Application Of Biomass-derived Self-supporting Carbon Electrodes In Li-O₂/Li-CO₂ Batteries

The metal-gas battery has become a hot research topic due to its high theoretical energy density and environmentally friendly characteristics.Among them,lithium-oxygen（Li-O₂）batteries have the largest theoretical energy density,so they have attracted much attention.In addition,lithium-carbon dioxide（Li-CO₂）batteries provide the possibility of integrating carbon dioxide capture and energy storage.However,both batteries currently have problems such as low specific capacity,high overpotential,and poor cycle stability.Generally,the structure and catalytic activity of the cathode determine the electrochemical performance of Li-O₂ and Li-CO₂ batteries.Therefore,the design and research of the cathode is one of the current research hotspots.In this paper,an integrated electrode with a three-dimensional structure is prepared by using natural kapok biomass,which is used as a cathode in Li-O₂ and Li-CO₂ batteries,showing good electrochemical performance.The content and results of the relevant research are as follows:（1）Kapok-derived carbon（KC）was prepared by high-temperature pyrolysis,and highly dispersed ultrafine Ir O₂ nanoparticles（Ir O₂-KC）were loaded on the KC surface by hydrothermal method,which was used as a cathode catalyst for Li-O₂ batteries.The Ir O₂-KC material has a 3D cross-linked free-standing structure.The Li-O₂ battery with Ir O₂-KC cathode has a high initial discharge specific capacity(10.74 m Ah cm^-2),a low overpotential（1.38 V）,and an ultra-long cycle of 389 cycles.The discharge product Li₂O₂ can be formed and decomposed reversibly,and the Ir O₂-KC material remain stable during the cycle.The Li-O₂ battery with Ir O₂-KC cathode can light the LED lamp in various deformation states in a real air atmosphere.Its high performance is attributed to the 3D cross-linked free-standing structure,nitrogen doping,and uniformly loaded Ir O₂nanoparticles to redistribute the charge on the carbon surface uniformly,providing sufficient storage space for Li₂O₂,promoting electrolyte penetration and Li⁺/O₂ transport,promoting the formation and decomposition of thin film Li₂O₂ products.（2）Highly dispersed ultra-fine Ru nanoparticles（Ru-KC）are loaded on the surface of KC by hydrothermal method,and successfully applied to high-performance cathodes of Li-CO₂ batteries.The Ru-KC material has a 3D cross-linking free-standing structure.The Ru-KC cathode Li-CO₂battery shows a low potential（0.79 V）,a good cycle stability（256 cycles,2032 h）.In addition,the LED lamp can be lit in various deformation states in a CO₂ atmosphere.Its high performance is attributed to the catalytic activity provided by the 3D cross-linked free-standing structure,nitrogen doping,and uniformly loaded Ru nanoparticles,which provides sufficient storage space for Li₂CO₃,promoting electrolyte penetration and Li⁺/CO₂ transport,promoting formation/decomposition of film-like Li₂CO₃ products.（3）To further develop metal-free cathodes,we prepared a porous 3D cross-linked free-standing carbon and graphene oxide（GO）composite material（GO/KC）and successfully applied it to the high-performance cathode of Li-CO₂ batteries.By adding ruthenocene redox mediator to the electrolyte,the GO/KC cathode Li-CO₂ battery showed a low overpotential of 0.81 V,a high discharge specific capacity of 13.95 m Ah cm^-2,a high Coulomb efficiency of 97.99%,and 385cycles of stable circulation.Its high performance is attributed to a large number of porous structures and 3D cross-linked structures,and more importantly,the redox pair formed by ruthenocene reduces the overpotential.This work not only provides a novel strategy for balancing electrochemical performance,low cost and reproducibility,but also provides ideas for the design of binder-free,free-standing electrodes and the development of flexible batteries.In addition,it provides a reference for the application development of redox mediators（RMs）in Li-CO₂ batteries.