CO2 Nanoenrichment and Nanoconfinement in Cage of Imine Covalent Organic Frameworks for High-Performance CO2 Cathodes in Li-CO2 Batteries

The Li-CO2 battery is an emerging green energy technology coupling CO2 capture and conversion. The main drawback of present Li-CO2 batteries is serious polarization and poor cycling caused by random deposition of lithium ions and big insulated Li2CO3 formation on the cathode during discharge. Herein, covalent organic frameworks (COF) are identified as the porous catalyst in the cathode of Li-CO2 batteries for the first time. Graphene@COF is fabricated, graphene with thin and uniform imine COF loading, to enrich and confine CO2 in the nanospaces of micropores. The discharge voltage is raised by higher local CO2 concentration, which is predicted by the Nernst equation and realized by CO2 nanoenrichment. Moreover, uniform lithium ion deposition directed by the graphene@COF nanoconfined CO2 can produce smaller Li2CO3 particles, leading to easier Li2CO3 decomposition and thus lower charge voltage. The graphene@COF cathode with 47.5% carbon content achieves a discharge capacity of 27833 mAh g(-1) at 75 mA g(-1), while retaining a low charge potential of 3.5 V at 0.5 A g(-1) for 56 cycles.