New stainless steel composite for encapsulation of lithium-ion batteries

Aluminum pouches have been predominantly used in battery development to date, as aluminum offers a number of advantages. It is thermal conductive, corrosion-resistant, easy to process and particularly lightweight, which is important in sectors such as the automotive industry. However, there is still significant room for improvement in terms of fire safety. An aluminum fire requires extreme effort to extinguish and bring under control. In some specific circumstances it can start at temperatures as low as 650–1000 °C, especially in the presence of aluminum dust or thin foil.

Innovative solutions for greater durability and improved fire safety

The aim of the ongoing cooperation project is to develop pouches based on stainless steel. The concept combines a steel shell with an innovative high-barrier composite material. In close cooperation with industrial partners from South Korea and Fraunhofer ISC, a requirements profile for the pouches is first being drawn up with a view to fire protection, mechanical and chemical resistance and durability.

Technical film development for optimum safety

The Fraunhofer IVV team of experts is contributing its comprehensive expertise in coatings, lamination and polymer processing to the development of a new generation of lithium-ion battery encapsulation materials. Based on the jointly defined catalog of requirements, multi-layer laminate structures are being designed and evaluated in terms of material combinations and processing technologies.

In subsequent pilot productions on the institute's technical equipment, the base film – intended as a sealing film in the overall system – is manufactured by compounding and extrusion. The functional properties are added by coating and lamination processes accompanied by the evaluation of a special adhesive developed in the project. The patented ORMOCER® material from Fraunhofer ISC is used for optimized adhesive bonding and increased corrosion protection.

In an iterative process involving characterization, pilot production and material selection, the team is developing films with optimal properties. The research objectives focus primarily on seal strength even at higher temperatures, good adhesive bonding between polymer film and steel and the tightness of the sealing and sealing layer. These parameters are crucial for the safe and long-lasting function of battery pouches in demanding application scenarios.