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GHz nanoscale electrical and dielectric measurements of the solid-electrolyte interface and applications in the battery manufacturing line

Periodic Reporting for period 2 - NanoBat (GHz nanoscale electrical and dielectric measurements of the solid-electrolyte interface and applications in the battery manufacturing line)

Reporting period: 2021-10-01 to 2023-03-31

The NanoBat project aims to progress the measurement and analysis of batteries by developing advanced methods for assessing their electrical impedance and electrochemistry at various nanoscale sized interfaces. The new test methods are designed to be faster, more sensitive, and more accurately calibrated than existing techniques. By focusing on battery compartments and interface layers, such as the nanoscale electrode SEI (solid electrolyte interface), NanoBat enables improved characterization speed and accuracy in battery manufacturing processes and is validated by physics and electrical modeling methods. This is demonstrated through pilot lines, open workshops, and high-throughput quality tests in industrial settings.
The implementation of the new broad-band frequency methods in battery quality tests enhances grading and classification efficiency, as well as production efficiency, leading to reduced waste and costs. In Europe, the production of environmentally friendly batteries is crucial for achieving a clean energy transition and maintaining competitiveness in the automotive and battery production markets. Thus, NanoBat focuses on four thematic fields:
• Nanotech instrumentation for enhanced imaging of nanoscale surface processes
• Broad-band frequency test methods for studying battery interface layers including calibration, modeling, and data analytics of advanced battery tests.
• Tests in battery production pilot lines and automotive batteries, and evaluation of new battery materials. Increase efficiency in battery production and foster open innovation in the field.
In the first project action, new nanotechnology instrumentation and methods were implemented. Five scanning microscopy techniques were adapted to conduct battery research and investigate the SEI across various dimensions from nano- to millimeter-scale. The research findings were published in nine renowned scientific journals, including Chem Rev., with an impact factor of 72. For example, scanning microwave microscope specifically designed for battery research was constructed and tested in a liquid environment. Scanning electrochemical microscopy (SECM) was employed within an Argon-filled glovebox, utilizing newly developed operating modes, demonstrating the successful development for battery research in liquid. A chip-based nanoscale sensor method was developed and demonstrated with the capability to perform a scan of 200x200 pixels in less than 20 seconds, covering an area of 300um x 1000 um.

In the second project action, advanced broad-band frequency test methods were developed for studying battery interface layers. A metrological calibration method was developed for electrochemical impedance spectroscopy (EIS) and self-discharge measurements (SDM). A standard operating procedure was prepared with the guidance of a national metrology institute. The calibration process was successfully implemented in a large measurement station using test standards, ensuring accurate and reliable measurements. For the first time, an uncertainty analysis was conducted for battery EIS to improve cell classification. A dielectric resonator scanner was designed and calibrated with the aid of electromagnetic simulations to study battery layers. New models were developed specifically for batteries, including FEM of battery cells based on multiphysics and equivalent circuit models. Several journal papers and proceedings were published, demonstrating the application of modeling techniques in connecting nanotechnology and electronic measurements and allowing for a clear assessment of aging in LIBs.

Work on the third project area, advanced materials and pilot lines, included integrating a fast high-voltage quality test for battery separators and virtual quality gates in a pilot-line setting. A data communication link was established between the test device and the pilot line database. These modeling results, along with the corresponding environmental impact assessment, formed the relevant KPIs. Battery materials development encompassed the exploration of graphene anode samples and studies focusing on beyond lithium materials. Research efforts were undertaken to investigate the formation and evolution of electrode interface layers during cycling on Mg-metal, using advanced nanoscale techniques.

In the fourth project subject area, various activities were carried out to assess the environmental impact of efficient battery quality handling. A comprehensive case study was conducted to analyze the reduction of CO2 emissions achieved through the implementation of new in-line test methods. The development of virtual quality gates for end-of-line testing of battery cells was initiated, aiming to enhance quality control processes. To enable high-throughput measurements, a measure station concept was successfully demonstrated. A dedicated measurement setup was created to facilitate testing and cycling of a 7 kWh battery module. An Open Innovation Environment (OIE) website was established, providing access to an open platform tools section. NanoBat-Modeler, an open platform GUI workbench, was developed and made available on the OIE. Standardized characterization and modeling procedures were established and stored on the project's webpage, aligning with EMCC and EMMC guidelines.

Overall, five scientific workshops were organized, attracting over 130 active participants. These workshops served as platforms for renowned experts to share their insights and discuss the progress made in the field. Specific sessions were dedicated to students, where they presented short video presentations showcasing their laboratory work.
Progress beyond the state of the art encompasses three main areas. Firstly, advanced nanoscale imaging tools were developed to study the critical SEI layer, incorporating broad-band frequency spectroscopy. Secondly, new calibration methods were devised for impedance spectroscopy and self-discharge measurement. We demonstrate how electrical impedance calibration and metrological uncertainty analysis enhance cell classification, providing a quantitative assessment with a confidence level. Calibration eliminates systematic errors from impedance measurements, while measurement uncertainty is determined through metrological error propagation, and confidence levels are assigned to cell classification. Thirdly, our OIE offers valuable workflows for the effective implementation of the new methods, contributing to the wider measurement and modeling ecosystem.
Regarding project impact, metrology-grade calibrated in-line impedance spectroscopy has been successfully executed for testing and evaluating forming, aging, and cycling at pilot lines. This implementation includes virtual quality gates, modeling, and data analytics techniques. Ongoing efforts focus on implementing multiplexed testing for module fabrication and cell sorting, leveraging electrode interface layer properties. Fast qualification algorithms that utilize real test data and modeling data are being utilized. NanoBat effectively demonstrated the application of its nanoscience-based impedance models and metrological test methods in pilot-line manufacturing and OEM field tests. Key players in the European battery manufacturing field, such as BMW, SAFT, Infineon, and Atos, actively participated as members of the stakeholder group and collaborated on research and publications.
Connecting Nanotech and EIS measurements