MOF-Derived CoSe 2 Nanoparticles/Carbonized Melamine Foam as Catalytic Cathode Enabling Flexible Li-CO 2 Batteries with High Energy Efficiency and Stable Cycling.

Rechargeable aprotic Li-CO 2 batteries have aroused worldwide interest owing to their environmentally friendly CO 2 fixation ability and ultra-high specific energy density. However, its practical applications are impeded by the sluggish reaction kinetics and discharge product accumulation during cycling. Herein, a flexible composite electrode comprising CoSe 2 nanoparticles embedded in 3D carbonized melamine foam (CoSe 2 /CMF) for Li-CO 2 batteries is reported. The abundant CoSe 2 clusters can not only facilitate CO 2 reduction/evolution kinetics but also serve as Li 2 CO 3 nucleation sites for homogeneous discharge product growth. The CoSe 2 /CMF-based Li-CO 2 battery exhibits a large initial discharge capacity as high as 5.62 mAh cm -2 at 0.05 mA cm -2 , a remarkably small voltage gap of 0.72 V, and an ultrahigh energy efficiency of 85.9% at 0.01 mA cm -2 , surpassing most of the noble metal-based catalysts. Meanwhile, the battery demonstrates excellent cycling stability of 1620 h (162 cycles) at 0.02 mA cm -2 with an average overpotential of 0.98 V and energy efficiency of 85.4%. Theoretical investigations suggest that this outstanding performance is attributed to the suitable CO 2 /Li adsorption and low Li 2 CO 3 decomposition energy. Moreover, flexible Li-CO 2 pouch cell with CoSe 2 /CMF cathode displays stable power output under different bending deformations, showing promising potential in wearable electronic devices.