Synthesis and characterization of novel materials for aqueous zinc-ion batteries.

Abstract

The industrial revolutions in the past centuries have led to extraordinary changes in social life, transportation, and production activities, with energy utilization reflecting the progress of industrial technology and human civilization. The primary energy sources that have been used to power all tech-dependent human activities are fossil fuels, such as crude oil and natural gas, with no little consequences. In fact, pollution arising from fossil fuel combustion has had a devastating impact on the natural environment and on human health. In addition, the natural reserves of fossil fuels are limited. Therefore, these energy sources are not sustainable from multiple points of view. Hence, the focus of research has shifted to environmentally benign sustainable energy. The development of renewable energies and the need for means of transport with reduced CO2 emissions have generated new interest in storage, which has become a key component of sustainable development. As electrochemical storage systems, there are many different types of batteries and most of them are subject to further research and development. Recently, several battery technologies, such as redox flow, sodium sulfur, lead carbon, or lithium ion, have been proposed as possible systems for large-scale stationary energy storage, but they suffer from low charging rates, high operating temperatures and the use of hazardous materials in their components and/or high costs. These drawbacks limit their integration into the electrical power grid. Metal-ion aqueous rechargeable batteries have become a low-cost, safe, and environmentally friendly alternative to traditional technologies. Several cells based on lithium intercalation electrodes have been developed in recent years. However, the lower energy density and the scares availability of the lithium brought to the necessity for energy storage systems based on alternative elements. A new family of open-framework materials with the Prussian Blue crystal structure have been recently studied as materials for positive electrodes in potassium-ion batteries, showing excellent specific charge retention and rate capability. Over the last years, aqueous Zn-ion batteries (ZIBs) have brought great interest due to their applicability as cheap and environmentally friendly energy storage devices for power grid applications. Among the potential active materials, which can be used in this type of battery, open framework Prussian Blue (PB) and its analogues (PBAs) have attracted the attention of the researchers thanks to their excellent properties. Because of the large interstitial sites, PBAs facilitate the reversible intercalation of hydrated ions from an aqueous electrolyte. Belonging to the Prussian blue analogues (PBAs) family, copper hexacyanoferrate (CuHCF) has been shown to be a promising candidate as positive electrode material for aqueous ZIBs. In addition, CuHCF can be synthesized through a simple synthesis. Despite CuHCF can be produced through an easy co-precipitation route, the synthesis of the desired phase is not straightforward to control. Such complications in controlling the synthesis’ reaction mechanism have been evaluated in previous studies. The measurements carried out with zinc as the reference electrode differ in terms of life cycle from the measurements made with Ag / AgCl as RE. These results led to the consideration that the potassium chloride solution of the reference electrode somehow plays a role in the life span of the electrode due to potential losses of the solution in the electrolyte. For this reason, it was decided to further evaluate the role of the electrolyte. Therefore, the purpose of this thesis is to investigate the effect of the presence of potassium chloride as an electrolyte in the co-presence of zinc sulfate. Furthermore, the effect of an excess of potassium ions in the synthesis of the material was also evaluated.