ASSIGNMENT 1

DEVELOPMENT OF SUPERIONIC GLASS FOR BATTERY

MOHD RAFEEZ BIN RAZI A11SC0120
MOHD SYAKIR BIN MOHD NASIR A11SC0220
MUHAMMAD MUHSIN BIN TAHIR A11SC0008

PROF DR RAHIM BIN SAHAR

Abstract

Development of rechargeable batteries can be effectively store renewable energy, wind power and solar power. It is important to developed to reduce the greenhouse emissions. Rechargeable sodium batteries are more suitable compare to lithium-ion batteries because they use abundant and ubiquitous sodium sources.

Introduction

Sodium-ion rechargeable batteries, using abundant sodium sources, are suitable for use in distributed power systems that store renewable energy at individual houses [1]. Currently, sodium−sulphur (NAS) batteries [2] are used for large-scale storage, because they have high energy densities of up to 760 Wh kg−1. However, NAS batteries need to be operated at temperatures up to 300 °C to use liquid-state sulphur-positive electrodes and sodium-negative electrodes and to enhance the conductivity of β-alumina solid electrolyte, a well-known Na+ ion conductor. Research regarding Li+ ion conducting electrolytes and found that solid sulphide electrolytes made from the system Li2S–P2S5 have a high conductivity and a wide electrochemical window [5] ,making them suitable for all-solid-state lithium secondary batteries that have excellent cycling and rate performances [6]. In this study, we developed a sulphide glass-ceramic electrolyte by crystallization of high-temperature cubic Na3PS4 phase from the glassy state. The prepared electrolyte showed a sodium-ion conductivity of 2×10−4 S cm−1 at room temperature. This high conductivity was achieved by stabilization of cubic Na3PS4 and large reduction of grain-boundaries in a glass-ceramic pellet. A room-temperature operation of all-solid-state rechargeable sodium batteries with a powder-compressed glass-ceramic electrolyte was first realized and this achievement is the first step toward realizing all-solid-state NAS batteries.

Materials and Methods

Preparation Na3PS4 glass and glass-ceramic electrolytes

Na3PS4 glass was prepared by a mechanochemical technique using a planetary ball mill (Fritsch, Pulverisette 7). The materials of 75 mol% Na2S (Aldrich) and 25 mol% P2S5 (Aldrich) were hand-ground and the mixture was then placed into a zirconia (ZrO2) vessel (internal volume of 45 ml) with 500 ZrO2 balls (4 mm in diameter). The mechanochemical reaction was performed for 20 h at a fixed rotation speed of the base disc of 510 r.p.m. to form Na3PS4 glass powders.

Characteristics of Solid Electrolytes

A stainless-steel disk as the working electrode and a sodium foil as the counter electrode were attached to each face of the pellet. The potential sweep was performed by using a potentiostat/galvanostat device[7] with a scanning rate of 5 mV s−1 at room temperature.

Evaluation of All-Solid-State Sodium Batteries

An all-solid-state test cell was fabricated using TiS2 the working electrode, Na3PS4glass-ceramic as the solid electrolyte, and a Na–Sn alloy as the counter and reference electrodes. The working electrode was a composite of TiS2 active material and the solid electrolyte powders, because sodium ion paths to the active material are required to operate the cell.

Results
Crystallization of Na3PS4 glass electrolytes

As shown in Figure, a crystalline phase was precipitated after heating the Na3PS4 glass at 270 °C, which is above the first crystallization temperature determined by DTA. The XRD pattern of the glass-ceramic (that is, crystallized glass) was indexed by a cubic phase based on a tetragonal phase of Na3PS4

Figure 1
Electrical conductivity of Na3PS4 solid electrolytes

The absolute values of impedance |Z| as a function of frequency of β-alumina behave completely differently from those of the Na3PS4 glass and glass-ceramic. The glass-ceramic has smaller impedance than β-alumina in the high-frequency range from 104to 107 Hz, whereas the impedance of β-alumina at 70 °C is six orders of magnitude larger than that of glass-ceramic at low frequencies in the range 0.1 to 10 Hz. This is clear evidence that the Na3PS4 glass-ceramic pellet possesses a higher ionic motion than the β-alumina pellet.

Figure 2
Conductivity of the Na3PS4 glass and glass-ceramic electrolytes.

Temperature dependences of the conductivities of the Na3PS4 glass (open circles) and the glass-ceramic prepared at 270 °C (solid circles). Conductivities of several Na+ ion conductors reported so far are also shown as a comparison.

Figure 3

Application to all-solid-state sodium batteries

The electrochemical window of the sulphide glass-ceramic electrolyte with cubic Na3PS4was examined by performing cyclic voltammetry measurements. As shown in Fig. 4, reversible sodium deposition and dissolution currents were observed at about 0 V versus Na+/Na, and no remarkable oxidation currents were observed up to 5 V

Figure 4
Discussion

Superionic glass have attracted much attention in recent years because of their possible application in solid state battery and other electrochemical device [8,9]. Among the superionic glasses, silver oxy salts glass has been the most attractive system to be studied because easy to preparation, wide temperature range and composition and low melting point [10]. AgPO3 glass has low ionic conductivity at room temperature 10-7 S.cm-1 . However, its combination with silver halides such as AgCl, AgBr and AgI will increase the ionic conductivity. Glass are attractive as electrolytes because only the cations can move [11] and therefore transport numbers of cations are unity. One can readily visualize as shown in (figure 1), the building of rocking chair cells where Li+ ions can be decanted backwards and forwards between the negative and positive electrodes

Figure 1

Figure 1, The concept of the rocking chair cell incorporating a Li+ ion conducting glass. The example id for a Li/MnO2 cell. Carbon is increasingly used as a matrix for intercalating atomic lithium. t+ is the transport number of cations. Depending on the glass conductivity this may be a thin film device Glasses for this purpose need conductivities as low as 10-6 Scm-1 at ambient temperature. Bates and coworkers [12,13] use ‘Lipon’ electrolyte which is a new Lithium phosphorus oxynitride glass of typical composition, Li3.3PO3.9N0.17, prepared by sputtering Li3PO4 in pure N2. Glass in the LiI-Li3PO4 –P2S5 system, with still higher conductivities of 2 x 10-5 Scm-1. The presence of LiI reduces the electrochemical stability.

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