Operando Techniques for Conversion Reaction Engineering in High-Energy Lithium Sulfur Solid State Batteries

M-ERA.net transnational project

This M-era.net transnational project addresses Topic 1, Sustainable advanced materials for energy of the M-ERA.NET 2024 call text. All the specified objectives of this Topic 1 are integral to our project “OCULUS”, which aims to meet the key performance indicators for solid-state and “beyond-Li-Ion / Gen 4&5” batteries as well as affordable, sustainable, and clean energy storage.

Lithium-Sulfur batteries (LSB) have been identified as one of the most promising beyond Li-ion concepts (estimated TRL level for the liquid system 5-7), combining sustainable materials with one of the highest possible gravimetric energy densities of all rechargeable battery technologies. LG Energy Solutions has developed this cell concept for almost a decade, reaching specific energies larger than 400 Wh/kg over 200 cycles. However, the major challenges of liquid LSBs are poor cycle life due to dissolved polysulfide species and limited practical energy densities due to high amounts of liquid electrolyte. All-solid-state Li-S batteries (LS-SSBs) using solid sulfidic electrolyte avoid these intrinsic performance-limiting processes on the cathode side and lead to high active material utilization. Consequently, particularly high energies per weight can be theoretically achieved, which is important for real-world applications such as electric aviation / trucks.

The technology of LS-SSBs is currently on a TRL of 2-3 and is principally scalable using new, clean/solvent-free processing methods for solid state cells. However, some of the critical performance-limiting processes during (dis)charging have not been fully understood yet. On the cathode side, the composite micro- and nanostructure and accompanying conversion mechanism are poorly understood. On the anode side, the metallic, ductile lithium creeps along the grain boundaries and pores of the solid electrolyte separator film leading to early cell death.

The project OCULUS aims to develop a reversibly cyclable, scalable high-energy all-solid-state lithium-sulfur cell concept without indium excess in the anode (TRL 4). Advanced materials sustainably processed both for cathode and anode will be the key in order to maximize the electrochemical performance. The material design will be guided by operando scattering, operando spectroscopy, and cryo electron microscopy. The specific innovation objectives of OCULUS are:

1.   A working scalable, lightweight cell stack comprising a metallic lithium anode, separator layer, and sulfur/carbon/argyrodite cathode with bundled findings from all partners and analyses for real-world applications (TRL 4)

2.   Nano- and microstructured cathode composite maximizing active material utilization by using a proprietary, scalable graphene suspensions (TRL 4).

3.   A lightweight lithium/carbon fiber/graphene composite preventing lithium creeping and dendrites that can be implemented into a cell stack (TRL 3-4).

4.   Development of operando methods: The aim is to identify the underlying mechanisms and performance-limiting processes and derive strategies to overcome those obstacles. For this purpose, new operando setups, suiting the conditions of solid-state sulfur batteries, will be developed (TRL2-3).

The OCULUS consortium, with partners from Slovenia, Austria, and Germany is perfectly aligned to achieve these ambitious goals through materials innovation (SX, TUD, IWS), advanced operando/in-situ characterization (PLUS, NIC), as well as clean coating/dispersion process development (IWS, SX). The involved consortium is ideal to tackle the scientific challenges and exploit a route towards commercialisation: It includes internationally recognized experts with a large existing patent portfolio and longstanding experience in transfer projects, SX as an industrial (SME) partner, and an industrial advisory board along the value chain. OCULUS will respond to key challenges of future energy-storage devices, establishing the consortium members as competitive innovation drivers with technological leadership made in Europe.