Systhesis And Electrochemical Properties Of Three Dimensional Mxene Aerogels For Electrochemical Energy Storage And Conversion

Energy as the material basis for the survival of human society,is the most basic driving force for the development of modern society and the prosperity of national economy.The traditional energy system is dominated by non-renewable fossil fuels.With the swift and violent development of human society,energy consumption growing with each passing day and environmental problems caused by overuse have become bottlenecks restricting the sustainable,harmonious and rapid expansion of human society.It is all the more urgent to develop highly efficient,clean and renewable energy technology.On the one hand,renewable energy technology contains the exploitation and utilization of clean renewable energy abundant in nature.On the other hand,it relies on highly efficient and large-scale energy storage technology.MXene is a new two-dimensional transition metal carbon/nitrogen/carbonitride material with graphene-like structure.It has ultra-high conductivity,excellent hydrophilicity,ion intercalation and abundant surface functional groups,as well as super-high mechanical strength and chemical stability,which is considered as a nova in the field of electrochemical energy storage and conversion.Based on two-dimensional MXene nanosheets with high conductivity and abundant surface groups,it has been achieved that the construction of porous three-dimensional self-supporting MXene aerogels with anti aggregation and stacking and fine regulation of their structural properties.Based on capacitive mixing,the three-dimensional MXene aerogels as electrode material have achieved the extraction of salinity gradient energy and efficient conversion to electricity.Through chemical coupling of the three-dimensional MXene aerogels with nano Li₂S,a late-model lithium secondary battery have been constructed with high energy density and high safety.The content of the paper is as follows:?1?A three-dimensional porous MXene/graphene composite aerogel with anti stacking and multistep channel structure was synthesized by hydrothermal technology using active multifunctional small molecule ethylenediamine as reducing agent and crosslinking agent.Based on the chemical coupling between MXene and lithium sulfide?Li₂S?,Li₂S nanoparticles were uniformly loaded on the surface of three-dimensional MXene aerogels,and combined with the physical confinement and chemisorption dual mechanisms,MXene aerogels could effectively inhibit the dissolution,diffusion and loss of polysulfide,as well as through electrochemical catalysis,the activation and decomposition barriers of Li₂S were reduced,and the redox kinetics of Li-S battery was accelerated.Therefore,a cathode of Li-S battery was successfully constructed with high loading and high areal capacities.The electrodes with Li₂S loading of 3.0-9.0 mg cm^-2 can deliver high capacities of 550-720 mAh g^-1 at the current rate of 0.2-2.0 C with excellent cyclic stability.The cathode with high Li₂S loading up to 9 mg cm^-2shows the highest areal capacities of 5.04 mAh cm^-2.It could be directly applied to pair with high-capacity Fe₃O₄ based anode for developing metallic Li-free secondary batteries with a high reversible capacity of 436 mAh g^-1 and a specific energy of 350 Wh kg^-1.?2?Based on the technology of ice template directional casting and intercrystalline pressure of ice crystals as driving force,MXenes were physically established to controllably construct oriented three-dimensional MXene aerogels with surface chemical properties regulation.The3D MXene aerogels have abundant and order pore structure,stable structure of the pore wall and high conductivity,which is helpful to enhance ion and electron transport properties of the electrodes,and significantly improve the concentration-dependent voltage of the electrodes because of abundant negative groups on the surface.Combining the MXene aerogel?MA?and an anion exchange membrance?AEM?,concentration capacitors were assembled to extract salinity gradient energy.The concentration-dependent voltage and peak short circuit current density could reach 304 mV and 47 A m^-2,respectively.The high average power densities output could reach up to 650 mW m^-2.