d-Orbital Induced Electronic Structure Reconfiguration toward Manipulating Electron Transfer Pathways of Metallo-Porphyrin for Enhanced AlCl Storage.

The positive electrodes of non-aqueous aluminum ion batteries (AIBs) frequently encounter significant issues, for instance, low capacity in graphite (mechanism: anion de/intercalation and large electrode deformation induced) and poor stability in inorganic positive electrodes (mechanism: multi-electron redox reaction and dissolution of active materials induced). Here, metallo-porphyrin compounds (employed Fe, Co, Ni, Cu, and Zn as the ion centers) are introduced to effectively enhance both the cycling stability and reversible capacity due to the formation of stable conjugated metal-organic coordination and presence of axially coordinated active sites, respectively. With the regulation of electronic energy levels, the d-orbitals in the redox reactions and electron transfer pathways can be rearranged. The 5,10,15,20-tetraphenyl-21H,23H-porphine nickle(II) (NiTPP) presents the highest specific capacity (177.1 mAh g), with an increment of 32.1% and 77.1% in comparison with the capacities of HTPP and graphite, respectively, which offers a new route for developing high-capacity positive electrodes for stable AIBs.