Thermodynamics-Guided Screening and Mechanistic Insights for Advanced Cathodes Toward High-Energy-Density...

Achieving high energy density remains the most critical challenge for rechargeable aluminum batteries (RABs), especially for high-capacity transition metal-based cathodes suffering from relatively low working voltage in acidic ionic liquid (IL) electrolytes. Here, we propose a thermodynamics-guided screening paradigm, in which the theoretical redox potentials are derived and calculated from the Nernst equation and Gibbs free energy (ΔG), thereby effectively predicting and screening cathodes with high working voltage. Based on this, we synthesize Co₃(PO₄)₂ with a distinct crystal structure, which is further employed as a model cathode to validate the feasibility of the abovementioned theoretical screening strategy. Electrochemical tests demonstrate that the Al||Co₃(PO₄)₂ cell operates at a range of 1.20-1.50 V with a specific capacity of 198.01 mAh g^{- 1} and an ultra-high energy density of 247.4 Wh kg^{- 1}, which is in excellent agreement with the thermodynamic predictions. Importantly, the cell could stably cycle for over 14 500 cycles with almost negligible capacity decay. Mechanistic analyses indicate that redox mechanism mainly involves Al³⁺ adsorption/desorption and shallow intercalation/de-intercalation processes. On balance, this simple and universal strategy offers an insightful idea for enhancing the working voltage of cathodes, while providing clear design guidelines for the development of high-energy-density energy storage systems.