| Porous organic polymers(POPs)are a class of novel porous materials composed of C,H,N,O and other light elements.They have large specific surface areas,excellent physical and chemical stabilities,definite chemical compositions,widely accessible monomers,and flexibly predesigned structures.These features make them to be a research hotspot in recent years.This thesis focuses on the applications of POPs in the field of energy storage,for which a series of crystalline or amorphous POPs have been synthesized and they applications in lithium-sulfur batteries or supercapacitors have been studied.It consists of the following five parts.In chapter 1,we summarize the research background and current progress of POPs,lithium-sulfur batteries and supercapacitors.In the last part of this chapter,the objective of this thesis has been discussed.In chapter 2,we have designed and synthesized a new COF with extended?-conjugated units,and its application as cathode material in lithium-sulfur batteries has been investigated.The COF exhibits a sulfur loading of 88.4%,and its extended conjugated system provides an elaborated platform for sufficient Li-S redox reaction,which enables the Li-S battery to release a specific capacity of 1617 m A h g-1 at 0.1 C(1675 m A h g-1 in theoretical value)and still maintains a high capacity and coulombic efficiency after 528 cycles at 0.5 C.On the other hand,density functional theory(DFT)calculations are performed to reveal the relationship between the structure and performance of the COF.In chapter 3,three porous organic polymers with different pore surface polarity have been designed and synthesized,and further used as cathode materials for lithium-sulfur batteries.Thermogravimetric analysis shows that their sulfur loadings are 70%.On the basis of the study on the electrochemical performance of the three POPs,it is found that a high pore wall polarity is favorable for improving performance of the cathodes,and the lithium-sulfur battery assembled by the POP containing two types of polar functional groups shows the best electrochemical performance,with a capacity of 847.5 m A h g-1at 1.0 C,a coulombic efficiency of 99.0%after 425 cycles,and a capacity decay rate of 0.08%per cycle,which is much better than the other two POPs that have different pore surface polarity.Both the experimental results and DFT calculations have revealed that a synergistic effect between the two types of polar functional groups in the POP plays a crucial role in inhibiting the shuttle of polysulfides.In chapter 4,We have synthesized two heteroporous covalent organic frameworks and used them as cathode materials for lithium-sulfur batteries.They exhibit sulfur loading of 73%.The experimental results show that the uniformly distributed polar functional groups in the mesopores and micropores of the COF can effectively inhibit the shuttle of polysulfides.The as-prepared cathode exhibits a capacity of 561 m A h g-1 at 2.0 C,and the capacity remains at518.5 m A h g-1 after 290 cycles at 1.0 C,with a coulombic efficiency close to 100%.The effectiveness of the COF material design is further demonstrated by comparative experiments.In chapter 5,the heteroporous COF with bipyridine unit as building blocks has been synthesized.Due to the poor conductivity of POPs,their application in electrochemistry is largely limited.Therefore,the as-prepared COF is further carbonized at different temperatures to afford porous carbon materials,which have been used as electrode materials for supercapacitors.The experimental results reveal that the porous carbon material obtained by carbonization at 800?exhibits better specific capacitance and good cycle stability,with no loss of capacity being observed after 2000 charge and discharge cycles. |
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