| Electrochemical energy storage is an important part and key supporting technology in the fields of consumer electronics,electric vehicles and smart grids.The cumulative installed capacity of the global electrochemical energy storage market in2020 is about 2.8 GW,among which the installed capacity of lithium-ion batteries(LIBs)is as high as 1.4 GW,which plays an important role in the energy sector.Electrode material is a key factor that determines the energy storage characteristics of LIBs and the cost of the device,and can be divided into inorganic materials(metals,non-metals or their compounds)and organic materials(small molecule compounds,organic polymers).However,inorganic electrode materials have problems such as large volume fluctuations,short service life,or high material costs,while organic electrode materials face limitations such as poor conductivity and low rate performance.Therefore,this dissertation is based on inorganic nanophase selection,organic polymer design and synthesis method regulation,develops new organic-inorganic composite electrode materials,and studies the material structure through cyclic voltammetry,constant current charge and discharge,and electrochemical impedance technology.The structure-activity relationship with lithium storage performance,lithium storage mechanism and regulation laws,seek new ideas for solving the challenges faced by single inorganic or organic electrode materials.Its innovative work includes the following three parts:(1)A simple one-step in-situ hydrothermal polymerization method has been established to control the preparation of Sn O2 nanocrystalline/polyimide(Sn O2@PI)composite electrode materials.Through the simultaneous hydrothermal reaction of triaminotriphenylamine,biphenyltetracarboxylic dianhydride monomer and Sn Cl4·5H2O,the polyimide macromolecular chain can inhibit the growth of Sn O2nanoparticles and prevent the aggregation of Sn O2 due to the spatial confinement effect.Ultrafine(<5 nm)Sn O2 nanocrystals are uniformly embedded in the polyimide matrix phase.The polyimide matrix can be used as a Sn O2 protective layer to suppress the volume change during electrode charging/discharging and improve the cycle and rate performance of the electrode.At the same time,the carbonyl group in the polyimide chain has redox activity,which can improve the ion conductivity of the electrode and give a certain specific capacity.Using Sn O2@PI composite material as the negative electrode,it is found that when the current density is 0.1 A g-1,the reversible capacity is 897 m Ah g-1,and when it increases to 2.0 A g-1,it remains at 479 m Ah g-1,which is lower than the specific capacity.The retention rate(53%)is higher than that of pure Sn O2 anode(39%),and after 150 cycles of cycles,the Sn O2@PI composite anode still retains a specific capacity of 653 m Ah g-1 at 0.5 A g-1,showing a higher specific capacity,excellent rate performance and cycle stability.(2)Designed and developed a new type of CNT@CPAN heterostructure anode material with carbon nanotubes(CNTs)as the conductive core and cyclized acrylonitrile(CPAN)as the electroactive shell.In situ solution radical polymerization of CNTs and acrylonitrile to produce petaloid polyacrylonitrile coated CNTs,and thermal cyclization in an inert gas,the CPAN layer thickness of 40?52 nm,uniformly coated CNT@CPAN Core-shell structure composite material.At the same time,the quasi-one-dimensional CNT@CPAN overlap each other to build a three-dimensional porous network structure,provide a rich internal pore structure,and fully expose the unsaturated multi-electron redox active sites in the CPAN chain(C=N,C=C).With CNT@CPAN as the negative electrode,the reversible capacity is as high as 1176 m Ah g-1 when the current density is 0.1 A g-1,and it is maintained at 439 m Ah g-1 when the current density is increased to 2 A g-1,and at 10 A g-1 After 5000 times of charging and discharging,the specific capacity is still as high as 330 m Ah g-1,and it is found that the specific capacity,rate and cycle performance of CNT@CPAN are better than pure CPAN anode.(3)The nano-silicon(?50 nm)/polyacrylonitrile composite material was pre-synthesized by in-situ precipitation polymerization,followed by thermal cyclization to obtain the nano-silicon/cyclized polyacrylonitrile(Si@CPAN)composite material.With Si@CPAN as the negative electrode,the stable conjugated chain structure of CPAN can inhibit the large volume change of nano-Si during charge and discharge,improve the rate capability and cycle stability,while maintaining the ultra-high specific capacity advantage of Si.The results show that the reversible capacity of Si@CPAN anode at 0.2 A g-1 is 1032 m Ah g-1,and the specific capacity is stable at 546 m Ah g-1after 70 cycles at 1.0 A g-1,which is much higher than that of the specific capacity of the pure nano Si anode(162 m Ah g-1). |
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