Bio-inspired Mxene Based Multiple Heterostructure Composites For Advanced Sodium/potassium Ions Storages

Of late years,as the rapid development of the era of energy consumption,together with the growing shortage of fossil fuels,scientists from all over the world commit themselves to achieve new breakthroughs in energy storage technology,for the sake of building a community with shared future for mankind.Secondary sodium/potassium ions batteries(SIBs/PIBs)are considered as ideal alternative energy storage devices in future.Therefore,exploring advanced high-performance anodes has been becoming a primary task for promoting commercial development.As an emerging two-dimensional(2D)functional material,transitional metal carbides(MXene)open up many more interfacial assembling possibilities,benefiting from intrinsic unique physico-chemistry,such as metallic conductivity and rich surficial functional groups.Still,the nature of 2D morphology and carbides of MXene brings about the self-stacking and rapid capacity decay issues,during the long-term charging/discharging cycles.Additionally,transitional metal chalcogenides(TMC)have been proved as a promising anode for SIBs and PIBs with high reversibility and high theoretical specific capacity.However,continuous Na⁺/K⁺ions insertion/extraction into/out of anodes can destroy the microstructure of nanomaterials,resulting from the huge volume variation.Therefore,the unsatisfying cyclic stability cannot meet the requirement in practical application.To tackle the above-mentioned scientific issues,this thesis focuses on the investigation on the novel interfacial assembly technology.By feat of microorganism-derived carbon matrix as the building blocks,TMC-based compounds acted as the external decoration,to prepare multiple heterostructure anodes via optimal structural design and tunable synthesis.Multiple anodes with heterostructure endows abundant storage site and various diffusion pathways for active ions,further enhanced the larger radius Na⁺/K⁺ions migration rates,refined the sluggish diffusion kinetics,as well as boost the ions storage capacities.1.Firstly,we proposed a microbial fungus as an adsorption carrier,using a microbe-assisted adsorption assembly strategy to achieve a 2D/1D heterostructure with N-doped carbon matrix for high performance SIBs/PIBs anodes.The hydroxyl/amino group in the fungal cell wall bonding with hydroxyl groups of MXene nanosheets by forming hydrogen bonds.Compared to the multilayer Ti₃C₂T_x MXene,the porous surficial structure and open ion channels can deliver higher reversible Na⁺/K⁺ions capacities.The ion diffusion kinetic analysis and density functional calculation revealed that this 2D/1D porous heterostructure can taking full advantages of inherent advantages of 2D materials,further promoting adsorption and transport towards sodium/potassium ions.2.Secondly,we proposed the concept of"Janus"interfacial assembly technology to realize biologically derived carbon matrix supporting MXene-based ternary heterostructure hybrids materials,modified with transition metal chalcogenides(MSe=Cu_1.75Se,Ni Se₂ and Co Se₂)owing to the various physico-chemical properties of MXene nanosheets.MXene nanosheets were uniformly coated on the surface of microbe fungal fibers by forming hydrogen bonds between functional groups.Then,the electrostatic self-assembly of between the electronegative MXene nanosheets with the positively charged transition metal ions on the surface of matrix was achieved through coulomb force.The MSe@MXene@CNRib ternary hetreostructure was obtained after gas phase selenization.The systematic kinetic analysis and theoretical calculation of revealed that the interfacial ion transport ability of ternary heterostructures is several orders of magnitude higher than that of pure MXene anodes,together with excellent long-term cyclic stability.3.Thirdly,MXene nanosheets were used as the highly conductive layer,to prepare MXene conductive layer supporting carbon-based Fe_x-1Se_x heterostructure hybrid anodes by a step-by-step assembly strategy.Without MXene nanosheets as the conductive layer,the transition metal ions migrated into the interior of microbe fungi via biological leaching effect,to form the fungal-derived carbon coated Fe_x-1Se_x heterostructure hybrids.By contrast,as a highly conductive layer,MXene supporting ternary heterostructure Fe_x-1Se_x heterojunction with higher degree of exposure,can fulfil its full advantage of high theoretical capacity,further achieving high rate capabilities in sodium/potassium ion battery application.The assembled full SIBs/PIBs devices based on the ternary heterostructure exhibit excellent cyclic robustness.4.Based on the previous work,we choose vanadium-based MXene as the precursor,using the above-mentioned assembly strategy,to achieve the carbon based Cu_0.87Se modified V₂CT_x MXene derivative V₂O₃ ternary heterostructure anode material.In vanadium-based oxides,the high electrochemical reactivity generated by the multivalent states of vanadium element is conducive to further improving the electrochemical performance.Compared with the pure V₂CT_x MXene coated carbon hybrid fiber,the Cu_0.87Se modified carbon-based V₂O₃heterostructure deliver more electrochemically active sites.Along with the ion storage behavior,the co-existence of transition metal selenide/oxide“heterojunction”impart higher conductivity and energy storage capacity.In conclusion,we used low-cost and high-biosafe microbe fungi as adsorbents and structural building blocks,to realize the optimal design and tunable preparation of MXene-based multiple heterostructures,which address the capacity decay and self-stacking obstacles in SIBs/PIBs applications of 2D MXene materials,and further improved the cycling stability of TMC materials as well.