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PolySafe: Making lithium-ion batteries safer

The aim of PolySafe is to increase the specific energy and safety of lithium-ion batteries by using novel current collectors. The focus here is on metal-polymer composite current collectors, which make the thermal runaway of battery cells much more difficult and thus reduce the risk of fire. In addition to the Battery LabFactory Braunschweig of the Technical University of Braunschweig, partners from research and industry are involved in the project, which is funded with almost four million euros.

In addition to the weight advantage over pure metal current collectors used today, the metal-polymer current collectors allow the circuit to be interrupted when a critical temperature is reached. When this temperature is reached, the current collector melts, interrupting the current flow and thus the short circuit. Current collectors are thin metal foils that conduct electricity well. The active material responsible for energy storage in batteries is applied to them.

The feasibility of manufacturing the metal-polymer electricity collectors has already been demonstrated jointly by VON ARDENNE GmbH and Fraunhofer FEP as part of the Saxon research project PolyCollect. The physical vapor deposition process was able to produce aluminum layers up to 1 micron thick on polymer substrates with thicknesses up to 8 microns. However, there are too few data from prototype cells with this material so far, which is why the application-oriented evaluation of this technology is still pending. This is now to be done within the framework of PolySafe. The aim of the research project is to qualify a process chain adapted to the metal-polymer current collectors for the production of battery cells in different formats (round cell, pouch cell) and to investigate the safety advantage in different cell designs and chemistries in an application-oriented manner.

In addition to the integration of the manufactured metal-polymer current collectors in battery cells, the project partners want to adapt and optimise aluminium or copper-polymer current collectors in a dedicated manner to the requirements of the respective cell design. The challenge is to design the polymer substrates and the coating process in such a way that a thickness comparable to current metal foils as well as an optimal electrical conductivity of the metal layer is guaranteed. At the same time, the production costs of electricity collectors are to be brought to a competitive level.

The Battery LabFactory Braunschweig (BLB) of the TU Braunschweig contributes its expertise in the production process and characterization of electrodes and pouch cells for lithium-ion batteries. The metal-polymer current collectors will be investigated with regard to their suitability for integration into the production processes of lithium-ion batteries and – if necessary – the production processes will be specifically adapted.

About the Battery LabFactory Braunschweig (BLB)
As a transdisciplinary centre, the BLB of the TU Braunschweig networks 14 institutes for the holistic research and development of battery electric storage technologies and covers the entire value-added cycle from material production to cell manufacturing to recycling to close the material cycle. In a “Joint Pilot Facility”, electrode and cell production as well as cell conditioning will be mapped in technical, automated processes on a pilot to pilot scale (battery technology platform 1000 square meters, including 200 square meters of drying room, plus 700 square meters of technical rooms for analytics and post-mortem analysis), so that defined cells can be produced on a large scale for battery demonstrators.

Specifically brought into the project i) the process and product competence in electrode production established since 2007, (ii) competence in manufacturing, joining and handling technology in the field of cell assembly, packaging, contacting (iii) methodological competence for energy-oriented modelling and life cycle assessment; and (iv) elaborate procedures for formation and cycling for cell conditioning and diagnostic methods.

Responsibilities of the partners
VON ARDENNE GmbH is responsible for the coordination of the PolySafe research project. In addition, based on the results of the technological development at Fraunhofer FEP, the Dresden-based company will contribute its know-how to the technical design of a production plant for the deposition of the metal layers, which meets both the technological and the economic requirements for the production of metal-polymer electricity collectors.

Brückner Maschinenbau GmbH & Co.KG is working on the development of polymer films which are adapted to the requirements of metallization as well as to the application in batteries. The aim is to develop innovative polymer substrates and surface treatments and scale them up to roll scale. The most promising materials will be made available as substrates for metallization.

The scientists at Fraunhofer FEP are developing a suitable technological process control for the deposition of the aluminum and copper layers in a roll-to-roll process. The aim is to understand the influence of parameters of the strip run, the substrate pre-treatment as well as the metal evaporation in a holistic way and to develop optimal process settings to achieve the technological and economic requirements.

The Fraunhofer IST is researching the suitability of metal-polymer current collectors for novel battery cell generations, with a particular focus on lithium-metal anodes. Special emphasis will be placed on the manufacturing steps of the lithium metal anodes and the resulting cells.

VARTA Microbattery takes care of the integration of the new electrodes with metal-polymer current collectors in full cells and the standard-compliant safety testing. In particular, the processing and safety of round cells with metal-polymer current collectors will be investigated and compared with pure metal foils.

Project Data:
PolySafe is a research project to increase the safety of lithium-ion batteries by means of metal-polymer composite current collectors and is funded by the Federal Ministry of Education and Research (BMBF) with around four million euros (funding code 03XP0408E). The project started in August 2021 and will run for three years. In addition to the TU Braunschweig, the following companies are involved: VON ARDENNE GmbH (coordination), Brückner Maschinenbau GmbH & Co. KG, Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP, Fraunhofer Institute for Surface Engineering and Thin Films IST and Varta Microbattery GmbH.