Structural Modulation Of Indium Selenide Based Composites And Their Electrochemical Sodium Storage Properties

In recent years,sodium-ion batteries（SIBs）have attracted wide attention due to their advantages of abundant sodium resources and low cost.Although SIBs have similar working principle to lithium-ion batteries,the traditional graphite anode has a very low sodium storage capacity（<32 m A·h/g）when applied in SIBs.Therefore,the development of high-performance anode materials that are suitable for SIBs has great practical significance.Among many promising anode materials,metal selenides with high theoretical specific capacity have been widely studied.In₂Se₃,as a kind of typical narrow-band（1.7-2.4 e V）metal selenides,is expected to become an alternative anode material for sodium storage.But the problems such as low intrinsic conductivity and serious volume change seriously hinder its practical application.Regarding these problems,diminution of the particle dimension and the combination with conductive matrices are widely considered to be the most effective modification strategy.At present,two-dimensional layered materials,such as reduced graphene oxide（r GO）and Ti carbides（MXene）,have been proved to have excellent matrix properties.To this end,the following research work has been down in this study aiming at the structure regulation of In₂Se₃based composites and their electrochemical performance:（1）In（OH）₃nanoparticles were prepared by solvent thermal method.By means of a liquid nitrogen quenching treatment upon the mixed suspension containing In（OH）₃NPs and graphene oxide,then freeze-dried and gas-phase selenization,high-loading In₂Se₃NPs on the surface of r GO with uniform dispersion is achieved.The material characterization and electrochemical performance tests of the composites were conducted systematically.It was found that the presence of r GO matrix effectively dispersed the In₂Se₃nanoparticles and alleviated the volume expansion of In₂Se₃during the sodiation/desodiation processes.In a diglyme electrolyte system,the repeated discharge-charge cycles caused the pulverization of In₂Se₃particles,and then induced transformation of In₂Se₃crystals fromγtoβphase.This unique crystal transformation phenomenon significantly improved the cycling stability of the In₂Se₃NP/r GO electrode materials.By optimizing the loading amount of In₂Se₃,the In₂Se₃NP/r GO-0.06 electrode exhibited the best sodium storage performance.For example,the initial reversible capacity reached 425 m A·h/g at the current density of 0.1 A/g,and the capacity retention ratio was as high as 80.8%even after1000 cycles at 4 A/g.Moreover,the optimized electrode had excellent rate capability.A reversible capacity of 281 m A·h/g with high capacity retention of 76.4%still can be retained at the current density of 20.0 A/g.（2）In-MOF was prepared by the strategy of constructing metal-organic framework.Compound the as-prepared In-MOF with polydopamine（PDA）coated MXene then freeze-dried.After an in-situ selenization,a carbon-coated indium selenide/nitrogen-doped carbon-coated MXene（In₂Se₃@C/NC-MXene）composite was developed.The In-MOF was converted to carbon-coated indium selenide nanoparticles during gas-phase selenization process.The carbon coating can effectively inhibit the sintering and growth of In₂Se₃particles,improve the dispersibility and relieve volume expansion.The PDA-treated MXene formed nitrogen-doped carbon coated MXene after annealing,which effectively inhibited the surface oxidation of MXene.The double-carbon layer protected structure effectively addresses the problems of In₂Se₃nanoparticle agglomeration and the integrated instability of electrode structure upon sodiation/desodiation,and meanwhile improves the electron transfer and ion diffusion dynamics.Thus the In₂Se₃@C/NC-MXene composite exhibits excellent sodium storage performance.The initial reversible capacity at 0.1 A/g reached 461.1 m A·h/g.The capacity retention ratio of the electrode at1 A/g after 1000 cycles is 82%.Even at the high current density of 6 A/g,it can still releases a reversible capacity of 309.5 m A·h/g and a high capacity retention of 74%,demonstrating the excellent rate ability.