Design Of Three-dimensional Electrode Material Based On Layered Transition Metal Carbides For High Performance Sodium-ion Batteries

Sodium ion batteries?SIBs?have recently attracted extensive attention because of the natural abundance of sodium resources and low cost for large-scale electrical energy storage.The similarities in energy storage mechanisms between SIBs and Lithium-ion batteries?LIBs?have enabled the development of SIBs relatively rapid with the accumulated experiences in LIBs.Therefore,the useful cathode materials for SIBs have been extensively studied.However,graphite and Si-based materials,commercial anode for LIBs,both exhibit their incompetence for SIBs systems.Thus,it's still a tremendous challenge to explore proper anode materials.2D materials have been extensively investigated as potential electrodes for energy storage,especially MXenes and transition metal dichalcogenides?TMDCs?.Both of them have certain advantages and limitations in energy storage.The intriguing 2D transition metal carbides/carbonitrides,also called MXenes,are increasingly being investigated as anodes as for SIB application owing to the merits of their metallic conductivity,low diflfusion barrier for Na+,and good mechanical properties.However,the electrochemical properties of MXenes were hindered by the tendency of layers restacking and modest capacities depended on the synthesis conditions and surface chemistry.TMDCs,as a typical high capacity material,have been extensively reported for SIBs anode material.Unfortunately,the huge volume charge and inherent poor conductivity cause that TMDCs electrodes exhibited a huge capacity fading,poor rate performance and undesirable cycling stability.The combination MXene with these high-performance layered materials can effectively improve the electrochemical properties of MXene.The main research contents in this paper foucus on the high-performance electrode materials based on MXene materials,including heterolayered structure composite material was synthesized by combinating metallic conductivity MXene and high capacity TMDcs.The details are as follows:?1?hierarchical MOS2/Ti3C2Tx composite was successfully prepared by a hydrothermal method using ammonium molybdate and thiourea.The unique nanosheet-on-layer architecture with uniform MoS2 nanosheets anchored on the MXene Ti3C2Tx showed excellent electrochemical properties as an anode material for SIBs.The MoS2/Ti3C2Tx electrode presents remarkably cycling stability,delivering a high reversible capacity of 250.9 mAh g-1 at 100 mA g-1 after 100cycles with 88%retention of the initial reversible capacity.Moreover,the electrode manifests a superior rate capability:even at a high current density of 1000 mA g-1,a capacity of 160 mAh g-1 can be obtained.Such excellent electrochemical performance is attributed to its hierarchical architecture.The ultrasmall MoS2 nanosheets expanding the distance between Ti3C2Tx layers provide more feasible Na+ absorption active sites and better ion transportation.Furthermore,Ti3C2Tx layers act as a substrate that can inhibit further agglomeration of MoS2 nanosheets,which not only improved the gravimetric capacity but also exhibited the good cycling stability and rate performance.?2?We fabricated a heterolayered structure of MXene flakes assembled with SnS2 nanoplates via vacuum-assisted filtration.SnS2 nanoplates was prepared by hydrothermal method using SnC14 and thioacetamide.MXene flakes that exfoliated by TBAOH could offer a steady interconnected conductive network and resist volume fluctuation of SnS2.Compared with the poor mass diffusion in the bulk MXene flakes,the addition of SnS2 nanoplates can offer numerous nanoscale diffusion paths and feasible Na+ absorption active sites achieving fast kinetics.Benefiting from high capacity SnS2,larger interlayer spacing and heterolayered structure,MX/SnS2₁:5 delivered a reversible capacity of 322 mAh g-1 after 200 cycles at 100 mA g"1,as well as outstanding rate capacity and long-term cylability even after experiencing temperature arised from 0 ? to 20 ?.These results demonstrate that MX/SnS2 electrode is a promising anode for SIBs.?3?a novel HEMM method with DMSO as solvent and intercalator,f-Ti3C2Tx_DMSO can be prepared in large-scale and high stability.The f-Ti3C2TxDMSO with larger interlayer space,smaller size and modified surface retains 2D layered morphology,and provides maximum access of electrolyte to electrodes.In contrast,the HEMM treatment without the protection of DMSO promotes the transformation from Ti3C2Tx to TiO2 and carbon.The f-Ti3C2Tx DMSO electrode exhibits a good reversible capacity of 267 mAh g-1 at 100 mA g-1,which is much higher than pristine MXene.A stable capacity of 196 mAh g-can be achieved in f-Ti3C2TxDMSO electrode after 500 cycles.Noted that a greatly enhanced rate performance is observed,a high capacity of 110 mAh g 1 can be achieved at high current density of 2 A g-1,making the f-Ti3C2Tx_DMSO electrode more desirable anode for SIBs.