| Rapid development of the energy storage field puts higher requirements on energy storage devices.Hence,enhancing capacity and rate ability,and prolonging battery cycle life is significant.Molybdenum-based materials with open structure,multivalent,low toxicity,and easy preparation characteristics are favored by researchers.The representative compound molybdenum dioxide（Mo O2）has a tunnel crystal configuration,high compacted density,and moderate oxidation/reduction potential,becoming one of the anode candidates for alkali metal ion batteries.However,the serious volume effect of Mo O2 in the charge/discharge process leads to poor electrochemical cycle stability and limited cycle life.Another compound molybdenum disulfide（Mo S2）has a typical sandwich-like layered structure.Easy-modified layer spacing and large specific surface area not only provide plenty of storage sites but also for larger-sized ions embedding,however,the layer structure tends to collapse under large current density conditions,causing a short cyclic lifespan.Moreover,Poor conductivity of Mo S2 results in unsatisfied rate performances.Nanoparticlization,composite engineering,interface engineering,layer spacing regulation,and phase adjustment strategies solve the problems to some extent,but there are still some scientific problems to be solved urgently.Based on those strategies,the composition and structure of Mo O2 and Mo S2 are optimized for enhancing the stability of electrodes and prolonging batteries’life.The major contents and research results are summarized below:（1）Quantitative manipulation of covalent bonds for preparing the stable Mo O2composite electrode.In this work,the composite engineering strategy was adopted to quantitatively manipulate Mo-N covalent between nitrogen-rich carbon matrix and uniformed carbon layer-protected Mo O2 nanoparticles（named Mo O2-2@N-C）.Optimizing covalent bond content not only prevents Mo O2 volume expansion from falling off the carbon matrix but also prevents the extra amount of carbon material introduced to weakening the energy density of batteries,then,the relationship among"covalent bond content-active substance content-cycle stability"is well balanced.Mo O2-2@N-C shows 2700 cycles life at 1000 m A/g which is 100times than unmodified Mo O2.Assembled full cell Mo O2-2@N-C//Li Fe PO4 drives colored LEDs successfully,showing the practical application potential.In addition,the"gel encapsulation-post annealing"method has been successfully applied in the preparation of various transition metal oxide-based anodes,demonstrating its universality.（2）Induced high-quality SEI layer at anode interface for preparing the stable Mo S2composite electrode.It is difficult to prepare uniform Mo S2 nanoparticles in hydrothermal processes because the nucleation/growth conditions of Mo S2 are difficult to accurately control.Hence,inducing uniform and stable solid electrolyte membranes（SEI）on Mo S2 surfaces is a challenge.In this work,by electrospinning method,combined with composite engineering and interface regulate strategy,the surface with uniform nanoparticles of 800-Mo S2/CNFs is regulated by the assembly behavior of ammonium tetrathiomolybdate at high temperature,further inducing a stable SEI layer.The formation and morphological evolution of the SEI layer are characterized by ex-situ TEM and impedance at different charging/discharge stages.The SEI layer of 800-Mo S2/CNFs prevents Mo S2 from direct contact with the electrolyte to produce byproducts and avoid the dissolution of active substances,improving the cycle stability.As a result,800-Mo S2/CNFs show a life of 2000 cycles at 1000 m A/g and stable rate performances.（3）Confined Mo S2 into a unique composite matrix for preparing the stable composite electrode.The matrix of Mo S2 can release stress in the electrochemical cycle process,enhancing the cycle life.However,Mo S2 is easily detached from the matrix surface under high current densities.Inspired by plant growth in nature,in this work,the composite engineering strategy was used to construct a new type matrix Ti O2@C for Mo S2 to prepare c-Mo S2.Mo S2（analogous to plants）is implanted inside the Ti O2@C matrix（analogous to soil）to prevent it from collapsing.In addition,the chemical bonds between the Ti O2@C and Mo S2 avoid the loss of active substances under high current densities.Benefiting from that,c-Mo S2 shows good stability at high current density conditions in lithium-ion batteries（LIBs）and sodium-ion batteries（SIBs）（LIBs:5000 m A/g with 600 cycles;SIBs:1000 m A/g with 1000 cycles）.At the same time,c-Mo S2can work at low-temperature conditions（0oC,-25oC）,and c-Mo S2//Li Ni Co Mn O2 full cell successfully drives three parallel LED lights,showing a huge practical application potential.（4）Embedded organic small molecules in the Mo S2 layer for preparing the stable composite electrode.The interlayer spacing of thermodynamically stable phase Mo S2 is limited,and the electrostatic interaction between zinc ions and Mo S2 is strong,resulting in low capacity and poor rate performances.In addition,the oxidation of Mo S2 in the water medium leads it to dissolve,causing limited cycle life.In this work,layer spacing regulation and composite engineering strategies were adopted to realize small organic molecules embedded and GQDs layer-protected Mo S2（named:0.1GQD-GW/Mo S2）.The small molecule enlarges the interlayer spacing,stabilizes the structure,increases the hydrophilicity,reduces the zinc ion diffusion energy barrier,and improves the electrochemical cycle stability of Mo S2.The GQDs prevent the Mo S2 dissolution and effectively extend the 0.1GQD-GW/Mo S2 cycle life.Finally,0.1GQD-GW/Mo S2 shows stable cycle ability at room/low temperature（room temperature:1000 cycles life at 1000 m A/g;-25oC:2000 cycles at 500 m A/g）.The successful application of flexible battery Zn//0.1GQD-GW/Mo S2 indicates the practical application potential. |
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