Berlin 2005 – scientific programme

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M: Metallphysik

M 32: Poster TU B (Symposium Tomographic Methods in Materials Research M-32.32-55)

M 32.6: Poster

Monday, March 7, 2005, 14:30–16:30, Poster TU B

Mg-Ni-Y alloys as new negative electrode materials for Ni-MH rechargeable batteries — •Bogdan Khorkounov, Angelika Teresiak, Margitta Uhlemann, Annett Gebert, and Ludwig Schultz — IFW Dresden, Postfach 270116, 01171 Dresden

Mg₂Ni has a large theoretical discharge capacity, but slow hydrogen sorption kinetics and poor corrosion resistance. Microstructural refinement and further alloying are needed. Mg-Ni-Y alloys with amorphous/nanocrystalline structure are investigated regarding their hydrogenation behaviour and cyclic electrode performance. Mg_63−xNi₃₀Y_x-alloys absorb electrochemically up to 2,2 wt. % [H]. The thermal behaviour of Mg-Y-Ni ribbons in the as quenched and hydrogen-charged state was studied by in situ XRD. Crystallisation starts at 423 K with formation of Mg₂(Ni,Y), metastabile Mg₆Ni, Mg. Samples with [H] < 0.6 wt. % show the same phase formation during heat treatment. The formation of Mg₆Ni is inhibited by increasing [H]. Mg₆Ni decomposes at > 523 K into Mg, Mg₂Ni. [H] = 1.42 wt. % leads to the formation of the fcc complex compound Mg₂NiH₄ at 523 K under a hydrogen atmosphere of 0.5 MPa besides Mg₂NiH_0.2−0.3, YH₂, YH₃, MgH₂. Y improves the corrosion and cycle life stability of Mg₂Ni-based electrodes, but decreases the discharge capacity. The effects of alloy composition, microstructure and electrode preparation on the discharge characteristics are discussed.