Ultrahigh discharge voltage plateau of 3.2 V achieved in Li-CO₂ batteries using iron polyphthalocyanine

Rechargeable lithium-carbon dioxide (Li-CO₂) batteries offer great potential for greenhouse gas use and high-energy-density storage. However, their practical application is hindered by the formation of a thermodynamically stable Li₂CO₃ (lithium carbonate) product that is hard to decompose during charging. Highly crystalline and conductive reticular material iron polyphthalocyanine (pFe^IIPc) as a solid-state redox mediator into Li-CO₂ batteries tailors the cathode reaction pathway, enabling stable Li₂C₂O₄ (lithium oxalate) generation and an extraordinary discharge plateau of 3.2 V beyond the theoretical limit. Beyond delivering an ultrahigh discharge capacity of 28,790 milliampere-hours per gram and reversible cyclability over 1400 hours (cutoff capacity of 1000 milliampere-hours per gram) at 100 milliamperes per gram, the Li-CO₂ batteries exhibit excellent temperature adaptability (-40 to 80°C). The Li-CO₂ pouch cells using pFe^IIPc as the solid-state redox mediator achieve a high energy density of 678 watt-hours per kilogram on the basis of total device mass and maintain reversible cycling for 251 hours. Our work pioneers a promising pathway toward practical high-efficiency Li-CO₂ batteries.