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.