Lightweight, affordable and long-lasting: Toward application-oriented lithium-sulfur batteries

One of the main problems with existing lithium-sulfur batteries is their low cycle stability. In recent years, many solutions have therefore been pursued to eliminate the main cause of capacity loss and premature cell failure, the polysulfide shuttle. It has been shown that the covalent bonding of the active material sulfur to a polymer is particularly promising. A high capacity and rate capability can be achieved with simultaneous cycle stability. However, the low sulfur content of the sulfurized poly(acrylonitrile) (S-PAN) used to date prevents further steps towards commercialization. The Institute of Polymer Chemistry at the University of Stuttgart (IPOC) has recently developed a new type of sulfurized polymer based on particularly cost-effective poly(propylene) (PP). The sulfurized poly(propylene) (S-PP) is characterized by a 50 % higher sulfur content than S-PAN and consequently potentially higher energy density, high rate capability and stable cycling behavior. It is now aimed to further improve S-PP among other S-polymers and to scale up their synthesis using energy-efficient and industry-relevant processes.

Project consortium with complementary skills

The project consortium consists of two research institutes, one industrial company and three associated project participants and is coordinated by the Institute of Engineering Thermodynamics of the German Aerospace Center (DLR-TT) in Stuttgart during the three-year project period.

At the DLR-Institute of Engineering Thermodynamics, the S-PP material from the University of Stuttgart will be transferred into high-energy lithium-sulfur pouch cells with an optimized cathode composition and increased sulfur loading. Sustainable cathode production based on aqueous dispersions or by means of dry coating processes will be implemented. In addition to optimizing benchmark liquid electrolytes, the Institute of Polymer Chemistry at the University of Stuttgart, together with the IoLiTec GmbH, will investigate gel electrolytes that can be polymerized in situ to increase safety in cell operation.

Furthermore, operando characterizations in the field of electrochemical, microscopic and spectroscopic methods will provide detailed insights into the cell processes and thus enable the identification of limitations. These experimental activities are supported by modeling work at the DLR-Institute of Engineering Thermodynamics. The influence of sulfur loading, electrode architecture and morphology, as well as the electrolyte volume on the reaction kinetics and sulfur utilization will be investigated.

Through the close cooperation of the project consortium consisting of DLR-TT, the University of Stuttgart and IoLiTec GmbH, as well as the associated project participants Institute for Particle Technology (iPAT) of the TU Braunschweig, Schaeffler AG and ADEKA Europe GmbH, multi-layer lithium-sulfur pouch cells with high energy density (> 200 Wh/kg or > 200 Wh/l) will ultimately be constructed and an ecological and economic evaluation carried out. This will demonstrate the application potential in the field of stationary and mobile storage and provide a perspective for Li-S batteries based on sulfurized polymers.

Project consortium

Deutsches Zentrum für Luft- und Raumfahrt (DLR)

The Institute of Engineering Thermodynamics at the German Aerospace Center (DLR) in Stuttgart has more than 180 employees conducting research in the field of efficient and resource-saving energy storage and next-generation energy conversion technologies. The experimental and model-based development of batteries is carried out in the Electrochemical Energy Technology and Computational Electrochemistry departments.

University Stuttgart – Institute of Polymer Chemistry (IPOC)

The Chair of Macromolecular Materials and Fiber Chemistry of the Institute of Polymer Chemistry (IPOC) at the University of Stuttgart deals with lithium, sodium and magnesium-sulfur batteries, among other things, and has extensive experience in the synthesis and characterization of the corresponding battery components as well as in the production and electrochemical characterization of the corresponding metal-sulfur batteries.

IoLiTec GmbH

IoLiTec Ionic Liquid Technologies GmbH, based in Heilbronn, was founded in 2003 and is a multi-award-winning, innovative, dynamic and goal-oriented company. In addition to a constantly growing standard product range of currently around 300 ionic liquids as well as around 40 intermediates and 150 nanomaterials, which are sold in quantities ranging from grams to tons, IoLiTec also offers accompanying R&D services and custom synthesis.

Associated participants

TU Braunschweig – Institute for Particle Technology (iPAT)

The Working Group Battery Process Engineering at the Institute for Particle Technology (iPAT) at TU Braunschweig deals with procedural aspects of electrochemical storage technologies, from basic research to process and manufacturing technology of the industrial production of electrodes. The research areas cover the entire process technology from the raw material to the finished electrode as well as laboratory cell assembly and the recycling of lithium-ion batteries. All of these topics are supported by simulative studies at the institute.

Schaeffler Technologies AG

The Schaeffler Group has been driving forward groundbreaking inventions and developments in the field of motion technology for over 75 years. With innovative technologies, products, and services for electric mobility, CO₂-efficient drives, chassis solutions, Industry 4.0, digitalization, and renewable energies, the company is a reliable partner for making motion more efficient, intelligent, and sustainable – over the entire life cycle. The motion technology company manufactures high-precision components and systems for drive train and chassis applications as well as rolling and plain bearing solutions for a large number of industrial applications. The Schaeffler Group generated sales of EUR 15.8 billion in 2022. With around 84,000 employees, the Schaeffler Group is one of the world’s largest family-owned companies. With more than 1,250 patent applications in 2022, Schaeffler is Germany’s fourth most innovative company according to the DPMA (German Patent and Trademark Office).

ADEKA Europe GmbH