Fluorination mechanism and its effects on the electrochemical properties of metal hydrides

Fluorination of hydriding alloys has been found effective for improving durability and initial discharge characteristics of hydride electrodes in Ni-MH rechargeable batteries. However, it has also been found that it decreases the discharge capacity because of the fluoride formed on the surface which decreases the electrical conductivity of the electrode. A more advanced technique has been developed in this laboratory to implant metallic Ni in the fluoride layer to form a functionally graded surface layer. The proposed fluorination technique considerably improves the durability and initial activation characteristics of AB(5)-types of hydride, electrodes and also the initial activation characteristics of AB(2) electrodes. The fluorination was found effective for removing the oxide layer which acts as an impedance to electrochemical hydrogen uptake.