Dichalcogenide Electronegativity Engineering Enables Low-Redox-Potential Organic Anodes for High-Performance Calcium-Ion Batteries.

Organic anodes for calcium-ion batteries (CIBs) generally rely on extended conjugated structures to host high-density redox couples for enhanced capacity. However, this design often lowers frontier molecular orbital energies, resulting in undesirably high redox potentials (> -0.6 V) that compromise cell voltages. Here we propose a dichalcogenide electronegativity engineering by introducing a family of diphenyl dichalcogen compounds (Ph-2S, Ph-2Se, and Ph-2Te) featuring dual sulfide, selenide, telluride motifs, as high-performance CIB anodes. The decreasing electronegativity along dichalcogenide bonds (S─S > Se─Se > Te─Te) progressively elevates the lowest unoccupied molecular orbital energy from -2.80 (Ph-2S) to -2.50 (Ph-2Se) and -2.00 eV (Ph-2Te), shifting the redox potentials to increasingly negative values of -0.76, -0.82, and -0.84 V, respectively. Moreover, Ph-2Te shows the strongest redox activity to start four-electron Te-conversion with 98% utilization (vs. 65% of Ph-2Se and 31% of Ph-2S). Consequently, Ph-2Te anode liberates the highest capacity of 257 mAh g-1, outperforming Ph-2S (152 mAh g-1) and Ph-2Se (223 mAh g-1). Notably, Ph-2Te anode enables state-of-the-art CIBs with a high redox voltage (1.2 V), an active-material-pair level energy density (68 Wh kg-1), and a long lifespan (5000 cycles). This work establishes dichalcogenide engineering as a promising strategy toward low-redox-potential organic anodes for advanced CIBs.