Tailoring Li–CO₂ Electrochemistry Based on 4,4′-Bipyridine Redox Cycle

The aprotic Li–CO 2 battery provides a tantalizing solution for simultaneous CO 2 capture and electrical energy storage. Nevertheless, current Li–CO 2 batteries based on ordinary reaction pathways, e.g., reducing CO 2 to CO, oxalate, carbon, etc., often suffer from poor energy efficiency and severe parasitic reactions. Thus, exploring new Li–CO 2 electrochemistry is of fundamental interest and practical importance. Herein, we report a new concept of a Li–CO 2 battery that can realize both reversible capture/release of CO 2 and highly efficient energy storage based on the redox cycle of 4,4′-bipyridine (BPD). Direct spectroscopic evidence coupled with theoretical calculations reveals that BPD first coordinates with CO 2 to form a [BPD···2CO 2 ] complex that can further be reduced via a two-electron pathway into Li 2 [BPD-2CO 2 ] upon discharge; upon recharge the reaction is reversed, regenerating BPD and CO 2 . The BPD-assisted Li–CO 2 battery minimizes the overpotential required to drive the discharge/charge reaction, eliminates the undesired parasitic reactions associated with pristine Li–CO 2 batteries, and delivers a high discharge capacity (>1000 mAh/g c ). This work represents a significant step forward toward truly reversible Li–CO 2 batteries by the rational design of redox molecules that can participate in and regulate the conventional Li–CO 2 electrochemistry.