Improved NiMH performance by a surface treatment that creates magnetic Ni-clusters

• A method to create more active reaction surfaces for a MH-anode is presented.
• Nickel containing clusters are created in the surface and their sizes correlate with properties.
• Their sizes can be estimated by the magnetic response.
• Electrochemical performance can thus be estimated by the magnetic response.

A surface treatment method has been developed to activate the surface of an AB5 type (La20 Ce7 Pr1 Nd4 Al2 Mn5 Co6 Ni55) alloy. In the process the surface is covered with a porous surface layer containing needle shaped rare earth hydroxides after etching by a potassium hydroxide solution. TEM studies show in addition the presence of a denser surface oxide layer with embedded Ni containing clusters covering the bulk alloy. The magnetic properties of the alloy powders change with the surface treatment. In addition to a paramagnetic component of the bulk alloy, surface treated alloy also displays superparamagnetic and ferromagnetic properties. In electrochemical half-cell tests, the alloy shows better high-rate dischargeability with increasing presence of magnetic clusters in the metal hydride particles surface.