Preparation And Properties Of Light-Assisted Li-CO₂ Battery Anode Materials

Lithium-carbon dioxide（Li-CO₂）batteries have emerged as a new type of energy storage and conversion device and offer an eco-friendly way to reduce carbon dioxide emissions to mitigate global warming.Based on the reaction of 4Li+3CO₂?2Li₂CO₃+C（E₀=2.80v vs.Li/Li⁺）,the theoretical energy density of Li-CO₂ batteries is up to 1876 Wh kg^-1.However,the low electrochemical activity of CO₂ leads to high polarization in the discharge process.Moreover,due to the wide gap insulation discharge product Li₂CO₃,a high operating voltage（above 4.0 V）is required during the charging process.There is a large polarization during discharge and charging,which results in low energy efficiency and hinders the practical application of Li-CO₂ batteries.In addition,other battery components,such as electrolytes,may undergo electrochemical decomposition at high charging voltages.Therefore,reducing the overpotential is crucial for the further development of Li-CO₂ batteries.Starting from the main problems faced by Li-CO₂ batteries at present,this paper haveproposed the concept of"photoassisted charging-discharging process of Li-CO₂batteries",and designed and prepared two kinds of positive electrode materials,SiC/RGO and g-C₃N₄/C.The electrochemical performance of SiC/RGO and g-C₃N₄/C as photocatalytic hybrid positive electrode of photoassisted Li-CO₂ batteries have been systematically studied,and the reaction mechanism of photoassisted Li-CO₂ batteries has been deeply studied through various characterization methods.The specific research includes the following aspects:（1）Aphotoassisted Li-CO₂ battery system has been constructed using SiCnanosheets grown on reduced go（SiC/RGO）as a photocatalytic hybrid positive electrode.During the discharge process,photogenerated electrons promote the kinetics of the CO₂ reduction reaction.Therefore,the discharge voltage of the battery is increased to 2.77 V,which is very close to the theoretical potential（2.80 V）of Li-CO₂ batteries.In addition,the holes generated in the optical electrode during charging promote the decomposition of Li₂CO₃,thus effectively reducing the overpotential of Li-CO₂ batteries.The system achieved an ultra-low over potential of 0.424 V with an energy efficiency of 84.4%（excluding solar energy）,higher than reported in the literature to date（<80%）.（2）Nanosheet composites composed of graphite carbon nitride（g-C₃N₄）and carbon have been prepared by simple pyrolysis and subsequent carbon thermal activation.By comparing the electrochemical performance of g-C₃N₄/C as a cathode of Li-CO₂ battery with or without illumination,it has been found that g-C₃N₄/C has a better effect under illumination.The g-C₃N₄/C cathode achieves an ultra-low over-potential of 0.381 V during the charging and discharging process of Li-CO₂ battery through the action of electrons and holes generated under the light,and the energy efficiency is 87.4%（excluding solar energy）.The battery can be stabilized for 204 cycles,and the discharge specific capacity is6200mAh/g.In the absence of light,the over potential of the battery is 1.534 V,the battery can only circulate 153 times,and the discharge specific capacity is 679.6mAh/g.These findings demonstrate the potential of photoassisted electrochemical processes to solve the overpotential problem in Li-CO₂ batteries.