Preparation Of POSS-based Composite Membrane Based On Environmentally Friendly Polymerization Chemistry And Study On The Separation Performance Of Dye Wastewater

Lithium-ion batteries（LIBs）are one of the most widely used energy storage devices in our daily life due to their high energy density,high voltage,long cycle life,low self-discharge rate,lack of memory effect,etc.To promote the further development of LIBs,it is crucial to further improve their energy density,power density,cycle life,and safety.Currently,graphite is the most widely used commercial anode electrode material.However,due to the relatively low working potential of the graphite anode,it is easy to cause the decomposition of electrolyte and the formation of lithium dendrites on the surface of the graphite,which may lead to safety issues.Besides,the low theoretical specific capacity(～372 mAh g^-1)and slow lithium ion insertion/desorption kinetics of graphite may hinder the improvement of battery energy density and power density.Therefore,it is of great significance to develop new anode materials that can replace graphite.Among anode materials,some transition metal compounds（such as Fe,Mo,Ti,etc.）have the advantages of rich resources,relatively cheap price,a moderate specific capacity,and high safety,which make them potential choices as anodes for LIBs.However,transition metal compounds suffer poor electronic conductivity and large volume change during charging and discharging,which restrict the improvement of their rate performance and cycle life.Neverthless,reasonable nanostructure design and carbon composite are expected to buffer its volume change,improve the electronic conductivity of the electrode,and shorten the lithium ion diffusion path,which are beneficial to achieving high-performance transition metal compound-based anodes.However,for most of the previously reported transition metal compounds/carbon composites,the improvement of electrode cycle life is limited because the transition metal compound particles are not effectively constrained and protected by carbon.As for carbon coated transition metal compound composites,the particle size of the transition metal compound and the carbon layer thickness have not been effectively controlled,which hinders their performance.In view of this,we have designed and prepared a series of carbon constrained transition metal compound nanocomposites in this dissertation,and have systematically studied their electrochemical properties.As a result,the composite anodes exhibited large specific capacity,high rate capability,and long life,which systematically expounded the advantages of carbon constrained transition metal compound nanocomposites design.The main contents are as follows:（1）Nitrogen-doped carbon coated TiNb₂O₇ hollow interconnected nanospheres（H-TNO@C）were prepared by a sacrificial template method and subsequent carbon coating method.In this unique hybrid nanostructure,its large specific surface area can increase the contact area between the electrode and electrolyte to improve the utilization rate of electrode materials;the thin shell of TNO hollow nanospheres can shorten the diffusion distance of lithium ions;the nitrogen-doped carbon layer with high conductivity and interconnection can ensure rapid charge transfer,and constrain the stress,strain,and particle agglomeration of TNO during charging and discharging.Consequently,the H-TNO@C anode achieved a large specific capacity(271 mAh g^-1 at 0.2 C)and good rate performance(151 mAh g^-1 at 10 C),which is obviously superior to the pure TNO nanoparticles and TNO hollow nanospheres anodes.Moreover,the H-TNO@C anode also showed an extremely long cycle life（5000 cycles）,which is superior to most of the previously reported carbon-coated TNO anodes.This work indicates that the carbon-constrained composite nanomaterials design can effectively improve the lithium storage performance of the anode,which provides a reference for the subsequent modification design of metal compound anode materials.（2）A simple one-pot synthesis method was developed to prepare nitrogen doped carbon nanosheet（NC）/metal nitride（TMNs）nanoparticles composite（TMNs@NC）.The NC and TMN are formed at the same time in the synthesis process,and the existence of NC can effectively constrain the growth of TMN particles,leading to the small nanoparticle size of the TMN and the good morphology of the NC.In this hybrid material,small TMNs particle size and the NC constrained structure can greatly improve the stability of TMNs particles and facilitate rapid electron and lithium ion transport;the rich pore structure in the composites,and the rich doped N and defects in NC can create plenty of active sites for enhanced lithium storage,and obtain large surface capacitance contributions.Consequently,the typical VN@NC anode achieved a large specific capacity(720 mAh g^-1 at 0.1 A g^-1),excellent rate performance(307 mAh g^-1 at 10 A g^-1),and outstanding long cycle stability（78%capacity retention after 3000 cycles）,which makes it possible to be appies as the anode for LIBs.This one-pot synthesis method provides a new opportunity to prepare low-cost TMNs based nanocomposites.（3）A Fe/Fe_xN nanoparticles embedded NC nanocomposite（Fe/Fe_xN@NC-1）was prepared under controlled synthesis conditions.In the unique composite,the presence of Fe/Fe_xN can catalyze the reversible formation of solid electrolyte interlayer（SEI）film to achieve additional lithium storage capacity;the existence of Fe/Fe_xN can also introduce more defects in the NC during the preparation process,creating more active sites for lithium storage;the NC constraint structure can greatly improve the stability of Fe/Fe_xN particles,and ensure rapid electron transport;the pseudocapacitance based on NC defect lithium storage and SEI reversible formation ensure good rate capability at high current densities.Consequently,the Fe/Fe_xN@NC-1 anode showed a large specific capacity(665mAh g^-1 at 0.1 A g^-1),excellent magnification performance(291 mAh g^-1 at 10 A g^-1),and long cycle stability（85.3%capacity retention after 5000 cycles）,which was significantly superior to the simple NC electrode and Fe₃N@NC electrode.Furthermore,a lithium ion capacitor was constructed using B,N co-doped carbon nanofibers（BNC）as cathode and Fe/Fex N@NC-1 as the anode.Thanks to the matched anode and cathode kinetics and the stable electrode structure,the lithium ion capacitor has simultaneously achieved a high energy density(141.6 Wh kg^-1),high power density(18.1 kW kg^-1),and a long cycle life（80.6%capacity retention after 5000 cycles）.This work can provide a new idea for the structural design of transition metal compound anode materials with high capacith and long cycle life.