Dimensionality of MnO2 cathodes as a key factor governing kinetics in Alumninium-ion batteries

Along with the non-stopping technological expansion, modern societies are in need of a constant energetic supply. Equipment with a stationary and non-stationary objective must have battery or capacitor devices adapted to its requirements, where energy storage has to be efficient. The Lithium-ion technology remains the most demanded system. However, the high cost and limited amount of lithium available has led to research for alternative systems: Na, K, Mg, Al, Ca and Zn [1]. One of the most promising alternative among next-generation energy storage system is the aluminium-ion battery (AIB) which has a higher theoretical volumetric (8046 mA h cm^-3) and gravimetric (2980 mA h g^-1) capacity, but also due to its low cost, sustainability and low flammability [2,3].

Electrochemical activity of different MnO₂ phases as electrodes of aluminium-ion batteries (AIBs) is studied. For this purpose, different simple synthesis routes have been carried out to obtain on the one hand, MnO₂ rod-like with tunnelled structure (α-MnO₂) and on the other MnO₂ hexagonal micro-pellets with lamellar structure (δ-MnO₂). α-MnO₂ showed an outstanding capacity (Q) of 120 mA h g^-1 at current densities of 100 mA g^-1, which remains stable after 100 cycles with efficiencies over 90%.  δ-MnO₂ showed a good capacity of 80 mA h g^-1 at current densities of 50 mA g^-1 after 50 cycles and 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. Further cyclic voltammetry (CV) measurements at different rates allowed a kinetic study of the diffusive and capacitive-controlled mechanisms. The results were interpreted concerning the influence of dimensionality (1D and 2D) of the MnO₂ phases obtained.

Audience take-away:

• New battery technologies
• Learn about rechargeable aluminium batteries
• Understand the importance of the chemical and physical structure of materials in their electrochemical behaviour.