Rechargeable K‐CO 2 Batteries with a KSn Anode and a Carboxyl‐Containing Carbon Nanotube Cathode Catalyst

Metal K‐CO 2 batteries suffer from large polarization and safety hazards, which mainly result from the difficult decomposition of K 2 CO 3 and dendrite growth. Moreover, the battery redox mechanism remains not fully understood. Here we report K‐CO 2 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 CO 2 ⇄ 2 K 2 CO 3 + C + 4 Sn. Compared with K metal, the less active and dendrite‐free KSn anode effectively enhances the safety and stability of CO 2 batteries. More importantly, the strong electrostatic interaction between MWCNTs‐COOH and K 2 CO 3 weakens the C=O bond in K 2 CO 3 and thus facilitates K 2 CO 3 decomposition. As a result, the K‐CO 2 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 CO 2 ‐based batteries.