Construction And Energy Storage Properties Of Metal Organic Coordination Polymers And Derived Sulfide Based Electrode Materials

With the rapid development of mobile electronic devices,lithium-ion batteries?LIBs?have been widely used in business due to their high energy/power density and long cycle life.Na and K elements have similar chemical properties to Li,and they have higher resource abundance and lower cost.Therefore,sodium ion batteries?SIBs?and potassium ion batteries?PIBs?are considered to be ideal energy storage devices instead of LIBs.Because the negative electrode materials play an important role in battery performance,it is urgent to develop high-performance sodium/potassium ion battery negative electrode materials.The advantages of metal organic coordination polymer and derived sulfide electrode materials are:simple synthesis method,low cost,high theoretical capacity;but there are also problems such as poor conductivity,easy to powder during charging and discharging.In this paper,through the composite optimization of the structure and components of the material,the conductivity of the electrode material is improved,the reactive sites are increased,and the volume change in the process of charging and discharging is buffered,so as to improve the sodium/potassium storage capacity of organometallic coordination polymers and derivative sulfide based composite materials.The main research results are as follows:?1?Fe-CPNWs/RGO composite films were prepared by solvothermal method,vacuum assisted filtration technology and subsequent high temperature thermal reduction technology,and their mechanical flexibility was characterized in detail.The behavior of sodium ion storage as a flexible self-supporting electrode was studied by means of phase,morphology and electrochemical properties.The one-dimensional iron-based complex nanowires shorten the transmission distance of ions and electrons,and the coating of reduced graphene oxide greatly improves the electronic conductivity and mechanical flexibility of the composite films.Further analysis shows that the redox center of the coordination polymer is the carboxyl and aminegroups of the organic part.The composite film electrode material shows excellent rate performance in the voltage range of 0.01-3.0 V(404-120 mAh g^-1 at the current density range of 100-3000 mA g^-1),and has good cycle stability under the condition of high current density(the reverse capacity can be maintained at 100 mAh g^-1 after 4000 cycles of current density of1000 mA g^-1).?2?For the first time,Mn based coordination polymer nanowires?Mn-CPNWs?were synthesized by microwave-assisted solvothermal method.Mn-CPNWs/GO composite films obtained by vacuum assisted filtration were used as precursors.After the process of in-situ sulfurization,MnS@CNWs/rGO self-supporting films were prepared.The multi-dimensional composite film electrode has excellent mechanical flexibility,electrochemical performance and long cycle stability.On the one hand,MnS nanoparticles embedded in one-dimensional carbon nanowires buffer the volume expansion of electrode materials in the process of charge and discharge;on the other hand,the synergistic effect between multi-dimensional composite carbon substrate improves the electron and ion transfer rate and flexibility of the film composite electrode.When the self-supporting electrode is used as the anode material for sodium ion battery,it has high reversible capacity(specific capacity is about 560 mAh g^-1 when the current density is 100 mA g^-1),excellent multiplying capacity(reversible capacity is about 147 mA g^-1 at the current density is 2 A g^-1)and super long cyclling life(reversible capacity is still about 150 mA g^-1 after 10000 cycles at 1 A g^-1).?3?One dimensional vanadium based MOF?MIL-47as?was synthesized by a simple hydrothermal method as the precursor,and the hollow tube?V₃S₄@C NS-HNTs?assembled by V₃S₄@C nanosheets was successfully prepared by in-situ vulcanizatio.The macro tubular structure,micro V₃S₄ NiAs crystal structure and interface carbon coating can not only improve the electrochemical conductivity and stability of the composite electrode,but also contribute to the adsorption/diffusion of alkali metal ions.This makes the electrode material have high capacity and excellent rate performance when storing alkali metal ions.The electrochemical behavior and storage mechanism analysis show that the electrode materials with this structure exhibit selective alkali metal ion storage behavior,that is,through intercalation and pseudo capacitance reaction to store potassium and through conversion reaction to store lithium and sodium ions.Therefore,when the electrode material is applied to the negative electrode of PIBs,the reversible capacity is lower than that of LIBs and SIBs,but the cycle life is longer(1 A g^-1,after 4000 cycles,?182 mAh g^-1).