MOF-Derived CoSe₂ Nanoparticles/Carbonized Melamine Foam as Catalytic Cathode Enabling Flexible Li–CO₂ Batteries with High Energy Efficiency and Stable Cycling

Rechargeable aprotic Li–CO₂ batteries have aroused worldwide interest owing to their environmentally friendly CO₂ 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 CoSe₂ nanoparticles embedded in 3D carbonized melamine foam (CoSe₂/CMF) for Li–CO₂ batteries is reported. The abundant CoSe₂ clusters can not only facilitate CO₂ reduction/evolution kinetics but also serve as Li₂CO₃ nucleation sites for homogeneous discharge product growth. The CoSe₂/CMF-based Li–CO₂ 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 CO₂/Li adsorption and low Li₂CO₃ decomposition energy. Moreover, flexible Li–CO₂ pouch cell with CoSe₂/CMF cathode displays stable power output under different bending deformations, showing promising potential in wearable electronic devices.