Design,Synthesis And Electrochemical Properties Of The Silicon And Tin Based Fibrous Electrodes And Fiber-Shaped Lithium-Ion Batteries

With the advancement of the micro and nano-fabrication technology,a growing attention has been paid to the design and manufacture of the electronic devices with feartures like portability,wearability and weavability.Consequently,it brings with a new frontier to develop highly adaptable energy-supplying systems.Lithium-ion battery,taking advantage of high-energy density,environmentally friendly and resources-saving,has been widely applied to different kinds of electronic devices.Obviously,conventional power sources cannot satisfy these desires owing their bulk,rigidness,inherent unalterable shapes and low bonding strength between the active material and current collector.Moreover,the weight percentage of the inactive material is still too high.This dissertation tries makes use of inexpensive carbon-based materials associated with alloy-type electrode materials,such as tin,silicon.A series of highly flexible one-dimensional fibrous anodes and cathodes have been fabricated and their electrochemical properties have been tested at various flexible states.Finally,the all-fiber-based lithium-ion battery has been assembled by the as-prepared electrodes and flexible substances and shows outstanding performance.The main contents and innovations can be concluded in the following statements:1.In order to find a low-cost and facile way to produce silicon-based fibrous electrode,we demonstrate a novel one-step approach to fabricate 1D electrode.By an in-situ polymerization method,a 3D interconnected Si/PPy/CF electrode has been successfully fabricated.The nanostructure can be well designed by controlling the reaction time of insitu ploymerzation process.The optimized electrodes gain following advantages:(1)The protective PPy layer effectively relieves the expansion of the Si during lithiation process and can act as a glue adhering the Si NPs firmly onto the CF substrate and protecting Si from losing activity,(2)with the help of phytic acid,PPy forms a 3D interconnected conductive structure,promoting the conductivity of active materials and efficiently improving the accessibility of the electrolyte to electrode.(3)The toughness and strength of the CF ensure the electrochemical performance of electrode under a series of flexible status.The as-prepared fiber shows a capacity of 2287 m Ah/g at 0.1 C(1C= 4.2 A/g)after 100 cylces.When the rate of current density achieves as high as 4C,the capacity shows a capacity of 936 m Ah/g.Moreover,we also test different sealing methods and different packaging materials for the half-cell electrochemical tests under flexible condition.We find that the one with silicone tube sealing by hot melt glue shows the best electrochemical performance during bending and folding tests.The electrode reveals 2120 m Ah/g after bending and folding.When the test conducts 100 cycles at bending status,the reversible capacity retains at 2197 m Ah/g,which is 96.1% of the initial capacity.The synthetic method is proved to be a facile and low-cost method to manufacture flexible fiber-shaped electrodes,which shows a potential application towards wearable devices.2.The conventional configuration of the 1D cable/wire-type flexible lithium-ion batteries are usually designed in parallel,twisted and coaxial structure.However,these designs are not able to balance the capacity of anode and cathode and finally fail to meet with the trend of next-generation high capacity anode.The common method is to increase the mass loading of cathode and it may solve the problems to some extent,but the overloading will sacrifice the cycling and rate performance in the end.To deal with the shortcomings,we design and fabricate a self-healable all-fiber-based quasi-solid-state lithium-ion battery.We use the annealed spring-like Li Co O2 nanopartiles@r GO(ASLG)fiber as cathode materials,the annealed Sn O2 quantum dots@r GO(ASG)fiber as anode materials.the poly(vinylidenefluoride-co-hexafluoropropylene,PVDF-co-HFP)soaked in Li Cl O4 with EDC/EC(50/50 v/v)is acted as gel electrolyte and a self-healable carboxylated polyurethane(PU)is used as package layer.There are some advantages of the as-prepared electrodes and the all-fiber-shaped lithium-ion battery.On one hand,the active materials of r GO-based electrodes can mitigate the stacking of graphene caused by the intersheet ?-? bond.On the other,the porous r GO substrate simultaneously promotes the flexible,thermal,mechanical and electrochemical stability of the electrode,offering an easy access to reach a higher surface area sites and minimize ionic resistance.Meanwhile,the adjustable length of the spring-shaped cathode maeks it easy to match the capacity with anode and promotes the flexibility with a high space utilization as well as the capacity matching between highcapacity anode and low capacity cathode.By the outstanding configuration of the fibrous electrodes,the capacity retention of the full cell is as high as 80% after 50 cycles.3.In order to relieve to concern on the safe problem of the fiber-shaped lithium-ion battery,we use the self-healing PU to heal the lithium-ion battery when the injury occurrs.The LIB shows 82.6 m Ah/g after bending and even knotting states,and it retains 50.1 m Ah/g after 5th healing process at a current density of 0.1 A/g,which implies a capacity of 82.2% and 50.3% retention(a 5.5% decrease compared with unbending one),respectively.It shows an outstanding flexible and self-healing abilities under complex motion environment and cutting-healing process.The idea and design of the all-fiber-based quasisolid-state lithium-ion battery may open new chances for next-generation wearable electronic devices.