Binder-Free VO Cathode for High Energy Density Rechargeable Aluminum-Ion Batteries.

Nowadays, research on electrochemical storage systems moves into the direction of post-lithium-ion batteries, such as aluminum-ion batteries, and the exploration of suitable materials for such batteries. Vanadium pentoxide (VO) is one of the most promising host materials for the intercalation of multivalent ions. Here, we report on the fabrication of a binder-free and self-supporting VO micrometer-thick paper-like electrode material and its use as the cathode for rechargeable aluminum-ion batteries. The electrical conductivity of the cathode was significantly improved by a novel in-situ and self-limiting copper migration approach into the VO structure. This process takes advantage of the dissolution of Cu by the ionic liquid-based electrolyte, as well as the presence of two different accommodation sites in the nanostructured VO available for aluminum-ions and the migrated Cu. Furthermore, the advanced nanostructured cathode delivered a specific discharge capacity of up to ~170 mAh g and the reversible intercalation of Al for more than 500 cycles with a high Coulomb efficiency reaching nearly 100%. The binder-free concept results in an energy density of 74 Wh kg, which shows improved energy density in comparison to the so far published VO-based cathodes. Our results provide valuable insights for the future design and development of novel binder-free and self-supporting electrodes for rechargeable multivalent metal-ion batteries associating a high energy density, cycling stability, safety and low cost.