The Sodium Storage Mechanism Of Indium Sulfides/selenides Derived From Indium-based Metal Organic Framework

Sodium ion capacitors(SICs)provide high energy density,high power density and long lifespan as a new type of electrochemical energy storage device.SICs have the dual characteristics of batteries and supercapacitors,which have the advantages of higher energy density than conventional supercapacitors and higher power density than sodium ion batteries.It is suitable for the needs of the age and widely used in large-scale energy storage in prospect.Therefore,the research on low-cost SICs technology for large-scale energy storage applications has important strategic significance.As one of the core components of SICs,the anode materials has been the key to the overall performance and index of SICs.Focusing on the construction of sodium ion capacitors with both high energy density and high power density,the paper has rational electrode structure design of indium sulfides/selenides derived from indium-based metal organic framework to prepare the pseudocapacitive sodium storage anode materials with high capacity,high rate and high stability.The main research content can be divided into three aspects:(1)In order to solve the problem of poor rate performance and cycling performance of In6S7 due to serious volume expansion,the microspindles of carbon coated In6S7 nanoparticles containing nitrogen and sulfur was prepared by in-situ vulcanization reaction using metal organic skeleton compounds as precursors.By adjusting the calcination temperature,sulfurization products of different structural phases can be obtained.The optimal In6S7/NSC HMS composite material exhibits excellent Na+storage characteristics due to hollow and porous structure and continuous and highly conductive carbon network.By using in-situ XRD and ex-situ TEM,it is confirmed that the Na+ storage mechanism in In6S7/NSC HMS through highly reversible conversion and alloying reactions.The theoretical calculations of AIMD and CI-NEB have verified the rapid sodium storage kinetics of In6S7/NSC HMS electrodes.A SIC.prototype,assembled by employing In6S7/NSC HMS as anode and homemade active carbon as cathode,delivers a high energy density of 136.3 Wh kg-1,an extremely high power density of 47466 W kg-1 and an excellent cycling performance exceeding 20000 cycles.Three-electrode Swagelok cell confirms that these favorable properties of this SICs are mainly attributed to the matched and stable Na+storage behaviors of In6S7/NSC HMS anode with activated carbon cathode.It is worth noting that we for the first time demonstrate that the unremittingly pursued issue of kinetics mismatch between battery-type anode and capacitive cathode in SICs has been solved via a In6S7 anode with ultrahigh-rate sodium storage through the combined conversion and alloying reactions.(2)Selenium and sulfur belong to the same main group of elements and have similar physicochemical properties.Based on the exploration of indium sulfide materials in the early stage,it further inspired the research on indium selenide materials.We developed In2Se3/HPC composites derived from indium-based metal organic framework.The In2Se3/HPC composites has hollow and porous structure,which can provide efficient channels for the rapid transport of ions and electrons.At the same time,the porous carbon skeleton provides sufficient void space to alleviate internal mechanical stress during repeated charging and discharging processes.The In2Se3/HPC electrode exhibits good cycling stability and rate performance.The In2Se3/HPC electrode provided initial discharge/charge specific capacities of 613.2 and 570.7 mAh g-1 at a current density of 0.1 A g-1,with ICE of 93.1%.Even if the current density increases to 10.0 A g-1,the In2Se3/HPC electrode can still provide a high reversible capacity of 390.8 mAh g-1,and after 5000 cycles at a current density of 10.0 A g-1,it can still output a specific capacity of 294.5 mAh g-1,with a capacity retention rate of up to 74.1%.In addition,the reaction mechanism between In2Se3 and Na+(highly reversible conversion and alloying reactions)was revealed through ex-situ XRD characterization.In2Se3/HPC//PDPC SIC was further assembled by coupling the In2Se3/HPC as anode and PDPC as cathode.Benefit by the high pseudocapacitance characteristics of In2Se3/HPC,In2Se3/HPC//PDPC SIC is as high as 3.8 V in terms of the output voltage,providing high energy density of 106.1 Wh kg-1 and high power density of 48960.2 W kg-1.In addition,In2Se3/HPC//PDPC SIC exhibits good cycling performance.After 10000 cycles at a current density of 1.0 A g-1,the SIC can provide specific capacity of 36.4 mAh g-1,showing a capacity retention rate of 74.7%.During the whole cycling test,the CE values for In2Se3/HPC//PDPC SIC are almost close to 100%.(3)Considering the low intrinsic ionic and electronic conductivity of In2S3 materials limited its electrochemical kinetics in the process of exploring indium sulfide materials,the paper puts forward the strategy of combining doping,nanostructure design and carbon coating to prepare In2S3-xSex/NSC HPM composites.Electrochemical tests show that the sulfur selenide composite exhibits superior electrochemical performance than indium sulfide and indium selenide materials.The sodium storage mechanism of In2S3-xSex/NSC HPM was further revealed using ex-situ XRD.In2S3-xSex/NSC HPM electrodes achieve excellent electrochemical performance through highly reversible conversion and alloying reactions.At the same time,the structural evolution process and kinetic behavior during sodium storage are further studied.In addition,SIC was further assembled using In2S3-xSex/NSC HPM as the anode and PDPC as the cathode.In addition,In2S3-xSex/NSC HPM//PDPC SIC was further assembled by coupling the In2S3-xSex/NSC HPM as anode and PDPC as cathode.In2S3-xSex/NSC HPM//PDPC SIC provides high energy density of 110.6 Wh kg-1 and high power density of 49248.3 W kg-1.In addition,the SIC retains a specific capacity of 35.1 mAh g-1 after 10000 cycles at a current density of 1.0 A g-1,showing a capacity retention rate of 100%.