Structure and electrochemical properties of ball-milled Co-carbon nanotube composites as negative electrode material of alkaline rechargeable batteries

A series of cobalt-carbon nanotube (CNT) composites is synthesized by direct ball-milling of Co and CNT powders with different Co/CNT weight ratios. The microstructure, morphology and chemical state of the ball-milled Co-CNT composites are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). It is found that metallic Co nanoparticles of 50–100 nm in size are highly dispersed on the inactive CNT matrix after ball-milling. The electrochemical performance of Co-CNT composites as negative electrode material of alkaline rechargeable batteries is investigated by galvanostatic charge–discharge, linear polarization and cyclic voltammetry (CV) techniques. The results show that the Co-CNT composite (weight ratio 5/1, BM 10 h) displays the optimized electrochemical performance, including discharge capacity and cycle stability. The reversible faradaic reaction between Co and Co(OH)2 is dominant for ball-milled Co-CNT composites.

Research highlights
► Co-CNTs were used as negative electrode materials of alkaline rechargeable batteries.
► They show high discharge capacity, excellent retention rate and rate capability.
► Their electrochemical performances are much better than pure Co electrode.
► The discharge capacity is mainly due to the redox reaction between Co and Co(OH)2.