Sintering characteristics and energy applications of sodium superionic conductors(NASICON): A REVIEW

Abstract

Ionic conductors are increasing playing a crucial role in electronic devices, from electro chromic displays, lithium ion batteries for laptop computers and mobile phones, to gas sensors for detection of environmental pollutants, amongst others. Traditional materials exhibiting good ionic conductivity have been Na-Beta alumina based cells or those made from Li (CAO, Ni)O2. However, these materials and others that were subsequently produced have some defects, in terms of their stability in operation. When used in energy storage devices their conductivity and structure, 2-D or 1-D layered, etc., all impact on their overall performance. Thus the search for new materials lead to the synthesis of NASICONS which have better ionic conductivity comparable to beta alumina attributed to their 3-D structures suitable le for easy diffusion of ions and substitution ability by other ions of same size or less, like lithium in their flexible structures . Moreover, they can be synthesized at lower temperatures. These explain some of the attractions for research in these materials. However, there are still problems with the solid state synthesis of these materials which include the phase purity challenge, grain boundaries, amongst others which are the subject of this review. Several methods are being developed to improve or eliminate these defects through novel sintering techniques such as SPS and PLD for improved sintering properties, and thin film deposition techniques for NASIOCONs, respectively. Also, alternative materials that are easier to synthesize relative to NASICONs-the so-called NASICON analogues.