Optimization of the Electrolyte and Electrode Solid-solid Interface in a Solid-state Lithium Ion Battery: Application of Electrospray Technique.

Abstract

Over time, the demand for thin film lithium ion batteries has grown due to technological developments that have led to the miniaturization of electronic devices which require smaller power sources. However, lithium ion batteries use flammable organic liquids as electrolytes posing a safety concern. The pursuit of solid-state electrolytes, characterized by enhanced safety and high ionic conductivities has gained significant attention. Nevertheless, ensuring the integrity between them and electrodes is crucial because unlike liquids, solids do not flow freely over surfaces limiting their integration hence poor contacts at their interfaces. For the design of thin films with good contact at their interface, this study employed the electrospray technique. A literature survey was conducted and key electrospray parameters were identified. A comprehensive design schedule for electrosprayed thin films with different surface morphologies was then developed. In addition, the cone-jet stability windows for commonly used solvents were experimentally determined by measuring voltage and flow rate values that sustained a stable cone. Thin films with porous and dense morphologies were then deposited on aluminium foil substrates and characterization of their surface morphologies was performed using scanning electron microscopy. To address the safety challenge in conventional electrolytes, Li6PS5Cl solid-state electrolyte material was synthesized via solid-state method and its structural characterization was performed using x-ray diffraction. A bulk solid-state lithium ion cell was fabricated by pressing a three-layered pellet and characterized by galvanostatic cycling. As a result, the developed schedule provided a systematic way of designing thin films with different surface morphologies. The cone-jet stability windows for 2-propanol, ethylene glycol and NMP were defined using minimum and maximum flow rate values. From the morphological characterization of the deposited thin films, the observed surface morphologies were in agreement with the prediction of the design schedule. Using electrospray technique, thin films for solid-state lithium ion batteries with good contact at their interface were deposited without incorporating binders. The results of the galvanostatic cycling of the fabricated bulk solid-state lithium ion cells indicated low discharge capacities.