Electrochemical Performance Of MXene And Its Composites For Magnesium Batteries

There is a tremendous need to have perennial and continuous access to cost-effective electricity generated from the intermittent energy sources?wind,solar,geothermal,hydropower,wave etc.?.This will require development of inexpensive and efficient electrical energy storage devices.Magnesium based batteries have been gained wide attention owing to its low-cost,environmental friendly,non-toxic and high volumetric capacity.However Mg batteries still stay at the infancy stage of development and cathodic material are under urgent improvement.Recently,a kind of two-dimensional?2D?materials,transition-metal carbides?termed MXene?,have been attracted great attention in electrochemical energy storage devices?supercapacitors,lithium-ion and sodium-ion batteries?due to its excellent electrical conductivity as well as high volumetric capacity.However,they have not been reported for magnesium ions storage in Mg battery.Theoretical calculation demonstrated that bare Ti₃C₂ has a high capacity for Mg²⁺ions storage.While there are always functional groups on the surface of MXene materials reported so far,which greatly affect the electrochemical properties of MXene.Here in,the results showed that multivalent Mg²⁺ions cannot reversibly insert into MXene due to the presence of functional groups.Nevertheless,the combination of both the outstanding electrical conductivity and hydrophilic surface makes MXene the promising matrixes for supporting the active MoS₂ host.Furthermore,we demonstrate a simple strategy to achieve high magnesium storage capability for Ti₃C₂ MXene by preintercalating a cationic surfactant.On this basis,the capacity of MXene in Mg battery was enhanced through structural optimization.The specific research contents are as follows.1.MXene as a conductive substrate,the MoS₂/Ti₃C₂T_x composite has been successfully synthesized by one-step hydrothermal method.With the combination of few-layer MoS₂nanosheets and the high conductive MXene substrate,the composite exhibits enhanced capacity of165 mAh g^-1 at 50 mA g^-1 and outstanding rate performance as a cathode material of Mg batteries.2.MXene was successfully used as the cathode material for Mg²⁺ions storage in Mg battery by pre-intercalating a cationic surfactant cetyltrimethylammonium bromide?CTAB?.Experimental test and density functional theory simulations verify that intercalated CTA⁺cations reduce the elementary electronegativity of MXene,resulting in the significant improvement of diffusion barrier of Mg²⁺on MXene surface.Consequently,the MXene electrode exhibits a desirable specific capacity of 100 mAh g^-1 at 50 mA g^-1 as well as outstanding rate performance.3.Furthermore,the sandwich-like Ti₃C₂T_x/CNTs-CTAB compound was prepared by alternate vacuum filtration of CTAB-grafted carbon nanotubes dispersions and MXene suspension.The more open structure facilitates the transfer of electrolyte and provides more active sites for the storage of Mg²⁺.As the cathode of Mg battery,Ti₃C₂T_x/CNTs-CTAB compound exhibits a highter specific capacity of 154 mAh g^-1 at 50 mA g^-1,which is 1.5 times of the capacity for Ti₃C₂T_x/CTAB electrode.