Abstract
A series of AB5-type alloys with different particle and grain size were characterized electrochemically as materials for negative electrodes in Ni-MH batteries. Besides, the effect of alloy composition on the discharge capacity and cycle life was studied. Ball milling under hydrogen atmosphere was applied to reduce significantly the grain size of the alloys and to avoid the initial activation at the electrochemical charge/discharge cycling. The alloy morphology and microstructure after different mechanical treatments were characterized by XRD and SEM. The best effect in respect of discharge capacity and cycle life was achieved for the materials milled for 5 h under hydrogen atmosphere.
Highlights
Over decades, materials for negative electrodes in Ni-MH batteries are one of the most investigated topics in material science, the main reason being the growing need for new sources of energy and the few alternatives of the fossil fuels [1,2,3].Among all types of hydrogen storage alloys for Ni-MH battery application, AB5 type are of great importance, being even commercially implemented in rechargeable batteries for portable power tools and hybrid electrical vehicles (HEVs) due to their comparatively high energy density and low level of environmental toxicity [4,5,6]
A large number of investigation during the last decade have shown that substitution of La by Mm (Ce-rich or La-rich mish metal) and partial substitution of Ni by Co, Mn, Al, Cr, etc. lead to significant improvement of the electrochemical characteristics of LaNi5 and reduce the price of the final product [8,9,10]
There is no data if such treatment affects the electrochemical characteristics of the AB5-TM composites and how it depends on the milling conditions
Summary
Materials for negative electrodes in Ni-MH batteries are one of the most investigated topics in material science, the main reason being the growing need for new sources of energy and the few alternatives of the fossil fuels [1,2,3].Among all types of hydrogen storage alloys for Ni-MH battery application, AB5 type are of great importance, being even commercially implemented in rechargeable batteries for portable power tools and hybrid electrical vehicles (HEVs) due to their comparatively high energy density and low level of environmental toxicity [4,5,6]. The main drawback and limiting factor for the commercial application of LaNi5 alloy is its low theoretical electrochemical capacity of 372 mAh/g and high cost [7]. The AB5 alloys used in commercial Ni-MH batteries have typical composition of MmNi3.55Co0.75Mn0.4Al0.3 [11]. Another approach for improvement of the electrode characteristics is mechanical milling or alloying for the preparation of nanocrystalline AB5 alloys and AB5-TM (Transitional Metal) composites. The microstructure of the alloys and composites synthesized using mechanical milling strongly depends on the conditions used—milling time and velocity, gas atmosphere, etc. There is no data if such treatment affects the electrochemical characteristics of the AB5-TM composites and how it depends on the milling conditions
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