The Rolling of the Strip Metal-Hydride Electrodes

Abstract

There are some methods of the continuous fabrication of the metal hydride electrodes on the base of powders of AB₅ alloys. The first method involves the mixing of the powder with Teflon suspension and rolling the mixture with net-like nickel collector. The dependence of the strips thickness, porosity and electrochemical properties on the rolling conditions have been investigated.

The second method, the sandwich-type method, based on the preliminar mixture forming into the sheets and following rolling of one or two such sheets against a net-like current collector. The electrodes were fabricated with thickness from 0,2 to 1,0 mm. The porosity of the electrodes was 15–25 % and could be regulated. The specific electrochemical capacity of worked out electrodes was observed to be 250 mAh/g at the alloy capacity 280 mAh/g. Strip negative electrode is the composite material which is assembling from some layers. Electrodes are based on a metallic skeleton which is a conductive core too (Fig.1). Metalhydride powder alloy AB₅-type is mixed with Teflon PTFE suspension until a deformable, cohesive, “putty like” mixed material is obtained. A nickel grid was placed on a flat surface and an active powder rolled so that a thin layer was exuded through the interstices of the grid. A sandwich-type method is used, comprising the steps of blending the hydrogen storage alloy powder with PTFE, forming the mixture into a sheet and rolling one or two such sheets against a net like current collector.

Investigation of the mixture densification from the powder LaNi_2,5Co₂,4Al_0,1 and PTFE suspension under pressing in die of 15mm diameter have been carried out. Powder apparent density before of the suspension treatment was equal 3,69 g/cm³ and tap density — 4,45g/cm³. After treatment these values were equal 1,56 and 2,18g/cm³. Specific density of the mixed matter from powder alloy and 5% PTFE is equal 7,25g/cm³. Results of densification attribution of the such mixture under pressing are presented at the Table 1.