Metal hydride-based anodes are particularly interesting owing to their high capacity and low volume expansion. It has been demonstrated that MgH2 could be a candidate for conversion-type anode for Li-ion batteries . In fact, this material features high theoretical capacity 2037 mAh.g-1, compared to graphite-anode 372 mAh.g-1, and low charge-discharge polarization, being considered as an indicator of lifespan [2,8]. However, its application as anode is still a challenge owing to capacity fading after several cycles . MgH2 can interact with 2Li by undergoing a conversion reaction leading to the formation of 2LiH and Mg. Commercial MgH2 (particle size 25-100 µm) has shown poor electrochemical activity and practically no discharge capacity. Even with the addition of carbon black, this material loses its charge capacity after one discharge. However, the poor electric conductivity of MgH2has to be taken in consideration. Furthermore, the electrode formulation (shape, sampling and additives) can influence the cycling performance i.e. discharge/charge capacity and overvoltage-hysteresis [8-10]. Hence, design of representative electrodes with a modulated particle size is highly desirable for the understanding of the down capacity.
A systematic investigation of the morphology – property relation of MgH2 anode for Li-ion batteries is reported in this work. In particular, the aim is to present a comprehensive study of the contribution of the structural morphology to the electrochemical cycling of the tape-casted electrodes (~26µm thick) prepared from ball-milled MgH2. Samples with different particle size and microstructure were obtained by mechanical ball-milling in various conditions in both inert (Ar) and reducing atmospheres (H2) using different milling devices and cryo-milling. The discharge/charge electrochemical curves are discussed according to the ball-milling-induced structural morphology changes revealed by PXD and TEM analysis. New electrochemical impedance spectroscopy (EIS) measurements on the morphologically reproduced hydride anodes before and after battery tests are presented as function particle size, state of charge and cycle number. Advances on the use of EIS for in-situcharacterization of conversion-type anodes are also discussed.
This work is financially supported by 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.
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