Synergistic anion-cation descriptor for bidirectional electrocatalyst in Li-CO2 battery.

The slow kinetics of lithium carbonate (Li2CO3) nucleation/decomposition hinder voltage gap minimization in lithium-carbon dioxide (Li-CO2) batteries. Although symmetry-broken cation motifs can enhance reactivity, designing optimal catalysts remains challenging. Moving beyond cation-centric views, we recognize anions as active participants that regulate charge and stabilize intermediates, yet their degradation worsens the activity-stability trade-off. To address this, we develop a dual Φ descriptor quantifying anion-cation orbital coupling and reconstruction energy. It establishes a volcano correlation with the voltage gap in metal sulfides, showing that symmetry-broken units optimally balance binding and stability. Guided by this, we synthesize oriented WS2 rich in C4v configurations, achieving a record-low gap of 0.76 volts and superior cycling (>1268 hours) among dichalcogenides. This work shifts the paradigm from cation-only tuning to synergistic anion-cation design, repositioning anions as co-catalytic architects. By linking orbital insights to performance, we provide a universal descriptor for developing efficient, stable Li-CO2 batteries.