Estimating the size distribution of anode and cathode activating agents in the crushed products of nickel metal hydride batteries from hybrid vehicles and its classification

Nickel metal hydride batteries of hybrid vehicles contain Co and rare earth elements in the anode and cathode activating agents as well as in the main electrode component, Ni. The cathode electrodes comprise a porous Ni plate (cathode substrate) with nickel hydroxide as the cathode activating agent and the anode electrodes consist of a hydrogen storage alloy powder as the anode activating agent on a metal mesh substrate.A direct smelting method has been used to recover Ni from waste batteries, but the Co and rare earth elements are difficult to extract by this conventional method. To recycle Co and rare earth elements, physical pretreatment is necessary to separate the anode and cathode compounds before smelting. This study investigated the separation of anode and cathode activating agents in the < 0.075 mm fraction of crushed nickel metal hydride batteries using a cyclone and the anode activating agent was concentrated in the underflow product. After crushing the waste batteries a mixture of cathode and anode activating agents is recovered as fines, and a simple and fast size distribution measurement method for each activating agent is desirable to evaluate the physical separation results and improve the separation efficiency. The results show that further size classification of the < 0.075 mm fraction is effective to concentrate the anode activating agent for cylindrical type batteries.

Research Highlights►Nickel metal hydride batteries contain Ni and rare earth elements. ►Recycling treatment of fine fraction of crushed waste batteries was investigated. ►Separation of anode and cathode activating agents using cyclone was carried out. ►Size distribution of each activating was measured using BSE images.