Graphitic multi-walled carbon nanotube cathodes for rechargeable Al-ion batteries with well-defined discharge plateaus

One-dimensional multi-walled carbon nanotubes (MWCNTs) are promising electrode materials for rechargeable batteries. This paper reports that graphitic MWCNT (G-MWCNT) can serve as a cathode material for a rechargeable Al-ion battery and exhibits well-defined discharging plateaus at around 2 V. AlCl₄⁻intercalates and de-intercalates into/from the graphitic MWCNT rather than simply adsorbing on the surfaces. Hence, the Al||G-MWCNT cell exhibits good electrochemical performance with a specific capacity of 64 mA h g⁻¹ at a current density of 200 mA g⁻¹. The discharge capacity is almost unattenuated and maintained at about 58 mA h g⁻¹ (Coulombic efficiency: 99.5%) after 1000 charge/discharge cycles, which indicates that the Al||G-MWCNT cell has excellent cycling stability. In addition, the low self-discharging rate (~0.4% over 72 h of rest) suggests that the intercalated AlCl₄⁻ is stable in the spaces between the graphene layers of G-MWCNT. This work reveals that Al||G-MWCNT cells exhibit diffusion-controlled faradaic process rather than capacitor behavior, which may boost the development of aluminum batteries.