Preparation And Investigetion Of Novel Mxene-based Composite Electrode Materials For Lithium-carbon Dioxide Batteries

Energy shortage and greenhouse effect have been serious challenges to the sustainable development of human society.Lithium-carbon dioxide batteries utilize greenhouse gases（CO₂）as fuel,which is considered an important strategy for effective carbon sequestration and energy storage to achieving carbon neutral.However,the high decomposition voltage of insulated Li₂CO₃ seriously affects the cycle capacity and polarization voltage of the battery and reduces the service life of the battery.Therefore,it is urgent to find high performance catalyst to promote the decomposition of discharge products.In this paper,different kinds of composite catalysts of MXene and transition metal oxide were prepared by hydrothermal reaction,which enabled lithium-carbon dioxide batteries to have long cycle life and low overpotential.The morphology and structure of the catalysts and the electrochemical performance of assembled batteries were systematically studied,and the internal mechanism of their high electrochemical activity was also explained.In this paper,a kind of V₂C/V-Cu₂O lamellar composite material was prepared by in-situ microwave hydrothermal method with V₂C MXene as substrate.The effects of loading content of active material on battery performance were studied emphatically.The cathode material with low overpotential and good cyclic stability was obtained by simple preparation technology.The results show that the Cu₂O load is 50%,the composite has a low overpotential（～0.8V）and a 190 cycles at 100 m A g^-1 current density,and 252 cycles at a high magnification rate of 500 m A g^-1.The low overpotential and long cycle life of the composite show good catalysis and reversibility.Its performance is attributed to the composite V₂C/V-Cu₂O forms a three-dimensional fold lamellar structure,which provides a large active area,and the doping of V element enriches the active site.On this basis,the REDOX reaction of carbon dioxide was promoted and the overpotential of the battery was reduced.The Nb₂C MXene suspension obtained by liquid phase stripping method was used as substrate.By changing the content of Cu O reasonably,the Nb₂C-Cu O composite was quickly prepared by one-step hydrothermal method.The effect of different Cu O contents on the performance of Li-CO₂ battery was investigated,and a kind of composite with high rate performance,low overpotential and good cyclic stability was obtained.The results show that Nb₂C/50%Cu O composites exhibit an overpotential of 0.52 V,209 cycles of charge and discharge,and good rate performance at a current density of 200 m A g^-1.The excellent performance can be attributed that Nb₂C-Cu O composites have high conductivity and porous structure,which provides transport channels for electrons and ions.At the same time,it improves the catalytic activity and prolongates the cycle life of the battery.