/Electrochemical fabrication of lithium thin foils as anode component for Li-based batteries.

Electrochemical fabrication of lithium thin foils as anode component for Li-based batteries.

PhD - Leuven | More than two weeks ago

Production of thin lithium is key for future solid-state batteries

Rechargeable lithium metal batteries including Lithium-Sulphur batteries, need a thin lithium anode with high purity for high energy density and long cycle life. Today, lithium metal is typically produced from Li2CO3. In contrast to the price of Li2CO3, which is often used for benchmarking, pure lithium metal is actually a costly component. In addition, it has quite some CO2 footprint as it needs significant amounts of energy to produce. The lithium is extruded and cold rolled to produce Li foils. As such foils of few hundred micron can be produced. However, to limit cost and to increase energy density, only a few tens of microns are desired. Unfortunately, due to the soft nature of lithium, foils of few tens of micrometers are very difficult to manufacture at large volumes and too expensive for cost competitive high energy density Li-metal based cells. Hence, the production of thin lithium foils is currently a bottleneck. Physical vapor deposition of lithium on copper current collectors is one possibility, where even thicknesses down to 1 micron can be delivered. However, this is not a cost-effective technique either, especially for few tens of microns films. In this project, you will evaluate electrodeposition as a method for cost-effective production of thin lithium foils. After fabrication, the thin lithium metal foils will be used as anode for solid-state metal batteries and for Lithium-sulphur batteries.

Even though it is a very attractive method, electroplating of lithium metal is far from straightforward as it is extremely reactive such that it reacts with all known solvents and even anions used to make up the electroplating baths. This results in non-pure deposits with poor morphology, especially at higher current densities (>1mA/cm2) where powdery deposits and dendritic growth are obtained. The decomposition of the electrolyte typical forms a decomposition layer, often referred to as SEI in analogy with the “solid-electrolyte interphase” layer which is formed during the initial formation step on graphite electrodes in lithium-ion batteries. The SEI is indeed an in-situ formed dense layer of solid electrolyte passing Li-ions while shielding the carbon from direct (electronic) contact with liquid electrolyte components. However, the decomposition layer on lithium metal is often not such a dense or continuous layer and does not protect the lithium as an SEI on graphite does. This poor protection and discontinuous nature of the in-situ formed coating contributes to the poor morphology and dendrite formation. This should not be surprising as the SEI forming step on graphite is a slow and tedious process yet fully controlled by current and potential. Lithium, on the other hand, is instantaneously exposed to the electrolyte once formed and the decomposition is rapid and uncontrolled. Therefore, one of the main challenges is to effectively shield the lithium from the electroplating bath during plating. This can be done either by in-situ or ex-situ formation of protective coatings. These coatings need to pass Li-ions and remain stable on the surface during plating. Additives are one way to control self-healing of the protective layer. To control the film morphology, the initial nucleation and growth behavior needs to be controlled. You will study the electrochemical nucleation and growth for different surface functionalization’s and under protective coatings. In addition, the lithium has to have high purity. You will need to develop methodologies to study lithium without exposure to air or other reactive ambients. Finally, you will assemble the lithium foils into solid-state cells and into Li-S cells to check for their functionality. The work will be conducted in the battery laboratory at imec, Leuven.

Required background: Chemstry, materials science, engineering

Type of work: experimental

Supervisor: Philippe Vereecken

Daily advisor: Maarten Debucquoy

The reference code for this position is 2022-071. Mention this reference code on your application form.