Electrochemical Performance of Tunnelled and Layered MnO2 Electrodes in Aluminium-Ion Batteries: A Matter of Dimensionality

Electrochemical activity of different MnO 2 phases as electrodes of aluminium-ion batteries (AIBs) is studied. For this purpose, different simple synthesis routes have been carried out to obtain different structures and morphologies: rod-like with tunnelled structure ( α -MnO 2 ) and hexagonal micro-pellets with lamellar structure ( δ -MnO 2 ). α -MnO 2 showed an outstanding capacity (Q) of 120 mA h g −1 at current densities of 100 mA g −1 , which remained stable after 100 cycles with efficiencies over 90%. δ -MnO 2 showed a good Q of 80 mA h g −1 at current densities of 50 mA g −1 after 50 cycles with efficiencies over 95%. Moreover, cyclic voltammetry (CV) measurements at different rates allowed for a better understanding of the electrochemical behaviour and revealed the contribution relation of diffusive and capacitive-controlled mechanisms in the corresponding AIB system. Besides, cyclic voltammetry (CV) measurements at different rates allowed a kinetic study of the diffusive and capacitive-controlled mechanisms. Conclusions were obtained regarding the dimensionality of α -MnO 2 (1D) and δ -MnO 2 (2D) and their electrochemical behaviour in AIBs−1