Research On Sodium Storage Properties Of MXenes By Organic Molecules Intercalated

Interlayer engineering is an effective method to reduce the ionic diffusion barrier and improve the electrochemical kinetics by adjusting the interlayer spacing of two-dimensional materials.Different organic molecules are intercalated into MXenes（Ti₂C、Ti₃C₂）two-dimensional materials,which can explore the influence of expanded interlayer spacing on the storage rate capability and diffusion kinetics capability.The reaction mechanism of different organic compounds in the ion transport process was also studied.The research content is displayed as follow:1.Electrostatic self-assembly method is used to intercalate positively charged asparagine（LAG）molecules into Ti₂C interlayer（LAG-Ti₂C）.LAG molecules not only expand the interlayer spacing of Ti₂C,but also inhibit the Ti₂C layers self-stacking during the sodium ion insertion/extraction process.LAG-Ti₂C exhibits reversible specific capacities of 113.1 m Ah g^-1 at 0.1 A g^-1 after 1000 cycles,and the coulombic efficiency（CE）is close to 100%.The reversible specific capacities of LAG-Ti₂C are92.6,86.6,78.3,69.2and 52.5 m Ah g^-1 corresponding to the 0.2,0.5,1.0,2.0,and 5.0A g^-1,respectively.The results showed that LAG-Ti₂C exhibits faster ion diffusion rate and higher rate capability than pure Ti₂C.2.Molecular welding strategy is used to prepare Diphenic acid（DHA）welded Ti₃C₂（DHA-Ti₃C₂）by dehydration condensation reaction.The interlayer spacing of Ti₃C₂ layers can be effectively regulated by controlling the DHA content.With the increase of DHA content,the interlayer spacing of Ti₃C₂ are 1.26（2DHA-Ti₃C₂）,1.28（3DHA-Ti₃C₂）,1.40（4DHA-Ti₃C₂）and 1.31 nm（5DHA-Ti₃C₂）,respectively.The welded DHA molecule can expand the interlayer spacing and stabilize the layer structure,which can improve ion diffusion kinetic performance and alleviate volume expansion during the alkali metal ions insertion/extraction process.When the interlayer spacing is 1.40 nm,the sodium ion battery shows excellent ion diffusion kinetics and high rate capability,The 4DHA-Ti₃C₂ exhibits reversible specific capacity of 156.0m Ah g^-1 at 0.1 A g^-1 after 1700 cycles and remains a high CE of 99.29%.The 2DHA-Ti₃C₂（1.20 nm）shows excellent ion diffusion kinetics and high rate capability in lithium ion battery.2DHA-Ti₃C₂ can restore to initial states at 0.1A g^-1 after suffering severely cycles of high current density at 5.0 A g^-1 and remains 97%capacity retention.The stabled interlayer structure of DHA-Ti₃C₂ can be illustrated by ex-XRD,which alleviate the volume expansion of the material.3.Electrostatic self-assembly and molecular welding methods are used to intercalate dimethyl sulfolone（DMSO）,（3-amino-propyl）triethoxysilane（APTSE）,2,2-biphenyl dicarboxylic acid（DHA）and 1,4,5,8-naphthalene tetramethylanhydride（NTCDA）into Ti₂C layers,and prepared fewer layers Ti₂C（DT）,amino functionalized Ti₂C（ADT）,DHA molecular welding Ti₂C（ADT-DHA）and NTCDA molecular welding Ti₂C（ADt-Ntc DA）.Compared with DT(101.38 m Ah g^-1),the specific capacity of ADT is 114.1 m Ah g^-1after 900 cycles of 0.1 A g^-1,which is mainly attributed to amino groups provided abundant active sites to sodium ion storage.The specific capacities of ADT-DHA and ADT-NTCDA reached 160 m Ah g^-1 and 115.7 m Ah g^-1after 900 cycles under the current density of 0.1 A g^-1.It is attributed to the molecular welding reaction can increase the interlayer spacing and provide stable layer structure,which is conducive to improving ion diffusion kinetics and high rate capability.