Facile synthesis of manganese oxide/aligned carbon nanotubes over aluminium foil as 3D binder free cathodes for lithium ion batteries†
Lithium ion batteries have attracted a lot of attention due to their high energy density, but they have relatively lower power density and poorer cyclic stability compared with supercapacitors. Manganese oxide is a promising electrode material for lithium ion batteries due to its low cost, low toxicity, high theoretical capacity, and wide availability. However, it suffers from serious capacity fading which impedes its commercial application. In this work, aligned carbon nanotubes (ACNTs) were grown directly over Al foil as 3D current collectors and then manganese oxide thin film was coated over ACNTs through a spontaneous reduction of potassium permanganate. The obtained 3D manganese oxide/ACNT coaxial nanotube arrays on Al foils provide remarkable advantages such as the large surface area of the 3D thin manganese oxide layer, the very low electric resistance of the electrode, excellent lithium ion diffusion in the manganese oxide layer and in the channel between the tubes, and excellent elastic properties to tolerate the large volume changes during charge and discharge. As a result, a remarkable improvement of rate capability and stability of the lithium ion batteries was achieved. The 3D thin film electrodes can deliver a capacity of 308 mA h g−1 at 0.1 C which is identical to the theoretical capacity of 95 mA h g−1 at 20 C and maintain a capacity of 133 mA h g−1 after 100 cycles at 1 C. The continuous growth of a solid electrolyte interface (SEI) layer due to trace amounts of water remaining in the manganese oxide layers has been identified as the main cause of the capacity fading. The stability was improved but the initial capacity decreased with increasing annealing temperature in the inert gas.