Active cyano groups to coordinate AlCl₂⁺ cation for rechargeable aluminum batteries

Rechargeable aluminum batteries, owing to the abundant Al resources and high safety guarantee, have been exploited as the ideal power sources for large-scale energy storage. However, the application of aluminum batteries is still restricted by the unsatisfactory positive electrodes due to low capacity, electrode variation or poor cycle stability of inorganic materials. As an alternative route for addressing the critical issues, multi-cyano organic molecules are proposed as the positive electrode materials for stable rechargeable aluminum batteries. With the first-principle calculation of the electron distribution, molecular energy levels and theoretical specific capacity, the results suggest that the electron-deficient cyano groups in organic molecules can reversibly coordinate/dissociate with positively charged Al-complex ions (i.e. AlCl₂⁺). According to the molecule design and experiment results, tetracyanoquinodimethane (TCNQ) with high conductivity is identified as the optimized cyano-organic positive electrode material. The as-assembled cell delivers a high specific capacity of 180 mAh g⁻¹ at first cycle and a discharge plateau ~1.6 V, along with long-term operation beyond 2000 cycles and coulombic efficiency of ~100%. The design principle here opens a new platform to utilize stable cyano-organic molecules as positive electrode materials for high-energy-density aluminum batteries, offering opportunities to design and exploit high-performance rechargeable Al-organic batteries.