first-calcined powder was ground to make a finely-grained powder. Next, the first-calcined powder was second-calcined under air at 1100 °C for 12 h. The second-calcined powder was ground and milled in a planetary mill for 30 min. The

Results and discussion

The constitution of the seawater battery [7], [8], [9] is schematically illustrated in Fig. 1. It consists of an anode and cathode, which are separated by a dense ceramic solid electrolyte. The anode is composed of the current collector, active material, and organic liquid electrolyte (NaCF3SO3 in Triethylene glycol dimethyl ether (TEGDME)). The cathode is composed of the current collector and seawater. Seawater works as the active cathode material. The current collector is needed to provide a

Conclusions

A seawater battery was assembled, and two different fast Na ion-conducting ceramics, β"-Al2O3 and NASICON-type, were investigated as the solid electrolyte for a seawater battery. Their stability in seawater is crucial for the electrochemical performance of the seawater battery. Since β"-Al2O3 allows protonated species of H3O+ to move through its conduction plane into the anode side of the seawater battery, a reasonable electrochemical performance has not been observed in the seawater battery

Acknowledgements

This work was supported by the 2015 Research Fund (1.150034.01) of UNIST (Ulsan National Institute of Science and Technology) and the National Research Foundation of Korea (NRF-2014R1A2A1A11052110)

References (36)

  • Brian. L. Ellis et al.

    Curr. Opin. Solid State Mater. Sci.

    (2012)
  • J.-K. Kim et al.

    ChemElectroChem

    (2015)
  • H.Y.P. Hong

    Mater. Res. Bull.

    (1976)
  • J.B. Goodenough et al.

    Mater. Res. Bull.

    (1976)
  • G. Flor et al.

    Solid State Ionics

    (1981)
  • A. Ahmad et al.

    Solid State Ionics

    (1987)
  • R.O. Fuentes et al.

    Solid State Ionics

    (2001)
  • F. Mauvy et al.

    Talanta

    (1999)
  • M.I. Rojas et al.

    Electrochim. Acta

    (1998)
  • X. Lu et al.

    J. Power Sources

    (2010)
  • M.W. Breiter et al.

    Mater. Res. Bull.

    (1977)
  • G.C. Farrington et al.

    Mater. Res. Bull.

    (1978)
  • F. Harbach

    Solid State Ionics

    (1983)
  • A. Ponrouch et al.

    Electrochem. Commun.

    (2013)
  • J.J. Auborn et al.

    Solid State Ionics

    (1981)
  • P.G. Komorowski et al.

    Solid State Ionics

    (1991)
  • J.-M. Tarascon

    Nat. Chem.

    (2010)
  • J.B. Goodenough

    Energy Environ. Sci.

    (2014)
  • Cited by (67)

    View all citing articles on Scopus
    View full text