Preparation Of Co-Based,Manganese-Based And Carbon-Based Nanocomposites And Their Applications In Electrochemical Energy Storage Devices

After entering the 21st century,the rapid development of portable electronic products and electric vehicles has greatly increased the demand for energy storage devices.Lithium-ion batteries（LIBs）have attracted the interest of researchers due to their large performance advantages,and LIBs with higher energy density and power density have been extensively developed.Due to the large consumption of lithium resources,the research of aqueous zinc ion batteries（AZIBs）and sodium ion batteries（SIBs）has also emerged.The excellent performance of the battery mainly depends on the electrode material,so it is urgent to study the electrode materials applied to different batteries.In this paper,cobalt selenide（Co Se₂）/cobalt selenide（Co Se）,manganese oxide（Mn₃O₄）and carbonaceous materials were used as research objects.Co Se₂/Co Se bird’s nest（Co Se₂/Co Se BNs）,Mn₃O₄ nanocrystals@3D honeycomb hierarchical porous network scaffold carbon（Mn₃O₄@HPNS）and three-dimensional hierarchical honeycomb macroporous/mesoporous/microporous carbon（HH carbon）were synthesized by boiling method,hydrothermal method,and carbonization treatment.The lithium storage performance of Co Se₂/Co Se,the zinc storage performance of Mn₃O₄ and the sodium storage performance of pure carbon materials were improved by nanostructure design and compounding with high conductive carbon matrix.The main research contents and conclusions of this dissertation are as follows:（1）Raspberry-like Co-ethylene glycol precursor was synthesized by hydrothermal reaction.Further selenization to a hierarchical hollow superstructure Co Se₂/Co Se nest assembled by Co Se₂ and Co Se nanocrystals.The structure has a nano-scale hollow structural unit,a layered porous superstructure shell and a large hollow interior.Co Se₂/Co Se bird’s nest has excellent cycle performance,high reversible capacity and satisfactory rate performance(1361 m Ah g^-1 after 1000 cycles at 1 A g^-1,579 m Ah g^-1after 2000 cycles at 2 A g^-1,and 315 m Ah g^-1 after 1000 cycles at 5 A g^-1).Electrochemical kinetic analysis and ex-situ material characterization show that the surface capacitance behavior controls the electrochemical reaction,and the composites have low reaction impedance,fast and stable Li⁺diffusion and excellent structural stability.The superior lithium storage performance is attributed to the unique superstructure bird’s nest.Large specific surface area,abundant hierarchical pores and openings lead to high electrochemical activity,thus providing high reversible capacity.Small hollow nanosphere units,a sufficiently thick hierarchical porous superstructure shell and a large hollow interior bring strong synergistic effects to improve cycle performance.The tight coupling between Co Se₂/Co Se nanocrystals and hollow nanospheres ensures high conductivity.This work greatly enriches the understanding of the structural design of high-performance cobalt selenide anodes.（2）Three-dimensional honeycomb hierarchical porous network scaffold carbon was synthesized by a unique PVP-SiO₂ boiling method using boiling bubbles as soft templates and SiO₂ nanospheres as hard templates.Subsequently,Mn O₂ nanosheets grew tightly on the carbon matrix and further decomposed into Mn₃O₄ nanocrystals.The obtained Mn₃O₄nanocrystals@3D honeycomb hierarchical porous network scaffold carbon has abundant mesopores and large specific surface area(92 m² g^-1).When used as a cathode material for zinc ion batteries,the as-synthesized composite exhibits high reversible capacity(546.2 m Ah g^-1 at a current density of 0.5 A g^-1),remarkable cycle stability(97.8 m Ah g^-1 after 600 cycles at 3 A g^-1)and excellent rate performance(15.7 m Ah g^-1 at a current density of 10 A g^-1).The kinetic analysis shows that the storage mechanism of zinc includes the diffusion process of Zn²⁺and H⁺and the capacitance process,and is dominated by capacitance storage.Excellent zinc storage performance benefits from structural advantages.The unique carbon matrix improves the electronic conductivity of Mn₃O₄,which is beneficial to the penetration of electrolyte and supports Mn₃O₄nanocrystals well.The small size and large specific surface area of Mn₃O₄ nanocrystals promote a significant capacitance storage effect.（3）Three-dimensional honeycomb carbon with abundant macropores,mesopores and micropores was constructed by using SiO₂ nanospheres and microspheres as hard templates,various boiling bubbles as soft templates,polyvinylpyrrolidone as assembly agent and carbon source.The hierarchical honeycomb carbon calcined at 1000℃has a discharge capacity of 146 m Ah g^-1 after 3000 cycles at 1 A g^-1.The high reversible capacity,stable cycle performance and good rate performance are mainly due to the hierarchical honeycomb porous structure with high defects,high porosity and large specific surface area.This is an excellent anode material for sodium ion batteries.