Investigation Of Electrochemical Energy Storage Properties For Heterogenous Metal Compounds

Lithium secondary batteries have the advantages on high capacity,rich resources and environmental friendliness.However,many constraints hindered its further development.For example,the theoretical capacity of carbon have only 372 m Ah g^-1.Although metal compounds have high theoretical capacity,their poor conductivity,volume expands and the slow solid phase diffusion of lithium ions could not be ignored.The dissolution and shuttle effect of polysulfides in lithium-sulfur batteries can cause serious capacity loss.The emergence of heterogenous materials provides new ideas for alleviating the above problems.It combines the advantages of each component material,has synergistic properties that a single material could not have,and the built-in electric field induced at interface can promote charge transfer,improve electrochemical performance,especially in rate performance.In this paper,the electrochemical energy storage behavior of heterostructure materials in lithium secondary batteries has been systematically analyzed and studied.The specific content is as follows:1.Heterointerface plays the key role to adjust and enhance the charge transport properties of composite electrode materials in Li-ion batteries.Tungsten trioxide/zinc oxide(WO₃/ZnO)heterostructure electrode is fabricated by WO₃hexagonal flower arrays with a deposited layer of ZnO QDs supported by conductive carbon cloth substrate.The built-in electric fields induced at interface help to enhance Li-ions transport in charge-discharge processes.As expected,the WO₃/ZnO heterostructure composite electrode exhibits remarkable reversible discharge capacity(?1500 m Ah g^-1at 0.28C),high rate performance(?500 m Ah g^-1at 9.0C),and excellent cycling stability(1100 m Ah g^-1at 1C after 300 cycles).This result shows that the heterointerface plays a vital role in adjusting the charge transport properties of the electrode materials.2.Nanocube CoO@Co₉S₈-rGO heterostructure with rich-phase boundaries are prepared using ZIF-67 as precursor.In our system,Co O@Co₉S₈-rGO consisting of a typical p-n heterojunction at heterointerface,induces a built-in electric field that boosts the overwhelming transport of the ion/electron.The thin nanosheet structure of Co O increases surface area which exposes more active sites and benefits infiltration of electrolyte.The rGO enhances electronic conductivity of the heterogeneous Co O@Co₉S₈-rGO.As expected,the Co O@Co₉S₈-rGO heterogeneous electrode exhibits remarkable reversible discharge capacity(912 m Ah g^-1at 0.1 A g^-1),high rate performance(586 m Ah g^-1at 5 A g^-1),and excellent cycling stability(600 m Ah g^-1at 1 A g^-1after 500 cycles).This result shows that the heterointerface plays a vital role in adjusting the charge transport properties of the electrode materials.3.Hollow heterostructure NC@SiO₂@Co P/NC is designed for cathode of Li-S batteries.The existence of the hollow structure not only effectively increases the sulfur loading,but also serves as a framework for physically confined polysulfides.Co P derived from ZIF-67 has a better catalytic effect on the conversion of polysulfides.M-SiO₂not only improves the stability of the material structure,but also the adsorption effect of m-SiO₂on polysulfides can not be ignored.Therefore,in order to improve the conductivity of the material,m-SiO₂coated with a layer of N-rich doped carbon,which not only improves the conductivity but also further enhances the conversion of polysulfides.As a cathode,the Li-S battery has better performance.It delivers an initial capacity of 1450 m Ah g^-1at 0.1C,and even at 3 C,reaches capacity of 700 m Ah g^-1.The long cycle results show that it still maintains a high specific capacity of 400 m Ah g^-1with a single-cycle attenuation rate of 0.05%over 1000 cycles at 1C,which indicates its excellent electrochemical performance.4.The hetero-electrocatalyst(MoS₂@Co S₂)is synthesized by hydrothermal to modify separator for Li-S batteries.In detailed,absorptive MoS₂nanosheets can not only adsorb Li PSs but also offer a transport channel of lithium-ion.And half-metallic Co S₂affords high electrocatalytic activity for polysulfide redox reactions.More importantly,the specific architecture enables intimate interphase boundary between MoS₂nanosheet and Co S₂nanocube,which realizes rapid charge transfer by inducing a built-in electric field due to heterojunction.The built-in electric field could be a bridge that closely connects adsorptive MoS₂and catalytic Co S₂,which smooth absorption-diffusion-catalysis of Li PSs,further avoid the accumulation of polysulfides and improving the utilization rate of sulfur,especially,under high current density.As a result,MoS₂@Co S₂-PP delivers an initial capacity as high as 1480 m Ah g^-1at 0.1 C and 811 m Ah g^-1at 3 C.The long-term cycle shows decay rate of each cycle is 0.05%at 1C.Even at sulfur loading of 6 mg cm^-2,the high reversible capacity of 4.5 m Ah cm^-2is obtained at 0.2 C and the low E/S ratio of 7?L mg^-1,indicting its great potential in practical applications...