HIGH POWER BATTERIES PROBED BY NEUTRON SCATTERING

Rechargeable Lithium Ion and Metal Hydride batteries show excellent performance in the Hybrid Electric Vehicles offering advantages of delivering high power densities, showing fast charge-discharge performance, long service life and low-temperature operation as well as demonstrating excellent safety features for the Ni-Metal hydride batteries. The focus of the project HIBAT is in performing in operando studies of the phase-structural transformations in the electrodes of the Nickel-Metal Hydride and Li ion batteries as related to the parameters of their charge and discharge with use of neutron scattering. HIBAT is collaboration between Institute for Energy Technology, Norwegian University of Science and Technology and European Spallation Source, and is joining together expertise and complementary efforts of these three institutions with leading groups from Switzerland (Paul Scherrer Institute) and France (Institute of Chemistry of Materials Paris East, CNRS) working in the field and focusing on the development of novel electrode materials for the high power rechargeable batteries. Neutron scattering is a non-destructive tool which allows to study the structure and dynamics of the solid state matter. Deep penetration capability of neutrons into the solid state materials contributes to the development of various unique and powerful tools for the investigations of the materials structure and properties. Here neutron diffraction and neutron radiography (imaging) stand as two complementary techniques to probe the processes at the atomic scale (neutron diffraction) and, furthermore, to assess the performance of the batteries at a macroscopic scale (neutron imaging). Both commercial batteries and custom-made in the IFE and CNRS laboratories electrodes were utilized allowing to control the rates of electrochemical processes during the experiments using neutrons. These experiments showed that the battery performance is controlled by temperature and by the current densities of the processes in electrodes. A "rocking" chair mechanism quantified a transport of Li-ions from the cathode to form lithiated graphite derivatives in the anode of the LIB or hydrogen exchange between the deuterated electrolyte and the metal hydride anode to form the hydrides of the Mg-based (La,Nd,Mg)Ni3 alloys. Several neutron imaging experiments on prismatic lithium ion batteries of various types have been performed at PSI allowing to clearly distinguishing the macroscopic developments in the studied batteries during their charge and discharge. Ten papers were published in international journals based on the results of the project. 5 oral presentations were given at international conferences, including plenary, invited and oral presentations by V.A. Yartys at 14th International Symposium on Metal-Hydrogen Systems. Manchester, 2014; Int. Symp. Materials for Energy Storage and Convertion mESC-IS 2015, Turkey; Int.Conf. on Nanotechnology, Nanomaterials and Thin Films for Energy Applications. Liverpool, UK, 2016; MCARE2016 (Materials Challenges in Alternative and Renewable Energy, April 2016, USA); MH2016 (International Symposium on Metal-Hydrogen Systems. Fundamentals and Applications, August 2016, Switzerland); 14th INTERNATIONAL SYMPOSIUM ON PHYSICS OF MATERIALS (ISPMA 14), Prague, 10.9-15.9.2017 and 2nd International Symposium on Materials for Energy Storage and Conversion mESC-IS 2017, Cappadocia, Turkey. 26-28.09.2017).

Characterization of crystal structures allows understanding of interrelation between physical and chemical properties of the materials, their structure and bonding. Institute for Energy Technology hosts a research reactor JEEP II which is utilized to pro be by neutrons various materials for energy storage. The European Spallation Source is a multi-disciplinary research center based on the world's most powerful neutron source. This new facility will enable new opportunities for research in the fields of m aterials science, energy storage, fundamental chemistry and physics. The present proposal focuses on the development of experimental tools and investigations of the mechanism of transformations in the high performance rechargeable batteries probed by neut ron scattering. Particular emphasis is on the development of the experimental neutron cells adopted to examine performance of the rechargeable batteries by use of neutron diffraction. Experiments will be performed in situ in real conditions, i.e. in opera ndo. The high resolution powder diffractometers utilizing high flux neutron sources will enable fast data collection for the electrodes which are not possible to probe with X-rays. It is aimed to perform time resolved measurements probing phase-structura l transformations proceeding at fast rates, in just a few minutes. Neutron imaging will be also utilized to characterize dynamic processes in the operating batteries. Two different types of the rechargeable batteries will be in focus, metal hydride and Li -ion ones. Use of neutron scattering will allow locating light atoms (H and Li) and to characterize kinetics and mechanism of the processes of charge and discharge of the electrodes at high current densities. The work will contribute to the development of the advanced batteries having high discharge capacity and offering improved performance in demand for the advanced autonomous energy systems, electric vehicles and grid regulation.