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

The aprotic Li–CO2 battery provides a tantalizing solution for simultaneous CO2 capture and electrical energy storage. Nevertheless, current Li–CO2 batteries based on ordinary reaction pathways, e.g., reducing CO2 to CO, oxalate, carbon, etc., often suffer from poor energy efficiency and severe parasitic reactions. Thus, exploring new Li–CO2 electrochemistry is of fundamental interest and practical importance. Herein, we report a new concept of a Li–CO2 battery that can realize both reversible capture/release of CO2 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 CO2 to form a [BPD···2CO2] complex that can further be reduced via a two-electron pathway into Li2[BPD-2CO2] upon discharge; upon recharge the reaction is reversed, regenerating BPD and CO2. The BPD-assisted Li–CO2 battery minimizes the overpotential required to drive the discharge/charge reaction, eliminates the undesired parasitic reactions associated with pristine Li–CO2 batteries, and delivers a high discharge capacity (>1000 mAh/gc). This work represents a significant step forward toward truly reversible Li–CO2 batteries by the rational design of redox molecules that can participate in and regulate the conventional Li–CO2 electrochemistry.