Aluminium-ion battery

Aluminium-ion batteries (AIB) are a class of rechargeable battery in which aluminium ions serve as charge carriers. Aluminium can exchange three electrons per ion. This means that insertion of one Al³⁺ is equivalent to three Li⁺ ions. Thus, since the ionic radii of Al³⁺ (0.54 Å) and Li⁺ (0.76 Å) are similar, significantly higher numbers of electrons and Al³⁺ ions can be accepted by cathodes with little damage. Al has 50 times (23.5 megawatt-hours m^-3) the energy density of Li-ion batteries and is even higher than coal.

The trivalent charge carrier, Al³⁺ is both the advantage and disadvantage of this battery. While transferring 3 units of charge by one ion significantly increases the energy storage capacity, the electrostatic intercalation of the electrodes with a trivalent cation is too strong for well-defined electrochemical behaviour. Theoretically, the gravimetric capacity of Al-ion batteries is 2980 mAh/g while its volumetric capacity would be 8046 mAh/ml for the dissolution of Al to Al³⁺. In reality, however, the redox reaction is more complicated and involves other reactants such as AlCl₄⁻. When this is taken into account, theoretical gravimetric capacity becomes 67 mAh/g.

Rechargeable aluminium-based batteries offer the possibilities of low cost and low flammability, together with high capacity. The inertness and ease of handling of aluminium in an ambient environment offer safety improvements compared with Li-ion batteries. Al-ion batteries can be smaller and may also have more charge-discharge cycles. Thus, Al-ion batteries have the potential to replace Li-ion batteries.