Preparation And Mechanism Research Of MXenes Based On Ambient Temperature Organic Ionic Liquid Aluminum Battery

With the urgent need of human beings for emerging clean energy,aluminum batteries are favored by researchers around the world.However,some key problems existing in the room temperature organic ionic liquid aluminum battery restrict its further development.The choice of positive electrode material is critical to the electrostatic effect between[AlCl4]-(or Al3+)and positive electrode material,which has a close influence on the electrochemical performance of aluminum batteries.Therefore,the positive electrode material is the top priority of the study of aluminum batteries.The two-dimensional layered material MXenes is widely used in electrochemical energy storage devices and exhibits excellent electrochemical performance.At present,the huge MXenes family has as many as 60 different material systems,and each system of MXenes has its own advantages in performance.Therefore,the emerging two-dimensional crystal material MXenes,which has the dual characteristics of carbon-based materials and transition metal compounds,is expected to achieve the high energy density and long-cycle stability of aluminum batteries:Herein,a two-dimensional layered composite of D-Ti3C2Tx@S@TiO2 is prepared by a simple method.The elemental sulfur reacted with the exposed Ti-ions to form Ti-S bonds,which play a supporting role to maintain the original structure of the material and prevent the superposition of layers between the materials,and nano-particles of TiO2 grow in situ on the surface after further oxidation treatment,which improve the stability of the material.D-Ti3C2Tx@S@TiO2 performs excellent electrochemical performance in aluminum batteries,the discharge specific capacity is 151 mAh g-1 after 120 cycles,and the capacity retention rate is 72.3%.In order to further increase the specific capacity of MXenes in aluminum batteries,MXenes@Te composite materials were prepared by high-temperature evaporation method.The research results show that mechanical peeling is very important for the preparation of MXenes@Te composites.The intercalated MXenes materials can load more Te and exhibit excellent electrochemical performance in aluminum batteries.Surprisingly,the discharge specific capacity is 258 mAh g-1 after 150 cycles at 0.6 A g-1.Furthermore,the valence change behavior of Te is studied.Te is oxidized to Te4+when the battery is fully charged to 2.4 V.In contrast to the charging process,the high-valence Te4+is reduced again during discharging.Te is reduced to lower-valence Te2-when the discharge voltage is lower than 0.6 V.In order to simplify the modification process of MXenes,with the help of electrostatic adsorption,the MXenes material was modified with Ag+,and the composite material MXenes@Ag was prepared.This method not only simplifies the collection of MXenes materials,but also modifies the functional groups on its surface.More importantly,the electrochemical performance of the two-dimensional material MXenes@Ag is studied in aluminum battery,and shows extraordinary long cycle lifetime with high specific capacity.The discharge specific capacity is about 150 mAh g-1 after 2000 cycles at the current density of 0.5 A g-1.Furthermore,the energy-storage mechanism of MXenes@Ag in aluminum batteries is studied,which shows that is mainly the intercalation/de-intercalation of[AlCl4]-,and accompanied by a small amount of Al3+ intercalated/de-intercalated.Further,we learn from the energy storage mechanism of aluminum batteries,and for the first time achieved fluorine-free and water-free electrochemical preparation of MXenes in Lewis acid at room temperature.This opens up a new way for the green preparation of MXenes.In addition,the electrochemical performance of the etched V2AlC(E-V2AIC)in aluminum batteries was studied.The one-stop preparation and application process prevent the MXenes from contacting water and air,and the MXenes etched in the aluminum battery is more conducive to the intercalation/de-intercalation of Al3+.Therefore,E-V2AlC exhibited excellent electrochemical performance in aluminum batteries.Under the current density of 0.5 A g-1,the specific discharge capacity is about 100 mAh g-1 after 6500 cycles.In addition,the energy storage mechanism and Faraday energy storage method of E-V2AlC in aluminum batteries were studied.The diffusion coefficient D of Al3+ was studied by galvanostatic intermittent titration technique(GITT).The reasons for its excellent electrochemical performance are clarified from the perspective of kinetics.