Optimization of metal hydride anodes and LiBH4-based electrolytes for all-solid-state lithium ion batteries

Dr Abdelouahab El Kharbachi
Institute for Energy Technology, Norway & Helmholtz Institute Ulm for Electrochemical Energy Storage, Germany.

Magnesium hydride (MgH2) has been demonstrated to be a candidate for conversion-type anode for Li-ion batteries [1]. In fact, this material features high theoretical capacity 2037 mAh.g-1, compared to graphite-anode, and low charge-discharge polarization. However, the reversible capacity is still a challenge owing to the poor conductivity of the involved entities (MgH2/LiH), along with compatibility issues with carbonate-based liquid electrolytes [2]. On the other hand, LiBH4 solid electrolyte has been first demonstrated in all-solid-state Li-ion battery in the presence of MgH2 anode [3], in which the enhanced mobility of the Li+ ions and H exchanges play a key role during the electrochemical cycling. Accordingly, we will present the mechanistic properties of MgH2 anode as function of milling conditions, particle size and cyclability. The effect of an electrochemically “active” oxide such as CoO on the cycling performance of MgH2 anode using LiBH4 solid electrolyte at 120°C (75MgH2·25CoO, 1376 mAh.g-1) will be addressed and discussed based on the XPS data.

The second part of this talk will deal with the optimization of the ionic conductivity of LiBH4 based electrolytes. In fact, the LiBH4-Li2S-P2S5 system has attracted attention owing to its interesting ionic properties for solid state battery electrolytes [4,5]. LiBH4 is a good Li-ion conductor only above its solid state phase transition temperature (Ttr ~110°C). The high-T phase can be stabilized by partly substituting BH4- with halides, e.g. Li(BH4)0.75I0.25, thus preserving high ionic conductivity on cooling down to RT. Hereby, we will show our approach of investigation of the properties of the Li(BH4)1-yXy (X = Cl, Br, I) phases when embedded in a 0.75Li2S·0.25P2S5 amorphous matrix for application in all-solid-state lithium batteries. The mixed systems were prepared by ball-milling and annealing procedures and their ionic conductivities were studied in a wide composition range by varying the weight ratio. The study is supplemented by electrochemical stability (I-E) measurements, vibrational spectroscopy (FTIR/Raman), DFT calculations and operando X-ray diffraction during battery cycling.

Authors
A. El Kharbachi*,a,b, M.H. Sørbya, B.C. Haubacka
(a) Institute for Energy Technology (IFE), P.O. Box 40, NO-2027 Kjeller, Norway
(b) Helmholtz Institute Ulm for Electrochemical Energy Storage (HIU), Helmholtzstr. 11, D-89081 Ulm, Germany.

Acknowledgements
This work received financial support from the Research Council of Norway under the program EnergiX, Project no. 244054, LiMBAT – “Metal hydrides for Li-ion battery anodes”. We acknowledge the skillful assistance from the staff of SNBL at ESRF, Grenoble, France.

References:
[1] Y. Oumellal, A. Rougier, G.A. Nazri, J.M. Tarascon, L. Aymard, Nat. Mater. 7 (2008) (11) 916.
[2] A. El Kharbachi, Y. Hu, M.H. Sørby, P.E. Vullum, J.P. Mæhlen, H. Fjellvåg, B.C. Hauback, The Journal of Physical Chemistry C 122 (2018) (16) 8750.
[3] L. Zeng, K. Kawahito, S. Ikeda, T. Ichikawa, H. Miyaoka, Y. Kojima, Chem. Commun. 51 (2015) (48) 9773.
[4] A. Unemoto, H. Wu, T.J. Udovic, M. Matsuo, T. Ikeshoji, S.-i. Orimo, Chem. Commun. 52 (2016) (3) 564.
[5] A. El Kharbachi, Y. Hu, K. Yoshida, P. Vajeeston, S. Kim, M.H. Sørby, S.-i. Orimo, H. Fjellvåg, B.C. Hauback, Electrochim. Acta 278 (2018) 332.

Biography

Dr El Kharbachi is a research scientist in the field of batteries at KIT/Helmholtz Institute Ulm (HIU) Germany. From 2015 to 2018 as a researcher, he led the Li-ion battery activities based on hydrides at the Institute for Energy Technology, Norway.
Abdelouahab graduated (DEA) from the University of Liège (Belgium) in non-aqueous electrochemistry and completed a PhD research studies in Materials Science and Engineering from Grenoble Institute of Technology (Grenoble-INP) in 2011. He has served as a research associate in France at both the CEA-Saclay (for ITER project) and LRCS Lab-Amiens (Laboratoire de Réactivité et Chimie des Solides). He was behind the discovery of the stability of tritium incorporated in nanodiamonds’ crystal lattice for biomedical applications. In 2018, he published 4 first-author publications related to his experiments on the implication of hydrides in Li-ion batteries.