New hydrogen absorbing alloys overcoming the availability of critical materials – MALHYCE

Despite the strong development of the high specific energy lithium batteries, Nickel-Metal Hydride (Ni-MH) battery market remains attractive for applications requiring high energy density, high life duration, no safety issues and reasonable costs, such as emergency lighting units and photovoltaic (PV) electricity storage. For all of these expanding markets, increasing the life duration is an essential technical and business objective.
The project MALHYCE aims to improve the Ni-MH technology by developing a new generation of advanced hydrogen absorbing materials adapted to industrial applications requiring very long calendar life.
The overall target of the project is to provide industrial Ni-MH batteries with a life duration increased by at least 25% compared to the current generation, while keeping all other technical characteristics unaffected and while overcoming rare earths availability and cost problems. Concerning the PV electricity storage market, life duration would be extended to 15 years at 20°C, far beyond all present products.
This goal requires the development and optimization of a new generation of (R,Mg)Nix type hydrogen absorbing materials with a specific capacity greater than 350mAh/g (i.e. 15 to 20% more than the current hydrogen absorbing material generation), a corrosion rate and a charge acceptance similar to those of existing LaNi5 type alloys.
The program involves also an economical challenge, as the development of this new generation of hydrogen absorbing alloys faces nowadays the problem of scarcity and cost of raw materials, especially in the case of the rare earths. Also rare earth elements such as samarium, gadolinium, and yttrium having a low sensitivity to cost and availability, will be evaluated in full or partial substitution of the rare earth R group. Such rare earths elements have been weakly studied in the field of alloys for electrochemical application and are not commercially used at present time for Ni-MH technology. A particular attention will be focused on the influence of these three rare earths on the nature of the phases, the corrosion rate, and the charge acceptance of the alloys.
In order to improve charge kinetics, a detailed study of the interfacial hydrogen absoption / desorption mechanism and a thorough characterization of the alloy surface will be implemented. For this purpose, the program aims in particular to characterize the (RMg)Nix surface alloy state by transmission electron microscopy and by in situ Raman spectroscopy.
Finally, this project will include a task concerning the definition and the optimization of long calendar life Ni-MH prototype cells, based on the use of the new (RMg)Nix type alloys. A first step will be focused on the improvement of the battery design in order to maximize life duration while keeping all other performances at the same level. Secondly, the best suited alloy compositions with respect to the specifications will be evaluated in the new designed Ni-MH prototype cells.