The Research On Layer Structure Regulation And Lithium Ions Storage Rate Capability Of Carbon-based Two-dimensional Materials

As we all know,the performance of materials is determined by its structure and the interlayer spacing is an important parameter of the layered structure in a two-dimensional（2D）material.Therefore,the expand of the interlayer spacing will directly affect the electrochemical performance of 2D materials.The ion diffusion in 2D materials mainly occurs between layers,expanding the interlayer spacing is an effective approach to weaken the van der Waals forces,decrease the ion diffusion barriers,and accelerate the ion diffusion rate,which will facilitate the diffusion dynamics and ions storage performance.The focus of the research is to tune interlayer spacing of the carbon-based 2D materials（Nb₂C,Ti₃C₂,and GO）by designing different methods.Therefore,studying the influence of interlayer spacing on ions diffusion kinetics and storage capability is essential for designing the 2D materials with high-rate capability.The main content is exhibited as follows:（1）According to the principle of electrostatic interaction,the positively charged p-phenylenediamine（PPDA）molecules are automatically intercalated between the negatively charged niobium carbide（Nb₂C）layers,which expands the interlayer spacing of Nb₂C layers from 1.18 nm to 1.27 nm.The study declares that enlarging the interlayer spacing of Nb₂C layers can effectively increase the specific surface area,thereby exposing more Li⁺diffusion channels and accessible active sites,which is conducive to rapid Li⁺diffusion and storage.As the results,the PPDA-Nb₂C with 1.27 nm interlayer spacing exhibits the higher Li⁺diffusion coefficient(1.5×10^-9～4.6×10^-7 cm² s^-1)than Nb₂C and an excellent Li⁺storage capacity with400 m Ah g^-1 capacity at 0.1 A g^-1.（2）The dehydration condensation reaction between amino functionalized Ti₃C₂(Ti₃C_2-NH₂)and maleic acid（MA）molecules is essential for obtaining the MA-Ti₃C₂ anode materials with 1.28 nm interlayer spacing by chemical welding approach.The MA molecules between the Ti₃C₂ layers enlarge the interlayer spacing and alleviate the volume expansion during de-intercalation process,which can enhance the structure durability and cycling stability of Ti₃C₂ layers.The MA-Ti₃C₂ with 1.28 nm interlayer spacing is for fast Li⁺diffusion(1.4×10^-8～5.8×10^-7 cm² s^-1),meanwhile MA-Ti₃C₂ electrode exhibits the reversible capacity of 240 m Ah g^-1at a current density of 0.1 A g^-1,even the capacity hardly decreases after 150 cycles.（3）According to the dehydration condensation between diacid molecules（xDA,x=2,4,6,8 and 10）with different lengths and the functionalized Ti₃C₂ layers,the molecular welding strategy is designed to controllably tune the interlayer spacing of Ti₃C₂.By linking xDA molecules with different lengths between Ti₃C₂ layers,xDA-Ti₃C₂ with interlayer spacings of1.24 nm,1.30 nm,1.35 nm,1.38 nm,and 1.45 nm are successfully obtained,and Li⁺diffusion dynamics and storage performance are studied.In the end,6DA-Ti₃C₂ with 1.35 nm interlayer spacing exhibits the highest diffusion coefficient(4.6×10^-7 cm² s^-1)and a capacity of 265.7m Ah g^-1 at 0.1 A g^-1after 200 cycles.（4）Based on the mechanism that the amino groups in diamine molecules（xDM,x=2,3,4,5 and 6）react with the carboxyl groups in graphene oxide（GO）to form amide bonds,xDM molecules with different lengths are selected to achieve the purpose of controllable adjustment interlayer spacing of GO.Among the GO-xDM electrode materials with interlayer spacing of 0.911 nm,0.947 nm,0.958 nm,0.995 nm,and 1.138 nm,GO-2DM demonstrates the suit interlayer spacing of 0.911 nm and the fastest Li⁺diffusion rate(2.4×10^-7 cm² s^-1).In addition,GO-2DM exhibits the high reversible capacity of 291.8 m Ah g^-1 at 0.1 A g^-1 and a superior rate capability with 120.8 m Ah g^-1 at 5.0 A g^-1.Moreover,the optimal sample and activated carbon were assembled for lithium-ion capacitors（LICs）to study storage performance.Different strategies are designed to adjust the interlayer spacing of the carbon-based 2D materials,meanwhile,the effects of the interlayer spacing on the diffusion dynamics and rate capability are clarified,which is beneficial for designing 2D materials with high-rate capability.