Rechargeable K-CO₂ Batteries with a KSn Anode and a Carboxyl-Containing Carbon Nanotube Cathode Catalyst

Metal K-CO₂ batteries suffer from large polarization and safety hazards, which mainly result from the difficult decomposition of K₂ CO₃ and dendrite growth. Moreover, the battery redox mechanism remains not fully understood. Here we report K-CO₂ batteries with KSn alloy as the anode and carboxyl-containing multi-walled carbon nanotubes (MWCNTs-COOH) as the cathode catalyst, proving the redox mechanism to be 4 KSn + 3 CO₂ ⇄ 2 K₂ CO₃ + C + 4 Sn. Compared with K metal, the less active and dendrite-free KSn anode effectively enhances the safety and stability of CO₂ batteries. More importantly, the strong electrostatic interaction between MWCNTs-COOH and K₂ CO₃ weakens the C=O bond in K₂ CO₃ and thus facilitates K₂ CO₃ decomposition. As a result, the K-CO₂ batteries show excellent cycling stability (an overpotential increase of 0.89 V after 400 cycles) and good rate performance (up to 2000 mA g^-1 ). This work paves a way to develop highly stable and safe CO₂ -based batteries.