Compatibility Investigation of Housing Materials for High Temperature Metallic Phase Change Material Storage

Abstract

The successful transition to sustainable energy sources depends crucially on the development of energy storage systems. For applications involving heating, thermal storage systems are the most evident choice. That is the case for cabin heating of electric vehicles such as city buses, where the use of thermal storage would reduce the capacity of electrical batteries needed. We show that metallic phase change materials (mPCMs) represent a promising solution. They have high latent heat and high density. This allows for a reduction of the storage volume compared with other materials. Further, they are characterised by high thermal conductivity, that enables fast charge and discharge. However, high operating temperatures, the reactivity of the molten metals and the periodic melting and solidification cycles can promote the corrosion of the container materials, making the selection of a suitable housing a key aspect. In this work, a thermal energy storage system for application in electric vehicle cabin heating that uses an Al-12.5wt%Si alloy as mPCMs is analysed in terms of the compatibility with alumina, 304 stainless steel and 304 stainless steel coated with alumina. The formation of reaction products and phases in the container-mPCM interface for a long-period at temperatures above the melting point of the metallic alloy has been studied. The effect of thermal cycling in these reactions has also been studied. The type and extent of phases formed under both conditions have been identified, exemplifying the influence of melting-solidification cycles as compared to static corrosion. We show that under given conditions alumina and alumina coated 304 stainless steel are suitable candidate materials for an Al-casting alloy based storage system for mobile applications and beyond.