Hierarchical Construction Of Carbon Based Storage Materials And Devices

With the development of the wearable equipment and flexible electronic devices,to exploit high performance lithium ion batteries with high energy and power density and good flexibility has particularly become one mainstream.The key challenge is to design and fabricate electrode materials with robust mechanical flexibility,short ion transport length and high specific capacity.In this dissertation,starting from electrospinning technique and the assembly at micro-and nano-scale for hierarchical structure construction,we have designed and fabricated a class of self-supported high-performance lithium anodes and cathodes and further assemblied into flexible prototype energy storage devices with excellent performance.First,design and construction of a novel conductive carbon skeleton framework.Via the combination of electrospinning technique with chemical vapor deposition(CVD)methods,we designed a novel flexible and conductive carbon skeleton network,where graphene rolls up into a hollow nanotube in which active materials are uniformly dispersed,thus forming mechanically robust,free-standing,interwoven nanocable webs.Through the addition of different salt solutions in the precursor,we can selectively synthesize graphitic carbon coating different electrochemical materials nanocable hybrid materials.Using this universal method,the as-prepared SnOxSiO2@G self-supported films,when used as binder-free lithium anodes,show high specific capacity(ca.1150 mAh g-1)as well as excellent cycling performance(almost 100% capacity retention after 200 cycles at a current density of 0.1 A g-1)Second,dimension control of the electrochemical active material and the adjustment of the contact mode of the composite interface based on the carbon nanocable skeleton framework.Via the HF etch and chemical or thermal treatment,nanoparticles are transformed into two dimensional nanoplates.With the confinement of SiO2,we further optimized the growth orientation of 2D materials.By introducing a unique side-to-face contact mode between graphene and 2D nanosheets such structure achieves a substantial improvement in the interfacial contact efficiency of two dimensional nano materials and thus ensures the rapid transmission of electron and ions.Remarkably,a pretty high capacity of 900 mAh g-1 with a long cycle life(700 cycles with almost 100% capacity retention)at 5 A g-1 is achieved,which belongs to one of the best results reported so far on MoS2-based electrode materials.Third,preparation of flexible cathodes and assembly of flexible lithium ion device based on the carbon nanocable skeleton.We successfully prepared a flexible web film composed of V2O5@G nanocables in which the V2O5 nanoparticles are encapsulated into a carbon nanotube,showing ultrafast and stable Li+ ion storage performance.Remarkably,an energy density of ca.360 Wh kg-1 at a power rate of 15.2 kW kg-1 is achieved based on the electrode materials.Furthermore,we fabricated a flexible Sn-V2O5 battery prototype,showing surprisingly good cycling stability and excellent mechanical properties.The as-fabricated battery cell exhibits a capacity of 80 mAh g-1 at a high current density of 20 C.Even over 200 bending cycles,the open circuit voltage remained at 3 V stably.At last,we proposed a preparation method of self-supported film which constructed by interwoven of nitrogen-enriched carbon nanofibers based on small organic molecule.Via the combination of electrospinning and low-temperature polymerization process,the designed and fabricated nitrogen-enriched porous carbon nanofibers not only possess a high-level nitrogen doping content and thus the abundant electrochemical active sites,but hold developed pore structure which is beneficial for the rapid ion diffusion of ion,showing excellent electrochemical performance as supercapacitor electrodes.Based on this,we designed and assembled the hybrid energy storage devices(lithium ion capacitors)with both high energy density and high power density.