Helmholtz-Zentrum Geesthacht, 2017-10-19
http://www.hzg.de/056061/index_0056061.html.en

"Novel Li-N-Transition metal hydride based materials for electrodes for electrochemical energy storage"

Nicola Berti / Early Stage Researcher at the Institut de Chimie et des Matériaux de Paris Est, Thiais, France

Working title of thesis

Novel Li-N-Transition metal hydride based materials for electrodes for electrochemical energy storage.

Objectives

Nowadays, Li-ion batteries are the most used rechargeable batteries available. Although the performance of these batteries has been improved considerably in the last decades, there is a common agreement that this technology is now close to its maximum efficiency unless new materials with higher storage capacity are found.

Recently it has been demonstrated, first by theoretical calculations and then by experimental studies, that many metal hydrides can react with lithium according to the general equation:

MHx + xLi+ + xe- M + xLiH

This conversion reaction can provide higher capacity than common graphite anodes (for instance, 2000 mAh/g for MgH2 vs. 370 mAh/g for graphite) with low polarization. However, the commercial use of these compounds as electrodes for Li-ion batteries has been hindered to date by their short cycle life and sluggish kinetics at room temperature.

Our project is focused on the synthesis and characterization of new Lithium-Nitrogen-Metal-Hydrogen (Li-N-M-H) based materials as negative electrodes for Li-ion batteries. The first aim is to understand the reaction mechanisms between metal hydrides and lithium and the processes that limit the reversibility during extended charge-discharge cycles. This understanding will guide us to test and choice suitable hydride materials from the Li-N-M-H system for this application. Furthermore, integration with the other components of the battery, such as new kind of electrolytes, will be taken into account. At the latest step, cost reduction and industrial production for distribution on global market will be considered. 

 

Tasks and methodology

The study will start with simple systems such as MgH2, TiH2 and MgH2-TiH2 composites in powder state. To ensure their reactivity, they will be prepared in nanocrystalline state by means of reactive ball milling (RBM). For a better understanding of reaction mechanisms, studies will be also performed on thin films prepared by electron beam deposition (EBD). Later, studies will be performed on Li-N-M-H imide/amide samples. The crystal structure of these materials will be studied by X-ray diffraction (XRD) and analysed by Rietveld refinement. Their microstructure will be examined by means of scanning electron microscope (SEM) and transmission electron microscope (TEM). Their hydrogenation properties through the measurement of Pressure-Composition Isotherms (PCI) using the Sieverts’ method, thermal desorption spectroscopy (TDS) and high pressure differential scanning calorimetry (HPDSC). Their electrochemical properties will be assessed by galvanostatic cycling, galvanostatic intermittent titration technique (GITT), cycling voltammetry and electrical impedance spectroscopy (EIS).

Short CV

I was born near Vicenza (Italy) and after my diploma in Biology at high school ITAS S.B. Boscardin I studied at University of Padua where I graduated in Material Science for both my Bachelor’s and Master’s Degree.
I became interested in energy storage during my Master studies and as a result I worked for several months as an intern with Professor A. Maddalena and the Hydrogen Group of Padua at the Department of Industrial Engineering for my Master’s Degree thesis.
My work was focused on synthesis and study of new materials for hydrogen storage in solid state for mobile applications. In a homemade reactor, milled magnesium powder was deposited within different carbon scaffolds (mechanically and chemically activated MWCNT and activated charcoal) by means of physical vapour deposition. Their properties were then analysed using techniques such as BET, DFT, XRD and Sievert measurements.
The nanoconfinement of magnesium in a nanostructure has led to a substantial decrease in the hydrogen desorption temperature compared to bulk magnesium.