Preparation Of Porous Nano-Carbon And Its Application For Electrochemical Energy Storage

In the existing energy storage methods,electrochemical energy storage technology is not restricted by the geographical terrain environment,can directly store and release electrical energy,and can be used from rural to urban,thus causing widespread concern in emerging markets and scientific research fields.In the composition of electrochemical energy storage devices,the microstructure of the electrode material is a direct factor affecting the electrochemical energy storage performance.Therefore,how to properly design an appropriate electrode structure to improve the energy storage performance of the electrode material is a very important research topic.The porous carbon material with micro-nano structure combines the advantages of high conductivity,high stability,structural variability,and low cost.It can not only be used directly as an electrode material to build a good electrochemical energy storage device,but also be used as a matrix.The compound of low-conductivity non-carbon material accelerates the electron transmission and relieves the volume expansion.In this thesis,the structural design of porous nano-carbon electrode materials is used as a guide,combining the current status of current microporous/mesoporous porous carbon materials design and electrochemical energy storage.Porous carbon with multiple morphologies,high specific ratios,and rich pore structure and its composite materials are applied to supercapacitors and lithium storage devices to obtain electrochemical energy storage devices with high rate,long cycle,and high load.The specific work includes the following two aspects:（1）Polymer nanofibers（PNFs）are produced by solution synthesis method,using triblock copolymer F127 as a structure directing agent,and an interface assembly process triggered by temperature control molecules.We have focused on controlling the factors that have such an important effect on the formation of PNFs,such as temperature,reaction raw materials,and reaction concentrations.And various methods have been used to reveal the growth process of PNFs by means of transmission electron microscopy（TEM）and scanning electron microscopy（SEM）.At the proper temperature,the triblock copolymer F127 begins to form fiber micelles.At the same time,molecularly triggered hexamethylenetetramine（HMT）generates formaldehyde and ammonia in situ.Then,the phenolic polymer will be assembled around the fiber micelles,and then PNFs are formed,and the diameter of the PNFs is precisely controlled in the range of 30⁸0 nm.Porous carbon fibers（Carbon Nanofibers,CNFs）prepared through subsequent carbonization and activation steps of PNF have rich micropores and an ultra-high specific surface area of 1175 m² g^-1.These microporous CNFs are used as electrode materials for supercapacitors.They still have excellent specific capacitance up to 295 F g^-1 at a high current density of 50 A g^-1.（2）Urea boric acid was used as precursor,polyvinylpyrrolidone（PVP）was used as binder,and Ketjen Black was used as the conductive matrix.The co-heat method was used to synthesize boron-nitrogen-doped high specific surface and high conductivity composite carbon materials（KB@BNC）,and investigated the effects of different amounts of precursors on the morphology and pore structure of boron-nitrogen-doped composite carbon.With the increase of urea boric acid precursor content,the specific surface area and pore volume of KB@BNC will decrease sharply,and the proportion of mesopores will also decrease sharply.The addition of urea boric acid will lead to the clogging of rich mesopores.When KB@BNC is applied to the cathode material of lithium-sulfur batteries,taking into account that boron and nitrogen have good adsorption properties for lithium polysulfide（LiPS）and sulfur storage requires a certain pore volume and specific surface area,the overall content of boron-nitrogen element Need to find a balance point.Through characterization and experimental methods such as XPS,when the nitrogen content is 5.91%and the boron content is 3.75%,the composite carbon material not only maintains a specific surface area of 1140 m² g^-1,but also has an ultra-high conductivity of2141 S m^-1.rate.When used as a cathode material for lithium-sulfur batteries,it still maintains a specific capacity of up to 690 mAh g-1 after 800 ultra-long cycles;when the sulfur load is increased to 4.01 mg cm^-2,the battery still has 100 cycles With a specific capacity of up to 914mAh g^-1,the retention rate is 89.5%compared to the first cycle.