Studies On Design And Electrochemical Energy Storage Of Conjugated Carbonyl Compound Composites With Micro/nanoporous Structures

Into the 21st century,the increasing demond for green and sustainable new energy has promoted the rapid development of energy storage technologies.Among various energy storage technologies,secondary batteries have become the research hotspot due to their effective storage and conversion of renewable green energy.However,the conventional secondary batteries have been unable to meet the requirements of the high specific capacity and excellent stability due to the limited theoretical specific capacity and structural unstability of transition metal-based electrode materials.Additionally,the large-scale usage of transition metal-based electrode materials with expensive price and limited reserves causes resource shortage,high cost and serious environmental pollutions.Therefore,it is of important scientific significance and practical value to create new kinds of green and sustainable electrode materials with high specific capacity and excellent stability for the development of secondary batteries.The electroactive conjugated carbonyl compounds,which can store energy by means of reversible redox reaction,have been considered as one kind of the most ideal electrode materials compared with the traditional transition metal-based electrode materials due to their low cost,abundant resources,environmental benignity,structural versatility and mechanical flexibility.Nevertheless,their practical applications were seriously hindered by the inherent poor electrical conductivity,low utilization rate and easy dissolution with low molecular weight in organic electrolytes.In view of this,a series of functionalized electroactive conjugated carbonyl compound composite electrode materials with multi-scale micro/nanoporous structures were prepared for lithium/sodium ion batteries and aqueous batteries through combining the molecular design and controlled structural construction to realize the excellent electrochemical performance and structure stability.In addition,the relationship between the multi-scale micro/nanoporous structures,mechanical properties,conductivities and energy storage mechanism of the obtained composite electrode materials was thoroughly analyzed,which provides a theoretical basis for the application of electroactive conjugated carbonyl compound composite electrode materials in new green secondary batteries.The main research contents and results of this thesis are summarized as follows:(1)Inspired by the micro/nanostructures of cell membranes and pearl shells,a flexible composite film with multi-scale micro/nanoporous lamellar structures consisting of 3,4,9,10-perylenetetracarboxylic dianhydride(PTCDA)/reduced graphene oxide(RGO)/carbon nanotubes(CNT)was constructed by layer-by-layer self-assembly and heating processes,which is denoted as PTCDA/RGO/CNT.The multi-scale micro/nanoporous lamellar structures can effectively absorb and store electrolyte,tightly anchor and encapsulate PTCDA,thereby inhibiting the dissolution of PTCDA and enhanceing its conductivity.With excellent mechanical properties and electrical conductivity,the PTCDA/RGO/CNT composite electrode was directly used in lithium/sodium ion batteries to achieve high specific capacity of 131.0 m A h g^-1and 126.0 m A h g^-1 respectively,excellent rate performance and 99%capacity retention after 500 cycles.Additionally,high specific energy densities of 132.6 W h kg^-1 and 104.4 W h kg^-1 were obtained in the flexible Li-ion and Na-ion full cells,respectively.(2)Inspired by wood's hierarchical microchannels toward the highly efficient storage and transport of ions and water during metabolism,a flexible composite nanofibrous membrane consisting of PTCDA/nitrogen-doped carbon/carbon nanotubes(PTCDA/NC/CNT)was constructed with multi-scale micro/nanotunnels by using electrospinning technique,carbon nanotube(CNT)composite and in-situ pyrolysis method.The PTCDA was uniformly dispersed and embedded in the nitrogen-doped carbon/carbon nanotube composite nanofibers by optimizing the preparation process.The results of analysis and test revealed that the micro/nanotunnel structure has ultra-strong capillarity,which could rapidly absorb and store the electrolyte,and effectively inhibits the agglomeration and dissolution of PTCDA particles in the electrolyte.In addition,the uniform composite of CNT also improves the overall conductivity and mechanical flexibility of the composite nanofiber membrane.The PTCDA/NC/CNT electrode can be directly used as a self-supporting cathode for sodium-ion batteries,which can achieve high specific capacity of 135.6 m A h g^-1(99.3%of its theoretical specific capacity),excellent rate performance and ultra-long cyclic stability(95%specific capacity maintained after500 cycles).The assembled all-organic rechargeable sodium-ion battery with robust PTCDA/NC/CNT cathode and Na₄-PTC/CNT anode delivers high specific energy density of 85 W h kg^-1 and power density of 2400 W kg^-1.(3)In order to solve the problem of small molecule dissolution and low utilization rate of naphthalene-based conjugated carbonyl compound,naphthalene-based polyamide acid was prepared by polycondensation.Then a flexible naphthalene-based polyimide nanofiber composite membrane containing nitrogen doped carbon and carbon nanotubes(NPI/NC/CNT)with hierarchical micro/nanoporous structures has been obtained through the thermal imidization of naphthalene-based polyamide acid,combined with electrospinning technique and heat treatment method.The results of analysis and test revealed that the NPI/NC/CNT composite membrane can effectively inhibit naphthalene-based small molecule dissolution and agglomeration benefitting from the molecular polymerization in situ to form uniform dispersion of naphthalene-based polyimide.Meanwhile,the conductivity of naphthalene-based polyimide,mechanical properties of composite membrane,theoretical capacity and utilization of NPI were significantly improved within NPI/NC/CNT composite membrane due to carbon nanotube composite and controlled construction of multi-scale micro/nanoporous structures.Consequently,the NPI/NC/CNT composite membrane can be directly used in lithium/sodium ion batteries to achieve excellent rate performance and ultra-long cycle stability(82.1 m A h g^-1 and 89.2 m A h g^-1 specific capacity maintained after 500 cycles),high ion diffusion coefficient(4.1×10^-13 cm² s^-1 and 1.19×10^-12 cm² s^-1)and low charge transfer impedance of 151.2?and 174.5?,respectively.In addition,the assembled flexible full battery achieves excellent rate performance and cycle stability(88.6%specific capacity maintained after 200 cycles).(4)An all-organic aqueous dual-ion battery(DIB)was assembled using NPI/NC/CNT and polyaniline/carbon nanofiber composites(PANI/CNF)as anode and cathode,respectively.The NPI/NC/CNT electrode possesses stable voltage window,high ionic diffusion coefficient(2.93×10^-8 cm² s^-1),excellent rate performance and ultra-long cyclic stability(98%specific capacity maintained after 5000 cycles).Besides,the all-organic aqueous DIB delivers high specific energy density of 114.3 W h kg^-1 and high power density of 18.6 k W kg^-1.