| The establishment of clean and efficient new energy structure is the urgent demand for sustainable development of current society.With the improvement of renewable energy technologies,it is urgent to develop secondary battery energy storage supporting technology.Due to the limitation of lithium resources and cost,lithium-ion batteries are facing severe challenges in the wide application of large-scale energy storage and other fields.Therefore,it is urgent to develop new secondary battery systems with rich resources and excellent performance.Sodium and magnesium elements have rich resources,low prices,and similar chemical properties with lithium,leading to potential application prospects for the development of sodium and magnesium ion batteries.In particular,the metal magnesium anode has high theoretical specific capacity and relatively low electrode potential.Furthermore,it doesn’t grow dendrites during dissolution and deposition in most electrolytes,resulting unique safety advantage for rechargeable magnesium batteries.However,sodium ion batteries and rechargeable magnesium batteries still face many challenges in the aspect of electrode materials.For relatively large ionic radius（Na+）and high charge density(Mg2+),sodium and magnesium storage mechanism has strict requirements on the host lattice of materials.Transition metal selenides can realize high-capacity sodium and magnesium storage through electrochemical conversion reaction,which have great application potential in sodium ion batteries and rechargeable magnesium batteries.However,the conversion compounds need to overcome large energy barriers and undergo the structural reorganization during the structural conversion process,leading to the poor electrochemical activity,inferior cycle performance and kinetic behavior.In view of the above problems,several kinds of metal selenide conversion electrode materials with nano-composite structure using hyperbranched polymer as template and electrode additive were investigated,and explored their application in sodium ion batteries and rechargeable magnesium batteries,providing theoretical guidance and technical support for the development of high-capacity sodium/magnesium conversion electrode materials.The main research contents and results in this thesis are as follows:（1）Fe S-AHP microflower composite was synthesized with amino-terminated hyperbranched polymer（AHP）as the template and electrode additive,and then Fe Se2-AHP composite microsphere sodium storage anode material was further prepared by liquid selenium ion exchange.The structure and sodium storage performance of the composite and the effect of AHP in the composite on the kinetic performance and long-cycle stability of Fe Se2 sodium storage were emphatically investigated.The experimental results show that the AHP in the Fe Se2-AHP composite are uniformly distributed in the Fe Se2 microspheres through the complexation with iron ions.The elastic molecular network constructed by AHP can buffer the volume expansion of the electrode,prevent the agglomeration of active components and effectively stabilize the structure of the electrode.The reversible capacity of Fe Se2-AHP electrode delivered584.8 m Ah g?1 at high current density of 20 A g?1,and remained 455.3 m Ah g?1 after2000 cycles at current density of 1 A g?1with capacity retention rate 93.3%,showing excellent rate and cycle performance.The full sodium ion battery with Na3V2（PO4）3/C as the cathode also showed good power output and practical application potential.（2）The Co Se2/Se-AHP composite was prepared by the selenization of the complex of AHP and cobalt ion.The composition,microstructure and magnesium storage properties of the composite were investigated.It is found that AHP and amorphous selenium are uniformly dispersed in the Co Se2/Se-AHP composite.The prepared Co Se2/Se-AHP-2 electrode showed the highest reversible magnesium storage capacity of 226.8 m Ah g?1 at the current density of 0.1 A g?1,a reversible capacity of 71.6 m Ah g?1at the high rate of 1.0 A g?1,and a high-capacity retention rate of 95%after 300cycles at a current density of 0.2 A g?1.The experimental results show that appropriate amount of selenium electroactive components in Co Se2 phase can greatly improve the magnesium storage activity of Co Se2.The organic/inorganic phase interface constructed by AHP in the active material can promote the charge transfer rate between phases,and effectively improve the kinetic behavior and rate performance of Co Se2.（3）The Cu9S5-AHP microflower composites were prepared by using AHP template,and then the Cu SxSey-AHP composite microspheres magnesium storage cathode materials were further prepared by Se2-exchange.The microstructure,magnesium storage characteristics and kinetic properties were studied.It was found that the selenium anion partially exchanged the sulfide ion in copper sulfide,and formed the compound containing Cu S,Cu Se and AHP.The synergistic effect of sulfur-selenide dianion ions in the composite can effectively enhance the electrical conductivity of the material and improve the magnesium storage activity of the composite.The Cu SxSey-AHP-1 composite electrode delivered 204.7 m Ah g?1 at 0.1 A g?1,and remained at 114.7m Ah g?1 at a current density of 0.2 A g?1 for 300 cycles.The results show that the synergistic effect of dianions can significantly improve the magnesium storage activity of the composite electrode,and greatly reduce the energy barrier of the conversion reaction,and promote the reversible multiple electrons structural conversion. |
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