| Developing novel electrodes and battery-related energy storage facilities with high energy density,high-rate capacity and long cycle stability has been the prerequisite to improve the energy utilization.Sodium ion batteries（SIBs）possess similar operating principle,lower cost and high security compared with lithium-ion batteries（LIBs）,have broad commercialization prospect in large-scale energy storage system.However,the inserrtion/desertion of Na+with larger intrinsic diameter can cause more serious volume effects,damage electrical contact and lead to irreversible capacity decline.Rechargeable lithium-oxygen batteries（LOBs）are competitive due to the superior high energy density（～3500 Wh kg-1）,but the sluggish electrochemical kinetics of lithium peroxide（Li2O2）discharge product can result in parasitic reactions which occur in Li2O2 formation/decomposition process,further lead to poor rate performance and cycle stability.Therefore,high-performance SIB anodes and LOB cathodes with optimized functional active sites can be fabricated by virtue of micro-nano structure design and electronic structure regulation,which can accelerate the pivotal redox kinetics and enhance the structural stability of electrodes.Two-dimensional transition metal carbides and carbonitrides（MXenes）with graphene-like structure couple metallic conductivity,solvophilic property,adjustable layer spacing and surface chemistry characteristics,have shown unique structural advantages and great application potential as electrode materials for high-performance energy storage devices.Herein,established in the structural characteristics of MXenebased hybrids,we fabiracated a series of high-performance electrodes of SIBs and LOBs,which pocess functionalized heterogeneous interface,optimized active site electron structure,improved ion adsorption-diffusion behavior,enhancd electrochemical kinetics and structural stability.Combined with the first principles calculations and experimental results,the "host-guest" cooperative optimization mechanism,pivotal redox reaction and the "structure-effect" relationship of SIBs and LOBs are revealed at atomic scale.（1）The Sb2Se3/Ti3C2 composites coupling monodispersed Sb2Se3 nanoparticles and high conductivity Ti3C2 MXene skeleton are fabricated through a solvothermal reaction and low temperature selenization process.Sb2Se3 nanoparticles embedded in MXene matrix shorten Na+diffusion path and possess highly reversible conversion reaction,significantly improve the energy density of SIBs and restrict the self-stacking of Ti3C2 matrix,which improve the utilization of electrochemical active sites.Ti3C2 nanosheets with nanoscale thickness and open interlayer structure promotes adequate infiltration of the electrolyte,increase the effective contact of the electrode/electrolyte,optimize the distribution of active sites,which can improve the intrinsic conductivity of the electrode and relieve the volume effect of the active component during the repeated Na+insertion/extraction processes,thus enhancing the structural stability.Functionalized heterogeneous internal interfaces are fabricated between Ti3C2 skeleton and Sb2Se3 nanoparticles,which facilitates electron/ion transportation,promotes charge transfer efficiency and accelerates vital electrochemical kinetics.The heterogeneous Sb2Se3/Ti3C2 electrodes couple insertion,conversion and alloying sodium storage mechanism,possess highly reversible electrochemical redox reaction and satisfactory specific capacity.The Sb2Se3/Ti3C2-based SIBs exhibit significantly improved energy density,rate capability and long cycle stability,can deliver the specific capacity of 495 mAh g-1 at 100 mA g-1,and 261.9 mAh g-1 can be obtained even at the high current density of 1 A g-1.（2）An alkali-induced strategy is carried to rapidly crinkle Ti3C2 nanosheets and construct a cross-linked conductive framework with three-dimensional（3D）porous structure.Mono-dispersed bimetallic NiCoP nanoparticles homogenously embedded in Ti3C2 skeleton are prepared by solvothermal and in situ phosphating treatment,which eventually obtain a well-designed NiCoP/Ti3C2 composite.The alkali-induced interconnected Ti3C2 framework possesses open pore structure,which facilitate adequate infiltration of the electrolyte and enhance electrical contact between electrode components.The 3D porous structure effectively relief the restacking of Ti3C2 nanosheets,realizing the expansion and optimization of electrochemical active sites.Bimetallic NiCoP nanoparticles which can deliver abundant redox active sites,improved electrical conductivity,enhanced structural stability,and highly reversible conversion sodium storage mechanism.The synergistic effect between NiCoP and Ti3C2 accelerates the electrons/ions diffusion at the interface,alleviate the volume expansion and agglomeration of NiCoP nanoparticles,which significantly enhanced the electrode structural stability.The NiCoP/Ti3C2-based SIBs facilitate the batterypseudocapacitance collaborative energy storage mechanism,can exhibit 82%contribution of pseudocapacitance at 0.3 mV s-1,demonstrate accelerated current response and electrochemical kinetics,and retain a specific capacity of 261.7 mAh g-1 at a current density of 1 A g-1 after 2000 cycles.（3）CNiCu-Ti3C2 composite was constructed by in-suit Lewis acidic etching strategy,which can achieve the removal of Al-atom layers and the decoration of NiCu bimetallic nanoclusters.Lewis acidic etching treatment can fundamentally remove the adverse surface-F terminations,greatly reduces the irreversible consumption of Na+,and improves the coulombic efficiency.The forceful metal-matrix interaction between Ti3C2 nanosheets and NiCu nanoclusters can induce the charge reconstruction of surface Ti-atoms,which can enhance the interfacial charge transfer kinetics,restrict the restacking of Ti3C2 nanosheets during the repeating charge/discharge process and realize the expansion and optimization of electrochemical active sites.The CNiCu-Ti3C2 anode exhibits significantly improved electrochemical properties,and provide a specific capacity of 318.6 mAh g-1 at 100 mA g-1,possesing a capacity retention rate of 97.9%after 100 cycles.DFT calculations reveal the strong "guest-support" interaction between NiCu nanoclusters and Ti3C2 matrix and modulation of electronic structure of active center on the atomic scale.The electron-rich region is formed on the surface to improve the charge exchange efficiency,which can greatly optimize the adsorption/diffusion behavior of Na+,inhibit the propagation of Na-dendrite and enhance the long cycle stability.The CNiCu-Ti3C2 based SIBs possess excellent pseudocapacitance characteristics,exhibiting a high contributionf 75.9%at the scan rate of 0.5 mV s-1.By virtue of facilitated high-rate capacity,the CNiCu-Ti3C2 anodes deliver a specific capacity of 180.2 mAh g-1 at the ultrahigh current density of 10 A g-1.（4）A CO2-assisted thermal-reaction strategy is developed to fabricate a highly efficient SASe-Ti3C2 single atomic electrocatalysts which are applied as advanced cathodes for high-performance Li-O2 batteries.Se single atoms（SAs）precisely fill the intrinsic surface Ti-vacancies and form strong Se-C interactions,which can induce the difference of electron delocalization and spin characteristics,regulate electron structure of isolated Se atomic centers and greatly activate the catalytic properties of Ti3C2 basal plane.The well-designed SASe-Ti3C2 electrode exhibits meliorative charge/discharge polarization（1.10 V vs Li/Li+）,ultrahigh discharge capacity（17260 mAh g-1 at 100 mA g-1）,and superior durability（170 cycles at 200 mA g-1）applied as LOB cathode,which possess enhanced catalytic activity and structural stability.Critically,DFT calculations potently identify that the interactions between Se SAs and Ti3C2 matrix can drastically regulate local charge reconstruction,enhance the intrinsic LiO2-absorption ability and optimal charge transfer efficiency,thus fundamentally modulating the nucleationgrowth process of Li2O2 products and finally construct a Li2O2/electrolyte/catalyst three-phase interface with good compatibility and stability... |
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