Manganese–carbon (Mn–C) interaction to host Al3+-ions in a β-MnO2–MWCNT composite cathode in rechargeable aluminium ion batteries

Abstract

Rechargeable aluminium ion batteries (AIBs) are one of the potential metal battery alternatives to Li-ion batteries. A perfect pair of cathode and electrolyte is a key factor in developing a grid-scale Al ion battery. In this context, we evaluated a prototypical MWCNT and β-MnO₂-20% composite (MWCNT/β-MnO₂), in which β-MnO₂ nanoparticles were grown on the surface of the MWCNT matrix by an ultra-sonication method followed by calcination at 400 °C and tested as a cathode system. The as-synthesized MWCNT/β-MnO₂-20% cathode material was completely characterized by techniques such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS) and thermo gravimetric analysis (TGA) to assess its composition and morphology. Its electrochemical performance was evaluated with the aid of various electroanalytical techniques, such as cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS). MWCNT/β-MnO₂-20% as a cathode system in AlCl₃/Et₃NHCl ionic liquid electrolyte showed a current density of 100 mA g⁻¹ and a discharge capacity of 269 mA h g⁻¹, and the resultant aluminium storage was around 60 cycles with a coulombic efficiency of 90%. Interestingly, this superior rate capability of the composite is due to the interdependent interaction between the β-MnO₂ particles and MWCNTs as revealed by XPS, FT-IR, XRD and EDS techniques, which provided evidence for an intercalation and de-intercalation of the AlCl₄⁻ ions into the cathode material during charge–discharge.